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Influence of Herbicides and Time of Application on Peanut (Arachis hypogaea L.) Injury and Yield.

Permanent Link: http://ufdc.ufl.edu/UFE0024901/00001

Material Information

Title: Influence of Herbicides and Time of Application on Peanut (Arachis hypogaea L.) Injury and Yield.
Physical Description: 1 online resource (62 p.)
Language: english
Creator: Boyer, James
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: acifluorfen, bentazon, imazapic, lactofen, metolachlor, paraquat, peanut
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: INFLUENCE OF HERBICIDES AND TIME OF APPLICATION ON PEANUT (Arachis hypogaea L.) INJURY AND YIELD By James A. Boyer August 2009 Chair: Greg MacDonald Major: Agronomy Dramatic changes in peanut weed management due to the development of herbicide resistant weed populations and shifts in weed spectrum have forced many southeastern peanut growers to consider the use of alternative herbicide programs. Most of these alternative programs utilize traditional herbicides that were common prior to 1996. These herbicides were primarily contact in activity, and resulted in a certain degree of foliar burn, with little to no peanut yield loss. Furthermore, these herbicides were researched extensively on Florunner variety, which is now no longer grown. Currently, a wide range of new varieties with greater yield potential and disease tolerance dominate the southeastern peanut growing region, but the impact of the older herbicide programs has not been evaluated on the new varieties. Project I evaluated the effect of paraquat application timing with and without bentazon on two peanut varieties. Varieties were AP-3 and Florida-07 and treatments included paraquat and paraquat + bentazon applied 14, 21, 28, 35 or 42 days after cracking (DAC). All treatments resulted in a delay in canopy closure but this delay was not always followed by yield reduction for either variety. The addition of bentazon reduced injury for some treatments in both years, but foliar injury appeared to be related to application timing rather than addition of bentazon. Project II evaluated the effects of paraquat applications as a function of variety, herbicide combinations, timing and application. Varieties were Andru II, AP-3 and C-99R and treatments included paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor applied 14 or 28 DAC. Bentazon lessened foliar injury while metolachlor increased foliar injury. Treatments applied 14 DAC exhibited 1/4 to 1/3 less injury than the 28 DAC treatments. Within an application timing, there appeared to be little difference between paraquat alone and combinations of metolachlor and/or bentazon with paraquat. There was little impact of any treatment on peanut yield. Project III evaluated the effect of lactofen and acifluorfen applications as a function of variety and timing. Varieties were Andru II (2007), ViruGard (2008), AP-3 and C-99R and treatments included lactofen and acifluorfen applied 4, 6, 8 or 10 weeks after planting (WAP). Delay in canopy closure did not necessarily result in reduced yield. Injury at 14 days after treatment (DAT) appeared to be related to yield in 2008 but not in 2007. Yield loss was observed for treatments with ? 15% injury 14 DAT, which included lactofen applied 8 and 10 WAP and acifluorfen at 10 WAP. In conclusion, there appeared to be a delay in foliar injury with paraquat + metolachlor combinations, but this effect was ameliorated by the addition of bentazon. However, there appeared to be little relation between herbicide treatment and peanut yield. Therefore, producers should consider the proper herbicide mixture that will provide economical and effective weed control, and not base herbicide selection on potential yield loss and/or foliar injury. It is likely that environmental conditions at the time or shortly after treatment plays a more important role in peanut injury than timing of application.
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 James Boyer.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: MacDonald, Greg.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024901:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024901/00001

Material Information

Title: Influence of Herbicides and Time of Application on Peanut (Arachis hypogaea L.) Injury and Yield.
Physical Description: 1 online resource (62 p.)
Language: english
Creator: Boyer, James
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: acifluorfen, bentazon, imazapic, lactofen, metolachlor, paraquat, peanut
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: INFLUENCE OF HERBICIDES AND TIME OF APPLICATION ON PEANUT (Arachis hypogaea L.) INJURY AND YIELD By James A. Boyer August 2009 Chair: Greg MacDonald Major: Agronomy Dramatic changes in peanut weed management due to the development of herbicide resistant weed populations and shifts in weed spectrum have forced many southeastern peanut growers to consider the use of alternative herbicide programs. Most of these alternative programs utilize traditional herbicides that were common prior to 1996. These herbicides were primarily contact in activity, and resulted in a certain degree of foliar burn, with little to no peanut yield loss. Furthermore, these herbicides were researched extensively on Florunner variety, which is now no longer grown. Currently, a wide range of new varieties with greater yield potential and disease tolerance dominate the southeastern peanut growing region, but the impact of the older herbicide programs has not been evaluated on the new varieties. Project I evaluated the effect of paraquat application timing with and without bentazon on two peanut varieties. Varieties were AP-3 and Florida-07 and treatments included paraquat and paraquat + bentazon applied 14, 21, 28, 35 or 42 days after cracking (DAC). All treatments resulted in a delay in canopy closure but this delay was not always followed by yield reduction for either variety. The addition of bentazon reduced injury for some treatments in both years, but foliar injury appeared to be related to application timing rather than addition of bentazon. Project II evaluated the effects of paraquat applications as a function of variety, herbicide combinations, timing and application. Varieties were Andru II, AP-3 and C-99R and treatments included paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor applied 14 or 28 DAC. Bentazon lessened foliar injury while metolachlor increased foliar injury. Treatments applied 14 DAC exhibited 1/4 to 1/3 less injury than the 28 DAC treatments. Within an application timing, there appeared to be little difference between paraquat alone and combinations of metolachlor and/or bentazon with paraquat. There was little impact of any treatment on peanut yield. Project III evaluated the effect of lactofen and acifluorfen applications as a function of variety and timing. Varieties were Andru II (2007), ViruGard (2008), AP-3 and C-99R and treatments included lactofen and acifluorfen applied 4, 6, 8 or 10 weeks after planting (WAP). Delay in canopy closure did not necessarily result in reduced yield. Injury at 14 days after treatment (DAT) appeared to be related to yield in 2008 but not in 2007. Yield loss was observed for treatments with ? 15% injury 14 DAT, which included lactofen applied 8 and 10 WAP and acifluorfen at 10 WAP. In conclusion, there appeared to be a delay in foliar injury with paraquat + metolachlor combinations, but this effect was ameliorated by the addition of bentazon. However, there appeared to be little relation between herbicide treatment and peanut yield. Therefore, producers should consider the proper herbicide mixture that will provide economical and effective weed control, and not base herbicide selection on potential yield loss and/or foliar injury. It is likely that environmental conditions at the time or shortly after treatment plays a more important role in peanut injury than timing of application.
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 James Boyer.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: MacDonald, Greg.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024901:00001


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INFLUENCE OF HERBICIDES AND TIME OF APPLICATION ON PEANUT ( Arachis hypogaea L.) INJURY AND YIELD By JAMES A. BOYER A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009 1

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2009 James A. Boyer 2

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To my wife, Kelle, she has always had the patience and kindness to always love me regardless of my faults; and our children, Katherine and Na than, for understanding and supporting me through this journey. I love you all and look forward to growing old with you. 3

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ACKNOWLEDGMENTS For their support and guidance at the Universi ty of Florida, I wish to express sincere appreciation to my graduate committee: Dr. Gr eg MacDonald, Dr. Jay Ferrell, Dr. Barry Brecke and Dr. Barry Tillman. Special thanks go to committee chair member Dr. Greg MacDonald, for providing the opportunity to further my educa tion and Dr. Jay Ferrell, for keeping me on schedule and continual guidance. Without their gentle prodding and constant encouragement, I never would have achieved this degree. Thank you to Dr. Daniel Colvin, my supervisor at the Plant Science Research and Education Unit, for allowing me to pursue this degree and supporting my efforts over the past 2 years in graduate school and 14 years throughout my career. I would also like to acknowledge Carl Vining and Michael Bucky Dobrow. Carl was extremely instrumental in my data collection and spray applications and Bucky provided many moments of comic relief while encouraging me through graduate school. Most of the field research would not have been possible without the support and hard work of the PSREU staff. My mother and father have been supportive, along with my brothers Willet and Rob and their families; thank you for providing encouragement and a refuge for me when I needed relief. 4

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TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4LIST OF TABLES ...........................................................................................................................7ABSTRACT .....................................................................................................................................9CHAPTER 1 THE EFFECT OF PARAQUAT ALONE AND IN COMBINATION WITH BENTAZON ON PEANUT INJURY A ND YIELD AS A FUNCTION OF APPLICATION TIMING .......................................................................................................11Introduction .............................................................................................................................11Materials and Methods ...........................................................................................................13Results and Discussion ...........................................................................................................15AP-3 .................................................................................................................................15Florida-07 ........................................................................................................................16Discussion ........................................................................................................................172 THE EFFECT OF PARAQUAT ALONE AND IN COMBINATION WITH METOLACHLOR AND/OR BENTAZON ON PEANUT INJURY AND YIELD FOR THREE DIFFERING MATURITY CULTIVARS ................................................................25Introduction .............................................................................................................................25Materials and Methods ...........................................................................................................28Results and Discussion ...........................................................................................................30Early Maturity Peanut (Andru II) ....................................................................................30Medium Maturity Peanut (AP-3) .....................................................................................31Late Maturity Peanut (C-99R) .........................................................................................32Discussion ........................................................................................................................323 THE EFFECT OF LACTOFEN AND ACIFLUORFEN APPLICATION TIMING ON PEANUT INJURY AND YIELD FOR TH REE VARYING MATURITY CULTIVARS ...41Introduction .............................................................................................................................41Materials and Methods ...........................................................................................................43Results and Discussion ...........................................................................................................45Early Maturity Peanut (Andru II and ViruGard) .............................................................45Medium Maturity Peanut (AP-3) .....................................................................................46Late Maturity Peanut (C-99R) .........................................................................................47Discussion ........................................................................................................................48 5

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LIST OF REFERENCES ...............................................................................................................57BIOGRAPHICAL SKETCH .........................................................................................................62 6

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LIST OF TABLES Table page 1-1 ANOVA table for the effect of paraquat alone and in combination with bentazon on peanut injury and yield as a function of application timing. ..............................................201-2 Influence of paraquat and paraquat + bent azon herbicides on per cent injury, days to row closure, and yield of AP-3 peanut in 2007. ................................................................211-3 Influence of paraquat and paraquat + bent azon herbicides on per cent injury, days to row closure, and yield of AP-3 peanut in 2008. ................................................................221-4 Influence of paraquat and paraquat + bent azon herbicides on per cent injury, days to row closure, and yield of Florida-07 peanut in 2007. ........................................................231-5 Influence of paraquat and paraquat + bent azon herbicides on per cent injury, days to row closure, and yield of Florida-07 peanut in 2008. ........................................................242-1 ANOVA table for the effect of paraquat alone and in combination with metolachlor and/or bentazon on peanut injury and yiel d for three differing maturity cultivars.^ .........342-2 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of Andru II peanut in 2006. ................................................................................................352-3 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of Andru II peanut in 2007. ................................................................................................362-4 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of AP-3 peanut in 2006. .....................................................................................................372-5 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of AP-3 peanut in 2007. .....................................................................................................382-6 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of C-99R peanut in 2006. ...................................................................................................392-7 Influence of paraquat, paraquat + bent azon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percen t injury, days to row closure, and yield of C-99R peanut in 2007. ...................................................................................................403-1 ANOVA table for the effect of lactofen and acifluorfen application timing on peanut injury and yield for three varying maturity cultivars. ........................................................50 7

