Field, greenhouse and laboratory experiments were implemented to investigate the effects of auxin herbicides on growth and yield of cotton in glyphosate based systems. Field experiments evaluated the effect of rate and timing of dicamba or 2,4-D exposure when applied in glyphosate-resistant cotton. Increasing rates of either dicamba or 2,4-D resulted in increased injury and yield reductions. Initial injury symptomology was similar for cotton exposed at vegetative and reproductive stages. When cotton was exposed to auxin herbicides during vegetative growth, injury increased with time, while foliar injury during reproductive growth was stagnant and often decreased with time. Subsequently, the strongest correlations to yield loss and injury were from later evaluations of vegetative timings. Recovery from injury due to auxin herbicide exposure was dependent upon favorable environmental conditions; however, recovery was often superficial and masked significant yield loss. Greenhouse studies evaluated the impact of the diglycolamine dicamba salt on the movement of 14C radio-labeled potassium salt glyphosate in barnyardgrass and johnsongrass. Increasing glyphosate rate increased total absorption of glyphosate in both species. Total absorption of glyphosate was not impacted by the presence of dicamba, for either johnsongrass or barnyardgrass. Dicamba did not consistently alter the translocation of glyphosate in johnsongrass; however, dicamba did reduce glyphosate translocation in barnyardgrass. Total amount of translocated glyphosate was 2.6 to 4.6% and 3.8 to 6.8% of applied in barnyardgrass and johnsongrass, respectively. Reduced translocation in barnyardgrass was a result of increased glyphosate accumulation in the distal portion of the treated leaf. Increasing the rate of glyphosate did overcome the dicamba induced antagonism; however, altered translocation of glyphosate has been documented to be a precursor to herbicide resistance.

No description available.

Research was conducted in 2013 and 2014 to evaluate the postemergence control of Palmer amaranth [Amaranthus palmeri (S.) Wats.] with mesotrione alone and in mixtures with fomesafen and/or glyphosate and to evaluate the impact of lactofen and planting date on growth, development, and yield of indeterminate soybean [Glycine max (L.) Merr.]. Studies included a greenhouse evaluation of different rates of mesotrione on the control of 5- and 10-cm Palmer amaranth and field studies evaluating the control of 5- to 10-cm Palmer amaranth with three rates of mesotrione applied alone and in mixtures with fomesafen and/or glyphosate. Lactofen studies include a planting date study evaluating one rate of lactofen applied at V2 soybean stage with planting dates of April 15, May 1, May 15, and June 1 and a lactofen timing study where one rate of lactofen was applied at soybean growth stages ranging from V1 to R5.

Corn or maize (Zea mays L.) has been grown in North America for many centuries, and an increase in corn production will continue to be needed. Agriculture producers must meet the demands of feeding and providing for an increasing population of people. In order to meet those needs, different production practices are being investigated as a way to increase grain yield. Field plots were conducted across the state of Kentucky in 2011 and 2012 to evaluate the interaction between hybrid, row width, and plant density on corn yield. The primary objectives were to test if 1) narrower rows increase grain yield, 2) higher plant densities increase yield in narrow and twin rows, and 3) the interactions among all factors. Three hybrids were evaluated in three row widths (76, 38 cm or twin) at target densities ranging from 74 000 to 124 000 plants ha-1. Interactions between hybrid, row width, and plant density occurred; however, effects on grain yield and plant physiological characteristics were small and variable across all environments. Plant density had the greatest impact on IPAR and grain yield. Field trials were conducted near Lexington and Princeton, Kentucky in 2011 and 2012 to evaluate the effects of row width on different weed management treatments in corn. The objectives were to 1) evaluate five weed management methods in three row widths (76, 38 cm or twin) and 2) estimate the effect of these practices on corn yield. Herbicides used within each weed management strategy included the residual herbicide S-metholachlor + atrazine (1.4 + 1.8 kg/ha) applied preemergence (PRE) and/or glyphosate (0.86 kg/ha) postemergence (POST). Weed management treatments consisted of a PRE only, PRE followed by POST, POST only, POST + PRE, and an untreated control. Row spacing had little effect on weed suppression and control except for two cases. In general, PRE followed by POST and POST + Residual treatments controlled weeds better compared to PRE only and POST only treatments. Corn yields were higher when a herbicide was used compared to applying no herbicide application. KEYWORDS: Row spacing, Plant Density, Corn Hybrids, Weed Management, Herbicide Application Timing

