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Influence of Saltwater on Weed Management in Seashore Paspalum


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INFLUENCE OF SALTWATER ON WEED MANAGEMENT IN SEASHORE PASPALUM By NICHOLAS B. POOL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2005

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Copyright 2005 by Nicholas B. Pool

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ACKNOWLEDGMENTS I would like to start by thanking God for my existence and for the support He has provided me throughout my life. I would also like to thank my parents and grandparents for their encouragement and support. They are the reason for my success thus far and will always be the most influential people in my life. I thank my friends for providing me with the experience of a lifetime. More specifically, I want to thank Travis Tueton, Mike Harrell, and Mark Mitchell for the encouragement they gave me to continue my education. I would especially like to thank Melissa Barron for being my best friend and biggest supporter. I am thankful for all the laughs and experiences we have had and will continue to have. I want to thank my major professors, Dr. Barry Brecke and Dr. Bryan Unruh, for the confidence they had in me and providing me the opportunity to continue a graduate career. I thank Dr. Greg MacDonald for offering his guidance and knowledge that made my graduate school experience easier. Also, I thank Dr. Laurie Trenholm and Dr. Jay Ferrell for being a part of my committee and assisting with my thesis. All of them have exposed me to a diverse range of weed science, providing me with a truly well rounded education. Finally, I thank everyone at the WFREC for their assistance with my research project. iii

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES.............................................................................................................vi LIST OF FIGURES..........................................................................................................vii ABSTRACT.....................................................................................................................viii CHAPTER 1 INTRODUCTION........................................................................................................1 Characteristics of Seashore Paspalum..........................................................................1 Water Quality and Consumption on Golf Courses.......................................................7 Weed Management on Golf Courses............................................................................9 Summary.....................................................................................................................16 2 TOLERANCE OF NEWLY SPRIGGED AND ESTABLISHED SEASHORE PASPALUM TO SALTWATER...............................................................................19 Introduction.................................................................................................................19 Methods and Materials...............................................................................................23 Results and Discussion...............................................................................................25 Newly Sprigged Seashore Paspalum...................................................................25 Established Seashore Paspalum...........................................................................26 3 SUCEPTIBILITY OF NINE TURFGRASS WEED SPECIES TO FIVE SALTWATER CONCENTRATIONS.......................................................................29 Introduction.................................................................................................................29 Methods and Materials...............................................................................................34 Greenhouse Studies.............................................................................................34 Field Studies........................................................................................................36 Results and Discussion...............................................................................................37 Greenhouse Studies.............................................................................................37 Broadleaf species..........................................................................................37 Grass and sedge species...............................................................................37 Field Studies........................................................................................................40 iv

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4 THE TOLERANCE OF SEASHORE PASPALUM TO HERBICIDES WHEN IRRIGATED WITH SALTWATER..........................................................................47 Introduction.................................................................................................................47 Methods and Materials...............................................................................................50 Results and Discussion...............................................................................................52 5 CONCLUSIONS........................................................................................................58 APPENDIX 2004 RAINFALL.........................................................................................62 LIST OF REFERENCES...................................................................................................63 BIOGRAPHICAL SKETCH.............................................................................................68 v

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LIST OF TABLES Table page 1-1 Paspalum cultivars, leaf texture, and year of introduction.......................................18 2-1 Saltwater effect on sprigged and established seashore paspalum............................27 3-1 Control of selected broadleaf weeds with saltwater in the greenhouse pooled data over years and evaluations................................................................................42 3-2 Control of selected annual grass weeds with saltwater in the greenhouse pooled data over years and evaluations................................................................................42 3-3 Control of selected perennial grass and sedge weeds with saltwater in the greenhouse pooled data over years and evaluations.................................................42 3-4 Control of southern crabgrass and cocks-comb kyllinga with two salt concentrations applied as a solution or granular in the field....................................43 3-5 Seashore paspalum quality as affected by saltwater in the field..............................43 4-1 List of herbicides tested on seashore paspalum under salinity stress.......................56 4-2 The effect of preemergence herbicides and salt concentrations on seashore paspalum quality 4 wk after herbicide application...................................................57 4-3 The effect of postemergence herbicides and salt concentrations on seashore paspalum quality 4 wk after herbicide application...................................................57 vi

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LIST OF FIGURES Figure page 2-1 Effect of saltwater concentration on seashore paspalum quality ratings 8 wk after initial application of saltwater..........................................................................28 3-1 Saltwater concentration effect on broadleaf weed control pooled over years and evaluations................................................................................................................44 3-2 Saltwater concentration effect on annual grass control pooled over years and evaluation.................................................................................................................45 3-3 Saltwater concentration effect on perennial grass and sedge control pooled over years and evaluation.................................................................................................46 vii

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science INFLUENCE OF SALTWATER ON WEED MANAGEMENT IN SEASHORE PASPALUM By Nicholas B. Pool August 2005 Chair: Barry Brecke Cochair: Bryan Unruh Major Department: Agronomy Greenhouse and field experiments were conducted in 2003 and 2004. Saltwater treatments consisting of 55 dS/m (1x = seawater), 41 dS/m (3/4x), 27 dS/m (1/2x), 13 dS/m (1/4x), and potable water (0x) were applied to established and newly sprigged seashore paspalum under greenhouse conditions. In the second study, 18 herbicides were applied to established seashore paspalum irrigated with saltwater treatments (1x, 3/4x, 1/2x, 1/4x and 0x) under greenhouse conditions. Saltwater treatments were applied 2 times per wk with 1 potable water treatment per wk for a total of 8 wk. Visual evaluations for turf quality were based on a scale of 0 (dead turf) to 9 (health turf). In a third study, 9 common turfgrass weeds were subjected to saltwater treatments (1x, 3/4x, 1/2x, 1/4x and 0x) applied 2 times per wk with 1 potable water treatment per wk. Visual evaluations for weed control were taken on a scale of 0 (no control) to 100 (complete control). Southern crabgrass and cocks-comb kyllinga susceptibility to saltwater was tested under field conditions in established Sea Isle 1 seashore paspalum. Plots were viii

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treated for 4 wk with a 1/4x or 1/2x concentration of salt applied as a liquid solution or as a granule and compared to a freshwater treatment. Turfgrass quality was compromised (ratings < 7) at the 3/4x and 1x rates of saltwater applied to established seashore paspalum while all levels of salt caused unacceptable injury to newly sprigged seashore paspalum. Herbicides that caused a major reduction in the quality of seashore paspalum were atrazine and metribuzin. These herbicides will cause damage when seashore paspalum is irrigated with any concentration of saltwater and should not be applied to seashore paspalum. Minor reductions in quality were observed after the application of bromoxynil, 2,4-D + dicamba + mecoprop, and imazaquin. These herbicides should not be applied to seashore paspalum irrigated with saltwater concentrations > 1/2x. Florida pusley was controlled at all rates of saltwater while Virginia buttonweed was controlled at all rates except 1/4x. Crabgrass, goosegrass, and tropical signalgrass were adequately controlled (>70%) at the 3/4x and 1x rates of saltwater while the 1x rate was needed to provide control of purple nutsedge and dollarweed. Bermudagrass and torpedograss exhibited high levels of tolerance at all salt concentrations. In the field study, crabgrass was effectively controlled at 1/2x rate of saltwater applied as a solution or as granular salt. The 1/4x rate was also effective granularly applied, but not applied as a solution. Kyllinga was controlled at the 1/2x rate either as a granular or solution, but the 1/4x rate was not effective using either method. In both studies, the granular application method provided better control of crabgrass and kyllinga compared to salt applied in solution. ix

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CHAPTER 1 INTRODUCTION Characteristics of Seashore Paspalum Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial warm season turfgrass that is native to tropical and subtropical regions of the world (Duncan and Carrow, 2000). Although seashore paspalum has existed for many years, it has only been used commercially for the past few decades (Table 1.1). Seashore paspalum spreads by rhizomes and stolons that root at the nodes forming a deep fibrous root system (Duble, 2000). It is generally propagated vegetatively from sod or sprigs because seed production has not been reliable due to self-compatibility issues (Duncan and Carrow, 2000). Breeders have been able to overcome this obstacle and one seed produced cultivar, Seaspray, has recently been released (Hughes, 2005). Seashore paspalum leaves are slightly coarser than those of common bermudagrass when mowed > 2.5 cm in height. When mowed < 2.5 cm, a finer textured dense turf is produced. Tiller production also increases as mowing height is decreased (Fry and Huang, 2004). Because of the increased tiller production, competition among plants is greater, resulting in a reduced leaf blade width response (Fry and Huang, 2004). A mowing height > 5 cm will cause the seashore paspalum turf to become spindly, increase thatch production, and shade itself out (Trenholm and Unruh, 2003). Compared to bermudagrass (Cynodon dactalon [L.] Pers.), seashore paspalum does well under flooded conditions (Anonymous, 1998). Seashore paspalum also tolerates drought similar to centipedegrass (Eremochloa ophiuroides spp. ) and better than 1

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2 bermudagrass (Duncan and Carrow, 2000). Seashore paspalum has cold tolerance similar to most hybrid bermudagrass (Cynodon mageniggii) cultivars (Duncan and Carrow, 2000). The fine-textured paspalums are often the last warm season turfgrasses to become dormant and generally require consecutive days with temperatures below freezing to reach full winter dormancy (Duncan and Carrow, 2000). Like bermudagrass, seashore paspalum does not tolerate shade (Trenholm and Unruh, 2002). Areas with a dense tree canopy pose a problem when attempting to maintain seashore paspalum beneath them. However, when subjected to long periods of low light (cloudy, overcast/hazy/foggy, or monsoonal conditions), seashore paspalum grows well (Jiang et al., 2004). Jiang et al. (2004) concluded that seashore paspalum does well under low light conditions compared to hybrid bermudagrass. Sea Isle 1 seashore paspalum had the slowest rate of decline in quality (1 = dead turf to 9 = healthy turf) with 8.0 at full sunlight, 7.2 at 70% shade, and 6.9 at 90% shade compared to the best hybrid bermudagrass (TifSport) with 7.7 at full sunlight, 6.3 at 70% shade, and 5.7 at 90% shade. Turf quality and photosynthetic rates of both turfgrass species declined as the duration of low light increased, but the seashore paspalum cultivars had a higher photosynthetic rate than the bermudagrass cultivars, suggesting the higher photosynthetic rates contribute to the tolerance of low light intensity in seashore paspalum (Jiang, 2004). Fertility requirements of seashore paspalum appear to be lower than most warm season turfgrass species that are utilized on golf courses. However, in situations where saline water is used for irrigation and the soil is routinely flushed with water to prevent salt toxicity, fertility requirement will increase due to increased leaching (Duncan and Carrow, 2000).

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3 The nitrogen requirement for seashore paspalum ranges from 97 to 390 kg ha-1 y-1 depending on the maintenance intensity of the turf (Duncan and Carrow, 2000). Turf mowed at greens height (< 0.5 cm) typically requires no more than 390 kg N ha-1 y-1 in tropical regions (Duncan and Carrow, 2000). Phosphorus requirements for seashore paspalum are similar to bermudagrass and supplemental phosphorus is only needed when levels present in the soil are reported low on a soil test (Trenholm and Unruh, 2002; Duncan and Carrow, 2000). Potassium must be supplied to seashore paspalum in salt affected areas because K+ loss through leaching is increased with the presence of Na+, Ca2+, and Mg2+ (Duncan and Carrow, 2000). Potassium should to be applied at 1.5 to 2 times the rate of nitrogen (Duncan and Carrow, 2000). The application of potassium has been shown to improve wear tolerance, stress tolerance, and salinity tolerance of seashore paspalum (Duncan and Carrow, 2000). Iron amendments can be applied in small amounts during the growing season to promote green up without promoting shoot growth (Trenholm and Unruh, 2003). Mn2+ and Zn2+ also aid in enhancing the ability of seashore paspalum to tolerate salinity by preventing cation and osmotic shock (Duncan, 2004). In high salinity situations where fresh water leaching is practiced, all micronutrients need to be monitored regularly for deficiencies due to excessive leaching of nutrients. Saline soil is defined as a soil having a saturated extract with an electrical conductivity > 4 decisemens per meter (dS/m) (US Salinity Laboratory, 1969). Ocean water is equivalent to approximately 54 dS/m, or 34,500 ppm (Duncan, 2004). Sodium chloride (NaCl) is the predominant component contributing to salinity in soils (Jungklang

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4 et al., 2003). Salinity levels in soils are becoming increasingly problematic due to the use of alternative water (effluent or brackish) for irrigation. Duncan and Carrow (1998) have cited seven major contributors to increased soil salinity: increased use of wastewater on turfgrass; golf course construction in coastal sites; the placement of golf courses bordering environmentally sensitive wetlands or other similar areas; the use of high sand root zone mixes where sands can more readily become salinized than fine textured soils; the increasing emphasis on water conservation practices; saltwater intrusion in irrigation aquifers, especially within 16 km of sea coasts; and the construction of golf courses on sites with poor soil conditions, not normally suitable for crop production. Salinity tolerance is a distinguishing physiological characteristic of seashore paspalum. Research on this physiological tolerance is limited because seashore paspalum has only been used commercially for the past decade. There are three mechanisms plants use to tolerate salinity. The first mechanism is selective ion uptake by the roots (Colmer, 2000; Rose-Fricker and Wipff, 2001). Plants that use this mechanism are considered to be salt excluders. Even with a high concentration of Na+ in the soil the plant is able to efficiently and selectively absorb essential ions. The second mechanism is the accumulation of salt in specific vacuoles within plant cells, from which the salt is translocated back to the soil in small concentrations (Colmer, 2000; Rose-Fricker and Wipff, 2001). Other plants, such as inland saltgrass (Distichlis spicata (L.) Greene.) and bermudagrass, have special glands, called salt glands or

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5 bladders, on the leaf surface that excrete salt (Colmer, 2000; Rose-Fricker and Wipff, 2001). Plants that use this mechanism are considered to be salt includers. The third mechanism is osmotic adjustment (Colmer, 2000; Fricker and Wipff, 2001; Marcum, 2004). The plants adjust their internal ion gradient to maintain turgor pressure, allowing it to continue water absorption in the presence of high salt concentrations. All of these mechanisms operate in salt tolerant plants, while one or more of these mechanisms may be lacking in a salt sensitive plant (Colmer, 2000). Seashore paspalum has the ability to efficiently select ions absorbed by the roots, and it is also able to secrete salt through salt glands on the leaf surface (Marcum, 1999). Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting (Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of the soil over time and must be managed properly when establishing and maintaining a high quality turf. Soils high in Na+ will have poor aeration and reduced water infiltration rates due to dispersal of soil particles in the soil profile (Mitra, 2000 and 2001). A form of soluble Ca2+ must be added to soils with a high exchangeable Na+ percentage to replace the Na+ on the cation exchange sites (Mitra, 2000 and 2001). Gypsum is the most common form of Ca2+ because it is water soluble and has little effect on soil pH (Mitra, 2001). Once the Na+ is removed from the exchange site, it must be leached from the soil profile with deep, infrequent irrigation (Mitra, 2000 and 2001). An additional method of dealing with salinity problems is to use salt tolerant species and/or cultivars (Qian et al., 2001).

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6 Several studies have been conducted testing the tolerance of seashore paspalum to various concentrations of saltwater. Noaman and El-Haddad (2000) exposed established seashore paspalum to three levels of salinity: 10 g/L (16 dS/m), 20 g/L (32 dS/m), and 40 g/L (64 dS/m). A reduction in plant height with increased salt concentration was apparent after 4 weeks (wk) and continued to decrease until the end of the experiment at 10 wk. Similarly, as salt concentration increased from 16 dS/m to 64 dS/m, plant biomass decreased by 70% (Noaman and El-Haddad, 2000). Marcum and Murdoch (1994) subjected seashore paspalum and five other warm-season turfgrasses [manilagrass (Zoisia matrella (L.) Merr.), St. Augustinegrass (Stenotaphrum secundatum (Walt.) Ktze.), Tifway bermudagrass, Japanese lawngrass (Zoisia japonica Steud.), and centipedegrass] to five saltwater concentrations: 1 mM (1 dS/m), 100 mM (9 dS/m), 200 mM (17 dS/m), 300 mM (26 dS/m), and 400 mM (34 dS/m). Seashore paspalum growth rates were higher than the other turfgrass species at 34 dS/m. Seashore paspalum quality ratings were also higher than the other turfgrasses at all saltwater concentrations (Marcum and Murdoch, 1994). Couillard and Wiecko (1998) evaluated saltwater tolerance on bermudagrass, and seashore paspalum. The turf was treated with ocean water at three concentrations: pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m) + 1/3 potable water, and 1/3 ocean water (19 dS/m) + 2/3 potable water. The watering schedule was twice daily for two different periods: 3 days (d) or 6 d. Following the saltwater stress periods, potable irrigation was applied to evaluate the recovery potential of seashore paspalum and bermudagrass over a period of 32 d after the salt-stress treatments began. Injury was observed on all plant species tested at all three ocean water concentrations.

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7 Bermudagrass and seashore paspalum both fully recovered from all treatments. The most injury occurred with pure ocean water after the 6 d salt-stress treatment. Wiecko (2003) exposed seashore paspalum, bermudagrass, St. Augustinegrass, and centipedegrass to three different salinity levels (54, 37, and 19 dS/m) over two short term salt stress durations (3 and 6 d). Seashore paspalum showed excellent salinity tolerance compared to all other plants tested with the maximum injury of 18% at 54 dS/m after the 6 d salt stress duration. Bermudagrass injury was 30% at 54 dS/m after the 6 d salt stress duration and only minor injury at lower salt concentrations. St. Augustinegrass showed up to 60% injury under the 6 d duration of 54 dS/m and centipedegrass showed complete necrosis (Wiecko, 2003). These studies indicate seashore paspalum can tolerate saline irrigation, but long-term quality can be compromised when irrigated with high salt concentration water. When establishing seashore paspalum, saline conditions may negatively impact turfgrass growth rate (Duncan and Carrow, 1999). Before selecting a grass species for a specific site, water and soil samples should be collected to analyze quality (Duncan and Carrow, 2000). If saline soils are present, amendments should be added to manage the problem before turfgrass is established in the area (Duncan and Carrow, 2000). Long-term salinity problems will persist in the soil if poor quality irrigation water is used (Duncan and Carrow, 2000). Proper irrigation scheduling and duration will help alleviate the problem by leaching the salts through the soil profile (Duncan and Carrow, 2000). Water Quality and Consumption on Golf Courses Water management is one of the most important aspects of golf course maintenance. On average, a golf course occupies approximately 55 hectares (137 acres), of which 65% is irrigated on a regular basis (Marella, 1999). According to a survey by

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8 Haydu and Hodges in 2002, golf courses in Florida use approximately 655 billion liters (173 billion gallons) of water per year. Recycled water accounts for 49% of the total water, while 29% comes from surface water and 21% from wells. There are five Water Management Districts in the state of Florida that regulate the use of water. These districts have the power to issue water use permits, impose regulations, and establish permit fees. There are several types of water use permits that are issued by Floridas Water Management Districts. Consumptive use permits (CUPs) are the most commonly issued permit and are required if water is withdrawn from a well 15 mm (6 in) in diameter or greater, if the annual average water use is 378,500 liters (100,000 gal) per day or greater, and if a pump is used that has the capability to pump 3.8 million liters (1 million gal) per day or greater (SJRWMD 2002). Because CUPs determine the duration and amount of potable water available to golf courses, alternative water sources that have fewer restrictions are being used. The United States Golf Association (USGA) lists several different irrigation water sources that are available to golf courses (Snow, 2004). Fresh water is the most common source of irrigation water and can be acquired from aquifers or retention ponds and lakes. Another source is tertiary treated effluent water. The turfgrass acts as a filter by extracting nutrients and breaking down chemicals in the effluent water that municipalities would otherwise discharge into nearby rivers or the ocean (Snow, 2004). Some areas in the southern U.S. including Arizona and Florida require the use of effluent water for turfgrass irrigation because of a limited supply of freshwater (Snow, 2004). Brackish water (salt concentration between fresh water and ocean water) or ocean water is also used as an irrigation source on golf courses. Bermudagrass and seashore

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9 paspalum are tolerant to certain levels of saltwater (Snow, 2004). Precise application of saltwater is required to prevent injury to existing plant populations that have a low salt tolerance. Reverse osmosis desalinization facilities can also be constructed on site to reduce the dissolved salt content of saline water to a usable level. Saline water (feedwater) is drawn from a source and pretreated by adjusting pH, removing suspended solids, and adding inhibitors to control scaling caused by calcium constituents (UNEP, 1997). The feedwater is then pressurized to the appropriate operating pressure for the water-permeable membrane (UNEP, 1997). The pressurized feedwater enters the membrane that inhibits dissolved salts from passing, while allowing the desalinized water to pass through (UNEP, 1997). Finally, the desalinized water is stabilized by degasification and adjustment of the pH (UNEP, 1997). These reverse osmosis desalinization plants are expensive, but are necessary in certain areas where freshwater is limited or too expensive to purchase in large quantities (Snow, 2004). Weed Management on Golf Courses Seashore paspalum exhibits exceptional salt tolerance, but is highly susceptible to injury from many postemergence herbicides (Wiecko, 2003). It may be possible to replace postemergence herbicides with saltwater to control some species of weeds (Wiecko, 2003). Weeds compete with turfgrass for light, nutrients, water, and physical space (Florkowski and Landry, 2002) and weed management is a major cost for turfgrass managers. On golf courses in the Southeast, average expenditures for herbicides in 1998 were $11,690 per course (Florkowski and Landry, 2002).

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10 Some of the more common weeds in turfgrass include dollarweed (Hydrocotyle spp.), Florida pusley (Richardia scabra L.), Virginia buttonweed (Diodia virginiana L.), goosegrass, southern crabgrass (Digitaria ciliaris (Retz.) Koel.), common bermudagrass, tropical signalgrass (Urochloa subquadripara [Trin.] R. Webster), torpedograss (Panicum repens L.), and purple nutsedge (Cyperus rotundus L.). Dollarweed is a perennial broadleaf that reproduces by seed, rhizomes, and tubers. The leaves are long stalked with the petiole attached to the center of the leaf that resembles an umbrella. Dollarweed is most commonly found in areas with excessive moisture (Murphy et al., 1996). Florida pusley is a summer annual broadleaf that reproduces by seed. The branched stem is hairy with thickened leaves that have an opposite arrangement. The white flowers are bunched at the end of the branches (Murphy et al., 1996). Virginia buttonweed is a perennial broadleaf that reproduces by seed, roots, and stem fragments. The stem is branched and hairy with an opposite leaf arrangement. The flower is white with four lobes at each leaf axil (Murphy et al., 1996). Goosegrass is a summer annual grass that reproduces by seed. The crown is generally white or silver in color and is usually found in areas with compacted soils. The leaves are smooth on both sides with a short-toothed membranous ligule (Murphy et al., 1996). Southern crabgrass is a summer annual grass that reproduces by seed. Stems are branched and root at the nodes. The leaves are usually hairy on both sides and have a toothed membranous ligule (Murphy et al., 1996).

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11 Common bermudagrass is a perennial grass that reproduces by stolons, rhizomes, and seed (Duble, 2004). The stolons and rhizomes root at the nodes to form a deep fibrous root system (Duble, 2004). The collar of the leaves have a fringe of short, white hairs (NewCROP, 1999). Tropical signalgrass is a summer annual grass that reproduces by seed. The stem is branched with a blanket-like growth pattern. The leaves are glossy with a coarse texture (Busey 2000). Torpedograss is a very persistent perennial grass that reproduces vegetatively or through rhizomes (Busey, 2002). The rhizome system is very robust with sharply pointed tips. The stems are stiff and erect with leaves that are folded or flat (Murphy et al., 1996). Purple nutsedge is a perennial sedge that reproduces primarily by oblong tubers that are covered with hairs. The leaves taper abruptly to a point unlike yellow nutsedge that tapers gradually to a point. The seed head has a purplish color and is formed on a triangular stem (Murphy et al., 1996). These weeds are a few of the most common weeds found in turfgrass in the Southeastern United States. Control of these weeds can be very difficult and expensive. Weeds can be controlled using cultural practices to produce a healthy, competitive turfgrass, in combination with herbicides. Cultural practices can greatly reduce weed pressure on turfed areas. Using cultural methods can reduce chemical use, which can reduce herbicide costs for weed control. Often, the most cost effective method of weed control is to have a healthy, dense turf (Unruh and Elliott, 1999). The turf will naturally out-compete many weed species.

