Characterization of Glyphosate Resistance and Management of Ragweed Parthenium (Parthenium Hysterophorus L.) in the Ever...

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Title:
Characterization of Glyphosate Resistance and Management of Ragweed Parthenium (Parthenium Hysterophorus L.) in the Everglades Agricultural Area of Florida
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1 online resource (62 p.)
Language:
english
Creator:
Fernandez, Jose V
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University of Florida
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Gainesville, Fla.
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Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Agronomy
Committee Chair:
ODERO,DENNIS C
Committee Co-Chair:
MACDONALD,GREGORY E
Committee Members:
GETTYS,LYN A
FERRELL,JASON ARDEN

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Subjects / Keywords:
herbicides -- noncrop -- parthenium -- ragweed
Agronomy -- Dissertations, Academic -- UF
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Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

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Abstract:
Ragweed parthenium (Parthenium hysterophorus L.) is an aggressive annual weed native to tropical America and considered a noxious weed in many parts of the world. Growers in the Everglades Agricultural Area (EAA) of south Florida have observed increasing occurrence of ragweed parthenium in the region. Growers have observed lack of control of ragweed parthenium with glyphosate, which is commonly used for weed control in noncrop areas and fallow fields. Because it is not considered a noxious weed in Florida, there is limited information on chemical control options and potential negative effects on crops in the region.   Project I determined whether ragweed parthenium in the EAA has evolved glyphosate resistance and evaluated whether reduced absorption and translocation are potential mechanisms of resistance to glyphosate. Ragweed parthenium biotype susceptible to glyphosate (S) from Mississippi and a suspected resistant biotype from the EAA (R) were compared using greenhouse dose-response assay. The R biotype fromthe EAA had a 40 to 67-fold level of resistance to glyphosate. Reduced absorption and translocation were not mechanisms of glyphosate resistance in the EAA biotype.   Project II evaluated the efficacy of different herbicides applied postemergence at the full and half label rates for control of rosette and flowering ragweed parthenium in noncrop areas using greenhouse and field studies, respectively.Aminocyclopyrachlor + chlorsulfuron, aminopyralid, saflufenacil +dimethenamid-P, and hexazinone provided 100% control of rosette and flowering ragweed parthenium 3 and 9 weeks after treatment, respectively, at both the full and half label rates. Glufosinate and 2,4-D at the full rate provided>80% control of both stages of growth. This information provides growers inthe EAA with herbicide options for ragweed parthenium control in noncrop areas.   Project III evaluated the effects of different concentrations of aqueous extracts of ragweed parthenium on germination and root growth of lettuce (Lactucasativa L.), radish (Raphanus sativusL.), and rice (Oryza sativa L.) grownin the EAA. All three species were affected by increasing concentration of ragweed parthenium aqueous extract. Rice was the most tolerant crop to ragweed parthenium aqueous extract followed by lettuce and radish.
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In the series University of Florida Digital Collections.
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Includes vita.
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Statement of Responsibility:
by Jose V Fernandez.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: ODERO,DENNIS C.
Local:
Co-adviser: MACDONALD,GREGORY E.

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lcc - LD1780 2013
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UFE0046386:00001


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CHARACTERIZATION OF GLYPHOSATE RESISTANCE AND MANAGEMENT OF RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) IN THE EVERGLADES AGRICULTURAL AREA OF FLORIDA By JOSE VENANCIO FERNANDEZ A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR TH E DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013

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2013 Jose Venancio Fernandez

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To my family for all their love, support, and encouragement

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4 ACKNOWLEDGMENTS I thank my major professor, Dr. Dennis C. Odero, for giving me the opportunity to join his research program. I am extremely grateful for his friendship, patience, support, and the knowledge he imparted on me. Appreciation is extended to the members of my committee: Drs. Gregory MacDonald, Jason Ferrell and Lyn Gettys for the advice provided during my gra duate program. I am indebted to Drs. MacDonald and Ferrell for their constant help and advice during the semesters I lived in Gainesville. I thank Dr. Ferrell for allowing me to make use of the weed shop a s place where I could feed my curiosity for plant r elated experiments. Special thanks to Drs. Peter Ditmar, Brent Sellers, and Ramon Leon who have provided advice and friendship. I also want to thank Nikol Havranek, Mike Durham, Hunter Smith, Sarah Berger, Anna Greis, Daniel Abe, Chris Rouse, and Ryan Mil ler for the friendship and support they provided to me while conducting my research. I would also like to thank the Agronomy Department faculty, staff and students for the knowledge I gained, for the support I received, and for the good time I had at the d epartment. I owe this achievement to my parents and siblings who with their constant support and encouragement have made me the person I am. I thank my dad for being strict and for showing me the value of respect and hard work. I thank my mom for teaching me to trust in God and for her true friendship.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 CONFIRMATION OF GLYPHOSATE RESISTANT RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) IN THE EVERGLADES AGRICULTURAL AREA ................................ ................................ ......................... 11 Glyphosate Resistance ................................ ................................ ........................... 11 Materials and Methods ................................ ................................ ............................ 13 Plant Material ................................ ................................ ................................ ... 13 Greenhouse Dose Response Assay ................................ ................................ 14 Absorption and Translocation ................................ ................................ ........... 16 Results and Discussion ................................ ................................ ........................... 18 Greenhouse Dose Response Assay ................................ ................................ 18 Absorption and Translocation ................................ ................................ ........... 19 Recovery of 14 C glyphosate ................................ ................................ ....... 19 Absorption of 14 C glyphosate ................................ ................................ ..... 20 Treated leaf section ................................ ................................ ................... 20 Above treated leaf section ................................ ................................ .......... 21 Be low treated leaf section ................................ ................................ .......... 21 Roots ................................ ................................ ................................ ......... 22 Autoradiography ................................ ................................ ......................... 22 2 RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) CONTROL IN NONCROP AREAS IN THE EVERGLADES AGRICULTURAL AREA ............... 27 Herbicide Efficacy ................................ ................................ ................................ ... 27 Materials and Methods ................................ ................................ ............................ 29 Field Study ................................ ................................ ................................ ....... 29 Greenhouse Study ................................ ................................ ........................... 30 Results and Discussion ................................ ................................ ........................... 32 Field Study ................................ ................................ ................................ ....... 32 Greenhouse Study ................................ ................................ ........................... 34 3 ALLELOPATHIC EFFECTS OF PARTHENIUM HYSTEROPHORUS L. EXTRACTS ON GERMINATION OF DIFFERENT CROPS GROWN IN THE EVERGLADES AGRICULTURAL AREA ................................ ................................ 39

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6 Allelopathy ................................ ................................ ................................ .............. 39 Materials and Methods ................................ ................................ ............................ 41 Whole Plant Aqueous Extraction ................................ ................................ ...... 41 Germination Assays ................................ ................................ ......................... 42 Statistical Analysis ................................ ................................ ............................ 43 Results and Discussion ................................ ................................ ........................... 44 Seed Germination ................................ ................................ ............................ 44 Radicle and Shoot Growth ................................ ................................ ................ 46 4 SUMMARY ................................ ................................ ................................ ............. 53 LIST OF REFERENCES ................................ ................................ ............................... 55 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 62

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7 LIST OF TABLES Table page 1 1 Parameter estimates and standard errors (in parenthesis) for the three parameter log logistic model (Equation 2) for ragweed parthenium susceptible and resistance biotypes in response to glyphosate. ........................ 23 1 2 Perc ent translocation of 14 C glyphosate in resistant (R) and susceptible (S) biotypes of ragweed parthenium hours after treatment (HAT) ............................ 23 2 1 Herbicide treatments, rates, and modes of action. ................................ ............. 36 2 2 Flowering ragweed parthenium control at locations within the E AA, Belle Glade, FL in 2012. ................................ ................................ .............................. 37 2 3 Percent dry weight reduction of greenhouse grown ragweed parthenium in response to herbicide treatments at 21 days after treatment. ............................. 38 3 1 Parameter estimates and standard errors (in parenthesis) for the two parameter expon ential decay model (Equation 1) and the four parameter Brain Cousens model (Equation 3). ................................ ................................ .... 49 3 2 Parameter estimates and standard e rrors (in parenthesis) for the linear regression model (Equation 2). ................................ ................................ ........... 49

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8 LIST OF FIGURES Figure page 1 1 Effect of glyphosate on ragweed parthenium fresh weight of resistant (R) and susceptible (S) biotypes for two experimental runs (Run 1 and 2). The x axis uses a logarithmic scale. ................................ ................................ .................... 24 1 2 Effect of glyphosate on ragweed parthenium dry weight of resistant (R) and susceptible (S) biotypes for two experimental runs (Run 1 and 2). The x axis uses a logar ithmic scale. ................................ ................................ .................... 25 1 3 Autoradiograph image of susceptible (left) and resistant (right) ragweed parthenium biotypes harvested 168 HAT. ................................ .......................... 26 3 1 Effect of ragweed parthenium aqueous extract on A) rice germination combined over two experimental runs, and B) shoot length for experimental runs 1 and 2. ................................ ................................ ................................ ....... 50 3 2 Effect of ragweed parthenium aqueous extract on A) radish germination for experiment al runs 1 and 2, and B) radicle length for experimental runs 1 and 2. ................................ ................................ ................................ ........................ 51 3 3 Effect of ragweed parthenium aqueous extract on A) lettuce germination for experimental runs 1 and 2, and B) radicle length for experimental runs 1 and 2. ................................ ................................ ................................ ........................ 52

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9 Abstract of Thesis Presented to the Graduate Sch ool of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science CHARACTERIZATION OF GLYPHOSATE RESISTANCE AND MANAGEMENT OF RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) IN THE EVERGLADES AGRICULTURAL AREA OF FLORIDA By Jose Venancio Fernandez December 2013 Chair: Dennis Odero Co chair: Gregory MacDonald Major: Agronomy Ragweed parthenium ( Parthenium hysterophorus L.) is an aggressive annual weed native to tropical Am erica and considered a noxious weed in many parts of the world. Growers in the Everglades Agricultural Area (EAA) of south Florida have observed increasing occurrence of ragweed parthenium in the region. Growers have observed lack of control of ragweed par thenium with glyphosate, which is commonly used for weed control in noncrop areas and fallow fields. Because it is not considered a noxious weed in Florida, there is limited information on chemical control options and potential negative effects on crops in the region. P roject I determined whether ragweed parthenium in the EAA ha s evolved glyphosate resistance and evaluated whether reduced absorption and translocation are potential mechanisms of resistance to glyphosate. Ragweed parthenium biotype susceptible to glyphosate (S) from Mississippi and a suspected resistant biotype from the EAA (R) were compared using greenhouse dose response assay. T he R biotype from the EAA had a 40 to 67 fold level of resistance to glyphosate. Reduced absorption and translocation were not mechanisms of glyphosate resistance in the EAA biotype.

