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Purple Nutsedge (Cyperus Rotundus L.) and Yellow Nutsedge (Cyperus Esculentus L.) Management with Tillage and the Herbic...

Permanent Link: http://ufdc.ufl.edu/UFE0041252/00001

Material Information

Title: Purple Nutsedge (Cyperus Rotundus L.) and Yellow Nutsedge (Cyperus Esculentus L.) Management with Tillage and the Herbicides Imazapic and Imazethapyr
Physical Description: 1 online resource (140 p.)
Language: english
Creator: Horrall, Derek
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: imazapic, imazethapyr, nutsedge, purple, tillage, yellow
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: PURPLE NUTSEDGE (CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE (CYPERUS ESCULENTUS L.) MANAGEMENT WITH TILLAGE AND THE HERBICIDES IMAZAPIC AND IMAZETHAPYR By Derek Duane Horrall May 2010 Chair: Barry J. Brecke Major: Agronomy Purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.) together, rank fifth in importance among all weeds in the United States. Both of these nutsedge species reduce peanut (Arachis hypogaea L.) yields by competing for water, light, and nutrients. They also reduce crop quality due to the contamination of harvested peanuts by nutsedge tubers. Due to the prolonged use of herbicides that differentially controlled yellow nutsedge, purple nutsedge has become an even greater problem in southeastern peanut fields. Imazapic (Cadre) and imazethapyr (Pursuit) were the first herbicides to provide effective postemergence purple nutsedge control in peanuts. Field and greenhouse studies were conducted to determine the effectiveness of imazapic and imazethapyr in controlling purple and yellow nutsedge, and to evaluate the impact these herbicides have on nutsedge tuber production. Tillage was also evaluated as a means of reducing purple nutsedge growth and reproduction. Tilling at two week intervals more than twice in May and June did not result in significantly lower purple nutsedge tuber numbers in July. Tilling at two week intervals more than three times throughout the season did not significantly reduce tuber numbers by September. Alternating tillage operations with glyphosate applications resulted in the greatest reduction in tuber number, weight, and viability at mid- and late-season sampling dates. In an herbicide screening study conducted for both purple and yellow nutsedge in the field, imazapic applied at the rate of 71g ha-1 early postemergence (EPOST) resulted in the greatest reduction of tuber numbers and tuber dry weights by July and September. Greenhouse studies indicated that EPOST applications of imazapic and imazethapyr 2 weeks after emergence (WAE) were more effective than those applied to purple and yellow nutsedge 4 and 6 WAE. Foliar-only treatments of purple and yellow nutsedge 2, 4, and 6 WAE provided better shoot control than soil-applied treatments. The greatest control of nutsedge, however, regardless of plant age, was obtained by treating both the foliage and soil. It was determined at the conclusion of a year-long greenhouse study that soil-applied imazapic provided better residual control of purple nutsedge than imazethapyr.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Derek Horrall.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Brecke, Barry J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-04-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041252:00001

Permanent Link: http://ufdc.ufl.edu/UFE0041252/00001

Material Information

Title: Purple Nutsedge (Cyperus Rotundus L.) and Yellow Nutsedge (Cyperus Esculentus L.) Management with Tillage and the Herbicides Imazapic and Imazethapyr
Physical Description: 1 online resource (140 p.)
Language: english
Creator: Horrall, Derek
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2010

Subjects

Subjects / Keywords: imazapic, imazethapyr, nutsedge, purple, tillage, yellow
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: PURPLE NUTSEDGE (CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE (CYPERUS ESCULENTUS L.) MANAGEMENT WITH TILLAGE AND THE HERBICIDES IMAZAPIC AND IMAZETHAPYR By Derek Duane Horrall May 2010 Chair: Barry J. Brecke Major: Agronomy Purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.) together, rank fifth in importance among all weeds in the United States. Both of these nutsedge species reduce peanut (Arachis hypogaea L.) yields by competing for water, light, and nutrients. They also reduce crop quality due to the contamination of harvested peanuts by nutsedge tubers. Due to the prolonged use of herbicides that differentially controlled yellow nutsedge, purple nutsedge has become an even greater problem in southeastern peanut fields. Imazapic (Cadre) and imazethapyr (Pursuit) were the first herbicides to provide effective postemergence purple nutsedge control in peanuts. Field and greenhouse studies were conducted to determine the effectiveness of imazapic and imazethapyr in controlling purple and yellow nutsedge, and to evaluate the impact these herbicides have on nutsedge tuber production. Tillage was also evaluated as a means of reducing purple nutsedge growth and reproduction. Tilling at two week intervals more than twice in May and June did not result in significantly lower purple nutsedge tuber numbers in July. Tilling at two week intervals more than three times throughout the season did not significantly reduce tuber numbers by September. Alternating tillage operations with glyphosate applications resulted in the greatest reduction in tuber number, weight, and viability at mid- and late-season sampling dates. In an herbicide screening study conducted for both purple and yellow nutsedge in the field, imazapic applied at the rate of 71g ha-1 early postemergence (EPOST) resulted in the greatest reduction of tuber numbers and tuber dry weights by July and September. Greenhouse studies indicated that EPOST applications of imazapic and imazethapyr 2 weeks after emergence (WAE) were more effective than those applied to purple and yellow nutsedge 4 and 6 WAE. Foliar-only treatments of purple and yellow nutsedge 2, 4, and 6 WAE provided better shoot control than soil-applied treatments. The greatest control of nutsedge, however, regardless of plant age, was obtained by treating both the foliage and soil. It was determined at the conclusion of a year-long greenhouse study that soil-applied imazapic provided better residual control of purple nutsedge than imazethapyr.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Derek Horrall.
Thesis: Thesis (Ph.D.)--University of Florida, 2010.
Local: Adviser: Brecke, Barry J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2011-04-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2010
System ID: UFE0041252:00001


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1 PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( CYPERUS ESCULENTUS L.) MANAGEMENT WITH TILLAGE AND THE HERBICIDES IMAZAPIC AND IMAZETHAPYR By DEREK DUANE HORRALL A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL O F THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2010

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2 2010 Derek Duane Horrall

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3 TABLE OF CONTENTS page LIST OF TABLES ...................................................................................................................... 5 LIST OF FIGURES .................................................................................................................... 9 ABSTRACT ............................................................................................................................. 10 CHAPTER 1 INTRODUCTION ............................................................................................................. 12 Morphology ....................................................................................................................... 15 Tuber Biology .................................................................................................................... 16 Tuber Formation ................................................................................................................ 18 Photosynthesis ................................................................................................................... 19 Cultural Control ................................................................................................................. 21 Mechanical Control ............................................................................................................ 23 Herbicides .......................................................................................................................... 24 History of the Imidazolinone Family of Herbicides ............................................................ 27 2 EFFECT OF TILLAGE AND GLYPHOSATE APPLICATION ON CONTROL OF PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( C. ESCULENTUS L.) ............................................................................................................. 34 Introduction........................................................................................................................ 34 Materials and Methods ....................................................................................................... 36 Tillage Study ............................................................................................................... 36 Glyphosate and Tillage Study ...................................................................................... 37 Results and Discussion ....................................................................................................... 39 Tillage Study ............................................................................................................... 39 Glyphosate and Tillage Study ...................................................................................... 41 3 IMAZAPIC AND IMAZETHAPYR FOR PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) CONTROL .............................................................................................. 52 Introduction........................................................................................................................ 52 Materials and Methods ....................................................................................................... 53 Results and Discussion ....................................................................................................... 54 Tuber Number ............................................................................................................. 54 Tuber Weight .............................................................................................................. 56 Tuber Germination ...................................................................................................... 56 4 EFFECTS OF GROWTH STAGE, SITE OF APPLICATION, AND RATE OF IMAZAPIC AND IMAZETHA PYR ON PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( C. ESCULENTUS L.) CONTROL .......... 68

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4 Introduction........................................................................................................................ 68 Materials and Met hods ....................................................................................................... 69 Site of Application ...................................................................................................... 70 Site of Application and Nutsedge Age ......................................................................... 70 Root Uptake ................................................................................................................ 71 Nutsedge Growth and Tuber Production ...................................................................... 72 Results and Discussion ....................................................................................................... 74 Site of Application ...................................................................................................... 74 Site of Application and Nutsedge Age ......................................................................... 75 Root Uptake ................................................................................................................ 78 Nutsedge Growth and Tuber Production ...................................................................... 79 5 INFLUENCE OF IMAZAPIC AND IMAZETHAPYR ON PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( C. ESCULENTU S L.) GROWTH AND REPRODUCTION ................................................................................ 105 Introduction...................................................................................................................... 105 Materials and Methods ..................................................................................................... 105 Results and Discussion ..................................................................................................... 108 6 EFFECTS OF RESIDUAL CONCENTRATIONS OF SOIL APPLIED IMAZAPIC AND IMAZETHAPYR ON THE GROWTH AND REPRODUCTION OF PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AS A FUNCTION OF TIME ......................... 114 Introduction...................................................................................................................... 114 Materials and Methods ..................................................................................................... 115 Results and Discussion ..................................................................................................... 117 7 CONCLUSIONS .............................................................................................................. 128 REFERENCES ....................................................................................................................... 131 B IOGRAPHICAL SKETCH ................................................................................................... 140

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5 LIST OF TABLES Table page 11 Imazapic chemistry and toxicity information ................................................................. 33 12 Imazethapyr chemistry and toxicity information ............................................................ 33 21 Effect of tillage on mid season purple nutsedge tuber density, three years combined ..... 45 22 Effect of tillage on lateseason purple nutsedge tuber density, three years combined ...... 46 23 Effect of tillage on mid season purple nutsedge tuber weight, t hree years combined ...... 47 24 Effect of tillage on lateseason purple nutsedge tuber weight, three years combined ...... 48 25 Effect of tillage on purple nutsedge tuber germination, three years combined ................ 49 26 Effect of glyphosate and tillage on purple nutsedge tubers, year one .............................. 50 27 Effect of glyphosate and tillage on purple nutsedge tubers, year two .............................. 50 28 Effect of glyphosate and tillage on yellow nutsedge tubers, year one ............................. 51 29 Effect of glyphosate and tillage on yellow nutsedge tubers, year two ............................. 51 31 Effect of herbicide treatments on mid season purple nutsedge tuber den sity, year one ... 58 32 Effect of herbicide treatments on lateseason purple nutsedge tuber density, year one .... 59 33 Effect of her bicide treatments on late season purple nutsedge tuber density, year two .... 60 34 Effect of herbicide treatments on mid season purple nutsedge tuber density, year three .............................................................................................................................. 61 35 Effect of herbicide treatments on lateseason purple nutsedge tuber density, year three .............................................................................................................................. 62 36 Effect of herbicide treatments on mid season purple nutsedge tuber weight, year one .... 63 37 Effect of herbicide treatments on lateseason purple nutsedge tuber weight, year one .... 64 38 Effect of herbicide treatments on lateseason purple nutsedge tuber weight, year two .... 65 39 Effect of herbicide treatments on lateseason purple nutsedge tuber weight, year three .............................................................................................................................. 66 310 Purple nutsedge tuber germination, years one, two, and three ........................................ 67

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6 41 Effect of foliar and soil + foliar applied herbicides on purp le nutsedge growth, year one ................................................................................................................................ 82 42 Effect of foliar and soil + foliar applied herbicides on yellow nutsedge growth, year one ................................................................................................................................ 82 43 Effect of herbicide rate, herbicide site of application, and stage of growth at application on purple nutsedge control, 4 weeks after treatment, years one and two ....... 83 44 Effect of herbici de, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge shoot height 4 weeks after treatment, years one and two .................. 84 45 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge shoot number 4 weeks after treatment, years one and two ................ 85 46 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge shoot dry weight 4 weeks after treatment, years one and two ........... 86 47 Effect of herbicide, herbicide rate, herbicide site of application, and stage o f growth on purple nutsedge regrowth 4 weeks after initial harvest (8 weeks after treatment), years one and two .......................................................................................................... 87 48 Effect of herbicide, herbicide rate, herbicide site of application, and s tage of growth at application on purple nutsedge regrowth shoot height 4 weeks after initial harvest, (8 weeks after treatment), years one and two .................................................................. 88 49 Effect of herbicide, herbicide rate, h erbicide site of application, and stage of growth at application on purple nutsedge shoot regrowth dry weight 4 weeks after initial harvest, (8 weeks after treatment), years one and two ..................................................... 89 410 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on yellow nutsedge control 4 weeks after treatment, years one and two .... 90 411 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot height 4 weeks after treatment, years one and two ................. 91 412 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot number 4 wee ks after treatment, years one an d two ............... 92 413 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot dry weight 4 weeks after treatment, years one and two .......... 93 414 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge regrowth 4 weeks after initial harvest (8 weeks after treatment), years one and two .......................................................................................................... 94

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7 415 Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on yellow nutsedge regrowth shoot height 4 weeks after initial harvest, (8 weeks after treatment), years one and two .................................................................. 95 416 Effect of herbicide, herb icide rate, herbicide site of application, and stage of growth at application on yellow nutsedge shoot regrowth dry weight 4 weeks after initial harvest, 8 weeks after treatment, years one and two ....................................................... 96 417 Effect of surface applied herbicide, herbicide rate, and stage of growth at application on purple nutsedge control, three years combined .......................................................... 97 418 Effect of surface applied herbicid e, herbicide rate, and stage of growth at application on purple nutsedge regrowth, three years combined ....................................................... 97 419 Effect of surface applied herbicide, herbicide rate, and stage of growth at appl ication on yellow nutsedge regrowth, three years combined ...................................................... 98 420 Effect of surface applied herbicide, herbicide rate, and stage of growth at application on yellow nutsedge regrowth, three years combined ...................................................... 98 421 Effect of herbicide on purple nutsedge control, two years combined .............................. 99 422 Effect of herbicide rate of appli cation on purple nutsedge control, two years combined ....................................................................................................................... 99 423 Effect of plant growth stage at time of herbicide application on purple nutsedge control, two years combined .......................................................................................... 99 424 Effect of herbicide and stage of growth at time of application on purple nutsedge growth, two years combined ........................................................................................ 100 425 Effect of herbicide rat e and stage of growth at time of application on purple nutsedge growth, two years combined ........................................................................................ 101 426 Effect of herbicide on yellow nutsedge control, two years combined ........................... 102 427 Effect of herbicide rate of application on yellow nutsedge control, two years combined ..................................................................................................................... 102 428 Effect of plant growth stage at time of herbicid e application on yellow nutsedge control, two years combined ........................................................................................ 102 429 Effect of herbicide and stage of growth at time of application on yellow nutsedge growth, two years combined ........................................................................................ 103 430 Effect of herbicide rate and stage of growth at time of application on yellow nutsedge growth, two years combined .......................................................................... 104

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8 51 Effect of preemergence herbicide treatments on purple nutsedge reproduction, years one and two ................................................................................................................. 110 52 Effect of early postemergence herbicide treatments on purple nutsedge reproduction, years one and t wo ........................................................................................................ 111 53 Effect of preemergence herbicide treatments on yellow nutsedge reproduction, years one and two ................................................................................................................. 112 54 Effect of earl y postemergence herbicide treatments on yellow nutsedge reproduction, years one and two ........................................................................................................ 113 61 Effects of residual concentrations of soil applied imazapic and imazethapyr on purple nutsedge c ontrol and tuber number and dry weight as a function of time ........... 120 62 Effects of residual concentrations of soil applied imazapic and imazethapyr on purple nutsedge shoot number and height, and shoot and root dry weight, as a function of time ........................................................................................................... 122 63 Corn root bioassay ....................................................................................................... 124

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9 LIST OF FIGURES Figure page 61 Imazapic dose response for corn root bioassay 1 MAT ................................................ 126 62 Imazethapyr dose response for corn root bioassay 1 MAT ........................................... 127

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10 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( CYPERUS ESCULENTUS L.) MANAGEMENT WITH TILLAGE AND THE HERBICIDES IMAZAPIC AND IMAZETHA PYR By Derek Duane Horrall May 2010 Chair: Barry J. Brecke Major: Agronomy Purple and yellow nutsedge ( Cyperus rotundus L. and C. esculentus L.) together, rank fifth in importance among all weeds in the United States. Both of these nutsedge species reduce peanut ( Arachis hypogaea L.) yields by competing for water, light, and nutrients. They also reduce crop quality due to the contamination of harvested peanuts by nutsedge tubers. Due to the prolonged use of herbicides that differentially controlled yellow nutsedge, purple nutsedge has become an even greater problem in southeastern peanut fields. Imazapic (Cadre) and imazethapyr (Pursuit) were the first herbi cides to provide effective post emergence purple nutsedge control in peanuts. Field and greenhouse studies were conducted to determine the effectiveness of imazapic and imazethapyr in controlling purple and yellow nutsedge, and to evaluate the impact these herbicides have on nutsedg e tu ber production. T illage was also evaluated as a means of reducing purple nutsedge growth and reproduction. Tilli ng at two week intervals more than twice in May and June did not result in significantly lower purple nuts edge tuber numbers in July Tilling at two week intervals more than three times throughout the season did not significantly reduce tuber numbers b y September

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11 Alternating tillage operations with glyphosate applications resulted in the greatest reduction i n tub er number, weight and viability a t mid and lateseason sampling dates. In an herbicide screening study conducted for both purple and yellow nutsedge in the field, ima zapic applied at the rate of 71 g ha1 early post emergence (EPOST) resulted in the greatest reduction of tuber numb ers and tuber dry weight s by July and September Greenhouse studies indicated that EPOST applications of imazapic and imazethapyr 2 weeks after emergence (WAE) were more effective than those applied to purple and yellow nutsedge 4 and 6 WAE. Foliar only treatments of purple and yellow nutsedge 2, 4, and 6 WAE provided better shoot control than soil applied treatments. The greatest control of nutsedge, however regardless of plant age, was obtained by treating both the foliage and soil. It was determined at the conc lusion of a year long greenhouse study that soil applied imazapic provided better residual control of purple nutsedge than imazethapyr.

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12 CHAPTER 1 INTRODUCTION Purple nutsedge ( Cyperus rotundus L.) and yellow nutsedge ( Cyperus esculentus L.) are flowerin g, monocotyledonous perennial p lants classified in the kingdom Plantae, class Angiospermae, subclass Monocotyledoneae, superorder Commelinidae, order Cyperales, and family Cyperaceae (Salisbury and Ross 1992). Cyperaceae is known as the sedge family. This family of plants consists of 146 genera and 5,315 species (Zomlefer 1994). Two hundred and twenty of these species are considered to be weeds, of which roughly 42% are among the 550 600 species in the genus Cyperus (Bendixen and Nandihalli 1987; Zomlefer 1994). Purple nutsedge is also known as purple nutgrass and cocograss. Additional common names for yellow nutsedge include yellow nutgrass, northern nutgrass (Bell et al. 1962), chufa (Bendixen and Nandihalli 1987), tigernut (Addy and Eteshola 1984), earth almond, ground almond, and rush nut (Salisbury and Ross 1992). Purple nutsedge is native to India (Holm et al. 1991a), while the region of origin for yellow nutsedge is unknown (Doll 1983b). Purple and yellow nutsedge are the worst and sixteenth worst wee ds in the world, respectively (Holm et al. 1991b). Purple nutsedge grows in more countries, regions, and localities than any other weed in the world (Holm et al. 1997). It occurs in Africa, Asia, Australia, Europe, North America, and South America. It is considered the world's worst weed, based on the number of countries where it is reported as a serious, principal, or common weed (Bendixen and Nandihalli 1987; Holm et al. 1991a). Purple nutsedge is an important weed in 52 crops in 92 tropical and subtropi cal countries. Low temperatures seem to limit its range to latitudes within 300 to 350 north and south of the equator (Holm et al. 1991a; Williams 1982). Competition with crops for light, water, and nutrients is the primary factor in determining degree of weediness.

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13 Purple nutsedge is a serious or principal weed in rice ( Oryza sativa L.), sugarcane ( Saccharum officinarum L.), corn ( Zea mays L.) cotton ( Gossypium hirsutum L .), and vegetable crops. P urple nutsedge is listed as one of the three most noxious weeds of rice in Ghana, Indonesia, Iran, Peru, South Africa, and Taiwan; of sugarcane in Argentina, India, Indonesia, Peru, and Taiwan; of corn in Ghana and the Philippines; of cotton in Sudan, Swaziland, Turkey, and Uganda; and of vegetable crops in Brazi l, Malaysia, Taiwan, and Venezuela. In some of these and other areas around the world, purple nutsedge is a significant pest in peanut ( Arachis hypogaea L.), soybean ( Glycine max L.) sorghum ( Sorghum vulgare Pers.), and many plantation crops such as coffee ( Coffea arabica L. ) and tea ( T hea sinensis and Camellia sinensis ) (Holm et al. 1991a). The widespread distribution of purple and yellow nutsedge is largely a function of the dissemination of tubers. Although both species produce viable seeds, they are insignificant for propagational purposes in most cultivated areas, mainly due to inadequate seedling vigor (Stoller and Sweet 1987). Though it is impossible to verify the exact means by which these weeds were so widely distributed, many plausible explanati ons exist (Bendixen and Nandihalli 1987). Nutsedge tubers and seeds may contaminate commercial seeds and feeds, and subsequently be distributed widely. Tubers are known to develop in Irish potato ( Solanum tuberosum L.) tubers and in other commercial "root" crops such as sweet potato [ Ipomea batatas (L.) Poir], sugar beet ( Beta vulgaris L.), and onion ( Allium cepa L.) It is also known that tubers are a contaminant in the harvest and bagging of these and other crops. Consequently, nutsedge is distributed wit h these foods and seed stocks. Nutsedge tubers can also contaminate peanuts during harvest and shipment (Bendixen and Nandihalli 1987).

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14 Tubers are brought to farms on tillage and harvesting implements and are moved by rainwater into drainage ditches, wher e they may be carried further. Tubers are also brought into new areas by floodwaters and by surface irrigation water. Dissemination of floating tubers is of major concern in paddy rice. In addition, wind can sweep tubers along the soil surface for great di stances. Seeds might be able to survive being passed through the digestive tracts of birds and other animals, and thus be spread over their feeding ranges. Nutsedge often contaminates nursery stock; thus tubers might be distributed with transplanted, potte d, or balled plants (Holm et al. 1991a). The many possible reasons for the widespread occurrence of purple and yellow nutsedge suggests that their distribution is limited more by environmental conditions (e.g., cold temperatures, soil moisture content, an d degree of sunlight) than by a lack of means of dispersal (Bendixen and Nandihalli 1987). One theory as to how purple and yellow nutsedge spread to the United States is that tubers, rhizomes, and in some instances entire plants, were present in the soil u sed as ballast in the holds of ships originating from India and other regions where nutsedge was already established (Bendixen and Nandihalli 1987). Upon arrival in the U.S., the nutsedge contaminated ballast was discarded in order for the holds of the shi ps to be loaded with goods for the return voyages. Purple and yellow nutsedge combined rank fifth in importance among all weeds in the United States with quackgrass [ Elyfrigia repens (L.) Desv.] the only perennial weed ranking higher. Although purple nuts edge is considered to be the worst weed in the world, yellow nutsedge is more widespread and troublesome in the United States due to its ability to tolerate colder temperatures than purple nutsedge. Yel low nutsedge occurs in all 50 states, whereas purple n utsedge is seldom seen north of Arkansas, Tennessee, and Virginia (Bendixen and

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15 Nandihalli 1987; Holm et al. 1991b). Purple nutsedge also occurs in Hawaii and central and southern California, however, where it is especially troublesome in the production of sugarcane and vegetable crops (Holm et al. 1991a). In addition to being affected by low temperatures, purple nutsedge does not tolerate extremely low or high soil moisture, soils with a high salt content, or shading. When the overstory of such crops as plantation trees and sugarcane begins to shade the soil, the leaves of purple nutsedge yellow and die. The dormant tubers remain viable, however, and as soon as an opening in the canopy appears, the sedge begins to reestablish itself. Purple nutsedge is mo re sensitive to drought than yellow nutsedge (Bendixen 1973). Other than the aforementioned limitations, however, purple nutsedge grows prolifically in nearly every soil type, elevation, pH, and humidity, and can withstand the highest temperatures known in agriculture (Holm et al. 1991a; Holm et al. 1991b). Under optimum growing conditions, purple nutsedge is more competitive than yellow nutsedge (Bendixen 1973; Wills 1987). In the southeastern United States, purple and yellow nutsedge are most detrimenta l in peanut, cotton, corn, and vegetable crops. Heavy infestations of either nutsedge species are capable of lowering peanut yields by up to 25%. While good control of yellow nutsedge can be obtained in both cotton and peanut via the use of herbicides, pur ple nutsedge is easier to control in cotton than in peanut (York 1994). M orphology Purple and yellow nutsedge often grow in mixed stands, and thus may be difficult to distinguish one from the other before they have flowered (Holm et al. 1991b; Wills 1987) Their common names are derived from the color of their inflorescences. Purple nutsedge has a purplish brown inflorescence, while that of yellow nutsedge is golden brown (Doll 1983a; Wills 1987). Other distinguishing morphological characteristics include leaf color, leaf tip shape, plant

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16 height, as well as tuber shape, size, color, and taste (Doll 1983a; Doll 1983b; Holm et al. 1991a; Holm et al. 1991b). The leaves of purple nutsedge are dark green, with blunt tips that are similar in shape to the keel of a boat. Yellow nutsedge leaves, on the other hand, are paler green and more acuminate. The leaves of both species are in three ranks with closed sheaths and without ligules. The basal leaves of purple nutsedge are shorter than the inflorescence, while thos e of yellow nutsedge are longer than the inflorescence. Both species have triangular stems, which are common to all true sedges. Mature plant height for the species ranges from 20 30 cm for purple nutsedge to 25 50 cm for yellow nutsedge (Doll 1983a; Doll 1983b; Wills 1987; Wills and Briscoe 1970). Tubers of purple nutsedge are irregular in shape, hairy, nearly black, typically 1 3 cm in size, and occur in chains on wiry rhizomes. Contrastingly, yellow nutsedge tubers tend to be spherical, smooth (i.e., d evoid of hairs), generally range from 0.5 1 cm in size, and are not linked together by rhizomes. Its tubers may be red, tan, brown, or black. Newly formed tubers of both species are often white, and become darker with age. Those that have over wintered in the soil tend to be the darkest (Doll 1983a; Doll 1983b). Purple nutsedge tubers taste bitter, while those of yellow nutsedge are esculent; hence its species name, esculentus Tuber Biology The most impressive characteristic of purple nutsedge is its pr olific production of subterranean tubers, which are capable of remaining dormant and thus of sustaining the species through extreme environmental conditions such as drought, flooding, heat, or lack of soil aeration. The plant may grow to a depth of 100 cm in moist, fertile soils. Its rhizomes can puncture and pass completely through the roots and underground storage organs of vegetable root crops including Irish and sweet potatoes, sugar beet, onions, cassava ( Manihot esculenta