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3-2 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of Andru II peanut in 2007. ..................................................................513-3 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of ViruGard peanut in 2008. .................................................................523-4 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of AP-3 peanut in 2007. ........................................................................533-5 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of AP-3 peanut in 2008. ........................................................................543-6 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of C-99R peanut in 2007. .....................................................................553-7 Influence of lactofen an d acifluorfen herbicides on pe rcent injury, days to row closure, and yield of C-99R peanut in 2008. .....................................................................56 8

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Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science INFLUENCE OF HERBICIDES AND TIME OF APPLICATION ON PEANUT ( Arachis hypogaea L.) INJURY AND YIELD By James A. Boyer August 2009 Chair: Greg MacDonald Major: Agronomy Dramatic changes in peanut weed management due to the development of herbicide resistant weed populations and shifts in weed spectrum have forced many southeastern peanut growers to consider the use of alternative herbicide programs. Most of these alternative programs utilize traditional herb icides that were common prior to 1996. These herbicides were primarily contact in activity, and resulted in a certain degree of foliar burn, with little to no peanut yield loss. Furthermore, these herbic ides were researched extensively on Florunner variety, which is now no longer grown. Currently, a wide range of new va rieties with greater yield potential and disease tolerance dominate th e southeastern peanut growing region, but the impact of the older herbicide programs ha s not been evaluated on the new varieties. Project I evaluated the effect of paraquat application timing with and without bentazon on two peanut varieties. Varietie s were AP-3 and Florida-07 and treatments included paraquat and paraquat + bentazon applied 14, 21, 28, 35 or 42 days after cracking (DAC). All treatments resulted in a delay in canopy cl osure but this delay was not al ways followed by yield reduction for either variety. The addition of bentazon reduced injury for some treatments in both years, but foliar injury appeared to be related to application timing ra ther than addition of bentazon. 9

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10 Project II evaluated the effects of paraquat applications as a function of variety, herbicide combinations, timing and application. Varieties were Andru II, AP-3 and C-99R and treatments included paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor applied 14 or 28 DAC. Bentazon lessened foliar injury while metolachlor increased foliar injury. Treatments applied 14 DAC exhib ited 1/4 to 1/3 less in jury than the 28 DAC treatments. Within an applica tion timing, there appeared to be little difference between paraquat alone and combinations of metolachlor and/or be ntazon with paraquat. There was little impact of any treatment on peanut yield. Project III evaluated the effect of lactofen and acifluorfen a pplications as a function of variety and timing. Varieties were Andru II (2007), ViruGard (2008), AP-3 and C-99R and treatments included lactofen and acifluorfen a pplied 4, 6, 8 or 10 weeks after planting (WAP). Delay in canopy closure did not ne cessarily result in reduced yiel d. Injury at 14 days after treatment (DAT) appeared to be related to yield in 2008 but not in 2007. Yield loss was observed for treatments with 15% injury 14 DAT, which included lactofen applied 8 and 10 WAP and acifluorfen at 10 WAP. In conclusion, there appeared to be a delay in foliar injury with paraquat + metolachlor combinations, but this effect was ameliorated by the addition of bentaz on. However, there appeared to be little relation be tween herbicide treatment and pea nut yield. Therefore, producers should consider the proper herbicide mixture th at will provide economical and effective weed control, and not base herbicide se lection on potential yield loss and/ or foliar injury. It is likely that environmental conditions at the time or shortl y after treatment plays a more important role in peanut injury than timing of application.

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CHAPTER 1 THE EFFECT OF PARAQUAT ALONE AND IN COMBINATION WITH BENTAZON ON PEANUT INJURY AND YIELD AS A FUNCTION OF APPLICATION TIMING Introduction Weed management in peanuts prior to the mid 1990s relied heavily on early postemergence herbicide applications (Wehtje et al. 1992a; Wilcut et al. 1990b; Wilcut et al. 1994a; Wilcut et al. 1994b; Wilcut et al. 1994c). The herbicides used were primarily contact in activity, and peanut injury was common and was accepted by growers ( D.L. Colvin personal communication ). Paraquat is a widely used contact he rbicide in the southeastern United States that has been used for many years in early-sea son weed control in peanuts (Johnson et al. 1993; Senseman 2007). Peanuts sustain considerable foliar injury, but genera lly recover within 2-3 weeks of application (Wehtje et al. 1991a; Wehtje et al. 1992c). This herbicide continues to be widely used because of broad-spectrum weed c ontrol and relatively low cost (Cardina et al. 1987; Wehtje et al. 1986; Wilcut et al. 1987a; Wilcut et al. 1987b; Wilcut et al. 1989; Wilcut et al. 1990a). Paraquat affects the light reac tions in photosynthesis where it causes the formation of reactive oxygen (Fedtke 1982). This results in cell membrane disr uption that can be observed soon after application (Senseman 2007). Paraquat affects both peanut and weeds, but generally weeds are damaged and killed whereas peanuts on ly sustain moderate de foliation and leaf burn (Wehtje et al. 1986). This potentia l for leaf burn limits applications to 28 days after emergence. To alleviate some of the phytotoxicity, bentaz on is commonly added to paraquat (Grey et al. 1992; Wilcut et al. 1993). In the late 1980s, growers began utilizing the combination of bentazon and paraquat, as it was observed that less peanut in jury occurred. Researchers confirmed this phenomenon; the safening effect of bentazon is due to reduced paraquat uptake (Wehtje et al. 1992a) and possibly 11

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from interactions in photosynthetic electron flow prior to paraquat activit y (Pfister et al. 1974; Suwanketnikom et al. 1982). Since the registration of imazapic in 1996, ma ny peanut producers have reduced paraquat usage in their production systems. The broad spectrum foliar and soil activity of imazapic allowed growers to rely almost exclusively on this herbicide for postemergen ce weed control. In addition to controlling many of the most common weeds in southeastern peanut production, it results in little to no visu al injury (Dotray et al. 2001; Matocha et al. 2003). However, the past decade of intense imazapic usage has led to the increasing occurrence of weed resistance and a shift in weed spectrum. The two most noteworthy species that will escape imazapic are acetolactate synthase (A LS)-resistant Palmer amaranth ( Amaranthus palmeri S. Watson) and Bengal dayflower (Commelina benghalensis L.). Normally, imazapic controls Palmer amaranth with both preemergence and postemergence activity. ALS resistant Palmer amaranth exhibits high levels of resistan ce to imazapic and has been found across the southeastern United States (Vencill et al. 2002). Bengal dayflower is tolerant to imazapic and di splays little or no change in growth after application (Steptoe et al. 2006). Bengal dayflower is an exotic invasive weed species that has become widely distributed across the southeas tern United States over the past five years (Webster et al. 2005). These weed problems have forced many growers to reconsider contact herbicides, but there has been limited research with new varieties. Even if growers do not have ALS resistant palmer amaranth, alternative herbic ides are highly recommended to avoid resistant biotypes from developing or becoming endemic (S ellers et. al 2008). Paraquat is one of the leading contact postemergence herbicides av ailable to combat resistance issues. 12

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Paraquat and bentazon have a long record of effective weed control, but peanut tolerance and potential yield reduction continues to be a question for growers. The current label recommendations for paraquat were based on data collected on the Florunner variety, which is no longer grown. Florunner was a mid-season vari ety that reached maturity approximately 134 days after planting (Norden et al. 1969). Curren tly, a wide range of new varieties with greater yield potential and disease tolerance dominate th e southeastern peanut gr owing region. The new peanut varieties differ in maturity that ranges from 120 to 145 days after planting. The emergence of herbicide resistant weeds a nd exotic weed species will likely increase the use of paraquat across the pean ut growing regions of the sout h. However, the current label recommendation, which is 28 days after peanut emer gence, is in question. Some growers believe that the intense paraquat injury is more likely to reduce peanut yield as applications near 28 days after emergence. Conversely, in times of slow weed emergence, others believe that paraquat applications beyond 28 days are warranted and not yield limiting. Therefore, the objectives of this research were 1) to determine whether peanut yield reduction is likely to occur if paraquat is applied before or after 28 days after emergen ce to two recently released mid-season maturity peanut cultivars and 2) to determine the safening effect of bentazon compar ed to paraquat alone. Materials and Methods Field experiments were conducted in 2007 a nd 2008 at the Plant Science Research and Education Unit in Citra, Florida, on a Sparr fi ne sand (loamy, siliceous, hyperthermic Grossarenic paleudult) with 1% organic matter. All experiments were initiated using a conventional tillage regime. Plots were 3.0 m wide, 7.6 m long and contained four rows sp aced 76.2 cm apart. Plots received optimum irrigation, fertil ity, insecticide and fungicide tr eatments as directed by the Florida Cooperative Extension Service. Seeds were planted at a depth of 5 cm with a seeding 13

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density of 17 seeds per meter of row (Wri ght et al. 2006). Planting occurred on May 23, 2007 and May 6, 2008. Each year aldicarb was applied in furrow at 3.2 kg ai/ha. The experimental area received a preemergence broadcast applic ation of pendimethalin (0.92 kg ai/ha) + diclosulam (0.42 kg ai/ha), and a postemergen ce application of imazapic (0.07 kg ai/ha). Supplemental hand-weeding was performed as needed to maintain weed-free conditions throughout the growing season. The experimental design was a randomized comp lete block with a split-plot treatment arrangement and four replications Peanut cultivar was the w hole plot factor and herbicide treatments were subplots. Cultivars included medium-season peanut cultivars (137-140 days), AP-3 (Gorbet 2007) and Florida-07 (Gorbet a nd Tillman 2009). Ten herbicide treatments consisting of paraquat at 0.14 kg/ha or paraquat at 0.14 kg/ha + be ntazon at 0.28 kg/ha applied to each variety at 14, 21, 28, 35 or 42 days after crac king (DAC). An untreated check was included for each cultivar. All herbicide treatments included a non-ionic surfactant at 0.25% v/v. All experimental treatments were applied using a CO2 backpack sprayer calibrated to deliver 187 L/ha. Peanut foliar injury was vi sually evaluated and peanut canopy width was measured 7, 14, and 28 days after application. Visu al estimations of injury were rated on a scale from 0% to 100% with 0% = no injury and 100% = complete plant necrosis. Days to canopy closure (when no soil was visible between the two center rows) was also recorded. The center two rows of each plot were dug according to maturity using a conventional digger-shaker-inverter. Matur ity was determined by the hull scrape method for each cultivar (Johnson 1987; Johnson et al. 1993; S holar et al. 1995). Peanuts we re allowed to field dry for approximately 3 days and commercial harvesting equipment was used to harvest each plot. 14

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Peanut yields (adjusted to mois ture conditions of 9%) were dete rmined and converted to a kg/ha basis. Data were subjected to analysis of variance to test treatment effects and interactions. Means were separated using Fisher s Least Significant Difference (LSD) test at the p<0.05 level. Results and Discussion Treatment by year and treatment by variety inte ractions for all parameters measured were significant and prevented pooling of data (Table 1-1). Therefore, data is presented by year and variety. AP-3 In 2007, the level of injury ranged from 19% to 55% 7 days after treatment (DAT) but peanuts fully recovered with no injury evident 28 DAT (Table 1-2). Paraquat injury to AP-3 ranged between 10% and 55% 14 DAT while para quat + bentazon caused between 10% and 40% injury. Paraquat applications ap plied 14 and 21 DAC resulted in gr eater peanut injury than the 28, 35 and 42 DAC application. At 14 DAT, simi lar levels of injury were observed with paraquat alone and paraquat + bentazon for each application timing. The exception was the 21 DAC treatment where the additi on of bentazon significantly reduced the injury compared to paraquat alone. Paraquat alone resulted in si gnificantly delayed canopy closure compared to the untreated check except for 35 DAC, but the delay was not observed with any bentazon combinations. In 2007, the yield of AP-3 was significantly reduc ed when paraquat was applied 14 DAC and 42 DAC and when paraquat + bentazon were applied 14 and 21 DAC. There were significant reductions in yield compared to the untreated check for paraquat alone at 14 and 42 DAC, and for paraquat + bentazon at 14 and 21 DAC. 15