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10 Project II evaluated the efficacy of different herbicides applied postemergence at the full and half label r ates for control of rosette and flowering ragweed parthenium in noncrop areas using greenhouse and field studies, respectively. Aminocyclopyrachlor + chlorsulfuron, aminopyralid, saflufenacil + dimethenamid P, and hexazinone provided 100% control of rosett e and flowering ragweed parthenium 3 and 9 weeks after treatment, respectively at both the full a nd half label rates. Glufosinate and 2,4 D at the full rate provided >80% control of both stages of growth. This information provides growers in the EAA with herbicide options for ragweed parthenium control in noncrop areas. Project III evaluated the effects of different concentrations of aqueous extracts of ragweed parthenium on germination and root growth of lettuce ( Lactuca sativa L.), radish ( Raphanus sat ivus L.), and rice ( Oryza sativa L.) grown in the EAA. All three species were affected by increasing concentration of ragweed parthenium aqueous extract. Rice was the most tolerant crop to ragweed parthenium aqueous extract followed by lettuce and radish

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11 CHAPTER 1 CON FIRMATION O F GLYPHOSATE RESISTANT RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) IN THE EVERGLADES AGRICULTURAL AREA G lyphosate Resistance Ragweed parthenium ( Parthenium hysterophorus L.) is a troublesome annual weed in the Asteraceae family native to the Gulf of Mexico and Argentina (Navie et al. 1996; Picman and Towers 1982). It is distributed across 24 US states but is most prevalent in Florida, Louisiana, and Texas (USDA NRCS 2013 ). In Florida, ragweed parthenium is common in the southern portion of the state (USDA NRCS 2013) including the Everglades Agricultural Area (EAA), where it is commonly found along field edges, canals, ditch banks, roadsides, and disturbed sites (Odero 201 2). The EAA consists of approximately 280,000 ha of cropland for cultivation of sugarcane ( Saccharum L. spp. hybrids), vegetables, rice ( Oryza sativa L.), and sod. The p rolific seed production (130,000 to 200,000 seeds m 2 ) (Joshi 1991; Pandey et al. 2003) as well as the ability to persist in soil and germinate over a wide range of temperatures ( Navie et al. 2004; Tamado et al. 2002b ), have contributed to the widespread distribution of ragweed parthenium in the EAA and surrounding areas. In addition, the s ubtropical environment of south Florida that allows year round germination, growth, and reproduction of ragweed parthenium has also contributed to its widespread distribution in the region. Glyphosate has been used repeatedly in noncrop areas and fallow fields in the EAA for many years to manage ragweed parthenium and other troublesome weed species However, growers in the EAA have recently observed reduced ragweed parthenium control with single or multiple glyphosate applications. Similarly, Odero

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12 (2012) reported no control of rosette and flowering ragweed parthenium in the EAA with glyphosate at 840 and 1,680 g ae ha 1 at two and three weeks after treatment (WAT). Previous reports have documented g lyphosate resistant ragweed parthenium in Colombia (Gomez 2009). Bekeko (2013) also reported reduced (< 25% ) ragweed parthenium control with glyphosate at 3 L ha 1 55 days after treatment in Ethiopia. In contrast, Reddy et al. (2007) reported 93 to 100% and 95% control of rosette and flowering ragweed parthenium three WAT, respectively with glyphosate at 840 g ae ha 1 in Mississippi. Singh et al. (2004) also reported 95 to 100% control of flowering ragweed parthenium 18 WAT with glyphosate at 2 7 00 and 5 4 00 g ae ha 1 respectively in India. However, the rate used in their study exceeds the labeled use rate for single glyphosate application in the United States. Similarly, rosette and flowering ragweed parthenium in noncrop areas in Pakistan were controlled 91 to 96%, respectively with glyphosate at 4 0 00 g ae ha 1 four WAT (Khan et al. 2012). Glyphosate inhibits 5 enolpyruvylshikimate 3 phosphate synthase (EPSPS), an enzyme involved in the biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan (Amrhein et al. 1980; Zimdahl 2007). So far, 171 biotypes of 24 different weed species have documented resistan ce to glyphosate (Heap 2013). Resistance to glyphosate in plants can be due to a mutation in the target site of action, reduced translocation or over expression of EPSPS (Powles and Preston 2006; Shaner et al. 2012). Mutation due to a single amino acid substitution of Pro 106 by Ser 106 in the coding region of EPSPS conferred resistance to goosegrass ( Eleusine indica ( L. ) Gaertn. ) (Baerson et al. 2002), Italian ryegrass ( Lolium multiflorum Lam.) (Perez Jones et al. 2007; Jasieniuk et al. 2008), and rigid rye grass ( Lolium rigidum Gaud.) (Wakelin

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13 and Preston 2006). Likewise, Gaines et al. (2010) reported that the genome of glyphosate resistant biotypes of Palmer amaranth ( Amaranthus palmeri L.) had 5 to more than 160 fold copies of the EPSPS genes compared to the susceptible biotypes. Reduced transloca tion of glyphosate which is the most frequently observed mechanism of resistance (Heap 2013) has been reported in ragweed parthenium, rigid ryegrass, horseweed ( Conyza canadensis (L.) Cronq.), giant ragweed ( Ambrosia trifida L.), Italian ryegrass, hairy fl eabane ( Conyza bonariensis (L.) Cronq.) and common lambsquarters ( Chenopodium album L.) (Lorraine Colwill et al. 2003; Perez Jones et al. 2007; Gomez 2009; Ge et al. 2010; Norsworthy et al. 2010; Yerka 2013). Therefore, the objectives of this study were to (1) confirm and characterize the level of glyphosate resistance of ragweed parthenium in the EAA using dose response bioassay and (2) determine if reduced absorption and/or translocation is the mechanism of this population of ragweed parthenium resistance to glyphosate. Materials and Methods Plant Material Ragweed parthenium seeds were collected at maturity at the University of Florida Everglades Research and Education Center (EREC) in Belle Glade, FL in 2012 from plants reported to survive multiple appl ications of glyphosate (accession R) at 840 g ae ha 1 in the EAA (Odero 2012). Similarly, seeds were collected from ragweed parthenium susceptible to glyphosate (accession S) at the same rate from the USDA ARS Jamie Whitten Delta States Research Center in Stoneville, MS in 2011. Collected seeds for each accession were stored in the dark at 2 C prior to use.

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14 Greenhouse Dose Response Assay The response of R and S accessions of ragweed parthenium to glyphosate were evaluated using greenhouse dose response e xperiments conducted at the University of Florida, Gainesville in 2013. Seeds from each accession were soaked in tap water for 24 hours and rinsed with tap water prior to planting in 45 0 cm 3 square pots using a commercial potting medium (Fafard Mixes for P rofessional Use, Conrad Fafard Inc., Agawan, MA 01001) mixed with 10 g of 14 14 14 slow release fertilizer (Osmocote Smart Release Plant Food, Scotts Sierra Horticultural Products Company, Marysville, OH 43040). The first and second experimental runs were planted on March 4, 2013 and April 15, 2013, respectively. At 14 days after emergence, plants were thinned to one plant per pot with similar sizes to obtain uniformity across all plants. Plants were watered as needed to ensure that moisture was not a limit ing factor and kept in a greenhouse maintained at 33/24 C day/night temperatures under natural light. Glyphosate (Roundup PowerMax, Monsanto Company, St. Louis, MO 63167) was applied at 0.105, 0.21, 0.42, 0.84, 1.68, 3.36, 6.72, 13.44, 26.88 53.76, and 107.52 kg ae ha 1 on rosette ragweed parthenium 20 cm in diameter from both accessions. These rates correspond to 1/8 to 128 the recommended glyphosate single application rate of 0.84 kg ae ha 1 Untreated controls for both accessions were included for c omparison. Above ground biomass of four additional plants of each biotype were harvested at treatment application and used to determine growth rate over a period of 21 days. Growth rate was calculated as: GR = ((AGB cont AGB app ) /21) [1]

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15 where GR is growth rate (g day 1 ), AGB cont is the average aboveground biomass of the untreated control 21 days after treatment application (g), and AGB app is the average aboveground biomass at treatment application (g). Glypho sate was applied using a moving nozzle spray chamber (Generation II Spray Booth, Devries Manufacturing Corp., Hollandale, MN 56045) calibrated to deliver 187 L ha 1 at 172 kPa. Treatments were applied on April 16, 2013 and May 27, 2013 for the first and se cond experimental runs, respectively. Plants were returned to the greenhouse following treatment application and maintained as previously described. Aboveground biomass was harvested at soil level 21 days after treatment and weighed to obtain aboveground f resh weight. The harvested plants were then dried in an oven at 60 C for 72 hours to obtain aboveground dry weight. The experiment was arranged as a completely randomized design with four replications of each treatment. Both aboveground fresh and dry wei ght data were expressed as a percentage of the untreated control for analysis. Data were tested for normality using R (R Development Core Team 2009) and arcsine square root transformed. Data were subjected to ANOVA and combined for analysis when there was no significant experimental run by treatment interaction using R (R Development Core Team 2009). However, transformation did not normalize data; therefore nontransformed data are presented. The aboveground fresh and dry weight data were fitted to the three parameter log logistic model (Equation 1) similar to that described by Seefeldt et al. (1995) but with the lower limit constrained to 0 using the drc package of R (R Development Core Team 2009; Ritz and Streibig 2005): Y = d / 1 + exp{ b [log( x ) log( e ) ]} [2]

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16 where Y is the response (aboveground fresh or dry weight expressed as a percentage of the untreated control), x is the glyphosate rate (kg ae ha 1 ), b is the slope of the curve at the inf l ection point, d is the upper limit or asymptote (%), e i s inflection point of the fitted curve (equivalent to the rate required to cause 50% response or ED 50 ). The resistance factor (RF) was calculated as ED 50 (R )/ ED 50 (S). Absorption and Translocation Absorption and translocation of 14 C glyphosate in R and S accessions of ragweed parthenium were determined in experiments conducted at the University of Florida, Gainesville in 2012. Plants for both accessions were grown in a manner similar to the dose response study on October 5, 2012 and October 26, 2012. Ro sette plants from both accessions 15 cm in diameter were treated with glyphosate at 840 g ae ha 1 Uptake and translocation were determined using 14 C labeled glyphosate ( 14 C glyphosate, Amersham Life Sciences Inc., Arlington Heights, IL 60004) with a specific activity of 3.17 kBq mg Once the spray application dried on the plant leaf surface following glyphosate application, the adaxial surface of one leaf located in the middle of each plant was marked and spiked with one 2.1 L droplet of 14 C radiol abeled material resulting in a total of 6.66 kBq mg 14 C glyphosate per plant. Plants were maintained in the greenhouse until harvest. Plants were harvested from pots 24, 72, and 168 hours after treatment (HAT) and radiolabeled leaves excised and washed with five sequential 1 ml aliquots of deionized water to determine percentage uptake. Unabsorbed 14 C from the leaf wash solution was quan tified with liquid scintillation spectrometry (LSS) Soil from the roots was washed using detergent and water.

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17 Whole plants and the excised treated leaf were placed on blotter paper in plant presses and oven dried at 70 C for 5 to 12 days. Dried plant s were covered with X ray film (Kodak X OMAT XAR 5 film, Sigma Aldrich, St. Louis, MO 63103) and stored 50 days at room temperature to produce autoradiographs. Following autoradiography, plants were sectioned into treated leaf (TL), leaves above treated le af (ATL), leaves below treated leaf (BTL), and roots (RTS). Plant sections were finely ground through a 20 mesh screen using a Wiley Mill (Wiley Mill, Arthur W. Thomas Company, Philadelphia, PA 19099). Ground tissue samples weighing 0.02 to 0.06 g were oxi dized to recover 14 C using a biological oxidizer (R. J. Harvey Biological Oxidizer, Model OX 500, R. J. Harvey Instrument Co., Hillsdale, NJ 07642). Percent recovery was the absorbed radioactivity plus the amount recovered from the leaf rinse. Translocated radioactivity is presented as the percent of absorbed radioactivity in plant parts (TL, ATL, BTL, and RTS). Radioactivity (translocation and absorption) in all plant parts was determined using LSS. The experiment was arranged in a completely randomized d esign with four replications and repeated twice. Plants from the first and second experimental runs were treated on October 30, 2012 and November 20, 2012, respectively. Data were tested for normality using PROC UNIVARIATE procedure in SAS 9.2 (SAS 2009) Data were subjected to arcsine square root transformation prior to ANOVA. When there was no significant experimental run by treatment interaction, data were combined for Transformatio n did not normalize data; therefore nontransformed data are presented.