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17 Crantz), and carrots ( Daucus carota L.), subsequently reducing their market value (Holm et al. 1991a). Purple nutsedge is capable of propagating at an exceptionally fast rate. In one study, a single purple nutsedge tuber placed in a field produced 1,900 plants and almost 7,000 tuber s, and covered an area approximately two meters in diameter after just one year (Holm et al. 1991b). In Brazil, purple nutsedge is known as tiririca ate amamnha, which translates as until tomorrow. This refers to the plants ability to regrow quickly f ollowing weeding (Williams 1976). Similarly, a single yellow nutsedge plant was shown to produce 7,000 tubers, with tuber populations of 1,000 per square meter in a single season (Hauser 1962a; Hauser 1962b; Horowitz 1972; Smith and Frick 1937; Stoller and Sweet 1987; Tumbleson and Kommedahl 1961). Tuber production in yellow and purple nutsedge begins four to six weeks after seedling emergence. Ninety five percent of the tubers for both species are formed within 45cm of the soil surface (Bell et al. 1962; Stoller and Sweet 1987; Tumbleson and Kommedahl 1961). Generally, more than 80% of tubers are located in the upper 15cm of the soil profile (Bayer 1987; Stoller and Sweet 1987). Rhizomes do not penetrate as deeply in finer textured soils such as those hig h in clay content. Tubers occur deeper in coarser textured soils, or in soils frequently disturbed by cultivation (Bayer 1987; Stoller and Sweet 1987) Tuber longevity in both species is dependent upon location in the soil profile. In general, the deeper a tuber is in the soil, the longer it will survive (Bayer 1987). Yellow nutsedge propagates predominately by vegetative parts, including rhizomes, tubers, and a basal bulb (Garg et al. 1967). The basal bulb develops in young seedlings as a swelling at the junction of the mesocotyl and coleoptile (Garg et al. 1967). These bulbs consist of a stem fragment (rhizome) with compressed internodes, which have meristems for roots,

PAGE 18

18 secondary rhizomes, leaves, and the flower stalk (Stoller and Sweet 1987). The basal bulb gives rise to rhizomes, which differentiate into either tubers or shoots (Garg et al. 1967). Tuber Formation The principal factor stimulating tuber production in yellow nutsedge is day length (Jansen 1971; Stoller and Sweet 1987). Photoperiods longer than 12 hours promote rhizome development and shoot production, while shorter photoperiods promote rhizome tuberization (Bell et al. 1962; Garg et al. 1967; Jansen 1971; Stoller and Sweet 1987). Thus, photoperiods shorter than 12 hours tend to cause rhizo mes to differentiate into tubers, while with photoperiods longer than 12 hours, rhizomes have a propensity to differentiate into basal bulbs and shoots (Garg et al. 1967; Stoller and Sweet 1987). Bell et al. (1962) showed that tuberization of yellow nutsed ge was promoted at photoperiods of 8 to 12 hours, and shoot formation at 16 hours (Jansen 1971). Tubers are produced on rhizomatous tissue containing numerous buds, a characteristic common to many stem tissues (Stoller and Sweet 1987). In yellow nutsedge grown with greater than 12 hours of daylight, buds on rhizomes sprout and initiate rhizomatous growth which develops into shoots typical of most monocots (Stoller and Sweet 1987). While photoperiod has been identified as the major stimulant for tuber prod uction and flowering in yellow nutsedge (Jansen 1971; Stoller and Sweet 1987), controversy exists regarding the role of photoperiodism in rhizome differentiation and subsequent tuber formation in purple nutsedge. Horowitz (1972) found that natural photoper iods of 1014 hours had no apparent effect on tuberization in purple nutsedge, whereas Hammerton (1975) found that day length was the major factor influencing purple nutsedge growth and development. Similarly, Williams (1982) noted that tuber production in purple nutsedge increased as day length decreased. In addition, Berger (1966) reported that tuber formation was induced by a short photoperiod of 10 hours, and inhibited by a photoperiod of 18 hours. Tuber formation can

PAGE 19

19 apparently occur throughout the year in tropical climates (Hammerton 1975; Horowitz 1972). Before tubers are formed, the plant complex usually includes many shoots interconnected by rhizomes capable of diverting resources into tubers. Thus, tuber formation in purple nutsedge may respond to excess carbohydrate levels, as well as to plant growth regulators, photoperiodism, and temperature (Stoller and Sweet 1987). In yellow nutsedge, 12 to 14 hour photoperiods promote flowering, and consequently seed production, whereas longer or shorter photoperiods are inhibitory (Jansen 1971). Purple nutsedge, on the other hand, is stimulated to flower in short photoperiods of six to eight hours, with the time from emergence to flowering ranging from three to eight weeks (Holm et al. 1991a). Photosynthesis Purple and yellow nutsedge are C 4 plants possessing the dicarboxylic acid photosynthetic pathway (Wills 1987). In addition to being able to convert CO2 into carbohydrates by the C 3 Calvin cycle common to all photosynthetically active plants, C 4 plants also possess the phosphoenolpyruvate pathway, through which CO2 is efficiently collected (Wills 1987). C 4 plants are efficient both in obtaining CO2 from the atmosphere and in recapturing CO2 that has been expelled through plant respiration. In addition, C 4 plants can assimilate CO2 at higher temperatures and light intensities than plants possessing only the C 3 pathway (Wills 1987). This phenomenon is demonstrated by the fact that C 4 species tend to exhibit their best growth rates at higher temperatur es than do C 3 species. Furthermore, most C 3 species light saturate at 20 to 30% of full sunlight, while C 4 plants usually saturate from 50% to greater than full sunlight (Wills 1987). Perennial species, such as purple and yellow nutsedge, that fix CO2 a t high rates under elevated temperatures and light intensities, and that possess the ability to spread

PAGE 20

20 by rhizomes, have the potential to become serious weed problems. As C 4 plants, purple and yellow nutsedge are sensitive to shading. While shading reduces tuber production in both species (Keeley and Thullen 1978; Stoller and Sweet 1987), it is debatable whether it reduces tuber numbers significantly. For instance, Patterson (1982) and Wills (1975) found that both species were able to efficiently divert dr y matter into tuber production even when grown under 90% shade. When nutsedge tubers sprout, one or more of the many buds on the tuber begin to grow. Yellow nutsedge buds are concentrated at the apical end of the tuber (Bendixen 1973), while purple nutsedge buds gather at nodes along the entire length of the tuber (Stoller and Sweet 1987). Typically, several buds sprout simultaneously while others remain dormant for subsequent sprouting (Stoller et al. 1972). Purple nutsedge tubers exhibit apical dominanc e, since the sprouting of the most apical buds inhibits sprouting of the more basal buds (Bayer 1987; Stoller and Sweet 1987). Yellow nutsedge tubers, however, break dormancy in acropetal order, beginning with the oldest, most basipetal bud (Bayer 1987; St oller and Sweet 1987). Yellow nutsedge tubers are capable of sprouting at least three times, with 60% of the total tuber dry weight, carbohydrate, starch, oil, and protein being expended on the first sprouting, while only 10% of these constituents are depl eted during each of the next two sproutings (Stoller et al. 1972). In addition to the preceding constituents, organic acids are apparently consumed during the sprouting of purple nutsedge tubers (Stoller and Sweet 1987). Carbohydrate levels in tubers and rhizomes of Cyperus species are dependent upon their function. Rhizomes of Cyperus species are not storage organs, but rather serve to transport carbohydrates from older to actively growing tubers and young sprouts. Hence, they contain

PAGE 21

21 more sugars than sta rch (Diethelm and Bocion 1993). Conversely, tubers contain more starch than sugars since they are storage organs. However, not all tubers possess the same starch to sugar ratio. The younger the tubers, the lower the ratio of starch to sucrose and reducing sugars. This is a consequence of their higher metabolic rates and net import of carbohydrates (Diethelm and Bocion 1993). Even young, actively growing tubers possess sufficient carbohydrates for sprouting, as long as dormancy is broken (Diethelm and Bocion 1993). Cyperus tubers store much greater amounts of carbohydrates than what is required for sprouting. Therefore, some essential step in carbohydrate metabolism must be almost completely inhibited in order for a strong herbicide effect to occur. An excep tion would be toxic effects caused by inhibition of an essential enzyme; however, at this time it is unknown which enzyme might be involved. The study of essential enzymes in transgenic plants has not yielded conclusive results. AGPase (ADP glucose pyropho sphorylase), an essential gene for starch synthesis, is an example. Diethelm and Bocion (1993) showed that potato tubers possessing the antisense gene for AGPase were found to have much lower starch content, but a significantly greater sugar concentration. Inhibition of starch synthesis in tubers led to a much higher number of tubers per potato plant, with the tubers being considerably smaller than those in the wild type. Although the antisense gene converted the tubers from starch to sugar storage organs, tubers displayed normal sprouting and subsequent plant development. These researchers concluded that the results from genetically altered plants indicate that a reasonable method of eradicating perennial plants such as Cyperus species through carbohydrate starvation does not seem feasible (Diethelm and Bocion 1993). Cultural Control An integrated program that utilizes several methods is usually most effective in controlling purple and yellow nutsedge (Wax 1975). Care should be taken not to transport tubers

PAGE 22

22 by cultivation and harvesting implements, and by other means stated earlier (Ho lm et a l 1991a). Purple and yellow nutsedge have also spread as production inputs have increased (Hauser et al. 1973). The augmentation of nutsedge densities is largely a cons equence of reduced competition due to better annual weed control and ameliorated growing conditions due to the increased use of soil amendments (Hauser et al. 1973). Rotating crops, and subsequently the herbicides applied to a given field, is known to ai d in nutsedge control (Wax 1975). Crop rotation may also increase a crops competitiveness against nutsedge by reducing insect, disease, and nematode damage ( and Brecke 1997). Crop selection should include fast growing, competitive crops that quickly form a canopy over the soil to shade nutsedge, thus reducing its growth and reproductive potential (Glaze 1987; Keeley and Thullen 1978). Crop selection also determines the planting date, and thus the timing and frequency of tillage possible, as well as the d uration of weed control required to produce economical yields (Glaze 1987). Delayed pla nting dates make additional preplant cultivations possible (William and Bendixen 1987). For most crops, the first four to eight weeks are the most critical in terms of c ompetition from nutsedge. The time required for a crop to produce a canopy sufficiently large to shade nutsedge varies with each crop, but is generally between four and sixteen weeks (Glaze 1987). Crops can become more competitive by using the narrowest pr actical row spacing, increasing seeding densities, applying fertilizers as indicated by soil tests, and by controlling insects and diseases ( Brecke and Stephenson, 2006a ; Doll 1983a; Glaze 1987). Besler et al. ( 2008) found both imazapic and diclosulam appl ied to peanut grown in a twinrow pattern pro vided better yellow nutsedge control than herbicide applications to peanut g rown in single row spacing.

PAGE 23

23 Mechanical Control The keys to successful mechanical control of nutsedge species are timeliness and freque ncy (Doll 1983a). Different theories exist as to the preferred timing of cult ivation. Doll ( 1983a) found tillage to be most effective when performed prior to nutsedge being well established, whereas Stoller and Wax (1973), Williams (1982), and Glaze (1987) observed maximum benefits in nutsedge control when cultivation was delayed until a substantial number of tubers had germinated. Disadvantages to mechanical weed control measures do exist. Preplant cultivatio n can promote tuber germination The first till age operation may kill many of the shoots, but dormant buds on tubers of both purple and yellow nutsedge are capable of sprouting another two or three times (Doll 1983a). Furthermore, subsequent cultivation often helps place non sprouted tubers in soil con ditions conducive to sprouting (Doll 1983a). Soil disturbance, however, can also move tubers closer to the soil surface where they are more susceptible to des ic cation and cold temperatures (Glaze 1987). Glaze (1987) claims purple nutsedge can be reduced t o manageable populations by plowing or disking at intervals of three weeks or less for a minimum of two years, and by planting a winter grain or hay crop. An obvious disadvantage to this is that fields must be fallowed. It is also costly in terms of both t ime and energy. Doll (1983a), however, claims that two to four cultivations prior to planting are sufficient to provide crop species a competitive advantage over nutsedge. Glaze (1987) concluded that in addition to practicing cultural methods such as high plant density and narrow row spacing, cultivation during the growing season, in conjunction with the use of herbicides, will eventually provide adequate pressure to maintain nutsedge populations at manageable levels.

PAGE 24

24 Research has shown that eradication o f nutsedge is possible. Smith and Mayton (1942) disked 11 fields infested with nutsedge every two, three, or four weeks for two years, and almost always achieved eradication. This frequency of cultivation is obviously not practical from a farmer's perspect ive. Irrigation in these studies was shown to reduce the number of tillage operations needed to achieve eradication by inducing tubers to sprout more readily than if left under natural rainfall conditions. Herbicides N onchemical control measures alone do not provide satisfactory control of nutsedge species in most cases (Wax 1975). Attempts to chemically eradicate purple nutsedge began in 1925 in India when Ranade and Burns applied a 2% solution of table salt and copper sulfate at two week intervals to a d ense stand. One hundred applications of table salt significantly reduced, but failed to eradicate the tubers. Copper sulfate merely caused leaf chlorosis, and had no effect on the tuber population (Doll 1983a). Banks (1983) conducted field and greenhouse e xperiments to determine the effects of soil applied herbicides on initial yellow nutsedge control, as well as their effects on shoot regrowth and tuber production. Herbicides evaluated included alachlor, fluridone, diethatyl, metolachlor, acetochlor, norfl urazon, and vernolate (Banks 1983). Herbicides were mixed in a sandy loam soil with a pH of 6.3 and 1.1% organic matter and transferred to plastic pots. Four yellow nutsedge tubers were placed in each pot. Shoot counts were taken at two week intervals to d etermine initial control for different periods after treatment. Also at two week intervals, original tubers from four pots in each replication were removed, washed, and transplanted in untreated soil. After eight weeks, counts on new shoots and tubers were taken for each pot (Banks 1983). O nly fluridone and norflurazon provided 100% control of yellow nutsedge when visually rated eight weeks after planting in treated soil in a greenhouse Fluridone, norflurazon, and

PAGE 25

25 acetochlor were most effective in prevent ing new tuber production (Banks 1983) S oybeans were more competitive against yellow nutsedge in the field Fluridone was most effective, and norflurazon the least effective in reducing tuber and shoot populations of yellow nutsedge in cotton. However, tub ers in plots treated with fluridone tended to produce more shoots per tuber than the other treatments. All treatments except alachlor provided good control of yellow nutsedge in soybeans (Banks 1983). The acid amide herbicide metolachlor has been used to provide partial control of yellow nutsedge in several crops including corn and peanut, but it has only slight activity on purp le nutsedge (Webster and Coble 1997). The photosystem II inhibitor herbicide bentazon is applied POST in corn, soybean and peanut t o augment yellow nutsedge control but as with metolachlor, bentazon lacks adequate activity on purple nutsedge (Stroller et al. 1975). Diclosulam is a triazolopyrimidine sulfonanilide herbicide used in soybean and peanut (Dotray et al. 1998). Grichar et a l. ( 2008) reported greater than 80% control of yellow nutsedge in peanut when diclosulam was applied PRE at 0.018 or 0.026 kg ha1 followed by (fb) S metolachlor applied POST at 0.56, 1.12, or 1.46 kg ha1. The sulfonylurea halosulfuron controls both purp le and y ellow nutsedge in corn, but has limited activity on most grasses and certain broad leaf weeds ( Webster and Coble 1997). Mesotrione, a triketone herbicide, can be applied PRE and POST in corn to improve broadleaf weed control, while also providing a dded control of yellow nutsedge ( Armel et al. 2008). Trader et al. ( 2008) reported greater than 83% yellow nutsedge control in yellow summer squash with POST applications of halosulfuron at 18 and 27 g ha1 in combination wi th clomazone plus ethalfluralin PRE. N orsworthy et al. ( 2007) reported 66 % suppression of purple nutsedge in chi le pe pper ( Capsicum annuum L. ) from POST directed applications of

PAGE 26

26 halosulfuron at rates less than or equal to 36 g ha1. Halosulfuron can also be used POST to control both pur ple and yellow nutsedge in turfgrass (Czaronta 2004) Applying herbicides at rates below those recommended by the manufacturer has been considered a possible means of minimizing the risk of carryover, provided broadspectrum weed control is not compromised ( Troxler et al. 2001). For example, lower use rates alleviate carryover concerns with cotton. The manufacturer indicates cotton should not be planted within 17 months after imazapic application to peanut at the labeled rate (Anonymous, 2007). Grichar ( 2002) reported imazapic provided 90% yellow nutsedge control in peanut when applied at the rate of 40 g ha1, well below the labele d rate of 70 g ha1. Single applications and mixtures of imazapic, diclosulam, and flumioxazin provide residual control of yellow nutsedge as well as many broadleaf weeds in peanut when applied at labeled rates (Grichar 2002, Main et al. 2005). Reduced rates o f these herbicides can also be effective. Willingham et al. (2008) reported greater than or equal to 80% control of yellow nu tsedge, Florida beggarweed ( Desmodium tortuosum L.) hairy indigo ( Indigo fera hirsuta L.) and sicklepod ( Senna obtusifolia L.) in peanut resulting from diclosulam at 6 g ha1 (1/4 X) (1/4 the labeled use rate) plus flumioxazin at 20 g ha1 (1/4 X) applied PRE, fb imazapic POST at 17 g ha1 (1/4 X). Trifloxysulfuron is a POST herbicide developed for use in cotton, sugarcane, tomato and turfgrass. In cotton, trifloxysulfuron provides control of perennial nutsedges as well as several difficu lt to control broa dleaf weeds (Brecke and Stephenson 2006b). Most recently, the development of glyp h osate resistant cotton and soybean cultivars has provided growers another option in nutsedge management. POST applications of this otherwis e

PAGE 27

27 nonselective herbicide may prov id e an alternative to more conventional chemical control measures (Edenfield et al. 2005). History of t he Imidazolinone Family of Herbicides The imidazolinone herbicides were discovered in the mid 1970s and developed in the 1980s by scientists at Americ an Cyanamid Company in Princeton, New Jersey. Their discovery began via random screening tests in which a compound known as phthalamide was found to exhibit herbicidal activity at 4 kg ha1. This compound subsequently served as the template, or herbicide lead, from which chemicals with stronger activity were derived. Due to their lack of crop selectivity, the first imidazolinone herbicides to be synthesized were tested as total vegetation control agents. Modifications of these initial imidazolinones yielded compounds possessing greater selectivity, as well as higher levels of activity (Shaner and OConnor 1991). All members of the imidazolinone family of herbicides contain an imidazole ring. They differ, however, in the type of ring structure substitution a t the 2 (R) position of the imidazole ring. Three possible substitutions at this position include benzene, pyridine, and quinoline. Being weak acids, the water solubility of the imidazolinones is greatly affected by soil pH (Shaner and OConnor 1991). So lubility increases significantly as the soil pH rises from 5 to 7. Adsorption, conversely, is greater in low pH (acidic) soils. Since dissipation of the imidazolinones is due primarily to microbial degradation, leaching and carryover injury to rotational c rops are more of a concern in high pH (basic) soils in which microbial activity is typically reduced. Persistence also tends to be greatest in soils high in clay content and organic matter. Risks of leaching and carryover injury, however, are less of a con cern in Florida than in northern regions of the country, where cool temperatures often decelerat e microbial activity. L osses of these herbicides due to volatilization and photo degradation are negligible (Shaner and

PAGE 28

28 OConnor 1991). Rotational crops sensiti ve to carryover from imadazolinone herbicides include cotton, field corn, potato, canola ( Brassica napus L. and B. campestris L.) and sugarbeet (Moyer and Esau 1996). Imidazolinone herbicides inhibit the enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS) (Moberg and Cross 1990; Schloss 1990; Stidham and Shaner 1990). This is the same mechanism of action as that targeted by the sulfonylurea and triazolopyrimidine sulfonanilide families of herbicides, as well as the herbicide pyrithiobac (Kleschick et al. 1990; Moberg and Cross 1990). ALS is required by plants for the synthesis of the branched chain amino acids leucine, isoleucine, and valine. Secondary effects include reduced levels of RNA and DNA synthesis, and respiration. Activity is first seen in the growing points of susceptible plants, where amino acid demands are greatest. Most tolerant plant species are able to metabolize imidazolinones more quickly than susceptible ones. There is evidence, however, that some tolerant plants possess an altered form of the ALS enzyme that is not subject to inhibition by these herbicides (Shaner and OConnor 1991). Since the ALS enzyme occurs only in plants, imidazolinones pose little threat to humans or the environment. All but one has o ral LD50 values of 5,000 mg kg1 in rats. By comparison, the LD50 value of table salt for rats is 3,000 mg kg1 (Shaner and OConnor 1991; Tables 1.1 and 1.2). Imidazolinone herbicides are readily absorbed by roots and foliage, and are highly mobile once inside plants. They are translocated in both the xylem and phloem, and accumulate in meristematic tissues located in young, actively growing plant parts. Injury symptoms are characterized by cessation in growth, shortened internodes, and chlorosis followed by necrosis in the growing tips of roots and shoots, progressing to older plant parts. Treated plants may become purplish in color in response to a weakened root system. Although movement of these herbicides

PAGE 29

29 within plants is rapid, death usually does not occur for approximately two weeks (Shaner and OConnor 1991). Imidazolinone herbicides can be tank mixed with several different herbicides, including members of the dinitroaniline family of herbicides. Post emergence applications require the use of a nonio nic surfactant (Shaner and OConnor 1991). As a result of their versatility, low mammalian toxicity, environmental safety, and low use rates, the imidazolinones currently play a vital role in food production throughout the world (Shaner and OConnor 1991; Tables 1.1 and 1.2). Imazapic, ( ) 2(4 isopropyl 4methyl 5oxo 2imidazolin 2yl) 5methylnicotinic acid, and imazethapyr, ( ) 2(4 isopropyl 4methyl 5oxo 2imidazolin 2yl) 5ethylnicotinic acid, are the first herbicides to provide effective post emer gence purple nutsedge control in peanuts. Imazapic was registered for use in peanut in the spring of 1996 under the trade name Cadre. Imazethapyr was registered for use in peanut in the spring of 1991 under the trade name Pursuit (Wilcut et al. 1996). I m azap i c i s not labeled for use i n any crop other than peanut, wh i le i mazethapyr may also be used for weed control i n soybean, dry beans ( Phaseolus vulgari s L.), f i eld peas ( Pisum sativum L.), and alfalfa ( Medicago sativa L.) (Moyer and Esau 1996). Imazapi c is labeled for application in peanut postemergence, while imazethapyr may be applied PPI, pre e mergence, at cracking, and post emergence. The rate for both imazapic and imazethpyr in peanut is 71 g ha1. At cracking and early post emergence treatments provi de the best results for both herbicides ( Ferrell et al. 2009 ). Optimum weed control occurs when weeds are 2 4 in height At cracking and post emergence treatments require a non ionic surfactant at 0.25% v/v.

PAGE 30

30 Imazapic provides enhanced purple and yellow n utsedge control relative to imazethapyr (Richburg et. al 1994; Richburg et. al 1993). In addition, imazapic controls Florida begga rweed and sicklepod the two most common and troublesome weeds in peanut, whereas imazethapyr provides poor control of these w eeds (Wilcut et. al 1996). I mazapic provides a broader spectrum of grass control than imazethapyr. Grass weeds controlled by imazap i c include: broadleaf signalgrass ( Brachiaria platyphylla L.), large and smooth crabgrass ( Digitaria sanguinalis L. and D. i schaemum L.), goosegrass ( Eleusine indica L.), seedling johnsongrass ( Sorghum halepense L.), southern sandbur ( Cenchrus echinatus L.), and Texas panicum ( Panicum texanum L.). In addition imazapic controls the following broadleaf weeds: bristly starbur ( Ac anthospermum hispidum L.), common cocklebur ( Xanthium strumarium L.), coffee senna ( Cassi a occ i dental i s L.), Flor i da pusley ( R i chardi a scabra L.), ha i ry indigo common lambsquarters ( Chenopodi um album L.), morningglory sp. ( I pomea sp. L.), p i gweed sp ( Amar anthus sp. L.), pr i ckly s i da ( Si da spi nosa L.), wild po i nsett i a ( Euphorbi a heterophylla L.), and w i ld rad i sh ( Raphanis raphanistrum L.). Imazethapyr provides good control of seedling johnsongrass, and fair control of crabgrass and goosegrass. Broadleaf w eeds controlled by imazethapyr include: bristly starbur, common cocklebur, coffee senna, Flor i da pusley, morn i ngglory sp., p i gweed sp., pr i ckly s i da, w i ld po i nsett i a, and w i ld rad ish. Im azethapyr prov i des better w i ld po i nsett i a control than i mazap i c, where as i mazap i c prov i des better control of ha i ry i nd i go than imazethap y r (Colv i n and Brecke 1997). Similar to other members of the imidazolinone class of herbicides, persistence of imazapic and imazethapyr in soil is dependent upon degradation by soil microb es. Therefore, persistence is influenced by soil moisture content, soil temperature, and degree of herbicide

PAGE 31

31 adsorption to soil (Moyer and Esau 1998). Abundant rainfall and warm temperatures in the southeastern United States, p articularly in Florida, are c onducive to substantial microbial breakdown of t hese herbicides. Imazapic and imazethapyr persistence increases with increasing organic matter and clay content, and as soil pH decreases below 6.0. This is due to increased herbicide adsorption to soil unde r these conditions, thereby protecting them from degradation via microbes (Shaner and OConnor 1991; Loux and Reese 1993). The importance of purple and yellow nutsedge control to southeaster n peanut g rowers has been well documented (Dowler 1992). Both spec ies reduce yield and quality by competing for light, water, mineral nutrients, and interfere with pesticide applications (Wilcut 1994a). Furthermore, tubers and rhizomes may cause problems in peanut harvesting and processing (Richburg et al. 1996; York and Wilcut 1995; Wilcut et al. 1994a). In addition, nutsedge rhizomes can pierce peanuts, thereby predisposing them to secondary infection by pathogens (Ramirez 1982). T uber reduction is essential to any successful management system targeting these two peren nial weeds due to the important role tubers play in the reproduction and dissemination of purple and yellow nutsedge in southeastern peanut fields Little is known about the impact of imazapic and imazethapyr on purple nutsedge tuber populations and tuber germination. Tillage alone, or in conjunction with herbicide treatments, is a method growers may employ to manage purple and yellow nutsedge. No research has explored the effects a wide variety of tillage timings and frequencies may have on purple nutsedge tuber populations. Furthermore, no research has been conducted to examine the effects of r epeated glyphosate applications and tillage over multi ple years on purple and yellow nutsedge tuber numbers.