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12 One important step in producing a healthy turf is proper fertility. Different turfgrasses have different fertility requirements. Nitrogen, phosphorus, and potassium are important nutrient requirements for enhanced shoot and root growth. Aerification and verticutting are common cultural practices to control weeds and relieve turf stresses such as compaction and thatch on golf courses. Aerification consists of pulling soil core plugs 0.63 cm to 1.9 cm (0.25 to 0.75 in.) in diameter, ranging in depth of 5 to 10 cm (2 to 4 in.) (Unruh and Elliott, 1999). This process relieves soil compaction, improves surface drainage and water penetration, and reduces thatch (Unruh and Elliot, 1999). Verticutting consists of vertical knives spaced close together on a horizontal shaft that slice into the turf (Unruh and Elliott, 1999). This practice removes the organic matter (thatch) layer allowing the turf to grow horizontally and allows for a smooth putting surface. Deep verticutting should be avoided when maintaining seashore paspalum greens because this increases the potential for scalping (Duncan and Carrow, 2002). Light verticutting enhances stolon-rhizome-shoot growth and allows topdressing sand to integrate into the thatch layer producing a more firm, smooth surface less susceptible to scalping (Duncan and Carrow, 2000, 2002). A good quality topdressing sand for seashore paspalum should integrate easily into the surface at light rates without verticutting (Duncan and Carrow, 2002). Mowing is another very important cultural practice on a golf course. Improper mowing can weaken the turf reducing its density and quality (Unruh and Elliott, 1999), providing an opportunity for weeds to invade. Seashore paspalum does not tolerate scalping as well as bermudagrass or zoysiagrass and may take 4 to 6 wk to fully recover

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13 (Duncan and Carrow, 2002). When reducing the mowing height on seashore paspalum tees and greens, it should be done in gradual increments of 0.05 to 0.08 cm (0.02 to 0.03 in.) over 2 to 3 d (Duncan and Carrow 2002). When the turf is mowed properly, very little stress is put on the plant, allowing it to recover very quickly. Frequent mowing increases shoot growth, producing a dense canopy that makes it more difficult for weeds to invade (Unruh and Elliott, 1999). Finally, proper irrigation can be used to reduce weed pressure. Maintaining proper soil moisture levels is important for producing a healthy turf. Seashore paspalum is very responsive to irrigation duration and frequency and a shallow root system will result from frequent irrigation events of short durations (Duncan and Carrow, 2002). This also causes the turf to be more succulent, less drought tolerant, and more susceptible to scalping. Watering schedules should consist of long durations during applications with long intervals (1.25 to 2.5 cm of water every 4 to 7 days on a sand green) between applications to force the roots to grow deeper into the soil profile (Duncan, 2004; Duncan and Carrow, 2002). Various grass types require different moisture levels and weed species will also respond differently depending on moisture levels. For instance, dollarweed populations can be reduced in St. Augustinegrass turf by reducing irrigation levels (Busey, 2001). Herbicides are regularly used for weed control on golf courses. Some important considerations when selecting a herbicide are effectiveness, turfgrass tolerance, speed of control, toxicity, and cost (Unruh and Elliott, 1999). There is no single herbicide that will control all weeds in a desired turf stand, so proper identification is essential (Unruh and Brecke, 1998). Seashore paspalum is sensitive to many herbicides commonly used

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14 on other turfgrasses (Trenholm and Unruh, 2003; and CTAHR, 1998). Herbicides that are noninjurous to seashore paspalum include bensulide, pronamide, benefin, DCPA, pendimethalin, ethofumesate, quinclorac, MCPP + 2,4-D + dicamba, dithiopyr, 2,4-D + dicamba + dicloprop, dicamba, halosulfuron, mecoprop, and bentazon (Duncan and Carrow, 2000). However, dithiopyr, halosulfuron, oxadiazon, and prodiamine are the only herbicides labeled for use on seashore paspalum (Unruh et al., 2005). These herbicides could possibly be used at reduced rates in conjunction with saltwater irrigation to control weeds in seashore paspalum (Duncan and Carrow, 2000). Studies have been conducted to test the tolerance of seashore paspalum to several postemergence herbicides. In 1997, Johnson and Duncan tested the recommended rates and 3 times the recommended rates of diclofop, quinclorac, dicamba, imazaquin, halosulfuron, and 2,4-D + mecoprop + dicamba on four seashore paspalum accessions (AP 10, HI 25, PI 28960, and K-7). Seashore paspalum accessions varied in their response to the herbicides evaluated. Quinclorac and halosulfuron were the only herbicides that did not reduce the quality of any accession at the recommended rates. When quinclorac and halosulfuron rates increased, quality of HI 25 and K-7 was reduced. All accessions recovered completely even from the high rates within 4 to 8 wk after initial treatment. Dicamba had no effect on any of the accessions when applied at the labeled rate. Quality of the K-7 accession, however, was negatively affected by the increased rate of dicamba. Diclofop, imazaquin, and 2,4-D + mecoprop + dicamba reduced the quality of all paspalum accessions regardless of application rate. Full recovery from diclofop and

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15 imazaquin required 4 to 8 wk. Recovery from the labeled rates of 2,4-D + mecoprop + dicamba took 4 to 8 wk for all accessions, and none of the accessions recovered from the high rate by 8 wk. The overall conclusion from this study was that quinclorac, dicamba, and halosulfuron were safe on all accessions, diclofop and imaziquin were marginal, and 2,4-D + mecoprop + dicamba were considered injurious. A study was conducted by Unruh et al. (2005) testing the tolerance of Salam seashore paspalum to postemergence herbicides for control of grass (clethodim, ethofumesate, metsulfuron, sethoxydim, and quinclorac), broadleaf (clopyralid, dicamba, and 2,4-D + mecoprop + dicamba), and sedge (bentazon, halosulfuron, imazapic, imazaquin, and trifloxysulfuron-sodium) species. Metsulfuron, quinclorac, clopyralid, dicamba, 2,4-D + mecoprop + dicamba, bentazon, halosulfuron, and imazaquin caused less than 15% injury at the recommended rates and are considered safe for seashore paspalum. Clethodim, sethoxydim, ethofumesate, imazapic, and trifloxysulfuron-sodium caused greater than the acceptable standard of 20% injury and are considered not safe for application to seashore paspalum. The high level of salt tolerance may allow the use of saltwater for weed control in place of injurious postemergence herbicides (Wiecko, 2003). Couillard and Wiecko (1998) evaluated injury from saltwater on large crabgrass (Digitaria sanguinalis (L.) Scop.) and mimosa-vine (Mimosa pudica Torr.). They treated both species with ocean water at three concentrations: pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m) + 1/3 potable water, and 1/3 ocean water (19 dS/m) + 2/3 potable water. The weeds were watered twice daily for two different periods: 3 d or 6 d. Following the saltwater stress periods, potable irrigation was applied to evaluate the recovery potential over a period of

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16 32 days after the salt-stress treatments began. Injury was observed on both plant species tested at all three ocean water concentrations. Mimosa only recovered from the 1/3x ocean water treatment subjected to 3 d salt-stress. Complete crabgrass control was only achieved with pure ocean water under 6 d salt-stress. Other studies were conducted by Wiecko (2003) with the addition of goosegrass, alyceclover (Alysicarpus vaginalis (L.) DC.), and yellow nutsedge (Cyperus esculentus L.) to the species previously evaluated. Mimosa-vine showed complete necrosis at 54 dS/m and 37 dS/m under both salt stress durations, respectively. Alyceclover showed >90% injury at 34,500 ppm under both salt stress durations, and >70% at 37 dS/m. Large crabgrass and goosegrass showed >90% injury at 54 dS/m. Yellow nutsedge had the greatest salt tolerance among the weeds with injury <40% at all salt concentrations (Wiecko, 2003). Based on these studies, ocean water can be used as an alternative to herbicides to control weeds in certain turfgrasses (Couillard and Wiecko, 1998). Most annual grass and broadleaf weed species cannot tolerate continuous irrigation with saltwater or saltwater blends (wastewater) (Duncan and Carrow, 2000). Summary During early root growth and establishment, all plants are more sensitive to saline conditions causing desiccation of the plant and reducing water infiltration and aeration of the soil (Duncan and Carrow, 2000). Salinity will also cause nutrient deficiencies or imbalances resulting in toxicities that will influence plant growth and development (Duncan and Carrow, 2000). Genetic resistance to these stresses and toxicities is valuable for managing turf successfully on saline soils (Duncan and Carrow, 2000).

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17 While considerable research has been conducted to determine the tolerance of established seashore paspalum to saltwater, little information is available concerning saltwater tolerance in newly sprigged seashore paspalum. Thus, research was conducted to compare salt tolerance of established with newly sprigged seashore paspalum. Some research has been conducted to evaluate susceptibility of selected weed species to saltwater. However, additional information about the effectiveness of saltwater for control of additional weed species is needed. Research was conducted with eight weed species to determine the level of control that can be achieved with saltwater alone. This will help determine the contribution to overall weed management that can be expected from saltwater irrigation. Tolerance of seashore paspalum to many postemergence herbicides has been determined over the past decade. However, herbicide response of seashore paspalum in salt-affected areas has not yet been determined and seashore paspalum may be more sensitive to injury as salt-stress increases. Susceptibility to herbicide injury under salt stress was also tested on seashore paspalum.

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18 Table 1-1 Paspalum cultivars, leaf texture, and year of introduction. Cultivar Leaf texture Year Introduced Saltene intermediate 1951 Salpus intermediate Futurf intermediate 1972 Adalayd (Excalibur) intermediate 1975 Fidalayel intermediate Tropic Shore course 1991 Mauna Kea intermediate Salam fine (fairway/sports) 1998 Sea Isle 2000 fine (greens/tees) 1999 to present Sea Isle 1 fine (fairway/tees/sports) Durban Country Club fine (fairway/tees/roughs) Sea Dwarf fine (greens/tees) Sea Green fine (greens/tees) Seaway fine (fairway/sports) Seaspray (seeded) fine (fairway/sports)

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CHAPTER 2 TOLERANCE OF NEWLY SPRIGGED AND ESTABLISHED SEASHORE PASPALUM TO SALTWATER Introduction Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial, warm season turfgrass that is native to tropical and subtropical regions of the world (Duncan and Carrow, 2000). Although seashore paspalum has existed for many years, it has only been used commercially for the past few decades. Seashore paspalum spreads by rhizomes and stolons that root at the nodes forming a deep fibrous root system (Duble, 2000). It is generally propagated vegetatively from sod or sprigs because seed production has not been reliable (Duncan and Carrow, 2000). Research into the self-incompatibility issues has led to the introduction of one seed produced cultivar, Seaspray (Hughes, 2005). The leaves of seashore paspalum are slightly coarser than those of common bermudagrass when mowed > 2.5 cm in height. When mowed < 2.5 cm, a finer textured dense turf is produced. Tiller production will increase as mowing height is decreased and the width of the leaf blade is reduced as a result of competition among plants (Fry and Huang, 2004). A mowing height > 5 cm causes the seashore paspalum turf to become spindly, increase thatch production, and shade itself out (Trenholm and Unruh, 2003). In flooded conditions seashore paspalum does well compared to bermudagrass (Anonymous, 1998). Seashore paspalum also tolerates drought similar to centipedegrass and better than bermudagrass (Duncan and Carrow, 2000). The cold tolerance of seashore paspalum is similar to most hybrid bermudagrass cultivars (Duncan and Carrow, 19

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20 2000). The fine-textured paspalums are often the last warm season turfgrasses to go into full winter dormancy and generally require consecutive days with temperatures below freezing to reach full winter dormancy (Duncan and Carrow, 2000). Like bermudagrass, seashore paspalum does not tolerate shade, however, when low light conditions (cloudy, overcast/hazy/foggy, and monsoonal conditions) are present, seashore paspalum does well under low light conditions compared to hybrid bermudagrass (Jiang et al., 2004; Trenholm and Unruh, 2002). Fertility requirements of seashore paspalum appear to be lower than most warm season turfgrass species that are utilized on golf courses. However, in situations where saline water is used for irrigation and the soil is routinely flushed with water to prevent salt toxicity, fertility requirements will increase due to increased leaching and all micronutrients need to be monitored regularly for deficiencies. (Duncan and Carrow, 2000). Salinity levels, predominantly sodium chloride (NaCl), in soils are becoming increasingly problematic due to the use of alternative water (effluent or brackish) for irrigation (Duncan and Carrow, 1998; Jungklang, 2003). There are three physiological mechanisms plants use to tolerate salinity. The first mechanism is selective ion uptake by the roots (Colmer, 2000; Rose-Fricker and Wipff, 2001). The plant is able to efficiently and selectively absorb needed ions even with a high concentration of Na+ in the soil. The second mechanism is the accumulation of salt in specific vacuoles within plant cells, from which the salt is retranslocated back to the soil or excreted by salt glands on the leaf surface (Colmer, 2000; Rose-Fricker and Wipff, 2001). Finally, the plant uses osmotic adjustment to maintain turgor pressure allowing it to continue water absorption in the

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21 presence of high salt concentrations (Colmer, 2000; Fricker and Wipff, 2001; Marcum, 2004). Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting (Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of the soil over time and must be managed properly when establishing and maintaining a high quality turf. Soils high in Na+ will have poor aeration and reduced water infiltration rates due to dispersal of soil particles in the soil profile (Mitra, 2000 and 2001). A form of soluble Ca2+ must be added to soils with a high exchangeable Na+ percentage to replace the Na+ on the cation exchange sites (Mitra, 2000 and 2001). Gypsum is the most common form of Ca2+ because it is water soluble and has little effect on soil pH (Mitra, 2001). Once the Na+ is removed from the exchange site, it must be leached from the soil profile with deep, infrequent irrigation (Mitra, 2000 and 2001). An additional method of dealing with salinity problems is to use salt tolerant species and/or cultivars (Qian, 2001). Several studies have been conducted testing the tolerance of seashore paspalum to various concentrations of saltwater. Noaman and El-Haddad (2000) exposed established seashore paspalum to three levels of salinity: 10 g/L (16 dS/m), 20 g/L (32 dS/m), and 40 g/L (64 dS/m). The plant height reduction with increased salt concentration was apparent after 4 wk and continued to decrease until the end of the experiment at 10 wk. Similarly, as salt concentration increased from 16 dS/m to 64 dS/m, plant biomass decreased by 70% (Noaman and El-Haddad, 2000). Marcum and Murdoch (1994) subjected seashore paspalum and five other warm-season turfgrasses [manilagrass (Zoisia matrella (L.) Merr.), St. Augustinegrass (Stenotaphrum secundatum (Walt.) Ktze.), Tifway bermudagrass, Japanese lawngrass

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22 (Zoisia japonica Steud.), and centipedegrass] to five saltwater concentrations: 1 mM (1 dS/m), 100 mM (9 dS/m), 200 mM (17 dS/m), 300 mM (26 dS/m), and 400 mM (34 dS/m). Seashore paspalum growth rates were higher than the other turfgrass species at 34 dS/m. Seashore paspalum quality ratings were also higher than the other turfgrasses at all saltwater concentrations (Marcum and Murdoch, 1994). Couillard and Wiecko (1998) evaluated saltwater for tolerance on bermudagrass, and seashore paspalum. The turf was treated with ocean water at three concentrations: pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m) + 1/3 potable water, and 1/3 ocean water (19 dS/m) + 2/3 potable water. The watering schedule was twice daily for two different periods: 3 d or 6 d. Following the saltwater stress periods, potable irrigation was applied to evaluate the recovery potential of seashore paspalum and bermudagrass over a period of 32 d after the salt-stress treatments began. The most injury for bermudagrass and seashore paspalum occurred with pure ocean water after the 6 d salt-stress treatment. In all instances, bermudagrass and seashore paspalum both fully recovered from all treatments when watered with potable water. Wiecko (2003) exposed seashore paspalum, bermudagrass, St. Augustinegrass, and centipedegrass to three different salinity levels (54, 37, and 19 dS/m) over two short term salt stress durations (3 and 6 d). Seashore paspalum showed excellent salinity tolerance compared to all other plants tested with the maximum injury of 18% at 54 dS/m after the 6 d salt stress duration. Bermudagrass injury was 30% at 54 dS/m after the 6 d salt stress duration and only minor injury at lower salt concentrations. St. Augustinegrass showed up to 60% injury under the 6 d duration of 54 dS/m and centipedegrass showed complete necrosis (Wiecko, 2003).

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23 These studies indicate seashore paspalum can tolerate saline irrigation, but quality can be compromised long-term when irrigated with high salt concentration water. When establishing seashore paspalum, saline conditions may negatively impact turfgrass growth rate (Duncan and Carrow, 1999). The salinity tolerance during establishment of seashore paspalum has not yet been determined. The objective of this study was to determine the tolerance of both newly sprigged and established seashore paspalum to various concentrations of saltwater. Methods and Materials Studies were conducted under greenhouse conditions at the University of Florida in Gainesville in 2004. Strips of sod were cut with a sod cutter from a two year old stand of Sea Isle 1 seashore paspalum. Plugs were cut from the sod strips using a golf cup cutter 15 cm in diameter. The native soil was washed from the plugs and then plugs were transplanted into 15 cm in diameter by 17 cm deep (3,000 cm3 volume) plastic pots containing a growing medium of USGA (1993) greens mix (80% sand and 20% organic matter). The intact seashore paspalum plugs were planted level with the rim of the pots. After transplanting, the pots were placed in a greenhouse receiving full sun and maintained at a temperature range of 27o to 32o C. A slow release 18-9-18+Mn+Fe fertilizer was applied at a rate of 24.5 kg N ha-1 1 wk after planting. The plugs were irrigated with potable water during a 3 wk rooting period. Separate pots were planted with seashore paspalum sprigs. Plugs were harvested as described above and separated into sprigs. The sprigs were planted (200 ml/pot) in pots measuring 15 cm diameter by 17 cm deep containing USGA greens mix. A 2.5 cm layer of the greens mix was then applied, covering the sprigs to allow for good growing medium to stolon contact.

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24 Saltwater applications were initiated immediately after sprigging (January 19 in 1st study and March 3rd in repeated study) and were applied to both sprigged and established seashore paspalum (transplanted 3 wk prior to initiation of saltwater treatment). Saltwater treatments were applied twice per week (Mon. and Wed.), with one potable water treatment per week (Fri.) applied to prevent salt accumulation on the growing medium surface. The five saltwater (NaCl) concentrations utilized for this study were as follows: untreated (0X), 13 dS/m (1/4X), 27 dS/m (1/2X), 41 dS/m (3/4X), and 55 dS/m (1X). The 55 dS/m (1X) concentration is equivalent to ocean water and the untreated (0X) is potable water. Each irrigation event consisted of 200 ml of saltwater or potable water, which was equivalent to 1 cm of water (irrigation) per event, totaling the standard 3 cm of water (irrigation) recommended for seashore paspalum weekly (Duncan and Carrow, 2000). All pots were maintained at 2 cm using rechargeable grass shears. Chlorothalonil [2,4,5,6-tetrachloroisophthalonitrile] and chlorpyrifos [0,0-diothyl 0-(3,5,6-trichloro-2-pyridinyl) phosphorothioate] were applied preventively at 14.5 kg ai ha-1 and 1 kg ai ha-1, respectively, to control fungal disease and insects (Anonymous 2004a, 2004b). Visual quality ratings were taken at 4 wk and 8 wk after initiation of saltwater applications with a range from 0 (dead turf) to 9 (green, healthy, ideal turf). The experimental design was a randomized complete block design with four replications. The sprigged and established seashore paspalum studies were evaluated separately. Data were analyzed in PROC GLM using an ANOVA to test all possible interactions of saltwater treatment, replication, and trial, and means were separated using least significant difference (LSD) at the 5% probability level (SAS, 2004). Regression

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25 analysis was utilized to show the response of both sprigged and established seashore paspalum quality to saltwater concentration. Results and Discussion There were no interactions between trials, therefore the data were pooled. There was an interaction between treatment and timing of visual evaluation. Therefore data are presented separately for the 4 wk and 8 wk evaluations. Newly Sprigged Seashore Paspalum Quality of newly sprigged seashore paspalum was affected by saltwater treatments. After 4 wk of treatment, quality ratings decreased as saltwater concentration increased. The sprigs had a quality rating of 6.5 when irrigated with potable water, but decreased to 2.5 when irrigated with 27 dS/m saltwater (Table 2.1). At 55 dS/m, the seashore paspalum sprigs were nearly dead 4 wk after initial treatment with quality rating of only 1.0 (Table 2.1). A similar trend was observed 8 wk after the initial saltwater treatments. The sprigs treated with potable water were well established by 8 wk with a quality rating of 7.5 (Table 2.1). Seashore paspalum quality declined to 2.0 at 27 dS/m and 0.5 at 55 dS/m (Figure 2.1 and Table 2.1). The regression model indicates the quality rating of seashore paspalum will decrease below 6.5 when irrigated with saltwater < 13 dS/m 8 wk after the initial saltwater treatments (Figure 2.1). Alternative irrigation water with a salt concentration range between 27 dS/m to 55 dS/m will reduce the growth rate of even the most salt tolerant paspalum cultivar by 50% if the salts are not replaced and consistently moved through the soil (Duncan and Carrow, 2000). Due to the lack of tolerance to salinity, newly sprigged seashore paspalum should be irrigated with potable water during establishment to reduce stress and promote healthy growth.

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26 Established Seashore Paspalum Once established, seashore paspalum exhibited excellent salinity tolerance. Seashore paspalum quality ratings were acceptable ( 6.5) at 13 dS/m and 27 dS/m salt, but declined to 6.0 and 4.5 at 41 dS/m and 55 dS/m, respectively 4 wk after initial saltwater treatments (Table 2.1). Turfgrass quality increased over time with ratings of 8.0, 7.5, and 6.5 at 13 dS/m, 27 dS/m, and 41 dS/m, respectively 8 wk after saltwater irrigation initiation (Table 2.1). Quality was below the 6.5 minimum acceptable level only at 55 dS/m. The regression model indicates the quality rating of established seashore paspalum will decrease to 6.5 at 33 dS/m 8 wk after the initial saltwater treatment (Figure 2.1). The largest reduction in quality was observed 4 wk after initiation of the saltwater treatments. The increase in quality over time may have been due to the ability of established seashore paspalum to physiologically adjust to the saline conditions for an extended period of time. Growth rate measurements were not taken, but a reduced growth rate was visually evident as saltwater concentration increased. Newly sprigged seashore paspalum is sensitive to saltwater concentrations 13 dS/m. Growth rate is reduced and the time of establishment increases as saltwater concentration increases. Saltwater concentration > 27 dS/m will cause desiccation and eventual death of the sprigs. Established seashore paspalum exhibited a high tolerance to saltwater irrigation. Although seashore paspalum did not maintain acceptable quality when irrigated with pure ocean water (55 dS/m), it is able to tolerate irrigation with salinity levels up to 41 dS/m. This characteristic will allow turf managers, located near the coast or those who have water restrictions, to use alternative water sources (effluent and brackish) for irrigation with salt concentrations up to 41 dS/m.

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27 Table 2-1 Saltwater effect on sprigged and established seashore paspalum. Seashore Paspalum quality ratinga Established Sprigged Salt Concentrationb 4 wksc 8 wksc 4 wksc 8 wksc 0 9.0 9.0 6.5 7.5 13 7.5 8.0 4.0 5.0 27 6.5 7.5 2.5 2.0 41 6.0 6.5 1.5 1.0 55 4.5 4.0 1.0 0.5 LSD (0.05) 2.0 2.0 2.5 3.0 aQuality ratings range from 0 (dead turf) to 9 (healthy turf). bSalt Concentrations in decisemens per meter (dS/m). cWeeks of exposure to saltwater concentrations.

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28 Salt Concentration (dS/m) 010203040506 0 Quality rating (0-9) 02468 Established seashore paspalum Sprigged seashore paspalum Newly sprigged paspalum(y = -0.13x + 6.7) r2=0.91Established paspalum (y = -0.08x + 9.27) r2=0.92 Figure 2-1 Effect of saltwater concentration on seashore paspalum quality ratings 8 wk after initial application of saltwater (data pooled over trials).

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CHAPTER 3 SUCEPTIBILITY OF NINE TURFGRASS WEED SPECIES TO FIVE SALTWATER CONCENTRATIONS Introduction Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial warm season turfgrass that is native to tropical and subtropical regions of the world (Duncan and Carrow, 2000). It has existed for years, but has only been used commercially for the past few decades. Seashore paspalum spreads by rhizomes and stolons that root at the nodes and forms a deep fibrous root system (Duble, 2000). It is generally propagated vegetatively, because seed produced have low viability (Trenholm and Unruh, 2002), although seeded varieties are under development. Seashore paspalum is a desirable turfgrass that has a high salt tolerance (Duncan and Carrow, 2000). Weeds compete with turfgrass for light, nutrients, water, and physical space (Florkowski, 2002) and weed management is a major cost for turfgrass managers. On golf courses in the Southeast, the average expenditures for herbicides in 1998 were $11,690 (Florkowski, 2002). Some of the more common weeds in turfgrass include dollarweed (Hydrocotyle spp.), Florida pusley (Richardia scabra L.), Virginia buttonweed (Diodia virginiana L.), goosegrass (Eleusine indica [L.] Gaertn.), southern crabgrass (Digitaria ciliaris [Retz.] Koel.), common bermudagrass (Cynodon dactalon [L.] Pers.), tropical signalgrass (Urochloa subquadripara [Trin.] R. Webster), torpedograss (Panicum repens L.), and purple nutsedge (Cyperus rotundus L.). 29

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30 Dollarweed is a perennial broadleaf that reproduces by seed, rhizomes, and tubers. The leaves are long stalked with the petiole attached to the center of the leaf that resembles an umbrella. Dollarweed is most commonly found in areas with excessive moisture (Murphy et al., 1996). Florida pusley is a summer annual broadleaf that reproduces by seed. The branched stem is hairy with thickened leaves that have an opposite arrangement. The white flowers are bunched at the end of the branches (Murphy et al., 1996). Virginia Buttonweed is a perennial broadleaf that reproduces by seed, roots, and stem fragments. The stem is branched and hairy with an opposite leaf arrangement. The flower is white with four lobes at each leaf axil (Murphy et al., 1996). Goosegrass is a summer annual grass that reproduces by seed. The crown is generally white or silver in color and is usually found in areas with compacted soils. The leaves are smooth on both sides with a short-toothed membranous ligule (Murphy et al., 1996). Southern crabgrass is a summer annual grass that reproduces by seed. Stems are branched and root at the nodes. The leaves are usually hairy on both sides and have a toothed membranous ligule (Murphy et al., 1996). Common bermudagrass is a perennial grass that reproduces by stolons, rhizomes, and seed (Duble, 2004). The stolons and rhizomes root at the nodes to form a deep fiberous perennial root system (Duble, 2004). Seeded varieties are currently being developed and tested (Evers and Davidson, 2004). The collar of the leaves have a fringe of short, white hairs (NewCROP, 1999).