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18 Results and Discussion Greenhouse Dose Response Assay A run by treatment interaction was detected for both R and S ragweed parthenium biotype s aboveground fresh and dry weight data T he interaction was likely attributed to differences in growth rate between the two experimental runs. Although, both experimental runs were grown for the same duration of time and the plants had similar size at treatment application, GR for the R and S biotype was 2.54 and 2.63 g day 1 for the first experimental run, and 1.81 and 1.63 g day 1 for the second experimental run, respectively. The differences in GR may be related to the transition of ragweed parthenium from the rosette to flowering stage. Dur ing the transition phase plants have an accelerated development of branches and accumulat e higher amounts of biomass in time. Consequently a difference of few days in biomass accumulation can drastically impact the response to the herbicide application. Therefore, data were analyzed separately by experimental run for each biotype and separate regression curves were fitted using Equation 2 to model ragweed parthenium aboveground biomass reduction as a function of glyphosate rate (Figure 1 1 and 1 2). Mode l parameters are provided in Table 1 1. Both above ground fresh and dry weight of R and S ragweed parthenium biotypes decreased as glyphosate rate increased (Figure 1 1 and 1 2). The rate of glyphosate required to provide 50% aboveground ragweed parthenium growth reduction (ED 50 ) differed between the R and S biotypes (Table 1 1). The ED 50 values for aboveground fresh weight for the S biotype were estimated to be 0.18 and 0.41 kg ae ha 1 for the first and second experimental runs, respectively while ED 50 val ues for the R

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19 biotype were estimated to be 12.09 and 24.62 kg ae ha 1 for the first and second experimental runs, respectively. The ED 50 values for aboveground dry weight for the S biotype were estimated to be 0.17 and 0.34 kg ae ha 1 for the first and sec ond experimental runs, respectively compared to 6.80 and 14.48 kg ae ha 1 for the first and second experimental runs, respectively for the R biotype. The R biotype had a 60 to 67 fold and 40 to 43 fold greater glyphosate resistance based on aboveground f resh and dry weight, respectively when compared to the S biotype (Table 1 1 ). Variations in resistance levels between the experiments was most likely due to differences in ragweed parthenium growth rates during the transition from rosette to flowering stag e The level of ragweed parthenium resistance to glyphosate in this study is much higher than previously reported values of 3 to 21 fold resistance for common ragweed ( Ambrosia artemisiifolia L.), giant ragweed, common lambsquarters, and horseweed (VanGes sel 2001; Westhoven et al. 2008; Brewer and Oliver 2009; Norsworthy et al. 2010). The higher level of glyphosate resistance reported in this study may be attributed to a different mechanism of resistance by ragweed parthenium population in the EAA. Absorp tion and T ranslocation There was no significant experimental run by treatment interaction for the R and S ragweed parthenium biotypes; therefore, data were combined for analysis for each biotype. Recovery of 14 C glyphosate Recovery of 14 C glyphosate was 79 and 89% of the total 14 C glyphosate applied for the R and S ragweed parthenium biotypes, respectively 24 HAT (Table 1 2). At 168 HAT, recovered 14 C glyphosate had significantly decreased to 74% for the S biotype.

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20 However, there was no significant difference in recovered 14 C glyphosate for the R biotype over time. Furthermore, no significant difference in recovery was observed 168 HAT between both biotypes. Similar decrease in 14 C glyphosate recovery over time has b een reported for sicklepod ( Senna obtusifolia (L.) Irwin and Barneby) and common ragweed (Walker and Oliver 2008; Brewer and Lawrence 2009). Sandberg et al. (1980) also reported that up to 50% of the applied 14 C glyphosate was not recovered from excised le aves within 25 days af ter treatment. Absorption of 14 C glyphosate There was no significant difference in 14 C glyphosate absorption over time for the R ragweed parthenium biotype (Table 1 2). In contrast, absorption of 14 C glyphosate increased over time for the S ragweed parthenium biotype. At 168 HAT, 14 C glyphosate absorption had increased by 25% for the S biotype compared to 24 HAT. When compared across biotypes, the R biotype had absorbed significantly higher 14 C glyphosate absorption 72 HAT, but no diff erence in absorption was observed 168 HAT between both biotypes. This shows that reduced glyphosate absorption is not a mechanism of glyphosate resistance by ragweed parthenium population in the EAA. Similarly, Koger and Reddy (2005) reported that the abso rption of four susceptible and four resistant biotypes of horseweed was similar suggesting that absorption was not involved as a mechanism of glyphosate resistance. Treated leaf section At 24 HAT, 69 and 70% of 14 C glyphosate applied remained on the trea ted leaf of the R and S ragweed parthenium biotypes, respectively (Table 1 2). There was a significant reduction in the amount of 14 C glyphosate that remained on the treated leaf

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21 168 HAT for both biotypes. A total of 45 and 53% of 14 C glyphosate translocat ed from the treated leaf to the rest of the plant in the S and the R biotypes, respectively 168 HAT. However, no difference in translocation of the 14 C glyphosate was observed between biotypes showing that reduced translocation is not a factor that confers glyphosate resistance to ragweed parthenium in the EAA. In contrast, previous research showed that glyphosate resistant Italian ryegrass and horseweed biotypes had a higher concentration of 14 C glyphosate in the treated leaf (Koger and Reddy 2005; Perez J ones et al. 2007). Above treated leaf section Translocation of 14 C glyphosate above the treated leaf increased over time for both R and S ragweed parthenium biotypes (Table 1 2). A total of 18 and 30% of 14 C glyphosate translocated to the leaf above the treated leaf in the R and S biotypes, respectively. However, no significant difference in 14 C glyphosate translocation was observed between biotypes indicating that 14 C glyphosate was symplastically translocated in both biotypes which is the typical glyph osate movement in plants. Below treated leaf section There was no difference in 14 C glyphosate translocation to below the treated leaf over time within and between ragweed parthenium biotypes (Table 1 2). This shows that the plant tissue below the treated leaf was not a metabolic sink tissue which agrees with reports from Walker and Oliver (2008) Similarly, Kirkwood et al. (2000) reported that < 5% of the applied 14 C glyphosate translocated to the older leaves in barnyardgrass ( Echinochloa crus galli L.) 120 HAT illustrating that older plant leaves are not metabolic sinks.

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22 Roots There was no significant difference in 14 C glyphosate translocation to roots of the S ragweed parthenium biotype over time (Table 1 2). In contrast, 14 C glyphosate transloca tion increased from 16 to 32% at 24 to 168 HAT for the R biotype. Furthermore, significantly more 14 C glyphosate translocated to roots of the R compared to the S biotype 168 HAT. In contrast, Kirkwood et al. (2000) reported that 14 C glyphosate translocatio n in barnyardgrass was higher 72 HAT and decreased 120 HAT. Autoradiography The images from the autoradiography show that h igh concentration of 14 C glyphosate was observed in the treated leaf for both biotypes168 HAT (Figure 1 3). Although most of the 14 C glyphosate remained in the treated leaf, basipetal translocation to roots was observed for both biotypes. The results of this study confirm glyphosate resistance in ragweed parthenium occurring in the EAA of south Florida. Therefore, glyphosate at the labeled use rate or higher will not be effective in providing ragweed parthenium control in the EAA. Repeated use of glyphosate for ragweed parthenium control in the EAA over the past several years probably led to evolution of ragweed parthenium resis tance in the region. Growers in the EAA need to use herbicides with other modes of action for control of ragweed parthenium in noncrop areas and fallow fields Furthermore, reduced glyphosate translocation, which is a mechanism of glyphosate resistance in many weed species (Heap 2013) was not observed on ragweed parthenium from the EAA. Therefore, further research is needed to determine the mechanism of resistance of ragweed parthenium from the EAA to glyphosate

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23 Table 1 1. Parameter estimates and standard errors (in parenthesis) for the three parameter log logistic model (Equation 2) for ragweed parthenium susceptible and resistance biotypes in response to glyphosate Biotype Weight type Run Model parameters (SE) RF b b d e a Resistant Fresh 1 0.82 (0.14) 97.48 (4.44) 12.09 (2.72) 67 Susceptible 1 1.74 (0.44) 102.06 (6.81) 0.18 (0.03) Resistant 2 1.11 (0.18) 98.53 (3.24) 24.62 (4.08) 60 Susceptible 2 3.28 (1.13) 93.43 (5.45) 0.41 (0.04) Resistant Dry 1 0.89 (0.13) 99.23 (4.13) 6.80 (1.30) 40 Susceptible 1 1.34 (0.28) 100.96 (6.27) 0.17 (0.02) Resistant 2 1.23 (0.22) 96.57 (3.09) 14.48 (2.04) 43 Susceptible 2 2.18 (0.51) 95.65 (6.19) 0.34 (0.04) a e is equivalent to the rate required to cause 50% response or ED 50 b RF is the resistance factor (RF) calculated as the ratio of ED 50 of the resistant and susceptible biotype. Table 1 2. Percent translocation of 14 C glyphosate in resistant (R) and susceptible (S) biotypes of ragweed parthenium hours after treatment (HAT). ab HAT Total recovery Total absorption Translocation TL ATL BTL RTS R S R S R S R S R S R S -------------------------------------------------------------------% -------------------------------------------------------------------24 78.85 88.73 60.23 41.23 69.03 70.35 11.73 10.29 3.18 5.16 16.08 14.21 72 73.43 80.80 68.29* 48.00 58.26 60.88 16.16 20.34 2.66 4.85 22.91 13.96 168 68.78 73.95 60.03 66.39 46.50 55.43 18.35 29.76 3.20 3.40 31.96 11.41 LSD (0.05) NS 7.61 NS 11.60 14.13 13.46 6.59 9.16 NS NS 11.30 NS a Abbreviations: TL, treated leaf; ATL, above treated leaf; BTL, below treated leaf; RTS, roots. b Means and standard error in parenthesis within a column followed by the same letter not significantly different (P < 0.05). t test within an evalua tion.

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24 Figure 1 1. Effect of glyphosate on ragweed parthenium fresh weight of resistant (R) and susceptible (S) biotypes for two experimental runs (Run 1 and 2). The x axis uses a logarithmic scale.

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25 Figure 1 2. Effect of glyphosate on ragweed partheni um dry weight of resistant (R) and susceptible (S) biotypes for two experimental runs (Run 1 and 2). The x axis uses a logarithmic scale.

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26 Figure 1 3. Autoradiograph image of susceptible (left) and resistant (right) ragweed parthenium biotypes harvested 168 HAT.

