Glyphosate has played an important role in agricultural production systems, especially after the release of glyphosate resistant crops. With increased usage and an overall reliance on chemical control, weed resistance to glyphosate has occurred and is now a major issue. The objective of this research was to investigate weed control levels provided by glufosinate, 2,4-D, and clethodim as an alternative to glyphosate. Multiple POST applications generally provided superior weed control in comparison to a single early-POST application. No programs provided greater than d after mid-POST application. Applications of glufosinate or glufosinate + 2,4-D fb clethodim + glufosinate, glufosinate + 2,4-D, or clethodim + glufosinate + 2,4-D provided adequate broadleaf weed control throughout the rating period. Although POST-only programs are an option, they are not a sustainable weed control practice. herbicides into a weed control program as well as alternative weed control methods.

Crop ScienceVolume 57, Issue 1 p. 62-70 Research Cotton Maturity Determination through Vertical Mapping Curtis Schaefer, Corresponding Author Curtis Schaefer curtis.schaefer@ttu.edu Plant and Soil Sciences, Texas Tech UnivCorresponding author (curtis.schaefer@ttu.edu).Search for more papers by this authorBob Nichols, Bob Nichols Cotton Inc.Search for more papers by this authorGuy Collins, Guy Collins Crop Science, North Carolina State UnivSearch for more papers by this authorJared Whitaker, Jared Whitaker Crop and Soil Sciences, Univ. of GeorgiaSearch for more papers by this authorCraig Bednarz, Craig Bednarz Bayer CropScience LPSearch for more papers by this authorChris Main, Chris Main Dow AgroSciencesSearch for more papers by this authorGlen Ritchie, Glen Ritchie Texas Tech UnivSearch for more papers by this author Curtis Schaefer, Corresponding Author Curtis Schaefer curtis.schaefer@ttu.edu Plant and Soil Sciences, Texas Tech UnivCorresponding author (curtis.schaefer@ttu.edu).Search for more papers by this authorBob Nichols, Bob Nichols Cotton Inc.Search for more papers by this authorGuy Collins, Guy Collins Crop Science, North Carolina State UnivSearch for more papers by this authorJared Whitaker, Jared Whitaker Crop and Soil Sciences, Univ. of GeorgiaSearch for more papers by this authorCraig Bednarz, Craig Bednarz Bayer CropScience LPSearch for more papers by this authorChris Main, Chris Main Dow AgroSciencesSearch for more papers by this authorGlen Ritchie, Glen Ritchie Texas Tech UnivSearch for more papers by this author First published: 01 January 2017 https://doi.org/10.2135/cropsci2016.03.0168Citations: 10 Assigned to Associate Editor Vasu Kuraparthy. All rights reserved. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume57, Issue1January–February 2017Pages 62-70 RelatedInformation

Field studies were conducted in Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, and Tennessee during 2010 and 2011 to determine the effect of glufosinate application rate on LibertyLink and WideStrike cotton. Glufosinate was applied in a single application (three-leaf cotton) or sequential application (three-leaf followed by eight-leaf cotton) at 0.6, 1.2, 1.8, and 2.4 kg ai ha −1 . Glufosinate application rate did not affect visual injury or growth parameters measured in LibertyLink cotton. No differences in LibertyLink cotton yield were observed because of glufosinate application rate; however, LibertyLink cotton treated with glufosinate yielded slightly more cotton than the nontreated check. Visual estimates of injury to WideStrike cotton increased with each increase in glufosinate application rate. However, the injury was transient, and by 28 d after the eight-leaf application, no differences in injury were observed. WideStrike cotton growth was adversely affected during the growing season following glufosinate application at rates of 1.2 kg ha −1 and greater; however, cotton height and total nodes were unaffected by glufosinate application rate at the end of the season. WideStrike cotton maturity was delayed, and yields were reduced following glufosinate application at rates of 1.2 kg ha −1 and above. Fiber quality of LibertyLink and WideStrike cotton was unaffected by glufosinate application rate. These data indicate that glufosinate may be applied to WideStrike cotton at rates of 0.6 kg ha −1 without inhibiting cotton growth, development, or yield. Given the lack of injury or yield reduction following glufosinate application to LibertyLink cotton, these cultivars possess robust resistance to glufosinate. Growers are urged to be cautious when increasing glufosinate application rates to increase control of glyphosate-resistant Palmer amaranth in WideStrike cotton. However, glufosinate application rates may be increased to maximum labeled rates when making applications to LibertyLink cotton without fear of reducing cotton growth, development, or yield.