PAGE 32

32 Previous research has not examined the effects imazapic and imazethapyr have on purple and yellow nutsedge shoot number and weight, shoot regrowth potential, root weight, and tuber number and weight when these herbicides are applied at several different rates to different sites of herbicide uptake, and also to plants of varying ages. Finally, no research has been performed to determine the degradation rates of imazapic and imazethapyr in soil over a twelve month period. Data are lacking on how various concentrations of these herbicides in soil affect purple nut sedge growth and reproduction over an extended period of time. The objectives of this research, therefore, were to determine the effects of imazapic and imazethapyr on mid and lateseason tuber densities, as well as lateseason tuber germination. Additio nal field studies examined the influence of tillage timing and frequency on the growth and reproduction of purple nutsedge. The effects of repeated glyphosate applications and tillage over multiple years on purple and yello w nutsedge tuber populations were also explored. Greenhouse studies examined the role herbicide rate and site of uptake, plant age, and growth medium play in reducing purple and yellow nutsedge shoot number and weight, root weight, tuber number and weight, and shoot regrowth potential. Fi nally, the ability of soil applied imazapic and imazethapyr to suppress purple nutsedge tubers after various incubation periods of up to one year after treatment was determined.

PAGE 33

33 Table 1 1. Imazapic chemistry and toxicity informationa pK a b 3.9 K ow c 0.1 6 at pH 5, 0.01 at pH 7, and 0.002 at pH 9 Vapor Pressure <10 7 mm Hg at 60 C Water Solubility 2,200 mg L 1 at pH 7 and 25 C Acute oral toxicity (rat) LD 50 > 5,000 mg Kg 1 a Ahrens, 1994. b Ionization constant of carboxylic acid. c Octanol / Water p artitioning coefficient. Table 1 2. Imazethapyr chemistry and toxicity informationa pK a b 3.9 K ow c 11 at pH 5, 31 at pH 7, and 16 at pH 9 Vapor Pressure < 10 7 mm Hg at 60 C Water Solubility 1,400 mg L 1 at pH 7 and 25 C Acute oral toxicity (rat) LD 50 > 5,000 mg K g 1 a Ahrens, 1994. b Ionization constant of carboxylic acid. c Octanol / Water partitioning coefficient.

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34 CHAPTER 2 EFFECT OF TILLAGE AND GLYPHOSATE APPLICATI ON ON CONTROL OF PUR PLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSEDGE ( C. ESCULENTUS L. ) Introduction Purple nutsedge is considered a serious weed of many agronomic and horticultural crops throughout the tropical and subtropical regions of the world (Bendixen and Nandihalli 1987), as well as in some warm temperate areas (H olm et al. 1991a). In the southeastern United States, purple nutsedge is a serious weed of cotton (Byrd 1992), peanut (Dowler 1992), and several vegetable crops (Morales Payan et al. 1998a; Morales Payan et al. 1998b; Morales Payan et al. 1997; Morales Pay an and Stall 1997; Santos et al. 1996). Yellow nutsedge is also a serious weed of many crops throughout the world (Holm et al. 1991b), and along with purple nutsedge, has become an increasingly problematic weed of cotton, peanut, and various vegetable crop s in the southeastern United States over the past 40 years (Bendixen and Nandihalli 1987). Purple and yellow nutsedge reduce crop yield and quality by competing for light, water, and mineral nutrients, serving as hosts for certain species of pathogens, arthropods, and nematodes, and by interfering with pesticide applications and harvest equipment (Richburg et al. 1996; York and Wilcut 1995; Wilcut et al. 1994). Nutsedge infestations may also increase the cost of cleaning and processing harvested crops, es pecially those similar in size to nutsedge tub ers, such as peanut. Sharp nutsedge rhizomes can pierce underground crops such as peanut, carrot, onion, potato, cassava, and yam, thereby predisposing them to secondary infection by pathogens that can impart an offensive flavor (Ramirez and Bendixen 1982.) The emergence of purple nutsedge as the worlds worst weed is due in part to the decreased use of hand hoeing, deep plowing, and cultivation as a mean s of weed control (Mercado 1979; Glaze 1987). Advantages of pre plant tillage include the promotion of tuber germination and the movement of tubers closer to the soil surface where they are more

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35 susceptible to cold temperatures and drying (Glaze 1987). Cultivation of peanut beyond early season is not advised du e to possible yield reductions and the increased incidence of disease caused by soil borne pathogens (Wilcut et al. 1996). Tillage performed under dry conditions has been shown to be more effective in decreasing purp le nutsedge tuber numbers compared to wh en the soil is moist (Day and Russell 1955). Repeated cultivation that severs roots and rhizomes, coupled with tuber des ic c ation from subseque nt exposure, were effective in rapidly reducing tuber viability (Ranade and Burns 1925). H erbicides have become th e favored method of controlling nutsedge due to the increased popularity of conservation tillage, as well as the need for viable control measu res in noncrop areas ( Earl et al. 2004; Ferrell et al. 2004). G lyphosate [ (N phosphonomethyl glycine) ] is a poste mergence herbicide that has exhibited an ability to suppress resprouting of parent purple and yellow nutsedge tubers (Pereira et al. 1987; Doll a nd Piedrahita 1982). Glyphosate has been used extensively for the control of purple and yellow nutsedge because of its ability to translocate via rhizomes to basal bulbs and tubers ( Bryson et al. 1994; Sprankle et al. 1975). Pereira and Crabtree (1986) found yellow nutsedge tubers to be relatively strong sinks for glyphosate accumulation. Keeley et al. (1985) indicated that translocation of 14C labeled glyphosate into yellow nutsedge tubers decreased as plant age increased from 2 to 6 weeks, while Zandstra and Nishimoto (1977) found glyphosate translocation to be approximately the same in purple nutsedge plants from 2 to 6 weeks of age. Suwunname k and Parker (1975), however, reported considerably greater glyphosate activity on purple nutsedge when applied 3 weeks versus 9 weeks after planting. A combination of systemic, post emergen ce herbicides and repeated tillage is considered to be the most effective method of reducing purple nutsedge infestations (Neeser et al. 1997,

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36 Doll 1994). Intensive nutsedge control programs that incorporate both cultivation and herbicides usually result in an increase in crop yields (Glaz e 1987). Tillage following application of glyphosate improves purple nutsedge control and reduces tuber populations (Pereira et al. 1987). Chase and Appleby (1979) found that an interval of at least three day s between gly phosate application and tillage all ows adequate herbicide translocation to the purple nutsedge tubers. Much of the research examining the effectiveness of tillage for the control of purple nutsedge dates back to the preherbicide era of weed control (Smith and Frick 1937; Smith and Mayton 1939, 1942). Most of the work looking at the effects of tillage on nutsedge control has consisted of one to three tillage operations early in the season. No research has examined the effects a wide variety of tillage timings and frequencies have on purple nutsedge tuber populations. Furthermore, no research has been conducted to examine the effects of the combination of repeated glyphosate applications and tillage over multiple years on mid and lateseason purple and yel low nutsedge tuber populations. Thre e field studies were conducted at the West Florida Research and Education Center near Jay, FL. The first study examined the influence of tillage timing and frequency on the growth and reproduction of purple nutsedge. Two additional studies were conducted t o examine the combined effects of repeated glyphosate applications and tillage over multiple years on purple and yellow nutsedge tuber populations. Materials and Methods Tillage Study A study was conducted over three years to determine the influence of cu ltivation timing and frequency on the growth and reproduction of purple nutsedge. S tudy site s differed from year to year but each site had a history of extremely heavy purple nutsedge infestations. No crop was planted. Soil type for all three sites was a Red Bay fine sandy loam; fine loamy, kaolinitic,

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37 thermic Rhodic Kandiudult. Plots were arranged in a randomized complete block design having four replicat ion s of treatments Plot size was 3 .1 x 7.6 m. Land preparation included plowing, disking, and field cultivating the entire study area, including the control plots, prior to initiating treatments. Treatments consisted of tilling to a depth of approximately 15 cm with a single pass of a PTO driven roto tiller. T reatments were applied at 2 week intervals, f rom 2 to 10 weeks following initial land preparation performed in May. Following is a list of the 16 tillage treatment intervals: control (not tilled following initial land preparation), 2 week only, 2 + 4 week, 4 week only, 2 + 4 + 6 week, 4 + 6 week, 6 w eek only, 2 + 4 + 6 +8 week, 4 + 6 + 8 week, 6 + 8 week, 8 week only, 2 + 4 +6 + 8 + 10 week, 4 + 6 + 8 +10 week, 6 + 8 + 10 week, 8 + 10 week, and 10 week only. Tillage was implemented in all three years of the study. F our soil cores measuring 10 cm in di ameter b y 30 cm deep were randomly collected from each plot in Y ear one and sifted through a screen to remove tubers. Mid and late season1Glyphosate and Tillage Study samp les were collected in June and August re spectively. F our, 25 x 25 c m by 30 cm deep sample s were randomly collected per plot in July and October of Y ear two. T wo, 25 x 25 c m by 30 cm deep sam ples were collected from each plot in July and September of Y ear three. T he number of tubers present from 0 to 10, 10 to 20, and 20 to 30 cm fro m the soil surface was recorded o n a per m2 basis for each of the three years t he study was conducted Two field studies were conducted to evaluate the effect of repeated tillage and glyphosate applications on the reproductive capabilities of purple and yellow nutsedge. One study site was 1 All field studies were conducted during the summer months. Midand late -season refer to early and late -summer sampling dates, respectively.

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38 an area known to have a heavy infestation of purple nutsedge, while the other study site possessed a dense population of yellow nutsedge. No crop was planted at either site. Soil type for the study involving purple nutsedge wa s a Red Bay sandy loam (Rhodic Paleudult), while the soil type for the yellow nutsedge study was a Fuquay loamy sand (Plinthic Paleudult). T he procedures were identical for both studies o ther than soi l type and weed species present The study areas were d isked twice and then field cultivat ed several times on 18 May of Y ear one. T he experimental design was a randomized complete block with treatments replicated four times. Perm anent plots measuring 6.1 x 9.1 m were maintained for two years. The large plot s izes provided ample space for taking mid and late season tuber sam ples each year. In Y ear one, two 1 m2 x 23 cm deep samples were collected per plot and sifted through a screen to collect tubers. Mid season samples of purple and y ellow nutsedge tubers wer e collected on 18 and 20 July respectively. Lateseason tub er samples were collected on 3 and 10 September for purple and yellow nutsedge, respectively. T wo m2 by 23 cm deep samples were collected per plot the second year Mid and lateseason samples of both purple and y ellow nutsedge tubers were collected on 25 July and 31 October respectively. These experiments consisted of 3 treatments. Control plots mimicked the natural reproductive process of nutsedge via tuber production. A second treatment em ploying the application of glyphosate approximately every 3 to 4 weeks from May to October of each year attempted to reduce the reproduction of existing tubers with herbicide alone Glyphosate was applied at the rate of 4,482 g a .i. ha1 via a tractor moun ted boom sprayer using compressed CO2 as the propellant. The sprayer was operated at 220 kPa of pressure to deliver a spray volume of

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39 187 L ha-1. For the third treatment, plots were first tilled to a depth of approximately 15 cm using a tractor P TO operate d rototiller to stimulate tuber sprouting. Once an appreciable number of nutsedge shoots had emerged (approximately 25 plants m2) plots were then treated with glyphosate. This cycle of cultivation, in conjunction with subsequent applications of glyphosa te, was repeated throughout the growing season in an effort to deplete the nutsedge tuber bank. Data were subjected to analysis of variance, and t reatment means were compared using Fisher's Protected LSD Tes t at the P = 0.05 level of significance Since n o interactions among years were found, data were pooled over three years for the tillage study. Statistical analysis did not indicate an interaction between treatment and tuber sampling depth T herefore, data were pooled across all depths. Results a nd Disc ussion Tillage Study For both the mid season and lateseason control plots, more than twice as many tubers were found in the upper 10 cm of the soil than from 20 to 30 cm (Tables 21, 22). Other researchers found 90% of tubers in the top 15 cm of the so il (Nishimoto 2001). Similarly, this study found 80% of tubers in the top 20 cm of untreated controls. R epeated cultivations reduced tuber numbers in the upper 10 cm of the soil profile more than it did for depths greater than 10 cm. Tilling at 2 + 4 + 6 + 8 weeks res ulted in the lowest tuber populations at mid season (Table 21) N o treatments however, were statistically better at reducing tuber densities at all sampling depths by mid season than tilling at 2 and 4 weeks, or at 4 and 6 weeks. Tilling at 2 + 4 + 6 + 8 + 10 weeks resulted in a 92 % reduction in end of season tuber density in the upper 20 cm of soil compared to the nontreated control plots. This is similar to previous research that found continuous cultivation provide d a 90% reduction in tuber densities (Edenfield et al. 2005). Tilling three times (2 + 4 + 6 weeks, 4 + 6 + 8 weeks, or 6 + 8 + 10

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40 weeks ) reduced tuber density by 70 to 87% compared to the nontreated control at the time of late season sampling (Table 22). I ncreasing the number of t illage events did not further reduce tuber density significantly. One or two tillage events were generally less effective at reducing t uber density than three This agrees with previous research that concluded that a single cultivation did not impact purpl e nutsedge tuber density (Holm, 1962b). The effect of tillage on total tuber weights was similar to its effect on tuber population. While tilling at 2 + 4 + 6 + 8 weeks resulted in the lowest to tal tuber weights at mid season from depths of 020 cm and f rom 0 30 cm, no treatments were significantly better at lowering total tuber weight than two cultivations at either 2 + 4 weeks or at 4 + 6 weeks (Table 23) Similarly, this study showed that t otal tuber weights at the time of late season sampling gener ally decreased as the number of cultivations increased (Table 24). However, while plots tilled at 2 + 4 + 6 + 8 + 10 weeks had the least amount of tuber biomass, they were not statistically different than plots that were only tilled at 4 + 6 weeks. Two cu ltivations earlier in the season (2 + 4 weeks) appeared to allow more time for tuber regeneration throughout the summer, while two cultivations late in the season (6 + 8 or 8 + 10 weeks) were less effective in reducing the growth of tubers that had been al lowed to grow unchecked during the fi rst half of the growing season. Percent germination of tubers at both the mid and lateseason sampling dates w as lowest in plots tilled three to five times beginning 2 weeks after initiation of the study (Table 25). M ore than three cultivations did not significantly reduce percent germination of tubers. By lateseason, tuber germination in these plots was reduced by approximately 50% relative to the non treated control. A single c ultivation at four weeks, however, lowered lateseason germination rates just

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41 as much. A single cultivation at 10 weeks appeared to stimulate tuber germination, as indicated by a germination rate of 77% versus 63% for the control (Table 25) A number of researchers have suggested frequent cu ltivation as a satisfactory means of controlling purple nutsedge. Smith and Mayton (1938, 1942) concluded that, except on poorly drained soils, plowing every three weeks for two years provided adequate control. Similarly, Westmoreland et al. (1955) recomme nded thorough disking at 2 to 3 week intervals for two growing seasons in order to eradicate purple nutsedge. According to Glaze (1987), purple nutsedge can be reduced to manageable levels in two years by plowing or disking at intervals of 3 weeks or less, and by planting a winter cover crop of either grain or hay. Sinha and Thakur (1967) considered 3 to 4 weeks to be the optimum tillage frequency for nutsedge control. Thullen and Keeley (1975) found that repeated tillage operations at 4 week intervals were required in order to reduce yellow nutsedge density. Infrequent tillage may result in the breakage of tuber chains, thus releasing apical dominance and stimulating the sprouting of purple nutsedge tubers (Webster 2003). Cultivation intervals longer tha n o ne month increased the population while s horter intervals between cultivations decrease the ability of the plant to build up food reserves (Stamper and Melville 1956). Since tuber carbohydrate reserves and plant vigor decrease with each subsequent sprouti ng, repeated tillage may result in nutsedge plants that are more susceptible to additional control measures such a s herbicides (Wax et al. 1972). Glyphosate and Tillage Study Our research showed that multiple treatments of glyph osate at the rate of 4,482 g resulted in a 3 9% reduction in purple nutsedge tubers by late season in Y ear one of the study c ompared to the nontreated control (Table 2 6) Tuber densities were reduced by 67% by the end of the second year. Similarly, Akin and Shaw (2001) saw a 42% red uction in tubers following multiple

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42 applications of glyphosate at the rate of 420 g followed by a single application at 280 g On the other hand, Webster et al. (2008) found that a single glyphosate application at the rate of 2,570 g reduced purple and ye llow nutsedge tuber densities by 75% and 83% of the nontreated control, respectively. T he greatest reduction in purple nutsedge tuber number, weight, and viab ility by late season resulted from the use of multiple applications of both glyphosate and tillage (Tables 26, 2 7). This treatment resulted in 66% and 80% fewer tubers than the control by late season in Y ears one and two, respectively Multiple treatments of glyphosate resulted in a 67% reduction in tubers. This is unlike the results from previous re search that found that purple nutsedge control in soybean can be achieved without the use of cultivation (Edenfield et al. 2005). The lack of crop competition with nutsed ge may have reduced the effectiveness of the glyphosate only treatment. Only the combination of glyphosate and tillage significantly reduced lateseason purple nutsedge tuber weights by year two. L ateseason yellow nutsedge tuber densities were reduced by 45% and 65% in Y ear one following treatments of multiple applications of glyphosate and glyphosate + tillage, respectively ( Table 2 8). F ewer differences were seen between treatments for yellow nutsedge compared to purple nutsedge in Y ear two. A lternating tillage with applications of glyphosate did not provide as much additional control co mpared to glyphosate alone as it had for the control of purple nutsedge (Table 2 9). Neither treatment reduced yellow nutsedge tuber numbers or weights significantly. Previous research had shown a single application of glyphosate could reduce yellow nutsed ge tuber densities by more than 50% (Nelson and Renner 2002). Results from t he tillage study indica te that at least two early season tillage operations are necessary to significantly reduce lateseason purple nutsedge tuber density, weight, and percent

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43 germination M ore than two early season tillage operations may not provide southeastern peanut growers with significantly better lateseason purple nutsedge control Supplementing glyphosate treatments with t illage operations resulted in significantly fewe r purple nut sedge tubers than the untreated control. Both purple nutsedge tuber density and tuber weight were significantly reduced by multiple applications of glyphosate and multiple glyphosate combined with multiple tillage operations in Y ear two Simila r to the results for purple nutsedge, the most significant reductions in yellow nutsedge tuber numbers, wei ghts, and germination rates in Y ear one resulted from the treatment consisting of multiple applications of glyphosate and tillage. No treatments sign ificantly reduced lateseason yellow nutsedge tuber numbers, we ights, or germination rates by Y ear two These results indicate that, when practical, incorporating tillage and/or glyphosate treatments with existing purple nutsedge management systems can aid in depleting tuber populations. Furthermore, yellow nutsedge tuber numbers may be less affected by tillage operations than purple nutsedge. Previous research has examined how frequency and time of year of glyphosate application affect nutsedge control. Za ndstra et al. (1974) were able to reduce purple nutsedge tuber populations by 92% in one season following repeated cultivations and glyphosate applications in a fallow field in Hawaii. Tubers were collected once at the end of the study by sampling the uppe r 13cm of soil from 0.1 m2 of each treatment. Studies with yellow nutsedge have indicated that at least two years of frequent tillage is required to reduce plant populations t o manageable levels (Glaze 1987; William and Bendixen 1987). Nelson and Renner (2002) saw a 53% reduction in yellow nutsedge tuber density following a single application of glyphosate. Repeated applications of glyphosate in Australia have controlled purple nutsedge in both fallow fields and in cotton (Charles 1995). According to Bell e t al. (1962), a two year fallow consisting

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44 of either continuous tillage or continuous herbicide treatment is required to achieve a 90% reduction of viable nutsedge tubers in soil. Cools and Locascio (1977) reported better control of purple nutsedge when gl yphosate was applied in the summer or fall rather than in the spring. Because tuber production is accelerated by short photoperiods, it is important to utilize tillage, herbicides, or alternative control measures to prevent tuber production during the late fall (Bell et al. 1962).

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45 Table 2 1. Effect of tillage on mid season purple nutsedge tuber density three years combined Depth of S ample (cm) Time of Tillage 0 10 10 20 20 30 0 30 -------------------------Number of Tubers m 2 --------------------Control 74 a a 48 a b 31 ab 154 a 2 week 47 bc 30 cd 24 a bcd 101 b 2 + 4 18 de 16 def 18 cdef 53 cde 2 + 4 + 6 9 e 8 f 7 f 24 e 2 + 4 + 6 + 8 6 e 7 f 9 f 22 e 2 + 4 + 6 + 8 + 10 9 e 9 e f 7 f 25 e 4 week 39 c 24 c de 1 6 cd ef 80 bc d 4 + 6 19 de 14 ef 10 ef 43 de 4 + 6 + 8 14 e 14 ef 13 d ef 41 de 4 + 6 + 8 + 10 12 e 13 ef 13 de f 38 e 6 week 41 c 33 bc 21 b cde 95 b 6 + 8 36 cd 31 c d 18 cd ef 86 bc 6 + 8 + 10 35 cd 21 cd e f 23 bcd 86 bc 8 week 65 ab 53 a 35 a 153 a 8 + 10 61 ab 48 a b 35 a 144 a 10 week 76 a 47 a b 29 abc 151 a LSD 1 9 1 5 1 1 41 a Values followed by different letters indicate significant diff erences according to LSD test ( P =0.05)

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46 Table 2 2. Effect of tillage on lates e ason purple nutsedge tuber density three years combined Depth of S ample (cm) Time of Tillage 0 10 10 20 20 30 0 30 -------------------Number of Tubers m 2 -------------------------Control 86 a a 65 a 36 a 181 a 2 week 72 ab 47 bc 30 ab 150 abc 2 + 4 31 de 25 efgh i 15 cde 72 fgh 2 + 4 + 6 12 fg 11 ijk 9 e 23 i 2 + 4 + 6 + 8 7 g 9 jk 10 de 26 i 2 + 4 + 6 + 8 + 10 6 g 6 k 9 e 20 i 4 week 53 c 33 c def g 20 bcde 105 def 4 + 6 27 ef 21 fghi j 12 cde 61 ghi 4 + 6 + 8 12 fg 14 hij k 14 cde 39 ghi 4 + 6 + 8 + 10 8 g 11 ij k 13 cde 32 hi 6 week 48 cd 35 cde f 23 bc 107 def 6 + 8 31 de 28 defg 22 bcd 80 efg 6 + 8 + 10 16 efg 19 ghij k 22 bcd 56 ghi 8 week 59 bc 41 bcd 28 ab 126 bcd 8 + 10 49 cd 37 cde 29 ab 115 cde 10 week 74 a b 53 ab 37 a 165 ab LSD 18 14 1 2 41 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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47 Table 2 3. Effect of tillage on midseason purple nutsedge tuber weight three years combined Depth of S ample (cm) Time of Tillage 0 10 10 20 20 30 0 30 ----------------Tuber Fresh W eight (g m 2 ) -----------------Control 89 a a 54 ab 34 ab 177 a 2 week 53 bc 35 b cd 25 abcd 113 bc 2 + 4 18 ef g 16 def 20 bcdef 55 d h 2 + 4 + 6 8 g 8 f 7 f 22 g 2 + 4 + 6 + 8 5 g 6 f 9 f 19 g 2 + 4 + 6 + 8 + 10 7 g 8 f 7 f 22 g 4 week 44 c de 28 cde 19 cdef 91 c f 4 + 6 19 def g 16 d ef 10 ef 45 efg 4 + 6 + 8 13 f g 13 ef 12 def 38 fg 4 + 6 + 8 + 10 12 f g 12 ef 11 d ef 35 fg 6 week 47 c d 38 bc 24 abcde 109 bcd 6 + 8 45 cd e 38 bc 19 cdef 102 cde 6 + 8 + 10 40 cde f 29 cde 24 abcde 92 cdef 8 week 76 ab 59 a 36 a 171 a 8 + 10 85 a 60 a 37 a 181 a 10 week 81 a b 53 ab 31 abc 166 ab LSD 2 8 19 1 4 57 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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48 Table 2 4. Effect of tillage on lateseason purple nuts edge tuber weight three years combined Depth of S ample (cm) Time of Tillage 0 10 10 20 20 30 0 30 ------------------Tuber Fresh Weight (g m 2 ) --------------------Control 99 a a 77 a 44 ab 193 a 2 week 83 a b 55 bc 29 bcd 167 ab 2 + 4 32 d efg 25 efghi 17 defg 75 c g 2 + 4 + 6 8 gh 9 ij 7 fg 25 gh 2 + 4 + 6 + 8 5 gh 6 ij 9 efg 21 gh 2 + 4 + 6 + 8 + 10 4 h 4 j 6 g 14 h 4 week 55 c de 35 cdefg 22 cdef 113 bcde 4 + 6 29 efgh 20 fghij 12 efg 61 defgh 4 + 6 + 8 11 f gh 13 hij 13 efg 37 fgh 4 + 6 + 8 + 10 6 gh 8 ij 11 efg 26 gh 6 week 58 b cd 41 cde 24 cde 123 bc 6 + 8 37 def 30 defgh 23 cde 90 cdef 6 + 8 + 10 15 f gh 18 ghij 22 cde f 56 efgh 8 week 73 a bc 47 bcd 35 abc 155 ab 8 + 10 50 cde 39 cdef 29 bcd 118 bcd 10 week 87 a 66 ab 46 a 200 a LSD 2 7 20 15 58 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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49 Table 2 5. Effect of tillage on purple nutsedge tuber germination three years combined Time of Tillage Mid Season Late Season -----------------Germination (%) --------------------Control 71 bcd a 63 bcd 2 week 81 ab c 52 d e 2 + 4 71 bcd 48 ef 2 + 4 + 6 51 f 34 g 2 + 4 + 6 + 8 50 f 36 fg 2 + 4 + 6 + 8 + 10 54 ef 36 fg 4 week 82 ab 45 e fg 4 + 6 75 bcd 52 de 4 + 6 + 8 66 e 54 cde 4 + 6 + 8 + 10 66 e 46 efg 6 week 90 a 60 bcd 6 + 8 76 bcd 68 ab 6 + 8 + 10 77 abcd 62 bcd 8 week 79 abc d 67 ab 8 + 10 77 a bcd 65 a bc 10 week 68 cd 77a LSD 13 12 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05) .

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50 Table 2 6. Effect of glyphosate and tillage on pu rple nutsedge tubers, year one Mid seaso n Late season Treatment Tubers Tuber Weight Germination Tubers Tuber Weight Germination (No. m 2 ) (g m 2 ) (%) (No. m 2 ) (g m 2 ) (%) Nontreated Control 808 a a 490 a 71 846 a 475 a 68 a Repeated Glyphosate 540 b 267 b 68 518 b 218 b 56 b Alternating Glyphos ate + Tillage all season 225 c 110 c 61 289 c 117 c 46 c LSD 51 49 NS 71 49 8 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Sampling depth = 23 cm Table 2 7. Effect of glyphosate and tillage on purple nutsedge tubers, year two Mid season Late season Treatment Tubers Tuber Weight Germination Tubers Tuber Weight Germination (No. m 2 ) (g m 2 ) (%) (No. m 2 ) (g m 2 ) (%) Nontreated Co ntrol 325 a a 180 a 40 a 469 a 0 Multiple Glyphosate 216 b 115 ab 32 ab 155 b 0 Multiple Glyphosate + Multiple Tillage 154 b 85 b 30 b 93 b 0 LSD 92 79 8 63 NS a Values followed by different letters indicate significa nt differences according to LSD test ( P =0.05) Sampling depth = 23 cm.