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31 Tropical signalgrass is a summer annual grass that reproduces by seed. The stem is branched with a blanket-like growth pattern. The leaves are glossy with a coarse texture (Busey 2000). Torpedograss is a very persistent perennial grass that reproduces vegetatively or by soil transfer (Busey, 2002). The rhizome system is very robust with sharply pointed tips. The stems are stiff and erect with leaves that are folded or flat (Murphy, 1996). Purple nutsedge is a perennial sedge that reproduces primarily by oblong tubers that are covered with hairs. The leaves taper abruptly to a point unlike yellow nutsedge that tapers gradually to a point. The seed head has a purplish color and is formed on a triangular stem (Murphy et al., 1996). These weeds are a few of the most common and troublesome weeds found in turfgrass in the Southeastern United States (Webster, 2000). Control of these weeds can be very difficult and expensive. Weeds can be controlled using cultural practices to produce a healthy, competitive turfgrass, in combination with herbicides. Aerification and verticutting are common cultural practices on golf courses to control weeds and relieve turf stresses such as compaction and thatch. Aerification consists of pulling soil core plugs 0.63 cm to 1.9 cm (0.25 to 0.75 in.) in diameter, ranging in depth of 5 to 10 cm (2 to 4 in.) (Unruh and Elliott, 1999). This process relieves soil compaction, improves surface drainage and water penetration, and reduces thatch (Unruh and Elliot, 1999). Vertical mowing consists of vertical knives spaced close together on a horizontal shaft that slice into the turf (Unruh, and Elliott, 1999). This practice removes the organic matter (thatch) layer, allowing the turf to grow horizontally and allows for a smooth

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32 putting surface. When maintaining seashore paspalum greens, deep verticutting should be avoided (Duncan and Carrow, 2002). Light verticutting enhances stolon-rhizome-shoot growth and allows topdressing sand to integrate into the thatch layer, producing a more firm, smooth surface that is less susceptible to scalping (Duncan and Carrow, 2000 and 2002). A good quality topdressing sand should integrate easily into the surface at light rates without verticutting (Duncan and Carrow, 2002). Mowing is a very important cultural practice on golf courses. Improper mowing can weaken the turf, which reduces the density and quality (Unruh and Elliott, 1999), allowing for weed invasion. Seashore paspalum does not tolerate scalping as well as bermudagrass or zoysiagrass and may take 4 to 6 wk to fully recover (Duncan and Carrow, 2002). When lowering the mowing height on seashore paspalum gradual increments of 0.05 to 0.08 cm (0.02 to 0.03 in.) over 2 to 3 d is best (Duncan and Carrow 2002). When the turf is mowed properly, very little stress is put on the plant, allowing it to recover very quickly. Frequent mowing increases shoot growth, producing a dense canopy that makes it more difficult for weeds to invade (Unruh and Elliott, 1999). Finally, proper irrigation can be used to reduce weed pressure. Maintaining proper soil moisture levels is important for producing a healthy turf. Seashore paspalum is very responsive to irrigation duration and frequency and a shallow root system will result from frequent irrigation events of short durations (Duncan and Carrow, 2002). This also causes the turf to be more succulent, less drought tolerant, and more susceptible to scalping. Watering schedules should consist of long durations during applications with long intervals (1.25 to 2.5 cm of water every 4 to 7 d on a sand-based green) between applications to encourage the roots to grow deeper into the soil profile (Duncan, 2000;

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33 Duncan and Carrow, 2002). Various grass types require different moisture levels and weed species are also dependent on moisture levels. For instance, dollarweed populations can be reduced in St. Augustinegrass turf by reducing irrigation levels (Busey, 2001). Seashore paspalum exhibits exceptional salt tolerance, but is susceptible to injury from many postemergence herbicides (Wiecko, 2003). Dithiopyr, halosulfuron, oxadiazon, and prodiamine are the only herbicides labeled for use on seashore paspalum (Unruh et al., 2005). Dithiopyr, oxadiazon, and prodiamine are herbicides commonly used preemergence for annual grass control. Halosulfuron is commonly used postemergence for sedge control. Seashore paspalums high level of salt tolerance may allow the use of saltwater for weed control in place of injurious postemergence herbicides (Wiecko, 2003). Couillard and Wiecko (1998) evaluated saltwater for control/tolerance on crabgrass, and mimosa. They treated these species with ocean water at three concentrations: pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m), and 1/3 ocean water (19 dS/m). The weeds were watered twice daily for two different periods: 3 d or 6 d. Following the saltwater stress periods, potable water irrigation was applied to evaluate recovery potential over a period of 32 d after the salt-stress treatments began. Mimosa only recovered from the 1/3x ocean water treatment subjected to 3 d salt stress. Complete crabgrass control was only achieved with pure ocean water under 6 d salt stress. Similar studies were conducted by Wiecko in 1999 and 2000 with the additional species goosegrass, alyceclover (Alysicarpus vaginalis (L.) DC.), and yellow nutsedge (Cyperus esculentus L.). Alyceclover injury was similar to mimosa injury, and

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34 goosegrass injury was similar to crabgrass injury. Yellow nutsedge was the most tolerant to salt stress, fully recovering from all treatments. Based on these studies, ocean water can be used as an alternative to herbicides to control weeds in certain turfgrasses (Couillard and Wiecko, 1998). Most annual grass and broadleaf weed species cannot tolerate continuous irrigation with saltwater or saltwater blends (wastewater) (Duncan and Carrow, 2000). Few golf courses have the capabilities to use saltwater for irrigation, but it is becoming more common in coastal environments (Duncan and Carrow, 2000). Weeds are a common problem when trying to maintain a high quality turf. Since many golf courses border environmentally sensitive areas chemical control of weeds is not always feasible. The susceptibility of many turfgrass weeds to saltwater has not been determined. The objective of this study was to determine the potential of using saltwater for control of selected common turfgrass weeds. Methods and Materials Greenhouse Studies Two greenhouse studies were conducted at the University of Florida, West Florida Research and Education Center (WFREC) near Jay during 2003 and 2004. Nine turfgrass weeds (torpedograss, dollarweed, Virginia buttonweed, large crabgrass, common bermudagrass, purple nutsedge, goosegrass, Florida pusley, and tropical signalgrass) were evaluated for saltwater susceptibility. Weeds listed in Tables 3.1, 3.2, and 3.3 were transplanted as mature plants from the field, with the exception of crabgrass and tropical signalgrass, which were established from seed. The weeds were planted in 15 cm in diameter by 16.5 cm deep (3,000 cm3 volume) pots that were filled with a United States Golf Association (USGA, 1993) greens

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35 mix (80% sand and 20% sphagnum peat moss). The weeds were placed in a greenhouse receiving full sun maintained at a temperature range of 27o to 32o C. The transplanted weeds were irrigated with freshwater for 3 wk to allow for rooting and recovery from transplanting. The seeded weeds were allowed to establish with potable water irrigation for 5 wk. Plants were gradually thinned to a final density of 3 plants per pot. Saltwater treatments were initiated (July 30 in 2003 and August 2 in 2004) after establishment and continued for 8 wk in 2003 and 4 wk in 2004. Saltwater treatments were applied twice per wk (Mon. and Wed.), with one potable water treatment per wk (Fri.) applied to prevent salt accumulation on the growing medium surface. The saltwater (Na+Cl-) concentrations were as follows: untreated (0X), 13 dS/m (1/4X), 27 dS/m (1/2X), 41 dS/m (3/4X), and 55 dS/m (1X). The 55 dS/m (1X) concentration is equivalent to ocean water and the untreated (0X) is potable water. Each irrigation event consisted of 200 ml per pot of saltwater or potable water equivalent to 1 cm of water (irrigation) per event totaling the standard 3 cm of water (irrigation) weekly for seashore paspalum (Duncan and Carrow, 2000). The aerial reproductive structures of the annual weeds were removed weekly to prevent the weeds from completing their life cycle. Weed control was visually evaluated at 8 wk in 2003 and 4 wk in 2004 after initial saltwater exposure using a scale of 0 (no control) to 100 (complete control). The experimental design was a randomized complete block with four replications. Data were analyzed in PROC GLM using an ANOVA to test all possible interactions of saltwater treatment, replication, and year, and means were separated using least significant difference (LSD) at the 5% probability level (SAS, 2004). Regression analysis was utilized to model the response of weed control to saltwater concentration.

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36 Field Studies Field studies were also conducted in the summer of 2004 at the University of Florida, WFREC near Jay, Florida to support results found in the greenhouse experiments. Southern crabgrass and cocks-comb kyllinga (Kyllinga squamulata Thonn. ex. Vahl.) control with NaCl were tested in separate studies in a 2 yr old stand of Sea Isle 1 seashore paspalum. Individual plot size was 1.5 m by 1.5 m. Crabgrass was seeded at a rate of 480 kg ha-1 in early May and allowed to establish until treatments were initiated in early June. An existing uniform area of cocks-comb kyllinga infested seashore paspalum was selected in a separate area and treatments were initiated in early July. Saltwater treatments were applied twice per wk (Tues. and Thurs.). Plots were treated for 4 wk with either a liquid solution of NaCl at 13 dS/m (1/4 ocean water) or 27 dS/m (1/2 ocean water) concentration of salt or an equivalent amount of NaCl applied to each plot as granules. Granular NaCl applications were watered in with 30 L of water per plot. Potable water applications were dependent on the daily afternoon rainfall events that normally occur during the summer in the Southeast coastal region of the United States (Appendix A). Visual evaluations of percent turfgrass injury on a scale of 0 (no injury) to 100 (dead turf) or percent weed control on a scale of 0 (no control) to 100 (complete control) were taken 4 wk after initial treatment. The experimental design was a randomized complete block with four replications. Data were analyzed in PROC GLM using an ANOVA to test all possible interactions and means were separated using least significant difference (LSD) at the 5% probability level (SAS, 2004).

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37 Results and Discussion Greenhouse Studies There were no interactions between studies or between 4 wk and 8 wk evaluations, therefore weed control data were pooled over studies and evaluations. Broadleaf species Florida pusley and Virginia buttonweed were the most sensitive broadleaf species to saltwater treatments. All saltwater concentrations killed Florida pusley and all but the lowest concentration controlled Virginia buttonweed (Table 3.1). The data for Florida pusley and Virginia buttonweed were fit to exponential rise to max regression models with r2 values of 1.00 and 0.96, respectively (Figure 3.1). Dollarweed was the least sensitive broadleaf species with complete control achieved only at 55 dS/m salt concentration (Table 3.1). Dollarweed control increased as salt concentration of the irrigation water increased fitting a linear regression model (r2 = 0.99) (Figure 3.1). The sensitivity of Florida pusley and Virginia buttonweed to saltwater irrigation was expected because broadleaf and legume species are generally more sensitive to salinity than grassy species (Wiecko, 2003; Greub et al., 1985). The tolerance of dollarweed to high concentrations of saltwater irrigation could be due to extensive rhizome and tuber systems allowing the plant to regrow after each potable water soil flushing treatement. Grass and sedge species Goosegrass and southern crabgrass control with saltwater was similar. At 13 dS/m, goosegrass and southern crabgrass control was 39 and 25%, respectively, increasing to 53 and 51% at 27 dS/m, respectively, and to 74 and 81%, respectively, at 41 dS/m (Table

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38 3.2). Complete mortality was observed at 55 dS/m for both species (Table 3.2). Control of goosegrass and southern crabgrass corresponded with a linear regression model with r2 values of 0.97 and 0.99, respectively (Figure 4.2). Wiecko (2003) exposed goosegrass and crabgrass to saltwater twice daily for 3 and 6 d durations and observed similar results. Both weed species were controlled > 90% with a saltwater concentration of 55 dS/m, while 18 dS/m saltwater concentration provided little control (Wiecko, 2003). Tropical signalgrass control with saltwater was similar to that observed with goosegrass and southern crabgrass (Table 3.3 vs. Table 3.2). Control at 13 dS/m was 33%, increased to 73% at 41 dS/m and 100% control at 55 dS/m. Tropical signalgrass control corresponded to a linear regression model (r2 = 0.98) as saltwater concentration increased resulting in complete mortality at 55 dS/m (Table 3.3 and Figure 3.3). Bermudagrass tolerance to saltwater irrigation was similar to seashore paspalum tolerance (Chapter 2), and injury symptoms were mostly stunting of the bermudagrass with some yellowing of the leaf tissue at the highest saltwater concentrations. Bermudagrass injury at saltwater concentrations of 13 dS/m and 27 dS/m was only 9 and 24%, respectively (Table 3.3). However, injury increased to 43 and 66% as saltwater concentrations increased to 41 dS/m and 55 dS/m, respectively (Table 3.3). This injury corresponded to a linear regression model with an r2 value of 0.98 (Figure 4.3). Similar results were found where bermudagrass quality was not compromised with saltwater concentrations < 20 dS/m, but quality was reduced at 40 dS/m 4 WAT (Munshaw, 2004). Torpedograss was tolerant to all concentrations of saltwater irrigation showing a reduction in growth as the only injury symptom. Less than 20% control was observed at 13 dS/m, 27 dS/m, and 41 dS/m, while control at 55 dS/m was only 35% (Table 3.3).

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39 The data was consistant to a linear regression model with an r2 value of 0.96 (Figure 3.3). Torpedograss is a rhizomatous perennial that is found along shorelines, canals, and poorly drained soils and can form dense floating mats in water up to 6 ft deep (USDA, 2003). The tolerance shown by torpedograss in this study could be attributed to the growth habit and ability for the plant to adapt to stressful environments allowing the plant to survive long periods of time under salinity stress (USDA, 2003). Further testing of torpedograss is necessary to determine the long-term effects of saline irrigation. Purple nutsedge control was minimal at 13 dS/m (15% control). As saltwater concentration increased to 27 dS/m, control increased to 41% and 81% control at 55 dS/m (Table 3.3). Control was modeled using linear regression with an r2 value of 0.99 (Figure 3.3). Purple nutsedge is a difficult weed to control and few herbicides have been effective in the past (Grey et al., 2003). Imazapic will provide > 90% control of purple nutsedge and halosulfuron combined with the right adjurvant will provide 100% control (McDaniel, 2001). Other herbicides, such as sulfentrazone, diclosulam, and flumioxazin, will provide < 70% control (Grey et al., 2003). Irrigation with a salt concentration of 41 dS/m will provide up to 60% control which is equivalent to some herbicides. Seashore paspalum will maintain health and quality with saline irrigation up to 41 dS/m (Chapter 2). These studies indicate saline irrigation could be used as an alternative to herbicides for control of specific weeds. Successful control of Florida pusley was accomplished at 13 dS/m and Virginia buttonweed at 27 dS/m saltwater. Goosegrass, southern crabgrass, and tropical signalgrass were controlled at 41 dS/m. Saline irrigation as a single approach will control these weeds while maintaining a quality seashore paspalum turf. Additional measures, such as cultural practices or integrating reduced-rate

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40 herbicides, need to be utilized to control dollarweed, common bermudagrass, torpedograss, and purple nutsedge at saltwater concentrations up to 41 dS/m. Field Studies In the field study, southern crabgrass was controlled only 35 to 65% at 13 dS/m but control increased to greater than 85% at 27 dS/m when salt was either applied as a solution or as a granular (Table 3.4). At 13 dS/m, cocks-comb kyllinga control was no more than 60% using either granular or solution, but control improved to greater than 70% at 27 dS/m with either application method (Table 3.4). In both studies, the granular application method provided better control of southern crabgrass and cocks-comb kyllinga compared to salt applied in solution. The reduced control from the solution may be due to salt leaching through the root zone more quickly than the granular applied salt. There were no interactions between studies for seashore paspalum quality. Therefore, turf quality data were pooled over both studies. Seashore paspalum was injured < 20% for all treatments (Table 3.5). Salt applied as a granular increased turf injury by 5% over that observed with the solution at both concentrations due to localized foliar burn (Table 3.5). An uneven application of the granular salt caused the leaf tissue to burn in areas where the salt was concentrated on the surface and not completely moved into the root zone. Results from these studies indicate that saltwater can provide effective control for weed species such as southern crabgrass, goosegrass, tropical signalgrass, Florida pusley, and Virginia buttonweed but not dollarweed, common bermudagrass, torpedograss, or purple nutsedge. Inland areas that do not have access to saline water may still be able to utilize the ability of seashore paspalum to tolerate salinity by applying specific rates of

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41 granular salt to control some weed species. Precautions must be taken to effectively move the granular salt into the root zone by means of potable water irrigation. Further research should be conducted to link specific concentrations with the control of specific weed species.

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42 Table 3-1. Control of selected broadleaf weeds with saltwater in the greenhouse pooled data over years and evaluations. Weed Control a Salt Concentration HYDSPb RICSCb DIOVIb ---------------------% ---------------------13 dS/m 26 100 49 27 dS/m 52 100 100 41 dS/m 66 100 100 55 dS/m 100 100 100 LSD (0.05) 18 0 20 aPercent control compared to untreated check. bHYDSP=dollarweed, RICSC=Florida pusley, DIOVI=Virginia buttonweed Table 3-2. Control of selected annual grass weeds with saltwater in the greenhouse pooled data over years and evaluations. Weed Control a Salt Concentration ELEINb DIGSAb --------------% --------------13 dS/m 39 25 27 dS/m 53 51 41 dS/m 74 81 55 dS/m 96 100 LSD (0.05) 21 19 aPercent control compared to untreated check. bELEIN=goosegrass, DIGSA=large crabgrass Table 3-3. Control of selected perennial grass and sedge weeds with saltwater in the greenhouse pooled data over years and evaluations. Weed Control a Salt Concentration UROSUb CYNDAb PANREb CYPROb --------------------------% --------------------------13 dS/m 33 9 4 15 27 dS/m 60 24 16 41 41 dS/m 73 43 19 60 55 dS/m 100 66 35 81 LSD (0.05) 6 9 14 14 aPercent control compared to untreated check. bUROSU=tropical signalgrass, CYNDA=common bermudagrass, PANRE=torpedograss, CYPRO=purple nutsedge

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43 Table 3-4. Control of southern crabgrass and cocks-comb kyllinga with two salt concentrations applied as a solution or granular in the field. Treatmenta DIGSA b KYLZZ b ------% Control ------Freshwater 0 0 13 Solution 35 45 13 Granular 65 60 27 Solution 85 70 27 Granular 90 80 LSD (0.05) 7 12 a Concentrations are decisemens per meter (dS/m). bDIGSA=southern crabgrass, KYLZZ=cocks-comb kyllinga Table 3-5. Seashore paspalum quality as affected by saltwater in the field. Treatmenta Seashore paspalum % Injury Freshwater 0 13 Solution 5 13 Granular 15 27 Solution 10 27 Granular 20 LSD (0.05) 4 aConcentrations are decisemens per meter (dS/m).

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44 Salt Concentration 010203040506 0 % Control 020406080100 Dollarweed Observed FL Pusley Observed VA Buttonweed Observed FL Pusley Predicted Control VA Buttonweed Predicted Control Dollarweed Predicted Control y = 100 (1 e-1.72x)r2 = 1.00y = 1.9.34(1-e-0.06x)r2 = 0.96y = 1.33+(1.74x)r2 = 0.99 Figure 3-1 Saltwater concentration effect on broadleaf weed control pooled over years and evaluations. Dollarweed data were fit to a linear regression model y = a + (mx) while Florida pusley and Virginia buttonweed data were fit to an exponential rise to max regression model y = a*(1 e-b*x) to predict control at a specific concentration.

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45 Salt Concentration 010203040506 0 % Control 020406080100 Goosegrass Observed Crabgrass Observed Goosegrass Predicted Control Crabgrass Predicted Control y = 7.79 + (1.64x)r2 = 0.97y = 0.99 + (1.86x)r2 = 0.99 Figure 3-2 Saltwater concentration effect on annual grass control pooled over years and evaluation. Data were fit to a linear regression model y = a + (mx) to predict control at a specific concentration.

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46 Salt Concentration 010203040506 0 % Control 020406080100 Bermudagrass Observed Torpedograss Observed Tropical Signalgrass Observed Purple Nutsedge Observed Bermudagrass Predicted Control Torpedograss Predicted Control Tropical Signalgrass Predicted Control Purple Nutsedge Predicted Control y = 5.78+(1.74x)r2 = 0.98y = -1.30+(1.49x)r2 = 0.99y = -4.06+(1.19x)r2 = 0.98y = -1.90+(0.62x)r2 = 0.96 Figure 3-3 Saltwater concentration effect on perennial grass and sedge control pooled over years and evaluation. Data were fit to a linear regression model y = a + (mx) to predict control at a specific concentration.

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CHAPTER 4 THE TOLERANCE OF SEASHORE PASPALUM TO HERBICIDES WHEN IRRIGATED WITH SALTWATER Introduction Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial warm season turfgrass that is native to tropical and subtropical regions of the world (Duncan and Carrow, 2000). Although seashore paspalum has existed for many years, it has only been used commercially for the past few decades. Seashore paspalum spreads by rhizomes and stolons that root at the nodes forming a deep fibrous root system (Duble, 2000). It is generally propagated vegetatively from sod or sprigs because seed production has not been reliable (Duncan and Carrow, 2000), though one seeded cultivar has been developed (Hughes, 2005). Sodium chloride (NaCl) is the predominant component contributing to soil salinity (Jungklang, 2003). Saline levels in soils are becoming increasingly problematic due to the use of alternative water (effluent or brackish) for irrigation. Salinity tolerance is a distinguishing physiological characteristic of seashore paspalum. There are three mechanisms plants use to tolerate salinity: selective of ion uptake by the roots, accumulation of salt in specific vacuoles within plant cells then retranslocated back to the soil or excreted by salt glands on the leaf surface, and osmotic adjustment (Colmer, 2000; Rose-Fricker and Wipff, 2001; Marcum, 2004). Seashore paspalum has the ability to efficiently select ions absorbed by the roots, and it is also able to secrete salt through salt glands on the leaf surface (Marcum, 1999). 47

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48 Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting (Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of the soil over time and must be managed properly to establish and maintain a high quality turf. Studies have been conducted testing the tolerance of seashore paspalum to various concentrations of saltwater. Seashore paspalum exhibits exceptional salt tolerance, but is highly susceptible to injury from postemergence herbicides (Wiecko, 2003). The high level of salt tolerance may allow saltwater to be used as an alternative to herbicides or in combination with reduced-rate herbicides to control weeds in certain turfgrasses (Couillard and Wiecko, 1998). Few golf courses have the capabilities to use saltwater for irrigation, but it is becoming more common in coastal environments (Duncan and Carrow, 2000). Herbicides are regularly used for weed control on golf courses. Some important considerations when selecting an herbicide are effectiveness, turfgrass tolerance, speed of control, toxicity, and cost (Unruh and Elliott, 1999). There is no single herbicide that will control all weeds in a desired turf stand, so proper identification is essential (Unruh and Brecke, 1998). Seashore paspalum is sensitive to many herbicides commonly used on other turfgrasses (Trenholm and Unruh, 2002, 2003; and CTAHR, 1998). Herbicides that are noninjurous to seashore paspalum are bensulide, pronamide, benefin, DCPA, pendimethalin, ethofumesate, quinclorac, MCPP + 2,4-D + dicamba, dithiopyr, 2,4-D + dicamba + dicloprop, dicamba, halosulfuron, mecoprop, and bentazon (Duncan and Carrow, 2000). However, dithiopyr, halosulfuron, oxadiazon, and prodiamine are the only herbicides labeled for use on seashore paspalum (Unruh et al., 2005). These

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49 herbicides could possibly be used at reduced rates in conjunction with saltwater irrigation to control weeds in seashore paspalum (Duncan and Carrow, 2000). In 1997, Johnson and Duncan tested the recommended rates and 3 times the recommended rates of diclofop, quinclorac, dicamba, imazaquin, halosulfuron, and 2,4-D + mecoprop + dicamba on four seashore paspalum accessions (AP 10, HI 25, PI 28960, and K-7). Seashore paspalum accessions varied in their response to the herbicides evaluated. Quinclorac and halosulfuron were the only herbicides that did not reduce the quality of any accession at the recommended rates. When quinclorac and halosulfuron rates increased, quality of HI 25 and K-7 was reduced. All accessions recovered completely even from the high rates within 4 to 8 wk after initial treatment. Dicamba had no effect on any of the accessions when applied at the labeled rate. Quality of the K-7 accession, however, was affected by the increased rate of dicamba. Diclofop, imazaquin, and 2,4-D + mecoprop + dicamba reduced the quality of all paspalum accessions regardless of application rate. Full recovery from diclofop and imazaquin required 4 to 8 wk. Recovery from the labeled rates of 2,4-D + mecoprop + dicamba took 4 to 8 wk for all accessions, and none of the accessions recovered from the high rate by 8 wk. The overall conclusion from this study was that quinclorac, dicamba, and halosulfuron were safe on all accessions, diclofop and imaziquin were marginal, and 2,4-D + mecoprop + dicamba were considered injurious. A study was conducted by Unruh et al. (2005) testing the tolerance of Salam seashore paspalum to postemergence herbicides for control of grass (clethodim, ethofumesate, metsulfuron, sethoxydim, and quinclorac), broadleaf (clopyralid, dicamba,

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50 and 2,4-D + mecoprop + dicamba), and sedge (bentazon, halosulfuron, imazapic, imazaquin, and trifloxysulfuron-sodium) species. Metsulfuron, quinclorac, clopyralid, dicamba, 2,4-D + mecoprop + dicamba, bentazon, halosulfuron, and imazaquin caused less than 15% injury at the recommended rates and are considered safe for seashore paspalum. Clethodim, sethoxydim, ethofumesate, imazapic, and trifloxysulfuron-sodium caused greater than the acceptable standard of 20% injury and are considered not safe for application to seashore paspalum. Growth of many weed species is suppressed when irrigated with saltwater while growth of seashore paspalum is not affected (Duncan and Carrow, 2000). Tolerance of seashore paspalum to preemergence and postemergence herbicides has not been determined when irrigated with saltwater and the turfgrass is potentially more sensitive to injury as salt-stress increases. The objective of this study was to determine the tolerance of seashore paspalum to commonly used turfgrass herbicides when irrigated with multiple concentrations of saltwater. Methods and Materials Two greenhouse studies were conducted at the University of Florida, West Florida Research and Education Center (WFREC) near Jay in the summer of 2004. Strips of sod were cut with a sod cutter from a two year old stand of Sea Isle 1 seashore paspalum. Plugs were cut from the sod strips using a golf cup cutter 15 cm in diameter. The native soil was washed from the plugs and then plugs were transplanted into 15 cm in diameter by 17 cm deep (3000 cm3 volume) plastic pots containing a growing medium of USGA greens mix (80% sand and 20% organic matter). The intact seashore paspalum plugs were planted level with the rim of the pots.