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In 2008, there was significant foliar injury for all treatments when ev aluated 7 DAT (Table 1-3). Addition of bentazon did not affect differen ces in injury compared to paraquat alone. At 14 DAC, injury from all treatments was greatly reduced, much more so than observed in 2007. Once again applications on or before 28 DAC, resulted in greater injury compared to applications made 35 and 42 DAC. Peanuts fully recovered from foliar injury by 28 DAT, but nearly all treatments slowed canopy closure by up to 12 days. The addition of bentazon to paraquat reduced peanut injury and canopy closur e delay, but no trends were observed and few conclusions can be drawn relative to the benefits of bentazon. The greatest delays in canopy closure were observed in 2007. Paraquat at 14 and 42 DAC delayed canopy closure by 16 and 17 days, respectivel y, compared to the untreated control. The greatest delay in 2008 canopy closure was 12 days from paraquat applications applied 14 and 21 DAC. No application timing or herbicide combination resulted in yield reduction for AP-3 in 2008. The addition of bentazon reduced injury for so me treatments in both years. All treatments resulted in a delay in canopy cl osure for both years and yield reductions were observed in 2007 for paraquat and paraquat + bentazon combinations Paraquat is labeled for use up to 28 days after emergence, but 2007 applications applied 14 DAC caused significant yield loss. It is unknown why yield reduction was observed with treatments applied 14 DAC and not at 35 DAC. Florida-07 In 2007, all treatments applied to Florida-07 caus ed injury that ranged from 10% to 51% at 7 and 14 (DAT) (Table 1-4). Substantial injury was observed 7 DAT for all treatments. Measured 7 DAT, all treatments resulted in 40% injury with the exception of paraquat alone or in combination with bentazon applied at 35 DAC. Interestingly, these two tr eatments resulted in 16

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greater foliar injury 14 DAT compared to 7 DAT while all other trea tments showed much reduced injury. As with AP-3, foliar injury appeared to be more closely associated with application timing than with the addition of bentazon. For example Florida-07 at 14 DAT, peanut treated 28 DAC exhibited significantly less injury compared to all other treatments, regardless of whether bentazon was included. This was also noted fo r AP-3 in 2007. Peanuts showed no foliar injury by 28 DAT for any treatment and only the paraquat alone 42 DAC resulted in a significant delay in canopy closure. The only two treatments that resulted in significant yield reductions were paraquat applied alone 14 DAC and paraquat + bentazon applied 42 DAC. In 2008, all treatments resulted in >30% foliar injury 7 DAT but peanuts recovered more quickly in 2008, with 20% injury when evaluated one we ek later 14 DAT (Table 1-5). No injury was observed 28 DAT, but all treatments caused a delay in canopy cl osure, regardless of the addition of bentazon. In 2007, Florida-07 had canopy closure quicker than the AP-3 and paraquat applied 42 DAC caused the greatest delay in canopy closure for Florida-07. Florida-07 had slower canopy closure than AP-3 in 2008, and a ll applications caused significant delays in days to canopy closure compared to the untre ated. The longest delay in canopy closure was observed following paraquat applied 14 DAC. No significant yield reduc tion was observed for any treatment in 2008. The yield loss in 2007 is noteworthy because the 14 DAC application is within the label recommendations. Discussion Overall, there was no relationship between de lay in canopy closure a nd yield reduction. Bentazon reduced visual injury in some of the treatments, but lesse ned injury did not always lead to increased yield. These data indicate that some varieties are more sensitive to paraquat treatments, and the earlier growth stages are sometimes the most susceptible to paraquat injury. 17

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Other research has shown some similarities a nd differences from these results. English pea ( Pisum sativum L.) injury from paraquat was reduced when bentazon was added, similar to what was observed in the study reported here. Paraqu at alone produced more visual injury than paraquat plus bentazon, but the English pea r ecovered by 21 DAT (Bellinder et al. 1997). English pea yield was not reduced with either treatment if the pl ant had adequate time to recover from herbicide injury before flower deve lopment and pod filling (Bellinder et al. 1997). Grey et al. (1995) reported the addition of be ntazon reduced visual injury ratings by 25% from paraquat alone in peanut. In two of the three years, peanut yield was higher in an earlypostemergence paraquat application comp ared to paraquat plus bentazon. Other research has shown that peanut toleranc e is acceptable if the paraquat application is made prior to 28 days after emergence and that fo liar injury did not lead to yield loss (Wehtje et al.1991b; Wilcut et al. 1989; Wilcut et al. 1994a) These data indicate that delaying paraquat applications until 21 to 35 days after emergence might allow the peanut to better recover from paraquat injury. Wehtje showed the addition of bentazon did not improve peanut yi eld as compared to paraquat alone (Wehtje et al. 1992a). His work also showed that weeds sensitive to paraquat were not controlled with the addition of bent azon indicating that it sa fens weeds to paraquat injury similar to the way it safens peanut foliage (Weh tje et al. 1992a). Another trend is the differences between 2007 and 2008. If you look at recovery from foliar burn, this was much more evident in 2008 co mpared to 2007. There was also no yield loss in 2008 from the treatments. This suggests that growth conditions in the first 2-3 weeks after paraquat applications are critical to yield. If the peanuts, in ge neral, show >15% foliar injury 14 DAT, then a loss in yield could be observed regardless of bentazon or timing of application. 18

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Weeds compete with peanut for light, water, nu trients and physical sp ace. If producers are making a decision on whether to use a contact herbicid e, they have need to weigh the benefit of a herbicide with potential yield loss against the amount of yi eld loss due to weed pressure. Paraquat or paraquat + bentazon are useful tools for peanut growers, but the application decisions need to made on a case by case basis. 19

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Table 1-1. ANOVA table for the e ffect of paraquat alone and in combination with bentazon on peanut injury and yield as a function of application timing. Class Variable DF1 --------------% injury2------------Days to Closure2 Yield2 7 DAT314 DAT 28 DAT variety (maturity) 1 0.4557 0.4742 0.0291 0.0019 <0.0001 year (2007/2008) 1 0.0003 <0.0001 0.0291 <0.0001 <0.0001 treatment 10 <0.0001 <0.0001 0.1388 <0.0001 <0.0001 replication 3 0.9704 0.2829 0.1873 0.0007 0.5694 year variety 1 0.1600 0.0112 0.0291 <0.0001 <0.0001 year treatment 10 <0.0001 <0.0001 0.1388 0.0029 0.2976 year variety treatment 20 0.1491 0.0155 0.0846 0.5613 0.9728 1 DF = degrees of freedom. 2 Pr > F. 3 DAT = days after treatment. 20

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Table 1-2. Influence of paraquat and paraquat + bentazon herbicides on pe rcent injury, days to row closure, and yield of AP-3 peanut in 2007. Herbicide Timing --------------% injury1------------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 54a638bc 0a 88a 2810cd paraquat 21 53a 55a 0a 84a-c 3180a-c paraquat 28 39cd 10de 0a 86ab 3280ab paraquat 35 19e 28bc 0a 70d 3240ab paraquat 42 44bc 26b-d 0a 89a 2750d paraquat + bentazon 14 55a 40ab 0a 79a-d 3060b-d paraquat + bentazon 21 49ab 23cd 0a 83a-d 3080b-d paraquat + bentazon 28 34d 10de 0a 74b-d 3310ab paraquat + bentazon 35 19e 28bc 0a 70d 3370ab paraquat + bentazon 42 44bc 25b-d 0a 84a-c 3240ab untreated 0 0f 0e 0a 72cd 3510a 1 Visual assessment of peanut foliar damage a nd stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are signific antly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 21

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Table 1-3. Influence of paraquat and paraquat + bentazon herbicides on pe rcent injury, days to row closure, and yield of AP-3 peanut in 2008. Herbicide Timing --------------% injury1-----------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 56a613ab 0a 63a 7010cd paraquat 21 50bc 14a 0a 63a 7690a-c paraquat 28 26e 10ab 0a 58b 8130a paraquat 35 34d 6bc 0a 58b 8010ab paraquat 42 49bc 6bc 0a 58b 6770d paraquat + bentazon 14 54ab 10ab 0a 56b 7410b-d paraquat + bentazon 21 54ab 11ab 0a 63a 7380b-d paraquat + bentazon 28 29de 11ab 0a 54bc 7740ab paraquat + bentazon 35 28e 9ab 0a 58b 7620a-c paraquat + bentazon 42 46c 6bc 0a 51c 7010cd untreated 0 0f 0c 0a 51c 7300b-d 1 Visual assessment of peanut foliar damage a nd stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are signific antly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 22

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Table 1-4. Influence of paraquat and paraquat + bentazon herbicides on pe rcent injury, days to row closure, and yield of Florida-07 peanut in 2007. Herbicide Timing --------------% injury1-----------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 48ab635ab 0a 70ab 2730b paraquat 21 48ab 24c 0a 68ab 3380ab paraquat 28 40c 13d 0a 67b 3300ab paraquat 35 23d 29bc 0a 65b 3480ab paraquat 42 44bc 28c 0a 77a 3040ab paraquat + bentazon 14 51a 39a 0a 65b 3380ab paraquat + bentazon 21 45bc 26c 0a 68ab 2890ab paraquat + bentazon 28 41c 10d 0a 63b 3700ab paraquat + bentazon 35 19d 28c 0a 67b 3300ab paraquat + bentazon 42 45bc 28c 0a 72ab 2760b untreated 0 0e 0e 0a 63b 3870a 1 Visual assessment of peanut foliar damage a nd stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are signific antly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 23

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24 Table 1-5. Influence of paraquat and paraquat + bentazon herbicides on pe rcent injury, days to row closure, and yield of Florida-07 peanut in 2008. Herbicide Timing --------------% injury1-----------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 59a616ab 3a 68a 5610c paraquat 21 53bc 13ab 0b 67a 6280ab paraquat 28 33e 11ab 1ab 63a 6560ab paraquat 35 36de 16ab 0b 67a 6330ab paraquat 42 48c 11ab 0b 63a 5570c paraquat + bentazon 14 56ab 20a 0b 63a 6210ab paraquat + bentazon 21 51bc 15ab 1ab 63a 6090a-c paraquat + bentazon 28 31e 13ab 0b 66a 6630a paraquat + bentazon 35 34e 14ab 0b 63a 6420ab paraquat + bentazon 42 41d 9bc 0b 63a 6040bc untreated 0 0f 0c 0b 54b 6110a-c 1 Visual assessment of peanut foliar damage a nd stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters are signific antly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test.