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51 Table 2 8. Effect of glyphosate and tillage on yellow nutsedge tubers, year one Mid season Late season Treatment Tubers Tuber Weight Germination Tubers Tuber Weight Germinati on (No. m 2 ) (g m 2 ) (%) (No. m 2 ) (g m 2 ) (%) Nontreated Control 627 a a 246 a 81 639 a 258 a 75 a Multiple Glyphosate 424 b 152 b 77 349 b 121 b 63 b Multiple Glyphosate + Multiple Tillage 210 c 67 c 63 226 c 67 c 49 c LS D 164 59 NS 84 39 8 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Sampling depth = 23 cm. Table 2 9. Effect of glyphosate and tillage on yellow nutsedge tubers, year two Mid season La te season Treatment Tubers Tuber Weight Germination Tubers Tuber Weight Germination (No. m 2 ) (g m 2 ) (%) (No. m 2 ) (g m 2 ) (%) Nontreated Control 106 a 34 42 147 43 0 Multiple Glyphosate 57 27 21 111 41 0 Multiple Glyphosat e + Multiple Tillage 36 8 18 85 31 0 LSD NS NS NS NS NS 0 a Significance was calculated according to LSD test ( P =0.05) Sampling depth = 23 cm.

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52 CHAPTER 3 IMAZAPIC AND IMAZETHAPYR FOR PURPLE NUTS EDGE (CYPERUS ROTUNDUS L.) CONTROL Intr oduction Purple and yellow nutsedge have become increasingly troublesome weeds in southeastern peanut and cotton fields since the introduction of herbicides (Bendixen and Nandihalli, 1987). The widespread use of dinitroaniline herbicides has reduced compe tition from grass and small seeded broadleaved weeds for purple and yellow nutsedge (Grichar 1992). Purple nutsedge was not listed among the top ten problem weeds in Mississippi Delt a cotton fields during the 1950s, when less than 10% of the cotton acreage was treated with herbicides (Wills 1977). By 1961, 75% of the cotton acreage in the Mississippi Delta was treated with herbicides, and by 1963, purple nutsedge had become the second and third most severe weed on sandy and clay soils, respectively (Wills 1 977). Similar trends were observed throughout the southeastern United States during this period. Herbicides have not only resulted in an increased nutsedge population, they have also helped determine which nutsedge species has become most prevalent. Due t o the increasing u se of herbicides since the 1960s, most notably metolachlor and bentazon, that differentially controlled yellow nutsedge, purple nutsedge has now replaced yellow nutsedge as the dominant nutsedge species in the southeast. Purple nutsedge reduces peanut yield and quality by competing for light, water, and nutrients, as well as by interfering with pesticide applications and harvesting (Wilcut, 1994a). Since tubers play a prominant role in the reproduction and dissemination of purple nutsedge reducing tuber populations should comprise a key component of any program to control this weed. Imazapic and imazethapyr were the first herbicides to provide effective postemergence purple nutsedge control in peanuts (Wilcut et al. 1996). Little is known concerning the impact of

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53 these herbicides on purple nutsedge tuber populations and tuber germination. The objective of this research was to determine the effects of imazapic and imazethapyr on mid and lateseason tuber densities and lateseason tuber ger mination of purple nutsedge. Materials and Methods A field study was conducted over three consecutive summers at the University of Floridas West Florida Research and Education Center near Jay, Florida to evaluate the effects of herbicide application rate and purple nutsedge growth stage on the effica cy of imazapic and imazethapyr. The study site consisted of a monoculture of purple nutsedge. No crop was planted. Soil type was an Orangeburg sandy loam (thermic Typic Paleudult) with 1.5% organic matter and a pH of 5.3. Plot si ze was 3.1 by 7.6 m. Imazapic or imazethapyr were applied preplant incorporated (PPI), early postemergence (EP ), mid post emergence ( M P), or late postemergence (LP) at the rates of 35 and 71 g a.i. ha1. Average height of purple nutsedge for the postemergence treatments was 5, 11, and 19 cm for the EP, M P, and LP treatments, respectively. Vernolate or metolachlor were applied PPI at the rates of 2241 and 2801 g, respectively. Glyphosate was applied EP, MP, or LP at the rate of 3361 g. Ear ly postemergence M P, and LP treatments of imazapic and imazethapyr included a nonionic surfactant at 0.25% v/v. Treatments were applied using either a CO2pressurized backpack sprayer or tractormounted boom sprayer using compressed air as the propellant. Each sprayer was calibrated to deliver a spray volume of 187 L ha1. All runs of the study were arranged as randomized complete block designs consisting of 4 replications. In July and November of Y ear one four soil cores measuring 10 cm in diameter b y 30 cm deep were randomly collected from each plot and sifted throug h a screen to remove tubers. In Y ear two, four 25 x 25 cm by 30 cm deep samples were collected from each plot in September. Two, 25 x 25 cm by 30 cm deep samples were collected in July and September of Y ear three.

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54 Data for tuber densities were obtained by excavating and sifting the soil from each plot and recording the number of tubers present from 0 to 10, 10 to 20, and 20 to 30 cm from the soil surface. The area of soil sampled differed from year to year, but all tuber number data were reported as m2 by 30 cm of soil Only firm, n on decayed tubers were counted. Late season samples for tuber densities were collected for all three years. In addition, mid season sample s were collected in Y ears o ne and three. Total and average tuber fresh weights for each treatment were recorded for the 3 different soil profiles. A maximum of 50 tubers per profile per treatment were then planted in pots in the greenhouse. After s ix weeks, percent tuber germinatio n for tubers from the different pro files within each treatment was recorded. Data for lateseason tuber weights were c ollected for all three years. M id season sample s were also collected in Y ear one. Data for tuber germination was determined at seasons en d for all three years. Data were subjected to analysis of variance (ANOVA), and treatment means were compared using Fishers Protected LSD at the 5% level of probability. Results a nd Discussion Tuber N umber An interaction between years prevented the combi ning of data for tuber number, weight, and germination across the three years the study was conducted. L ate post emergence treatments were not applied until after the mid season tuber samples were taken in Y ear one. H erbicide treatments had the greatest eff ect on tuber numbers within 10 cm of the soil surface (Table 31). Imazapic appli ed EP at the rate of 71 g provided the greatest reduction of tubers at both mid and late season (Tables 3 1, 32). Treatments statistically equivalent to imazapic 71 g EP at reducing tuber numbers in the upper 30 cm of the soil by late season in Y ear one included imazethapyr 71 g PPI, imazapic 35 g EP, imazethapyr 71g EP, glyphosate MP, imazapic 71 g MP, glyphosate

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55 LP, and imazapic 71g LP (Table 3 2). MP glyphosate treatments lowered tuber densities by lateseason more than those applied either EP or LP. Glyphosate applied MP reduced late season tuber numbers by 69% compared to the nontreated control. Webster et al. (2008) found that a single glyphosate applic ation at the rate of 2 570 g reduced purple nutsedge tuber densities by 75% compared to th e nontreated control. Similarly, Edenfield et al. (2005) found that glyphosate applied at 900 g reduced tuber numbers by 71%. Imazapic 71 g EP was best at reducing tuber number by seaso ns end in Y ear two also ( Table 3 3). Imazapic reduced the total number of tubers found in the soil by 84% compared to the nontreated control. Imazet hapyr 71 g PPI, metolachlor 2801 g PPI, imazethapyr 71g EP, imazapic 71 g MP, and g lyphosate 3 361 g MP were s tatistically as good at lower ing tuber numbers as imazapic 71 g EP. In Y ear three untreated plots, 54 and 41% of tubers were found in the upper 10 cm of the soil for the mid and lateseason samples, respectively ( Tables 3 4, 3 5). The greatest re ductio n in tuber numbers by mid seas on was obtained using vernolate PPI with 79% fewer tubers than the nontreated control ( Table 3 4). In contrast, other research found only a 37% reduction of purple nutsedge tubers in plots treated with vernolate (Warren and C oble 1999). The largest overall reduction in tubers by lateseason was provided by imazapic ap plied MP at the rate of 71 g (84% reduction compared to nontreated) Imazethapyr applied at the same rate and timing provided a 75% reduction in tuber numbers ( Ta ble 3 5) These results are similar to other research that showed a 92 and 73% reduction in purple nutsedge tuber densities following imazapic and imazethapyr, respectively, applied 70 g EPOST in peanut (Warren and Coble 1999). By late season, only the LP tre atments of imazapic at 35 and 71 g and imazethapyr at 35 g failed to lower tuber numbers by at least 50% compared to the control

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56 Tuber W eight I mazapic 71 g EP and imazethapyr 71 g EP provided the greatest reduction of tuber weights at mid season (92% and 88%, respectively) in Y ear one, but were not significantly better than vernolate PPI or imazapic 35 g EP ( Table 36). By late season in Y ear one, imazapic 71 g EP still provided the lowest tuber weights. Several other treatments, including imazethapyr 71 g PPI and vernolate 2 241 g PPI, as well as the LP treatments of glyphosate 3 361 g, imazapic 71 g and imazethapyr 71 g did just as well statistically (Table 3 7). I mazapic 71 g EP resulted in the lowest tuber weights in the upper 10 cm of the soil by la te season in Y ear two (Table 3 8). I mazapic 71 g EP lowered total tuber weight to 27 g (92% reduction) by late season co mpared to 310 g in the control ( Table 3 8). I mazapic 71 g MP resulted in the lowest tuber weight for 0 30 cm 13 compared to 194 g for the nontreated control in Y ear three ( Table 39 ). Imazapic 71 g EP reduced tuber weights as much as imazapic 71 g MP in the upper 10 cm of the soil. Of the four treatment timings, MP treatments generally resulted in the lowest tuber weights. MP treatments yielded an average tuber weight of 0.67 g, compared to 0.74, 0.94 and 0.96 g for EP, PPI, and LP, respectively. Tub er G ermination L ateseason percent tuber germination ranged from 11% for imazapic 71 g MP, to 72% for the untreated control in the first year ( Table 3 10). For Y ear two e nd of season percent germination of tubers ranged from a low of 20% for metolachlor PPI, to a high o f 65% for the control (Table 3 10). Glyphosate and imazapic were the only treatments that significantly reduced the germin ation of pu rple nutsedge tubers at mid season in the first year of the experiment. This control was apparent only when the treatments were applied MP in Y ear one. In Y ears two and three, all herbicides had a significant impact on reducing tuber germination at both mid and lateseason except when the treatments were applied LP.

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57 G lyphosate LP resulted in the lowest lateseason pe rcent germination of tubers in Y ear three at 10%, compared to 76% for the non treated control (Table 3 10) Similarly, Edenfield et al. (2005) reported germinatio n rates of 9 and 75% for sequential glyphosate treatments of 1 100 g and a nontreated control, respectively. Early postemergence treatments generally resulted in the lowest germination rates for tubers at the end of the growin g season. EP treatments resulted in an average germination rate of 24%, compared to 38% for MP treatments, 49% for both PPI and LP treatments and 76% for the untreated Imazapic, imazethapyr, metolachlor, and vernolate all provided significant control of purple nutsedge. No individual herbicide, however, stood out statistically as being superior to the others in controlling this weed. Generally, treatments applied after weed emergence resulted in better control than PPI treatments. Tuber number, weight, and germination were all lower when treated EP or MP than when treated PPI or LP. As stated earlier, the lowest tuber densities at time of late season sampling resulted from imazapic 71 g applied EP in Years one and two, and MP in Y ear three. These low tuber populations correlate with the high visual ratings of percent control observed for these treatments, as well as for glyphosate. These results suggest that EP and MP treatments can be as effective as PPI treatments, but that waiting until LP is not a realistic option when attempting to reduce tuber densities, weights, and germination rates within a growing season.

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58 Table 3 1. Effect of herbicide treatments on m id season purple nutsed ge tuber density, year one a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences a ccording to LSD test ( P =0.05) cLP treatments were not applied by date of mid season sampling. Treatment Rate Timing % Control a Depth of S ample (cm) b (g ha 1 ) 0 10 10 20 20 30 0 30 -----------------Number of Tubers per m 2 of Soil ----------Control 0 0 f 35 b 26 bc 28 ab 88 abc I mazapic 35 PPI 63 cd 18 c 21 bcde f 18 cdef 57 d I mazapic 71 PP I 70 bcd 14 cd 15 efghi 17 c defg 46 defg I mazethapyr 35 PPI 47 de 17 c 17 efgh 16 defg 50 def I mazethapyr 71 PPI 53 d 11 cde 13 fghi 14 efg 39 fgh V ernolate 2,241 PPI 47 de 9 def 8 ij 17 cdef g 34 gh G lyphosate 3,361 EP 67 bcd 15 cd 23 bcde 20 b cde 57 d I mazapic 35 EP 87 abc 6 efg 10 hi 12 efg 28 hi I mazapic 71 EP 93 ab 1 g 1 j 9 g 11 j Imazethapyr 35 EP 67 bcd 13 cde 12 ghi 15 efg 40 fgh I mazethapyr 71 EP 83 abc 2 fg 1 j 11 fg 19 ij G lyphosate 3,361 MP 100 a 9 def 12 ghi 18 cdef 39 fgh Imazapic 35 MP 17 f 11 cde 19 defg 29 a 59 d Imazapic 71 MP 20 ef 9 def 9 hij 24 abcd 42 efgh Imazethapyr 35 MP 47 de 15 cd 20 cdefg 20 bcde 55 de Imazethapyr 71 MP 20 ef 8 d efg 19 defg 16 defg 44 efg Glyphosate 3,361 LP c 38 ab 25 bcd 16 defg 79 bc I mazapic 35 LP 39 ab 19 defg 17 cdef g 76 c Imazapic 71 LP 33 b 29 ab 24 abcd 83 abc Imazethapyr 35 LP 40 ab 37 a 18 cdef 96 a Im azethapyr 71 LP 43 a 22 bcd e 25 abc 91 ab LSD (0.05) 28 7 8 8 14

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59 Table 3 2. Effect of herbicide treatments on l ateseason purple nutsed ge tuber density, year one Treatment Rate Timing % Control a Depth of S ample (cm) b ( g ha 1 ) 0 10 10 20 20 30 0 30 -------------Number of Tubers per m 2 of S oil ----------------Control 0 0 i 29 a 24 a 29 a 81 a I mazapic 35 PPI 53 fg 19 b 24 a 20 abcde 63 ab I mazapic 71 PPI 53 fg 12 b cdefg 17 ab 28 ab 56 bcd I mazethapyr 35 PPI 33 h 18 bc 15 bc 12 de 45 bcdef I mazethapyr 71 PPI 47 gh 9 defghi 14 bc 9 e 33 efgh V ernolate 2,241 PPI 47 gh 5 ghi 13 bcd 21 abcd 39 defg G lyphosate 3, 361 EP 13 i 11 c defgh 13 bcd 18 a bcde 42 cdef I mazapic 35 EP 73 bcde 7 efghi 12 cd 15 cde 34 efgh I mazapic 71 EP 90 ab 3 i 6 d 9 e 18 h I mazethapyr 35 EP 60 defg 14 bcde 10 cd 17 bcde 41 c defg I maze thapyr 71 EP 70 cdef 8 d efghi 9 cd 12 de 29 fgh G lyphosate 3,361 MP 70 cdef 4 i 6 d 12 de 22 gh I mazapic 35 MP 60 defg 13 bcdef 12 cd 19 abcde 44 b cdef I mazapic 71 MP 77 bcd 8 defghi 10 cd 1 5 cde 33 efgh I mazethapyr 35 MP 57 efg 15 bcd 13 bcd 14 cde 48 bcde f I mazethapyr 71 MP 63 cdefg 19 b 16 bc 13 c de 47 bcdef G lyphosate 3,361 LP 97 a 5 ghi 9 cd 18 a bcde 32 efgh I mazapic 35 LP 73 bc de 11 cdefgh 20 ab 19 abcde 49 bcde I mazapic 71 LP 80 abc 6 fghi 12 cd 18 abcde 37 d efg h I mazethapyr 35 LP 53 fg 18 bc 15 bc 27 ab 60 bc I mazethapyr 71 LP 73 bcde 9 defghi 9 cd 24 abc 39 defg LSD (0.05) 16.73 7 7 1 1 19 a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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60 Table 3 3. Effect of herb i ci de treatments on l ateseason purple nutsed ge tuber density, year two Treatment Rate Timing % Control a Depth of S ample (cm) b (g ha 1 ) 010 1020 2030 030 ---------------Nu mber of Tubers per m 2 of Soil ----------------Contr ol 0 0 h 103 a 67 a 87 a 257 a I mazapic 35 PPI 63 egf 42 b 56 ab 52 bc 150 b I mazapic 71 PPI 90 ab 32 bc 44 bc 60 b 135 bc I mazethapyr 35 PPI 70 cdefg 32 bc 40 bcde 53 bc 125 bcd I mazethapyr 7 1 PPI 78 abcdef 27 bcd 25 defg 36 cde 87 defg h V ernolate 2,241 PPI 58 g 21 bcd 42 bcd 48 bcd 112 bcdef M etolachlor 2,801 PPI 60 fg 21 bcd 32 cdef 31 de 84 defgh G yphosate 3,361 EP 88 abc 32 bc 22 efg 39 cde 92 cdefg I mazapic 35 EP 83 abcd 24 bcd 34 cdef 36 cde 91 cdefg I mazapic 71 EP 93 ab 7 d 7 g 23 e 40 h I mazethapyr 35 EP 67 defg 33 bc 39 bcde 47 bcd 119 bcde I mazethapyr 71 EP 75 bcdefg 27 bcd 21 e fg 26 e 74 efgh G yphosate 3,361 MP 95 a 12 cd 17 fg 21 e 51 gh I mazapic 35 MP 65 defg 30 bcd 42 bcd 56 bc 128 bcd I mazapic 71 MP 80 abcde 14 cd 22 efg 29 de 65 fgh I mazethapyr 35 MP 60 fg 38 b 33 cdef 40 bcde 111 bcdef I mazethapyr 71 MP 70 cdefg 25 bcd 35 cdef 31 de 91 cdefg LSD (0.05) 18 23 18 20 47 a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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61 Table 3 4. Effect of herbicide treatments on mid season purple nutsedge tuber density, year three Treatment Rate Timing % Control a Depth of Sample (cm)b (g ha 1 ) 0 10 10 20 20 30 0 30 -----------------Number of Tubers per m2 of Soil ------------------Control 0 0 g 75 a 31 abcd 34 b 140 ab Imazapic 35 PPI 80 bcd 11 d 22 cdefgh 43 a 75 def Imazapic 71 PPI 98 ab 12 d 20 defghi 28 bc 60 fgh Imazethapyr 35 PPI 70 de 14 d 27 bcdef 25 cd 67 efg Imazethapyr 71 PPI 95 ab 10 d 16 fghi 28 bc 54 fghi Vernolate 2,241 PPI 90 abc 5 d 9 i 16 efgh 29 i Metolachlor 2,801 PPI 58 e 10 d 23 cdefg 16 efgh 49 fghi Glyphosate 3,361 EP 80 bcd 11 d 21 defgh 24 cde 56 fghi Imazapic 35 EP 95 ab 12 d 20 defghi 15 gh 46 fghi Imazapic 71 EP 100 a 5 d 13 ghi 14 gh 32 hi Imazethapyr 35 EP 70 de 11 d 15 ghi 19 defgh 45 ghi Imazethapyr 71 EP 9 5 ab 12 d 17 fghi 13 h 41 hi Glyphosate 3,361 MP 99 a 10 d 18 eghi 13 h 40 gh i Imazapic 35 MP 98 ab 17 d 17 fghi 16 e fgh 49 fghi Imazapic 71 MP 100 a 5 d 11 hi 15 fgh 31 i Imazethapyr 35 MP 85 abcd 15 d 9 i 23 cdef 47 fghi Imazethapyr 71 MP 95 ab 11 d 12 ghi 18 defgh 41 hi Glyphosate 3,361 LP 73 cde 35 c 33 ab c 22 cdefg 90 cde Imazapic 35 LP 13 fg 51 b 36 ab 26 bcd 113 bc Imazapic 71 LP 20 f 68 a 42 a 43 a 153 a Imazethapyr 35 LP 10 fg 49 b 27 bcdef 18 defgh 94 cde Imazethapyr 71 LP 20 f 46 bc 29 bcde 29 bc 104 cd LSD (0.05) 18 12 11 8 29 a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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62 Table 3 5. Effect of herbicide treatments on l ateseason purple nutsedge tuber density, year three Treatment Rate Timing % Control a Depth of S ample b ( g ha 1 ) 0 10 cm 10 20 cm 20 30cm 0 30 cm ----------------Number of Tubers per m 2 of Soil -------------Control 0 0 i 73 a 47 a 58 a 178 a I mazapic 35 PPI 50 gh 32 b cd 23 cdef 28 cdef 83 cdef I mazapic 71 PPI 70 bcde 14 fghij 18 defg 32 cdef 63 defghi I mazethapyr 35 PPI 60 defg 22 defgh 30 bc 22 def 74 cdefgh I mazethapyr 71 PPI 70 bcde 12 ghij 19 defg 25 cdef 56 efghij V ernolate 2,241 PPI 80 abc 5 j 18 defg 26 cdef 49 ghij M etolachlor 2,801 PPI 50 gh 25 def 29 bcd 39 bc 92 bcd G lyphosate 3,361 EP 67 cdef 10 ij 18 defg 23 def 51 fghi j I mazapic 35 EP 73 bcd 10 ij 13 fgh 22 def 45 ghij I mazapic 71 EP 85 ab 5 j 12 fgh 21 e f 38 ij I mazethapyr 35 EP 53 fgh 19 efghi 16 efgh 18 f 54 efghij I mazethapyr 71 EP 78 abc 11 g hij 15 efgh 21 ef 46 g hij G lyphosate 3,361 MP 80 abc 7 ij 12 fgh 20 ef 39 ij I mazapic 35 MP 78 abc 14 fghij 13 fgh 17 f 43 hij I mazapic 71 MP 93 a 6 j 5 h 18 f 29 j I mazethapyr 35 MP 58 defg 28 cde 24 cde f 34 bcde 85 cde I mazethapyr 71 MP 80 abc 17 efghij 7 gh 20 ef 44 ghij G lyphosate 3,361 LP 70 bcde 20 efghi 23 cdef 40 bc 83 cdef I mazapic 35 LP 55 efgh 38 bc 35 a b c 32 cdef 105 bc I mazapic 71 LP 60 defg 23 defg 21 def 49 ab 94 bcd I mazethapyr 35 LP 40 h 44 b 37 ab 40 bc 121 b I mazethapyr 71 LP 65 cdefg 17 efghij 27 b cde 37 bcd 77 cd efg LSD (0.05) 17 1 2 1 2 15 33 a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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63 Table 3 6. E ffect of herbicide treatments on m id season purple nutsedge tuber weight year one Treatment Rate Timing Depth of S amplea (g ha 1 ) 010 cm 1020 cm 2030cm 030 cm -------------------------------------(g m 2 of S oil ) ------------------------------------Control 0 23 b c 19 a b 18 a 61 ab I mazapic 35 PPI 12 d 16 bcd 9 cd 36 ef I mazapic 71 PPI 6 efgh 7 fghij 8 cd 21 ghi I mazethapyr 35 PPI 10 de 9 efghi 10 bc 28 fgh I mazethapyr 71 PPI 6 efgh 7 fghij 8 cd 20 h i V ernolate 2,241 PPI 4 fgh 3 ijk 7 cd 14 ij G lyphosate 3,361 EP 9 def 14 bcde 11 bc 35 ef I mazapic 35 EP 3 gh 5 hijk 7 cd 14 ij I mazapic 71 EP 1 h 0 k 4 de 5 j I mazethapyr 35 EP 6 ef gh 6 ghijk 9 cd 20 hi I mazethapyr 71 EP 1 h 2 jk 4 de 7 j G lyphosate 3,361 MP 4 fg h 6 ghijk 10 bc 20 h i I mazapic 35 MP 7 def g 10 d efgh 15 ab 31 efg I mazapic 71 MP 7 def g 6 ghijk 12 bc 24 ghi I mazethapyr 35 MP 8 defg 10 defgh 9 cd 28 fgh I mazethapyr 71 MP 5 efg h 12 cdefg 10 bc 27 fgh G lyphosate 3,361 LP 20 c 13 b cdef 7 cd 40 de I mazapic 35 LP 22 c 10 defg h 9 cd 41 de I mazapic 71 LP 19 c 17 bc 12 bc 49 cd I mazethapyr 35 LP 29 a 25 a 12 bc 66 a I mazethapyr 71 LP 28 a b 13 b cde f 1 de 55 bc LSD (0.05) 5 6 5 10 a Values follo wed by different letters indicate significant differences according to LSD test ( P =0.05)

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64 Table 3 7 Effect of herbicide treatments on l ate season purple nutsedge tuber weight year one Treatment Rate Timing Depth of S amplea (g ha 1 ) 0 10 cm 10 20 cm 20 30cm 0 30 cm ------------------------------(g m 2 of S oil ) ----------------------------------------Control 0 14 b c 13 ab 13 abc 42 ab I mazapic 35 PPI 16 a 15 a 16 ab 44 a I mazapic 71 P PI 7 efg 10 abc 11 abcd 28 bcd I mazethapyr 35 PPI 10 de 11 abc 9 abcd 29 bcd I mazethapyr 71 PPI 6 fgh 12 abc 7 cd 24 cdef V ernolate 2,241 PPI 2 i j 6 c 10 abcd 19 c def G lyphosate 3,361 EP 6 fgh 10 abc 17 a 33 abc I mazapic 35 EP 2 ij 6 c 8 bcd 16 def I mazapic 71 EP 1 j 4 c 6 cd 11 f I mazethapyr 35 EP 9 d ef 7 c 12 abcd 29 bcd I mazethapyr 71 EP 4 ghij 5 c 6 cd 16 d ef G lyphosate 3,36 1 MP 2 ij 4 c 7 cd 13 e f I mazapic 35 MP 7 ef g 8 bc 12 abcd 27 cde I mazapic 71 MP 4 ghij 6 c 9 abcd 19 c def I mazethapyr 35 MP 11 cd 7 c 6 cd 24 cdef I mazethapyr 71 MP 5 ghi 6 c 4 d 15 d ef G lyphosate 3,361 LP 2 ij 5 c 11 abcd 18 def I mazapic 35 LP 6 fgh 11 abc 11 abcd 28 bcd I mazapic 71 LP 3 hij 6 c 8 bcd 17 def I mazethapyr 35 LP 18 a 8 bc 12 abcd 29 bcd I mazethapyr 71 LP 3 hij 5 c 11 abcd 19 cdef LSD (0.05) 3 5 8 1 4 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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65 Table 3 8 Effect of herbicide treatments on l ate season purple nutsedg e tuber weight year two Treatment Rate Timing Depth of S amplea (g ha 1 ) 010 cm 1020 cm 2030cm 030 cm ---------------------------------(g m 2 of S oil ) ---------------------------------Control 0 132 a 83 a 95 a 310 a I mazapic 35 PPI 53 b 76 a 61 bcd 190 b I mazapic 71 PPI 28 bcd 50 b 78 ab 157 bcd I mazethapyr 35 PPI 30 bcd 43 b c 56 bcde 129 bcde I mazethapyr 71 PPI 24 bcd 22 cdefg 26 fg 75 efg V ernolate 2,241 PPI 14 d 27 cdef 33 d efg 74 efg M etolachlor 2,801 PPI 22 cd 35 bcdef 34 defg 90 efg G lyphosate 3,361 EP 27 bcd 20 defg 32 efg 79 efg I mazapic 35 EP 27 bcd 38 bcde 36 defg 101 def I mazapic 71 EP 5 d 4 g 18 g 27 g I mazethapyr 35 EP 47 bc 54 b 67 a bc 168 bc I mazethapyr 71 EP 28 bcd 20 defg 27 fg 74 efg G lyphosate 3,361 MP 10 d 15 fg 19 g 44 fg I mazapic 35 MP 31 bcd 41 bc d 4 9 cdef 120 cde I mazapic 71 MP 12 d 19 efg 23 fg 53 fg I mazethapyr 35 MP 43 bc 40 bcd e 35 defg 134 bcde I mazethapyr 71 MP 27 bcd 40 bcd e 37 defg 104 c def LSD (0.05) 2 9 2 1 2 8 6 4 a Value s followed by different letters indicate significant differences according to LSD test ( P =0.05)