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51 After transplanting, the pots were placed in a greenhouse receiving full sun and were maintained at a temperature range of 27o to 32o C. A slow release 19-8-15 fertilizer was applied at a rate of 24.5 kg N ha-1 1 wk after planting. The plugs were irrigated with potable water during a 3 wk rooting period. A randomized complete block arranged in a split-plot experimental design with three replications was used. This was because the main plot was blocked while the sub-plot and replications were random in each block. Main plot factor consisted of five saltwater concentrations: 1) potable water (0x), 2) 13 dS/m (1/4x), 3) 27 dS/m (1/2x), 4) 41 dS/m (3/4x), and 5) 55 dS/m (1x). The 55 dS/m concentration is equivalent to ocean water. Sub-plot factor was 18 herbicide treatments with an untreated check and are listed in Table 4.1. Saltwater treatments were initiated July 17, 2004 for the initial study and July 22, 2004 for repeated study after establishment and continued for the duration of the study. Saltwater treatments were applied twice per week (Mon. and Wed.), with one potable water treatment per week (Fri.) applied to prevent salt accumulation on the growing medium surface. Each irrigation event consisted of 200 ml of saltwater or potable water equivalent to 1 cm of water (irrigation) per event totaling the standard 3 cm of water (irrigation) recommended for seashore paspalum weekly (Duncan and Carrow, 2004). All pots were maintained at 2 cm (0.75 in) using rechargeable grass shears. Chlorothalonil [2,4,5,6-tetrachloroisophthalonitrile] and chlorpyrifos [0,0-diothyl 0-(3,5,6-trichloro-2-pyridinyl) phosphorothioate] were applied preventively at 14.5 kg ai ha-1 and 1 kg ai ha-1, respectively, to control fungal disease and insects (Anonymous

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52 2004a, 2004b). After 2 wk of saltwater irrigation, herbicide treatments were applied at the recommended labeled rate to each saltwater concentration (Table 4.1). Data collected included visual quality ratings 4 wk after herbicide application on a scale from 0 (dead turf) to 9 (healthy turf). Data were subjected to ANOVA using PROC MIXED to test all possible fixed effects and interactions of saltwater concentration, herbicide treatment, and trial (SAS, 2004). PROC MIXED was used to allow replication to be tested as a random effect. Means were separated using least significant difference (LSD) at the 5% probability level. Results and Discussion There was an interaction between trials, so data are presented separately. In both trials, there was an interaction between saltwater concentrations and herbicide treatments. In general, the quality of seashore paspalum decreased as saltwater concentration increased regardless of herbicide application. Prodiamine, pendimethalin, oxadiazon, metolachlor, and dithiopyr are herbicides commonly used preemergence for summer annual grass control. In both trials, the herbicides alone without saltwater irrigation caused some reduction in turfgrass quality but ratings were 7.3 or higher, well above the minimum acceptable level of 6.5 (Table 4.2). Quality declined with increasing saltwater concentrations but reduction was no greater than for saltwater alone without herbicide (Table 4.2). These results indicate that salt stress did not impact seashore paspalum tolerance for prodiamine, pendimethalin, oxadiazon, metolachlor, or dithiopyr. Fenarimol is labeled as a fungicide, but like pronamide, is also an effective preemergence for controlling winter annual grasses. Pronamide did not affect seashore paspalum quality with potable water and fenarimol only reduced quality in trial 1 to 8.3,

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53 well above the minimum of 6.5. As with the preemergence treatments for summer grasses, there was a reduction in quality with increasing salt concentration, but no greater than for salt alone except for salt of 55 dS/m. At the highest salt concentration, quality declined from 6.7 for the untreated to 5.3 with both fenarimol and pronamide (Table 4.2). As with the summer annual grass control herbicides, seashore paspalum tolerance to pronamide or fenarimol was not affected by saltwater irrigation. Isoxaben and atrazine are applied preemergence to control many broadleaf weed species. Quality was lower with the use of isoxaben in some instances compared to the herbicide untreated in both trials, however, there was no consistent effect of saltwater on quality of turf treated with isoxaben (Table 4.2). The application of atrazine reduced the quality of seashore paspalum compared to the herbicide untreated at all saltwater concentrations in both trials. Atrazine reduced quality in both trials to unacceptable levels (5 or less). There was some indication that quality improved with saltwater treatment in trial 2 (Table 4.2) suggesting that the saltwater may be interfering with atrazine activity and that the efficacy of atrazine may have been slightly reduced when saltwater irrigation is applied. For annual and perennial grasses, quinclorac, metsulfuron, and metribuzin are herbicides often used as postemergence control. Quality was not different from the herbicide untreated when quinclorac or metsulfuron was applied in either trial 1 or trial 2 at salt concentrations of 27 dS/m or less (Table 4.3). Turf quality with both herbicides declined with increasing saltwater concentration, however the decline was similar to the saltwater alone treatment. Metribuzin reduced turf quality to 5 regardless of saltwater treatment in both trial 1 and 2 (Table 4.3). These results indicate that seashore paspalum

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54 remains tolerant to quinclorac and metsulfuron regardless of salt concentration while metribuzin is not tolerated, even when irrigated with potable water. Clopyralid, bromoxynil, bentazon, and 2,4-D + dicamba + mecoprop applied postemergence will control many broadleaf weed species. Clopyralid did not reduce turf quality when using potable irrigation water. Quality did decline as saltwater concentration increased, but turf quality was not different from the herbicide untreated in either trial (Table 4.3). Bentazon caused a reduction in quality without saltwater (0 ppm) in trial 1 and at 13 dS/m in trial 2 but quality remained 7.7 or greater (Table 4.3). Bentazon caused turf quality to decline more than the herbicide untreated as salt concentration increased 41 dS/m in trial 1 and 27 dS/m in trial 2 (Table 4.3). Bentazon may be interacting with the saltwater at high salt concentrations, reducing the quality of seashore paspalum to unacceptable levels. Bromoxynil and the 3-way mixture of 2,4-D + dicamba + mecoprop caused a reduction in seashore paspalum quality compared to the herbicide untreated at all saltwater concentrations in both trials. Quality declined to the minimum acceptable level of 6.5 or less at 13 dS/m saltwater concentration and continued to decline with increasing saltwater concentration (Table 4.3). Both bromoxynil and the 3-way mixture of 2,4-D + dicamba + mecoprop will injure seashore paspalum when irrigated with potable water, and should be used with caution when saltwater irrigation is utilized. Halosulfuron and imazaquin are herbicides used as postemergence for control of sedges. The quality of seashore paspalum declined as saltwater concentration increased and when halosulfuron was applied, quality was not affected compared to the herbicide untreated. Imazaquin reduced turfgrass quality at all saltwater concentrations compared

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55 to the herbicide untreated. Quality was reduced below the 6.5 minimum at 27 dS/m and should also be used with caution on seashore paspalum irrigated with saltwater (Table 4.3). When irrigated with saltwater concentrations of 41 dS/m and 55 dS/m, quality and growth rate of seashore paspalum is significantly reduced (Chapter 2). If the turf is further damaged by an herbicide application, the recovery time is increased due to the reduction in growth. Herbicides that caused a major reduction in the quality of seashore paspalum in this experiment were atrazine and metribuzin. These herbicides will cause damage when irrigated with potable water and any concentration of saltwater and should not be applied to seashore paspalum. Minor reductions in quality were observed after the application of bromoxynil, 2,4-D + dicamba + mecoprop, and imazaquin. These herbicides should not be applied to seashore paspalum irrigated with saltwater concentrations 27 dS/m.

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56 Table 4-1 List of herbicides tested on seashore paspalum under salinity stress. Common name Chemical name Application rate PREEMERGENCE Prodiamine [2,4-dinitro-N3,N3-dipropyl-6-(trifluoromethyl)-1,3-benzediamine] 1.1 kg ai ha-1 Pendimethalin [N-(1-ethylpropyl)-3,4-demethyl2,6-dinitrobenzenamine] 2.0 kg ai ha-1 Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-1, 3, 4-oxadiazolin-5-one] 2.9 kg ai ha-1 Dithiopyr [3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethyl ester] 0.3 kg ai ha-1 Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methtlethyl)acetamide 2.1 kg ai ha-1 Isoxaben [N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide and isomers 0.8 kg ai ha-1 Pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide 1.1 kg ai ha-1 Fenarimol [a-(2-chlorophenyl)-a-(4-chlorophenyl)-5-pyrimidinemethanol] 0.8 kg ai ha-1 POSTEMERGENCE Grass Quinclorac [3,7-dichloro-8-quinolinecarboxylic acid] 0.8 kg ai ha-1 Metsulfuron [Methyl Methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino]carbonyl]amino]sulfony] benzoate] 0.3 kg ai ha-1 Metribuzin [4-Amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] 3.4 kg ai ha-1 Broadleaf Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid, monoethanolamine salt) 0.3 kg ai ha-1 Bromoxynil (3,5-dibromo-4-hydroxybezonitrile) 0.6 kg ai ha-1 Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) 1.7 kg ai ha-1 Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] 1.1 kg ai ha-1 2,4-D Dicamba Mecoprop [(2,4-dichlorophenoxy)acetic acid] (3,6-dichloro-2-methoxybenzoic acid) [2-(4-chloro-2-methylphenoxy) propionic acid] 0.09 kg ai ha-1 0.4 kg ai ha-1 0.4 kg ai ha-1 Sedge Halosulfuron [methyl [[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonylaminosulfonyl]-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate] 0.07 kg ai ha-1 Imazaquin [2-4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl-3-quinolinecarboxylic acid] 0.5 kg ai ha-1

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57 Table 4-2 The effect of preemergence herbicides and salt concentrations on seashore paspalum quality 4 wk after herbicide application. Preemergence Herbicides Seashore paspalumc 0a 13a 27a 41a 55a T1b T2b T1b T2b T1b T2b T1b T2b T1b T2b Untreated 9.0 9.0 9.0 8.3 7.7 7.0 7.0 6.7 7.0 6.7 Dithiopyr 9.0 8.0 9.0 8.1 8.0 7.0 7.0 6.7 7.0 6.0 Pronamide 8.7 8.7 8.7 8.0 8.0 6.7 6.7 6.0 7.0 5.3 Metolachlor 8.7 7.7 8.7 7.8 8.0 6.0 6.7 6.3 6.3 5.7 Isoxaben 8.7 7.7 8.0 7.8 7.3 6.3 6.7 6.3 6.3 5.7 Fenarimol 8.3 8.7 9.0 8.1 7.7 6.7 6.7 6.7 6.7 5.3 Pendimethalin 8.3 8.0 9.0 8.1 7.7 6.7 6.7 6.3 6.7 5.7 Oxadiazon 8.3 7.7 8.3 7.6 7.7 7.0 7.0 6.3 7.0 5.7 Prodiamine 8.3 7.3 9.0 7.9 8.0 6.7 7.0 6.7 7.0 5.7 Atrazine 4.7 3.0 4.7 4.9 5.0 4.3 4.7 4.0 5.0 3.7 aSalt Concentrations in decisemens per meter (dS/m). bT1 = Trial 1 and T2 = Trial 2 cQuality ratings range from 0 (dead turf) to 9 (healthy turf). LSD0.05 = 0.55 (T1) and 0.80 (T2) for mean comparison of herbicide within a given salt concentration or salt concentration within a given herbicide. Table 4-3 The effect of postemergence herbicides and salt concentrations on seashore paspalum quality 4 wk after herbicide application. Postemergence Herbicides Seashore paspalumc 0a 13a 27a 41a 55a T1b T2b T1b T2b T1b T2b T1b T2b T1b T2b Untreated 9.0 9.0 9.0 8.3 7.7 7.0 7.0 6.7 7.0 6.7 Halosulfuron 9.0 8.7 9.0 7.9 7.7 7.0 6.3 6.7 7.0 5.3 Clopyralid 9.0 8.7 8.7 8.0 8.0 6.0 7.0 6.0 6.7 4.0 Quinclorac 8.3 8.7 9.0 8.1 7.7 6.3 7.0 5.7 6.7 6.0 Metsulfuron 8.3 8.3 8.7 7.8 7.0 7.0 6.7 6.3 6.3 6.0 Bentazon 8.0 8.7 9.0 7.8 7.7 5.7 6.3 6.3 6.0 4.3 Imazaquin 7.7 7.3 7.0 6.7 6.3 5.3 6.0 6.0 6.0 5.3 2,4-D/Dicamba/Mecoprop 7.7 7.0 7.0 6.5 6.3 5.0 5.3 6.0 4.3 4.3 Bromoxynil 7.3 7.7 7.7 6.6 6.0 6.0 5.3 5.7 5.7 5.7 Metribuzin 5.0 1.7 5.0 4.0 4.7 2.3 5.0 3.0 4.3 2.7 aSalt Concentrations in decisemens per meter (dS/m). bT1 = Trial 1 and T2 = Trial 2 cQuality ratings range from 0 (dead turf) to 9 (healthy turf). LSD0.05 = 0.55 (T1) and 0.80 (T2) for mean comparison of herbicide within a given salt concentration or salt concentration within a given herbicide.

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CHAPTER 5 CONCLUSIONS Seashore paspalum is a warm-season turfgrass that is replacing traditional turfgrasses in salt-affected areas due to its ability to tolerate saline conditions. Salinity levels in soils are becoming increasingly problematic due to the use of alternative water (effluent or brackish) for irrigation. When establishing seashore paspalum, saline conditions may negatively impact turfgrass growth rate (Duncan and Carrow, 1999). Studies were conducted to determine the tolerance of newly sprigged and established seashore paspalum to various saltwater concentrations. Decreasing growth rates of seashore paspalum sprigs were observed with all saltwater concentrations and death of the sprigs occurred at 8 wk with 55 dS/m saltwater. Newly sprigged seashore paspalum is sensitive to saltwater concentrations 13 dS/m and the time to full establishment will increase as saltwater concentration increases. Saltwater concentration > 27 dS/m will cause desiccation and eventual death of the sprigs. Due to the lack of tolerance to salinity, newly sprigged seashore paspalum should be irrigated with potable water during establishment to reduce stress and promote healthy growth. Established seashore paspalum exhibited a high tolerance to saltwater irrigation. Although seashore paspalum did not maintain an acceptable quality when irrigated with pure ocean water (55 dS/m), quality levels 6.5 were observed when irrigated with salinity levels up to 41 dS/m. This characteristic will allow turf managers located near 58

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59 the coast or those who have water restrictions to use alternative water sources (effluent and brackish) for irrigation that have salt concentrations up to 41 dS/m. Because seashore paspalum will maintain health and quality with saline irrigation up to 41 dS/m, saline irrigation may be used as an alternative to herbicides to control specific weeds. Successful control of Florida pusley was accomplished at 13 dS/m and Virginia buttonweed at 27 dS/m saltwater. Goosegrass, southern crabgrass, and tropical signalgrass were controlled at 41 dS/m. Saline irrigation as a single approach will control these weeds while maintaining a quality seashore paspalum turf. Additional measures, such as cultural practices or integrating reduced-rate herbicides, need to be utilized to control dollarweed, common bermudagrass, torpedograss, and purple nutsedge at saltwater concentrations up to 41 dS/m. In a field study, salt was applied as a granule and as a solution to seashore paspalum with a uniform population of southern crabgrass or cocks-comb kyllinga. The granular application method provided better control of southern crabgrass and cocks-comb kyllinga compared to salt applied in solution, but both methods provided > 70% control at 27 dS/m. The reduced control from the solution may be due to salt leaching through the root zone more quickly than the granular applied salt. Seashore paspalum injury was < 20% for all treatments. Salt applied as a granular increased turf injury by 5% over that observed with the solution at both concentrations due to localized foliar burn. Inland areas that do not have access to saline water may still be able to utilize the ability of seashore paspalum to tolerate salinity by applying specific rates of granular salt to control some weed species. Precautions must be taken to effectively move the

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60 granular salt into the root zone by means of potable water irrigation to prevent burning of the leaf tissue. Further research should be conducted to link specific concentrations with the control of specific weed species. Many weeds are suppressed in saline conditions, but salt tolerant weeds will require other means of control. Seashore paspalum is sensitive to many herbicides commonly used on other turfgrasses. Herbicide response of seashore paspalum in salt-affected areas has not yet been determined and may be more sensitive to injury as salt-stress increases. When irrigated with saltwater concentrations of 41 dS/m and 55 dS/m, quality and growth rate of seashore paspalum is significantly reduced. If the turf is further damaged by an herbicide application, the recovery time is increased due to the reduction in growth. Herbicides that caused a major reduction in the quality of seashore paspalum in this experiment were atrazine and metribuzin. After atrazine was applied, there was some indication that quality improved with saltwater treatment in trial 2, although quality remained 5, suggesting that the saltwater may be interfering with atrazine activity and that the efficacy of atrazine may have been slightly reduced when saltwater irrigation is applied. Metribuzin, however, reduced quality < 5 at all saltwater concentrations. These herbicides will cause damage when seashore paspalum is irrigated with potable water and any concentration of saltwater and should not be applied to seashore paspalum. Minor reductions in quality were observed after the application of bromoxynil, 2,4-D + dicamba + mecoprop, and imazaquin. Quality declined to < 6.5 at 27 dS/m saltwater and continued declining with increasing saltwater concentration. These herbicides should not be applied to seashore paspalum irrigated with saltwater concentrations 27 dS/m.

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61 Bentazon did not reduce seashore paspalum quality with irrigation up to 27 dS/m in trial 1 and 13 dS/m in trial 2, but as saltwater irrigation increased, quality was reduced more than the herbicide untreated. At high saltwater concentrations, bentazon may be interacting with the saltwater causing a greater reduction in the quality of seashore paspalum. Salt stress did not impact seashore paspalum tolerance for prodiamine, pendimethalin, oxadiazon, metolachlor, isoxaben, dithiopyr, pronamide, fenarimol, clopyralid, or halosulfuron. Quality was reduced as saltwater concentration increased, but the reduction was not different from the herbicide untreated.

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APPENDIX A 2004 RAINFALL Daily rainfall (cm) for the summer of 2004 at the WFREC near Jay, Florida. Day June July August 01 5.50 0.67 0.00 02 0.60 5.40 0.00 03 0.63 0.10 0.00 04 0.00 0.00 0.00 05 0.00 0.00 0.00 06 0.57 0.03 0.00 07 0.00 0.03 0.00 08 0.00 0.00 0.00 09 0.00 0.00 3.05 10 0.00 0.00 1.45 11 0.00 0.00 3.03 12 0.00 0.00 0.63 13 0.25 0.03 0.00 14 5.30 0.00 0.00 15 1.60 0.30 0.00 16 0.05 5.07 0.00 17 0.00 0.47 0.00 18 1.90 0.00 0.00 19 0.25 0.00 0.00 20 1.93 0.00 3.33 21 0.00 0.00 0.25 22 2.40 0.00 3.40 23 1.76 0.00 0.20 24 2.43 0.00 0.03 25 0.80 2.43 0.03 26 0.33 0.00 0.70 27 0.03 0.05 0.00 28 0.25 0.03 4.55 29 0.40 1.27 0.10 30 0.00 4.05 0.00 31 -2.10 0.05 62

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LIST OF REFERENCES Beard, J. 1973. Turfgrass: Science and Culture. Prentice-Hall, Inc., Englewood Cliffs, NJ. Bowman, D.C., D.A. Devitt, and W.W. Miller. 1995. The Effect of Salinity on Nitrate Leaching from Turfgrass. USGA Green Section Record. January/February 45-49. Busey, P. 2000. Tropical Signalgrass. University of Florida, Fort Lauderdale, FL. July 2005. http://turfscience.com/weeds/signal2.html. Busey, P. 2001. Irrigation Management of Dollarweed in St. Augustinegrass Lawns. Agronomy Journal Abstract. July 2005. http://turfscience.com/weeds/dollarweed.html. Busey, P. 2002. Reduction of Torpedograss (Panicum repens) Canopy and Rhizomes by Quinclorac Split Applications. Weed Technology 17:190-194. Colmer, T. 2000. Salt Tolerance in Plants. Australian Turfgrass Management 2.5 (October/November). Couillard, A., G. Wiecko. 1998. A Saline Solution: Seawater as a selective herbicide. Golf Course Management 66:5 Dean, D.E., D. A. Devitt, L.S. Verchick, and R.L. Morris. 1996. Turf Quality, Growth, and Water Use Influenced by Salinity and Water Stress. Agronomy Journal 88:844-849. Dow AgroSciences. 2004. Dursban Pro Specialty Insecticide, 9330 Zionville Rd., Indianapolis, IN 46268. Duble, R.L. 2004. Seashore Paspalum. Available by Texas Agriculture Extension Service. Texas A&M University System. July 2005. http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/seashore.html. Duble, R.L. 2004. Bermudagrass "The Sports Turf of the South". Available by Texas Cooperative Extension. July 2005. http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/bermuda.html. Duncan, R.R. 2004. Seashore Paspalum Management on Golf Courses. San Diego, CA. GCSAA Seminar. 63

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64 Duncan, R.R., and R.N. Carrow. 1998. Salt Affected Turfgrass Sites: Assessment and Management. Ann Arbor Press. Duncan, R.R., and R.N. Carrow. 1999. Establishment and Grow-in of Paspalum Golf Course Turf. Golf Course Management 67:5. Duncan, R.R., and R.N. Carrow. 2000. Seashore Paspalum: The Environmental Turfgrass Ann Arbor Press. Duncan, R.R., and R.N. Carrow. 2002. Thou Shalt Not Scalp Seashore Paspalum. Golf Course Management 70:4. El-Haddad, E.-S.H., and M.M. Noaman. 2001. Leaching Requirement and Salinity Threshold for the Yield and Agronomic Characteristics of Halophytes Under Salt Stress. Journal of Arid Environments 49:865-874. Evers, G.W., and A.D. Davidson. 2004. Comparison of Seeded and Vegetatively Propagated Bermudagrass. Texas A&M University. Agriculture Research and Education Center. Overton, Texas. March 2005. http://165.95.57.6/frt/pdf/gwefrt2.pdf. Florkowski, W.J., and G. Landry. 2002. An Economic Profile of Golf Courses in Georgia: Course and Landscape Maintenance 681. University of Georgia, Griffin, GA. Fry, J., and B. Huang. 2004. Applied Turfgrass Science and Physiology. John Wiley & Sons, Hoboken, NJ. Grey, T.L., Bridges, D.C., Prostko, E.P., Johnson, W.C., Eastin, E.F., Vencill, W.K., Brecke, B.J., Macdonald, G.E., Tredaway, J.A., Everest, J.W. 2003. Residual Weed Control With Imazapic, Diclosulam, And Flumioxazin In Southeastern Peanut. Peanut Science. 30:23-28. Haydu, J., and A. Hodges. 2002. Economic Dimensions of the Florida Golf Course Industry. IFAS, University of Florida, Gainesville. Hughes, P. 2005. New Paspalums Hit Market. Golfweek's SuperNews. March 11, 2005. Jiang, Yiwei, R.R. Duncan, and R.N. Carrow. 2004. Assessment of Low Light Tolerance of Seashore Paspalum and Bermudagrass. Crop Science 44:587-594. Johnson, B.J., and R.R. Duncan. 1997. Tolerance of Four Seashore Paspalum (Paspalum vaginatum) Cultivars to Postemergence Herbicides. Weed Technology 11:689-692. Johnson, J.B., and R.R. Duncan. 2001. Effects of Herbicide Treatments on Suppression of Seashore Paspalum (Paspalum vaginatum) in Bermudagrass (Cynodon spp.). Weed Technology 15:163-169.

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65 Jungklang, J., K. Usui, and H. Matsumoto. 2003. Differences in Physiological Responses to NaCl Between Salt-Tolerant (Sesbania rostrata Brem. & Oberm.) and Non-Tolerant (Phaseolus vulgaris L.). Weed Biology and Management 3:21-27. Lee, G., R.N. Carrow, and R.R. Duncan. 2004. Photosynthetic Responses to Salinity Stress of Halophytic Seashore Paspalum Ecotypes. Plant Science 166:1417-1425. Marcum, K.B. 1999. Salinity Tolerance Mechanisms of Grasses in the Subfamily Chloridoideae. Crop Science 39:1153-1160. Marcum, K.B. 2004. Use of Saline and Non-potable Water in the Turfgrass Industry: Constraints and Developments. International Crop Science Congress. October. Queensland, Australia. Marcum, K.B., and C.L. Murdoch. 1994. Salinity Tolerance Mechanisms of Six C4 Turfgrasses. Journal of the American Society for Horticultural Science 119:779-784. Marella, R.L. 1999. Water Withdrawals, Use, Discharge, and Trends in Florida, 1995: U.S. Geological Survey Water-Resourses Investigations Report. Tallahassee, Florida. 99-4002. McDaniel, G.M., W.E. Klingeman, W.T. Witte, and P.C. Flanagan. 2001. Choice of Adjuvant with Halosulfuron Affects Purple Nutsedge Control and Nursery Crop Tolerance. HortScience 36:1085-1088. Mitra, Shoumo. Salts Influence the Health of Turf. Golf Course Management. 68:07. Mitra, Shoumo. Managing Salts in Soil and Irrigation Water. Golf Course Management. 69:01. Munshaw, G., X. Zhang, and E Ervin. 2004. Pass the Salt. Golf Course Management. 72:09. Murphy, T.R., D.L. Colvin, R. Dickens, J.W. Everest, D. Hall, and L.B. McCarty. 1996. Weeds of Southern Turfgrasses UF/IFAS, Gainesville. NewCROP (Center for New Crops and Plant Products). 1999. Bermudagrass. Purdue University, West Lafayette, IN. Noaman, M.N., and E. El-Haddad. 2000. Effects of Irrigation Water Salinity and Leaching Fraction on the Growth of Six Halophyte Species. Journal of Agriculture Science, Cambridge 135:279-285. Qian, Y.L., S.J. Wilhelm, and K.B. Marcum. 2001. Comparitive Response of Two Kentucky Bluegrass Cultivars to Salinity Stress. Crop Science 41:1895-1900.

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66 Rose-Fricker, C., and J.K. Wipff. 2001. Breeding for Salt Tolerance in Cool-Season Turf Grasses. International Turfgrass Society Research Journal 9:206-212. Statisical Analysis Institute. 2004. SAS/STAT User's Guide Release. Release 9.0. Statisical Analysis Institute, Cary, NC. Seiler, G.J. 1998. Seed Maturity, Storage Time and Temperature, and Media Treatment Effects on Germination of Two Wild Sunflowers. Agronomy Journal 90:221-226. Snow, J.T. 2004. Water Conservation on Golf Courses. United States Golf Association (USGA) Green Section. November 2004. http://www.usga.org/turf/articles/environment/water/water_conservation.html. St. Johns River Water Management District (SFRWMD). 2002. Water Resource Permitting Program. March 2004. http://www.sjrwmd.com/programs/outreach/pubs/order/pdfs/fs_permitting.pdf. Syngenta Group Company. 2004. Daconil. 2200 Concord Pike, Wilmington, DE 19803. Trenholm, L.E. 2000. Seashore Paspalum for Florida Lawns. Available by Florida Cooperative Extension Service. University of Florida IFAS. July 2005. http://edis.ifas.ufl.edu/pdffiles/EP/EP05900.pdf. Trenholm, L.E., and J.B. Unruh. 2003. Seashore Paspalum Management for Home Lawn Use in Florida. Available by University of Florida Cooperative Extension Service Institute of Food and Agricultural Sciences EDIS. July 2005. http://purl.fcla.edu/UF/lib/EP153. UNEP (United Nations Environment Programme) -International Environmental Technology Centre. 1997. 2.1 Desalinization by Reverse Osmosis. Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean, Osaka/Shiga, Japan. University of Hawaii at Manoa Cooperative Extention Service (CTAHR). 1998. Seashore Paspalum. Honolulu, HI. TM-1. Unruh, J.B., and B.J. Brecke. 1998. Response of Turfgrass and Turfgrass Weeds to Herbicides. ENH-100. University of Florida (IFAS), Gainesville, FL. Unruh, J.B., and M.L. Elliot. 1999. Best Management Practices for Florida Golf Courses. 2nd ed. UF/IFAS, Gainesville. Unruh, J.B., D.O. Stephenson, B.J. Brecke, and L.E. Trenholm. 2005. Tolerance of 'Salam' Seashore Paspalum (Paspalum vaginatum) to Postemergence Herbicide Applications. Weed Technology. US Salinity Laboratory. 1969. Diagnosis and Improvement of Saline and Alkaline Soils. USDA Agriculture Handbook 60.