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27 CHAPTER 2 RAGWEED PARTHENIUM ( PARTHENIUM HYSTEROPHORUS L.) CONTROL IN NONCROP AREAS IN THE EVERGLADES AGRICULTURAL AREA Herbicide Efficacy Ragweed parthenium ( Parthenium hysterophorus L.) is an aggressive annual weed of tropical and subtropical environments in the Asteraceae family that is commonly associated with noncrop areas in the Everglades Agricultural Area (EAA) of south Florida. However, ragweed parthenium is presently encroaching into cultivated and fallow fields in the EAA w hich comprise of approximately 280,000 ha. Sugarcane ( Saccharum L. spp. hybrids) is the predominant crop in the EAA grown in rotation with lettuce ( Lactuca sativa L.), green bean ( Phaseolus vulgaris L.), sweet corn ( Zea mays L.), radish ( Raphanus sativus L .), and rice ( Oryza sativa L.). Consequently, it is important that the spread of ragweed parthenium from noncrop areas in the EAA into cultivated fields be curtailed before it adversely affects crop production. Ragweed parthenium is a major weed problem in cultivated fields in India, Australia, and Ethiopia (McFadyen 1992; Tamado et al. 2002a; Singh et al. 2004). Increased occurrence of ragweed parthenium in the EAA has been attributed to lack of effective control, its prolific seed production, and rapid g rowth habit which allows it to quickly form dense stands (Joshi 1991; Navie et al. 1998; Tamado et al. 2002b; Pandey et al. 2003; Navie et al. 2004; Dhileepan 2012; Odero 2012). Ragweed parthenium seeds are able to germinate over a wide range of temperatur e. Tamado et al. (2002b) reported 29 to 74% ragweed parthenium seed germination at fluctuating temperatures between 12/2 C to 35/25 C respectively. Most seedlings of ragweed parthenium emerge from shallowly buried seeds <0.5 cm in depth and no emergence occurs at depths >5 cm (Tamado et al. 2002b). After germination the seedlings form a

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28 basal rosette that later develops branches that can reach up to 2 m in height. Plants can start flowering and seed production one month after germination and are able to produce viable seeds for 6 to 8 months (Jayachandra 1971; Navie et al. 1996). Ragweed parthenium is also a C 3 C 4 intermediate species with a Kranz like leaf anatomy and partially suppressed photorespiration (Rajendrudu and Rama Das 1990; Pandey et al. 2003 ). Reduced photorespiration rates by C 3 C 4 intermediate species results in adaptive advantages at warm leaf temperatures that in C 3 plants can only be achieved through substantial costs to water use efficiency and/or nitrogen use efficiency (Schuster and Monson 1990). The adaptive growth advantage at warm temperatures enables ragweed parthenium to thrive and grow year round in the sub tropical environment of south Florida. Similar year round growth has been reported in Texas which is characterized by warm winter months (Reddy and Bryson 2005). Glyphosate has been the primary herbicide used to control ragweed parthenium in noncrop area s and fallow fields in the EAA because of its high efficacy, low cost, and lack of rotational restrictions. However, glyphosate has recently been reported to be ineffective for ragweed parthenium control in the EAA (Odero 2012). Ragweed parthenium is manag ed by mowing in the EAA, but it rapidly regenerates particularly during the rainy season between May to October. Currently, there is limited information on ragweed parthenium control in EAA with other herbicides. Several herbicides commonly used in cult ivated fields and noncrop areas have been reported to provide control of ragweed parthenium. Under field conditions, glyphosate, glufosinate, chlorimuron, halosulfuron, and 2,4 D provided 82 to 100% control of rosette ragweed parthenium three weeks after t reatment (WAT) while

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29 glyphosate, glufosinate, and trifloxysulfuron provided 86 to 95% control of flowering ragweed plants three WAT (Reddy et al. 2007). Khan et al. (2012) reported 96 and 87% rosette ragweed parthenium control and 91 and 75% flowering ragw eed parthenium control four WAT with glyphosate and metribuzin, respectively. Flumioxazin applied preplant in sorghum ( Sorghum bicolor (L.) Moench) provided 92 to 100% control (Grichar 2006) while s aflufenacil has been shown to be effective on rosette and flowering ragweed parthenium (Odero 2012). Parsons and Cuthbertson (2001) reported that ragweed parthenium was susceptible to imazapyr, oxadiazon, oxyfluorfen, pendimethalin, and thiobencarb and recommended atrazine + 2,4 D, picloram + 2,4 D, dicamba, and hexazinone as the most cost effective options for control in noncrop areas. There is a potential for use of broadleaf herbicides such as aminocyclopyrachlor, chlorsulfuron, aminopyralid, clopyralid, fomesafen, dimethenamid P, imazapic, mesotrione, and par aquat for control of ragweed parthenium in noncrop areas in the EAA. Therefore, the objective of this study was to determine the efficacy of herbicides with different modes of action commonly used in cultivated and noncrop areas for broadleaf weed control on rosette and flowering ragweed parthenium in the EAA. Materials and Methods Field Study Field studies were conducted in 2012 at two locations ( 26. 53 latitude and 80. 49 longitude for location 1; 26. 53 latitude, and 80.45 longitude for location 2) approxi mately 2.25 km apart at the Hillsboro Sugar Farm near Belle Glade, FL. Both locations had heavy ragweed parthenium infestation along canals adjacent to sugarcane fields. The experiment was arranged in a randomized complete block design with four replicatio ns

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30 of each treatment. Plots were 3 m wide by 6 m long at both locations. Herbicide treatments, rates (0.5 and 1.0 labeled use rate), and mode of action are listed in Table 2 1. A nontreated control was included for comparison. Nonionic surfactant (Prefere nce, Winfield Solutions, LLC., St. Paul, MN 55164 ), methylated seed oil (Destiny HC, Winfield Solutions, LLC., St. Paul, MN 55164 ) or crop oil concentrate (Prime Oil, Winfield Solutions, LLC., St. Paul, MN 55164 ) were used as adjuvants for the different he rbicides (Table 2 1). Herbicide t reatments were applied on May 31 and June 15, 2012 at location 1 and 2, respectively All plants were flowering and ranged in height between 84 and 92 cm All herbicides were applied using a CO 2 pressurized backpack spraye r calibrated to deliver 187 L ha 1 at 276 kPa Visual evaluation of percent control was assessed at 3, 6 and 9 WAT using a scale of 0 to 100%, with 0 representing no control, and 100 representing complete control. All data were tested for normality using PROC UNIVARIATE procedure in SAS 9.2 (SAS 2009) Data were subjected to arcsin e square root transformation prior to ANOVA to evaluate treatment main effects as well as interactions. Data were combined across locatio n s when no significant location by treatment interaction occurred. Means normalize data; therefore non transformed data are presented. Greenhouse Study Greenhouse studies w ere conducted in 2012 at the University of Florida in Gainesville. Ragweed parthenium seeds were collected from Hillsboro Sugar Farm near Belle Glade, FL in 2012 and stored at 4 C prior to use in the experiment. Seeds were soaked for 24 hours and rinsed w ith tap water prior to planting in 450 cm 3 pots using

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31 commercial potting mixture (Fafard Mixes for Professional Use, Conrad Fafard Inc., Agawan, MA 01001) mixed with 10 g of 14 14 14 slow release fertilizer (Osmocote Smart Release Plant Food, Scotts Sierra Horticultural Products Company, Marysville, OH 43040). Ragweed parthenium was thinned to one plant per pot with similar sizes 14 days after emergence to obtain uniformity across all plants. Plants were kept in a greenhouse maintained at 33/24 C day/night temperatures under natural light and watered as needed to ensure that moisture was not a limiting factor. The experiment was arranged as a completely randomized design with four replications and repeated in time. The first and second experimental runs w ere planted on August 29, 2012 and September 26, 2012, respectively. Herbicides treatments and rates were similar to the field study (Table 2 1). Herbicides were applied using a moving nozzle spray chamber (Generation II Spray Booth, Devries Manufacturing Corp., Hollandale, MN 56045) calibrated to deliver 187 L ha 1 at 276 kPa on rosette ragweed parthenium averaging 25 cm in diameter. Applications were made on September 28, 2012 and October 27, 2012 for the first and second experimental runs, respectively. Rosette ragweed parthenium control was visually evaluated 21 days after treatment (DAT) using a scale of 0 to 100 with 0 being no control and 100 being complete plant death. Plants were harvested at soil level 21 DAT and dried in an oven for 72 hours at 60 C to obtain aboveground dry weight. Aboveground dry weight was expressed as a percent of the untreated control. Data was then expressed as percent aboveground dry weight reduction of rosette ragweed parthenium. Data were tested for normality using PROC UNIVARIATE procedure in SAS 9.2 (SAS 2009) and arcsine square root transformed prior to ANOVA to evaluate treatment

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32 main effects as well as interactions. Data were combined across experimental run when no significant experimental run by treatment interact ion occurred. Means were normalize data; therefore nontransformed data are presented. Results and Discussion Field Study A t reatment by location interaction was observed; therefore data were analyzed separately by location for each evaluation timing. There was significant herbicide treatment effect on flowering ragweed parthenium control 3 to 9 WAT. Saflufenacil + dimethenamid P and hexazinone were highly effecti ve and rapid in controlling flowering ragweed parthenium, providing 100% control at all rates and evaluation timings (Table 2 2). Odero (2012) reported that saflufenacil at 12.5 g ha 1 provided complete control of flowering ragweed parthenium 3 WAT. Safluf enacil applied alone has previously been shown to have good efficacy on broadleaf weed control. Geier et al. (2009) reported that saflufenacil at 6 to 30 g ha 1 provided >92% control of blue mustard ( Chorispora tenella (Pallas) DC), flixweed ( Descurainia s ophia (L.) Webb.), Palmer amaranth (Amaranthus palmeri S. Watts.), redroot pigweed (Amaranthus retroflexus L.), and tumble pigweed ( Amaranthus albus L.) 3 WAT Flixweed was controlled 94 to 99% by saflufenacil at 13 to 50 g ha 1 three WAT (Frihauf et al. 2 010). Saflufenacil has been used to achieve control of small sized weed species (Geier et al. 2009 ; Frihauf et al. 2010 ), but the results of this study demonstrate that saflufenacil was very efficient in controlling very tall flowering ragweed parthenium u p to 92 cm in height. Hexazinone is used to provide control of many annual, biennial, and perennial weeds. For example, hexazinone

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33 applied at 420 to 840 g ha 1 Capsella bursa pastoris L.) in alfalfa ( Medico s ativa L.) (Wilson and Orloff 2008). Aminocyclopyrachlor + chlorsulfuron and aminopyralid initially provided 75 to 94% control of flowering ragweed parthenium 3 WAT. By 6 WAT, both herbicides had provided complete control of flowering ragweed parthenium. Am inocyclopyrachlor and aminopyralid are pyridine based herbicides used for broadleaf weed control in noncrop areas. Reed et al. (2013) reported >90% control of Virginia buttonweed ( Diodia virginiana L.), a problematic broadleaf weed in noncrop areas with se quential application of aminocyclopyrachlor at 110 g ha 1 Aminopyralid has been shown to provide effective control of yellow starthistle ( Centaurea solstitialis L.) and Canada thistle ( Cirsium arvensis L. Scop.) (Enloe et al. 2007; Kyser et al. 2011). Clo pyralid, 2,4 D, and glufosinate controlled flowering ragweed parthenium 85 to 99% at 9 WAT at their labeled use rate. Ragweed parthenium control with 2,4 D has shown variable results ranging from 35 to 70% in flowering plants (Reddy et al. 2007; Singh et a l. 2004). Tamado and Milberg (2004) reported control ranging from 30 to 100% of biomass reduction using 1,440 g ha 1 of 2,4 D. Glufosinate has been shown to provide 80 to 89% control of flowering ragweed parthenium plants (Reddy et al. 2007; Singh et al. 2 004). Both rates of imazapic provided 75 to 91% control of flowering ragweed parthenium 6 WAT. At 9 WAT, imazapic at 5.6 g ha 1 provided 93% control at location 1 compared to 61% control at location 2. Fomesafen, imazethapyr, mesotrione, oxyfluorfen, and p araquat provided <48% control of flowering ragweed parthenium 9 WAT with the exception of the full rate of fomesafen at location 1. Similarly, Reddy et al. (2007) reported poor control of flowering ragweed parthenium with paraquat, acifluorfen, and