Nitrogen (N) management strategies for cotton may need to be modified because of the use of new high yielding cultivars and improved cropping systems. The objective of this research was to determine the optimal N application rate and critical leaf N concentration for contemporary high yielding cotton under no-tillage systems. A strip-plot trial was conducted on eleven private farms in Crockett, Fayette, Gibson, Haywood, Lake, and Lauderdale counties from 2009 through 2010 in Tennessee. Five N treatments of 0, 45, 90, 134, and 179 kg N ha−1 were evaluated as side-dress N of urea and ammonium nitrate solution in strip plots in a randomized complete block design with three replicates. Eight out of the eleven location–years showed significant yield responses to side-dress N applications. Applying 45–146 kg N ha−1 (including pre-plant and side-dress N) was sufficient for maximum cotton yields at the N responsive location–years. The results of this study indicate that the current N fertilizer recommendations for cotton may be more than adequate for some upland soils but inadequate for some other upland fields. A range of 34.4–47.4 g kg−1 of leaf N concentration at early bloom is required for cotton to reach to maximum lint yield. These critical leaf N values were somewhat greater than the current sufficient N range, which suggests that the current critical leaf N concentrations for cotton in the southern U.S. may need to be modified; contemporary high yielding varieties require slightly higher N application rates to maximize yields.

Research was conducted in 2010 and 2011 at the West Tennessee Research and Education Center in Jackson, TN to investigate irrigation response in cotton. The objective of this study was to evaluate plant response to four different irrigation regimes by using main-stem node counts, quantification of canopy light interception, and canopy temperature, while making comparisons across two soils that vary in depth to a sandy layer. PHY 375 WRF cottonseed was planted in a no-tillage system in 9-m rows on 97-cm spacing with 10.5-12 seed m(-1) of row. Irrigation was applied from drip tape lying in the row furrow at rates of 0, 1.27, 2.54, and 3.81 cm week(-1). Comparisons were made across deep soils (no sand layer within the top 89 centimeters of soil) and shallow soils (sand layer within the top 61 centimeters of soil). Plant height, number of nodes, nodes above white flower (NAWF), canopy light interception, and canopy temperature were monitored during the blooming period of the crop each year to determine differences in irrigation response. Cotton plants grown in deep soils had higher vegetative biomass, total number of nodes, plant height, light interception, fiber quality, yield, and reduced canopy temperature compared to plants grown in the shallow soil. Similarly, irrigation increased cotton plant vegetative biomass, total number of nodes, plant height, light interception, fiber quality, yield, and reduced canopy temperature compared to dryland cotton. Results from this trial indicate that differences in physiological growth patterns, canopy density, canopy temperature, lint yield, and fiber quality are evident when compared across irrigation amounts and soil depths.

A standardized experiment was conducted during 2009 and 2010 at 20 location‐years across U.S. cotton ( Gossypium hirsutum L.)‐producing states to compare the N use requirement of contemporary cotton cultivars based on their planting seed size. Treatments consisted of three cotton varieties with planting seed of different numbers of seed per kg and N rates of 0, 45, 90, and 134 kg ha –1 . Soil at each trial location was sampled and tested for nitrate presence. High levels of soil nitrate (>91 N‐NO 3 – kg ha –1 ) were found in Arizona and western Texas, and soil nitrate in the range of 45 to 73 kg N‐NO 3 – ha –1 was found at locations in the central United States. Cotton lint yield responded to applied N at 11 of 20 locations. Considering only sites that responded to applied N, highest lint yields were achieved with 112 to 224 kg ha –1 of applied plus pre‐plant residual soil NO 3 —translating to an optimal N requirement of 23 kg ha –1 per 218 kg bale of lint produced. Among the varieties tested those with medium‐sized seed produced higher yields in response to N than did larger and smaller seeded varieties. Varieties with larger seed had longer and stronger fibers, higher fiber length uniformity than small seeded varieties and decreased micronaire. Seed protein and oil increased and decreased slightly in response to increasing amounts of soil nitrate plus applied N, respectively.