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67 USDA (United States Department of Agriculture). 2003. Plant Guide: Torpedograss. July 2005. http://plants.usda.gov USGA (United States Golf Assosiation). 1993. USGA Recommendations for a Method of Putting Green Construction. USGA Greens Section Record. March/April. Vencill, W.K. 2002. Herbicide Handbook. 8th ed. Weed Science Society of America, Lawrence, Kansas. Webster, T.M. 2000. Weed SurveySouthern States, Grass Crops. Proc. South. Weed Sci. 53:247-274. Wiecko, G. 2003. Ocean Water as a Substitute for Postemergence Herbicides in Tropical Turf. Weed Technology 17:788-791. WSSA (Weed Science Society of America). 1999. Definition of Terms Used in Weed Science. RF-WG-042. University of Florida, Gainesville, Florida.

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BIOGRAPHICAL SKETCH Nicholas Bradley Pool is the son of Gene Pool and Susan Owens. He was born on January 29, 1979, and raised on a corn and soybean family farm in Avon, Illinois. Nick graduated from Avon High School in 1997 and attended Spoon River College where he received his Associate of Science degree. In the Fall of 1999, he attended one semester majoring in recreation, parks, and tourism at Western Illinois University. In January of 2000 he was accepted to the University of Florida where he graduated in the summer of 2003 with his Bachelor of Science degree in environmental horticulture with an emphasis in turfgrass science. He immediately began his graduate career under the direction of Dr. Barry Brecke and Dr. Bryan Unruh and is currently a candidate for a Master of Science degree in agronomy with an emphasis in weed science. After graduation, Nick is planning to enter the work force in the golf course industry. 68


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INFLUENCE OF SALTWATER ON WEED MANAGEMENT IN SEASHORE
PASPALUM















By

NICHOLAS B. POOL


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2005































Copyright 2005

by

Nicholas B. Pool















ACKNOWLEDGMENTS

I would like to start by thanking God for my existence and for the support He has

provided me throughout my life. I would also like to thank my parents and grandparents

for their encouragement and support. They are the reason for my success thus far and

will always be the most influential people in my life.

I thank my friends for providing me with the experience of a lifetime. More

specifically, I want to thank Travis Tueton, Mike Harrell, and Mark Mitchell for the

encouragement they gave me to continue my education. I would especially like to thank

Melissa Barron for being my best friend and biggest supporter. I am thankful for all the

laughs and experiences we have had and will continue to have.

I want to thank my major professors, Dr. Barry Brecke and Dr. Bryan Unruh, for

the confidence they had in me and providing me the opportunity to continue a graduate

career. I thank Dr. Greg MacDonald for offering his guidance and knowledge that made

my graduate school experience easier. Also, I thank Dr. Laurie Trenholm and Dr. Jay

Ferrell for being a part of my committee and assisting with my thesis. All of them have

exposed me to a diverse range of weed science, providing me with a truly well rounded

education. Finally, I thank everyone at the WFREC for their assistance with my research

project.
















TABLE OF CONTENTS



A C K N O W L E D G M E N T S ......... .................................................................................... iii

LIST OF TABLES ............. ..... ......................... .......... ............ vi

L IST O F F IG U R E S .... ...... ................................................ .. .. ..... .............. vii

A B S T R A C T .......................................... .................................................. v iii

CHAPTER

1 IN TR OD U CTION ............................................... .. ......................... ..

Characteristics of Seashore Paspalum ........................................ ...................... 1
W ater Quality and Consumption on Golf Courses ...................................................7
W eed M management on Golf Courses................................ ......................... ........ 9
S u m m ary ...................................... .................................................. 16

2 TOLERANCE OF NEWLY SPRIGGED AND ESTABLISHED SEASHORE
PASPALUM TO SALTWATER .................................. .......................... 19

Introduction..................................... .................................. ........... 19
M methods and M materials ....................................................................... ..................23
Results and D discussion ........................... ...... ..... ...... .. ........ ..... 25
Newly Sprigged Seashore Paspalum .......................................................25
E established Seashore Paspalum .................................... .................................... 26

3 SUSCEPTIBILITY OF NINE TURFGRASS WEED SPECIES TO FIVE
SALTWATER CONCENTRATIONS .............................. ...................................29

Introduction .......................................................................... 29
M methods and M materials ....................................................................... ..................34
G reenhouse Studies ......................... .. .................... .. .. ...... ........... 34
F field Stu dies ........................................................................36
Results and D discussion ........................... ...... ..... ...... .. ........ ..... 37
G reenhouse Studies ......................... .. .................... .. .. ...... ........... 37
Broadleaf species .............. ................. ..................... .. ............ 37
G rass and sedge species ........................................ .......... ............... 37
F field Stu dies .......................................................................4 0










4 THE TOLERANCE OF SEASHORE PASPALUM TO HERBICIDES WHEN
IRRIGATED W ITH SALTW ATER ............................ .......................................47

In tro d u ctio n ............................................................................................................ 4 7
M methods and M materials ........................................................................ ..................50
R results and D discussion ............................ ...... ... .. ...... .............. 52

5 C O N C L U SIO N S ..................... .... .......................... .. .... ........ .... ............ 58

APPENDIX 2004 RAINFALL ............................................................. ...............62

L IST O F R E FE R E N C E S ............................................................................. .............. 63

B IO G R A PH IC A L SK E TCH ...................................................................... ..................68









































v















LIST OF TABLES


Table page

1-1 Paspalum cultivars, leaf texture, and year of introduction................................. 18

2-1 Saltwater effect on sprigged and established seashore paspalum ..........................27

3-1 Control of selected broadleaf weeds with saltwater in the greenhouse pooled
data over years and evaluations....................... .... ............................. 42

3-2 Control of selected annual grass weeds with saltwater in the greenhouse pooled
data over years and evaluations....................... .... ............................. 42

3-3 Control of selected perennial grass and sedge weeds with saltwater in the
greenhouse pooled data over years and evaluations...............................................42

3-4 Control of southern crabgrass and cocks-comb kyllinga with two salt
concentrations applied as a solution or granular in the field...............................43

3-5 Seashore paspalum quality as affected by saltwater in the field............................43

4-1 List of herbicides tested on seashore paspalum under salinity stress....................56

4-2 The effect of preemergence herbicides and salt concentrations on seashore
paspalum quality 4 wk after herbicide application............... .............. .............57

4-3 The effect of postemergence herbicides and salt concentrations on seashore
paspalum quality 4 wk after herbicide application............... .............. .............57
















LIST OF FIGURES

Figure page

2-1 Effect of saltwater concentration on seashore paspalum quality ratings 8 wk
after initial application of saltw ater ................................................... .............. 28

3-1 Saltwater concentration effect on broadleaf weed control pooled over years and
ev alu atio n s............................. ........................................................ ............... 4 4

3-2 Saltwater concentration effect on annual grass control pooled over years and
ev a lu a tio n ......................................................................... 4 5

3-3 Saltwater concentration effect on perennial grass and sedge control pooled over
years and evaluation. ...................... .................. ................... ......... 46















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

INFLUENCE OF SALTWATER ON WEED MANAGEMENT IN SEASHORE
PASPALUM

By

Nicholas B. Pool

August 2005

Chair: Barry Brecke
Cochair: Bryan Unruh
Major Department: Agronomy

Greenhouse and field experiments were conducted in 2003 and 2004. Saltwater

treatments consisting of 55 dS/m (lx = seawater), 41 dS/m (3/4x), 27 dS/m (1/2x), 13

dS/m (1/4x), and potable water (Ox) were applied to established and newly sprigged

seashore paspalum under greenhouse conditions. In the second study, 18 herbicides were

applied to established seashore paspalum irrigated with saltwater treatments (lx, 3/4x,

1/2x, 1/4x and Ox) under greenhouse conditions. Saltwater treatments were applied 2

times per wk with 1 potable water treatment per wk for a total of 8 wk. Visual

evaluations for turf quality were based on a scale of 0 (dead turf) to 9 (health turf). In a

third study, 9 common turfgrass weeds were subjected to saltwater treatments (lx, 3/4x,

1/2x, 1/4x and Ox) applied 2 times per wk with 1 potable water treatment per wk. Visual

evaluations for weed control were taken on a scale of 0 (no control) to 100 (complete

control). Southern crabgrass and cocks-comb kyllinga susceptibility to saltwater was

tested under field conditions in established 'Sea Isle 1' seashore paspalum. Plots were









treated for 4 wk with a 1/4x or 1/2x concentration of salt applied as a liquid solution or as

a granule and compared to a freshwater treatment.

Turfgrass quality was compromised (ratings < 7) at the 3/4x and lx rates of

saltwater applied to established seashore paspalum while all levels of salt caused

unacceptable injury to newly sprigged seashore paspalum. Herbicides that caused a

major reduction in the quality of seashore paspalum were atrazine and metribuzin. These

herbicides will cause damage when seashore paspalum is irrigated with any concentration

of saltwater and should not be applied to seashore paspalum. Minor reductions in quality

were observed after the application of bromoxynil, 2,4-D + dicamba + mecoprop, and

imazaquin. These herbicides should not be applied to seashore paspalum irrigated with

saltwater concentrations > 1/2x. Florida pusley was controlled at all rates of saltwater

while Virginia buttonweed was controlled at all rates except 1/4x. Crabgrass, goosegrass,

and tropical signalgrass were adequately controlled (>70%) at the 3/4x and lx rates of

saltwater while the lx rate was needed to provide control of purple nutsedge and

dollarweed. Bermudagrass and torpedograss exhibited high levels of tolerance at all salt

concentrations. In the field study, crabgrass was effectively controlled at 1/2x rate of

saltwater applied as a solution or as granular salt. The 1/4x rate was also effective

granularly applied, but not applied as a solution. Kyllinga was controlled at the 1/2x rate

either as a granular or solution, but the 1/4x rate was not effective using either method.

In both studies, the granular application method provided better control of crabgrass and

kyllinga compared to salt applied in solution.














CHAPTER 1
INTRODUCTION

Characteristics of Seashore Paspalum

Seashore paspalum (Paspalum vaginatum 0. Swartz) is a perennial warm season

turfgrass that is native to tropical and subtropical regions of the world (Duncan and

Carrow, 2000). Although seashore paspalum has existed for many years, it has only been

used commercially for the past few decades (Table 1.1). Seashore paspalum spreads by

rhizomes and stolons that root at the nodes forming a deep fibrous root system (Duble,

2000). It is generally propagated vegetatively from sod or sprigs because seed production

has not been reliable due to self-compatibility issues (Duncan and Carrow, 2000).

Breeders have been able to overcome this obstacle and one seed produced cultivar,

Seaspray, has recently been released (Hughes, 2005).

Seashore paspalum leaves are slightly coarser than those of common bermudagrass

when mowed > 2.5 cm in height. When mowed < 2.5 cm, a finer textured dense turf is

produced. Tiller production also increases as mowing height is decreased (Fry and

Huang, 2004). Because of the increased tiller production, competition among plants is

greater, resulting in a reduced leaf blade width response (Fry and Huang, 2004). A

mowing height > 5 cm will cause the seashore paspalum turf to become spindly, increase

thatch production, and shade itself out (Trenholm and Unruh, 2003).

Compared to bermudagrass (Cynodon dactalon [L.] Pers.), seashore paspalum does

well under flooded conditions (Anonymous, 1998). Seashore paspalum also tolerates

drought similar to centipedegrass (Eremochloa ophiuroides spp. ) and better than









bermudagrass (Duncan and Carrow, 2000). Seashore paspalum has cold tolerance similar

to most hybrid bermudagrass (Cynodon mageiiiggii) cultivars (Duncan and Carrow,

2000). The fine-textured paspalums are often the last warm season turfgrasses to become

dormant and generally require consecutive days with temperatures below freezing to

reach full winter dormancy (Duncan and Carrow, 2000).

Like bermudagrass, seashore paspalum does not tolerate shade (Trenholm and

Unruh, 2002). Areas with a dense tree canopy pose a problem when attempting to

maintain seashore paspalum beneath them. However, when subjected to long periods of

low light (cloudy, overcast/hazy/foggy, or monsoonal conditions), seashore paspalum

grows well (Jiang et al., 2004). Jiang et al. (2004) concluded that seashore paspalum

does well under low light conditions compared to hybrid bermudagrass. 'Sea Isle 1'

seashore paspalum had the slowest rate of decline in quality (1 = dead turf to 9 = healthy

turf) with 8.0 at full sunlight, 7.2 at 70% shade, and 6.9 at 90% shade compared to the

best hybrid bermudagrass ('TifSport') with 7.7 at full sunlight, 6.3 at 70% shade, and 5.7

at 90% shade. Turf quality and photosynthetic rates of both turfgrass species declined as

the duration of low light increased, but the seashore paspalum cultivars had a higher

photosynthetic rate than the bermudagrass cultivars, suggesting the higher photosynthetic

rates contribute to the tolerance of low light intensity in seashore paspalum (Jiang, 2004).

Fertility requirements of seashore paspalum appear to be lower than most warm

season turfgrass species that are utilized on golf courses. However, in situations where

saline water is used for irrigation and the soil is routinely flushed with water to prevent

salt toxicity, fertility requirement will increase due to increased leaching (Duncan and

Carrow, 2000).









The nitrogen requirement for seashore paspalum ranges from 97 to 390 kg ha-1 y-1

depending on the maintenance intensity of the turf (Duncan and Carrow, 2000). Turf

mowed at greens height (< 0.5 cm) typically requires no more than 390 kg N ha-1 y-1 in

tropical regions (Duncan and Carrow, 2000).

Phosphorus requirements for seashore paspalum are similar to bermudagrass and

supplemental phosphorus is only needed when levels present in the soil are reported low

on a soil test (Trenholm and Unruh, 2002; Duncan and Carrow, 2000).

Potassium must be supplied to seashore paspalum in salt affected areas because K

loss through leaching is increased with the presence of Na Ca2+, and Mg2+ (Duncan and

Carrow, 2000). Potassium should to be applied at 1.5 to 2 times the rate of nitrogen

(Duncan and Carrow, 2000). The application of potassium has been shown to improve

wear tolerance, stress tolerance, and salinity tolerance of seashore paspalum (Duncan and

Carrow, 2000).

Iron amendments can be applied in small amounts during the growing season to

promote green up without promoting shoot growth (Trenholm and Unruh, 2003). Mn2+

and Zn2+ also aid in enhancing the ability of seashore paspalum to tolerate salinity by

preventing cation and osmotic shock (Duncan, 2004). In high salinity situations where

fresh water leaching is practiced, all micronutrients need to be monitored regularly for

deficiencies due to excessive leaching of nutrients.

Saline soil is defined as a soil having a saturated extract with an electrical

conductivity > 4 decisemens per meter (dS/m) (US Salinity Laboratory, 1969). Ocean

water is equivalent to approximately 54 dS/m, or 34,500 ppm (Duncan, 2004). Sodium

chloride (NaC1) is the predominant component contributing to salinity in soils (Jungklang









et al., 2003). Salinity levels in soils are becoming increasingly problematic due to the use

of alternative water (effluent or brackish) for irrigation. Duncan and Carrow (1998) have

cited seven major contributors to increased soil salinity:

* increased use of wastewater on turfgrass;

* golf course construction in coastal sites;

* the placement of golf courses bordering environmentally sensitive wetlands or
other similar areas;

* the use of high sand root zone mixes where sands can more readily become
salinized than fine textured soils;

* the increasing emphasis on water conservation practices;

* saltwater intrusion in irrigation aquifers, especially within 16 km of sea coasts; and

* the construction of golf courses on sites with poor soil conditions, not normally
suitable for crop production.

Salinity tolerance is a distinguishing physiological characteristic of seashore

paspalum. Research on this physiological tolerance is limited because seashore paspalum

has only been used commercially for the past decade.

There are three mechanisms plants use to tolerate salinity. The first mechanism is

selective ion uptake by the roots (Colmer, 2000; Rose-Fricker and Wipff, 2001). Plants

that use this mechanism are considered to be "salt excluders." Even with a high

concentration ofNa+ in the soil the plant is able to efficiently and selectively absorb

essential ions.

The second mechanism is the accumulation of salt in specific vacuoles within plant

cells, from which the salt is translocated back to the soil in small concentrations (Colmer,

2000; Rose-Fricker and Wipff, 2001). Other plants, such as inland saltgrass (Distichlis

spicata (L.) Greene.) and bermudagrass, have special glands, called salt glands or









bladders, on the leaf surface that excrete salt (Colmer, 2000; Rose-Fricker and Wipff,

2001). Plants that use this mechanism are considered to be "salt includess"

The third mechanism is osmotic adjustment (Colmer, 2000; Fricker and Wipff,

2001; Marcum, 2004). The plants adjust their internal ion gradient to maintain turgor

pressure, allowing it to continue water absorption in the presence of high salt

concentrations.

All of these mechanisms operate in salt tolerant plants, while one or more of these

mechanisms may be lacking in a salt sensitive plant (Colmer, 2000). Seashore paspalum

has the ability to efficiently select ions absorbed by the roots, and it is also able to secrete

salt through salt glands on the leaf surface (Marcum, 1999).

Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting

(Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of

the soil over time and must be managed properly when establishing and maintaining a

high quality turf. Soils high in Na+ will have poor aeration and reduced water infiltration

rates due to dispersal of soil particles in the soil profile (Mitra, 2000 and 2001). A form

of soluble Ca2+ must be added to soils with a high exchangeable Na+ percentage to

replace the Na+ on the cation exchange sites (Mitra, 2000 and 2001). Gypsum is the most

common form of Ca2+ because it is water soluble and has little effect on soil pH (Mitra,

2001). Once the Na+ is removed from the exchange site, it must be leached from the soil

profile with deep, infrequent irrigation (Mitra, 2000 and 2001). An additional method of

dealing with salinity problems is to use salt tolerant species and/or cultivars (Qian et al.,

2001).









Several studies have been conducted testing the tolerance of seashore paspalum to

various concentrations of saltwater. Noaman and El-Haddad (2000) exposed established

seashore paspalum to three levels of salinity: 10 g/L (16 dS/m), 20 g/L (32 dS/m), and 40

g/L (64 dS/m). A reduction in plant height with increased salt concentration was

apparent after 4 weeks (wk) and continued to decrease until the end of the experiment at

10 wk. Similarly, as salt concentration increased from 16 dS/m to 64 dS/m, plant

biomass decreased by 70% (Noaman and El-Haddad, 2000).

Marcum and Murdoch (1994) subjected seashore paspalum and five other warm-

season turfgrasses [manilagrass (Zoisia matrella (L.) Merr.), St. Augustinegrass

(Stenotaphrum secundatum (Walt.) Ktze.), Tifway bermudagrass, Japanese lawngrass

(Zoisiajaponica Steud.), and centipedegrass] to five saltwater concentrations: 1 mM (1

dS/m), 100 mM (9 dS/m), 200 mM (17 dS/m), 300 mM (26 dS/m), and 400 mM (34

dS/m). Seashore paspalum growth rates were higher than the other turfgrass species at 34

dS/m. Seashore paspalum quality ratings were also higher than the other turfgrasses at all

saltwater concentrations (Marcum and Murdoch, 1994).

Couillard and Wiecko (1998) evaluated saltwater tolerance on bermudagrass, and

seashore paspalum. The turf was treated with ocean water at three concentrations: pure

ocean water (54 dS/m), 2/3 ocean water (37 dS/m) + 1/3 potable water, and 1/3 ocean

water (19 dS/m) + 2/3 potable water. The watering schedule was twice daily for two

different periods: 3 days (d) or 6 d. Following the saltwater stress periods, potable

irrigation was applied to evaluate the recovery potential of seashore paspalum and

bermudagrass over a period of 32 d after the salt-stress treatments began. Injury was

observed on all plant species tested at all three ocean water concentrations.









Bermudagrass and seashore paspalum both fully recovered from all treatments. The most

injury occurred with pure ocean water after the 6 d salt-stress treatment.

Wiecko (2003) exposed seashore paspalum, bermudagrass, St. Augustinegrass, and

centipedegrass to three different salinity levels (54, 37, and 19 dS/m) over two short term

salt stress durations (3 and 6 d). Seashore paspalum showed excellent salinity tolerance

compared to all other plants tested with the maximum injury of 18% at 54 dS/m after the

6 d salt stress duration. Bermudagrass injury was 30% at 54 dS/m after the 6 d salt stress

duration and only minor injury at lower salt concentrations. St. Augustinegrass showed

up to 60% injury under the 6 d duration of 54 dS/m and centipedegrass showed complete

necrosis (Wiecko, 2003).

These studies indicate seashore paspalum can tolerate saline irrigation, but long-

term quality can be compromised when irrigated with high salt concentration water.

When establishing seashore paspalum, saline conditions may negatively impact turfgrass

growth rate (Duncan and Carrow, 1999). Before selecting a grass species for a specific

site, water and soil samples should be collected to analyze quality (Duncan and Carrow,

2000). If saline soils are present, amendments should be added to manage the problem

before turfgrass is established in the area (Duncan and Carrow, 2000). Long-term

salinity problems will persist in the soil if poor quality irrigation water is used (Duncan

and Carrow, 2000). Proper irrigation scheduling and duration will help alleviate the

problem by leaching the salts through the soil profile (Duncan and Carrow, 2000).

Water Quality and Consumption on Golf Courses

Water management is one of the most important aspects of golf course

maintenance. On average, a golf course occupies approximately 55 hectares (137 acres),

of which 65% is irrigated on a regular basis (Marella, 1999). According to a survey by









Haydu and Hodges in 2002, golf courses in Florida use approximately 655 billion liters

(173 billion gallons) of water per year. Recycled water accounts for 49% of the total

water, while 29% comes from surface water and 21% from wells.

There are five Water Management Districts in the state of Florida that regulate the

use of water. These districts have the power to issue water use permits, impose

regulations, and establish permit fees. There are several types of water use permits that

are issued by Florida's Water Management Districts. Consumptive use permits (CUPs)

are the most commonly issued permit and are required if water is withdrawn from a well

15 mm (6 in) in diameter or greater, if the annual average water use is 378,500 liters

(100,000 gal) per day or greater, and if a pump is used that has the capability to pump 3.8

million liters (1 million gal) per day or greater (SJRWMD 2002). Because CUPs

determine the duration and amount of potable water available to golf courses, alternative

water sources that have fewer restrictions are being used.

The United States Golf Association (USGA) lists several different irrigation water

sources that are available to golf courses (Snow, 2004). Fresh water is the most common

source of irrigation water and can be acquired from aquifers or retention ponds and lakes.

Another source is tertiary treated effluent water. The turfgrass acts as a filter by

extracting nutrients and breaking down chemicals in the effluent water that municipalities

would otherwise discharge into nearby rivers or the ocean (Snow, 2004). Some areas in

the southern U.S. including Arizona and Florida require the use of effluent water for

turfgrass irrigation because of a limited supply of freshwater (Snow, 2004).

Brackish water (salt concentration between fresh water and ocean water) or ocean

water is also used as an irrigation source on golf courses. Bermudagrass and seashore









paspalum are tolerant to certain levels of saltwater (Snow, 2004). Precise application of

saltwater is required to prevent injury to existing plant populations that have a low salt

tolerance.

Reverse osmosis desalinization facilities can also be constructed on site to reduce

the dissolved salt content of saline water to a usable level. Saline water (feedwater) is

drawn from a source and pretreated by adjusting pH, removing suspended solids, and

adding inhibitors to control scaling caused by calcium constituents (UNEP, 1997). The

feedwater is then pressurized to the appropriate operating pressure for the water-

permeable membrane (UNEP, 1997). The pressurized feedwater enters the membrane

that inhibits dissolved salts from passing, while allowing the desalinized water to pass

through (UNEP, 1997). Finally, the desalinized water is stabilized by degasification and

adjustment of the pH (UNEP, 1997). These reverse osmosis desalinization plants are

expensive, but are necessary in certain areas where freshwater is limited or too expensive

to purchase in large quantities (Snow, 2004).

Weed Management on Golf Courses

Seashore paspalum exhibits exceptional salt tolerance, but is highly susceptible to

injury from many postemergence herbicides (Wiecko, 2003). It may be possible to

replace postemergence herbicides with saltwater to control some species of weeds

(Wiecko, 2003).

Weeds compete with turfgrass for light, nutrients, water, and physical space

(Florkowski and Landry, 2002) and weed management is a major cost for turfgrass

managers. On golf courses in the Southeast, average expenditures for herbicides in 1998

were $11,690 per course (Florkowski and Landry, 2002).









Some of the more common weeds in turfgrass include dollarweed (Hydrocotyle

spp.), Florida pusley (Richardia scabra L.), Virginia buttonweed (Diodia virginiana L.),

goosegrass, southern crabgrass (Digitaria ciliaris (Retz.) Koel.), common bermudagrass,

tropical signalgrass (Urochloa subquadripara [Trin.] R. Webster), torpedograss

(Panicum repens L.), and purple nutsedge (Cyperus rotundus L.).

Dollarweed is a perennial broadleaf that reproduces by seed, rhizomes, and tubers.

The leaves are long stalked with the petiole attached to the center of the leaf that

resembles an umbrella. Dollarweed is most commonly found in areas with excessive

moisture (Murphy et al., 1996).