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34 clomazo ne. Acifluorfen is a protoporphyrinogen oxidase inhibitor like fomesafen and oxyfluorfen while clomazone is a 4 hydroxyphenylpyruvate dioxygenase inhibitor like mesotrione. Similar to report by Odero (2012), glyphosate provided little to no control of flowering ragweed parthenium in the present study. In contrast, Reddy et al. (2007) reported 95% flowering ragweed parthenium control with glyphosate at 840 g ha 1 Singh et al. (2004) also reported that glyphosate at 2,700 to 5,400 g ha 1 provided >95% control of flowering ragweed parthenium. Greenhouse Study There was a significant experimental run by treatment interaction for percent dry weight re duction; therefore data were analyzed by experimental run. In the greenhouse, aminocyclopyrachlor + chlorsulfuron, aminopyralid, hexazinone, saflufenacil + dimethenamid P, 2,4 D provided 100% aboveground dry weight reduction of rosette ragweed parthenium a t 21 DAT (Table 2 3). Glufosinate provided 95 and 100% reduction in dry weight, regardless of the use rate. Similarly, Reddy et al. (2007) reported 93 to 95% control of rosette ragweed parthenium with glufosinate at 410 g ha 1 Clopyralid, flumioxazin, fo mesafen and imazapic provided 97 to 100% aboveground dry weight reduction of rosette ragweed parthenium regardless of the use rate in the first experimental run. However, aboveground dry weight reduction from application of flumioxazin and fomesafen ranged from 81 to 94% and 63 to 69% for clopyralid and imazapic for the second experimental run respectively Imazethapyr, mesotrione, oxyfluorfen, and paraquat provided 4 0 to 9 6 % dry weight reduction of rosette ragweed parthenium. Similar to the field study, g lyphosate provided little or no activity on rosette ragweed parthenium. Odero (2012) reported no dry weight reduction of rosette ragweed

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35 parthenium following application of glyphosate at up to 1,680 g ha 1 at 14 DAT. However, Reddy et al. (2007) reported 9 3 to 100% control of rosette ragweed parthenium with glyphosate at 840 g ha 1 at 21 DAT under field conditions These results show that saflufenacil + dimethenamid P and hexazinone can be used to provide rapid burndown and complete control of flowering ragweed parthenium in noncrop areas in the EAA. Aminocyclopyrachlor + chlorsulfuron and aminopyralid are also highly effective on flowering ragweed parthenium control. Aminocyclopyrachlor + chlorsulfuron, 2,4 D amine, aminopyralid glufosinate, hexazinone and saflufenacil + dimethenamid P also provided complete control of rosette ragweed parthenium. The herbicides that provided effective ragweed parthenium control included synthetic auxins, glutamine synthase inhibitors, protoporphyrinogen oxidase inhibit ors, and photosystem II inhibitors. Protoporphyrinogen oxidase inhibitors, flumioxazin and fomesafen can also be used as options for effective control of ragweed parthenium particularly early at the rosette stage of development. This information provides growers in the EAA with different herbicide options for control of ragweed parthenium with no response to glyphosate in noncrop areas. Furthermore, growers can use these different herbicide modes of action to develop herbicide rotation programs that can he lp prevent development of ragweed parthenium resistance to other herbicides. Due to the high efficacy of low use rate herbicides aminocyclopyrachlor and aminopyralid on ragweed parthenium, future research should be conducted to determine if rates lower tha n those used in this study can provide effective control.

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36 Table 2 1. Herbicide treatments, rates, and modes of action Herbicide treatment a Rate Mode of action c (g ai ha 1 ) A minocyclopyrachlor+chlorsulfuron + NIS 833+33 Synthetic auxin + ALS inhibition A minocyclopyrachlor+chlorsulfuron + NIS 166+66 Synthetic auxin + ALS inhibition 2,4 D amine 1120 Synthetic auxin 2,4 D amine 2240 Synthetic auxin A minopyralid + NIS 70 b Synthetic auxin A minopyralid + NIS 123 b Synthetic auxin Clopyralid 105 b Synthetic auxin Clopyralid 210 b Synthetic auxin Flumioxazin + NIS 53.5 PPO inhibition Flumioxazin + NIS 107 PPO inhibition Fomesafen + NIS 210 PPO inhibition Fomesafen + NIS 420 PPO inhibition Oxyfluorfen + NIS 224 PPO inhibition Oxyfluorfen + NIS 450 PPO inhibition Saflufenacil+dimethenamid P + MSO 40+350 PPO inhibition + Inhibition of VLCFA Saflufenacil+dimethenamid P + MSO 90+790 PPO inhibition + Inhibition of VLCFA Imazapic + NIS 2.8 b ALS inhibition Imazapic + NIS 5.6 b ALS inhibition Imazethapyr + NIS 35 b ALS inhibition Imazethapyr + NIS 70 b ALS inhibition Mesotrione + COC 52.5 Inhibition of HPPD Mesotrione + COC 105 Inhibition of HPPD Glyphosate 420 b EPSPS inhibition Glyphosate 840 b EPSPS inhibition Glufosinate 127 Glutamine synthase inhibition Glufosinate 254 Glutamine synthase inhibition Paraquat + NIS 420 Photosystem I inhibition Paraquat + NIS 840 Photosystem I inhibition Hexazinone 560 Photosystem II inhibition Hexazinone 1120 Photosystem II inhibition a Abbreviations: COC, crop oil concentrate at 1.0% v/v, MSO, methylated seed oil at 1.0% v/v; NIS, nonionic surfactant at 0.25% v/v. b Herbicide rates are listed in g ae ha 1 c Abbreviations: ALS, acetolactate synthase ; PPO, protoporphyrinogen oxidase; VL CFA, very long chain fatty acids; HPPD, 4 hydroxyphenylpyruvate dioxygenase ; EPSPS, 5 enolpyruvylshikimate 3 phosphate synthase.

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37 Table 2 2. Flowering ragweed parthenium control at locations within the EAA, Belle Glade, FL in 2012 Herbicide treatment a Weeks after treatment c Rate 3 6 9 ( g ai ha 1 ) L1 L2 L1 L2 L1 L2 --------------------------% -------------------------A minocyclopyrachlor + chlorsulfuron + NIS 83+33 88 75 100 100 100 100 A minocyclopyrachlor + chlorsulfuron + NIS 166+66 94 88 100 100 100 100 2,4 D amine 1120 45 56 28 89 40 93 2,4 D amine 2240 74 71 93 100 94 99 A minopyralid + NIS 70 b 80 76 100 100 100 100 A minopyralid + NIS 123 b 88 78 100 100 100 100 Clopyralid 105 b 48 35 53 68 50 69 Clopyralid 210 b 54 35 96 88 98 98 Flumioxazin + NIS 53.5 35 8 29 25 26 18 Flumioxazin + NIS 107 33 8 34 45 30 48 Fomesafen + NIS 210 33 35 26 64 20 55 Fomesafen + NIS 420 58 59 70 59 74 45 Oxyfluorfen + NIS 224 11 2 13 23 13 29 Oxyfluorfen + NIS 450 17 14 18 49 23 49 Saflufenacil + dimethenamid P + MSO 40+350 100 100 100 100 100 100 Saflufenacil + dimethenamid P + MSO 90+790 100 100 100 100 100 100 Imazapic + NIS 2.8 b 69 53 75 81 75 66 Imazapic + NIS 5.6 b 79 51 91 84 93 61 Imazethapyr + NIS 35 b 48 24 33 23 45 25 Imazethapyr + NIS 70 b 45 33 24 33 20 14 Mesotrione + COC 52.5 14 13 15 49 20 48 Mesotrione + COC 105 13 7 20 39 26 35 Glyphosate 420 b 5 0 15 0 23 0 Glyphosate 840 b 9 0 26 10 18 1 Glufosinate 127 60 84 40 79 48 75 Glufosinate 254 86 96 86 91 93 85 Paraquat + NIS 420 19 4 24 19 25 10 Paraquat + NIS 840 10 7 15 30 18 10 Hexazinone 560 100 100 100 100 100 100 Hexazinone 1120 100 100 100 100 100 100 Untreated check 0 0 0 0 0 0 LSD (0.05) 16 13 23 22 26 30 a Abbreviations: COC, crop oil concentrate at 1.0% v/v, MSO, methylated seed oil at 1.0% v/v; NIS, nonionic surfactant at 0.25% v/v. b Herbicide rates are listed in g ae ha 1 c L1 is location 1; L2 is location 2.

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38 Table 2 3. Percent dry weight reduction of greenhouse grown ragweed parthenium in response to herbicide treatments at 21 days after treatment Herbicide treatment a Rate Run 1 Run 2 ( g ai ha 1 ) ---------------------% --------------------------A minocyclopyrachlor + chlorsulfuron + NIS 83+33 100 100 A minocyclopyrachlor + chlorsulfuron + NIS 166+66 100 100 2,4 D amine 1120 100 100 2,4 D amine 2240 100 100 A minopyralid + NIS 70 b 100 100 A minopyralid + NIS 123 b 100 100 Clopyralid 105 b 100 69 Clopyralid 210 b 100 69 Flumioxazin + NIS 53.5 100 92 Flumioxazin + NIS 107 100 83 Fomesafen + NIS 210 100 81 Fomesafen + NIS 420 100 94 Oxyfluorfen + NIS 224 96 47 Oxyfluorfen + NIS 450 77 57 Saflufenacil + dimethenamid P + MSO 40+350 100 100 Saflufenacil + dimethenamid P + MSO 90+790 100 100 Imazapic + NIS 2.8 b 100 65 Imazapic + NIS 5.6 b 97 63 Imazethapyr + NIS 35 b 69 40 Imazethapyr + NIS 70 b 79 49 Mesotrione + COC 52.5 80 60 Mesotrione + COC 105 90 67 Glyphosate 420 b 13 13 Glyphosate 840 b 0 0 Glufosinate 127 100 95 Glufosinate 254 100 95 Paraquat + NIS 420 60 60 Paraquat + NIS 840 62 69 Hexazinone 560 100 100 Hexazinone 1120 100 100 Untreated check 0 0 LSD (0.05) 12 14 a Abbreviations: COC, crop oil concentrate at 1.0% v/v, MSO, methylated seed oil at 1.0% v/v; NIS, nonionic surfactant at 0.25% v/v. b Herbicide rates are listed in g ae ha 1

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39 CHAPTER 3 ALLELOPATHIC EFFECTS OF PARTHENIUM HYSTEROPHORUS L. EXTRACTS ON GERMINATION OF DIFFERENT CROPS G ROWN IN THE EVERGLADES AGRICULTURAL AREA Allelopathy Ragweed parthenium ( Parthenium hysterophorus L.) is an annual weed in the Asteraceae family native to tropical and subtropical America common in the Everglades Agricultural Area (EAA) of south Florida. It is typically associated with noncrop areas such as canals, ditch banks, and field edges in the EAA. Invasion of cultivated fields by ragweed parthenium has recently been noted by several growers in the EAA. The EAA is dominated by sugarcane ( Saccharum L. spp. hybrids) grown in rotation with vegetables and rice ( Oryza sativa L .) during the sugarcane fallow period. The main vegetables grown in the EAA include sweet corn ( Zea mays L.), green bean ( Phaseolus vulgaris L.), lettuce ( Lactuca sativa L.), and radish ( Raphanus sativus L.) cultivated in approximately 21,000 ha (Christian Miller, personal communication). Rice is cultivated in 6,100 ha in the EAA (Ron Rice, personal communication). Interference of ragweed parthenium via competition can adversely affect crop yield by removing or reducing essential factors for crop growth s uch as water, light, and nutrients. Tamado et al. (2002) reported that competition of three ragweed parthenium plants m 2 resulted in 67% yield reduction in sorghum ( Sorghum bicolor (L.) Moench) and up to 97% yield reduction at higher densities. Ragweed pa rthenium has been reported to interfere with several crops, weed species, and trees through addition of phytotoxic allelochemicals to the environment (Kanchan and Jayachandra 1979; Mersie and Singh 1987; Swaminathan et al. 1990; Batish et al. 2002; Tefera 2002; Singh et al. 2003; Singh et al. 2005; Wakjira et al. 2005; Belgeri et al. 2011; Mishra and Nautiyal

