@article{chandi_milla-lewis_jordan_york_burton_zuleta_whitaker_culpepper_2013, title={Use of AFLP Markers to Assess Genetic Diversity in Palmer Amaranth (Amaranthus palmeri) Populations from North Carolina and Georgia}, volume={61}, ISSN={["1550-2759"]}, DOI={10.1614/ws-d-12-00053.1}, abstractNote={Glyphosate-resistant Palmer amaranth is a serious problem in southern cropping systems. Much phenotypic variation is observed in Palmer amaranth populations with respect to plant growth and development and susceptibility to herbicides. This may be related to levels of genetic diversity existing in populations. Knowledge of genetic diversity in populations of Palmer amaranth may be useful in understanding distribution and development of herbicide resistance. Research was conducted to assess genetic diversity among and within eight Palmer amaranth populations collected from North Carolina and Georgia using amplified fragment length polymorphism (AFLP) markers. Pair-wise genetic similarity (GS) values were found to be relatively low, averaging 0.34. The highest and the lowest GS between populations were 0.49 and 0.24, respectively, while the highest and the lowest GS within populations were 0.56 and 0.36, respectively. Cluster and principal coordinate (PCO) analyses grouped individuals mostly by population (localized geographic region) irrespective of response to glyphosate or gender of individuals. Analysis of molecular variance (AMOVA) results when populations were nested within states revealed significant variation among and within populations within states while variation among states was not significant. Variation among and within populations within state accounted for 19 and 77% of the total variation, respectively, while variation among states accounted for only 3% of the total variation. The within population contribution towards total variation was always higher than among states and among populations within states irrespective of response to glyphosate or gender of individuals. These results are significant in terms of efficacy of similar management approaches both in terms of chemical and biological control in different areas infested with Palmer amaranth.}, number={1}, journal={WEED SCIENCE}, publisher={Weed Science Society}, author={Chandi, Aman and Milla-Lewis, Susana R. and Jordan, David L. and York, Alan C. and Burton, James D. and Zuleta, M. Carolina and Whitaker, Jared R. and Culpepper, A. Stanley}, year={2013}, pages={136–145} }
 @article{whitaker_york_jordan_culpepper_2010, title={Palmer Amaranth (Amaranthus palmeri) Control in Soybean with Glyphosate and Conventional Herbicide Systems}, volume={24}, ISSN={["1550-2740"]}, DOI={10.1614/wt-d-09-00043.1}, abstractNote={Glyphosate typically controls Palmer amaranth very well. However, glyphosate-resistant (GR) biotypes of this weed are present in several southern states, requiring the development of effective alternatives to glyphosate-only management strategies. Field experiments were conducted in seven North Carolina environments to evaluate control of glyphosate-susceptible (GS) and GR Palmer amaranth in narrow-row soybean by glyphosate and conventional herbicide systems. Conventional systems included either pendimethalin orS-metolachlor applied PRE alone or mixed with flumioxazin, fomesafen, or metribuzin plus chlorimuron followed by fomesafen or no herbicide POST.S-metolachlor was more effective at controlling GR and GS Palmer amaranth than pendimethalin; flumioxazin and fomesafen were generally more effective than metribuzin plus chlorimuron. Fomesafen applied POST following PRE herbicides increased Palmer amaranth control and soybean yield compared with PRE-only herbicide systems. Glyphosate alone applied once POST controlled GS Palmer amaranth 97% late in the season. Glyphosate was more effective than fomesafen plus clethodim applied POST. Control of GS Palmer amaranth when treated with pendimethalin orS-metolachlor plus flumioxazin, fomesafen, or metribuzin plus chlorimuron applied PRE followed by fomesafen POST was equivalent to control achieved by glyphosate applied once POST. In fields with GR Palmer amaranth, greater than 80% late-season control was obtained only with systems of pendimethalin orS-metolachlor plus flumioxazin, fomesafen, or metribuzin plus chlorimuron applied PRE followed by fomesafen POST. Systems of pendimethalin orS-metolachlor plus flumioxazin, fomesafen, or metribuzin plus chlorimuron applied PRE without fomesafen POST controlled GR Palmer amaranth less than 30% late in the season. Systems of pendimethalin orS-metolachlor PRE followed by fomesafen POST controlled GR Palmer amaranth less than 60% late in the season.}, number={4}, journal={WEED TECHNOLOGY}, author={Whitaker, Jared R. and York, Alan C. and Jordan, David L. and Culpepper, Stanley}, year={2010}, pages={403–410} }