Florida pusley is a summer annual broadleaf that reproduces by seed. The

branched stem is hairy with thickened leaves that have an opposite arrangement. The

white flowers are bunched at the end of the branches (Murphy et al., 1996).

Virginia buttonweed is a perennial broadleaf that reproduces by seed, roots, and

stem fragments. The stem is branched and hairy with an opposite leaf arrangement. The

flower is white with four lobes at each leaf axil (Murphy et al., 1996).

Goosegrass is a summer annual grass that reproduces by seed. The crown is

generally white or silver in color and is usually found in areas with compacted soils. The

leaves are smooth on both sides with a short-toothed membranous ligule (Murphy et al.,

1996).

Southern crabgrass is a summer annual grass that reproduces by seed. Stems are

branched and root at the nodes. The leaves are usually hairy on both sides and have a

toothed membranous ligule (Murphy et al., 1996).









Common bermudagrass is a perennial grass that reproduces by stolons, rhizomes,

and seed (Duble, 2004). The stolons and rhizomes root at the nodes to form a deep

fibrous root system (Duble, 2004). The collar of the leaves have a fringe of short, white

hairs (NewCROP, 1999).

Tropical signalgrass is a summer annual grass that reproduces by seed. The stem is

branched with a blanket-like growth pattern. The leaves are glossy with a coarse texture

(Busey 2000).

Torpedograss is a very persistent perennial grass that reproduces vegetatively or

through rhizomes (Busey, 2002). The rhizome system is very robust with sharply pointed

tips. The stems are stiff and erect with leaves that are folded or flat (Murphy et al.,

1996).

Purple nutsedge is a perennial sedge that reproduces primarily by oblong tubers

that are covered with hairs. The leaves taper abruptly to a point unlike yellow nutsedge

that tapers gradually to a point. The seed head has a purplish color and is formed on a

triangular stem (Murphy et al., 1996).

These weeds are a few of the most common weeds found in turfgrass in the

Southeastern United States. Control of these weeds can be very difficult and expensive.

Weeds can be controlled using cultural practices to produce a healthy, competitive

turfgrass, in combination with herbicides. Cultural practices can greatly reduce weed

pressure on turfed areas. Using cultural methods can reduce chemical use, which can

reduce herbicide costs for weed control. Often, the most cost effective method of weed

control is to have a healthy, dense turf (Unruh and Elliott, 1999). The turf will naturally

out-compete many weed species.









One important step in producing a healthy turf is proper fertility. Different

turfgrasses have different fertility requirements. Nitrogen, phosphorus, and potassium

are important nutrient requirements for enhanced shoot and root growth.

Aerification and verticutting are common cultural practices to control weeds and

relieve turf stresses such as compaction and thatch on golf courses. Aerification consists

of pulling soil core plugs 0.63 cm to 1.9 cm (0.25 to 0.75 in.) in diameter, ranging in

depth of 5 to 10 cm (2 to 4 in.) (Unruh and Elliott, 1999). This process relieves soil

compaction, improves surface drainage and water penetration, and reduces thatch (Unruh

and Elliot, 1999).

Verticutting consists of vertical knives spaced close together on a horizontal shaft

that slice into the turf (Unruh and Elliott, 1999). This practice removes the organic

matter (thatch) layer allowing the turf to grow horizontally and allows for a smooth

putting surface. Deep verticutting should be avoided when maintaining seashore

paspalum greens because this increases the potential for scalping (Duncan and Carrow,

2002). Light verticutting enhances stolon-rhizome-shoot growth and allows topdressing

sand to integrate into the thatch layer producing a more firm, smooth surface less

susceptible to scalping (Duncan and Carrow, 2000, 2002). A good quality topdressing

sand for seashore paspalum should integrate easily into the surface at light rates without

verticutting (Duncan and Carrow, 2002).

Mowing is another very important cultural practice on a golf course. Improper

mowing can weaken the turf reducing its density and quality (Unruh and Elliott, 1999),

providing an opportunity for weeds to invade. Seashore paspalum does not tolerate

scalping as well as bermudagrass or zoysiagrass and may take 4 to 6 wk to fully recover









(Duncan and Carrow, 2002). When reducing the mowing height on seashore paspalum

tees and greens, it should be done in gradual increments of 0.05 to 0.08 cm (0.02 to 0.03

in.) over 2 to 3 d (Duncan and Carrow 2002). When the turf is mowed properly, very

little stress is put on the plant, allowing it to recover very quickly. Frequent mowing

increases shoot growth, producing a dense canopy that makes it more difficult for weeds

to invade (Unruh and Elliott, 1999).

Finally, proper irrigation can be used to reduce weed pressure. Maintaining proper

soil moisture levels is important for producing a healthy turf. Seashore paspalum is very

responsive to irrigation duration and frequency and a shallow root system will result from

frequent irrigation events of short durations (Duncan and Carrow, 2002). This also

causes the turf to be more succulent, less drought tolerant, and more susceptible to

scalping. Watering schedules should consist of long durations during applications with

long intervals (1.25 to 2.5 cm of water every 4 to 7 days on a sand green) between

applications to force the roots to grow deeper into the soil profile (Duncan, 2004; Duncan

and Carrow, 2002). Various grass types require different moisture levels and weed

species will also respond differently depending on moisture levels. For instance,

dollarweed populations can be reduced in St. Augustinegrass turf by reducing irrigation

levels (Busey, 2001).

Herbicides are regularly used for weed control on golf courses. Some important

considerations when selecting a herbicide are effectiveness, turfgrass tolerance, speed of

control, toxicity, and cost (Unruh and Elliott, 1999). There is no single herbicide that

will control all weeds in a desired turf stand, so proper identification is essential (Unruh

and Brecke, 1998). Seashore paspalum is sensitive to many herbicides commonly used









on other turfgrasses (Trenholm and Unruh, 2003; and CTAHR, 1998). Herbicides that

are noninjurous to seashore paspalum include bensulide, pronamide, benefin, DCPA,

pendimethalin, ethofumesate, quinclorac, MCPP + 2,4-D + dicamba, dithiopyr, 2,4-D +

dicamba + dicloprop, dicamba, halosulfuron, mecoprop, and bentazon (Duncan and

Carrow, 2000). However, dithiopyr, halosulfuron, oxadiazon, and prodiamine are the

only herbicides labeled for use on seashore paspalum (Unruh et al., 2005). These

herbicides could possibly be used at reduced rates in conjunction with saltwater irrigation

to control weeds in seashore paspalum (Duncan and Carrow, 2000).

Studies have been conducted to test the tolerance of seashore paspalum to several

postemergence herbicides. In 1997, Johnson and Duncan tested the recommended rates

and 3 times the recommended rates of diclofop, quinclorac, dicamba, imazaquin,

halosulfuron, and 2,4-D + mecoprop + dicamba on four seashore paspalum accessions

(AP 10, HI 25, PI 28960, and K-7).

Seashore paspalum accessions varied in their response to the herbicides evaluated.

Quinclorac and halosulfuron were the only herbicides that did not reduce the quality of

any accession at the recommended rates. When quinclorac and halosulfuron rates

increased, quality of HI 25 and K-7 was reduced. All accessions recovered completely

even from the high rates within 4 to 8 wk after initial treatment.

Dicamba had no effect on any of the accessions when applied at the labeled rate.

Quality of the K-7 accession, however, was negatively affected by the increased rate of

dicamba.

Diclofop, imazaquin, and 2,4-D + mecoprop + dicamba reduced the quality of all

paspalum accessions regardless of application rate. Full recovery from diclofop and









imazaquin required 4 to 8 wk. Recovery from the labeled rates of 2,4-D + mecoprop +

dicamba took 4 to 8 wk for all accessions, and none of the accessions recovered from the

high rate by 8 wk. The overall conclusion from this study was that quinclorac, dicamba,

and halosulfuron were safe on all accessions, diclofop and imaziquin were marginal, and

2,4-D + mecoprop + dicamba were considered injurious.

A study was conducted by Unruh et al. (2005) testing the tolerance of 'Salam'

seashore paspalum to postemergence herbicides for control of grass (clethodim,

ethofumesate, metsulfuron, sethoxydim, and quinclorac), broadleaf (clopyralid, dicamba,

and 2,4-D + mecoprop + dicamba), and sedge (bentazon, halosulfuron, imazapic,

imazaquin, and trifloxysulfuron-sodium) species. Metsulfuron, quinclorac, clopyralid,

dicamba, 2,4-D + mecoprop + dicamba, bentazon, halosulfuron, and imazaquin caused

less than 15% injury at the recommended rates and are considered safe for seashore

paspalum. Clethodim, sethoxydim, ethofumesate, imazapic, and trifloxysulfuron-sodium

caused greater than the acceptable standard of 20% injury and are considered not safe for

application to seashore paspalum.

The high level of salt tolerance may allow the use of saltwater for weed control in

place of injurious postemergence herbicides (Wiecko, 2003). Couillard and Wiecko

(1998) evaluated injury from saltwater on large crabgrass (Digitaria sanguinalis (L.)

Scop.) and mimosa-vine (Mimosapudica Torr.). They treated both species with ocean

water at three concentrations: pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m) +

1/3 potable water, and 1/3 ocean water (19 dS/m) + 2/3 potable water. The weeds were

watered twice daily for two different periods: 3 d or 6 d. Following the saltwater stress

periods, potable irrigation was applied to evaluate the recovery potential over a period of









32 days after the salt-stress treatments began. Injury was observed on both plant species

tested at all three ocean water concentrations.

Mimosa only recovered from the 1/3x ocean water treatment subjected to 3 d salt-

stress. Complete crabgrass control was only achieved with pure ocean water under 6 d

salt-stress.

Other studies were conducted by Wiecko (2003) with the addition of goosegrass,

alyceclover (Alysicarpus vaginalis (L.) DC.), and yellow nutsedge (Cyperus esculentus

L.) to the species previously evaluated. Mimosa-vine showed complete necrosis at 54

dS/m and 37 dS/m under both salt stress durations, respectively. Alyceclover showed

>90% injury at 34,500 ppm under both salt stress durations, and >70% at 37 dS/m. Large

crabgrass and goosegrass showed >90% injury at 54 dS/m. Yellow nutsedge had the

greatest salt tolerance among the weeds with injury <40% at all salt concentrations

(Wiecko, 2003).

Based on these studies, ocean water can be used as an alternative to herbicides to

control weeds in certain turfgrasses (Couillard and Wiecko, 1998). Most annual grass

and broadleaf weed species cannot tolerate continuous irrigation with saltwater or

saltwater blends (wastewater) (Duncan and Carrow, 2000).

Summary

During early root growth and establishment, all plants are more sensitive to saline

conditions causing desiccation of the plant and reducing water infiltration and aeration of

the soil (Duncan and Carrow, 2000). Salinity will also cause nutrient deficiencies or

imbalances resulting in toxicities that will influence plant growth and development

(Duncan and Carrow, 2000). Genetic resistance to these stresses and toxicities is

valuable for managing turf successfully on saline soils (Duncan and Carrow, 2000).









While considerable research has been conducted to determine the tolerance of established

seashore paspalum to saltwater, little information is available concerning saltwater

tolerance in newly sprigged seashore paspalum. Thus, research was conducted to

compare salt tolerance of established with newly sprigged seashore paspalum.

Some research has been conducted to evaluate susceptibility of selected weed

species to saltwater. However, additional information about the effectiveness of

saltwater for control of additional weed species is needed. Research was conducted with

eight weed species to determine the level of control that can be achieved with saltwater

alone. This will help determine the contribution to overall weed management that can be

expected from saltwater irrigation.

Tolerance of seashore paspalum to many postemergence herbicides has been

determined over the past decade. However, herbicide response of seashore paspalum in

salt-affected areas has not yet been determined and seashore paspalum may be more

sensitive to injury as salt-stress increases. Susceptibility to herbicide injury under salt

stress was also tested on seashore paspalum.









Table 1-1 Paspalum cultivars, leaf texture, and year of introduction.
Cultivar Leaf texture Year Introduced
Saltene intermediate 1951
Salpus intermediate
Futurf intermediate 1972
Adalayd (Excalibur) intermediate 1975
Fidalayel intermediate
Tropic Shore course 1991
Mauna Kea intermediate
Salam fine (fairway/sports) 1998
Sea Isle 2000 fine (greens/tees) 1999 to present
Sea Isle 1 fine (fairway/tees/sports)
Durban Country Club fine (fairway/tees/roughs)
Sea Dwarf fine (greens/tees)
Sea Green fine (greens/tees)
Seaway fine (fairway/sports)
Seasprav (seeded) fine (fairway/sports)














CHAPTER 2
TOLERANCE OF NEWLY SPRIGGED AND ESTABLISHED SEASHORE
PASPALUM TO SALTWATER

Introduction

Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial, warm season

turfgrass that is native to tropical and subtropical regions of the world (Duncan and

Carrow, 2000). Although seashore paspalum has existed for many years, it has only been

used commercially for the past few decades. Seashore paspalum spreads by rhizomes

and stolons that root at the nodes forming a deep fibrous root system (Duble, 2000). It is

generally propagated vegetatively from sod or sprigs because seed production has not

been reliable (Duncan and Carrow, 2000). Research into the self-incompatibility issues

has led to the introduction of one seed produced cultivar, Seaspray (Hughes, 2005).

The leaves of seashore paspalum are slightly coarser than those of common

bermudagrass when mowed > 2.5 cm in height. When mowed < 2.5 cm, a finer textured

dense turf is produced. Tiller production will increase as mowing height is decreased and

the width of the leaf blade is reduced as a result of competition among plants (Fry and

Huang, 2004). A mowing height > 5 cm causes the seashore paspalum turf to become

spindly, increase thatch production, and shade itself out (Trenholm and Unruh, 2003).

In flooded conditions seashore paspalum does well compared to bermudagrass

(Anonymous, 1998). Seashore paspalum also tolerates drought similar to centipedegrass

and better than bermudagrass (Duncan and Carrow, 2000). The cold tolerance of

seashore paspalum is similar to most hybrid bermudagrass cultivars (Duncan and Carrow,









2000). The fine-textured paspalums are often the last warm season turfgrasses to go into

full winter dormancy and generally require consecutive days with temperatures below

freezing to reach full winter dormancy (Duncan and Carrow, 2000).

Like bermudagrass, seashore paspalum does not tolerate shade, however, when low

light conditions (cloudy, overcast/hazy/foggy, and monsoonal conditions) are present,

seashore paspalum does well under low light conditions compared to hybrid

bermudagrass (Jiang et al., 2004; Trenholm and Unruh, 2002).

Fertility requirements of seashore paspalum appear to be lower than most warm

season turfgrass species that are utilized on golf courses. However, in situations where

saline water is used for irrigation and the soil is routinely flushed with water to prevent

salt toxicity, fertility requirements will increase due to increased leaching and all

micronutrients need to be monitored regularly for deficiencies. (Duncan and Carrow,

2000).

Salinity levels, predominantly sodium chloride (NaC1), in soils are becoming

increasingly problematic due to the use of alternative water (effluent or brackish) for

irrigation (Duncan and Carrow, 1998; Jungklang, 2003). There are three physiological

mechanisms plants use to tolerate salinity. The first mechanism is selective ion uptake by

the roots (Colmer, 2000; Rose-Fricker and Wipff, 2001). The plant is able to efficiently

and selectively absorb needed ions even with a high concentration ofNa+ in the soil. The

second mechanism is the accumulation of salt in specific vacuoles within plant cells,

from which the salt is retranslocated back to the soil or excreted by salt glands on the leaf

surface (Colmer, 2000; Rose-Fricker and Wipff, 2001). Finally, the plant uses osmotic

adjustment to maintain turgor pressure allowing it to continue water absorption in the









presence of high salt concentrations (Colmer, 2000; Fricker and Wipff, 2001; Marcum,

2004).

Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting

(Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of

the soil over time and must be managed properly when establishing and maintaining a

high quality turf. Soils high in Na+ will have poor aeration and reduced water infiltration

rates due to dispersal of soil particles in the soil profile (Mitra, 2000 and 2001). A form

of soluble Ca2+ must be added to soils with a high exchangeable Na+ percentage to

replace the Na+ on the cation exchange sites (Mitra, 2000 and 2001). Gypsum is the most

common form of Ca2+ because it is water soluble and has little effect on soil pH (Mitra,

2001). Once the Na+ is removed from the exchange site, it must be leached from the soil

profile with deep, infrequent irrigation (Mitra, 2000 and 2001). An additional method of

dealing with salinity problems is to use salt tolerant species and/or cultivars (Qian, 2001).

Several studies have been conducted testing the tolerance of seashore paspalum to

various concentrations of saltwater. Noaman and El-Haddad (2000) exposed established

seashore paspalum to three levels of salinity: 10 g/L (16 dS/m), 20 g/L (32 dS/m), and 40

g/L (64 dS/m). The plant height reduction with increased salt concentration was apparent

after 4 wk and continued to decrease until the end of the experiment at 10 wk. Similarly,

as salt concentration increased from 16 dS/m to 64 dS/m, plant biomass decreased by

70% (Noaman and El-Haddad, 2000).

Marcum and Murdoch (1994) subjected seashore paspalum and five other warm-

season turfgrasses [manilagrass (Zoisia matrella (L.) Merr.), St. Augustinegrass

(Stenotaphrum secundatum (Walt.) Ktze.), Tifway bermudagrass, Japanese lawngrass









(Zoisiajaponica Steud.), and centipedegrass] to five saltwater concentrations: 1 mM (1

dS/m), 100 mM (9 dS/m), 200 mM (17 dS/m), 300 mM (26 dS/m), and 400 mM (34

dS/m). Seashore paspalum growth rates were higher than the other turfgrass species at 34

dS/m. Seashore paspalum quality ratings were also higher than the other turfgrasses at all

saltwater concentrations (Marcum and Murdoch, 1994).

Couillard and Wiecko (1998) evaluated saltwater for tolerance on bermudagrass,

and seashore paspalum. The turf was treated with ocean water at three concentrations:

pure ocean water (54 dS/m), 2/3 ocean water (37 dS/m) + 1/3 potable water, and 1/3

ocean water (19 dS/m) + 2/3 potable water. The watering schedule was twice daily for

two different periods: 3 d or 6 d. Following the saltwater stress periods, potable

irrigation was applied to evaluate the recovery potential of seashore paspalum and

bermudagrass over a period of 32 d after the salt-stress treatments began.

The most injury for bermudagrass and seashore paspalum occurred with pure ocean

water after the 6 d salt-stress treatment. In all instances, bermudagrass and seashore

paspalum both fully recovered from all treatments when watered with potable water.

Wiecko (2003) exposed seashore paspalum, bermudagrass, St. Augustinegrass, and

centipedegrass to three different salinity levels (54, 37, and 19 dS/m) over two short term

salt stress durations (3 and 6 d). Seashore paspalum showed excellent salinity tolerance

compared to all other plants tested with the maximum injury of 18% at 54 dS/m after the

6 d salt stress duration. Bermudagrass injury was 30% at 54 dS/m after the 6 d salt stress

duration and only minor injury at lower salt concentrations. St. Augustinegrass showed

up to 60% injury under the 6 d duration of 54 dS/m and centipedegrass showed complete

necrosis (Wiecko, 2003).









These studies indicate seashore paspalum can tolerate saline irrigation, but quality

can be compromised long-term when irrigated with high salt concentration water. When

establishing seashore paspalum, saline conditions may negatively impact turfgrass growth

rate (Duncan and Carrow, 1999). The salinity tolerance during establishment of seashore

paspalum has not yet been determined. The objective of this study was to determine the

tolerance of both newly sprigged and established seashore paspalum to various

concentrations of saltwater.

Methods and Materials

Studies were conducted under greenhouse conditions at the University of Florida in

Gainesville in 2004. Strips of sod were cut with a sod cutter from a two year old stand of

'Sea Isle 1' seashore paspalum. Plugs were cut from the sod strips using a golf cup cutter

15 cm in diameter. The native soil was washed from the plugs and then plugs were

transplanted into 15 cm in diameter by 17 cm deep (3,000 cm3 volume) plastic pots

containing a growing medium of USGA (1993) greens mix (80% sand and 20% organic

matter). The intact seashore paspalum plugs were planted level with the rim of the pots.

After transplanting, the pots were placed in a greenhouse receiving full sun and

maintained at a temperature range of 270 to 320 C. A slow release 18-9-18+Mn+Fe

fertilizer was applied at a rate of 24.5 kg N ha-1 1 wk after planting. The plugs were

irrigated with potable water during a 3 wk rooting period.

Separate pots were planted with seashore paspalum sprigs. Plugs were harvested as

described above and separated into sprigs. The sprigs were planted (200 ml/pot) in pots

measuring 15 cm diameter by 17 cm deep containing USGA greens mix. A 2.5 cm layer

of the greens mix was then applied, covering the sprigs to allow for good growing

medium to stolon contact.









Saltwater applications were initiated immediately after sprigging (January 19 in 1st

study and March 3rd in repeated study) and were applied to both sprigged and established

seashore paspalum (transplanted 3 wk prior to initiation of saltwater treatment).

Saltwater treatments were applied twice per week (Mon. and Wed.), with one potable

water treatment per week (Fri.) applied to prevent salt accumulation on the growing

medium surface.

The five saltwater (NaC1) concentrations utilized for this study were as follows:

untreated (OX), 13 dS/m (1/4X), 27 dS/m (1/2X), 41 dS/m (3/4X), and 55 dS/m (1X).

The 55 dS/m (IX) concentration is equivalent to ocean water and the untreated (OX) is

potable water. Each irrigation event consisted of 200 ml of saltwater or potable water,

which was equivalent to 1 cm of water (irrigation) per event, totaling the standard 3 cm

of water (irrigation) recommended for seashore paspalum weekly (Duncan and Carrow,

2000). All pots were maintained at 2 cm using rechargeable grass shears. Chlorothalonil

[2,4,5,6-tetrachloroisophthalonitrile] and chlorpyrifos [0,0-diothyl 0-(3,5,6-trichloro-2-

pyridinyl) phosphorothioate] were applied preventively at 14.5 kg ai ha-1 and 1 kg ai ha-1,

respectively, to control fungal disease and insects (Anonymous 2004a, 2004b).

Visual quality ratings were taken at 4 wk and 8 wk after initiation of saltwater

applications with a range from 0 (dead turf) to 9 (green, healthy, ideal turf). The

experimental design was a randomized complete block design with four replications. The

sprigged and established seashore paspalum studies were evaluated separately. Data

were analyzed in PROC GLM using an ANOVA to test all possible interactions of

saltwater treatment, replication, and trial, and means were separated using least

significant difference (LSD) at the 5% probability level (SAS, 2004). Regression









analysis was utilized to show the response of both sprigged and established seashore

paspalum quality to saltwater concentration.

Results and Discussion

There were no interactions between trials, therefore the data were pooled. There

was an interaction between treatment and timing of visual evaluation. Therefore data are

presented separately for the 4 wk and 8 wk evaluations.

Newly Sprigged Seashore Paspalum

Quality of newly sprigged seashore paspalum was affected by saltwater treatments.

After 4 wk of treatment, quality ratings decreased as saltwater concentration increased.

The sprigs had a quality rating of 6.5 when irrigated with potable water, but decreased to

2.5 when irrigated with 27 dS/m saltwater (Table 2.1). At 55 dS/m, the seashore

paspalum sprigs were nearly dead 4 wk after initial treatment with quality rating of only

1.0 (Table 2.1). A similar trend was observed 8 wk after the initial saltwater treatments.

The sprigs treated with potable water were well established by 8 wk with a quality rating

of 7.5 (Table 2.1). Seashore paspalum quality declined to 2.0 at 27 dS/m and 0.5 at 55

dS/m (Figure 2.1 and Table 2.1). The regression model indicates the quality rating of

seashore paspalum will decrease below 6.5 when irrigated with saltwater < 13 dS/m 8 wk

after the initial saltwater treatments (Figure 2.1).

Alternative irrigation water with a salt concentration range between 27 dS/m to 55

dS/m will reduce the growth rate of even the most salt tolerant paspalum cultivar by 50%

if the salts are not replaced and consistently moved through the soil (Duncan and Carrow,

2000). Due to the lack of tolerance to salinity, newly sprigged seashore paspalum should

be irrigated with potable water during establishment to reduce stress and promote healthy

growth.









Established Seashore Paspalum

Once established, seashore paspalum exhibited excellent salinity tolerance.

Seashore paspalum quality ratings were acceptable (> 6.5) at 13 dS/m and 27 dS/m salt,

but declined to 6.0 and 4.5 at 41 dS/m and 55 dS/m, respectively 4 wk after initial

saltwater treatments (Table 2.1). Turfgrass quality increased over time with ratings of

8.0, 7.5, and 6.5 at 13 dS/m, 27 dS/m, and 41 dS/m, respectively 8 wk after saltwater

irrigation initiation (Table 2.1). Quality was below the 6.5 minimum acceptable level

only at 55 dS/m. The regression model indicates the quality rating of established

seashore paspalum will decrease to 6.5 at 33 dS/m 8 wk after the initial saltwater

treatment (Figure 2.1).

The largest reduction in quality was observed 4 wk after initiation of the saltwater

treatments. The increase in quality over time may have been due to the ability of

established seashore paspalum to physiologically adjust to the saline conditions for an

extended period of time. Growth rate measurements were not taken, but a reduced

growth rate was visually evident as saltwater concentration increased.

Newly sprigged seashore paspalum is sensitive to saltwater concentrations > 13

dS/m. Growth rate is reduced and the time of establishment increases as saltwater

concentration increases. Saltwater concentration > 27 dS/m will cause desiccation and

eventual death of the sprigs. Established seashore paspalum exhibited a high tolerance to

saltwater irrigation. Although seashore paspalum did not maintain acceptable quality

when irrigated with pure ocean water (55 dS/m), it is able to tolerate irrigation with

salinity levels up to 41 dS/m. This characteristic will allow turf managers, located near

the coast or those who have water restrictions, to use alternative water sources (effluent

and brackish) for irrigation with salt concentrations up to 41 dS/m.






27


Table 2-1 Saltwater effect on sprigged and established seashore paspalum.
Seashore Paspalum quality rating
Established Sprigged
Salt Concentrationb 4 wksc 8 wksc 4 wksc 8 wksc
0 9.0 9.0 6.5 7.5
13 7.5 8.0 4.0 5.0
27 6.5 7.5 2.5 2.0
41 6.0 6.5 1.5 1.0
55 4.5 4.0 1.0 0.5
LSD (0.05) 2.0 2.0 2.5 3.0
aQuality ratings range from 0 (dead turf) to 9 (healthy turf).
bSalt Concentrations in decisemens per meter (dS/m).
cWeeks of exposure to saltwater concentrations.