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66 Table 3 9. Effect of herbicide treatments on l ateseason purple nutsedge tuber weight year three Treatment Rate Timing Depth of S amplea (g ha 1 ) 0 10 cm 10 20 cm 20 30cm 0 30 cm --------------------------------(g m 2 of S oil ) ----------------------------------------Control 0 87 a 57 a 51 a 194 a Imazapic 35 PPI 37 c 27 bcd 21 d efgh 85 cd Imazapic 71 PPI 15 d efgh 26 bcde 32 bcdef 73 cdef Imazethapyr 35 PPI 16 d ef 32 b 21 d efgh 69 cdefg Imazethapyr 71 PPI 7 efgh 20 bcdef 23 defgh 50 defghi Vernolate 2,241 PPI 2 gh 12 efgh 20 e fgh 34 ghij Metolachlor 2,801 PPI 26 cd 26 bcd e 37 abcde 89 c Glyphosate 3,361 EP 10 e fgh 19 bcdef 18 fgh 47 efghij Imazapic 35 EP 7 e fgh 8 fgh 16 fgh 32 hij Imazapic 71 EP 1 h 4 gh 16 fgh 22 ij Imazethapyr 35 EP 16 def 14 defgh 9 h 40 fghij Imazethapyr 71 EP 7 efgh 9 fgh 19 fgh 35 ghij Glyphosate 3,361 MP 5 fgh 7 fghi 18 fgh 29 hij Imazapic 35 MP 8 e fgh 9 fgh 12 gh 29 hij Imazapic 71 MP 1 h 1 h 10 h 13 j Imazethapyr 35 MP 25 cd 19 bcdef 24 cdefgh 68 cdefg Imazethapyr 71 MP 13 d efgh 4 gh 13 gh 31 hij Glyphosate 3,361 LP 14 defgh 17 cdefg 28 bcdefg 59 cdefgh Imazapic 35 LP 34 c 32 b 24 cdefgh 89 c Imazapic 71 LP 20 de 19 bcdef 41 abc 80 cde Imazethapyr 35 LP 58 b 49 a 43 ab 149 b Imazethapyr 71 LP 20 de 30 bc 38 abcd 88 c LSD (0.05) 13 14 1 7 35 a Values followed by differen t letters indicate significant differences according to LSD test ( P =0.05)

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67 Table 3 10. Purple nutsedge tuber germination, years one, two, and three Treatment Rate Timing Mid Season Late Season (g ha 1 ) Year One Year Three Year One Year T wo Year Three ---------------------------------Tuber Germination (%) -------------------------------Control 0 21 ab a 85 a 72 a 65 a 76 ab I mazapic 35 PPI 8 b cde 58 b 42 bcde 28 bc 51 bcdef I mazapic 71 PPI 11 abcde 48 bcd 40 bcdef 35 abc 40 defgh I mazethapyr 35 PPI 17 abcd e 50 bcd 53 abc d 35 abc 35 defghi I mazethapyr 71 PPI 17 abcd e 55 bc 55 abc 43 abc 49 cdefg V ernolate 2,241 PPI 10 a bcde 31 de 26 defg 29 bc 3 8 defgh M etolachlor 2,801 PPI 81 a 20 c 83 a G lyphosate 3,361 EP 14 abcde 28 de 37 bcdefg 23 bc 30 efghi I mazapic 35 EP 5 de 38 bcde 14 fg 41 abc 14 hi I mazapic 71 EP 9 bcde 33 cde 53 ab cd 47 abc 23 ghi I mazethapyr 35 EP 11 abcde 25 e 29 cdefg 54 ab 27 e fghi I mazethapyr 71 EP 12 abcde 43 bcde 35 bcdefg 36 abc 26 f ghi G lyphosate 3,361 MP 4 e 40 bcde 20 efg 26 bc 53 bcde I mazapic 35 MP 7 c de 56 b 19 efg 34 abc 34 efghijk I mazapic 71 MP 5 d e 90 a 11 g 35 abc 19 ijk I mazethapyr 35 MP 11 abcde 37 bcde 31 cdefg 46 abc 36 defghi I mazethapyr 71 MP 16 abcde 55 bc 46 abcde 43 abc 47 cdefg G lyphosate 3,361 LP 18 abc d 54 bc 61 ab 10 i I mazapic 35 LP 23 a 81 a 56 abc 68 abc I mazapic 71 LP 13 abcde 94 a 42 bcde 57 abcd I mazethapyr 35 LP 19 abc 86 a 53 abcd 60 abcd I maz ethapyr 71 LP 12 abcde 83 a 38 bcdefg 50 bcdef LSD (0.05) 1 3 22 27 3 1 2 6 a Values followed by different letters in dicate significant differences accordin g to LSD test ( P =0.05) .

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68 CHAPTER 4 EFFECT S OF GROWTH STAGE, SITE OF APPL ICATION, AND RATE OF IMAZAPIC AND IMAZETHAPYR ON PURPLE NUTSEDGE (CYPERUS ROTUNDUS L. ) AND YELLOW NUTSEDGE ( C. ESCULENTUS L .) CONTROL Introduction P e anut slowly shades row middles due to its short stature thus allowing for weed emergence over a longer period of time compared to other agronomic crops. Furthermore, peanuts long growing season provides ample time for multiple flushes of weed germination (Henning et al. 1982; Wilcut et al. 1994). Subsequently, a broad spectrum, soil applied herbicide that pr ovides residual weed control throughout the growing season i s an integral component to peanut weed management programs. Imazethapyr was registered for weed control in peanut in 1991 (Shaner 1991). It was the first herbicide to provide residual control of numerous annual, broadleaved weeds and purple and yellow nutsedge in peanuts (Wilcut et al. 1991). Unfortunately, it does not control Florida beggarweed ( Desmodium tortuosum L.) or sicklepod ( Senna obtusifolia L.), the two most common and troublesome weed s found in southeastern pean ut fields (Dowler 1992; Wilcut et al. 1996). Imazapic was first labeled for use in peanut in 1996. Imazapic provides a spectrum of annual grass and broadleaf weed control similar to imazethapyr (Richburg et al. 1995), wi th the following advantages: Florida beggarweed and sicklepod control (Wilcut et al. 1996), and enhanced purple and yellow nutsedge control (Richburg et al. 1994; Richburg et al. 1993). Purple and yellow nutsedge are among the most economically important weeds i n Florida (Dowler 1992), resulting in substantial yield losses in various crops including peanut. They reduce peanut yield by competing for light, water, and nutrients, by serving as hosts for pathogens and nematodes, and by interfering with pesticide appl ications In addition, tubers and

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69 rhizomes may cause difficulties in peanut harvesting, cleaning, and processing (Richburg et al. 1996; York and Wilcut 1995; Wilcut et al. 1994a). Furthermore, nutsedge rhizomes can pierce peanuts, thereby predisposing them to secondary infection by pathogens that may render them distastef ul (Ramirez and Bendixen 1982). Prior research has not examined the effects imazapic and imazethapyr have on purple and yellow nutsedge shoot number and weight, root weight, tuber number and weight, and regrowth potential, as well as overall control when applied to different sites of uptake at several rates to plants of varying growth stages The objectives of this research were to ascertain the effects of weed growth stage, site of herbicid e uptake, and rate of imazapic and imazethapyr application on a several growth parameters for purple and yellow nutsedge Materials and Methods Four greenhouse studies were conducted. Three experiments were performed over four summers at the University of Floridas West Florida Research and Education Center located near Jay, Florida. A fourt h greenhouse experiment was conducted over two years in Gainesville Natural light consisting of approximately 13 14 h/day of sunlight was used. For one experiment, pla nts were grown in sand. The remaining three studies utilized a growth medium of one part Metro Mix 3002For the first three studies, purple and yellow nutsedge tubers were planted into 3.8 L plastic pots at a de nsity of five tubers per pot, 1.5 to 2cm deep Herbicides were applied using a and three parts Orangeburg sandy loam soil Nutsedge tubers used in these experiments were collected at the West Florida Research and Education Center. 2 Horticultural grade vermiculite,bark, Ca nadian sphagnum peat moss, horticultural grade perlite, processed bark ash, starter nutrient charge, dolomitic limestone and wetting agent. SunGro Horticulture, 15831 N.E. 8th Street, Suite 100, Bellevue, WA 98008.

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70 CO2pressurized, backpack sprayer calibrated to deliver a spray vol ume of 187 L ha1. Post emergence treatments included imazapic or imazethapyr, and included a nonionic surfactant at 0.25% ( v/v) and a nontreated control. Watering was delayed 24 h following treatments to allow sufficient time for herbicide absorption. Si te of Application T wo week old purple and yellow nutsedge plants 7.5 cm and 10 cm tall, respectively, were treated with imaza pic at the rates of 0, 35, and 71 g a.i. ha1, and imaz ethapyr at the rates of 0 and 71 g. Herbicides were applied to either the foliage and soil combined, or to only the foliage. Foliar only treatments were achieved by covering the soil with vermiculite prior to the application of herbicides, and removing it once treatments had been completed. Shoot fresh weight and dry weight data were collected from an initial harvest taken one month following treatment. Shoot fresh weights were obtained by clipping shoots off at soil level and weighing them immediately. Shoots were then transferred to paper bags and placed in a dryer for a minimu m of two weeks in order to obtain dry weight data. A reg rowth harvest was taken 2 months following treatment (1 month after the initial harvest) at which time shoot number, shoot fresh weight, and shoot dry weight were recorded Site of Application and N utsedge Age A study was conducted dur ing two summers to evaluate the effects both nutsedge age and the site of herbicide application have on nutsedge control. Imazapic and imazethapyr w ere applied at the rates of 0, 35, and 71 g on the same day to 2 4 and 6 week old purple and yellow nutsedge plants. Plant heights at the three different growth stages were 7.5, 14, and 20 cm for purple nutsedge and 10, 23, and 28 cm for yellow nutsedge Herbicide treatments were made to either the soil only the foliage only, or to both the nutsedge foliage and the soil.

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71 Soil only treatments were applied in the greenhouse directly onto soil via a syringe. Care was taken to not allow any herbicide to contact the nutsedge foliage. Foliar only treatments were made by cover ing the soil with vermiculite prior to the application of herbicides, and removing it once treatments had been completed. Foliar only and foliar plus soil treatments were applied as follows: Nutsedge plants growing in 3.8 L pots were arranged in rows on th e ground outside of the greenhouse. Herbicides were applied via a CO2pressurized, backpack sprayer calibrated to deliver a spray volume of 187 L ha1. Treated plants were subsequently transferred to the greenhouse. Pots were not watere d for 2 days followi ng treatments in order to allow adequate time for herbicide absorption, and especially in the case of the soil only treatments, to prevent herbicide leaching. Data collected for this study were the same as those collected for the other greenhouse studies conducted in Jay. Root Uptake In an effort to better evaluate the uptake of these herbicides via roots, the previously described plant growth stage study was conducted over three summers using nutsedge grown in sterile, masonry sand instead of soil. Imazap ic and imazethapyr were applied at the rates of 0, 35, and 71 g, while metolachlor was applied at the rate of 2,801 g. Treatments were applied on the same day to 2, 4 and 6 week old purple and yel low nutsedge plants by applying herbicides directly onto sand via a syringe. Care was taken to not allow any herbicide to contact the nutsedge foliage. Plants were sub irrigated to prevent leaching of herbicide. Sub irrigation was achieved by setting 3.8L pots containing nutsedge plants into approximately 5cm tall, circular, plastic containers. Water was then poured into these circular containers where it was allowed to enter holes located al ong the bottom sides of the 3.8 L pots. Two paper towels placed in the bottom of each pot prevented sand from escaping t hrough the holes. Sub irrigation was conducted

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72 approximately every 48 hours. Hoaglands solution was applied to the sand surface every four to five days to maintain soil fertility. Visual ratings of percent control were taken one month following treatment In addition, s hoot dry weight data were collect ed from an initial harvest conducted at this time by clipping shoots off at soil level. Shoots were then transferred to paper bags and placed in a dryer for a minimum of two weeks in order to obtain dry weight data. A whole plant harvest was performed one month following the initial harvest (2 months after treatmen t). For the whole plant harvest, nutsedge shoots were once a gain clipped off at soil level. Next, s and was removed f rom the 3.8 L pots and sifted through a wire mesh screen. T ubers were then separated from r oots/rhizomes Dry weights for shoot regrowth, tubers, and roots were obtained after placing them in paper bags and drying them for a minimum of two weeks. Nutsedge Growth and Tuber Production A greenhouse experiment was conducted to determine the effects of herbicide ra te and time of application on the reproductive capabilities of purple and yellow nutsedge. The upper 13 cm of a fine, loamy, siliceous, thermic Typic Paleudult Orangeburg sandy l oam having 1.5% organic matter and a pH of 5.3 was collected at the University of Floridas West Florida Research and Education Center located near Jay, Florida, and subsequently transported to the University of Floridas main campus in Gainesville, Florid a. The soil was then sifted through a screen in order to remove any existing purple and yellow nutsedge tubers. Plastic pots were filled with one part Metro Mix 300 and three parts Orangeburg sandy loam. Purple nutsedge tubers were collected at the Univer sity of Floridas Plant Science Research and Education Unit, located near Citra, Florida. Yellow nutsedge tubers were collected at the University of Floridas Horticultural Science Research Unit in Gainesville, Florida. Imazapic a nd imazethapyr were applie d pre plant incorpo rated (PPI) postemergence 2 weeks

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73 after emergence (WAE), and 4 WAE at the rates of 0, 18, 35, 71, and 141 g. This is equivalent to 0, 1/4, 1, and 2 times the labeled rate of these two herbicides when used for weed control in peanuts. For the PPI treatments, the herbicides were applied to the soil and then thoroughly mixed with the soil. Treated soil was then placed in 7 x 7 x 9 cm pots. Either unsprouted or sprouted tubers were planted in th e treated soil at a density of five tubers per pot 1.5 to 2cm deep. For the PPI treatments requiring sprouted tubers, yellow nutsedge tubers were placed onto trays lined with wet paper towels in a growth chamber for one week at a temperature of 30 C and a light duration of 14 h. Purple nutsedge tubers were either stored in moist newspapers at 25 C for 2 weeks, or in a growth chamber in the same manner as previously described for yellow nutsedge tubers. Sprouted buds and roots on tubers were removed prior to planting. In addition, imazapic and im azet hapyr were applied at the same five rates to purple and yellow nutsedge plants 2 or 4 weeks af ter shoot emergence (WAE). Plant heights at 2 and 4 weeks were 7.5 and 13.5 cm for purple nutsedge, and 11 and 19 cm for yellow nutsedge. Postemergence treatm ents included a nonionic surfactant applied at 0.25% v/v. For the 2 and 4 WAE treatments, purple and yellow nutsedge tube rs were first planted into 31x 46x 5 c m pla stic trays containing moist Metro Mix 300. After sprouting, plants were transplanted int o pots at a density of 5 plants per pot and allowed to grow for either 2 or 4 weeks before treatment. Tuber planting was staggered so that all treatments could be applied the same day. Plants were not watered for 24 h following treatment in order to allow sufficient time for foliar absorption of the herbicides. Subsequently, plants were watered overhead daily. Herbicides were applied using a CO2pressurized, backpack sprayer calibrated to deliver a spray volume of 187 L ha1. Visual ratings of purple and y ellow nutsedge control were taken one

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74 month after treatment. An initial harvest of shoots was also conducted at this time. A full plant harvest was taken one month later (2 months after treatment), and data for shoot regrowth dry weight, root dry weight, a nd tuber number and fresh weight were recorded. This study was conducted twice. Treatments for all four greenhouse experiments were arranged as randomized, complete, block designs having four replications. Treatment differences were determined by usi ng an alysis of variance (ANOVA). L east significant difference (LSD) values were calculated at a significance level of P = 0.05. Results a nd Discussion Site of Application All treatments significantly reduced two week old purple nuts edge fresh weight, dry weig ht, and shoot number compared to the untreated control (Table 4 1) There were no differences among herbicide treatments for initial harvest dry weights of purple nutsedge Imazapic 71 g applied to the soil and foliage combined resulted in low er initial an d regrowth harvest fresh weights t han the same rate of imazethapyr applied to either the foliage alone or to soil and foliage combined Both the 35 and the 71 g rate of imazapic applied to either the foliage alone, or to the foliage and soil combined, resu lted in fewer shoot s for the regrowth harvest than the 71 g rate of imazethapyr applied to either application site. As was the case with purple nutsedge, all treatments significantly reduced tw o week old yellow nutsedge shoot fresh and dry weights at initi al harvest, and also regrowth harvest shoot number s and fresh and dry weights (Table 4 2). Shoot number at initial harvest was lower for imazapic 35 g and imazapic 71 g soil + foliage compared to imazethapyr. Regrowth fresh weight was reduced by imazapic 7 1 g foliage and foliage + so il compared to imazapic 35 g foliage only. Similar to purple n utsedge, there were no differences among herbicide treatments for initial

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75 harvest dry weights. Unlike p urple nutsedge, there were no d ifferences among treatments for initial harvest fresh weights There were also no differences among treatments for shoot regrowth dry weights. Site of Application and Nutsedge Age S oil plus foliage treatments generally did not provide bett er control of pu rple nutsedge than foliage only treatmen ts regardless of purple nutsedge age at time of application (Table 4 3). Best co ntrol at the two week stage resulted from either the 71 g rate of imazapic or imazethapyr, or the 35 g rate of imazapic, each applied to the soil and foliage combined, or to foliage alone. Imazapic 71 g applied to the soil plus foliage, or to foliage alone, r esulted in the best control of four week old purple nutsedge. Only for six week old purple nutsedge did imazapic 71 g provide better control when applied to the soi l and foliage combined versus the foliage alone. All treatments significantly re duced shoot height for four and sixweek old purple nutsedge at initial harvest compared to the untreated check (Table 4 4). Altho ugh c ombined soil and foliar applications wer e no better than fo liage alone treatments, either was better than soil only treatments. There were no significant differences among herbicides and rates with respect to reducing purple nutsedge shoot heights. As with shoot height, soil plus foliage treatm ents did not provide a significant ly greater reduction in purple nutsedge shoot numbers at initial harvest 4 WAT compared to foliage only treatments (Table 4 5). Bo th were better than soil onl y treatments. Imazapic 71 g applied to either the soil and folia ge combined, or only to foliage, resulted in the fewest shoots for both four and sixweek old purple nutsedge. Shoot dry weight for purple nutsedge at i nitial harvest was again no different for plants receiving soil plus foliage applications versus foliag e applications alone (Table 4 6). The lo w and high rate of imazapic and the high rate of imazethapyr applied to either of these two sites

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76 provided equivalent reductions in shoot dry weight for two four an d six week old purple nutsedge. For plants of al l three age groups, the h igh rates of imazapic and imazethapyr provided no added benefits over the low rate of imazapic. All treatments reduced regrowth shoot number compared to the non treated control. There were no differences between imazapic or imazeth apyr treatments for foliar or foliar + soil applications to two week old purple nutsedge. When applied to four week old purple nutsedge, imazapic at 71 g reduced shoo t number more than imazethapyr (Table 4 7). Regrowth shoot height of t wo week old purple nutsedge was reduced equally well by the low and high rates of both herbicides when applied to either foliage alone, or to foliage plus soil (Table 4 8). Regro wth shoot height of four week old weeds w as reduced more by either rate of imazapic when applied to either of these two sites of application. Finall y, regrowth shoot dry weight was lowest for all three ages of plants following treatme nts of imazapic at the 71 g rate when applied to either the soil plus foliage, or the foliage alone (Table 4 9). The lo w rate of imazapic was equally effective at lowering regrowth shoot dry weight for two week old plants. F oliar only treatments generally provided control of yellow nutsedge equal to that of foliage plus soil treatments as in the case of purple nutsedge. F or yellow nutsedge 4 WAT, the best control resulted from im azapic at either 35 or 71 g to soil plus foliage or foliage alone for two week old plants imazapic 71 g to soil plus foliage for four week ol d plants, and imazapic 71 g applied to soil plus foliag e or foliage alone for six week old plant s (Table 4 10). The lowest shoot heights measured 4 WAT for two week old yellow nutsedge were the result of imazapic applied at either 35 or 71 g to soil plus foliage or foliage alone (Table 4 11). Imazapic 71 g so il + foliage reduced shoot hei ght more than imazapic 35 g soil only or imaz ethapyr 35 g soil only when applied to four week old yellow nutsedge. When applied to six -

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77 week old yellow nutsedge, foliar or foliar + soil treatments reduced shoot height more than soil only treatments. Imazapic also provided the lowest yellow nut sedge shoot numbers at initial harvest (Table 412). Imazapic applied to the foliage only at either 35 or 71 g, as well as at 71 g to the soil plus foliage, resulted in the fewest number of shoots for two week old yellow nutsedge. The high rate of imazapic applied to the soil and foliage of four week old yellow nutsedge resulted in the fewest s hoots Imazapic 35 g applied to the soil plus foliage or to the soil alone, and imazapic 71 g appli ed to the soil and foliage combined, provided the fewest number of shoots for six week old plants. The lo west shoot dry weights fo r two week old yellow nutsedge resulted from the 35 and 71 g rate of imazapic applied to either the soil and foliage combined, or to the foliag e only (Table 4 13). Similarly, th e lowest shoot dry weights of four week old plants was the result of treatments of imazapic at the rate of 35 g to the soil and foliage, and the 71 g rate applied to either the soil and foliage combined, o r to foliage alone. For six week old plants, the high rate of imazapic applied to the soil and foliage combined or to the foliage alone, and the high rate of imazethapyr applied to the soil and foliage combined provided the lowest shoot dry weights at init ial harvest (4 WAT). Results for the regrowth harvest of yellow nutsedge were si milar to those for the initial harves t. Treat ments of imazapic at 35 or 71 g resulted in the fewest numb er of shoots and shortest plants (Table s 414, 4 15 ). Plants that we re f our weeks old at time of treatment had fewer shoots regrow than two or six week old plants. Once again, soil plus foliage and foliage only treatments outperformed soil only treatments Yellow nutsedge shoot regrowth dry weight

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78 was lowest for all three ag e groups following imazapic 71 g applied to the soil and foliage combined or to the foliage alon e (Table 4 16). Root Uptake Results from th is study indicate that regardless of plant age, root uptake alone of either imazapic, imazethapyr, or metolachlor does not provide adequate control of either purple or yellow nutsedg e (T ables 4 17, 4 18, 4 19, 4 20 ). No root only treatment provided greater than 60% control of purple nutse dge (Tables 417). Control decreased as plant age at time of treatment increased fro m 2 to 6 weeks. At the initi al harvest 4 WAT, there were no differences between imazapic and imazethapyr in terms of reducing shoot dry weights of 2and 4 we ek old purple nutse dge The 71 g rate of each, however was better than metolachlor. I mazapic 71 g resulted in the lowest dry weights f or 6 week old p lants (Table 4 17) Imazethapyr 71 g resulted in the lo west shoot regrowth dry wei ghts for twoweek old pur ple nu tsedge (Table 4 18). Th ere were fewer differences among treatments for four week old plants and all treatments reduced shoot dry weights similarly The only treatment resulting in significantly less regrowth shoot dry weight compared to the control for s ix week old plants was the 71 g rate of imazethapyr. The 71 g rate of either imazapic or imazethapyr were the only two treatments to significantl y reduce root dry weight f or all three age groups of purple nutsedge (Table 4 18). Thes e same two treatments also provided the greatest level of tuber dry weight reduction All treatments provided significant control of two and four week yellow nutsedge compared to the untreated c ontrol (Table 4 19). For six week old plants, only metolachlor and the high rates of imazapic and imazethapyr provided significant control. Shoot dry weight at initial harvest was not significant for two and sixweek old yellow nuts edge (Table 4 19) The

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79 71 g rate of imazapic and imazethapyr were the only treatments to signific antly reduce shoot dry weight of four week old plants. Imazapic 71 g and metolachlor were the only tr eatments to significantly reduce regrowth shoot dry weight of two week old yellow nutsedge (Table 420). These treatments, plus the 71 g rate of imazethapyr provided the lowest regrowth shoot dry weights of four week old plants. The low rate of imazethapyr was the only treatment to not reduce regrowth shoot dry weight of six week old plants relative to the control. The 71 g rate of imazapic was the only treatment to significantly reduce yellow nuts edge root dry weight for all three age groups (Table 420). No treatment provided significant reductions in tuber dry weights of four we ek old yellow nutsedge and imazapic 71 g was the only treatment to provide significant reductions in tuber dry weights for two and sixweek old p lants (Table 4 20). Nutsedge Gro wth and Tuber Production Imazapic provided better control of purple and yellow nutsedge than imazethapyr (Table 421, 426). The greatest control of purple and yellow nutsedge was seen at the 141 g rate. However, there was no significant difference between the level of control at the 71 and 141 g rates (Table 422, 427). The greatest control of purple and yellow nutsedge was observed for plants treated 4 WAE (Table 423, 4 28). Treating unsprouted purple nutsedge tubers resulted in the worst control (Table 423). Imazapic provided better control of purple nutsedge at the unsprouted, sprouted, and 2 WAE growth stages (Table 4 24). There was no difference among herbi cides at 4 WAE. Imazapic provided significantly better control of yellow nutsedge at all four growth stages (Table 429). The 141 g herbicide rate provided the best control of purple nutsedge at all plant growth stages, but was only significantly better than the 71 g rate when applied to unsprouted tubers (Table 4 25). The 141 g rate also provided the best control of yellow nutsedge at all growth

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80 stages, but was only significantly better than the 71 g rate when applied to yellow nutsedge 2 WAE (Table 4 30). Reduction in purple and yellow nutsedge shoot dry weight 1 and 2 MAT improved as herbicide rate increased (Table 422, 4 27). Yellow nutsedge shoot dry weights 1 and 2 MAT decreased as age of plant increased (Table 4 28). The same was true for purple nutsedge shoot dry weights 1 MAT (Table 423). Unsprouted purple nutsedge tubers was the only gr owth stage for which imazapic was better than imazethapyr at reducing shoot dry weights 1 and 2 MAT (Table 4 24). Imazapic provided greater reduction in yellow nutsedge shoot dry weights 1 and 2 MAT at all growth stages compared to imazethapyr (Table 4 29) Purple nutsedge shoot dry weights for all four growth stages decreased as herbicide rates increased. The 141 g rate was only significantly better than 71 g for unsprouted tubers (Table 425). The only time the 141 g rate was significantly better than 71 g at reducing yellow nutsedge shoot dry weights 1 MAT was at the unsprouted and 2 WAE growth stages (Table 4 30). Imazapic was better than imazethapyr at reducing yellow nutsedge tuber number by 2 MAT, but not better at reducing purple nutsedge tubers (Table 4 21, 426). Yellow nutsedge tuber number decreased significantly with each increase in herbicide rate (Table 4 27). Postemergence treatments of purple and yellow nutsedge resulted in better control of tubers than preemergence treatments (Table 4 23, 428). Imazapic treatments only resulted in significantly lower purple nutsedge tuber numbers at the unsprouted stage (Table 4 24) In contrast, imazapic resulted in significantly fewer nutsedge tuber numbers at all but the unsprouted stage of growth (Table 429). Results from these studies indic ate that efficacy of imazapic and imazethapyr aga inst purple and yellow nutsedge was not enhanced when applied to the foliage and soil combined

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81 versus to the foliage alone. In general, imazapic 71 g provided the greatest control of two, four and six week old purple and yellow nutsedge. Imazapic 35 g often resulted in better control of both purple and yellow nutsedge than imazethapyr 71 g. Results from th e root uptake study indicate that regardless of plant age, roo t uptake alone of either imazapic, imazethapyr, or metolachlor did not provide adequate control of either purple or yellow nutsedge. It is possible that the efficacy of the soil applied treatments in the root uptake study may have been adversely affected b y the inability of nutsedge to adequately uptake t he herbicide treatments from sand. Finally, u nsprouted tubers were found to be easier to control than sprouted tubers. Postemergence treatments were more effective in reducing tuber numbers than PPI treatme nts. D ata from these studies suggests that soil absorption of imazapic and imazethapyr may not be required to obtain significant control of either purple or yellow nutsedge. Imazapic appears to offer enhanced purple and yellow nutsedge control over imazet hapyr regardless of application timing or site of herbicide uptake. Richbury et al. (1994) also reported good control of purple and yellow nutsedge with soil and foliar applications of imazapic and imazethapyr. Grichar (2002) reported that imazethapyr appl ied postemergence controlled yellow nutsedge more consistently than when applied pre plant incorporated.