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CHAPTER 2 THE EFFECT OF PARAQUAT ALONE AND IN COMBINATION WITH METOLACHLOR AND/OR BENTAZON ON PEANUT INJURY AND YIELD FOR THREE DIFFERING MATURITY CULTIVARS Introduction Peanut producers in the s outheastern United States relied heavily on contact postemergence herbicides for weed control prior to 1996 (Wehtje et al. 1992a; Wilcut et al. 1990b; Wilcut et al. 1994a; Wilcut et al. 1994b; W ilcut et al. 1994c). Dinoseb was the principle postemergence herbicide treatment for 25 years until the EPA cancelled all registrations in 1986 (Wilcut et al. 1989). Dinoseb was one of the most economical and effective weed control measures used at that time (Buchanan et al. 1983). After the cancellation of dinoseb, paraquat was registered for peanut use in 1988 and became the standard for at-cracking weed control in southeastern peanut producti on (Wehtje et al. 1991a). Paraquat is quickly absorbed into leaf tissue, producing oxygen-free radicals (Fedtke 1982). This formation of reactive oxygen dest roys cells and cell membranes (Fedtke 1982; Senseman 2007). Paraquat works primarily by c ontact but can be translocated in the xylem (Brian 1969; Thrower et al. 1965). Even though xyl em mobility is possi ble, the application method limits movement in the xylem. Paraquat provides acceptable control of gra ss and many broadleaf weeds found in peanuts when applied within three weeks of ground cracking (Wehtje et al. 1986; Wilcut et al. 1989). Ground cracking is when the peanut plant is be tween the emergence of the hypocotyl and the appearance of first true leav es (Boote 1982). Paraquat causes foliar injury when applied postemergence, but the peanuts ove rcome leaf defoliation with no im pact to yield (Wehtje et al. 1986). Peanuts are tolerant to this leaf defoliation if th e application is made prior to pegging and pod development, which is approximately four w eeks after emergence (Wehtje et al. 1986). The 25

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paraquat label allows applications up to 28 days after peanut emergence (Anonymous 2009). But, as stated previously, this application can result in temporary defoliation (Wehtje et al. 1986). To alleviate some of the phytotoxicity, be ntazon is commonly added to paraquat (Grey et al. 1992; Wilcut et al. 1993). In the late 1980s, researchers confirmed the combination of paraquat and bentazon lessened peanut injury (Wehtje et al. 1992a; Wehtje et al. 1992b). The safening is due to the bentazon interference of paraquat ab sorption (Wehtje et al. 1992a). In contrast, peanut producers believe that metolachlor increases paraquat injury to peanut ( D.L. Colvin personal communication ). Metolachlor is an effective tool in controlling Bengal dayflower (Culpepper et al. 2004; Prostko et al. 2005; Webster et al. 2006). Metolachlor is a growth inhibitor that can be used on a wide range of crops including peanut, corn, potato, soybean and cotton (Senseman 2007). Despite the injury potential, metol achlor was widely used to control certain broadleaf weeds and yellow nutsedge in peanuts (Cardina and Swann 1988; Wehtje et al. 1988; Wilcut et al. 1989; Wilcut et al. 1990b; W ilcut et al. 1994a). Many peanut producers have reduced paraquat, metolachlor and bentazon usage in their production systems since the registration of imazapi c. Imazapic is a broad spectrum herbicide that has foliar and soil activity. This com pound was registered in 1996, and has allowed growers to rely on imazapic for postemergence weed cont rol. Imazapic controls many of the most commonly occurring weeds in peanut with little visual injury and no yi eld reduction (Dotray et al. 2001; Matocha et al. 2003). The past 13 years of repeated imazapic usage has led to the increasing occurrence of weed resistance and a shift in weed spectrum. The two problematic species are acetolactate synthase (ALS)-resistant Palmer amaranth ( Amaranthus palmeri S. Watson) and Bengal dayflower 26

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( Commelina benghalensis L.). Normally, imazapic contro ls Palmer amaranth with both preemergence and postemergence activity, but AL S resistant Palmer amaranth has quickly become one of the most troublesome weeds in th e southeastern United States. High levels of Palmer amaranth resistance to imazapic have been found across the southeastern United States (Vencill et al. 2002). Bengal dayflower is an exotic invasive weed species that ha s increased in distribution over the past five years (Webster et al. 2005). Bengal dayflower is tolerant to imazapic and glyphosate (Steptoe et al. 2006; Webster et al. 20 05). Glyphosate-resistant crops such as cotton, soybean and corn have aided the spread of this weed due to the ineffec tiveness of glyphosate on Bengal dayflower (< 55% control w ith glyphosate) (Culpepp er et al. 2004). The lack of residual herbicides and reduced tillage systems favor ed in glyphosate-resistant crop programs has allowed the prevalence of this weed to incr ease (Brecke et al. 2005, Spader and Vidal 2000; Webster et al. 2005, 2006). To combat these issues, growers have been forced to reconsider the use of residual herbicides such as metolachlor and contact herb icides such as paraquat (Webster et al. 2007). Even if growers do not have resistant weed populations, alternative herbicides are highly recommended to avoid resistance (Selle rs et. al 2008). It is also im portant to rotate herbicides of various mechanisms of action, incorporate non-c hemical controls such as cultivation and not allow resistant weeds to re produce (Jordan et al. 2007). Peanut tolerance to paraquat, bentazon and metolachlor continues to be a concern of growers, especially with the new peanut varieties. There is li mited research on yield impact of these herbicides on new varieties, and the current label recommendations for paraquat were based on data collected in the 1980s on the Fl orunner variety. Florunner was a mid-season 27

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maturity variety that reached maturity in appr oximately 134 days after planting (Norden et al. 1969), but is no longer grown in th e southeastern United States. Currently, a wide range of new varieties with greater yield potential and disease tolerance domi nate the southeastern peanut growing region. The newer peanut varieties di ffer in maturity requiring from 120 to 145 days after planting to reach maturity. Herbicide resistant weeds and exotic invasive s will likely increase th e use of paraquat and metolachlor across the peanut growing regions. Some producer s believe that the intense paraquat injury is more likely to reduce peanut yield as applications a pproach the 28 days after emergence label restriction. The obj ectives of this resear ch were to determine 1) whether peanut yield reduction is likely to occur when paraquat is applied before 28 days after emergence, 2) whether bentazon reduces any negative yield im pact of paraquat alone, and 3) whether metolachlor increases the injury potential of paraquat. Materials and Methods Field experiments were conducted in 2006 a nd 2007 at the Plant Science Research and Education Unit in Citra, Florida on a Sparr fi ne sand (loamy, siliceous, hyperthermic Grossarenic paleudult) with 1% organic matter. All experiments were initiated using a conventional tillage regime. Plots were 3.0 m wide, 7.6 m l ong and contained four rows spaced 76.2 cm apart. Plots received optimum irrigation, fertil ity, insecticide and fungicide tr eatments as directed by the Florida Cooperative Extension Service. Seeds were planted at a depth of 5 cm with a seeding density of 17 seeds per meter of row (Wri ght et al. 2006). Planting occurred on May 17, 2006, and June 14, 2007. Each year aldicarb was applied in furrow at 3.2 kg ai/ha. The experimental area received a preemergence broadcast applic ation of pendimethalin (0.92 kg ai/ha) + diclosulam (0.42 kg ai/ha), and a postemergen ce application of imazapic (0.07 kg ai/ha). 28

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Supplemental hand-weeding was performed as needed to maintain weed-free conditions throughout the growing season. The experimental design was a randomized comp lete block with a split-plot treatment arrangement and four replications Peanut cultivar was the w hole plot factor and herbicide treatments were subplots. Cultivars included early (Andru II), mid (A P-3) and late (C-99R) season peanut cultivars (Gorbet 2006; Gorbet 2007; Gorbet and Shokes 2002). Eight herbicide treatments consisting of paraquat at 0.14 kg/ ha, paraquat at 0.14 kg/ ha + bentazon at 0.28 kg/ ha, paraquat at 0.14 kg/ ha + metolachlor at 1.42 kg/ ha or paraquat at 0.14 kg/ ha + bentazon at 0.28 kg/ ha + metolachlor at 1.42 kg/ ha applied to each variety at 14 or 28 days after cracking (DAC). An untreated check was included for each cultivar. All herbicide treatments included a non-ionic surfactant at 0.25% v/v. All experimental treatments were applied using a CO2 backpack sprayer calibrated to deliver 187 L/ha. In 2006, visual ratings of peanut foliar injury were performed 7 days after application. In 2007, peanut foliar injury was vi sually rated and peanut canopy width measured 7, 14, and 28 days after application. Injury was vi sually rated on a scale from 0% to 100% with 0% = no injury and 100% = complete plant necr osis. Days to canopy closure (when no soil was visible between the two cente r rows) was also recorded. The center two rows of each plot were dug acco rding to maturity by a conventional diggershaker-inverter. Maturity was determined by the hull scrape method for each cultivar (Johnson, 1987; Johnson et al. 1993; Sholar et al. 1995). Peanuts were allowed to field dry for approximately 3 days and commercial harvesting equipment was used to harvest each plot. Peanut yields (adjusted to mois ture conditions of 9%) were dete rmined and adjusted to a kg/ha basis. 29

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Data were subjected to analysis of variance to test treatment effects and interactions. Means were separated using Fisher s Least Significant Difference (LSD) test at the p<0.05 level. Results and Discussion Statistical analysis detected a significant treatment by year and treatment by variety interaction (Table 2-1). Therefore, data were not pooled and the result s are presented by year and variety. Early Maturity Peanut (Andru II) In 2006, significant differences in peanut inju ry were detected 7 days after treatment (DAT) (Table 2-2). Injury resu lting from treatment applications ranged from 9% to 18% 7 DAT. Overall, applications 28 DAC were more inju rious than 14 DAC treatments, regardless of paraquat combination. All treatme nts had significant yield reductio ns compared to the untreated control. The combination of paraquat plus metolachlor applied 28 DAC resulted in the largest yield reduction of 1440 kg/ha. Paraquat alone applied 14 and 28 DAC caused the next largest yield reduction of 1060 and 1010 kg/ha, respectivel y. Paraquat + bentazon + metolachlor applied 14 or 28 DAC resulted in the least yi eld reduction of 660 and 700 kg/ha, respectively. This indicates the safening effect of bentazon is more pronounced with later applications of paraquat + metolachlor. In 2007, much greater injury was observed 7 DAT from applications made at 28 DAC compared to 14 DAC (Table 2-3). There also appeared to be no diffe rences between paraquat alone and combination with either metolachlor or bentazon or the three-way combination, within an application timing. Interestingly, this tre nd did not continue when evaluated 14 DAT, where 28 DAC treatments showed injury levels similar to the 14 DAC treatments. Injury actually increased for all 14 DAC from 7 DAT to th e 14 DAT evaluation period, but by 28 DAT, no injury was observed from any treatment. 30

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Canopy closure was significantly delayed for a ll applications and ranged from 13 to 27 days longer than the untreated control. The longest delay in canopy closure resulted from paraquat applied 28 DAC. Paraquat + bentazon a pplied 28 DAC was the second longest delay of 24 days. Significant reductions in peanut yield were observed with paraquat alone applied 14 and 28 DAC, paraquat + bentazon applied 28 DAC paraquat + metolachlor applied 14 DAC ranging from 630 to 890 kg/ha. In general, the la rger yield reductions o ccurred with the 14 DAC treatments. This is interesting considering that the least visual injury ra tings 7 DAT had the most yield reduction in this early matu rity cultivar. Even though the mo st visual injury was observed with the 28 DAC treatments, the peanuts recovere d quicker and had no loss in yield compared to the 14 DAC treatments. Medium Maturity Peanut (AP-3) In 2006, AP-3 exhibited minimal injury rangi ng from 4% to 11% (Table 2-4). As previously observed, the peanuts had generally recovered from th e foliar injury by 28 DAT (data not shown). AP-3 yields were not reduced by any treatment in 2006. AP-3 in 2007 was injured most from the 28 DAC treatments with injury ranging from 10% to 43% 7 DAT (Table 2-5), and peanut recovere d by 28 DAT with no foliar injury visible from any treatment. At 7 DAT, injury levels were sim ilar within each applica tion timing. In general, the 14 DAC applications showed 1/4 to 1/3 less injury compared to the 28 DAC application. However, by 14 DAT, the injury from the 14 DAC treatment increased compared to 7 DAT, while the injury from the 28 DAC decreased, resu lting in similar levels of injury for both application timings. There appe ared to be little difference between paraquat alone or the combination of metolachlor and/or bentazon with paraquat. Row closur e was delayed the most (>20 days) by paraquat applied 28 DAC, paraquat + metolachlor applied 28 DAC and paraquat + bentazon + metolachlor applied 14 DAC, and the least (1 day) by para quat alone applied 14 31