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40 2012). Allelopathy in ragweed parthenium is attributed mainly to parthenin, a potent phytotoxic sesquiterpene lactone that can constitute up to 8% of (Rodriguez et al. 1976). Allelochemicals play an important role in regulating the structure of plant communities by impacting plant dominance and productivity in both natural and agricultural ecosystems (Kohli et al. 2001). For example, allelochemicals from ragweed parthenium leaf or root tissue added to the field resulted in reduced germination, number of nodules, and root biomass of green bean and cowpea ( Vigna sinensis L.) (Kanchan and Jayachandra 1979). This study also showed a reduct ion in branching and yield of tomato ( Lycopersicum esculentum Mill.) grown in plots where ragweed parthenium leaf tissue was added. Ragweed parthenium has been reported to exhibit autotoxicity (Kumari and Kohli 1987). However, survival and colonization of ragweed parthenium probably occurs because either the allelochemicals do not escape from the environment fast enough for a critical concentration to be reached or do not persist for sufficiently long time to affect the species (Kumari and Kohli 1987). All elochemicals produced by ragweed parthenium can potentially adversely affect both emergence and growth of crop species cultivated in the EAA. Previous studies on allelopathic effect of ragweed parthenium on crops have been conducted using flower, leaf, ste m, and root extracts of ragweed parthenium (Mersie and Singh 1987; Tefera 2002; Singh et al. 2003; Singh et al. 2005; Wakjira et al. 2005; Belgeri et al. 2011). For example, Mersie and Singh (1987) reported that extracts from different parts of the ragweed parthenium resulted in allelopathic inhibition of root growth of field corn, ryegrass ( Lolium multiflorum Lam.), wheat ( Triticum aestivum L.), and soybean ( Glycine max (L) Merr.), but the effects were species and extract concentration

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41 dependent. Because r agweed parthenium present in fields get s incorporated into the soil when fields are cultivated, research on the allelopathic potential of the whole plant (flowers, leaves, stems, and roots) on germination of crops grown in the EAA is needed. Therefore, the objective of this study was to determine the allelopathic effect of an aqueous ragweed parthenium extract on germination of green bean, sweet corn, radish, lettuce, and rice cultivated in the EAA. Materials and Methods Whole Plant Aqueous Extraction The effect of whole ragweed parthenium plant residue on germination of crops (green bean, sweet corn, radish, lettuce, and rice) grown in the EAA was evaluated in growth chamber experiments at the University of Florida, Gainesville in 2013. Ragweed parthenium plants with flowers, seeds, leaves, stems, and roots were collected from Hillsboro Sugar Farm near Belle Glade, FL (26 53 latitude and 80. 43 longitude) in 2012. Whole plants were oven dried at 60 C for 5 days and finely ground using a Thomas 4 Wiley mill (Thomas Scientific, Swedesboro, NJ 08085). The ground powder was placed in polythene bags and stored in darkness at 2 C prior to use. Eight percent (w/v) aqueous extract solution of ragweed parthenium was prepared by mixing 60 g of the ground powder wi th 750 ml of distilled water in a dark container and kept at room temperature over a 24 hour period. The extract was filtered by vacuum filtration using a Buchner funnel and flask with Whatman No. 1 filter paper (Whatman No. 1 filter paper, Whatman Interna tional Ltd., Maidstone, U.K.) and stored in a dark container at 2 C prior to use. Seven treatment solutions of 0.0625, 0.125, 0.25,

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42 0.5, 1.0, 2.0 and 4.0% were prepared by diluting the 8.0% aqueous solution with distilled water. A control treatment consi sting of distilled water was also included. Germination Assays each species were pla ced on 10 cm diameter Petri dishes lined with Fisherbrand P8 filter paper (Fisherbrand P8 filter paper, Fisher Scientific, Pittsburgh, PA 15275) and moistened with 10 ml of each treatment of the aqueous extract solutions. Petri dishes were sealed with Para film paper (Parafilm M Laboratory Film, Pechiney Plastic Packaging, Chicago, IL 60631) to prevent desiccation and placed in growth chambers with day/night temperature of 26 C and 16 hour photoperiod. Germination was recorded 7 days after initiation of th e experiment. Seeds were considered germinated when the radicle was visible for green bean, sweet corn, radish, and lettuce. Rice was considered germinated when the coleoptile was visible. Radicle length for green bean, sweet corn, radish, and lettuce were measured 7 days after germination. Similarly, shoot length of rice was measured 7 days after germination because reduced oxygen conditions may cause the coleoptile to emerge before the root in rice (Moldenhauer and Slaton (2011).The experiment was arrange d as a completely randomized design with four replications of each treatment for each plant species and repeated twice. The first run and second experimental runs were planted on July 21, 2013, and August 4, 2013, respectively. Data from sweet corn and gre en bean are not presented because of poor germination.

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43 Statistical Analysis All data were tested for normality using PROC UNIVARIATE procedure in SAS 9.2 (SAS 2009) and arcsine square root transformed. Analysis of variance was conducted and data combine d across experimental run when no significant experimental run by treatment interaction occurred. Transformation did not normalize data; therefore nontransformed data are presented. The relationship between germination and radicle growth of radish, lettuce and shoot length of rice with ragweed parthenium aqueous extract were described using nonlinear and linear regression models. Linear and nonlinear regression models were fitted using the nlme and drc packages of R, respectively (Ritz and Streibig 2005; R Development Core Team 2009; using the qpcR package of R (Ritz and Spiess 2008). The two parameter expon ential decay model (Equation 1) was used to describe the relationship between radish and lettuce germination, and ragweed parthenium aqueous extract: Y = d exp ( x/b ) [1] where Y is the response (percentage germination or radicle length), x is t he aqueous extract solution concentration, d is upper limit or asymptote of the fitted curve, and b is the slope of the fitted curve. Linear regression model (Equation 2) was used to describe the relationship between rice germination and ragweed partheniu m aqueous extract: Y = a + bx [2] where Y is the response (percentage germination or radicle length), x is the aqueous extract solution concentration, a is the intercept of the fitted line, and b is the slope of the fitted line.

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44 Radish and lettu ce radicle length relationship with ragweed parthenium aqueous extract were described using Equation 2. The four parameter Brain Cousens model (Equation 3) obtained by extending the three parameter log logistic model to take into account the inverse u shap ed hormesis effect was used to describe the relationship between rice shoot length and ragweed parthenium aqueous extract: Y = d + fx / 1 + exp{ b [log( x ) log( e )]} [3] where Y is the response ( shoot length), x is the aqueous extract solution concentration, b is the slope of the curve after the maximal hormetic effect, d is the upper limit or asymptote, e is the lower bound of the aqueous dose causing 50% response, and f is the theoretical upper bond of the horm esis effect (the rate of growth stimulation at aqueous extract solution concentration close to zero). In the Brain Cousens model unlike the three parameter log logistic mode l the parameter e is no longer the inflection point and b losses its interpretation as relative slope at the inflection point (Cedergreen et al. 2005). Results and Discussion Seed Germination There was significant experimental run by treatment interaction for lettuce and radish germination but not for rice. T herefore, data were analyzed separately by experimental run for lettuce and radish, and pooled across experimental runs for rice. The two parameter exponential decay model (Equation 1) provided the best fit to model lettuce and radish seed germination as a function of ragweed parthenium aqueous extract concentration (Figures 3 2A and 3 3A) The linear regression model (Equation 2) provided the best fit to describe rice germination as a function of ragweed parthenium

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45 aqueous extract concentration (Figure 3 1A). Model parameters are listed in Table 3 1 and 3 2. There was reduction in germination of the three crops as ragweed parthenium aqueous extract concentration increased. The ragweed parthenium aqueous extract concentration required to provide 50% reduc tion in germination (ED 50 ) was estimated to be 0.72 and 1.15% for lettuce, and 0.87 and 0.39% for radish, for experimental run 1 and 2, respectively. The ED 50 for rice was predicted to be 0.09% of ragweed parthenium aqueous extract concentration. Variable response of different crops to ragweed parthenium aqueous extract has been previously reported (Mersie and Singh 1987; Kohli et al. 1996; Belz et al. 2007). Kohli et al. (1996) reported that pigeon pea ( Cajanus cajan L. Millsp.) and cowpea ( Vigna unguicula ta L. Walp.) were highly susceptible to leaf leachates of ragweed parthenium, resulting in 84 and 100% reduction in germination respectively, followed by onion ( Allium cepa L.), radish, and pepper ( Capsicum annuum L.) with 67, 50, and 45% reduction in germination, respectively. In the same study, leachates of ragweed parthenium reduced germination of Egyptian clover ( Trifolium alexandrinum L.) and alfalfa ( Medicago sativa L.) by 0 and 5% respectively Similarly, Belz et al. (2007) reported that the concentration of parthenin required to provide 50% reduction in germination of lettuce and barnyardgrass ( Echinochloa crus galli L.) were 450 and 645 g of parthenin ml 1 of deionized water, respectively. W akjira et al. (2005) reported germination reduction of up to 100% in lettuce using aqueous extracts of flowers, leaves, stems, and roots with concentrations of 5, 10 and 15% w/v. In contrast, germination of wheat was not affected by parthenin concentration ranging from 0.02 to 0.1 mg of parthenin ml 1 of distilled water (Batish et al. 1997). Research has shown that flowers followed by leaves have more allelopathic

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46 effect than stem and roots of ragweed parthenium (Kanchan and Jayachandra 1979; Mersie and Sin gh 1986; Pandey 1994; Tefera 2002; Wakjira 2005). Rodriguez et al. (1976) reported that up to 8 and 5% dry weight of flowers and leaves of ragweed parthenium, respectively w h ere sesquiterpene lactones in which parthenin was the major component. This can be related to the higher allelopathic effects of flowers compared to the leaves. Radicle and Shoot Growth There was a significant experimental run by treatment interaction for lettuce and radish radicle growth, and rice shoot growth. Therefore, data were an alyzed separately by experimental run for each species. The linear regression model (Equation 2) provided the best fit to describe lettuce and radish radicle length as a function of ragweed parthenium aqueous extract concentration (Figure 3 2B and 3 3B). T he four parameter Brain Cousens model (Equation 3) provided the best fit to model rice shoot length as a function of ragweed parthenium aqueous extract concentration (Figures 3 1B). Model parameters are listed in Table 3 1 and 3 2. Similar to germination, radicle length reduction was observed as the concentration of the ragweed parthenium aqueous extract solution increased for lettuce and radish. However, there was a biphasic relationship between rice shoot length and ragweed parthenium aqueous extract sol ution. Low concentrations of the aqueous extract solution resulted in a hormetic effect on rice shoot growth. The hormetic effect was higher for experimental run 1 ( f = 9.10) compared to 2 ( f = 6.82). Allelochemicals can result in hormetic responses in pla nt species (Duke 2011). Low concentration of parthenin has been shown to have a hormetic effect on wheat, barnyardgrass, and weeping lovegrass