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82 Table 4 1. Effect of foliar and soil + foliar applied herbicides on purple nutsedge growth year one Initial Harvest Regrowth Harvest Treat ment Rate Herbicide Placement Fresh Weight Dry Weight Shoot Fresh Weight (g ha 1 ) (g) (g) (No.) (g) Control 0 32.91 a a 5.91 a 37.0 a 14.32 a I mazapic 35 Foliage 5.55 bc d 1.03 b 12.3 c 6.05 b c I mazapic 35 Soil + F oliage 3 .78 bc d 0.82 b 10.8 c 4.00 bc d I mazapic 71 Foliage 2.41 c d 0.46 b 3.5 c 1.25 c d I mazapic 71 Soil + F oliage 2.34 d 0.51 b 1.8 c 0.30 d I mazethapyr 71 Foliage 6.38 b c 1.25 b 28.8 ab 7.43 b I mazethapyr 71 Soil + F oliage 6.50 b 1.29 b 25.0 b 7.02 b LSD 3.9 0.7 11 .0 4. 5 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 2. Effect of foliar and soil + foliar applied herbicides on yellow nutsedge growth year one Initial Harvest Regrowth Harvest Treatment Rate Herbicide Placement Fresh Weight Dry Weight Shoot Fresh Weight Dry Weight (g ha 1 ) (g) (g) (No.) (g) (g) Control 0 25.15 a a 5.08 a 14.5 a 10.18 a 2.02 a I mazapi c 35 Foliage 3.27 b 0.63 b 3.0 bc 2.82 b 0.37 b I mazapic 35 Soil + F oliage 3.10 b 0.69 b 1. 8 c 0.94 b c 0.09 b I mazapic 71 Foliage 1.76 b 0.41 b 1. 3 c 0.74 c 0.06 b I mazapic 71 Soil + F oliage 1.07 b 0.14 b 1. 3 c 0.39 c 0.0 9 b I mazethapyr 71 Foliage 3.27 b 0.74 b 4. 8 bc 1.62 b c 0.24 b I mazethapyr 71 Soil + F oliage 2.85 b 0.60 b 6. 3 b 1.16 b c 0.54 b LSD 6 .3 1.4 3.9 2.5 0.7 a Values followed by different letters indicate significant differe nces according to LSD test ( P =0.05)

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83 Table. 4 3. Effect of herbicide rate, herbicide site of application, and stage of growth at application on purple nutsedge control, 4 weeks after treatment, years one and two Plant Age at Treatment (Weeks) Treat ment Rate Herbicide Placement 2 4 6 (g ha 1 ) ------------------% Control a --------------Control 0 0.0 f b 0 f 00 h I mazapic 35 Soil + Foliage 9 0 a b 54 c 61 c I mazapic 35 Soil Only 6 5 cd 40 d 36 ef I mazapic 35 Foliag e Only 8 5 ab c 58 c 61 c I mazapic 71 Soil + Foliage 9 8 a 94 a 89 a I mazapic 71 Soil Only 5 0 de 60 c 50 d I mazapic 71 Foliage Only 9 3 a 94 a 76 b I mazethapyr 35 Soil + Foliage 7 0 bc d 43 d 51 d I mazethapyr 35 Soil Only 3 f 25 e 19 g I mazethapyr 35 Foliage Only 3 5 e 38 d 46 de I mazethapyr 71 Soil + Foliage 8 3 abc 75 b 69 b c I mazethapyr 71 Soil Only 0 f 41 d 34 f I mazethapyr 71 Foliage Only 8 0 abc 61 c 54 d LSD 19 11 7 a Control bas ed on scale of 0 to 10 0 0 = no control, 10 0 = complete control. b V alues followed by different letters indicate significant differences according to LSD test ( P =0.05)

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84 Table 4 4. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge shoot height 4 weeks after treatment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 4 6 (g ha 1 ) --------Shoot Height (cm) -----Control 0 13.4 a a 13.6 a I m azapic 35 Soil + Foliage 7.3 d 9.0 bc I mazapic 35 Soil Only 9.0 b c 8.8 bcd I mazapic 35 Foliage Only 7.0 c d 6.3 f I mazapic 71 Soil + Foliage 6.0 d 6.5 ef I mazapic 71 Soil Only 7.0 c d 7.5 cdef I mazapic 71 Foliage Only 5.5 d 6.5 ef I mazethapyr 35 Soil + Foliage 6.8 d 6.8 def I mazethapyr 35 Soil Only 10.0 b 9.8 b I mazethapyr 35 Foliage Only 7.3 c d 5.8 f I mazethapyr 71 Soil + Foliage 6.5 d 6.8 def I mazethapyr 71 Soil Only 10. 8 b 8.5 bcde I mazethap yr 71 Foliage Only 6.3 d 7.8 bcdef LSD 1.5 2.0 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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85 Table 45. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge shoot number 4 weeks after treatment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 4 6 (g ha 1 ) --------Number of Shoots --------Control 0 13.5 a a 18.3 a I ma zapic 35 Soil + Foliage 9.8 cd 13.8 b I mazapic 35 Soil Only 13.5 a 13.3 b c I mazapic 35 Foliage Only 10.3 bcd 8.5 e I mazapic 71 Soil + Foliage 8.3 d e 8.0 e I mazapic 71 Soil Only 9.8 cd 11.3 cd I mazapic 71 Foliage Only 7.5 e 8.8 e I mazethapyr 35 Soil + Foliage 8.3 d e 12.0 bc d I mazethapyr 35 Soil Only 11.0 bc 13.8 b I mazethapyr 35 Foliage Only 10.8 bc 11.0 d I mazethapyr 71 Soil + Foliage 10.3 bcd 12.8 b cd I mazethapyr 71 Soil Only 12.0 ab 11.5 cd I mazethapyr 71 Foliage Only 9.0 cd e 12.0 bc d LSD 3 .0 3.9 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 86

86 Table 4 6. Effect of herbicide, herbicide rate, herbicide site of applicati on, and stage of growth on purple nutsedge shoot dry weight 4 weeks after treatment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) -------------Shoot Dry Wt (g) -------------Control 0 5.17 a a 4.39 a 8.07 a I mazapic 35 Soil + Foliage 0.77 g h 1.49 def 2.63 ef g I mazapic 35 Soil Only 2.21 de 2.47 bc d 4.27 c I mazapic 35 Foliage Only 0.64 gh 1.61 c de f 2.51 efg I mazapic 71 Soil + Foliage 0.45 h 0 .73 f 1 .45 h I mazapic 71 Soil Only 1.44 ef g 1.79 b cde 3.15 de f I mazapic 71 Foliage Only 0.48 h 0.76 f 1.85 gh I mazethapyr 35 Soil + Foliage 1.81 de f 1.99 bcd e 3.39 cde I mazethapyr 35 Soil Only 3.75 b c 4.23 a 6.18 b I mazethapyr 35 F oliage Only 3.82 b 2.55 bc 3.19 de f I mazethapyr 71 Soil + Foliage 0.50 g h 1.13 ef 2.36 gh I mazethapyr 71 Soil Only 2.78 c d 2.78 b 3.92 cd I mazethapyr 71 Foliage Only 1.05 fg h 1.58 c def 2.86 ef LSD 0.9 0.9 1.1 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 87

87 Table. 4 7. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on purple nutsedge regrowth 4 w eeks after initial harvest (8 w eeks after treatment), years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 (g ha 1 ) ---------Number of Shoots --------Control 0 13.4 a a 6.4 a I mazapic 35 Soil + Foliage 1.8 e 0.5 ef I mazapic 35 Soil Only 2.1 de 4.3 bc I mazapic 35 Foliage Only 1.1 e 0.0 f I mazapic 71 Soil + Foliage 1.2 e 0.0 f I mazapic 71 Soil Only 4.0 d 1.0 ef I mazapic 71 Foliage Only 1.1 e 0.0 f I mazethapyr 35 Soil + Foliage 1.9 e 3.0 d I mazethapyr 35 Soil Only 9.7 b 4.5 bc I mazethapyr 35 Foliage Only 7.4 c 5.0 b I mazethapyr 71 Soil + Foliage 1.2 e 1.5 e I mazethapyr 71 Soil Only 7.7 bc 3.8 cd I mazethapyr 71 Foliage Only 1.9 e 2.8 d LSD 2 .1 1.2 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 88

88 Table 4 8. Effect of herbicide, herbicide rate, herbicide site of application and stage of growth at application on purple nutsedge regrowth shoot height 4 w eeks after initial harvest, ( 8 w eeks after treatment) years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 (g ha 1 ) ---Regrowth Shoot Height ( cm ) --Control 0 4.1 a a 16.4 a I m azapic 35 Soil + Foliage 1.4 e 0.8 e I mazapic 35 Soil Only 1.3 e 10.5 cd I mazapic 35 Foliage Only 0.9 e 0.0 e I mazapic 71 Soil + Foliage 0. 8 e 0. 0 e I mazapic 71 Soil Only 2. 5 cd 6.8 d I mazapic 71 Foliage Only 0.8 e 0.0 e I mazethapyr 35 Soil + Foliage 0.9 e 15. 8 ab I mazethapyr 35 Soil Only 3. 8 ab 14. 8 ab I mazethapyr 35 Foliage Only 1. 7 de 13. 3 abc I mazethapyr 71 Soil + Foliage 1.0 e 11. 8 bc I mazethapyr 71 Soil Only 2.8 bc 15.5 ab I mazethapyr 71 Foliage Only 0. 8 e 12.5 abc LSD 0.9 4.5 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 89

89 Table 4 9. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on purple nutsedge shoot regrowth dry weight 4 w eeks after initial harvest, ( 8 w eeks after treatment ) years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ------Shoot Regrowth Dry Wt (g) ------Control 0 8.60 a a 12.47 a 13.53 a Imazapic 35 Soil + Foliage 0.33e 4.15 ef 5.65 de Imazapic 35 Soil Only 3.44 c 8.22 b 9.25 b Imazapic 35 Foliage Only 0.32 e 6.17 cd 5.82 d e Imazapic 71 Soil + Folia ge 0.03 e 2.12 g 2.25 f Imazapic 71 Soil Only 1.42 d 6.08 c d 6.19 d e Imazapic 71 Foliage Only 0.32 e 1.31 g 2.20 f Imazethapyr 35 Soil + Foliage 2.93 c 5.74 d e 5.68 d e Imazethapyr 35 Soil Only 5.05 b 8.57 b 11.63 a Imazethapyr 35 Foliage Only 5.55 b 8.00 bc 7.13 cd Imazethapyr 71 Soil + Foliage 0.13 e 2.15 fg 4.45 e Imazethapyr 71 Soil Only 3.08 c 7.77 bc 8.52 b c Imazethapyr 71 Foliage Only 1.44 d 5.54 e 6.40 d e LSD 1 .2 2.1 1.9 a Values fo llowed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 90

90 Table 4 10. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on yellow nutsedge control 4 weeks after treat ment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ----------------% Control a ------------Control 0 0 g b 0 i 0 h I mazapic 35 Soil + Foliage 91 ab 75 c 61 b c I mazap ic 35 Soil Only 41 de f 43 gh 40 fg I mazapic 35 Foliage Only 89 a b 68 cd 58 b cd I mazapic 71 Soil + Foliage 99 a 10 a 85 a I mazapic 71 Soil Only 75 c 56 ef 61 b c I mazapic 71 Foliage Only 99 a 88 b 76 a I mazethapyr 35 Soi l + Foliage 43 d e 38 h 43 ef g I mazethapyr 35 Soil Only 44 d 34 h 34 g I mazethapyr 35 Foliage Only 33 e f 34 h 34 g I mazethapyr 71 Soil + Foliage 86 b 71 cd 65 b I mazethapyr 71 Soil Only 68 c 49 fg 51 cde I mazethapyr 71 Fol iage Only 70 c 61 de 50 de f LSD 9 13 8 a Control based on scale of 0 to 10 0 0 = no control, 10 0 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 91

91 Table 4 11. Effe ct of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot height 4 weeks after treatment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ----------Shoot Height (cm) ---------Control 0 22.0 a a 11.8 a 20.3 a I mazapic 35 Soil + Foliage 4.0 d ef 5.5 b c 6.5 cd I mazapic 35 Soil Only 6.8 cd 7.0 a b 8.5 cd I mazapic 35 Foliage Only 2.0 f 5.5 b c 8.5 cd I mazapic 71 Soil + Foliage 5.3 c de 2.3 c 5.3 d I mazapic 71 Soil Only 7.8 c 6.3 b c 10.3 c I mazapic 71 Foliage Only 3.3 e f 4.3 b c 5.3 d I mazethapyr 35 Soil + Foliage 6.5 cd 6.0 b c 7.8 cd I mazethapyr 35 Soil Only 8.0 c 7.8 a b 14.5 b I maze thapyr 35 Foliage Only 7.0 cd 6.0 b c 8.5 cd I mazethapyr 71 Soil + Foliage 7.3 c 5.8 b c 7.0 cd I mazethapyr 71 Soil Only 17.00 b 6.3 b c 9.8 c I mazethapyr 71 Foliage Only 6.3 cde 5.0 b c 8.0 cd LSD 2.9 3.6 3.8 a Values followed by different letters indicate significant differences according to LSD test (P=0.05)

PAGE 92

92 Table4 12. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot number 4 wee ks after treatment, year s one an d two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) --------Number of Shoots -----------Control 0 16.8 a a 16.0 a 9.3 a I mazapic 35 Soil + Foliage 5.8 cd 11.3 b 5.0 de f I mazapic 35 Soil Only 11.0 b 10.8 b c 5.3 cde f I mazapic 35 Foliage Only 2.0 de 10.5 bc 5.8 cde I mazapic 71 Soil + Foliage 1.5 e 2.5 d 4.0 ef I mazapic 71 Soil Only 11.3 b 10.3 bc 7.3 abc I mazapic 71 Foliage Only 1. 8 de 6.8 c 3.5 f I mazethapyr 35 Soil + Foliage 10.5 b 11.0 b 6.0 bcd e I mazethapyr 35 Soil Only 12.0 b 10.3 bc 8.0 ab I mazethapyr 35 Foliage Only 11.8 b 10.3 bc 6.3 bcd I mazethapyr 71 Soil + Foliage 10.5 b 11.0 b 5.8 cde I mazethapyr 71 Soil Only 11.8 b 11.0 b 8.0 ab I mazethapyr 71 Foliage Only 9.0 bc 9.5 bc 6.3 bcd LSD 3.6 3.9 2.5 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 93

93 Table 4 13. Effect of herbicid e, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge shoot dry weight 4 weeks after treatment years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ---------Shoot Dry Wt (g) -----------Control 0 7.41 a a 9.26 a 11.41 a I mazapic 35 Soil + Foliage 0.92 f g 1.50 ghi 4.13 ef I mazapic 35 Soil Only 4.50 c 5.13 d 7.24 b c I mazapic 35 Foliage Only 1.35 f g 2.33 e fg 5.19 de I mazapic 71 Soil + Foliage 0.88 f g 0.69 i 1.54 g I mazapic 71 Soil Only 2.61 de 3.27 e 4.29 ef I mazapic 71 Foliage Only 0.75 g 1.26 hi 2.55 fg I mazethapyr 35 Soil + Foliage 4.15 c 4.80 d 4.78 de I mazethapyr 35 Soil Only 4.42 c 6.70 b 7.39 b I mazethapyr 35 Foliage Only 6.32 b 6.23 bc 5.25 cd e I mazethapyr 71 Soil + Foliage 1.88 ef 1.92 f gh 3.45 ef g I mazethapyr 71 Soil Only 3.10 d 5.42 cd 6.73 bc d I mazethapyr 71 Foliage Only 2.81 de 2.65 ef 4.42 ef LSD 1.2 1.4 1.7 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 94

94 Table 4 14. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth on yellow nutsedge regrowth 4 w eeks after initial harvest (8 w eeks after treatment), years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ------------Number of Shoots -----------Control 0 17. 8 a a 28.0 ab 9.8 b cd I mazapic 35 Soil + Foliage 7.3 de 0.0 d 0.0 e I mazapic 35 Soil Only 9. 8 bc 5.8 d 4.3 de I mazapic 35 Foliage Only 6.5 e 0.0 d 4.8 de I mazapic 71 Soil + Foliage 7.3 d e 0.0 d 0.0 e I mazapic 71 Soil Only 11. 3 b 0.8 d 5.3 d e I mazapic 71 Foliage Only 7. 3 d e 0.0 d 0.0 e I mazethapyr 35 Soil + Foliage 8.0 cde 10.5 cd 13.5 abc I mazethapyr 35 Soil Only 10. 8 b 23.3 ab 8.3 cd I mazethapyr 35 Foliage Only 9.3 bcd 33.5 a 19.3 a I mazethapyr 71 Soil + Foli age 10. 3 b 10.0 cd 8.8 cd I mazethapyr 71 Soil Only 9.5 bc 18.5 bc 10.0 bcd I mazethapyr 71 Foliage Only 7. 0 e 19.0 bc 15.0 ab LSD 2 .4 10.6 6.1 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 95

95 Table 4 15. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on yellow nutsedge regrowth shoot height 4 w eeks after initial harvest, ( 8 w eeks after treatment ) years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 4 6 (g ha 1 ) -Regrowth Shoot Height ( cm ) --Control 0 8.00a a 8.5 a I mazapic 35 Soil + Foliage 0.00 d 0.00 g I mazapic 35 Soil Only 1.25 c d 2.50 cdef I maz apic 35 Foliage Only 0.00 d 0.75 fg I mazapic 71 Soil + Foliage 0.00 d 0.00 g I mazapic 71 Soil Only 0.25 d 2.25 def I mazapic 71 Foliage Only 0.00d 0.00 g I mazethapyr 35 Soil + Foliage 1.75 c d 4.25 bcd I mazethapyr 35 Soil Onl y 4.75 b 5.75 b I mazethapyr 35 Foliage Only 4.25 b 4.50 bc I mazethapyr 71 Soil + Foliage 2.00 c d 2.00 efg I mazethapyr 71 Soil Only 4.50 b 4.25 bcd I mazethapyr 71 Foliage Only 3.25 b c 3.25 cde LSD 2 .0 2.2 a Values follo wed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 96

96 Table 4 16. Effect of herbicide, herbicide rate, herbicide site of application, and stage of growth at application on yellow nutsedge shoot regrowth dry weight 4 w e e ks after initial harvest, 8 w eeks after treatment, years one and two Plant Age at Treatment (Weeks) Treatment Rate Herbicide Placement 2 4 6 (g ha 1 ) ----Shoot Regrowth Dry Wt (g) ----Control 0 9.71 a a 12.55 a 15.21 a I m azapic 35 Soil + Foliage 0.26 f 2.41 f g 4.29 ef I mazapic 35 Soil Only 4.72 cd 5.44 cd 7.53 c I mazapic 35 Foliage Only 1.08 f 2.88 e fg 5.64 cde I mazapic 71 Soil + Foliage 0.00 f 0.31 h 1.43 g I mazapic 71 Soil Only 3.77 d 4.3 0 d ef 5.23 d e I mazapic 71 Foliage Only 0.00 f 0.95 g h 2.43 f g I mazethapyr 35 Soil + Foliage 4.28 c d 6.38 c 6.67 cd I mazethapyr 35 Soil Only 6.27 bc 6.68 c 9.60 b I mazethapyr 35 Foliage Only 6.89 b 8.87 b 7.60 b c I mazethapyr 71 Soil + Foliage 1.44 e f 2.61 f g 3.96 e f I mazethapyr 71 Soil Only 4.18 d 5.49 cd 6.40 cd I mazethapyr 71 Foliage Only 3.44 d e 4.71 c de 6.49 cd LSD 1.6 1.9 2.0 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 97

97 Table 4 17. Effect of surface applied herbicide, herbicide rate, and stage of growth at application on purple nutsedge control, three years combined Visual Control Shoot Dry W eight Treatment Rate Plant Age at Treatment (Weeks) Plant Age at Treatment (Weeks) (g ha 1 ) 2 4 6 2 4 6 ------------------% Control a -------------------------------------(g) -----------------------Control 0 0.00 d b 0 c 0 e 3.27 a 4.66 a 5.81 a Im azapic 35 2.31 c 36 b 26 b c 2.47 a bc 3.21 b c 5.11 ab Imazapic 71 5.25 a 49 a 32 ab 1.74 c 2.75 c 2.24 c Imazethapyr 35 4.19 b 35 b 21 cd 2.09 b c 3.39 bc 4.76 b Imazethapyr 71 6.00 a 54 a 37 a 1.64 c 2.58 c 4.37 b Metolac hlor 2,801 1.56 c 10 c 11 d 2.90 ab 4.14 ab 5.32 ab LSD 1.4 13 12 0.6 0.8 0.9 a Control based on scale of 0 to 1 0 0, 0 = no control, 10 0 = complete control. b Values followed by different letters indicate significant differences accor ding to LSD test ( P =0.05) Table 4 18. Effect of surface applied herbicide, herbicide rate, and stage of growth at application on purple nutsedge regrowth, three years combined Regrowth Shoot Dry Weight Root Dry Weight Tuber Dry Weight Treatment Rate Plant Age at Treatment Plant Age at Treatment Plant Age at Treatment (g ha 1 ) 2 Week 4 Week 6 Week 2 Week 4 Week 6 Week 2 Week 4 Week 6 Week --------------------------------------------------(g) -----------------------------------------------------------Control 0 3.86 a a 4.39 a 5.05 a 2.65 a 3.47 a 5.21 a b 4.09 a 4.54 a 5.97 a Imazapic 35 2.37 c 2.77 b c 4.20 ab 1.94 a bc 2.24 bc 5.54 a 3.08 b 4.47 a 5.01 ab c Imazapic 71 1.10 d 2.05 c 3.13 a b 1.13 c 1.69 c 3.54 cd 2.00 c 2.61 b c 4.27 bc Imazethapyr 35 2.47 b c 3.06 b 3.46 ab 1.84 a bc 2.86 ab 4.21 bcd 3.81 ab 3.42 b 5.07 ab Imazethapyr 71 1.03 e 2.12 b c 2.63 b 1.38 b c 1.54 c 3.34 d 1.99 c 2.18 c 4.00 c Metolachlor 2,801 3.43 a b 3.03 b c 4.02 ab 2.22 ab 3.10 a b 4.44 b c 3.81 ab 4.45 a 5.40 a LSD 0.9 1.1 1.9 0.6 0.8 1.6 0.8 0.6 1.0 a Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

PAGE 98

98 Table 4 19. Effect of surface applied herbicide, herbicide rate, and stage of growth at application on yellow nutsedge regrowth, three years combined Visual Control Shoot Dry W eight Treatment Rate Plant Age at Treatment Plant Age at Treatment (g ha 1 ) 2 Week 4 Week 6 Week 2 Week 4 Week 6 Week ------------------% Control a ----------------------------------------(g) --------------------------Control 0 0 e b 0 c 0 b 2.43 3.27 a 3.70 I mazapic 35 1 9 cd 31 b 9 ab 2.29 2.59 a b 3.45 I mazapic 71 49 a 44 a 20 a 1.60 2.06 b 3.13 Imazethapyr 35 1 4 d 3 6 ab 4 b 2.53 2.59 ab 3.79 Imazethapyr 71 28 bc 43 a 15 a 2.09 2.21 b 3.58 M etolachlor 2,801 37 b 3 9 ab 16 a 2.09 2.39 a b 3.60 LSD 13 11 7 NS 0.6 NS a Control based on scale of 0 to 1 00, 0 = no control, 10 0 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 20. Effect of surface applied herbicide, herbicide rate, and stage of growth at applicatio n on yellow nutsedge regrowth, three years combined Regrowth Shoot Dry Weight Root Dry Weight Tuber Dry Weight Plant Age at Treatment Plant Age at Treatment Plant Age at Treatment Treatment Rate 2 Week 4 Week 6 Week 2 Week 4 Week 6 Week 2 We ek 4 Week 6 Week (g ha 1 ) -----------------------------------------------------------------(g) ------------------------------------------------------------------Control 0 3.01 a a 4.12 a 5.45 a 2.48 a 3.12 a 4.27 a 2.72 a 3.22 4.06 a Imazapic 35 2.16 ab c 2.91 b 4.39 bc 1.60 a b 2.19 a b 3.33 a bc 2.38 a b 2.74 3.24 ab Imazapic 71 1.18 c 1.86 c 3.44 c 0.90 b 1.29 b 2.78 c 1.62 b 2.35 2.75 b Imazethapyr 35 2.83 ab 3.35 ab 4.89 ab 2.34 a 2.41 a 3.80 ab 2.70 a 2.55 3.73 ab Imazethapyr 71 2.24 a b 2.79 bc 4.34 bc 2.09 a 2.34 a 3.12 b c 2.58 a b 2.51 3.55 ab Metolachlor 2,801 1.89 b c 2.82 b c 4.39 bc 1.56 ab 2.14 a b 3.98 ab 2.29 a b 2.32 3.34 abc LSD 0.6 0.9 1.0 0.5 0.6 0.7 0.6 NS 0.7 a Values followed by different letters in dicate significant differences according to LSD test ( P =0.05) .