Decisions on cotton variety selection are typically based on producers past experience with the varieties and production sites. New germplasm is available every year for purchase and it is important for producers to note genotypic and phenotypic differences in varieties in their region in order to obtain high yields and good fiber quality. Research was conducted to evaluate cotton growth, fiber quality, and yield stability during 2010 and 2011 at fifteen on-farm production locations that were categorized into locations receiving greater than and less than 7.6 cm of precipitation during the blooming period. Each experimental site included four to twelve cotton rows spaced 97 cm apart with varying plot lengths. Varieties evaluated include: DP 0912 B2RF, DP 0920 B2RF, DP 1034 B2RF, FM 1740B2F, PHY 375 WRF, and ST 4288B2F. No-tillage or reduced tillage production systems were utilized with 10.5-12 seed m -1 of row at a planting depth of two cm. Plant height, number of nodes, nodes above white flower (NAWF), lint yield, yield quality, and yield stability were monitored and determined in order to evaluate variety response grown in multiple environments. Varieties did respond differently in this trial, indicating that differences in physiological growth patterns, lint yield, yield quality, and yield stability are evident when comparing varieties and amount of precipitation received during the blooming period. Therefore, quantifying the stability of commonly used varieties in the Midsouth United States is valuable knowledge to those who are making cultivar decisions in areas of variable rainfall. C otton (Gossypium hirsutum L.) is cultivated in a wide range of climates and environments in the United States and around the world. These environments have a large impact on the growth, development, and quality of the crop. Environmental factors, some influenced by managing inputs and some not, will determine the crop’s success by impacting plant growth and development, yield, and yield quality (Wells and Stewart, 2010). Therefore, producers and crop managers have to manage the crop to maximize yield potential regardless of what uncontrollable circumstances may be present in the environment (Wells and Stewart, 2010). Research has shown that cotton crops have no limit when it comes to plant development due to its indeterminate, perennial nature (Hearn and Constable, 1984). Limitations in cotton-producing environments such as, soil type, water availability, nutrient availability, and heat unit accumulation often relate to the extensiveness of the vegetative and reproductive growth of the crop, ultimately affecting yield. Another factor influencing crop production,

J.T. Irby, D. M. Dodds, and D.B. Reynolds*, Plant and Soil Sciences, Mississippi State University, 117 Dorman Hall, Box 9555, Mississippi State, MS 39762; C.L. Main, (formerly) West Tennessee Research and Education Center, University of Tennessee, 605 Airways Blvd., Jackson, TN 38301; L.T. Barber, University of Arkansas, Division of Agriculture, 2301 S. University Ave., Little Rock, AR 72203; K.L. Smith, (formerly) Dept. of Crop, Soil, and Environmental Science, University of Arkansas—Monticello, Monticello, AR 71656; and A.M. Stewart, (formerly) LSU AgCenter, 8208 Tom Bowman Drive, Alexandria, LA 71302 *Corresponding author: dreynolds@pss.msstate.edu ABSTRACT