Within Arkansas, Louisiana, Mississippi, Missouri, and Texas, rice acreage is rotated with soybean due to both crops’ adaptability to the clay soils of the midsouthern USA. Two row patterns, two maturity groups, and six seeding rates were examined at Stoneville, MS, in 2009-2010, with respect to soybean growth and yield produced on silt loam soil. Optimal yield for MG IV was 333,000 seed ha-1 (297,000 plants ha-1). Twin-row soybean increased seed yield 7 to 10% more than single-row due to greater LAI, NDVI, and node and pod production. Rice field experiments quantified N loss via ammonia volatilization and determined grain yield for various N sources and preflood application timing. Cumulative ammonia volatilization loss on Tunica clay was minimal (10% of applied N). Grain yields were 6% less when fertilizer was applied 10 days before flood (dbf) as compared to 1 dbf; N sources are available to minimize ammonia volatilization loss.

Research was conducted at the Mississippi State University Delta Research and Extension Center from 2015 to 2018 to (1) determine the effects of sub-lethal concentrations of paraquat, metribuzin, fomesafen, and cloransulam-methyl applied at different rice growth stages, determine the effects on rice growth of simulated off-target paraquat applications at varying concentration based on a proportionally decreased carrier volume characterize rice response to a sub-lethal concentration of paraquat in combination with common POST and residual herbicides, assess whether starter N fertilizer or different N fertilizer management strategies can aide in rice recover after exposure to a sub-lethal concentration of paraquat, and define a maximum soil concentration of S-metolachlor that will allow rice to germinate and emerge. Rice yield was negatively affected following exposure to paraquat applied any time after rice emergence. Paraquat applications to rice in early reproductive growth reduced rough rice yield and seed germination the greatest. Paraquat plus metribuzin injured rice 68 to 69% 14 and 28 d after treatment (DAT), which was 10 to 13% greater than following paraquat alone or paraquat plus fomesafen. Pooled across metribuzin and fomesafen treatments, paraquat reduced rough rice yields 23%. Paraquat plus 10 different residual herbicides injured rice ≥51% 28 DAT and reduced rough rice yields ≥21%. In spite of starter N fertilizer applications, paraquat injured rice ≥41%, reduced height 57%, reduced dry weight prior to flooding 77%, delayed maturity 10 d, reduced dry weight at maturity 33%, and reduced rough rice yield 35%. Similar results were observed in the N Fertilizer Timing Study. Soil concentrations of s-metolachlor 28 DAT were 30, 31, 32, 36, 61, and 488 ppm following exposure to s-metolachlor applied at 0, 1/64, 1/32, 1/16, 1/4, and 1X concentration. A soil analysis would be the best option to determine levels of s-metolachlor prior to planting rice if an off-target herbicide movement containing s-metolachlor occurred. These data indicate that paraquat can have negative impact on rice growth and development. Therefore, it is crucial that if environmental conditions are conducive for off-target herbicide movement extreme caution should be exercised when applying paraquat adjacent to fields devoted to rice production.