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47 ( Eragrostis curvula (Schrad.) Nees) by increasing root length (Batish et al. 1997; Belz et. al 2007). Similarly, pronounced hormesis at low doses of parthenin has been reported on mustard ( Sinapis arvensis L.) and lettuce seedlings (Belz 2008; Belz and Cedergreen 2010). The concentration of ragweed parthenium aqueous extract that reduced shoot length by 50% (ED 50 ) wa s 3.50 and 5.89% for the first and second experimen tal runs for rice, respectively. Pandey (1994) reported an increase in length and weight of roots of rice seedlings grown for 10 days in aqueous solutions of ragweed parthenium residue with concentrations of 0.10 and 0.25% compared to the untreated control. Similar observations have been reported in wheat, barnyardgrass, weeping lovegrass, and mustard (Batish et al. 1997; Belz et al. 2007; Belz 2008). The ED 50 values for lettuce radicle length were 0.20% fo r both experimental runs, and 0.21 and 0.23% for the first and second experimental runs, respectively for radish r adicle length. These results indicate that rice was 18.0 and 29.45 fold more tolerant than lettuce and 17.1 and 25.6 fold more tolerant than radish to residues of ragweed parthenium. In contrast, Belz et al. (2007) reported that lettuce roots were 1.5 to 3.9 f old more tolerant to aqueous extracts of ragweed parthenium when compared to barnyardgrass, weeping lovegrass, teff ( Eragrostis tef (Zuccagni) Trotter), and tropical whiteweed ( Ageratum conyzoides L.). Root growth of velvetleaf ( Abutilon theophrasti Medik. ) and ryegrass were reduced 75 and 15% in 4% aqueous solution of ragweed parthenium residues, respectively, indicating that broadleaf plants are more susceptible than grasses to ragweed parthenium allelochemicals (Mersie and Si n gh 1986). These results sh ow that ragweed parthenium aqueous extracts may affect germination of crops cultivated in the EAA. Therefore it is important to control ragweed

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48 parthenium before it encroaches into cultivated fields as it can have negative effects on crops in the EAA. Furt hermore, the results indicate that members of the Poaceae family such as rice or commercial sod are an option to consider for cultivation in areas with a history of high infestation levels of ragweed parthenium because they are more tolerant to the plant allelochemicals

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49 Table 3 1. Parameter estimates and standard errors (in parenthesis) for the two parameter exponential decay model (Equation 1) and the four parameter Brain Cousens model (Equation 3). Crop Response Run Model parameters (SE) b d e f ED 50 Lettuce Germination 1 1.04 (0.11) 87.05 (2.93) --0.72 (0.08) 2 1.67 (0.16) 92.23 (2.61) --1.15 (0.11) Radish Germination 1 0.87 (0.10) 84.94 (3.33) --0.60 (0.07) 2 0.39 (0.04) 93.70 (3.97) --0.27 (0.03) Rice Shoot length 1 3.37 (0.47) 28.56 (1.23) 2.52 (0.32) 9.10 (3.50) 3.59 (0.24) 2 3.04 (0.58) 23.28 (1.15) 3.61 (0.57) 6.82 (2.62) 5.89 (0.55) a ED 50 is equivalent to the rate required to cause 50% response. Table 3 2. Parameter estimates and standard errors (in parenthesis) for the linear regression model (Equation 2). Crop Response Run Model parameters (SE) R 2 ED 50 a b Rice Germination 1+2 76.14 (3.09) 6.38 (0.53) 0.71 0.09 Lettuce Radicle length 1 8.50 (0.57) 1.21 (0.16) 0.62 0.20 2 10.67 (0.53) 1.63 (0.17) 0.73 0.20 Radish Radicle length 1 10.03 (0.09) 1.65 (0.30) 0.47 0.21 2 8.50 (1.11) 1.44 (0.36) 0.32 0.23 a ED 50 is equivalent to the rate required to cause 50% response.

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50 Figure 3 1. Effect of ragweed parthenium aqueous extract on A) rice germination combined over two experimental runs, and B) shoot length for experimental runs 1 and 2.

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51 Figure 3 2. Effect of ragweed parthenium aqueous extract on A) radish germin ation for experimental runs 1 and 2, and B) radicle length for experimental runs 1 and 2.

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52 Figure 3 3. Effect of ragweed parthenium aqueous extract on A) lettuce germination for experimental runs 1 and 2, and B) radicle length for experimental runs 1 and 2.

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53 CHAPTER 4 SUMMARY Glyphosate no longer provides control of ragweed parthenium ( Parthenium hysterophorus L.) in fallow fields and in noncrop areas in the Everglades Agricultural Area (EAA). Furthermore, the use of glyphosate in this region opens up niches where ragweed parthenium is able to colonize and further proliferate because of reduced interference fro m other weeds. Dose response experiments using ragweed parthenium known to be susceptible to glyphosate from Mississippi and ragweed parthenium know n to survive glyphosate application from the EAA were able to confirm ragweed parthenium resistance to glyph osate in the EAA. However, reduced absorption and translocation were not the mechanism s of ragweed parthenium from the EAA resistance to glyphosate. Dose response experiments showed that ragweed parthenium from the EAA was 40 to 67 fold less sensitive to g lyphosate compared to the susceptible biotype from Mississippi. Out of 15 herbicides evaluated under field conditions, aminocyclopyrachlor + chlorsulfuron, aminopyralid, hexazinone, and saflufenacil + dimethenamid P provided complete control of flowering ragweed parthenium in the EAA at between 3 to 9 weeks after treatment (WAT). Furthermore, hexazinone and saflufenacil + dimethenamid P showed the most rapid burndown of flowering ragweed parthenium by providing complete control 3 WAT. Glufosinate and 2,4 D were also able to provide complete control of ragweed parthenium at the rosette stage of development. Flumioxazin and fomesafen provided acceptable control (>80%) of ragweed parthenium at the rosette stage. These herbicides can be grouped in four modes of action which include synthetic auxins, glutamine synthase inhibitors, protoporphyrinogen oxidase inhibitors, and

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54 photosystem II inhibitors. These results provide growers in the EAA with information to develop herbicide rotational programs that can help pr event development of ragweed parthenium resistance to other herbicides. If left uncontrolled, ragweed parthenium can encroach into cultivated fields and interfere with crop germination, growth, and development. Allelopathic effect of ragweed parthenium on germination of rice ( Oryza sativa L.), lettuce ( Lactuca sativa L.), and radish ( Raphanus sativus L.) was evaluated 7 days after exposure to aqueous extract solutions obtained by mixing whole plant tissue with distilled water in a weight by volume basis A ll crops exhibited germination and radicle or shoot growth reductions as the concentration of the aqueous extract solution of ragweed parthenium increased. However, the reduction in germination and radicle or shoot growth was species dependent. Results sho wed that rice was the most tolerant crop followed by lettuce to ragweed parthenium aqueous extract solution. Radish was the most susceptible to ragweed parthenium aqueous extract solution. This information can help EAA growers with decision making on suita ble crops to grow in fields with history of heavy ragweed parthenium infestation, thereby minimizing potential economic losses that might result from the negative effect of ragweed parthenium allelochemicals.

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55 LIST OF REFERENCES Amrhein N, Deus B, Gehrke Steinrcken HC (1980) The site of inhibition of the shikimate pathway by glyphosate II. Interference of glyphosate with chorismate formation in vivo and in vitro Plant Physiol 66:830 834 Baerson SC, Rodriguez DJ, Tran M, Feng Y, Biest NA, Dill GM (2002) Glyphosate r esistant g oosegrass Identi fication of a mutation in the target enzyme 5 enolpyruvylshikimate 3 phoshate s ynthase. Plant Physiol 129:1265 1275 Batish DR, Kohli RK, Sing HP, Saxena DB (1997) Studies on herbicidal activity of parthenin, a constituent of Parthenium hysterophorus towards bill y goat weed ( Ageratum conyzoides ). Curr Sci 73:369 371 Batish DR, Singh HP, Kohli RK Saxena DB Kaur S (2002) Allelopathic effects of parthenin against two weedy species, Avena fatua and Bidens pilosa Environ Exp Bot 47:149 155 Bekeko Z (2013) Effect of urea and common salt (NaCl) treated glyphosate on parthenium weed ( Parthenium hysterophorus L.) at Western Hararghe zone, Ethiopia. Afr J Agric Res 8 :30 36 3041 Belgeri AM, Navie SC, Adkins ST (2011) Screening parthenium weed ( Parthenium hysterophorus L.) seedlings for their allelopathic potential. Pages 13 17 in Proceedings of the 23 rd Asian Pacific Weed Sci ence Soci ety Conf erence. Queensland, Australia Belz RG (2008) Stimulation versus inhibition bioactivity of parthenin, a phytochemical for Parthenium hysterophorus L. Dose response 9:80 96 Belz RG, Cedergreen N (2010) Parthenin hormesis in plants depends on growth conditions. Environ Exp Bot 69:293 301 Be lz RG, Reinhardt CF, Foxcroft LC, Hurle K ( 2007 ) Residue allelopathy in Parthenium hysterophorus L. Does parthenin play a leading role? Crop Prot 26:237 245 Brewer CE, Oliver LR (2009) Confirmation and resistance mechanism in glyphosate resistant common ragweed ( Ambrosia artemisiifolia ) in Arkansas. Weed Sci 57:567 573 Cedergreen N, Ritz C, Streibig JC (2005) Improv ed empirical models describing H ormesis. Environ Toxicol Chem 24:3166 3172 Dhileepan K (2012) Reproductive variation in naturally occ urring populations of the weed Parthenium hysterophorus ( Astera ceae ) in Australia. Weed Sci 60:571 576

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56 Duke SO (2011) Phytochemical phytotoxins and hormesis a commentary. Dose response 9:76 78 Enloe SF, Lym FG, Wilson R, Westra P, Nissen S, Beck G, Moe ching M, Peterson V, Masters RA, Halstvedt M (2007) Canada thistle ( Cirsium arvense ) control with aminopyralid in range, pasture, and noncrop areas. Weed Technol 21:890 894 Frihauf JC, Stahlman PW, Geier PW (2010) Winterwheat and weed response to posteme rgence saflufenacil alone or in mixtures. Weed Technol 24:262 268 Gaines TA, Zhang W, Wang D, Bukun B, Chisholm ST, Shaner DL, Nissen SC, Patzoldt WL, Tranel PJ, Culpepper AS, Grey TL, Webster TM Vencill WK, Sammons RD, Jiang J, Preston C, Leach JE, Westra P (2010) Gene amplification confers glyphosate resistance in Amaranthus palmeri P Natl Acad Sci USA 107:1029 1034 Ge X, DA, Ackerman JJH, Sammons RD (2010) Rapid vacuolar sequestration: the horseweed glyphosate resis tance mechanism. Pes t Manag Sci 66:345 348 Geier PW, Stahlman PW, Charvat LD (2009) Dose response of five broadleaf weeds to saflufenacil. Weed Technol 23:313 316 Gomez C (2009) Resistance mechanism of Parthenium hysterophorus L. to glyphosate Ph.D. dissertation. Valle del Colombia 203 p Grichar, WJ (2006) Weed control and grain sorghum tolerance to flumioxazin. Crop Prot 25:174 177 Heap I. (2013) The International Survey of Herbicide Resis tant Weeds. Available at www.weedscience.org Accessed October 12 2013. Jasieniuk M, Ahmad R, Sherwood AM, Firestone JL, Perez Jones A, Lanini WT, Mallory Smith C, Stednick Z (2008) Glyphosate resistant Italian ryegrass ( Lolium multiflorum ) in California: distribution, response to glyphosate, and molecular evidence for an altered target enzyme. Weed Sci 56:496 502 Jayachandra (1971) Parthenium weed in Mysore state and its contr ol. Curr Sci 21:568 569 Joshi S (1991) Biocontrol of Parthenium hysterophorus L. Crop Prot 10:429 431 Kanchan S, Jayachandra ( 1 979) Allelopathic effects of Parthenium hysterophorus L. III. Inhibitory effects of the weed residue. Plant Soil 53:37 47.