Historically, weed control in cotton (Gossypium hirsutum L.) relied upon a combination of tillage, soil-applied herbicides, postemergencedirected herbicides, and hand weeding. More recently, weed control in cotton has become heavily reliant on transgenic technologies. Glyphosate-resistant and enhanced glyphosateresistant cotton were commercialized in 1997 and 2006, respectively. Glufosinate-resistant cotton was commercialized in 2004. Although Monsanto Company has been the traditional provider of glyphosate-resistant technology, Bayer CropScience identified a novel glyphosateresistant gene and released this technology to the market in 2011. In addition, Bayer CropScience introduced glyphosate/glufosinate-resistant cotton containing this new glyphosate-resistant trait plus the existing glufosinate-resistance trait. The new glyphosate-resistant technology is known as GlyTol(TM), whereas the glyphosate/glufosinate-resistant technology is known as GlyTol(TM) + LibertyLink((R)). Field experiments were conducted at 14 locations across Arkansas, Louisiana, Mississippi, and Tennessee from 2007 through 2009 to determine cotton response to multiple glyphosate and/or glufosinate applications. Glyphosate-resistant cotton was not visually injured by sequential glyphosate applications. Glyphosate/glufosinate-resistant cotton visual injury was 2% or less when treated with glypho-sate, glufosinate, or glyphosate plus glufosinate. A reduction in plant height of up to 4 cm was observed only with the glyphosate/glufosinateresistant cotton after two or three glufosinate applications were made; heights were not reduced by late season. Herbicide applications did not affect boll development or cotton yield. These data indicate GlyTol cotton has excellent tolerance to glyphosate applied topically and GlyTol + LibertyLink cotton has excellent tolerance to topical applications of glyphosate, glufosinate, and glyphosate plus glufosinate.

Historically, weed control in cotton (Gossypium hirsutum L.) relied upon a combination of tillage, soil-applied herbicides, postemergencedirected herbicides, and hand weeding. More recently, weed control in cotton has become heavily reliant on transgenic technologies. Glyphosate-resistant and enhanced glyphosateresistant cotton were commercialized in 1997 and 2006, respectively. Glufosinate-resistant cotton was commercialized in 2004. Although Monsanto Company has been the traditional provider of glyphosate-resistant technology, Bayer CropScience identified a novel glyphosateresistant gene and released this technology to the market in 2011. In addition, Bayer CropScience introduced glyphosate/glufosinate-resistant cotton containing this new glyphosate-resistant trait plus the existing glufosinate-resistance trait. The new glyphosate-resistant technology is known as GlyTol ™ , whereas the glyphosate/ glufosinate-resistant technology is known as GlyTol ™ + LibertyLink ® . Field experiments were conducted at 14 locations across Arkansas, Louisiana, Mississippi, and Tennessee from 2007 through 2009 to determine cotton response to multiple glyphosate and/or glufosinate applications. Glyphosate-resistant cotton was not visually injured by sequential glyphosate applications. Glyphosate/glufosinate-resistant cotton visual injury was 2% or less when treated with glyphosate, glufosinate, or glyphosate plus glufosinate. A reduction in plant height of up to 4 cm was observed only with the glyphosate/glufosinateresistant cotton after two or three glufosinate applications were made; heights were not reduced by late season. Herbicide applications did not affect boll development or cotton yield. These data indicate GlyTol cotton has excellent tolerance to glyphosate applied topically and GlyTol + LibertyLink cotton has excellent tolerance to topical applications of glyphosate, glufosinate, and glyphosate plus glufosinate.

Field studies were conducted in Georgia, North Carolina, South Carolina, Tennessee, and Virginia during 2006 to investigate tolerance of cotton to fomesafen applied preemergence (PRE). Fomesafen at seven rates, and two standard herbicides, pyrithiobac and fluometuron, were applied PRE to cotton in a weed-free environment. Cotton tolerance to fomesafen was directly related to rainfall that occurred from planting through cotton emergence. No injury was detected in South Carolina or Tennessee, but heavy rainfalls prior to cotton emergence in Georgia led to 3 to 9% early season visible stunting by fomesafen at 140 to 420 g a. i. ha(-1) and 11 to 15% stunting by fomesafen at 560 and 840 g ha(-1). In North Carolina and Virginia, rainfall during cotton emergence led to early season cotton necrosis ranging from 4 to 16% with fomesafen at 140 to 350 g ha(-1) and 12 to 45% by fomesafen at 420 to 840 g ha(-1). Early season injury by fomesafen at 280 g ha(-1) (recommended use rate) was equal to or less than pyrithiobac or fluometuron at 4 of 5 locations. Mid-season injury was 10% or less at all locations with fomesafen at 490 g ha(-1) or less. Plant heights were reduced 11 to 29% in Georgia and North Carolina when fomesafen was applied at rates greater than 420 g ha(-1). In Tennessee, heights were reduced 8% with fomesafen at 560 g ha(-1). Compared to the non-treated control, plant stands were reduced 23 to 28% only in North Carolina when fomesafen rates exceeded 350 g ha(-1). Lint yields followed trends in plant stand, with yield being reduced 23 to 25% by fomesafen at 560 to 840 g ha(-1) only in North Carolina. Cotton fiber quality and cotton fruit distribution or number of fruit set, were not adversely affected by herbicides.