PAGE 99

99 Table 4 21. Effect of herbicide on purple nutsedge control, two years combined Treatment Imazapic Imazethapyr Control a 4 WAT (%) 66 a b 60 b Shoot Dry Weight 1 MAT (g) 1.24 b 1.39 a Shoot Dry Weight 2 MAT (g) 0.73 b 0.87 a Tuber Number 2 MAT 5.7 a 5.9 a a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 22. Effect of herbicide rate of ap plication on purple nutsedge control two years combined Herbicide Rate Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) ----------------(g) ----------------0 0 d b 2.31a 2.12 a 8.22 a 18 54 c 1.68 b 1.07 b 6.13b 35 76 b 1.16 c 0.54 c 5.33 c 71 90a 0.84 d 0.20 d 4.81cd 141 95 a 0.59 e 0.08 d 4.50 d a Control based on scale of 0 to 100, 0 = no control, 100 = c omplete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 23. Effect of plant growth stage at time of herbicide application on purple nutsedge control, two years combined Plant Stage of Growth Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) --------------------(g) -------------------Unsprouted 46 c b 3.30 a 1.27 a 8.25 a Sprouted 66 b 1.31 b 0.56 c 5.68 b 2 WAE c 68 b 0 .43 c 0.83 b 4.70 c 4 WAE 73 a 0.24 d 0.54 c 4.56 c a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) c W AE = Weeks A fter Emergence.

PAGE 100

100 Table 4 24. Effect of herbicide and stage of growth at time of application on purple nutsedge control two years combined Herbicide Plant Growth Stage Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (%) ---------------------(g) ---------------Imazapic Unsprouted 54 a c 3.04 b 1.11 b 7.80 b Imazethapyr Unsprouted 38 b 3.56 a 1.43 a 8.70 a Imazapic Sprouted 68 a 1.28 a 0.53 a 5.90 a Imazethapyr Sprouted 64 b 1.34 a 0.60 a 5.45 a Imazapic 2 WAE c 69 a 0.39 a 0.77 a 4,73 a Imazethapyr 2 WAE 66 a 0.46 a 0.89 a 4.68 a Imazapic 4 WAE 73 a 0.26 a 0.52 a 4.55 a Imazethapyr 4 WAE 73 a 0.22 a 0.55 a 4.58 a a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) c WAE = Weeks A fter Emergence.

PAGE 101

101 Table 4 25. Effect of herbicide rate and stage of growth at time of application on purple nutsedge control two years combined Herbicide Rate Plant Growth Stage Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) ---------------------(g) ---------------Unsprouted 0 e b 4.76 a 2.38 a 12.31 a 18 Unsprouted 27 d 4.04 b 1.81 b 8.25 b 35 Unsprouted 51 c 3.13 c 1.17 c 7.50 bc 71 Unsprouted 68 b 2.65 d 0.68 d 7.0 bc 141 Unsprouted 82 a 1.91 e 0.30 e 6.19 c Sprouted 0 d 2.66 a 1.42 a 8.6 9 a 18 Sprouted 57 c 1.68 b 0.80 b 6.31 b 35 Sprouted 80 b 1.07 c 0.49 c 5.25 b 71 Sprouted 95 a 0.69 d 0.10 d 4.06 c 141 Sprouted 97 a 0.46 d 0.01 d 4.06 c 2 WAE c 0 d 1.11 a 2.68 a 4.94 ab 18 2 WAE 57 c 0.67 b 1.10 b 5.44 a 35 2 WAE 82 b 0.31 c 0.37 c 4.63 bc 71 2 WAE 99 a 0.03 d 0.02 d 4.31bc 141 2 WAE 100 a 0.00 d 0.00 d 4.19 c 4 WAE 0 d 0.72 a 2.02 a 6.94 a 18 4 WAE 73 c 0.35 b 0.55 b 4.50 b 35 4 WAE 92 b 0.12 c 0.12 c 3.94 b 7 1 4 WAE 100 a 0.00 d 0.00 c 3.88 b 141 4 WAE 100 a 0.00 d 0.00 c 3.56 b a Control based on scale of 0 to 10 0 0 = no control, 1 00 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) c WAE = Weeks A fter Emergence.

PAGE 102

102 Table 4 26. Effect of herbicide on yellow nutsedge control, two years combined Treatment Imazapic Imazethapyr Control a 4 WAT (%) 70 a b 42 b Shoot Dry Weight 1 MAT (g) 1.04 b 1.80 a Shoot Dry Weight 2 MAT (g) 0.27 b 0.51 a Tuber Number 2 MAT 3.27 b 3.76 a a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 27. Effect of herbicide rate of application on yellow nutsedge control, two years combined Herbicide Rate Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) --------------------(g) ------------------0 0 d b 2.89 a 1.17 a 6.78 a 18 41 c 1,69 b 0.53 b 4.38 b 35 59 b 1.31 c 0.24 c 3.11 c 71 86 a 0.76 d 0.03 d 2.03 d 141 92 a 0.45 e 0.00 d 1.27 e a Control based on scale of 0 to 100, 0 = no control, 100 = comple te control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) Table 4 28. Effect of plant growth stage at time of herbicide applicati on on yello w nutsedge control two years combined Plant Stage of Gr owth Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) --------------------(g) -------------------Unsprouted 50 c b 2.72 a 0.78 a 3.65 b Sprouted 58 b 1.54 b 0.43 b 4.98 a 2 WAE c 50 c 1.02 c 0.26 c 3.10 c 4 WAE 66 a 0.40 d 0.12 d 2.33 d a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) c WAE = Weeks A fter Emergence.

PAGE 103

103 Table 4 29. Effect of herbicide and stage of growth at time of applicat ion on yellow nutsedge control two years combined Herbicide Plant Growth Stage Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Numbe r 2 MAT (%) ---------------------(g) ---------------Imazapic Unsprouted 68 a b 1.88 b 0.55 b 3.80 a Imazethapyr Unsprouted 32 b 3.56 a 0.99 a 3.50 b Imazapic Sprouted 78 a 1.10 b 0.25 b 4.48 b Imazethapyr Sprouted 38 b 2.00 a 0.61 a 5.47 a Imazapic 2 WAE c 59 a 0.86 b 0.20 b 2.73 b Imazethapyr 2 WAE 41 b 1.18 a 0.31 a 3.48 a Imazapic 4 WAE 74 a 0.33 b 0.09 b 2.08 b Imazethapyr 4 WAE 58 b 0.47 a 0.14 a 2.58 a a Control based on scale of 0 t o 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05) c WAE = Weeks A fter Emergence.

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104 Table 4 30. Effect of herbicide rate and stage of growth at time of appli c ation on yellow nutsedge control two years combined Herbicide Rate Plant Growth Stage Control a 4 WAT Shoot Dry Weight 1 MAT Shoot Dry Weight 2 MAT Tuber Number 2 MAT (g ha 1 ) (%) ---------------------(g) ---------------Unsprouted o d c 5.17 a 2.31 a 7.25 a 18 Unsprouted 38 c 3.11 b 1.01 b 5.13 b 35 Unsprouted 52 b 2.70 b 0.44 c 2.88 c 71 Unsprouted 77 a 1.62 c 0.08 d 2.13 c 141 Unsprouted 83 a 0.99 d 0.00d 0.88 d Sprouted 0 c 3.76 a 1.28 a 10.31 a 18 S prouted 49 b 1.63 b 0.59 b 5.31 b 35 Sprouted 61 b 1.08 c 028 c 3.94 c 71 Sprouted 87 a 0.77 cd 0.00d 3.13 cd 141 Sprouted 91 a 0.49 d 0.00 d 2.19 d 2 WAE c 0 e 1.58 a 0.63 a 5.13 a 18 2 WAE 24 d 1.47 a 0.40 b 4.19 b 35 2 WAE 46 c 1.13 b 0.24 c 3.38 c 71 2 WAE 84 b 0.59 c 0.03 d 1.63 d 141 2 WAE 94 a 0.33 d 0.00 d 1.19 d 4 WAE 0 d 1.05 a 0.47 a 4.44 a 18 4 WAE 54 c 0.56 b 0.11 b 2.88 b 35 4 WAE 78 b 0.31 c 0.01 c 2.25 c 71 4 WAE 98 a 0.04 d 0.00c 1.25 c 141 4 WAE 99 a 0.01 d 0.00 c 0.81 d a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0 .05) c WAE = Weeks A fter Emergence.

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105 CHAPTER 5 INFLUENCE OF IMAZAPIC AND IMAZETH A PYR ON PURPLE NUTSEDGE ( CYPERUS ROTUNDUS L.) AND YELLOW NUTSE DGE ( C. ESCULENTUS L.) GROWTH AND REPRODUCTION Introduction Purple and yellow nutsedge combined rank fifth in importance among all weeds in the United States (Bendixen and Nandihalli 1987). Asexual reproduction via tubers is the most important means of nutsedge propagation (Bendixen and Nandihalli 1987; Wills 1987; Wills and Briscoe 1970). According to Rao (1 968) on e purple nutsedge tuber is capable of producing 99 new tubers in 90 days. Tubers also play an important role in nutsedge distribution. In the southeastern United States, tubers of both species are known to contaminate peanut during both harvest and shipment (Bendixen and Nandihalli 1987). R educing tuber populations is an essential component to any nutsedge control program b ecause of their important role in the reproduction and dissemination of purple and yellow nutsedge The objective of this study was to determine the effects herbicide rate and time of application have on the reproductive capabi lities of purple and yellow nut sedge. Materials and Methods Greenhouse experiments were conducted in Gainesville, Florida to determine the effect of preemergence (PRE) and early postemergence (EP) herbicide treatments on nutsedge growth and tuber production The upper 13 cm of a fine, loamy, siliceous, thermic Typic Paleudult Orangeburg sandy loam having 1.5% organic matter and a pH of 5.3 was collected at the Univ ersity of Floridas West Florida Research and Education Center located near Jay, Florida, and subsequently transported to the University of Floridas main campus in Gainesville, Florida. The soil was then sifted through a screen in order to remove any exis ting purple and yellow

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106 nutsedge tubers. Plastic pots were fil led with one part Metro Mix 300 and three parts Orangeburg sandy loam. Purple nutsedge tubers were collected at the University of Floridas Plant Science Research and Education Unit, located near Citra, Florida. Yellow nutsedge tubers were collected at the University of Floridas Horticultural Science Research Unit in Gainesville, Florida. For PRE treatments, yellow and purple nutsedge tubers were planted at a density of 5 tubers per pot, 1.5to 2.0 cm deep in 3.8 L pots Tubers of both species were presprouted to ensure viability. Y ellow nutsedge tubers were placed in trays lined with wet paper towels in a growth chamber for one week at a temperature of 30 C and a light duration of 14 h. Purple nutsedge tubers were either stored in moist newspapers at 25 C for 2 weeks, or in a growth chamber in the same manner as previously described for yellow nutsedge tubers. Buds and roots on tubers were removed prior to planting. Preparation of tubers for th e PRE treatments began 2 weeks following the preparation of tubers to be used for the EP treat ments. In doing so, both PRE and EP treatments could be applied simultaneously. For the EP treatments, purple and yellow nutsedge tubers were planted into 31 x 46 x 5 cm plastic trays containing adequately moist Metro Mix 300. After 2 weeks, sprouted tubers were transplanted into pots and allowed to grow for an additional 2 weeks, at which time they had at tained a height of 10 to 15 cm. Early post emergence treatm ents were applied at this time. Plants were not watered for 24 h following treatment in order to allow sufficient foliar absorption of the herbicides. Subsequently, plants were watered overhead daily. Imazapic and imazethapyr were applied either PRE or EP at 0, 18, 35, 71, and 141 g a.i. ha1, while metolachlor was applied at 0 700, 1400, 2 801, and 5 602 g. This is equivalent to 0, 0.25, 0.5, 1, and 2 times the labeled rate of these three herbicides when used for weed control in

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107 peanuts. These rates are act ive ingredients. Early post e mergence treatments included a nonionic surfactant applied at 0.25% v/v. The experiment was conducted twice. Herbicides were applied using a CO2pressurized, backpack sprayer calibrated to deliver a spray volume of 187 L ha1 wh en traveling at a speed of 4.83 km hr1. Visual ratings of purple and yellow nutsedge control were taken one month after treatment. An initial harvest of shoots was conducted at this time by clipping shoots off at soil level Shoots were then transferred to paper bags and placed in a dryer for a minimum of two weeks in order to obtain dry weight data. By monitoring the growth of pre sprouted tubers planted in untreated soil on the same day as those tuber s used in both the pre and post emergence portions of this experiment it was determined that 4 to 6 weeks were required for the onset of tuber production under normal circumstances. Therefore, a whole plant harvest was performed one month following the initial harvest (2 months after treatment) in an attempt to best ascertain the treatment effects on tuber production. For the whole plant harvest, nutsedge shoots were once again clipped off at soil level. Shoot regrowth dry weights were obtained by again placing shoots in paper bags and drying them for a minimum of two weeks. Next, soil was removed from the 3.8 L pots and carefully sifted through a wire mesh screen. Tubers were separated from roots/rhizomes and immediately counted and weighed. Treatments were arranged in the greenhouse as a randomized, complete, block design having four replications. Treatment differences were determined by using analysis of variance (ANOVA), with least significant difference (LSD) values calculated at a significance level of P = 0.05.

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108 Results a nd Discussion In general PRE t reatments control led purple nutsedge better tha n EP treatments Imazapic 71 g, however, controlled 100% of purple nutsedge when applied either PRE or EP ( Tables 5 1, 52). Imazethapyr 71 g also controlled 100% of purple nutsedge PRE, but control dropped to 95% when applied EP. Purple nutsedge control with metolachlor was inferior to both imazapic and imazethapyr. When metolachlor was applied PRE at twice the labeled rate for use in peanut, purple nutsedge control was still less than 60%. Other researchers h ave similarly found the addition of metolachlor to imazethapyr to not result in any improvement in cont rol of purple nutsedge (Grichar et al. 1992). Foliar dry weights 4 WAT were consistent with visual ratings of percent control, with im azapic and imazethapyr PRE at 71 and 141 g resulting in the lowest dry weights (Table 5 1). No re growth of foliage occurred with imazapic applied at either 71 or 141 g PRE or EP, nor with imazethapyr whe n applied PRE at the rates of 71 or 141 g (Tables 5 1, 52). Purple nut sedge tuber number and tuber weight at final harvest 8 WAT were lower for all herbicides when applied as PRE treatments versus EP treatments. Imazapic and imazethapyr PRE reduced tuber number and weights the most (Tables 5 1, 52) Other researchers have a lso reported similar purple nutsedge control from imazapic and imazethapyr, regardless of timing (Grichar, and Nester, 1997). PRE and EP treatments were equally effective in controlling yellow nutsedge, with the exception of metolachlor, which provided les s than 50% control EP even when applied at twice the labeled rate (Tables 5 3, 54). PRE treatments, h owever, resulted in lower shoot dry weights 4 WAT, as well as the fewest number of tubers and the lowest total tuber weights at the final harvest taken 8 WAT (Tables 5 3, 54). Expectedly metolachlor controlled yellow nutsedge much better than purp le nutsedge when applied PRE.

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109 Before drawing the conclusion from this research that imazapic and imazethapyr provide better purple and yellow nutsedge control wh en applied PRE versus EP, i t should be noted that growth of plants in the control p ots of both species for PRE treatments was roughly half that observed for EP treatments with regards to shoot dry weight, tuber number, and tuber weight. Plants grown from t ubers i n the growth chamber did not thrive as well as tubers grown with Metro Mix in the greenhouse. With this in mind PRE applications of both herbicides did provide significant control relative to the nontreated Results from this study demonstrate tha t PRE and EP treatments of imazapic, imazethapyr, and metolachlor can reduce yellow nutsedge tuber number c ompared to the untreated check. Only EP treatments of metolachlor failed to reduce purple nutsedge tuber density relative to the untreated control. I mazapic and imazethapyr provided better control of both nutsedge species than metolachlor. Yellow nutsedge control was equal for imazapic and imazethapyr when applied PRE, while imazapic provided slightly better yellow nutsedge control when applied EP. Similarly, Grichar (2002) reported better yellow nutsedge control and lower tuber density following imazapic applied postemergence (POST) compared to imazethapyr or metolachalor applied pre plant incorporated or imazethapyr applied POST. Grichar and Nester (1 997) reported similar yellow nutsedge control with soil applied treatments of imazapic and imazethapyr, but imazapic provided better POST control than did imazethapyr. The results from this study indicate that imazapic and imazethapyr reduced purple nutse dge tuber numbers equally well, regardless of timing. These results indicate that growers may utilize PRE or EP treatments of imazapic and imazethapyr to obtain significant control of purple and yellow nutsedge in terms of reducing tuber densities and over all tuber weight. Imazapic may provide farmers with superior yellow nutsedge control when applied EP.

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110 Table 5 1. Effect of pre emergence herbicide treatments on purple nutsedge reproduction, years one and two Initial Harvest Final Harvest Treatment Rate Control a Shoot Dry Weight Shoot Dry Weight Tuber Tuber Fresh Weight (g ha 1 ) (%) (g) (g) (No.) (g) Control 0 0 f b 1.51 0.98 9.5 a 5.24 a Imazapic 18 66 cd 1.01 0.31 6.3 b 3.28 abcd Imazapic 35 9 7 ab 0.31 0.06 5.0 b c 1.71 cde Imazapic 71 100 a 0.08 0.0 4.8 bc 1.72 cde Imazapic 141 1 0 0 a 0.03 0.0 3.5 c 0.87 e Imazethapyr 18 71 c 0.93 0.09 6.0 b 2.81 bcde Imazethapyr 35 8 9 b 0.46 0.02 4.8 cde 2.02 bcde Imazethapyr 71 10 0 a 0. 08 0.0 5.0 b c 1.88 bc de Imazethapyr 141 10 0 a 0.05 0.0 4.3 bc 1 .52 de Metolachlor 700 5 f 1.58 0.87 6.3 b 3.80 ab Metolachlor 1,400 3 0 e 1.28 0.68 5.3 bc 3.16 bcd Metolachlor 2,801 2 8 e 1.06 0.60 5. 4 bc 3.55 abc M etol achlor 5,602 5 9 d 0.58 0.13 5.0 bc 2.47 b cde LSD 1 0 NS NS 1.9 2 .0 a Control based on scale of 0 to 10 0 0 = no control, 10 0 = complete control. b Values followed by different letters indicate significant differences according to LSD t est ( P =0.05)

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111 Table 5 2. Effect of early post emergence herbicide treatments on purple nutsedge reproduction, years one and two Initial Harvest Final Harvest Treatment Rate Control a Shoot Dry Weight Shoot Dry Weight Tuber Tuber Fresh Weight (g ha 1 ) (%) (g) (g) (No.) (g) Control 0 0 g b 3.99 a 2.39 22.5 a 17.99 a Imazapic 18 6 5 cd 1.79 cd e 0.31 21.8 a 18.07 a Imazapic 35 88 b 1.53 d ef 0.18 13.8 bcde 10.31 b cd Imazapic 71 10 0 a 0.68 f 0.00 7.0 ef 4.26 e Ima zapic 141 1 0 0 a 0.80 ef 0.00 5.5 f 2.55 e Imazethapyr 18 5 0 e 2.70 b c 0.71 19.5 ab 17.43 a Imazethapyr 35 7 3 c 1.46 de f 0.35 11.5 cdef 6.75 c de Imazethapyr 71 9 5 ab 1.45 de f 0.13 9.5 def 6.55 cde Imazethapyr 141 9 9 a 0.59 f 0.06 9.3 def 5.23 de Metolachlor 700 1 g 3.67 a b 2.18 22. 8 a 15.71 ab Metolachlor 1,400 9 g 3.68 a b 1.38 19.3 ab 13.00 ab Metolachlor 2,801 2 5 f 2.42 c d 1.06 17.3 abc 11.34 bc Metolachlor 5,602 5 8 d 2.36 cd 0.83 16. 3 a bcd 11.13 bcd LSD 1 1 1 NS 7 .4 6 .3 a Control based on scale of 0 to 100, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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112 Table 5 3. Effect of pre emergence herbicide treatments on yellow nutsedge reproduction, years one and two Initial Harvest Final Harvest Treatment Rate Control a Shoot Dry Weight Tuber Tuber Fresh Weight (g ha 1 ) (%) (g) (No.) (g) Control 0 0 g b 2.58 7.9 a 2.03 Imazapic 18 5 7 ef 1.73 7.1 def 1.56 Imazapic 35 6 1 de 1.55 5.1 def 1.15 Imazapic 71 8 6 b 0.58 4.4 fgh 0.76 Imazapic 141 97 a 0.36 3.5 gh 0.35 Imazethapyr 18 6 2 c de 1.28 6.5 c 1.36 Imazethapyr 35 7 1 cd 0.94 5.5 c de 1.41 Imazethapyr 71 9 1 a b 0.42 4.3 fgh 0.99 Imazethapyr 141 9 9 a 0.17 3.4 h 0.53 Metolachlor 700 4 8 fg 1.41 6.5 c 1.70 Metolachlor 1,400 7 2 c 0.94 5.6 c d 1.38 Metolachlor 2,801 8 9 a b 0.69 4.8 d ef 1.04 M etolachlor 5,602 9 6 a b 0.45 4.5 efg 0.96 LSD 1 3 NS 1 .4 NS a Control based on scale of 0 to 10 0, 0 = no control, 100= complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05).

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113 Table 5 4. Effect of early post emergence herbicide treatments on yellow nutsedge reproduction, years one and two Initial Harvest Final Harvest Treatment Rate Control a Shoot Dry Weight Shoot Dry Weight Tuber Tuber Fresh Weight (g ha 1 ) (%) (g) (g) (No.) (g) Control 0 0 i b 6.02 a 5.84 a 11.6 a 5.79 a Imazapic 18 5 5 e 4.36 b 2.89 cd 6.6 d 3.31 d Imazapic 35 6 9 d 3.03 d 1.86 e 6.8 d 2.77 d ef Imazapic 71 8 8 b 2.36 d ef 0.51 f 4 .8 f 1.79 fg Imazapic 141 9 9 a 1.70 f 0.01 f 4.1 f 1.40 g Imazethapyr 18 1 6 h 4.41 b 3.79 bc 9.5 b 4.73 b Imazethapyr 35 3 8 fg 3.14 c d 2.49 d e 6.6 d 2.97 d e Imazethapyr 71 8 3 c 2.40 def 0.81 f 5.9 d e 2.27 e fg Imazethapyr 141 9 7 ab 1.83 ef 0.27 f 4.9 e f 1.49 g Metolachlor 700 1 1 h 4.76 b 4.34 b 10.1 b 5.16 ab Metolachlor 1,400 1 5 h 4.05 b c 3.22 c d 9.9 b 4.45 b c Metolachlor 2,801 3 4 g 3.16 c d 2.40 d e 8.4 c 3.58 c d M etolachlor 5,602 4 8 ef 2.7 7 de 1.72 e 8.3 c 3.24 de LSD 1 3 0.9 0.9 1.4 0.8 a Control based on scale of 0 to 10 0, 0 = no control, 100 = complete control. b Values followed by different letters indicate significant differences according to LSD test ( P =0.05)

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114 CHAPTER 6 EFFECTS OF RESIDUAL CONCENTRATIONS OF SOIL APPLIED IMAZAPIC AND IMAZETHAPYR ON THE GROWTH AND REPRODUCTI ON OF PURPLE NUTSEDGE (CYPERUS ROTUNDUS L. ) AS A FUNCTION OF T IME Introduction Purple nutsedge is considered the worlds worst weed based on the number of countries and crops in which it occurs (Holm et al. 1991a). In the southeastern United States, purple nutsedge reduces peanut ( Arachis hypogaea L.) yields by competing for water, light, and nutrients. It also reduces crop quality due to the contamination of harvested peanuts by nutsedge tubers (Bendixen and Nandihalli 1987). Due to the prolonged use of herbicides that differentially controlled yellow nutsedge, purple nutsedge has surpassed yellow nutsedge as the predominant nutsedge species in southeastern peanut fields (York 1994). The most impressive characteristic of purple nutsedge is its prolific production of subterranean tubers, which are capable of remaining dormant and thus of sustaining the species through extreme environmental conditions such as drought, flooding, heat, or lac k of soil aeration (Holm et al. 1991a). Tuber reduction must therefore be a vital component of any purple nutsedge control program. Imazapic (Cadre) and imazethapyr (Pursuit) were the first herbi cides to provide effective post emergence purple nutsedg e cont rol in peanuts (Wilcut et al. 1996). Imazapic provides enhanced purple nutsedge control relati ve to imazethapyr (Richburg et al. 1994; Richburg et al. 1993). Previous research concerning the persistence of imazapic in soil has focused on the potential carr yover injury to sensitive crops grown in rotation with peanut, such as cotton ( Gossypium hirsutum L.), grain sorghum (Sorghum bicolor L.), and corn ( Zea mays L.) (Matocha et al. 2003). Research examining the effects residual concentrations of imazapic in s oil have on purple nutsedge tubers over time is lacking.