Soybean is an important source of protein in animal feed, and growing demand for meat consumption worldwide has led to increased soybean production. Over 120 million metric tons of soybean were harvested in the United States in 2018, approximately one-third of the world production. In the Mid-Atlantic region, soybean is one of the most valuable field crops. Major foliar diseases that reduce soybean yield in the Mid-Atlantic region are frogeye leaf spot (FLS) and Cercospora leaf blight. In addition to crop rotation and host resistance, foliar fungicides, often with quinone outside inhibitor (QoI) active ingredients, are used to manage these soybean foliar diseases. Yield benefits of foliar fungicides have been inconsistent and this may be the result of low disease pressure, unfavorable environmental conditions for disease development, or the presence of fungal pathogen populations that have developed resistance to fungicides. The objectives of this research were 1) to develop a pyrosequencing-based assay to rapidly quantify QoI resistance frequencies in Cercospora sojina, the causal agent of FLS, 2) to examine the effects of fungicide application timings, disease pressure, and environmental factors on soybean yield, and 3) to develop a weather-based soybean foliar fungicide application decision aid for the Mid-Atlantic U.S. using a threshold decision rule. A pyrosequencing assay targeting the G143A mutation was designed, and a Virginia survey of C. sojina populations indicated that the G143A mutation conferring QoI resistance is widespread. In small plot fungicide application timing experiments, five weekly fungicide applications starting at beginning pod (R3) resulted in the greatest yield, but for single fungicide applications, R3 or 1 week after R3 resulted in the greatest yields. There was positive relationship between the cumulative number of disease favorable days (mean daily temperature 20-30°C and ≥ 10 hours of relative humidity >90%) from planting to R3 and disease severity at the full pod stage (r = 0.97, P = <0.01). Higher disease severity was associated with greater yield loss (r2 =0.53, P = 0.10) suggesting foliar fungicide applications are more likely to have yield benefits as the number of disease favorable days prior to R3 increase. A disease favorable-days threshold (FDT) using the environmental parameters indicated above was evaluated in on-farm experiments throughout Virginia, Maryland, and Delaware. Based on decision rules, FDT = 8 three weeks prior to R3 was the best predictor of a yield benefit with an R3 fungicide application. The decision aid was also able to correctly predict when a fungicide application would not be profitable ≥90% of the time. This weather-based decision aid along with monitoring of fungicide resistance development within the region will provide soybean growers in the Mid-Atlantic U.S. with tools to maximize yields and profitability. / Doctor of Philosophy / Soybean is the third most valuable field crop in the world, ranked only behind rice and wheat in value. Over 98% of the soybean crop is used for animal feed due to its high protein content. The United States is the largest soybean producer in the world, responsible for one-third of global production. Soybean is the top cash crop in the Mid-Atlantic region. Foliar fungal diseases can reduce the soybean yield by causing lesions on the leaves that reduce photosynthesis and cause premature defoliation. Frogeye leaf spot (FLS) caused by Cercospora sojina is a major yield reducing soybean foliar diseases in the Mid-Atlantic region. Foliar fungicides, often with quinone outside inhibitor (QoI) active ingredients, are used to manage the disease. However, fungicide efficacy has been inconsistent. Inconsistencies may be due to low disease pressure, improper application timing, or fungicide resistance. The purpose of this research was to investigate the fungicide efficacy inconsistencies and to develop management tools to improve yield and maximize profitability. Our objectives were to 1) develop a molecular assay to quantify frequencies of the mutation conferring fungicide resistance in Virginia populations of C. sojina, 2) examine the effects of fungicide application timings, disease severity, and weather on soybean yield, and 3) develop a weather-based soybean foliar fungicide application decision aid for the Mid-Atlantic U.S. The C. sojina fungicide resistance mutation was widespread in Virginia, but overall frequencies were relatively low compared to findings from Midwest and Southern states. In fungicide timing experiments, beginning pod (R3) applications resulted in the most consistent yield benefits, and disease severity and yield loss increased as the number of weather-based disease favorable days prior to R3 increased. We used data from on-farm experiments in Virginia, Maryland, and Delaware to develop a weather-based disease favorable-days threshold that increased the probability that a fungicide application at R3 would have a yield benefit in soybean. The results of our research have led improved fungal disease management recommendations for soybean in the Mid-Atlantic that will maximize yields and profitability.