 @article{culpepper_york_roberts_whitaker_2009, title={Weed Control and Crop Response to Glufosinate Applied to 'PHY 485 WRF' Cotton}, volume={23}, ISSN={["1550-2740"]}, DOI={10.1614/WT-08-168.1}, abstractNote={Field experiments were conducted in Georgia to evaluate weed control and crop tolerance with glufosinate applied to ‘PHY 485 WRF®’ cotton. This glyphosate-resistant cotton also contains a gene, used as a selectable marker, for glufosinate resistance. Three experiments were maintained weed-free and focused on crop tolerance; a fourth experiment focused on control of pitted morningglory and glyphosate-resistant Palmer amaranth. In two experiments, PHY 485 WRF cotton was visibly injured 15 and 20% or less by glufosinate ammonium salt at 430 and 860 g ae/ha, respectively, applied POST two or three times. In a third experiment, glufosinate at 550 g/ha injured cotton up to 36%. Pyrithiobac or glyphosate mixed with glufosinate did not increase injury compared to glufosinate applied alone;S-metolachlor mixed with glufosinate increased injury by six to seven percentage points. Cotton injury was not detectable 14 to 21 d after glufosinate application, and cotton yields were not reduced by glufosinate or glufosinate mixtures. A program of pendimethalin PRE, glyphosate applied POST twice, and diuron plus MSMA POST-directed controlled glyphosate-resistant Palmer amaranth only 17% late in the season.S-metolachlor included with the initial glyphosate application did not increase control, and pyrithiobac increased late-season control by only 13 percentage points. Palmer amaranth was controlled 90% or more when glufosinate replaced glyphosate in the aforementioned system. Pitted morningglory was controlled 99% by all glufosinate programs and mixtures of glyphosate plus pyrithiobac. Seed cotton yields with glufosinate-based systems were at least 3.3 times greater than yields with glyphosate-based systems because of differences in control of glyphosate-resistant Palmer amaranth.}, number={3}, journal={WEED TECHNOLOGY}, author={Culpepper, A. Stanley and York, Alan C. and Roberts, Phillip and Whitaker, Jared R.}, year={2009}, pages={356–362} }
 @article{whitaker_ritchie_bednarz_mills_2008, title={Cotton Subsurface Drip and Overhead Irrigation Efficiency, Maturity, Yield, and Quality}, volume={100}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2008.0036}, abstractNote={Subsurface drip (SSD) is used as a water‐efficient alternative to overhead irrigation in many crops. This study compared soil water, water use, crop maturity, lint yield, and fiber quality of cotton (Gossypium hirsutum L.) grown with SSD to cotton grown with overhead irrigation. Three experiments were conducted at two Georgia locations in 2004 and 2005. Treatments consisted of overhead irrigated, nonirrigated, SSD matched to overhead irrigation rates (SSD Matched), and SSD based on soil water (SSD Fed). Cotton maturity was affected by irrigation treatment as nonirrigated cotton matured earliest, whereas overhead irrigated cotton matured latest. Subsurface drip irrigated cotton produced similar or higher lint yields than overhead irrigated cotton. Subsurface drip provided adequate soil water and irrigation amounts were 4.4, 8.2, and 0.5 cm less than overhead irrigation at the three locations. Water use efficiency (WUE) of cotton SSD irrigated was 23 and 15% higher than overhead‐irrigated cotton in two experiments. Irrigation method did not substantially affect fiber quality; however, micronaire was higher in cotton from the SSD Fed treatment than cotton in the Overhead treatment in two locations. We conclude that SSD irrigation provides the same positive effects as overhead irrigation in cotton production while reducing irrigation water use and may allow for improved irrigation efficiency.}, number={6}, journal={AGRONOMY JOURNAL}, author={Whitaker, Jared R. and Ritchie, Glen L. and Bednarz, Craig W. and Mills, Cory I.}, year={2008}, pages={1763–1768} }
 @article{mills_bednarz_ritchie_whitaker_2008, title={Yield, quality, and fruit distribution in Bollgard/Roundup ready and Bollgard II/Roundup ready flex cottons}, volume={100}, ISSN={["0002-1962"]}, DOI={10.2134/agronj2006.0299}, abstractNote={New transgenic cotton (Gossypium hirsutum L.) technologies Bollgard II/Roundup Ready Flex (BGII/RRF) provide additional mechanisms for the cotton crop to retain early initiated fruiting structures positioned in the lower canopy. It may be possible, therefore, for early fruit retention to become too high with these new technologies resulting in early cutout and reduced yield. The objective of this investigation was to determine if glyphosate‐induced differences in early season retention occur between BGII/RRF and the older Bollgard/Roundup Ready (BG/RR) technologies and if so, to test if these differences in retention impact crop maturity, yield, or quality under irrigated and nonirrigated conditions. A study was conducted in 2004 and 2005 at two locations in southwestern Georgia to compare the two technologies under dryland vs. irrigation with or without flower removal. The BG/RR matured later than BGII/RRF when glyphosate was applied late at the seventh and 11th leaf stages. The BG/RR compensated for fruit loss by producing heavier remaining bolls. The BGII/RRF maturity was unaffected by the late glyphosate applications and produced a higher percentage of plants having a harvestable boll in the lower canopy than BG/RR. The BGII/RRF cotton had increased boll number and weight at the first sympodial position at lower main stem nodes while BG/RR produced more and heavier bolls on upper main stem nodes. Flower removal did not negatively affect BGII/RRF or BG/RR yields. Few differences in fiber quality were observed. The BGII/RRF retained more early reproductive structures than BG/RR but also cutout earlier. Yield differences between the two technologies may be due to agronomic performance of the variety backgrounds used.}, number={1}, journal={AGRONOMY JOURNAL}, author={Mills, Cory I. and Bednarz, Craig W. and Ritchie, Glen L. and Whitaker, Jared R.}, year={2008}, pages={35–41} }