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DAC. Paraquat + bentazon did not safen injury effects compared to paraquat alone, paraquat + metolachlor, or paraquat + be ntazon + metolachlor. AP-3 yi elds were not reduced by any treatments in 2007. Late Maturity Peanut (C-99R) In 2006, C-99R was injured 10% to 15% 7 DAT with few differences among herbicide treatments or timings of application (Table 2-6). Paraquat (14 and 28 DAC), paraquat + metolachlor (14 and 28 DAC), paraquat + be ntazon (14 DAC), and paraquat + bentazon + metolachlor (28 DAC) reduced C-99R yield by 610 to 860 kg/ha. C-99R in 2007 was injured the most (39% to 49%) from 28 DAC treatments (Table 2-7). As previously observed, peanut injury was le ss severe 7 DAT from treatments applied 14 DAC compared to those applied 28 DAC. However, injury increased from 7 DAT to 14 DAT for herbicides applied 14 DAC but decreased for ap plications 28 DAC. Peanut recovered from foliar injury by 28 DAT. There were no differen ces in injury among the herbicide treatments. Canopy closure was significantly delayed by al l treatments with paraquat applied 28 DAC and paraquat + metolachlor applied 14 and 28 DAC causing the longer delay (22 days). Similar to AP-3, the least delay in canopy closure was paraquat applied 14 DAC and the greatest delay was paraquat applied 28 DAC. The only treatment that reduced yield was paraquat applied 28 DAC. These results are similar to those reported for other cultivars. Less injury was observed for 14 DAC treatments at 7 DAT but increased injury by 14 DAT. Higher initial (7 DAT) injury was evident for the 28 DAC appli cation but decreased by 14 DAC. Discussion There is a limited amount of published rese arch describing the impact on peanut of paraquat and metolachlor combinations. Grey reported that bentazon and paraquat tank mix 32

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33 reduced foliar injury up to 25% (Grey et al. 1995). In the same study, paraquat alone yielded higher in 2 of the 3 years compared to paraquat and bentaz on (Grey et al. 1995). Richburg et al. reported that imazethapyr plus metolachlor applied preplant incorporated (PPI) followed by paraquat plus metolachlor at cracking reduced yield by 200 kg/ha averaged over a 3-year experiment compared with the sa me PPI followed by paraquat plus bentazon at cracking (Richburg et al. 1995). Johnson et al. reported that alachlor mixe d with paraquat followed by a paraquat application caused peanut to have early-season leaf re duction, later pod set a nd delayed maturity (Johnson et al. 1993). When peanut s were allowed to fully mature with delayed maturity from herbicide applications, peanut yield was not impacted (Johnson et al. 1993). Knauft et al. reported similar effects on peanut maturity (Knauft et al. 1990). In conclusion, there appeared to be a delay in foliar injury with paraquat + metolachlor combinations, but this effect was ameliorated by the addition of bentaz on. However, there appeared to be little impact of herbicide treatment on peanut yi eld. Therefore, producers should consider the proper herbicide mixture that will provide economical and e ffective weed control, and not base herbicide selection on potential yiel d loss and/or foliar injury. It is likely that environmental conditions at the time or shortly af ter treatment plays a more important role in peanut injury than timing of application. Weeds compete with peanut for light, water, nu trients and physical sp ace. If producers are making a decision on whether to use a contact herbicid e, they have need to weigh the benefit of a herbicide with potential yield loss against the amount of yi eld loss due to weed pressure. Paraquat, bentazon and metolachlor are useful to ols for peanut growers, but the application decisions need to made on a case by case basis.

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Table 2-1. ANOVA table for the e ffect of paraquat alone and in combination with metolachlor and/or bentazon on peanut injury and yiel d for three differing maturity cultivars.^ Class Variable DF1 --------------% injury2------------Days to Closure2 Yield2 7 DAT314 DAT 28 DAT variety (maturity) 3 <0.0001 <0.0001 year (2006/2007) 1 <0.0001 <0.0001 treatment 8 <0.0001 <0.0001 replication 3 0.2298 0.0631 year variety 2 0.4542 <0.0001 year treatment 8 <0.0001 0.2250 year variety treatment 32 <0.0001 0.0323 ^ Parameters including 14 DAT, 28 DAT and Days to Closure were not taken in 2006, therefore values could not be calculated. 1 DF = degrees of freedom. 2 Pr > F. 3 DAT = days after treatment. 34

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Table 2-2. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of Andru II peanut in 2006. Herbicide Treatment1 Timing % injury2 Yield DAC3 7 DAT4 (kg/ha) paraquat 14 9d54250bc paraquat 28 16ab 4300bc paraquat + bentazon 14 11cd 4550b paraquat + bentazon 28 13b-d 4470b paraquat + metolachlor 14 8d 4610b paraquat + metolachlor 28 18a 3870c paraquat + bentazon + metolachlor 14 11cd 4650b paraquat + bentazon + metolachlor 28 15a-c 4610b untreated 0 0e 5310a 1 Rates for herbicides are as follows: paraqua t 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 2Visual assessment of peanut foliar dama ge and stunting based on the following scale: 0 = no foliar burn or stunti ng; 100 = complete plant necrosis. 3 DAC = days after cracking. 4 DAT = days after treatment. 5 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 35

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Table 2-3. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of Andru II peanut in 2007. Herbicide Timing -------------% injury1-------------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 21c626a 0a 81ab 2980c paraquat 28 43a 14b 0a 86a 3050c paraquat + bentazon 14 16c 20ab 0a 72b 3470a-c paraquat + bentazon 28 36b 19b 0a 83ab 3240bc paraquat + metolachlor 14 19c 20ab 0a 81ab 3100c paraquat + metolachlor 28 41ab 14b 0a 79ab 3350a-c paraquat + bentazon + metolachlor 14 16c 18b 0a 74b 3320a-c paraquat + bentazon + metolachlor 28 39ab 20ab 0a 79ab 3820ab untreated 0 0d 0c 0a 59c 3870a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 36

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Table 2-4. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of AP-3 peanut in 2006. Herbicide Treatment1 Timing % injury2 Yield DAC3 7 DAT4 (kg/ha) paraquat 14 9a55590a paraquat 28 9a 5450a paraquat + bentazon 14 9a 5510a paraquat + bentazon 28 6ab 6035a paraquat + metolachlor 14 11a 5610a paraquat + metolachlor 28 8ab 5410a paraquat + bentazon + metolachlor 14 9a 5570a paraquat + bentazon + metolachlor 28 4bc 5880a untreated 0 0c 5350a 1 Rates for herbicides are as follows: paraqua t 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 2Visual assessment of peanut foliar dama ge and stunting based on the following scale: 0 = no foliar burn or stunti ng; 100 = complete plant necrosis. 3 DAC = days after cracking. 4 DAT = days after treatment. 5 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 37

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Table 2-5. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of AP-3 peanut in 2007. Herbicide Timing -------------% injury1-------------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 10c616cd 0a 74cd 2670ab paraquat 28 40ab 18b-d 0a 96a 2070d paraquat + bentazon 14 11c 18b-d 0a 83bc 2330b-d paraquat + bentazon 28 40ab 25a 0a 83bc 2410a-d paraquat + metolachlor 14 11c 20bc 0a 81b-d 2720a paraquat + metolachlor 28 43a 14d 0a 95a 2080d paraquat + bentazon + metolachlor 14 11c 22ab 0a 95a 2530a-c paraquat + bentazon + metolachlor 28 38b 18b-d 0a 84b 2400b-d untreated 0 0d 0e 0a 73d 2230cd 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 38

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Table 2-6. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of C-99R peanut in 2006. Herbicide Treatment1 Timing % injury2 Yield DAC3 7 DAT4 (kg/ha) paraquat 14 10b54330bc paraquat 28 13ab 4270bc paraquat + bentazon 14 10b 4240bc paraquat + bentazon 28 10b 4450a-c paraquat + metolachlor 14 10b 4260bc paraquat + metolachlor 28 15a 4120c paraquat + bentazon + metolachlor 14 11ab 4670ab paraquat + bentazon + metolachlor 28 10b 4080c untreated 0 0c 4940a 1 Rates for herbicides are as follows: paraqua t 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 2Visual assessment of peanut foliar dama ge and stunting based on the following scale: 0 = no foliar burn or stunti ng; 100 = complete plant necrosis. 3 DAC = days after cracking. 4 DAT = days after treatment. 5 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 39

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Table 2-7. Influence of paraquat, paraquat + bentazon, paraquat + metolachlor and paraquat + bentazon + metolachlor herbicides on percent injury, days to row closure, and yield of C-99R peanut in 2007. Herbicide Timing --------------% injury1------------Days to Closure2 Yield Treatment3 DAC4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) paraquat 14 13d623ab 0a 79b 3200a paraquat 28 45ab 24ab 0a 88a 2250b paraquat + bentazon 14 14d 26a 0a 83ab 3210a paraquat + bentazon 28 43bc 25a 0a 83ab 3340a paraquat + metolachlor 14 11d 24ab 0a 88a 3160a paraquat + metolachlor 28 49a 20b 0a 88a 2970a paraquat + bentazon + metolachlor 14 14d 24ab 0a 84ab 3290a paraquat + bentazon + metolachlor 28 39c 20b 0a 86ab 3560a untreated 0 0e 0c 0a 66c 3540a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: paraquat 0.14 kg/ha; bentazon 0.28 kg/ha; metolachlor 1.42 kg/ha. 4 DAC = days after cracking. 5 DAT = days after treatment. 6 Values reflect the mean of 4 replications. Means within a column followed by different letters ar e significantly different from each other at the 0.05 level according to Fischers Leas t Significant Difference (LSD) test. 40

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CHAPTER 3 THE EFFECT OF LACTOFEN AND ACIFLUORFEN APPLICATION TIMING ON PEANUT INJURY AND YIELD FOR THREE VARYING MATURITY CULTIVARS Introduction Peanut weed management has always relied heavily on postemergence herbicides in the southeastern United States (Wehtje et al. 1992a; Wilcut et al. 1990b; Wilcut et al. 1994a; Wilcut et al. 1994b; Wilcut et al. 1994c). Prior to 1996, herbicides were primarily contact in activity, and peanut injury was common and accepted by growers ( D.L. Colvin personal communication ). Prior to 1986, dinoseb was the most widely utilized herbicide for weed control in peanut systems (Buchanan et al. 1983). Th e Environmental Protection Agency cancelled all registrations of dinoseb in October of 1986, which removed one of the most effective, economical herbicide choices for peanut pr oducers (Buchanan et al. 1983). With the cancellation of dinoseb, researchers looked for replacement herbicides that provided similar weed control (Wilcut et al. 1989) Lactofen is a contact herbicide that is labeled for postemergence applications in peanut and soybean (Senseman 2007). Lactofen inhibits the enzyme protoporphyrinogen oxidase (Protox) which leads to the accumulation of protoporphyrin IX (PPIX) causing the formation of singlet oxygen. Singlet oxygen destroys cell membranes, resulting in rapid desiccation and disintegration (Duke 1991). Symptoms include chlo rosis initially and then necrosis within two days (Senseman 2007). The current lactofen product label allows minimum time from application to harvest of 45 days (Anonymous 2008). Acifluorfen is also a contact herbicide that is labeled for postemergence weed control in peanut and soybean (Senseman 2007). This herbic ide acts in a similar manner to lactofen, with peanut leaves exhibiting chlorosi s and eventually necrosis. The current acifluorfen product label allows minimum time from application to harvest of 75 days (Anonymous 2004). 41