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57 Kirkwood RC, Hetherinton R, Reynolds TL, Marshall G (2000) Absorption localization, translocation and act ivity of glyphosate in barnyardgrass ( Echinochloa crus galli (L) Beauv): influence of herbicide and surfactant concentration. Pest Manag Sci 56:359 367 Koger CH, Reddy KN, (2005) Role of absorption and translocation in the mechanism of glyphosate resistan ce in horseweed ( Conyza Canadensis ). Weed Sci 53:84 89 Khan H Marwat KB, Hassan G, Khan MA (2012) Chemical control of Parthenium hysterophorus L. at different growth stages i n non cropped area. Pak J Bot 44:1721 1726 Kohli RK, Rani D, Singh HP, Kumar S (1996) Response of crop seeds towards the leaf leachates of Parthenium hysterophorus L. Indian J Weed Sci 28:104 106 Kohli RK, Singh HP, Batish DR (2001) Allelopathy in Agroecosystems. New York, NY: Food Products Press. 447 p Kumari A, Kohli K (1987) Autotoxicity of ragweed parthenium ( Parthenium hysterophorus L.). Weed Sci 35:629 632 Kyser GB, Peterson V, Orloff SB, Wright SD, Ditomaso JM (2011) Control of yellow starthistle ( Centaurea solstitialis ) and coast fiddlene ck ( Amsinckia menziesii ) with aminopyralid. Invasive Plant Sci Manage 4:341 348 Lorraine Colwill DF, Powles SB, Hawkes TR, Hollinshead PH, Warner SAJ, Preston C (2003) Investigation into the mechanism of glyphosate resistance in Lolium rigidum Pestic Biochem Phys 74:62 72 McFadyen RC (1992) Biological control against parthenium weed in Australia. Crop Prot 11:400 407 Mersie W, Singh M ( 1987 ) Allelopathic effect of p arthenium ( Parthenium hysterophorus L.) e xtract and residue on some agronomic crops a nd wee ds. J Chem Ecol 13:1739 1747 Mishra S, Nautiyal CS (2012) Reducing the allelopathic effects of Parthenium hysterophorus L. on wheat ( Triticum aestivum L.) by Pseudomonas putida Plant. Growth Regul 66:155 165 Moldenhauer KK, Slaton NA (2001) Rice g rowth and development. Pages 7 14 in Slaton N.A., ed. Rice Production Handbook MP 192. Little Rock, AR: University of Arkansas Cooperative Extension Service.

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58 Navie SC, McFadyen RE, Panetta FD, Adkins SW ( 1996 ) The biology of Australian weeds 27. Parthenium hysterophorus L. Plant Prot Q 11:76 88 Navie SC, Panetta FD McFadyen RE, Adkins SW (1998) Behaviour of buried and surface sown seeds of Parthenium hysterophorus Weed Res 38:335 341 Navie SC, Panetta FD, McFadyen RE, Adkins SW (2004) Germinab le soil seedbanks of central Queensland rangelands invaded by the exotic weed Parthenium hysterophorus L. Weed Biol Manag 4:154 167 Norsworthy JK, Jha P, Steckel LE, Scott RC ( 2010 ) Confirmation and control of glyphosate resistant g iant r agweed ( Ambrosia trifida ) in Tennesse. Weed Technol 24:64 70 Odero DC (2012) Response of r agweed p arthenium ( Parthenium hysterophorus ) to saflufenacil and glyphosate. Weed Technol 26:443 448 Pandey DK (1994) Inhibition of salvinia ( Salvinia molesta Mitchell) by partheniu m ( Parthenium hysterophorus L.). II. Relative effect of flower, leaf, stem, and root residue on salvinia and paddy. J Chem Ecol 20:3123 3131 Pandey D K Palni LMS, Joshi SC (2003) Growth, reproduction, and photosynthesis of r agweed p arthenium ( Parthenium hysterophorus ) Weed Sci 51:191 201 Parsons WT, Cuthhbertson EG (2001) Noxious weeds of Australia. 2nd edn Australia : CSIRO. p p 292 296 Perez Jones A, Park K, Polge N, Colquhoun J, Mallory Smith CA 2007. Investigating the mechanism of glyphosate resistance in Lolium multiflorum Planta 226:395 404 Picman J, Towers GHN (1982) Sesquiterpene lactones in various populations of Parthenium hysterophorus Bioc hem Syst Ecol 10:145 153 Pinheiro J, Bates D, Debroy S, Sarkar D, R Development Core Team (2013). nlme: Linear and Nonlinear Mixed Effects Models. R package version 3.1 113 Powles SB, Preston C (2006) Evolved glyphosate resistance in plants: b iochemical and genetic basis of resistance. Weed Technol 20:282 289 R Development Core Team ( 2009 ) R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna: Austria. ISBN 3 900051 07 9, URL http://www.r project.org/ Rajendru G, Rama Da s VS (1990 ) C 3 like carbon isotope discrimination in C 3 C 4 intermediate Alternanthera and Parthenium species. Curr Sci 59:377 379

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59 Reddy KN, Bryson CT (2005) Why r agwee d p arthenium is not a pernicious weed in continental USA. Pages 61 64 in Proceedings of the Second International Conference on Parthenium Management. Bangalore, India: Univ ersity of Agricultural Sciences Reddy KN, Bryson CT, Burke IC (2007) Ragweed Parthenium ( Parthenium hysterophorus ) control with p reemergence and p ostemergence herbicid es. Weed Technol 21:982 986 Reed TV, Yu J, and McCullough PE (2013) Aminocyclopyrachlor efficacy for controlling Virginia buttonweed ( Diodia virginiana ) and smooth crabgrass ( Digitaria ischaemum ) in tall fescue. Weed Technol 27:488 491 Ritz C, Spiess AN (20 08) qpcR: an R package for sigmoidal model selection in quantitative real time polymerase chain reaction analysis. Bioinformatics 24:1549 1551 Ritz C, Streibig JC ( 2005 ) Bioassay analysis using R. J Stat Sofw 12:1 22 Rodriguez E, Dillon MO, Mabry TJ, Mit chell JC, Towers GHN (1976) Dermatologically active sesquiterpene lactones in trichomes of Parthenium hysterophorus L. Experientia 32:236 238 [ SAS ] Statistical Analysis Systems (2009) Version 9.2 of the SAS System for Microsoft Windows. Cary, NC: SAS Inst itute Inc. Sandberg CL, Meggitt WF, Penner D (1980) Absorption, translocation and metabolism of 14 C glyphosate in several weed species. Weed Res 20:195 200 Schuster WS, Monson RK (1990) An examination of the advantages of C 3 C 4 intermediate photosynthesis in warm environments. Plant Cell Environ 13:903 912 Seefeldt SS, Jensen JE, Feurst EP (1995) Log logistic analysis of herbicide dose response relationship. Weed Technol 9:218 227 Shaner DL, Lindenmeyer RB, Ostlie MH (2012) What have the mechanisms of resistance to glyphosate taug ht us? Pest Manag Sci 68:3 9 Singh HP, Batish DR, Pandher JK, Kohli RK (2003) Assessment of allelopathic properties of Parthenium hysterophorus residues. Agr Ecosyst E nviron 95:537 541

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60 Singh HP, Batish DR, Pandher JK, Kohli RK (2005) Phytotoxic effects of Parthenium hysterophorus residues on three Brassica species. Weed Bi ol Manag 5:103 109 Singh S, Yadav A, Balyan RS, Malik RK, Singh M (2004) Control of r agweed p arthenium ( Parthenium hysterophorus ) an d associated wee ds. Weed Technol 18:658 664 Swaminathan C, Vinaya Rai RS, Sureshi KK (1990) Allelopathic effects of Parthenium hysterophorus on germination and seedling growth of a few multi purpose trees and arable crops. Int Tree Crops J 6:143 150 Tama do T, Ohlander L, Milberg P ( 2002 a) Interference by the weed Parthenium hysterophorus L. with grain sorghum: influence of weed density and duration of competition. Int J Pest Manage 48:183 188 Tamado T, Schtz W, Milberg P ( 2002 b) Germination ecology of t he weed Parthenium hysterophorus in eastern Ethiopia. Ann Appl Biol 140:263 270 Tamado T, Milberg P (2004) Control of parthenium ( Parthenium hysterophorus ) in grain sorghum ( Sorghum bicolor ) in the smallholder farming system in Eastern Ethiopia. Weed Technol 18:100 105 Tefera T (2002) Allelopathic effects of Parthenium hysterophorus extracts on seed germination and seedling growth of Eragrostis tef J Agron Crop Sci 188:306 310 [USDA] U.S. Department of Agriculture ( 2013 ) Plants Profile: Parthenium h ysterophorus L. http://plants.usda.gov/core/profile?symbol=PAHY Accessed October 12 2013. VanGessel MJ (2001) Glyphosate resistant horseweed from Delaware. Weed Sci 49:703 705 Wakelin AM Preston C (2006) Inheritance of glyphosate resistance in several populations of rigid ryegrass ( Lolium rigidum ) from Australia. Weed Sci 54:212 219 Wakjira M, Berecha G, Bulti B (2005) Allelopathic effects of Parthenium hysterophorus extracts on seed ger mination and seedling growth of lettuce. Tr op Sci 45:159 162 Walker ER, Oliver LR (2008) Translocation and absorption of glyphosate in flowering sicklepod ( Senna obtusifolia ). Weed Sci 56:338 343 Westhoven AM, Kruger GR, Gerber CK, Stachler JM, Loux MM, Johnson WG (2008) Characterization of selected common lambsquarters ( Chenopodium album ) biotypes with tolerance to glyphosate. Weed Sci 56:685 691

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61 Wilson RG, Orloff SB (2008) Winter annual weed control with herbicides in alfalfa orchardgrass mixtures. Wee d Techno l 22:30 33 Yerka MK, Wiersma AT, Lindenmayer RB, Westra P, Johnson WG, de Leon N, Stoltenberg DE (2013) Reduced translocation is associated with tolerance of c ommon l ambsquarters ( Chenopodium album ) to glyph osate. Weed Sci 61:353 360 Zimdahl, RL (2007) Fundamentals of Weed Science. San Diego, CA: Academic Press. 666 p

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62 BIOGRAPHICAL SKETCH Jose V. Fernandez grew up in Tegucigalpa, Francisco Morazan, Honduras He attended Escuela Agricola Panamerican ZAMORANO wh ere he obtained a B achelor of Science degree in a gronomy in 2003. Since then, he worked as a farm manager for two beef and one dairy operation companies in his country. In 2011 he was accepted in the graduate weed science program in the Agronomy Department at the University of Florida. Under the supervision of Dr. Dennis Odero, he focused on ragweed parthenium management in the Everglades Agricultural Area. Following completion of his Master of Science degree, he plans to pursu e a Ph.D. degree in weed scien ce at the University of Florida