8 Established paspalum
V (y =-0.08x + 9.27)
r2=0.92

N 6 -

Newly sprigged paspalum
\ (y =-0.13x + 6.7)
4 r2=0.91
-N


2 V


Established seashore paspalum V
v Sprigged seashore paspalum '
0 1-1 1 1 1 --
0 10 20 30 40 50 60

Salt Concentration (dS/m)

Figure 2-1 Effect of saltwater concentration on seashore paspalum quality ratings 8 wk
after initial application of saltwater (data pooled over trials).














CHAPTER 3
SUSCEPTIBILITY OF NINE TURFGRASS WEED SPECIES TO FIVE SALTWATER
CONCENTRATIONS

Introduction

Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial warm season

turfgrass that is native to tropical and subtropical regions of the world (Duncan and

Carrow, 2000). It has existed for years, but has only been used commercially for the past

few decades. Seashore paspalum spreads by rhizomes and stolons that root at the nodes

and forms a deep fibrous root system (Duble, 2000). It is generally propagated

vegetatively, because seed produced have low viability (Trenholm and Unruh, 2002),

although seeded varieties are under development. Seashore paspalum is a desirable

turfgrass that has a high salt tolerance (Duncan and Carrow, 2000).

Weeds compete with turfgrass for light, nutrients, water, and physical space

(Florkowski, 2002) and weed management is a major cost for turfgrass managers. On

golf courses in the Southeast, the average expenditures for herbicides in 1998 were

$11,690 (Florkowski, 2002).

Some of the more common weeds in turfgrass include dollarweed (Hydrocotyle

spp.), Florida pusley (Richardia scabra L.), Virginia buttonweed (Diodia virginiana L.),

goosegrass (Eleusine indica [L.] Gaertn.), southern crabgrass (Digitaria ciliaris [Retz.]

Koel.), common bermudagrass (Cynodon dactalon [L.] Pers.), tropical signalgrass

(Urochloa subquadripara [Trin.] R. Webster), torpedograss (Panicum repens L.), and

purple nutsedge (Cyperus rotundus L.).









Dollarweed is a perennial broadleaf that reproduces by seed, rhizomes, and tubers.

The leaves are long stalked with the petiole attached to the center of the leaf that

resembles an umbrella. Dollarweed is most commonly found in areas with excessive

moisture (Murphy et al., 1996).

Florida pusley is a summer annual broadleaf that reproduces by seed. The

branched stem is hairy with thickened leaves that have an opposite arrangement. The

white flowers are bunched at the end of the branches (Murphy et al., 1996).

Virginia Buttonweed is a perennial broadleaf that reproduces by seed, roots, and

stem fragments. The stem is branched and hairy with an opposite leaf arrangement. The

flower is white with four lobes at each leaf axil (Murphy et al., 1996).

Goosegrass is a summer annual grass that reproduces by seed. The crown is

generally white or silver in color and is usually found in areas with compacted soils. The

leaves are smooth on both sides with a short-toothed membranous ligule (Murphy et al.,

1996).

Southern crabgrass is a summer annual grass that reproduces by seed. Stems are

branched and root at the nodes. The leaves are usually hairy on both sides and have a

toothed membranous ligule (Murphy et al., 1996).

Common bermudagrass is a perennial grass that reproduces by stolons, rhizomes,

and seed (Duble, 2004). The stolons and rhizomes root at the nodes to form a deep

fiberous perennial root system (Duble, 2004). Seeded varieties are currently being

developed and tested (Evers and Davidson, 2004). The collar of the leaves have a fringe

of short, white hairs (NewCROP, 1999).









Tropical signalgrass is a summer annual grass that reproduces by seed. The stem is

branched with a blanket-like growth pattern. The leaves are glossy with a coarse texture

(Busey 2000).

Torpedograss is a very persistent perennial grass that reproduces vegetatively or by

soil transfer (Busey, 2002). The rhizome system is very robust with sharply pointed tips.

The stems are stiff and erect with leaves that are folded or flat (Murphy, 1996).

Purple nutsedge is a perennial sedge that reproduces primarily by oblong tubers

that are covered with hairs. The leaves taper abruptly to a point unlike yellow nutsedge

that tapers gradually to a point. The seed head has a purplish color and is formed on a

triangular stem (Murphy et al., 1996).

These weeds are a few of the most common and troublesome weeds found in

turfgrass in the Southeastern United States (Webster, 2000). Control of these weeds can

be very difficult and expensive. Weeds can be controlled using cultural practices to

produce a healthy, competitive turfgrass, in combination with herbicides.

Aerification and verticutting are common cultural practices on golf courses to

control weeds and relieve turf stresses such as compaction and thatch. Aerification

consists of pulling soil core plugs 0.63 cm to 1.9 cm (0.25 to 0.75 in.) in diameter,

ranging in depth of 5 to 10 cm (2 to 4 in.) (Unruh and Elliott, 1999). This process

relieves soil compaction, improves surface drainage and water penetration, and reduces

thatch (Unruh and Elliot, 1999).

Vertical mowing consists of vertical knives spaced close together on a horizontal

shaft that slice into the turf (Unruh, and Elliott, 1999). This practice removes the organic

matter (thatch) layer, allowing the turf to grow horizontally and allows for a smooth









putting surface. When maintaining seashore paspalum greens, deep verticutting should

be avoided (Duncan and Carrow, 2002). Light verticutting enhances stolon-rhizome-

shoot growth and allows topdressing sand to integrate into the thatch layer, producing a

more firm, smooth surface that is less susceptible to scalping (Duncan and Carrow, 2000

and 2002). A good quality topdressing sand should integrate easily into the surface at

light rates without verticutting (Duncan and Carrow, 2002).

Mowing is a very important cultural practice on golf courses. Improper mowing

can weaken the turf, which reduces the density and quality (Unruh and Elliott, 1999),

allowing for weed invasion. Seashore paspalum does not tolerate scalping as well as

bermudagrass or zoysiagrass and may take 4 to 6 wk to fully recover (Duncan and

Carrow, 2002). When lowering the mowing height on seashore paspalum gradual

increments of 0.05 to 0.08 cm (0.02 to 0.03 in.) over 2 to 3 d is best (Duncan and Carrow

2002). When the turf is mowed properly, very little stress is put on the plant, allowing it

to recover very quickly. Frequent mowing increases shoot growth, producing a dense

canopy that makes it more difficult for weeds to invade (Unruh and Elliott, 1999).

Finally, proper irrigation can be used to reduce weed pressure. Maintaining proper

soil moisture levels is important for producing a healthy turf. Seashore paspalum is very

responsive to irrigation duration and frequency and a shallow root system will result from

frequent irrigation events of short durations (Duncan and Carrow, 2002). This also

causes the turf to be more succulent, less drought tolerant, and more susceptible to

scalping. Watering schedules should consist of long durations during applications with

long intervals (1.25 to 2.5 cm of water every 4 to 7 d on a sand-based green) between

applications to encourage the roots to grow deeper into the soil profile (Duncan, 2000;









Duncan and Carrow, 2002). Various grass types require different moisture levels and

weed species are also dependent on moisture levels. For instance, dollarweed

populations can be reduced in St. Augustinegrass turf by reducing irrigation levels

(Busey, 2001).

Seashore paspalum exhibits exceptional salt tolerance, but is susceptible to injury

from many postemergence herbicides (Wiecko, 2003). Dithiopyr, halosulfuron,

oxadiazon, and prodiamine are the only herbicides labeled for use on seashore paspalum

(Unruh et al., 2005). Dithiopyr, oxadiazon, and prodiamine are herbicides commonly

used preemergence for annual grass control. Halosulfuron is commonly used

postemergence for sedge control.

Seashore paspalum's high level of salt tolerance may allow the use of saltwater for

weed control in place of injurious postemergence herbicides (Wiecko, 2003). Couillard

and Wiecko (1998) evaluated saltwater for control/tolerance on crabgrass, and mimosa.

They treated these species with ocean water at three concentrations: pure ocean water

(54 dS/m), 2/3 ocean water (37 dS/m), and 1/3 ocean water (19 dS/m). The weeds were

watered twice daily for two different periods: 3 d or 6 d. Following the saltwater stress

periods, potable water irrigation was applied to evaluate recovery potential over a period

of 32 d after the salt-stress treatments began. Mimosa only recovered from the 1/3x

ocean water treatment subjected to 3 d salt stress. Complete crabgrass control was only

achieved with pure ocean water under 6 d salt stress.

Similar studies were conducted by Wiecko in 1999 and 2000 with the additional

species goosegrass, alyceclover (Alysicarpus vaginalis (L.) DC.), and yellow nutsedge

(Cyperus esculentus L.). Alyceclover injury was similar to mimosa injury, and









goosegrass injury was similar to crabgrass injury. Yellow nutsedge was the most tolerant

to salt stress, fully recovering from all treatments.

Based on these studies, ocean water can be used as an alternative to herbicides to

control weeds in certain turfgrasses (Couillard and Wiecko, 1998). Most annual grass

and broadleaf weed species cannot tolerate continuous irrigation with saltwater or

saltwater blends (wastewater) (Duncan and Carrow, 2000).

Few golf courses have the capabilities to use saltwater for irrigation, but it is

becoming more common in coastal environments (Duncan and Carrow, 2000). Weeds

are a common problem when trying to maintain a high quality turf. Since many golf

courses border environmentally sensitive areas chemical control of weeds is not always

feasible. The susceptibility of many turfgrass weeds to saltwater has not been

determined. The objective of this study was to determine the potential of using saltwater

for control of selected common turfgrass weeds.

Methods and Materials

Greenhouse Studies

Two greenhouse studies were conducted at the University of Florida, West Florida

Research and Education Center (WFREC) near Jay during 2003 and 2004. Nine turfgrass

weeds (torpedograss, dollarweed, Virginia buttonweed, large crabgrass, common

bermudagrass, purple nutsedge, goosegrass, Florida pusley, and tropical signalgrass)

were evaluated for saltwater susceptibility.

Weeds listed in Tables 3.1, 3.2, and 3.3 were transplanted as mature plants from the

field, with the exception of crabgrass and tropical signalgrass, which were established

from seed. The weeds were planted in 15 cm in diameter by 16.5 cm deep (3,000 cm3

volume) pots that were filled with a United States Golf Association (USGA, 1993) greens









mix (80% sand and 20% sphagnum peat moss). The weeds were placed in a greenhouse

receiving full sun maintained at a temperature range of 270 to 320 C. The transplanted

weeds were irrigated with freshwater for 3 wk to allow for rooting and recovery from

transplanting. The seeded weeds were allowed to establish with potable water irrigation

for 5 wk. Plants were gradually thinned to a final density of 3 plants per pot.

Saltwater treatments were initiated (July 30 in 2003 and August 2 in 2004) after

establishment and continued for 8 wk in 2003 and 4 wk in 2004. Saltwater treatments

were applied twice per wk (Mon. and Wed.), with one potable water treatment per wk

(Fri.) applied to prevent salt accumulation on the growing medium surface. The saltwater

(Na+C1) concentrations were as follows: untreated (OX), 13 dS/m (1/4X), 27 dS/m

(1/2X), 41 dS/m (3/4X), and 55 dS/m (IX). The 55 dS/m (IX) concentration is

equivalent to ocean water and the untreated (OX) is potable water. Each irrigation event

consisted of 200 ml per pot of saltwater or potable water equivalent to 1 cm of water

(irrigation) per event totaling the standard 3 cm of water (irrigation) weekly for seashore

paspalum (Duncan and Carrow, 2000). The aerial reproductive structures of the annual

weeds were removed weekly to prevent the weeds from completing their life cycle.

Weed control was visually evaluated at 8 wk in 2003 and 4 wk in 2004 after initial

saltwater exposure using a scale of 0 (no control) to 100 (complete control). The

experimental design was a randomized complete block with four replications. Data were

analyzed in PROC GLM using an ANOVA to test all possible interactions of saltwater

treatment, replication, and year, and means were separated using least significant

difference (LSD) at the 5% probability level (SAS, 2004). Regression analysis was

utilized to model the response of weed control to saltwater concentration.









Field Studies

Field studies were also conducted in the summer of 2004 at the University of

Florida, WFREC near Jay, Florida to support results found in the greenhouse

experiments. Southern crabgrass and cocks-comb kyllinga (Kyllinga squamulata Thonn.

ex. Vahl.) control with NaCl were tested in separate studies in a 2 yr old stand of 'Sea

Isle 1' seashore paspalum. Individual plot size was 1.5 m by 1.5 m. Crabgrass was

seeded at a rate of 480 kg ha-1 in early May and allowed to establish until treatments were

initiated in early June. An existing uniform area of cocks-comb kyllinga infested

seashore paspalum was selected in a separate area and treatments were initiated in early

July.

Saltwater treatments were applied twice per wk (Tues. and Thurs.). Plots were

treated for 4 wk with either a liquid solution of NaCl at 13 dS/m (1/4 ocean water) or 27

dS/m (1/2 ocean water) concentration of salt or an equivalent amount of NaCl applied to

each plot as granules. Granular NaCl applications were watered in with 30 L of water per

plot. Potable water applications were dependent on the daily afternoon rainfall events

that normally occur during the summer in the Southeast coastal region of the United

States (Appendix A).

Visual evaluations of percent turfgrass injury on a scale of 0 (no injury) to 100

(dead turf) or percent weed control on a scale of 0 (no control) to 100 (complete control)

were taken 4 wk after initial treatment. The experimental design was a randomized

complete block with four replications. Data were analyzed in PROC GLM using an

ANOVA to test all possible interactions and means were separated using least significant

difference (LSD) at the 5% probability level (SAS, 2004).









Results and Discussion

Greenhouse Studies

There were no interactions between studies or between 4 wk and 8 wk evaluations,

therefore weed control data were pooled over studies and evaluations.

Broadleaf species

Florida pusley and Virginia buttonweed were the most sensitive broadleaf species

to saltwater treatments. All saltwater concentrations killed Florida pusley and all but the

lowest concentration controlled Virginia buttonweed (Table 3.1). The data for Florida

pusley and Virginia buttonweed were fit to exponential rise to max regression models

with r2 values of 1.00 and 0.96, respectively (Figure 3.1).

Dollarweed was the least sensitive broadleaf species with complete control

achieved only at 55 dS/m salt concentration (Table 3.1). Dollarweed control increased as

salt concentration of the irrigation water increased fitting a linear regression model (r2

0.99) (Figure 3.1).

The sensitivity of Florida pusley and Virginia buttonweed to saltwater irrigation

was expected because broadleaf and legume species are generally more sensitive to

salinity than grassy species (Wiecko, 2003; Greub et al., 1985). The tolerance of

dollarweed to high concentrations of saltwater irrigation could be due to extensive

rhizome and tuber systems allowing the plant to regrow after each potable water soil

flushing treatment.

Grass and sedge species

Goosegrass and southern crabgrass control with saltwater was similar. At 13 dS/m,

goosegrass and southern crabgrass control was 39 and 25%, respectively, increasing to 53

and 51% at 27 dS/m, respectively, and to 74 and 81%, respectively, at 41 dS/m (Table









3.2). Complete mortality was observed at 55 dS/m for both species (Table 3.2). Control

of goosegrass and southern crabgrass corresponded with a linear regression model with r2

values of 0.97 and 0.99, respectively (Figure 4.2). Wiecko (2003) exposed goosegrass

and crabgrass to saltwater twice daily for 3 and 6 d durations and observed similar

results. Both weed species were controlled > 90% with a saltwater concentration of 55

dS/m, while 18 dS/m saltwater concentration provided little control (Wiecko, 2003).

Tropical signalgrass control with saltwater was similar to that observed with

goosegrass and southern crabgrass (Table 3.3 vs. Table 3.2). Control at 13 dS/m was

33%, increased to 73% at 41 dS/m and 100% control at 55 dS/m. Tropical signalgrass

control corresponded to a linear regression model (r2 = 0.98) as saltwater concentration

increased resulting in complete mortality at 55 dS/m (Table 3.3 and Figure 3.3).

Bermudagrass tolerance to saltwater irrigation was similar to seashore paspalum

tolerance (Chapter 2), and injury symptoms were mostly stunting of the bermudagrass

with some yellowing of the leaf tissue at the highest saltwater concentrations.

Bermudagrass injury at saltwater concentrations of 13 dS/m and 27 dS/m was only 9 and

24%, respectively (Table 3.3). However, injury increased to 43 and 66% as saltwater

concentrations increased to 41 dS/m and 55 dS/m, respectively (Table 3.3). This injury

corresponded to a linear regression model with an r2 value of 0.98 (Figure 4.3). Similar

results were found where bermudagrass quality was not compromised with saltwater

concentrations < 20 dS/m, but quality was reduced at 40 dS/m 4 WAT (Munshaw, 2004).

Torpedograss was tolerant to all concentrations of saltwater irrigation showing a

reduction in growth as the only injury symptom. Less than 20% control was observed at

13 dS/m, 27 dS/m, and 41 dS/m, while control at 55 dS/m was only 35% (Table 3.3).









The data was consistent to a linear regression model with an r2 value of 0.96 (Figure 3.3).

Torpedograss is a rhizomatous perennial that is found along shorelines, canals, and

poorly drained soils and can form dense floating mats in water up to 6 ft deep (USDA,

2003). The tolerance shown by torpedograss in this study could be attributed to the

growth habit and ability for the plant to adapt to stressful environments allowing the plant

to survive long periods of time under salinity stress (USDA, 2003). Further testing of

torpedograss is necessary to determine the long-term effects of saline irrigation.

Purple nutsedge control was minimal at 13 dS/m (15% control). As saltwater

concentration increased to 27 dS/m, control increased to 41% and 81% control at 55

dS/m (Table 3.3). Control was modeled using linear regression with an r2 value of 0.99

(Figure 3.3). Purple nutsedge is a difficult weed to control and few herbicides have been

effective in the past (Grey et al., 2003). Imazapic will provide > 90% control of purple

nutsedge and halosulfuron combined with the right adjurvant will provide 100% control

(McDaniel, 2001). Other herbicides, such as sulfentrazone, diclosulam, and flumioxazin,

will provide < 70% control (Grey et al., 2003). Irrigation with a salt concentration of 41

dS/m will provide up to 60% control which is equivalent to some herbicides.

Seashore paspalum will maintain health and quality with saline irrigation up to 41

dS/m (Chapter 2). These studies indicate saline irrigation could be used as an alternative

to herbicides for control of specific weeds. Successful control of Florida pusley was

accomplished at 13 dS/m and Virginia buttonweed at 27 dS/m saltwater. Goosegrass,

southern crabgrass, and tropical signalgrass were controlled at 41 dS/m. Saline irrigation

as a single approach will control these weeds while maintaining a quality seashore

paspalum turf. Additional measures, such as cultural practices or integrating reduced-rate









herbicides, need to be utilized to control dollarweed, common bermudagrass,

torpedograss, and purple nutsedge at saltwater concentrations up to 41 dS/m.

Field Studies

In the field study, southern crabgrass was controlled only 35 to 65% at 13 dS/m but

control increased to greater than 85% at 27 dS/m when salt was either applied as a

solution or as a granular (Table 3.4). At 13 dS/m, cocks-comb kyllinga control was no

more than 60% using either granular or solution, but control improved to greater than

70% at 27 dS/m with either application method (Table 3.4).

In both studies, the granular application method provided better control of southern

crabgrass and cocks-comb kyllinga compared to salt applied in solution. The reduced

control from the solution may be due to salt leaching through the root zone more quickly

than the granular applied salt.

There were no interactions between studies for seashore paspalum quality.

Therefore, turf quality data were pooled over both studies. Seashore paspalum was

injured < 20% for all treatments (Table 3.5). Salt applied as a granular increased turf

injury by 5% over that observed with the solution at both concentrations due to localized

foliar burn (Table 3.5). An uneven application of the granular salt caused the leaf tissue

to burn in areas where the salt was concentrated on the surface and not completely moved

into the root zone.

Results from these studies indicate that saltwater can provide effective control for

weed species such as southern crabgrass, goosegrass, tropical signalgrass, Florida pusley,

and Virginia buttonweed but not dollarweed, common bermudagrass, torpedograss, or

purple nutsedge. Inland areas that do not have access to saline water may still be able to

utilize the ability of seashore paspalum to tolerate salinity by applying specific rates of






41


granular salt to control some weed species. Precautions must be taken to effectively

move the granular salt into the root zone by means of potable water irrigation. Further

research should be conducted to link specific concentrations with the control of specific

weed species.










Table 3-1. Control of selected broadleaf weeds with saltwater in the greenhouse pooled
data over years and evaluations.
Weed Control a
Salt Concentration HYDSPb RICSCb DIOVIb
---------------------- % ----------------------
13 dS/m 26 100 49
27 dS/m 52 100 100
41 dS/m 66 100 100
55 dS/m 100 100 100
LSD (0.05) 18 0 20
aPercent control compared to untreated check.
bHYDSP=dollarweed, RICSC=Florida pusley, DIOVI=Virginia buttonweed


Table 3-2. Control of selected annual grass weeds with saltwater in the greenhouse
pooled data over years and evaluations.
Weed Control a
Salt Concentration ELEINb DIGSAb
--------------- % ---------------
13 dS/m 39 25
27 dS/m 53 51
41 dS/m 74 81
55 dS/m 96 100
LSD (0.05) 21 19
aPercent control compared to untreated check.
bELEIN=goosegrass, DIGSA=large crabgrass


Table 3-3. Control of selected perennial grass and sedge weeds with saltwater in the
greenhouse pooled data over years and evaluations.
Weed Control a
UROSU
Salt Concentration b CYNDAb PANREb CYPROb
--------------------------- % ---------------------------
13 dS/m 33 9 4 15
27 dS/m 60 24 16 41
41 dS/m 73 43 19 60
55 dS/m 100 66 35 81
LSD (0.05) 6 9 14 14
aPercent control compared to untreated check.
bUROSU=tropical signalgrass, CYNDA=common bermudagrass,
PANRE=torpedograss, CYPRO=purple nutsedge









Table 3-4. Control of southern crabgrass and cocks-comb kyllinga with two salt
concentrations applied as a solution or granular in the field.


Treatment


DIGSAb


------- % Control -------
Freshwater 0 0
13 Solution 35 45
13 Granular 65 60
27 Solution 85 70
27 Granular 90 80
LSD (0.05) 7 12
a Concentrations are decisemens per meter (dS/m).
bDIGSA=southern crabgrass, KYLZZ=cocks-comb kyllinga


KYLZZb


Table 3-5. Seashore paspalum quality as affected by saltwater in the field.
Treatment Seashore paspalum
% Injury
Freshwater 0
13 Solution 5
13 Granular 15
27 Solution 10
27 Granular 20
LSD (0.05) 4
aConcentrations are decisemens per meter (dS/m).






44




100 - --- ---

I y 100 (1 e- )
r2 = 1.00
08006x
80 y 1.9.34(1-e- ) /
2
r2 0.96
I ./

I / 2
SY60- y=1.33+(1.74x)
0 / r = 0.99

40 -
/, Dollarweed Observed
-/ FL Pusley Observed
20 VA Buttonweed Observed
S- FL Pusley Predicted Control
S/ VA Buttonweed Predicted Control
S------- Dollarweed Predicted Control
0 II1, ,
0 10 20 30 40 50 60

Salt Concentration

Figure 3-1 Saltwater concentration effect on broadleaf weed control pooled over years
and evaluations. Dollarweed data were fit to a linear regression model y = a +
(mx) while Florida pusley and Virginia buttonweed data were fit to an
exponential rise to max regression model y = a*(1 e-b*x) to predict control at
a specific concentration.










* Goosegrass Observed
A Crabgrass Observed
- Goosegrass Predicted Control
Crabgrass Predicted Control


y=7
2
r =



/

/
7-


1.79 + (1.64x)
0.97


* 7



y =0.99 + (1.86x)
r2 = 0.99


Salt Concentration


Figure 3-2 Saltwater concentration effect on annual grass control pooled over years and
evaluation. Data were fit to a linear regression model y = a + (mx) to predict
control at a specific concentration.


100 -



80 -


60 -


40 -



20 -


,7


..7
.J *
rj


lxl










A Bermudagrass Observed
100 Torpedograss Observed /
Tropical Signalgrass Observed /
Purple Nutsedge Observed
80 Bermudagrass Predicted Control
Torpedograss Predicted Control /
------ Tropical Signalgrass Predicted Control
6o Purple Nutsedge Predicte. Control
60 .
/ y= -.30+(1.49x /
/ =0.99

40 y =5.78+(1.74x)//
r2= 0.98 y = -4.06+(1.19x)
S/ r = 0.98

20 -/
y =-1.90+(0.62x)
Sr 0.96
0 0
0 10 20 30 40 50 60

Salt Concentration

Figure 3-3 Saltwater concentration effect on perennial grass and sedge control pooled
over years and evaluation. Data were fit to a linear regression model y = a +
(mx) to predict control at a specific concentration.














CHAPTER 4
THE TOLERANCE OF SEASHORE PASPALUM TO HERBICIDES WHEN
IRRIGATED WITH SALTWATER

Introduction

Seashore paspalum (Paspalum vaginatum O. Swartz) is a perennial warm season

turfgrass that is native to tropical and subtropical regions of the world (Duncan and

Carrow, 2000). Although seashore paspalum has existed for many years, it has only been

used commercially for the past few decades. Seashore paspalum spreads by rhizomes

and stolons that root at the nodes forming a deep fibrous root system (Duble, 2000). It is

generally propagated vegetatively from sod or sprigs because seed production has not

been reliable (Duncan and Carrow, 2000), though one seeded cultivar has been developed

(Hughes, 2005).

Sodium chloride (NaC1) is the predominant component contributing to soil salinity

(Jungklang, 2003). Saline levels in soils are becoming increasingly problematic due to

the use of alternative water (effluent or brackish) for irrigation.

Salinity tolerance is a distinguishing physiological characteristic of seashore

paspalum. There are three mechanisms plants use to tolerate salinity: selective of ion

uptake by the roots, accumulation of salt in specific vacuoles within plant cells then

retranslocated back to the soil or excreted by salt glands on the leaf surface, and osmotic

adjustment (Colmer, 2000; Rose-Fricker and Wipff, 2001; Marcum, 2004). Seashore

paspalum has the ability to efficiently select ions absorbed by the roots, and it is also able

to secrete salt through salt glands on the leaf surface (Marcum, 1999).