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The loss of dinoseb prompted the use of l actofen and acifluorfen for mid-season weed control, generally following an initial at-cracking paraquat applic ation. Following the registration of imazapic in 1996, however, many peanut producers reduced lactofen and acifluorfen usage in their weed control systems. The broad spectrum foliar and soil activity of imazapic allowed growers to rely almost exclusively on imazapic for postemergence weed control. Imazapic controls many of the most commonly occurring weeds in peanuts without resulting in any visual injury or yield reduction (Dotray et al. 2001; Matocha et al. 2003). However, the past decade of intense imazapic usage has led to an increase in resistant weeds and a shift in weed spectrum. The two mo st noteworthy species are acetolactate synthase (ALS)-resistant Palmer amaranth ( Amaranthus palmeri S. Watson) and Bengal dayflower ( Commelina benghalensis L.). Normally, imazapic controls Palmer amaranth with both preemergence and postemergence activity. High le vels of resistance to imazapic have been found across the southeastern United States in ALS resistant Palm er amaranth (Vencill et al. 2002). ALS resistant Palmer amaranth has quickly become one of the most troublesome weeds in the southeastern United States. Bengal dayflowe r is an exotic invasive weed species that has increased in distribution over the pa st five years and is tolerant to imazapic (Webster et al. 2005). These weed problems have forced many grow ers to reconsider the use of contact herbicides. Even if growers do not have resist ant weed populations, alternative herbicides are recommended to avoid resistance (Sellers et. al 2 008). Acifluorfen and lact ofen are some of the leading contact postemergence herbicid es to combat resistance issues. Acifluorfen and lactofen have a long record of effective weed control, but peanut tolerance and yield reduction continue to be a concern. The label reco mmendations for acifluorfen and lactofen are mainly based on data collected on the Florunner variety, which is no longer grown. 42

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Florunner was a mid-season maturity variety that reached maturity in approximately 134 days after planting (Norden et al. 1969). Currently, a wide range of ne w varieties with greater yield potential and disease tolerance dominate the s outheastern peanut gr owing region. The new peanut varieties have differing maturity da tes that range from 120 to 145 day maturity. With the emergence of herbicid e resistant weeds and new weed species, the use of lactofen and acifluorfen will likely increase across the peanut growing regions of the south. Therefore, the objective of this research was to determine th e effect of lactofen and acifluorfen herbicides, applied across a wide growing pe riod, on peanut injury and yiel d. Within this objective three peanut cultivars with varying maturity were evaluated. Materials and Methods Field experiments were conducted in 2007 a nd 2008 at the Plant Science Research and Education Unit in Citra, Florida on a Sparr fi ne sand (loamy, siliceous, hyperthermic Grossarenic paleudult) with 1% organic matter. All experiments were initiated using a conventional tillage regime. Plots were 3.0 m wide, 7.6 m l ong and contained four rows spaced 76.2 cm apart. Plots received optimum irrigation fertil ity, insecticide and f ungicide treatments as directed by the Florida Cooperative Extension Service to ensure optimum growth. Seeds were planted at a depth of 5 cm with a seeding density of 17 seeds pe r meter of row (Wright et al. 2006). Planting occurred on June 14, 2007 and May 6, 2008. Each y ear aldicarb was applied in furrow at 3.2 kg ai/ha. The later than normal planting date in 2007 occurred because an outbreak of Aspergillus niger resulted in near total stand loss and replanting was required. The experimental area received a preemergence broadcast application of pendimethalin (0.92 kg ai/ha + diclosulam (0.42 kg ai/ha), and a postemergence applicati on of imazapic (0.07 kg ai/ha). Supplemental 43

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hand-weeding was performed as needed to ma intain weed-free conditions throughout the growing season. The experimental design was a randomized comp lete block with a split-plot treatment arrangement and four replications Peanut cultivar was the w hole plot factor and herbicide treatments were the subplots. Cultivars in cluded early (Andru II 2007 and ViruGard 2008), mid (AP-3 2007 and 2008) and late (C-99R 2007 and 2008) season peanut cultivars (Gorbet 2006; Garcia y Garcia et al. 2007; Gorbet 2007; Gorbet and Shokes 2002). Andru II seed was not available in 2008. Eight he rbicide treatments consisting of acifluorfen at 0.42 kg/ha or lactofen at 0.21 kg/ha were applied to each vari ety at 4, 6, 8 or 10 weeks after planting (WAP). An untreated check was included for each cultivar All herbicide treatments included a crop oil concentrate at 1% v/v. All experimental treatments were applied with a CO2 backpack sprayer calibrated to deliver 187 L/ha. Visual ratings of peanut folia r injury and peanut ca nopy width were performed at 7, 14, and 28 days after application. Visual es timations of injury were rated on a scale from 0% to 100% with 0% = no injury and 100% = complete plant necr osis. Days to canopy closure (where no soil was visible between the two center rows) was also recorded. The center two rows of each plot were dug acco rding to maturity by a conventional diggershaker-inverter. Maturity was based on the hul l scrape method for each cultivar (Johnson 1987; Johnson et al. 1993; Sholar et al. 1995). Peanuts were allowed to field dry for approximately 3 days and commercial harvesting equipment was us ed to harvest each plot. Peanut yields (adjusted to moisture conditions of 9%) were determined and adjusted to a kg/ha basis. Data were subjected to analysis of variance to test treatment effects and interactions. Means were separated using Fisher s Least Significant Difference (LSD) test at the p<0.05 level. 44

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Results and Discussion Statistical analysis detected a significant treatment by year and treatment by variety interaction (Table 3-1). Therefore, data will be presented by year and variety. Early Maturity Peanut (Andru II and ViruGard) In 2007, significant differences in peanut inju ry were detected 7 days after treatment (DAT) (Table 3-2). Peanut injury resulting fr om lactofen and acifluor fen applications ranged from 19% to 49% at 7 DAT. Overall, applications made at 4 and 6 WAP were more injurious than later applications, but rega rdless of application timing, almost complete recovery of Andru II was observed by 28 DAT. The 4 WAP injury persisted more than other treatments. The 14 DAT evaluation of the 8 WAP treatment showed a lower degree of recovery compared to the other treatments, regardless of herbicide used. Lactofen applications made 4 and 6 WAP and acifluorfen applications 4 WAP de layed canopy closure by 7 to 12 da ys. However, applications made 8 and 10 WAP did not influence canopy closur e. This can partially be explained by the fact that the 8 and 10 WAP applica tions were made to peanuts that were already at, or near row closure. No differences in canopy closure rate were observed between acifluor fen and lactofen and application timing seems to be the most important criteria for predicting de layed canopy closure. Regardless of foliar injury and canopy closure de lay, no differences in yield were noted for the Andru II variety in 2007. ViruGard injury in 2008 was si milar to Andru II (Table 3-3). At 7 DAT, visual estimation of injury ranged from 26% to 51% for both lactof en and acifluorfen. Lactofen applied at 4 and 8 WAP was the most injurious ( 50%). Canopy closure was signi ficantly delayed with all applications except lactofen applied 10 WAP. Th is was due to row closure occurring prior to the 10 WAP application to ViruGard. The longest delay in canopy clos ure was 14 days for lactofen 45

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applied 6 and 8 WAP, and acifluorfen applied 8 a nd 10 WAP. ViruGard has a more erect growth habit than Andru II, and might explain th e extended days to canopy closure in 2008. Significant reductions in peanut yield, ranging from 500 to 1270 kg/ha, were observed as a result of lactofen applied 6, 8 and 10 WAP and acifluorfen applied 8 and 10 WAP. By 14 DAT, some recovery from foliar damage was observed for all treatments, but more rapid recovery occurred from the earlier app lication timings. For example, the 4 WAP application showed a 40% and 35% reduction in injury for lactofen and acifluorfen, re spectively. However, for 10 WAP the level of recovery for lactofen and aci fluorfen was 6% and 7%, respectively. By 28 DAT, all treatments showed minimal injury. Ther efore, the loss in yield appeared to be more associated with injury 14 DAT, where treatments exhibiting 18% injury resulted in yield reductions compared to the untreated control. Medium Maturity Peanut (AP-3) In 2007, AP-3 exhibited a wide range of injury with visual estimation ratings from 13% to 49% (Table 3-4). At each application timing aci fluorfen caused less injury than lactofen. As previously observed, plants had generally reco vered from the foliar injury by 28 DAT with 8% or less injury remaining. Once again, the greatest injury was observed when either herbicide was applied 4 WAP, and this continued to be eviden t 14 DAT. However, there appeared to be little difference in the level of recovery between the two herbicides regardless of application timing. In addition, there were no differences between the herbicides within application timing. Canopy closure was significantly delayed by the 4 WAP applications (16 days for lactofen and 20 days for acifluorfen). No other application timings resu lted in delayed canopy growth. The only application that resulted in a significant reduction in yi eld compared to the untreated was lactofen and acifluorfen applied 8 WAP. 46

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AP-3 in 2008 had the highest injury rating with early application (Table 3-5). Visual injury ratings ranged from 21% to 55%, and pl ants recovered by 28 DAT. At 7 DAT, all treatments showed significant foliar injury, with lactofen applied at 4 WAP resulting in >50% injury. Once again lactofen was more injuri ous than acifluorfen at each application timing. Peanuts recovered much quicker in 2008, although the level of da mage still evident at 14 DAT was greater for the 8 and 10 WAP applications for both herbicides. This trend continued in the 28 DAT observation, where only 3 treatments resu lted in significant in jury, and this was 5%. Row closure was delayed at 4 and 6 WAP for both herbicides up to 12 days. In general, yield loss was observed in these treatments showing > 15% injury 14 DAT, these being lactofen at 8 and 10 WAP and acifluorfen at 10 WAP. Late Maturity Peanut (C-99R) In 2007, when evaluated 7 DAT, lactofen caused greater injury than acifluorfen in C-99R when applied 6, 8 or 10 WAP (Table 3-6). No differences between acifluorfen and lactofen treatments were detected for the 4 WAP appli cation, where the injury from both herbicides was nearly 50%. The lowest level of injury for both herbicides was observed with the 6 WAP timing. As with the other varieties in 2007, recovery wa s slower for the 4 WAP treatments. By 14 DAT, few differences were observed between herbicides applied at the same timing. Less than 5% injury was observed by 28 DAT. Canopy closure was delayed following application of either lactofen or acifluorfen at 4 WAP. None of the other treatmen ts affected canopy closure. None of the treatments resulted in a yield reduction compared to the untreated. In 2008, visual injury estimation was similar fo r lactofen and acifluorfe n (Table 3-7). In general, more injury was observed with the 4 WAP treatments and less injury following applications 10 WAP. In both years, the 28 DAT visual injury rating was 6% or less. High 47