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115 A possible explanation as to how imazapic provides season long control of purple nuts edge is that it may have a substantially longer half life than other herbicides used to control purple nutsedge. As tubers are produced throughout the growing season, they are controlled by residual concentrations of early season imazapic treatments. Another possibility is that s ublethal doses of imazapic are able to p revent tubers from reproducing. Therefore, t he objectives of this study were to determine the degradation rates of imazapic and imazethapyr in soil, as well as to ascertain how purple nutsedge growth and reproduction respond to varying concentratio ns of these herbicides in soil. Mater ials a nd Methods Th e upper 13 cm of a fine, loamy, siliceous, thermic Typic Paleud ult Orangeburg sandy loam with 1.5% organic matter and a pH of 5.3 was collected at the University of Floridas West Florida Research and Education Center located near Jay, Florida, and subsequ ently transported to a greenhouse on the University of Floridas main campus in Gainesville, Florida. The soil was then sifted through a screen in order to remove any existing nutsedge tubers. Imazapic and imazethapy r were applied at a rate of 0 and 71 g a .i. ha1 to 7 cm X 7 cm X 9 cm plastic pots containin g the aforementioned soil. Seventy one g is the labeled rate for these herbicides when used in peanuts. Herbicides were applied using a CO2pressurized, backpack sprayer calibrated to deliver a spray vo lume of 187 L ha1. All of the soil used in the first run of the study w as treated on the same day Additional pots were treated in order to provide enough soil to conduct a corn root bioassay on each sampling date. Soil in the pots was mixed immediately following treatment to ensure even distribution of the herbicide in each pot. Bare soil in the pots was maintained near 50% field capacity

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116 throughout the duration of the experiment. Greenhouse conditions included a mean temperature of approximately 300C an d a day length of 1416 h. Purple nutsedge tubers were collected at the University of Floridas Plant Science Research and Education Unit, located near Citra, Florida. Tubers were planted on 15 occasions subsequent to treating the soil with herbicide: imm ediately following treatment, 2, 4, 6, and 8 weeks after treatment (WAT), and monthly thereafter up to one year following treatment. At the end of each incubation period, five tubers were planted into four control pots, four imazapictreated pots, and four imazethapyr treated pots. Tubers weighed an average of 0.85 g, and were planted to a depth of approximately 2 cm. Data were collected 4 WAP (weeks after planting), and included shoot number, height and dry weight, tuber number and dry weight, root dry wei ght, and visual rating of percent control. A corn root bioassay was performed at the end of each incubation period as a means of ascertaining the approximate concentration of either imazapic or imazethapyr remaining in the soil. Plastic, cone shaped, 3.81 x 20.96 cm tubes were filled with either imazapictreated, imazethapyr treated, or non treated soil. At the end of each of the 15 incubation periods, three kernels of Pioneer 32694 were planted 2 cm below the soil surface in each conetainer and allowed t o grow for one month at which time primary corn root length was measured. Soil in the cone tainers was continuously subirrigated. The greenhouse environment was the same as that for the other portions of this study. In addition to the corn root bioassa y, a herbicide rate titration or dose response for corn roots was performed three times by applying imazapic and imazethapyr to soil at the rates of 0, 18, 35, 71, and 141 g at the following coinciding incubation dates: 0, 4, and 8 months These rates corr espond to 0, 0.25 x, 0.5x, x, and 2x rates of these herbicides, with x being the labeled

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117 rate for use in peanut. Three kernels of Pioneer 32694 were planted in conetainers containing treated and untreated soil in the same manner as discussed previously. Once again, corn was allowed to grow for one month Data collected from these corn kernels planted in this newly treated soil were then compared to those collected from nutsedge tubers and corn planted in the incubated soil. Treatments were arranged in th e greenhouse as a randomized complete block design having four replications. Regression analysis was used to characterize the relationship between corn root length response and imazapic and imazethapyr concentration in soil. Treatment differences were determined by using analysis of variance (ANOVA), with least significant difference (LSD) values calculated at a significance level of P = 0.05. This study was conducted twice Results a nd Discussion Data from two runs of the study were combined. Reductions i n purple nutsedge shoot growth and tuber production were more pronounced at the onset of the study when concentrations of herbicides in soil were at their highest (Tables 6 1, 62) However, purple nutsedge growth from tubers planted int o soil treated with imazapic or imazethapyr at the labeled rate of 71g was still reduced by > 93% up to 5 MAT. At 7 MAT, tuber numbers for imazapic and imazethapyr treated soil were 49 and 52%, respectively, of the controls (Table 6 1). Control of nutsedge shoots by imazeth a pyr dropped off dramatically after 7 months. Control fell from 80% 7 MAT, to 53% 8 MAT. This corresponds with results from the corn root bioassay, which suggest a decline in the concentration of imazethapyr in soil over this one month period (between 7 and 8 MAT) (Table 63). Root length of corn grown in imazethapyr treated soil increased significantly over this one month period, from 13 cm 7 MAT, to 21 cm 8 MAT. These results also imply that once

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118 imazethapyr concentrat ions in soil reach below 18 g small decreases in herbicide concentration can result in significantly less nutsedge control. Corn root length was reduced by 50% when the herbicide concentration in soil was approximately 17.5 and 13 g ai ha1 for imazapic and imazethapyr, respectively (Figure s 6 1 and 62). While imazethapyr controlled just over half of nutsedge shoots 8 MAT, i mazapic provided 76% contr ol of shoot dry weight 9 MAT. These results in conjunction with data from the corn root bioassay (Table 6 3) suggests that imazapic may persi st longer in soil than imazethapyr at concentrations sufficient to cause plant injury Sublethal doses of imazapic and imazethapyr were shown to lower purple nuts e dge tuber populations and dry weights. Visual ratings of nutsedge control taken 12 MAT were only 33% for imazapic and 16% for imazethapyr. However, both herbicides provided significant reductions in tuber dry weights 12 MAT. Tuber numbers were also reduced by both herbicides 12 MAT. The half life of both imazapic and imazethapyr is 120 d when app lied at 71 g (WSSA 2002). Soil factors, climatic conditions, and herbicidal properties all help determine the length of time herbicid es persist in soil. Soils high in clay, organic matter or both generally have a greater potential for herbicide carryover due to an increased adsorption to soil colloids with a corresponding decrease in leaching and loss through volatilization. Degradation rates for herbicides generally increase with increased temperatur e and soil moisture because high er temperatures and moi sture conditions favor increased rates of both chemical and microbial decomposition. Chemical properties of a n herbicide that affect its persistence include water solubility, vapor pressure, and susceptibility to chemical and microbial alteration or degrad ation (Hager and Refsell 2008)

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119 Other researchers have reported that soil type could be an integral factor influen cing imazapic longevity in soil (Grey et al. 2005). Variations in soil pH, clay content, and concentrations of iron and aluminum hydr oxides ar e known to affect imidazolin one herbicide absorption to soil and weed efficacy (Pusino et al. 1997, Rigitano et al. 2000, W ehtje et al. 1987). Imida zolinone herbicides generally persist longer in soils high in clay content, and particularly in those high i n a l uminum and iron hydroxides. The positive charges of aluminum and iron increases the adsorption of these herbicides to the soil. Persistence also increases as organic matter content increases due to increased soil adsorption Adsorption of imida zolinone s generally increase s as pH f alls below 6. While the relatively low pH of our soil would seem to favor adsorption of imazapic and imazethapyr, the low clay content and 1.5% organic matter may ha ve helped limit their persistence. Future research on the effe cts of residual concentrations of soil applied imazapic and imazethapyr on the growth and reproduction of purple nutsedge may yield different results due to dissimilar edaphic factors. T he results of our study indicate that imazapic, and to a lesser extent imazethapyr, can aid in lowering purple nutsedge populations not only in a single peanut growing season, but also for a period of at least one year following initial application. This residual control may benefit growers by decreasing purple nutsedge infe stations necessary to be managed in subsequent crops

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120 Table 6 1. Effects of residual concentrations of soil applied imazapic and imazethapyr on purple nutsedge control and tuber number and dry weight as a function of time Treatment Rate Tuber Planting Control c 6 WAP Tuber Number Tuber Dry Weight Avg. Tuber Dry Weight (g ha 1 ) (Date) (%) (No.) (g) (g) Control 0 0 WAT a 0 b d 9.1 a 2.21 a 0.24 a Imazapic 71 0 WAT 9 9 a 5.0 b 0.82 b 0.16 ab Imazethapyr 71 0 WAT 100 a 5.3 b 0. 76 b 0.14 b Control 0 2 WAT 0 b 8.8 a 3.75 a 0.44 a Imazapic 71 2 WAT 86 a 5.0 b 1.08 b 0.22 b Imazethapyr 71 2 WAT 9 8 a 5.1 b 0.96 b 0.19 b Control 0 4 WAT 0 c 7.5 a 3.67 a 0.49 a Imazapic 71 4 WAT 99 a 4.4 b 1.25 b 0. 27 b Imazethapyr 71 4 WAT 86 b 5.6 ab 1.20 b 0.22 b Control 0 6 WAT 0 c 5.8 a 2.71 a 0.48 a Imazapic 71 6 WAT 10 0 a 3.9 b 1.06 b 0.27 b Imazethapyr 71 6 WAT 9 4 b 4.3 b 0.76 b 0.18 b Control 0 8 WAT 0 b 5.1 a 2.11 a 0.42 a Imazapic 71 8 WAT 9 8 a 4.3 a 0.99 b 0.22 b Imazethapyr 71 8 WAT 9 5 a 4.1 a 0.79 b 0.22 b Control 0 3 MAT b 0 b 5 .0 a 1.98 a 0.40 a Imazapic 71 3 MAT 9 9 a 4.6 ab 0.61 b 0.13 c Imazethapyr 71 3 MAT 95 a 4.0 b 1.12 b 0.25 b Control 0 4 MAT 0 0 b 6.5 a 2.31 a 0.35 a Imazapic 71 4 MAT 9 9 a 4.5 b 1.06 b 0.24 b Imazethapyr 71 4 MAT 96 a 4.6 b 1.17 b 0.25 b Control 0 5 MAT 0 b 8.5 a 2.98 a 0.35 a Imazapic 71 5 MAT 9 7 a 4.6 b 1.23 b 0.27 ab Imaze thapyr 71 5 MAT 9 3 a 4.8 b 0.94 b 0.20 b Control 0 6 MAT 0 b 7.8 a 2.82 a 0.37 a Imazapic 71 6 MAT 8 4 a 4.5 b 1.01 b 0.22 b Imazethapyr 71 6 MAT 83 a 5.4 b 1.19 b 0.23 b

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121 Table 6 1. Continued Treatment Rate Tube r Planting Control 6 WAP Tuber Number Tuber Dry Weight Avg. Tuber Dry Weight (g ha 1 ) (Date) (%) (No.) (g) (g) Control 0 7 MAT 0 b 8.9 a 3.26 a 0.37 a Imazapic 71 7 MAT 8 4 a 4.4 b 1.37 b 0.32 ab Imazethapyr 71 7 MAT 80 a 4.6 b 1.16 b 0.26 b Control 0 8 MAT 0 c 5.4 a 2.00 a 0.37 a Imazapic 71 8 MAT 7 5 a 4.4 b 1.13 b 0.25 b Imazethapyr 71 8 MAT 5 3 b 4.8 ab 1.36 b 0.2.9 b Control 0 9 MAT 0 c 5.3 a 2.01 a 0.38 a Imazapic 71 9 MAT 76 a 4.4 b 1.49 b 0.33 a Imazethapyr 71 9 MAT 4 0 b 5.0 a 1.84 ab 0.37 a Control 0 10 MAT 0 c 5.0 ab 2.17 a 0.43 a Imazapic 71 10 MAT 46 a 4.6 b 1.92 ab 0.41 a Imazethapyr 71 10 MAT 3 0 b 5.1 a 1.83 b 0.36 b Control 0 11 MAT 0 c 5.5 a 2.6 8 a 0.49 a Imazapic 71 11 MAT 4 4 a 5.0 b 2.38 a 0.48 a Imazethapyr 71 11 MAT 2 3 b 5.0 b 2.44 a 0.49 a Control 0 12 MAT 0 c 6.1 a 3.45 a 0.57 a Imazapic 71 12 MAT 3 3 a 5.1 b 2.64 ab 0.51 a Imazethapyr 71 12 MAT 16 b 5.1 d 2.46 b 0.48 a a WAT = Weeks After Treatment. bMAT = Months A fter Treatment c Control based on scale of 0 to 10 0, 0 = no control, 10 0 = complete control. dValues followed by different letters indicate significant differences according to LS D test ( P =0.05)

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122 Table 6 2. Effects of residual concentrations of soilapplied imazapic and imazethapyr on purple nutsedge shoot number and height, and shoot and root dry weight, as a function of time Treatment Rate Tuber Planting Shoot Number Shoot Height Shoot Dry Weight Root Dry Weight (g ha 1 ) (Date) (No.) (cm) (g) (g) Control 0 0 WAT a 5.1 a c 18.1 a 0.57 a 0.45 a Imazapic 71 0 WAT 0.1 b 0.0 b 0.04 b 0.01 b Imazethapyr 71 0 WAT 0.6 b 3.5 b 0.03 b 0.05 b Control 0 2 WAT 5.3 a 15.4 a 0.44 a 0.46 a Imazapic 71 2 WAT 0.3 b 1.9 b 0.03 b 0.01 b Imazethapyr 71 2 WAT 0.1 b 0.0 b 0.02 b 0.00 b Control 0 4 WAT 4.9 a 14. 3 a 0.33 a 0.69 a Imazapic 71 4 WAT 0.4 b 1.8 b 0.01 b 0.15 b Imazethapyr 71 4 WAT 0.4 b 0.8 b 0.03 b 0.07 b Control 0 6 WAT 5.3 a 11. 6 a 0.31 a 0.33 a Imazapic 71 6 WAT 0.4 b 0.5 b 0.00 b 0.05 b Imazethapyr 71 6 WAT 0.5 b 11.7 b 0.02 b 0.07 b Control 0 8 WAT 3.3 a 11. 2 a 0.42 a 0.34 a Imazapic 71 8 WAT 0.4 b 1.0 b 0.02 b 0.19 a Imazethapyr 71 8 WAT 0.1 b 0.3 b 0.04 b 0.23 a Control 0 3 MAT b 4.5 a 15.0 a 0.57 a 0.35 a Imazapic 71 3 MAT 0.1 b 1.0 b 0.01 b 0.04 b Imazethapyr 71 3 MAT 0.1 b 0.3 b 0.01 b 0.08 b Cont rol 0 4 MAT 4.4 a 7.9 a 0.21 a 0.23 a Imazapic 71 4 MAT 0.0 b 1.0 b 0.00 b 0.05 b Imazethapyr 71 4 MAT 0.3 b 0.3 b 0.02 b 0.05 b Control 0 5 MAT 4.6 a 13. 9 a 0.26 a 0.26 a Imazapic 71 5 MAT 0.3 b 0.2 b 0.02 b 0.06 b Imazet hapyr 71 5 MAT 0.9 b 0.0 b 0.05 b 0.04 b Control 0 6 MAT 4.9 a 14.3 a 0.27 a 0.41 a Imazapic 71 6 MAT 0.9 b 2.3 b 0.08 b 0.27 ab

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123 Table 6 2. Continued Treatment Rate Tuber Planting Shoot Number Shoot Height Shoot Dry Weight R oot Dry Weight (g ha 1 ) (Date) (No.) (cm) (g) (g) Imazethapyr 71 6 MAT 0.6 b 2.6 b 0.02 b 0.22 b Control 0 7 MAT 5.3 a 14. 4 a 0.47 a 0.36 a Imazapic 71 7 MAT 1.1 b 5. 5 b 0.11 b 0.33 a Imazethapyr 71 7 MAT 0.9 b 4.9 b 0.09 b 0.29 a Control 0 8 MAT 5.1 a 15.2 a 0.48 a 0.47 a Imazapic 71 8 MAT 1.1 c 5.2 b 0.48 c 0.19 b Imazethapyr 71 8 MAT 2.5 b 6.8 b 0.05 b 0.13 b Control 0 9 MAT 5.9 a 16.7 a 0.48 a 0.52 a Imazapic 71 9 MAT 1.5 c 4.1 c 0.08 c 0.18 c Imazethapyr 71 9 MAT 3.5 b 11.1 b 0.27 b 0.37 b Control 0 10 MAT 5.5 a 17.2 a 0.46 a 0.45 a Imazapic 71 10 MAT 4.1 b 10.3 b 0.30 b 0.18 b Imazethapyr 71 10 MAT 4.3 b 11.6 b 0.36 ab 0.30 b Control 0 11 MAT 5.4 a 1 5. 9 a 0.44 a 0.50 a Imazapic 71 11 MAT 3.1 b 8.6 c 0.24 b 0.20 b Imazethapyr 71 11 MAT 4.6 a 11.8 b 0.30 b 0.23 b Control 0 12 MAT 5.4 a 18.6 a 0.53 a 0.59 a Imazapic 71 12 MAT 3.8 b 12.4 b 0.32 b 0.26 b Imazethapyr 71 12 M AT 4.8 ab 16.5 a 0.46 ab 0.48 a a WAT = Weeks After Treatment. bMAT = Months A fter Treatment cValues followed by different letters indicate significant differences according to LSD test ( P =0.05)

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124 Table 6 3. Corn root bioassay Treatmen t Rate Corn Planting Root L ength (g ha 1 ) (Date) (cm) Control 0 0 WAT a 32.9 a c Imazapic 71 0 WAT 3.4 b Imazethapyr 71 0 WAT 4.8 b Control 0 2 WAT 31.3 a Imazapic 71 2 WAT 6.5 b Imazethapyr 71 2 WAT 5.7 b Control 0 4 WAT 31. 8 a Imazapic 71 4 WAT 1.8 c Imazethapyr 71 4 WAT 5.0 b Control 0 6 WAT 36.0 a Imazapic 71 6 WAT 4.4 c Imazethapyr 71 6 WAT 14.1 b Control 0 8 WAT 32.6 a Imazapic 71 8 WAT 7.2 b Imazethapyr 71 8 WAT 10.6 b Control 0 3 M AT b 33.8 a Imazapic 71 3 MAT 9.2 b Imazethapyr 71 3 MAT 12. 2 b Control 0 4 MAT 37.5 a Imazapic 71 4 MAT 8.9 b Imazethapyr 71 4 MAT 12.2 b Control 0 5 MAT 36.1 a Imazapic 71 5 MAT 11. 7 b Imazethapyr 71 5 MAT 12 0 b Control 0 6 MAT 31.0 a Imazapic 71 6 MAT 12.6 b Imazethapyr 71 6 MAT 13.6 b Control 0 7 MAT 35.0 a Imazapic 71 7 MAT 1 3.1 b Imazethapyr 71 7 MAT 12.9 b Control 0 8 MAT 33.2 a Imazapic 71 8 MAT 14.9 c Imazethapyr 71 8 MAT 21.0 b Control 0 9 MAT 34.3 a Imazapic 71 9 MAT 14.0 c Imazethapyr 71 9 MAT 24.8 b Control 0 10 MAT 32.5 a Imazapic 71 10 MAT 21.6 b Imazethapyr 71 10 MAT 25. 6 b Control 0 11 MAT 31.1 a Imazapic 71 11 MAT 24.0 b

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125 Table 6 3. Continu ed Treatment Rate Corn Planting Root L ength (g ha 1 ) (Date) (cm) Imazethapyr 71 11 MAT 27.9 a Control 0 12 MAT 31.8 a Imazapic 71 12 MAT 26.4 b Imazethapyr 71 12 MAT 32.7 a LSD 4.3 aWAT = Weeks after Treatment. bMAT = Mont hs after Treatment cValues followed by different letters indicate significant differences according to LSD test ( P =0.05).

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126 Figure 61. Imazapic dose response for corn root bioassay 1 MAT

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127 Figure 62. Imazethapyr dose response for corn root bioassa y 1 MAT

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128 CHAPTER 7 CONCLUSIONS Purple nutsedge ( Cyperus rotundus L.) is one of the most important weeds found in southeastern peanut fields. The proliferation of this perennial species is due primarily to reproducti on via tubers. The ability of a herbic ide to reduce tuber populations in peanut would be enhanced if it was able to provide effective post emergence control of purple nutsedge. Imazapic and imazethapyr were the first selective herbicides to offer such control in peanut. A field study was cond ucted during three consecutive summers to determine the effects various herbicide treatments had on purple nutsedge tuber populations at mid and lateseason. Treatments were applied PPI, EPOST, MPOST, and LPOST relative to peanut emergence. Tubers were sam pled from depths of 010, 1020, and 2030 cm. For Y e ars one and two, imazapic 71g a.i. ha1 EPOST resulted in the best reduction of tuber number and total tuber weight at mid and lateseason. For Y ear three, vernolate PPI resulted in the lowes t tuber num bers at mid season. Imazapic 71g MPOST provided the lowest tuber populations by late season, reducing tuber numbers to approximately 16% of the untreated control. End of season tuber germination rates were lowest in plots that received EPOST treatments. C hemical control measures alone are often unable to suppress purple and yellow nutsedge populations to manageable levels. Cultivation, either alone, or in conjunction with herbicide treatments, is another option growers have in combating these weedy species Three field studies were conducted. One study involved repeated tillage operations in purple nutsedge, and two consisted of combinations of repeated cultivation and glyphosate applications in either purple or yellow nutsedge. In the purple nutse dge tillage study, it was found that tilling twice, either at two and four weeks or four and six weeks, was best at reducing tuber number at mid season. Tilling more than

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129 three times did not significantly reduce lateseason tuber numbers from those found after til ling either at two + four + six weeks, or four + six + eight weeks, or six + eight + ten weeks. In the studies involving tillage and/or glyphosate treatments in either purple or yellow nutsedge, the best reduction in nutsedge tuber number, weight, and vi ability at mid and lateseason sampling dates was obtained from the combined use of multiple glyphosate applications and repeated tillage operations, as opposed to one or the other control measures independently. Greenhouse studies were performed in an attempt to better understand the effects plant growth stage and herbicide selection, rate, and site of application had on the control of purple and yellow nutsedge. Imazapic provided better control of purple and yellow nutsedge than did imazethapyr at all growth stages tested. Both nutsedge species were controlled better at 2 than at either 4 WAE or 6 WAE. Imazapic controlled yellow nutsedge more easily than purple nutsedge at all growth stages, with the exception of sprouted tubers. Although less efficaci ous to both species compared to imazapic, imazethapyr controlled purple nutsedge better than yellow nutsedge at all growth stages, including as either unsprouted or sprouted tubers. Imazapic and imazethapyr controlled unsprouted and sprouted tubers more easily than emerged plants. Whereas purple nutsedge tuber numbers and tuber weights were lower for PRE treatments than EPOST treatments, foliar only treatments provided better shoot control than soil applied treatments. The best control, how ever, of two fou r, and sixweek old purple and yellow nutsedge was obtained by treating both the foliage and soil. The 71g rate of imazapic applied to both the foliage and soil resulted in the lowest dry weights for purple and yellow nutsedge shoots harvested initially at 4 WAT, and again 8 WAT following a regrowth period of one month. A final greenhouse study was performed to determine if the enhanced efficacy of imazapic on purple nutsedge relative to imazethapyr was due to a longer half life in soil, as well

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130 as an abi lity to control tubers at sub lethal concentrations. Both herbicides reduced tuber populations by approximately 50% 7 MAT when applie d at the labeled rate of 71 g At the conclusion of the study 12 MAT, both imazapic and imazethapyr still provided reductio ns in tuber numbers and dry weights when herbicide concentrations were far below lethal levels. Imazapic, however, was better able to sustain vegetative control of purple nutsedge over the course of the year long study. S hoot control from imazethapyr fell from 80 to 53% between the 7and 8 month sampling periods Imazapic, on the other hand, still provided 76% control of nutsedge shoots 9 MAT. Shoot control at 12 MAT was 33 and 16% for imazapic and imazethapyr, respectively. Results indicate that imazapic provides better residual control of purple nutsedge than imazethapyr.

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131 REFERENCES Addy, E. O. and E. Eteshola. 1984. Nutritive value of a mixture of tigernut tubers ( Cyperus esculentus L. ) and baobab seeds ( Adansonia digitata L.). J. Sci. Food Agric. 35: 437440. Ahrens, W. H. (ed.). 1994. Herbicide Handbook, 7th Ed. Champaign, IL: Weed Science Society of America. Pp. 203 205. Akin, D. S. and D. R. Shaw. 2001. Purple nutsedge ( Cyperus rotundus ) and yellow nutsedge ( Cyperus esculentus ) control in glyphosate tolerant soybean ( Glycine max) Weed Technol. 15:564570. Armel, G. R., H. P. Wilson, R. J. Richardson, C. M. Whaley, and T. E. Hines. 2008. Mesotrione combinations with atrazine and bentazon for yellow and purple nutsedge ( Cyperus esculentus and C. rotundus ) control in corn. Weed Technol. 22: 391396. Anonymous. 2007. Cadre herbicide label. BASF Corp.' Research Triangle Park, NC. Banks, P. A. 1983. Yellow nutsedge ( Cyperus esculentus ) control, regrowth, and tuber production as affected by herbicides. Weed Sci. 31:419422. Bayer, D. E. 1987. Tuber dormancy, germination, apical dominance, and translocation in yellow and purple nutsedge. Proc. of the California Weed Conference. Pp. 90 92. Bell, R. S., W. H. Lachman, E. M. Rahn, and R. D. Sweet. 1962. Life hi story studies as related to weed control in the northeast. Rhode Island Agric. Exp. Station, Northeast Regional Publication. Bulletin 364:133. Bendixen, L. E. 1973. Anatomy and sprouting of yellow nutsedge tubers. Weed Sci. 21:501503. Bendixen, L. E. and U. B. Nandihalli. 1987. Worldwide distribution of purple and yellow nutsedge ( Cyperus rotundus and C. esculentus ). Weed Technol. 1:61 65. Berger, G. B. 1966. Dormancy, growth inhibition and tuberization of nutsedge Cyperus rotundus as affected by photoperiods. Ph.D. thesis, Univ. California, Riverside. Besler, B. A. W. J. Gr ichar, S. A. Senseman, R. G. Lemon, and T. A. Baughman. 2008. Effects of row pattern configurations and reduced (1/2 X) and full rates (1 X) of imazapic and diclosulam for control of yellow nutsedge ( Cyperus esculentes ) in peanut. Weed Technol 22: 558562. Black, C. C., T. M. Chen, and R. H. Brown. 1969. Biochemical basis for plant competition. Weed Sci. 17:338344. Brecke, B. J. and D. O. Stephenson IV. 2006a Weed management in singl e vs. thinrow peanut ( A rachis hypogaea) Weed Technol 20: 368376.

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140 BIOGRAPHICAL SKETCH Derek Duane Horrall is a native of Columbus, Indiana and a graduate of Columbus North High School. He received a Bachelor of Arts de gree in g eology from Hanover College Hanover, Indiana and a Master of Science degree in agronomy from Purdue University West Lafayette, Indiana. Derek served as an agricultural volunteer with the United States Peace Corps in Sngal, West Africa. He rece ived a degree in automotive t echno logy, with a specialization in chassis fabrication and high p erformance e ngines, from Wyoming Technical Institute (WyoTech) Blairsville, P ennsylvania. Derek hopes to obtain a teaching and research pos i tion at a university or conduct on farm research in the agricultural chemical industry