Salt injury to plants is exhibited as reduced growth, burning of leaf tips, and wilting

(Colmer, 2000). Alternative, non-potable water sources may increase the salinity level of

the soil over time and must be managed properly to establish and maintain a high quality

turf. Studies have been conducted testing the tolerance of seashore paspalum to various

concentrations of saltwater. Seashore paspalum exhibits exceptional salt tolerance, but is

highly susceptible to injury from postemergence herbicides (Wiecko, 2003).

The high level of salt tolerance may allow saltwater to be used as an alternative to

herbicides or in combination with reduced-rate herbicides to control weeds in certain

turfgrasses (Couillard and Wiecko, 1998). Few golf courses have the capabilities to use

saltwater for irrigation, but it is becoming more common in coastal environments

(Duncan and Carrow, 2000).

Herbicides are regularly used for weed control on golf courses. Some important

considerations when selecting an herbicide are effectiveness, turfgrass tolerance, speed of

control, toxicity, and cost (Unruh and Elliott, 1999). There is no single herbicide that

will control all weeds in a desired turf stand, so proper identification is essential (Unruh

and Brecke, 1998).

Seashore paspalum is sensitive to many herbicides commonly used on other

turfgrasses (Trenholm and Unruh, 2002, 2003; and CTAHR, 1998). Herbicides that are

noninjurous to seashore paspalum are bensulide, pronamide, benefin, DCPA,

pendimethalin, ethofumesate, quinclorac, MCPP + 2,4-D + dicamba, dithiopyr, 2,4-D +

dicamba + dicloprop, dicamba, halosulfuron, mecoprop, and bentazon (Duncan and

Carrow, 2000). However, dithiopyr, halosulfuron, oxadiazon, and prodiamine are the

only herbicides labeled for use on seashore paspalum (Unruh et al., 2005). These









herbicides could possibly be used at reduced rates in conjunction with saltwater irrigation

to control weeds in seashore paspalum (Duncan and Carrow, 2000).

In 1997, Johnson and Duncan tested the recommended rates and 3 times the

recommended rates of diclofop, quinclorac, dicamba, imazaquin, halosulfuron, and 2,4-D

+ mecoprop + dicamba on four seashore paspalum accessions (AP 10, HI 25, PI 28960,

and K-7).

Seashore paspalum accessions varied in their response to the herbicides evaluated.

Quinclorac and halosulfuron were the only herbicides that did not reduce the quality of

any accession at the recommended rates. When quinclorac and halosulfuron rates

increased, quality of HI 25 and K-7 was reduced. All accessions recovered completely

even from the high rates within 4 to 8 wk after initial treatment.

Dicamba had no effect on any of the accessions when applied at the labeled rate.

Quality of the K-7 accession, however, was affected by the increased rate of dicamba.

Diclofop, imazaquin, and 2,4-D + mecoprop + dicamba reduced the quality of all

paspalum accessions regardless of application rate. Full recovery from diclofop and

imazaquin required 4 to 8 wk. Recovery from the labeled rates of 2,4-D + mecoprop +

dicamba took 4 to 8 wk for all accessions, and none of the accessions recovered from the

high rate by 8 wk. The overall conclusion from this study was that quinclorac, dicamba,

and halosulfuron were safe on all accessions, diclofop and imaziquin were marginal, and

2,4-D + mecoprop + dicamba were considered injurious.

A study was conducted by Unruh et al. (2005) testing the tolerance of 'Salam'

seashore paspalum to postemergence herbicides for control of grass (clethodim,

ethofumesate, metsulfuron, sethoxydim, and quinclorac), broadleaf (clopyralid, dicamba,









and 2,4-D + mecoprop + dicamba), and sedge (bentazon, halosulfuron, imazapic,

imazaquin, and trifloxysulfuron-sodium) species. Metsulfuron, quinclorac, clopyralid,

dicamba, 2,4-D + mecoprop + dicamba, bentazon, halosulfuron, and imazaquin caused

less than 15% injury at the recommended rates and are considered safe for seashore

paspalum. Clethodim, sethoxydim, ethofumesate, imazapic, and trifloxysulfuron-sodium

caused greater than the acceptable standard of 20% injury and are considered not safe for

application to seashore paspalum.

Growth of many weed species is suppressed when irrigated with saltwater while

growth of seashore paspalum is not affected (Duncan and Carrow, 2000). Tolerance of

seashore paspalum to preemergence and postemergence herbicides has not been

determined when irrigated with saltwater and the turfgrass is potentially more sensitive to

injury as salt-stress increases. The objective of this study was to determine the tolerance

of seashore paspalum to commonly used turfgrass herbicides when irrigated with

multiple concentrations of saltwater.

Methods and Materials

Two greenhouse studies were conducted at the University of Florida, West Florida

Research and Education Center (WFREC) near Jay in the summer of 2004. Strips of sod

were cut with a sod cutter from a two year old stand of 'Sea Isle 1' seashore paspalum.

Plugs were cut from the sod strips using a golf cup cutter 15 cm in diameter. The native

soil was washed from the plugs and then plugs were transplanted into 15 cm in diameter

by 17 cm deep (3000 cm3 volume) plastic pots containing a growing medium of USGA

greens mix (80% sand and 20% organic matter). The intact seashore paspalum plugs

were planted level with the rim of the pots.









After transplanting, the pots were placed in a greenhouse receiving full sun and

were maintained at a temperature range of 270 to 320 C. A slow release 19-8-15 fertilizer

was applied at a rate of 24.5 kg N ha-1 1 wk after planting. The plugs were irrigated with

potable water during a 3 wk rooting period.

A randomized complete block arranged in a split-plot experimental design with

three replications was used. This was because the main plot was blocked while the sub-

plot and replications were random in each block. Main plot factor consisted of five

saltwater concentrations: 1) potable water (Ox), 2) 13 dS/m (1/4x), 3) 27 dS/m (1/2x), 4)

41 dS/m (3/4x), and 5) 55 dS/m (lx). The 55 dS/m concentration is equivalent to ocean

water. Sub-plot factor was 18 herbicide treatments with an untreated check and are listed

in Table 4.1.

Saltwater treatments were initiated July 17, 2004 for the initial study and July 22,

2004 for repeated study after establishment and continued for the duration of the study.

Saltwater treatments were applied twice per week (Mon. and Wed.), with one potable

water treatment per week (Fri.) applied to prevent salt accumulation on the growing

medium surface. Each irrigation event consisted of 200 ml of saltwater or potable water

equivalent to 1 cm of water (irrigation) per event totaling the standard 3 cm of water

(irrigation) recommended for seashore paspalum weekly (Duncan and Carrow, 2004).

All pots were maintained at 2 cm (0.75 in) using rechargeable grass shears.

Chlorothalonil [2,4,5,6-tetrachloroisophthalonitrile] and chlorpyrifos [0,0-diothyl 0-

(3,5,6-trichloro-2-pyridinyl) phosphorothioate] were applied preventively at 14.5 kg ai

ha-1 and 1 kg ai ha-1, respectively, to control fungal disease and insects (Anonymous









2004a, 2004b). After 2 wk of saltwater irrigation, herbicide treatments were applied at

the recommended labeled rate to each saltwater concentration (Table 4.1).

Data collected included visual quality ratings 4 wk after herbicide application on a

scale from 0 (dead turf) to 9 (healthy turf). Data were subjected to ANOVA using PROC

MIXED to test all possible fixed effects and interactions of saltwater concentration,

herbicide treatment, and trial (SAS, 2004). PROC MIXED was used to allow replication

to be tested as a random effect. Means were separated using least significant difference

(LSD) at the 5% probability level.

Results and Discussion

There was an interaction between trials, so data are presented separately. In both

trials, there was an interaction between saltwater concentrations and herbicide treatments.

In general, the quality of seashore paspalum decreased as saltwater concentration

increased regardless of herbicide application.

Prodiamine, pendimethalin, oxadiazon, metolachlor, and dithiopyr are herbicides

commonly used preemergence for summer annual grass control. In both trials, the

herbicides alone without saltwater irrigation caused some reduction in turfgrass quality

but ratings were 7.3 or higher, well above the minimum acceptable level of 6.5 (Table

4.2). Quality declined with increasing saltwater concentrations but reduction was no

greater than for saltwater alone without herbicide (Table 4.2). These results indicate that

salt stress did not impact seashore paspalum tolerance for prodiamine, pendimethalin,

oxadiazon, metolachlor, or dithiopyr.

Fenarimol is labeled as a fungicide, but like pronamide, is also an effective

preemergence for controlling winter annual grasses. Pronamide did not affect seashore

paspalum quality with potable water and fenarimol only reduced quality in trial 1 to 8.3,









well above the minimum of 6.5. As with the preemergence treatments for summer

grasses, there was a reduction in quality with increasing salt concentration, but no greater

than for salt alone except for salt of 55 dS/m. At the highest salt concentration, quality

declined from 6.7 for the untreated to 5.3 with both fenarimol and pronamide (Table 4.2).

As with the summer annual grass control herbicides, seashore paspalum tolerance to

pronamide or fenarimol was not affected by saltwater irrigation.

Isoxaben and atrazine are applied preemergence to control many broadleaf weed

species. Quality was lower with the use of isoxaben in some instances compared to the

herbicide untreated in both trials, however, there was no consistent effect of saltwater on

quality of turf treated with isoxaben (Table 4.2).

The application of atrazine reduced the quality of seashore paspalum compared to

the herbicide untreated at all saltwater concentrations in both trials. Atrazine reduced

quality in both trials to unacceptable levels (5 or less). There was some indication that

quality improved with saltwater treatment in trial 2 (Table 4.2) suggesting that the

saltwater may be interfering with atrazine activity and that the efficacy of atrazine may

have been slightly reduced when saltwater irrigation is applied.

For annual and perennial grasses, quinclorac, metsulfuron, and metribuzin are

herbicides often used as postemergence control. Quality was not different from the

herbicide untreated when quinclorac or metsulfuron was applied in either trial 1 or trial 2

at salt concentrations of 27 dS/m or less (Table 4.3). Turf quality with both herbicides

declined with increasing saltwater concentration, however the decline was similar to the

saltwater alone treatment. Metribuzin reduced turf quality to < 5 regardless of saltwater

treatment in both trial 1 and 2 (Table 4.3). These results indicate that seashore paspalum









remains tolerant to quinclorac and metsulfuron regardless of salt concentration while

metribuzin is not tolerated, even when irrigated with potable water.

Clopyralid, bromoxynil, bentazon, and 2,4-D + dicamba + mecoprop applied

postemergence will control many broadleaf weed species. Clopyralid did not reduce turf

quality when using potable irrigation water. Quality did decline as saltwater

concentration increased, but turf quality was not different from the herbicide untreated in

either trial (Table 4.3). Bentazon caused a reduction in quality without saltwater (0 ppm)

in trial 1 and at 13 dS/m in trial 2 but quality remained 7.7 or greater (Table 4.3).

Bentazon caused turf quality to decline more than the herbicide untreated as salt

concentration increased > 41 dS/m in trial 1 and > 27 dS/m in trial 2 (Table 4.3).

Bentazon may be interacting with the saltwater at high salt concentrations, reducing the

quality of seashore paspalum to unacceptable levels.

Bromoxynil and the 3-way mixture of 2,4-D + dicamba + mecoprop caused a

reduction in seashore paspalum quality compared to the herbicide untreated at all

saltwater concentrations in both trials. Quality declined to the minimum acceptable level

of 6.5 or less at 13 dS/m saltwater concentration and continued to decline with increasing

saltwater concentration (Table 4.3). Both bromoxynil and the 3-way mixture of 2,4-D +

dicamba + mecoprop will injure seashore paspalum when irrigated with potable water,

and should be used with caution when saltwater irrigation is utilized.

Halosulfuron and imazaquin are herbicides used as postemergence for control of

sedges. The quality of seashore paspalum declined as saltwater concentration increased

and when halosulfuron was applied, quality was not affected compared to the herbicide

untreated. Imazaquin reduced turfgrass quality at all saltwater concentrations compared









to the herbicide untreated. Quality was reduced below the 6.5 minimum at 27 dS/m and

should also be used with caution on seashore paspalum irrigated with saltwater (Table

4.3).

When irrigated with saltwater concentrations of 41 dS/m and 55 dS/m, quality and

growth rate of seashore paspalum is significantly reduced (Chapter 2). If the turf is

further damaged by an herbicide application, the recovery time is increased due to the

reduction in growth. Herbicides that caused a major reduction in the quality of seashore

paspalum in this experiment were atrazine and metribuzin. These herbicides will cause

damage when irrigated with potable water and any concentration of saltwater and should

not be applied to seashore paspalum. Minor reductions in quality were observed after the

application of bromoxynil, 2,4-D + dicamba + mecoprop, and imazaquin. These

herbicides should not be applied to seashore paspalum irrigated with saltwater

concentrations > 27 dS/m.









Table 4-1 List of herbicides tested on seashore paspalum under salinity stress.


Common name

Prodiamine

Pendimethalin

Oxadiazon

Dithiopyr


Metolachlor

Isoxaben

Pronamide
Fenarimol


Grass
Quinclorac
Metsulfuron


Metribuzin

Broadleaf
Clopyralid

Bromoxynil
Atrazine
Bentazon

2,4-D
Dicamba
Mecoprop
Sedge
Halosulfuron


Imazaquin


Chemical name
PREEMERGENCE
[2,4-dinitro-N3,N3-dipropyl-6-(trifluoromethyl)-1,3-
benzediamine]
[N-(1-ethylpropyl)-3,4-demethyl- 2,6-
dinitrobenzenamine]
[2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-
A-1, 3, 4-oxadiazolin-5-one]
[3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-
(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethyl
ester]
[2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-
1 -methtlethyl)acetamide
[N-[3-(1-ethyl-l -methylpropyl)-5-isoxazolyl]-2,6-
dimethoxybenzamide and isomers
[3,5-dichloro-N-(1,1 -dimethyl-2-propynyl) benzamide
[a-(2-chlorophenyl)-a-(4-chlorophenyl)-5-
pyrimidinemethanol]
POSTEMERGENCE

[3,7-dichloro-8-quinolinecarboxylic acid]
[Methyl Methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-
triazin-2-yl) amino]carbonyl]amino] sulfony]
benzoate]
[4-Amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-
triazin-5(4H)-one]

(3,6-dichloro-2-pyridinecarboxylic acid,
monoethanolamine salt)
(3,5-dibromo-4-hydroxybezonitrile)
(2-chloro-4-ethylamino-6-isopropylamino-s-triazine)
[3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-
one 2,2-dioxide]
[(2,4-dichlorophenoxy)acetic acid]
(3,6-dichloro-2-methoxybenzoic acid)
[2-(4-chloro-2-methylphenoxy) propionic acid]

[methyl [[(4,6-dimethoxy-2-pyrimidinyl)amino]
carbonylaminosulfonyl]-3-chloro-1-methyl-1-H-
pyrazole-4-carboxylate]
[2-4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-
imidazol-2-yl-3-quinolinecarboxylic acid]


Application rate

1.1 kg ai ha-

2.0 kg ai ha

2.9 kg ai ha

0.3 kg ai ha-


2.1 kg ai ha-

0.8 kg ai ha-

1.1 kg ai ha-
0.8 kg ai ha-


0.8 kg ai ha-
0.3 kg ai ha-


3.4 kg ai ha-


0.3 kg ai ha-

0.6 kg ai ha-
1.7 kg ai ha-
1.1 kg ai ha-

0.09 kg ai ha1
0.4 kg ai ha-
0.4 kg ai ha-

0.07 kg ai ha1


0.5 kg ai ha-









Table 4-2 The effect of preemergence herbicides and salt concentrations on seashore
paspalum quality 4 wk after herbicide application.
Preemergence Herbicides Seashore paspalum
Oa 13a 27a 41a 55a
T1b T2b T1b T2b T1b T2b T1b T2b T1b T2b


Untreated 9.0 9.0 9.0 8.3 7.7 7.0 7.0 6.7 7.0 6.7
Dithiopyr 9.0 8.0 9.0 8.1 8.0 7.0 7.0 6.7 7.0 6.0
Pronamide 8.7 8.7 8.7 8.0 8.0 6.7 6.7 6.0 7.0 5.3
Metolachlor 8.7 7.7 8.7 7.8 8.0 6.0 6.7 6.3 6.3 5.7
Isoxaben 8.7 7.7 8.0 7.8 7.3 6.3 6.7 6.3 6.3 5.7
Fenarimol 8.3 8.7 9.0 8.1 7.7 6.7 6.7 6.7 6.7 5.3
Pendimethalin 8.3 8.0 9.0 8.1 7.7 6.7 6.7 6.3 6.7 5.7
Oxadiazon 8.3 7.7 8.3 7.6 7.7 7.0 7.0 6.3 7.0 5.7
Prodiamine 8.3 7.3 9.0 7.9 8.0 6.7 7.0 6.7 7.0 5.7
Atrazine 4.7 3.0 4.7 4.9 5.0 4.3 4.7 4.0 5.0 3.7
aSalt Concentrations in decisemens per meter (dS/m).
bT1 = Trial 1 and T2 = Trial 2
CQuality ratings range from 0 (dead turf) to 9 (healthy turf).
LSDo.05 = 0.55 (T1) and 0.80 (T2) for mean comparison of herbicide within a given salt
concentration or salt concentration within a given herbicide.

Table 4-3 The effect of postemergence herbicides and salt concentrations on seashore
paspalum quality 4 wk after herbicide application.
Postemergence Herbicides Seashore paspalum
Oa 13a 27a 41a 55a
T1b T2b T1b T2b T1b T2b T1b T2b T1b T2b
Untreated 9.0 9.0 9.0 8.3 7.7 7.0 7.0 6.7 7.0 6.7
Halosulfuron 9.0 8.7 9.0 7.9 7.7 7.0 6.3 6.7 7.0 5.3
Clopyralid 9.0 8.7 8.7 8.0 8.0 6.0 7.0 6.0 6.7 4.0
Quinclorac 8.3 8.7 9.0 8.1 7.7 6.3 7.0 5.7 6.7 6.0
Metsulfuron 8.3 8.3 8.7 7.8 7.0 7.0 6.7 6.3 6.3 6.0
Bentazon 8.0 8.7 9.0 7.8 7.7 5.7 6.3 6.3 6.0 4.3
Imazaquin 7.7 7.3 7.0 6.7 6.3 5.3 6.0 6.0 6.0 5.3
2,4-D/Dicamba/Mecoprop 7.7 7.0 7.0 6.5 6.3 5.0 5.3 6.0 4.3 4.3
Bromoxynil 7.3 7.7 7.7 6.6 6.0 6.0 5.3 5.7 5.7 5.7
Metribuzin 5.0 1.7 5.0 4.0 4.7 2.3 5.0 3.0 4.3 2.7
aSalt Concentrations in decisemens per meter (dS/m).
bT1 = Trial 1 and T2 = Trial 2
CQuality ratings range from 0 (dead turf) to 9 (healthy turf).
LSDo.05 = 0.55 (T1) and 0.80 (T2) for mean comparison of herbicide within a given salt
concentration or salt concentration within a given herbicide.














CHAPTER 5
CONCLUSIONS

Seashore paspalum is a warm-season turfgrass that is replacing traditional

turfgrasses in salt-affected areas due to its ability to tolerate saline conditions. Salinity

levels in soils are becoming increasingly problematic due to the use of alternative water

(effluent or brackish) for irrigation. When establishing seashore paspalum, saline

conditions may negatively impact turfgrass growth rate (Duncan and Carrow, 1999).

Studies were conducted to determine the tolerance of newly sprigged and established

seashore paspalum to various saltwater concentrations.

Decreasing growth rates of seashore paspalum sprigs were observed with all

saltwater concentrations and death of the sprigs occurred at 8 wk with 55 dS/m saltwater.

Newly sprigged seashore paspalum is sensitive to saltwater concentrations > 13 dS/m and

the time to full establishment will increase as saltwater concentration increases.

Saltwater concentration > 27 dS/m will cause desiccation and eventual death of the

sprigs. Due to the lack of tolerance to salinity, newly sprigged seashore paspalum should

be irrigated with potable water during establishment to reduce stress and promote healthy

growth.

Established seashore paspalum exhibited a high tolerance to saltwater irrigation.

Although seashore paspalum did not maintain an acceptable quality when irrigated with

pure ocean water (55 dS/m), quality levels > 6.5 were observed when irrigated with

salinity levels up to 41 dS/m. This characteristic will allow turf managers located near









the coast or those who have water restrictions to use alternative water sources (effluent

and brackish) for irrigation that have salt concentrations up to 41 dS/m.

Because seashore paspalum will maintain health and quality with saline irrigation

up to 41 dS/m, saline irrigation may be used as an alternative to herbicides to control

specific weeds. Successful control of Florida pusley was accomplished at 13 dS/m and

Virginia buttonweed at 27 dS/m saltwater. Goosegrass, southern crabgrass, and tropical

signalgrass were controlled at 41 dS/m. Saline irrigation as a single approach will control

these weeds while maintaining a quality seashore paspalum turf. Additional measures,

such as cultural practices or integrating reduced-rate herbicides, need to be utilized to

control dollarweed, common bermudagrass, torpedograss, and purple nutsedge at

saltwater concentrations up to 41 dS/m.

In a field study, salt was applied as a granule and as a solution to seashore

paspalum with a uniform population of southern crabgrass or cocks-comb kyllinga. The

granular application method provided better control of southern crabgrass and cocks-

comb kyllinga compared to salt applied in solution, but both methods provided > 70%

control at 27 dS/m. The reduced control from the solution may be due to salt leaching

through the root zone more quickly than the granular applied salt. Seashore paspalum

injury was < 20% for all treatments. Salt applied as a granular increased turf injury by

5% over that observed with the solution at both concentrations due to localized foliar

burn.

Inland areas that do not have access to saline water may still be able to utilize the

ability of seashore paspalum to tolerate salinity by applying specific rates of granular salt

to control some weed species. Precautions must be taken to effectively move the









granular salt into the root zone by means of potable water irrigation to prevent burning of

the leaf tissue. Further research should be conducted to link specific concentrations with

the control of specific weed species.

Many weeds are suppressed in saline conditions, but salt tolerant weeds will require

other means of control. Seashore paspalum is sensitive to many herbicides commonly

used on other turfgrasses. Herbicide response of seashore paspalum in salt-affected areas

has not yet been determined and may be more sensitive to injury as salt-stress increases.

When irrigated with saltwater concentrations of 41 dS/m and 55 dS/m, quality and

growth rate of seashore paspalum is significantly reduced. If the turf is further damaged

by an herbicide application, the recovery time is increased due to the reduction in growth.

Herbicides that caused a major reduction in the quality of seashore paspalum in this

experiment were atrazine and metribuzin. After atrazine was applied, there was some

indication that quality improved with saltwater treatment in trial 2, although quality

remained < 5, suggesting that the saltwater may be interfering with atrazine activity and

that the efficacy of atrazine may have been slightly reduced when saltwater irrigation is

applied. Metribuzin, however, reduced quality < 5 at all saltwater concentrations. These

herbicides will cause damage when seashore paspalum is irrigated with potable water and

any concentration of saltwater and should not be applied to seashore paspalum.

Minor reductions in quality were observed after the application of bromoxynil, 2,4-

D + dicamba + mecoprop, and imazaquin. Quality declined to < 6.5 at 27 dS/m saltwater

and continued declining with increasing saltwater concentration. These herbicides should

not be applied to seashore paspalum irrigated with saltwater concentrations > 27 dS/m.









Bentazon did not reduce seashore paspalum quality with irrigation up to 27 dS/m in

trial 1 and 13 dS/m in trial 2, but as saltwater irrigation increased, quality was reduced

more than the herbicide untreated. At high saltwater concentrations, bentazon may be

interacting with the saltwater causing a greater reduction in the quality of seashore

paspalum.

Salt stress did not impact seashore paspalum tolerance for prodiamine,

pendimethalin, oxadiazon, metolachlor, isoxaben, dithiopyr, pronamide, fenarimol,

clopyralid, or halosulfuron. Quality was reduced as saltwater concentration increased,

but the reduction was not different from the herbicide untreated.















APPENDIX A
2004 RAINFALL


Daily rainfall (cm) for the
Day June
01 5.50
02 0.60
03 0.63
04 0.00
05 0.00
06 0.57
07 0.00
08 0.00
09 0.00
10 0.00
11 0.00
12 0.00
13 0.25
14 5.30
15 1.60
16 0.05
17 0.00
18 1.90
19 0.25
20 1.93
21 0.00
22 2.40
23 1.76
24 2.43
25 0.80
26 0.33
27 0.03
28 0.25
29 0.40
30 0.00
31 --


summer of 2004 at the WFREC near Jay, Florida.
July August
0.67 0.00
5.40 0.00
0.10 0.00
0.00 0.00
0.00 0.00
0.03 0.00
0.03 0.00
0.00 0.00
0.00 3.05
0.00 1.45
0.00 3.03
0.00 0.63
0.03 0.00
0.00 0.00
0.30 0.00
5.07 0.00
0.47 0.00
0.00 0.00
0.00 0.00
0.00 3.33
0.00 0.25
0.00 3.40
0.00 0.20
0.00 0.03
2.43 0.03
0.00 0.70
0.05 0.00
0.03 4.55
1.27 0.10
4.05 0.00
2.10 0.05















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BIOGRAPHICAL SKETCH

Nicholas Bradley Pool is the son of Gene Pool and Susan Owens. He was born on

January 29, 1979, and raised on a corn and soybean family farm in Avon, Illinois. Nick

graduated from Avon High School in 1997 and attended Spoon River College where he

received his Associate of Science degree. In the Fall of 1999, he attended one semester

majoring in recreation, parks, and tourism at Western Illinois University. In January of

2000 he was accepted to the University of Florida where he graduated in the summer of

2003 with his Bachelor of Science degree in environmental horticulture with an emphasis

in turfgrass science. He immediately began his graduate career under the direction of Dr.

Barry Brecke and Dr. Bryan Unruh and is currently a candidate for a Master of Science

degree in agronomy with an emphasis in weed science.

After graduation, Nick is planning to enter the work force in the golf course

industry.