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levels of injury were noted for all treatments 7 DAT, with lactofen showing greater injury compared to acifluorfen at all application timi ngs. Significant delays in canopy closure were observed following lactofen applied 4 and 6 WAP and acifluorfen applied 6 WAP. All treatments recovered rapidly with <20% injury by 14 DAT. The only exception was lactofen applied 10 WAP, and this was the only treatment that resulted in significan t yield loss. Another interesting observation was that the only treatments that sign ificantly delayed canopy closure (lactofen applied 4 and 6 WAP, acifluorfen applied 6 WAP) also resulted in yields greater than the untreated control. In 2007, no significant yield reduction was observed in any of the treatments, but 2008 yield reduction was obs erved for lactofen applied 10 WAP. Discussion Canopy closure did not appear to relate with yield reduction, while lactofen injury at 14 DAT related with yield in 2008 but not in 2007. The current lactofen label allows for a preharvest interval of 45 days, but these data indicate that lact ofen applications at 8 and 10 weeks after cracking (within preharvest interval) may result in yield loss for some cultivars. The current acifluorfen label allows fo r a preharvest interval of 75 days but these data indicate that acifluorfen might impact yield at 8 and 10 weeks with some cultivars. Overall, yield loss was more with lactofen than acifl uorfen from later applications. Previous research has shown that both early and late-season applicati ons of lactofen and acifluorfen reduced peanut yield, but the reasons for these reduc tions were not clear (Grichar 1997). Additionally, Wilson and Hines (1987) showed that snap bean yield was reduced more when acifluorfen was applied at the 1 to 2 leaf st age rather than the treatm ent at the 4 to 8 leaf stage. The injury rating for the 1 to 2 leaf stage was 81% in comp arison to 22% at the 4 to 8 leaf stage (Wilson and Hines 1987). 48

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In general, yield reduction incr eased with the later application timings in this experiment. This is interesting considering that the lowest visual injury ratings ha d the most yield reduction in the early maturity cultivar. It is hypothe sized that these late-seas on applications had the greatest impact on yield since the herbicide caused stress, including substantial foliar loss, to the plant during the pod-fill and matura tion phase of development. Prev ious research has shown that water stress, fertility, or plant stress during pod f ill impacted yield more than when these stresses occurred early in plant deve lopment (Knauft et al. 1990). Weeds compete with peanut for light, water, nu trients and physical sp ace. If producers are making a decision on whether to use a contact herbicid e, they have need to weigh the benefit of a herbicide with potential yield loss against the amount of yi eld loss due to weed pressure. Acifluorfen and lactofen are usef ul tools for peanut growers, but the application decisions need to made on a case by case basis. Caution should be used when making late season application even if the label allows for those applications. 49

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Table 3-1. ANOVA table for the e ffect of lactofen and acifluorfe n application timing on peanut injury and yield for three va rying maturity cultivars. Class Variable DF1 --------------% injury2------------Days to Closure2 Yield2 7 DAT314 DAT 28 DAT variety (maturity) 2 0.0027 0.0001 0.3112 <0.0001 <0.0001 year (2007/2008) 1 <0.0001 0.0014 <0.0001 <0.0001 <0.0001 treatment 8 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 replication 3 0.0153 0.0294 0.1718 0.7679 0.0078 year variety 2 0.1831 0.7717 0.1862 <0.0001 <0.0001 year treatment 8 <0.0001 <0.0001 <0.0001 0.0002 <0.0001 year variety treatment 32 0.0127 0.0010 0.3789 0.0005 0.0576 1 DF = degrees of freedom. 2 Pr > F. 3 DAT = days after treatment 50

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Table 3-2. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of Andru II peanut in 2007. Herbicide Timing --------------% injury1------------Days to Closure2 Yield Treatment3 WAP4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 49a6 31a 5a 74a 3220a lactofen 6 21cd 11c 4ab 69ab 3540a lactofen 8 26c 19b 5a 64bc 2860a lactofen 10 25c 9cd 5a 59cd 3130a acifluorfen 4 46a 28a 4ab 72a 3070a acifluorfen 6 21cd 8cd 1bc 64bc 3540a acifluorfen 8 26c 16b 3a-c 61cd 3620a acifluorfen 10 19de 5d 5a 57d 3550a untreated 0 0f 0e 0c 62cd 3010a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 51

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Table 3-3. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of Vi ruGard peanut in 2008. Herbicide Timing --------------% injury1-------------Days to Closure2 Yield Treatment3 WAP4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 51a6 11de 1bc 75a 6360a-c lactofen 6 44bc 18bc 0c 77a 5910cd lactofen 8 50ab 28a 6a 77a 5680de lactofen 10 34e 28a 0c 65b 5330e acifluorfen 4 41cd 6e 1bc 72a 6450ab acifluorfen 6 35de 13cd 0c 74a 6400ab acifluorfen 8 41cd 23ab 4ab 77a 5830d acifluorfen 10 26f 19b 0c 77a 6100b-d untreated 0 0g 0f 0c 63b 6600a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 52

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Table 3-4. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of AP-3 peanut in 2007. Herbicide Timing --------------% injury1------------Days to Closure2 Yield Treatment3 WAP4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 49a6 29a 5ab 79ab 2700a lactofen 6 18e 8d 3b-d 66c 2360a-c lactofen 8 34c 18b 5ab 62c 2020c lactofen 10 26d 8d 8a 64c 2480ab acifluorfen 4 41b 26a 4bc 83a 2630a acifluorfen 6 13f 10cd 1cd 71bc 2380a-c acifluorfen 8 25d 14bc 0d 69bc 2220bc acifluorfen 10 15ef 5de 5ab 66c 2490ab untreated 0 0g 0e 0d 63c 2630a 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 53

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Table 3-5. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of AP-3 peanut in 2008. Herbicide Timing --------------% injury1-------------Days to Closure2 Yield Treatment3 WAP4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 55a6 11ef 5a 63a 7910ab lactofen 6 44b 15c-e 0b 65a 7850a-c lactofen 8 44b 21ab 5a 53b 7200d lactofen 10 30d 25a 0b 54b 6490e acifluorfen 4 44b 9f 0b 61a 8360a acifluorfen 6 39c 13d-f 0b 63a 8110ab acifluorfen 8 38c 18bc 4a 54b 7590b-d acifluorfen 10 21e 16cd 0b 53b 7280cd untreated 0 0f 0g 0b 53b 7940ab 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 54

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Table 3-6. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of C-99R peanut in 2007. Herbicide Timing --------------% injury1-------------Days to Closure2 Yield Treatment3 WAP4 7 DAT5 14 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 48a6 31a 4ab 79a 3420ab lactofen 6 19de 10b 4ab 74a-c 3090bc lactofen 8 33b 10b 1bc 70bc 3030c lactofen 10 24cd 6c 4ba 69c 3270a-c acifluorfen 4 49a 29a 4ba 77ab 3340a-c acifluorfen 6 11f 10b 1bc 72a-c 3400ab acifluorfen 8 25c 6c 0c 70bc 3110a-c acifluorfen 10 16ef 5c 5a 70bc 3450a untreated 0 0g 0d 0c 67c 3100bc 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 55

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Table 3-7. Influence of lactof en and acifluorfen herbicides on percent injury, days to row closure, and yield of C-99R peanut in 2008. Herbicide Timing -------------% injury1------------Days to Closure2 Yield Treatment3 WAP4 7 DAT514 DAT 28 DAT 76.2 cm rows (kg/ha) lactofen 4 54a6 15bc 1b 63a 6330ab lactofen 6 43bc 15bc 0b 63a 5980a-c lactofen 8 41c 19ba 6a 56de 5510cd lactofen 10 30de 23a 0b 56de 5060d acifluorfen 4 46b 10c 1b 62ab 5690c acifluorfen 6 28e 10c 0b 63a 6470a acifluorfen 8 34d 15bc 5a 58cd 5910bc acifluorfen 10 23f 13bc 0b 54e 5620c untreated 0 0g 0d 0b 60bc 5730c 1 Visual assessment of peanut foliar damage and stunting based on the following scale: 0 = no foliar burn or stunting; 100 = complete plant necrosis. 2 Number of days required to achieve complete canopy closure between 76.2 cm wide row spacing. 3 Rates for herbicides are as follows: lactofen 0.21 kg/ha; acifluorfen 0.42 kg/ha. 4 WAP = weeks after planting. 5 DAT = days after treatment. 6 Values reflect the mean of 4 rep lications. Means within a column followed by different letters are significantly different from each other at the 0.05 level according to Fischers Least Significant Difference (LSD) test. 56

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LIST OF REFERENCES Anonymous. 2004. Ultra Blazer herbicide produc t label. EPA Registration 70506-60. Trenton, NJ: United Phosphorus Inc. 6 p. Anonymous. 2008. Cobra herbicide supplemental label. EPA Registration 59639-34. Walnut Creek, CA: Valent U.S.A. Corporation. 5 p. Anonymous. 2009. Gramoxone Inteon herbicide product label. EPA Registration 100-1217. Greensboro, NC: Syngenta. 55 p. Bellinder, R. R., R. W. Wallace, an d G. L. Jordan. 1997. English Pea ( Pisum sativum ) tolerance to paraquat and paraquat plus bentazon. Weed Technol. 11:39-44. Boote, K. J. 1982. Growth stages of peanut. Peanut Sci. 9:35-40. Brecke, B. J., D. O. Stephenson, and K. Hutto. 2005. Impact of tillage and herbicides on tropical spiderwort. Proceedings of the Tropical Spiderwort Symposium. Web page: http://mulch.cropsoil.uga. edu/weedsci/tsw2005/index.html Accessed: June 25, 2009. Brian, R. C. 1969. The influence of darkness on th e uptake and movement of diquat and paraquat in tomatoes, sugar beet, and pot atoes. Ann. Appl. Biol. 63:117-126. Buchanan, G. A., D. S. Murray, and E. W. Ha user. 1983. Weeds and their control in peanuts. Pages 206-209 in H. E. Pattee and C. T. Young, (eds.). Peanut Science and Technology. American Peanut Research and Education Society, Yoakum, TX 77995. Cardina, J. and C. W. Swa nn. 1988. Metolachlor effects on pea nut growth and development. Peanut Sci. 15:57-60. Cardina, J., A. C. Mixon, and G. R. Wehtje. 198 7. Low-cost weed control systems for close-row peanuts ( Arachis hypogaea ). Weed Sci. 35:700-703. Culpepper, A. S., J. T. Flanders, A. C. Yo rk, and T. M. Webster. 2004. Tropical spiderwort ( Commelina benghalensis ) control in glyphosat e-resistant cotton ( Gossypium hirsutum ). Weed Technol. 18:432-436. Dotray, P. A., T. A. Baughman, J. W. Keeling, W. J. Grichar, and R. G. Lemon. 2001. Effect of imazapic application timing on Texas peanut ( Arachis hypogaea ). Weed Technol. 15:2629. Duke, S. O., J. Lydon, J. M. Becerril, T. D. Sherman, L. P. Lehnen, Jr. and H. Matsumoto. 1991. Protoporphyrinogen oxidaseinhibiting herbicides. Weed Sci. 39:465-473. Fedtke, C. 1982. Biochemistry and physiology of herbicide action. Berlin: Springer-Verlag. 202 pp. 57