Field studies were conducted in Georgia, North Carolina, South Carolina, Tennessee, and Virginia during 2006 to investigate tolerance of cotton to fomesafen applied preemergence (PRE). Fomesafen at seven rates, and two standard herbicides, pyrithiobac and fluometuron, were applied PRE to cotton in a weed-free environment. Cotton tolerance to fomesafen was directly related to rainfall that occurred from planting through cotton emergence. No injury was detected in South Carolina or Tennessee, but heavy rainfalls prior to cotton emergence in Georgia led to 3 to 9% early season visible stunting by fomesafen at 140 to 420 g a.i. ha -1 and 11 to 15% stunting by fomesafen at 560 and 840 g ha -1 . In North Carolina and Virginia, rainfall during cotton emergence led to early season cotton necrosis ranging from 4 to 16% with fomesafen at 140 to 350 g ha -1 and 12 to 45% by fomesafen at 420 to 840 g ha -1 . Early season injury by fomesafen at 280 g ha -1 (recommended use rate) was equal to or less than pyrithiobac or fluometuron at 4 of 5 locations. Mid-season injury was 10% or less at all locations with fomesafen at 490 g ha -1 or less. Plant heights were reduced 11 to 29% in Georgia and North Carolina when fomesafen was applied at rates greater than 420 g ha -1 . In Tennessee, heights were reduced 8% with fomesafen at 560 g ha -1 . Compared to the non-treated control, plant stands were reduced 23 to 28% only in North Carolina when fomesafen rates exceeded 350 g ha -1 . Lint yields followed trends in plant stand, with yield being reduced 23 to 25% by fomesafen at 560 to 840 g ha -1 only in

Cotton (Gossypium hirsutum L.) responses to supplemental irrigation need to be reassessed in humid, short-season environments. We conducted a 4-year study on a Typic Hapludalf at Jackson TN, to measure yield and maturity responses of contemporary cultivars to supplemental irrigation; to describe boll retention and distribution patterns associated with maturity responses; and to estimate the percentage of years in which yields may respond to irrigation. Treatments consisted of three rates of supplemental drip irrigation (nominally 3.81, 2.54, and 1.27 cm wk-1, adjusted for rainfall and prior irrigation), plus a nonirrigated check. Irrigation increased lint yields significantly in 3 of 4 years, with quadratic rate responses. The average yield increase was 38% at the 2.54-cm wk-1 rate. Yields were maximized with 35 to 37 cm of total water (irrigation + rainfall) between 40 and 120 days after planting. Yields were limited more by the accumulation of heat units than water supply in 2009. Irrigation delayed crop maturity by an average of 0.56 days for every additional cm water from irrigation or rainfall. Full irrigation expanded the effective fruiting zone on the plant from about 6.6 to 8.5 sympodial branches, increasing first position boll retention, but it delayed crop maturity mainly by shifting the location of the highest harvestable boll. Response to water supply showed that a yield response to irrigation could be expected in years with < 28 cm rainfall between 40 and 120 days after planting. Assuming a planting date of 3 May, this condition occurred in 60% of years of historical rainfall data for this environment.