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Garcia y Garcia, A., L. C. Guerra, A. Suleim an, J. O. Paz, and G. Hoogenboom. 2007. Peanut water use under optimum conditions of growth and development: a simulation approach. Proceedings of the 2007 Georgia Wate r Resources Conference. Web page: http://cms.ce.gatech.edu/gwri/uploads/proceedings/2007/5.6.4.pdf Accessed: July 8, 2009. Gorbet, D. W. 2006. Registration of A ndru II peanut. Cr op Science.46:2712-2713. Gorbet, D. W. 2007. Registration of AP-3 peanut. Journal of Plan t Registrations. 1:126-127. Gorbet, D. W. and B. L. Tillman. 2009. Registration of Florida-07 pea nut. Journal of Plant Registrations. 3:14-18. Gorbet, D. W. and F. M. Shokes. 2002. Registration of C-99R peanut. Crop Science. 42:2207. Grey, T. L., G. R. Wehtje, R. H. Walker, and K. P. Paudel. 1995. Comparison of imazethapyr and paraquat-based weed control systems in peanut ( Arachis hypogaea ). Weed Technol. 9:813-818. Grey, T. L., J. W. Wilcut, and G. R. Weh tje. 1992. Weed control in peanuts utilizing imazethapyr, bentazon, and paraquat. Proceed ings Southern Weed Science Society. 45:105. Grichar, W. J. 1997. Influence of herbicides and timing of application on broadleaf weed control in peanut ( Arachis hypogaea ). Weed Technol. 11:708-713. Johnson III, W. C. 1987. The hull scrape method to assess peanut maturity. Georgia Cooperative Extension Service Bulletin. 958. Johnson III, W. C., J. R. Chamberlin, T. B. Br enneman, J. A. Todd, B. G. Mullinix, Jr., and J. Cardina. 1993. Effects of para quat and alachlor on peanut ( Arachis hypogaea ) growth, maturity, and yield. Weed Technol. 7:855-859. Jordan, D., D. Prostko, P. Dotray, J. Wilcut, T. Baughman, B. Brecke, J. Chapin, J. Faircloth, W. Faircloth, J. Ferrell, T. Gre y, J. Grichar, G. MacDonald, and C. Medlin. 2007. Managing herbicide-resistant weeds in peanuts in the Un ited States. North Carolina State University and A&T State University Cooperative Extension Service. AG-692. Knauft, D. A., D. L. Colvin, and D. W. Gorb et. 1990. Effect of paraquat on yield and market grade of peanut (Arachis hypogaea ) genotypes. Weed Technol. 4:866-870. Matocha, M. A., W. J. Grichar, S. A. Senseman, C. A. Gerngross, B. J. Brecke, and W. K. Vencill, 2003. The persistence of imazapic in peanut ( Arachis hypogaea ) crop rotations. Weed Technol. 17:325-329. Norden, A. J., R. W. Lipscomb, and W. A. Ca rver. 1969. Registration of florunner peanuts. Crop Sci. Volume 9, November-December. p. 850. 58

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Pfister, K., C. Buschmann, and H. K. Lichte nthaler. 1974. Inhibition of the photosynthetic electron transport by bentazon. Proceedings of the 3rd Intern ational Congress on Photosynthesis. Pp. 675-681. Prostko, E. P., A. S. Culepper, T. M. Webste r, and J. T. Flanders. 2005. Tropical spiderwort identification and control in Georgia fiel d crops. Tifton, GA: University of Georgia Cooperative Extension Service Bulletin. http://pubs.caes.uga.edu/caespubs/pubs/PDF/c884.pdf Accessed: June 25, 2009. Richburg III, J. S., J. W. Wilcut, and E. F. Eastin. 1995. Weed management in peanut ( Arachis hypogaea) with imazethapyr and metolachlor. Weed Technol. Volume 9:807-812. Sellars, B. A., J. A. Ferrell, and G. E. M acDonald. 2008. Managing against the development of herbicide resistant weed s: Sugarcane. University of Flor ida Cooperative Extension Service, SS-AGR-244. Senseman, S. A. 2007. Herbicide Handbook. 9th edit ion. Lawrence, KS: Weed Science Society of America. Pp. 12, 132-133, 188-192, & 209-210. Sholar, J. R., R. W. Mozingo, and J. P. Beasley, Jr. 1995. Peanut cultur al practices. Pages 354382 in H. E. Pattee and H. T. Stalker (eds.). Adva nces in Peanut Science. American Peanut Research and Education Societ y, Inc., Stillwater, OK. 614 p. Spader, V. and R. A. Vidal. 2000. Response curve of Commelina bengalensis to EPSPS enzyme inhibitory herbicides. Pest. Rev. Tec. Cien. 10:125-135. Steptoe, P. J., W. K. Vencill and T. L. Gre y. 2006. Influence of moisture stress on herbicidal control of an invasive weed, Benghal dayflower ( Commelina benghalensis ). J. Plant Dis. Protect. XX:907-914. Suwanketnikom, R., K. K. Hatzios, D. Penner, and D. Bell, 1982. The site of electron transport inhibition by bentazon (3-isopropyl-(1 H )-2,1,3-benzothiadiazin-(4)-(3 H )-one-2,2-dioxide) in isolated chloroplasts. Can. J. Botany. 60:409-412. Thrower, S. L., N. D. Hallam, and L. B. Th rower. 1965. Movement of diquat dibromide in leguminous plants. Ann. Appl. Biol. 55:253-260. Vencill, W. K., E. P. Prostko, and T. E. Webster. 2002. Is Palmer amaranth ( Amaranthus palmeri ) resistant to ALS and dinitroaniline herbicides? Proceedings Southern Weed Science Society. 55:189. Webster, T. M., M. G. Burton, A. S. Culpepper, A. C. York, and E. P. Prostko. 2005. Tropical Spiderwort ( Commoelina benghalensis ): A tropical invader thr eatens agroecosystems of the southern United States. Weed Technol. 19:501-508. Webster, T. M., M. G. Burton, A. S. Culpepper, J. T. Flanders, T. L. Grey, and A. C. York. 2006. Tropical spiderwort ( Commelina bengalensis ) control and emergence patterns in preemergence herbicide systems. Journal Cotton Science. 10:68-75. 59

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Webster, T. M., W. H. Faircloth, J. T. Flanders E. P. Prostko, and T. L. Grey. 2007. The critical period of Bengal dayflower ( Commelina bengalensis ) control in peanut. Weed Sci. 55:359364. Wehtje, G. R., J. A. McGuire, R. H. Walk er, and M. G. Patterson. 1986. Texas panicum ( Panicum texanum ) control in peanuts ( Arachis hypogaea ) with paraquat. Weed Sci. 34:308-311. Wehtje, G. R., J. W. Wilcut, and J. A. McGuire. 1992a. Influence of bentazon on the phytotoxicity of paraquat to peanuts ( Arachis hypogaea ) and associated weeds. Weed Sci. 40:90-95. Wehtje, G. R., J. W. Wilcut, and J. A. McGu ire. 1992b. Paraquat behavior as influenced by 2,4DB in peanut ( Arachis hypogaea ) and selected weeds. Peanut Sci. 19:51-55. Wehtje, G. R., J. W. Wilcut, and J. A. Mc Guire. 1992c. Paraquat phytotoxicity absorption, and translocation in peanut and selected weeds as influenced by chloramben. Weed Sci. 40:471-476. Wehtje, G. R., J. W. Wilcut, D. P. Dylews ki, J. A. McGuire, and V. T. Hicks. 1991a. Antagonism of paraquat phyt otoxicity in peanuts ( Arachis hypogaea ) and selected weed species by naptalam. Weed Sci. 39:634-639. Wehtje, G. R., J. W. Wilcut, J. A. McGuire, and T. V. Hicks. 1991b. Foliar penetration and phytotoxicity of paraquat as influenced by peanut cultivar. Peanut Sci. 18:67-71. Wehtje, G. R., J. W. Wilcut, T. V. Hicks, and J. A. McGuire. 1988. Relati ve tolerance of peanut to alachlor and metolachlor. Peanut Sci. 15:53-56. Wilcut, J. W., A. C. York, and G. R. Wehtje 1993. The control and interaction of weeds in peanut ( Arachis hypogaea ). Rev. Weed Sci. 6:151-176. Wilcut, J. W., A. C. York, and G. R. Wehtje. 1994a. The control and in teraction of weeds in peanut ( Arachis hypogaea ). Rev. Weed Sci. 6:177-205. Wilcut, J. W., G. R. Wehtje, and M. G. Patte rson. 1987. Economic assessme nt of weed control systems for peanuts ( Arachis hypogaea ). Weed Sci. 35:433-437. Wilcut, J. W., G. R. Wehtje, and R. H. Walk er. 1987. Economics of weed control in peanuts ( Arachis hypogaea ) with herbicides and cultiv ations. Weed Sci. 35:711-715. Wilcut, J. W., G. R. Wehtje, T. A. Cole, T. V. Hicks, and J. A. McGuire. 1989a. Postemergence weed control systems wit hout dinoseb for peanuts ( Arachis hypogaea ). Weed Sci. 37:385391. Wilcut, J. W., G. R. Wehtje, T. V. Hicks, and T. A. Cole. 1990a. Postemergence weed management systems for peanuts ( Arachis hypogaea ). Weed Technol. 4:239-244. 60

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Wilcut, J. W., G. R. Wehtje, T. V. Hick s, and T. A. Cole. 1990b. Postemergence weed management systems for peanuts. Weed Technol. 4:76-80. Wilcut, J. W., J. S. Richburg, III., E. F. Easti n, G. R. Wiley, F. R. Walls, Jr., and S. Newell. 1994b. Imazethapyr and paraquat systems fo r weed management in peanut ( Arachis hypogaea). Weed Sci. 42:601-607. Wilcut, J. W., J. S. Richburg, III., G. R. Wiley, F. R. Walls, Jr., S. R. Jones, and M. J. Iverson. 1994c. Imidazolinone herbicide systems for peanut ( Arachis hypogaea ). Peanut Sci. 21:2328. Wilson, H. P. and T. E. Hines. 1987. Snap bean ( Phaseolus vulgaris ) and common lambsquarters ( Chenopodium album ) response to acifluorfen. Weed Technol. 1:18-21. Wright, D. L., B. Tillman, E. Jowers, J. Marois, J. A. Ferrell, T. Katsvairo and E. B. Whitty. 2006. Management and cultural practices for peanuts. University of Florida Cooperative Extension Service, SS-AGR-74. 61

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62 BIOGRAPHICAL SKETCH James A. Boyer grew up in Weirsdale, FL. He is the son of Mr. and Mrs. Willet (Bud) Boyer, a retired citrus grower He attended Ocala Christian Academy and graduated in 1995. After graduation, he attended the University of Florida while working part-time for the Agronomy Department. He graduated with a Ba chelor of Science in Agricultural Operations Management in 1999 and pursued a job opportun ity in Punta Gorda, FL managing a 3,000-acre sod farm. The beginning of 2001, he accepted a pos ition as Coordinator of Research Programs at the Plant Science Research and Education Unit in Citra, FL and soon af ter married Kelle McRae on August 18th. Jims family expanded in March 2006 with Katherine and October 2008 with Nathan. They inspired him to pursue his masters degree, something he had always wanted. The fall of 2007 he was accepted into the graduate progr am at the University of Florida, pursuing a Master of Science degree in agronomy with a concentration in weed science under the supervision of Greg MacDonald. Jim has pres ented at the Florida Weed Science Society, presented for two years at the Southern Weed Science Society and played an active role in hosting the Southern Weed Science Society weed contest. He also won the paper contest at the Florida Weed Science Society in 2009. Following completion of his Master of Science degree, he plans to continue working at the Plant Science Research and Education Unit.