The United States is a world leader of soybean [Glycine max (L.) Merr.] production, but to maintain quality production at this level, soybean management needs to be continually monitored and improved. Sulfur (S) deficiencies in soybean have become more frequent in the U.S. due to fertilizer purity, emissions regulations, and higher yields. We completed a study for soybean grown in sandy loam soils in the mid-Atlantic coastal plain system to determine proper S fertilizer rate and application timing. Yields ranged from 1,236-4,051 kg ha-1. Neither S rate nor application timing influenced yield. S treatments increased methionine concentration (methionine = -0.0001 S rate2 + 0.002 S rate + 5.60). Sulfur fertilization can improve soybean quality and may impact marketability. Another study was conducted to determine optimal source and rate of S application for soybeans in the Mid-Atlantic coastal plain system. Yields ranged from 1,316-4,914 kg ha-1. While sulfur rate did not influence yield and fertilizer source responses were site-specific. Sulfur leaf tissue concentrations were directly related to S rate (S concentration = 0.004S rate + 2.103). Nutrient uptake responses to S fertility indicate the potential for S yield responses in the future when soils become S depleted and contain less available S. Soybean producers and retailers in the United States are interested in capitalizing on new edamame markets to provide a domestic product. To aid the shift from oilseed production to vegetable production, a study was conducted to determine the optimal N rate and N application timing for edamame yield and quality in the Mid-Atlantic coastal plain system. Nitrogen rate significantly increased yield one out of three years (Yield = 29.9N Rate + 3387) when all N was applied at planting but was not significant with split applications. Fertilizer rate and timing did not impact edamame maturity or final pod/bean quality. N fertilizer applied at-planting may aid edamame yield and profit for sandy loam soils in the mid-Atlantic, USA. Currently, mid-Atlantic coastal plain soils, coupled with S deposition, are able to supply enough S for soybean growth and development, but without fertilization soybean soils are being mined of S and will eventually become depleted. Sulfur must be monitored if future deficiencies are to be avoided. Nitrogen fertilizers may improve yield in vegetable soybean production. Both oilseed and vegetable soybean farmers should continue to monitor soil nutrient levels to ensure proper nutrition for soybean growth and development. / Doctor of Philosophy / Soybean (Glycine max L. [Merr.]) is a diverse crop used across various industries: from vegetables for human consumption to protein for animal feed or even additives for roofing sealants. The U.S. is a world leader in soybean production. To maintain quality production at this level, soybean management needs to be continually monitored and improved. Sulfur (S) and nitrogen (N) fertilizers are one current area of interest in soybean production and management. This dissertation will discuss both. Historically, acid rain, which contained high levels of S, provided all the necessary S for proper soybean growth and development. In recent years, industry emissions regulations have decreased the amount of S entering the air, thereby decreasing S deposits in acid rain. At the same time, soybean yields are increasing, and higher production requires higher amounts of inputs. Therefore, because S is a necessary input, it is being taken from the soil to meet the needs of high yielding soybean. Less and less S remains in the soil for future soybean crops. This study was conducted to determine proper sulfur fertilizer applications, to ensure quality and quantity soybean production for Virginia farmers. Yields ranged from 1,236-4,914 kg ha-1. Currently, soils contain sufficient S levels for proper growth and development, but if current trends persist sulfur deficiencies will become apparent in the future. Although the U.S. soybean production is abundant, most of the vegetable soybean, also called edamame, consumed in U.S. is imported. The interest in providing a domestic edamame product has led soybean farmers to reevaluate and adapt soybean production strategies to fit a vegetable crop. Edamame is the same species as oilseed soybeans commonly grown throughout the US, but instead of waiting until the seed is dry, edamame is harvested when the seed is still green. This study also was conducted to provide nitrogen fertilizer recommendations for Virginia soybean farmers hoping to adjust their farms to produce quality vegetable soybean. Nitrogen fertilizer improved edamame gross production one out of three years. Continual observation of soil nutrient levels and soybean health is necessary to ensure quality growth and production for both oilseed and vegetable soybean.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Steven Keeley / Common dandelion (Taraxacum officinale Weber) is an important perennial weed in turfgrass. Fall is considered the optimal time for postemergence herbicidal control of dandelions; however, applications in spring, when volatility damage to surrounding plants is an additional concern, are often needed. Therefore, we conducted research to determine the volatility of common broadleaf herbicides, and their efficacy when applied at spring and fall application timings. Volatility was determined by applying herbicides to turfgrass and using potted tomatoes as indicator plants. Tomatoes exposed to turfgrass treated with Trimec Classic, Confront, Surge, Escalade 2, and Imprelis exhibited little or no volatility damage, while exposure to Speedzone, 4 Speed XT, and Cool Power caused significant damage. In general, herbicides causing little or no damage were amine formulations. Two field studies determined the effect of spring and fall application timing on dandelion control with several herbicides. Herbicide applications in the spring coincided with dandelion anthesis stages: pre-bloom, peak bloom, and post-bloom. Results were dependent on dandelion pressure in the studies. In 2010, with lower pressure, there were no differences among herbicides at any spring timing when dandelion control was evaluated after one year; all herbicides gave ≥ 80% control. In 2011, with higher dandelion pressure, Imprelis SL and 4 Speed XT provided ≥ 96% dandelion control at the spring pre- and post-bloom timings, which was better than Surge, Escalade 2, Cool Power, and Confront. The best choices for spring efficacy combined with minimal to no volatility were Escalade 2 and Trimec Classic. Finally, because interest in organic dandelion control is increasing, we compared several organic weed control tactics with a conventional herbicide. In a two-year field study, the conventional herbicide gave much better control (> 96%) than any organic method. Horticultural vinegar corn gluten meal, and fertilizer-only gave < 25% control, while hand-weeding gave 58 to 71% control. While hand-weeding was the best of the organic tactics, the time required was considered prohibitive for turfgrass managers, unless initial weed levels were very low.

Com o objetivo de avaliar os efeitos de densidades de Aeschynomene rudis Benth. na cultura do arroz irrigado e a eficiência do herbicida ethoxysulfuron aplicado em duas épocas como pós-emergente, foi instalado um experimento no município de Taubaté, região do Vale do Paraíba-SP, no ano agrícola de 2001/2002. O cultivar de arroz Epagri 109 e a planta daninha A. rudis foram semeados em 30/10/2001 em solo drenado. Os tratamentos foram constituídos de quatro densidades de A. rudis (3, 6, 12 e 24 plantas por metro quadrado) e duas épocas de aplicação do herbicida ethoxysulfuron dentro de cada densidade (estádio de 4 e 6 folhas do A. rudis), e cinco parcelas testemunhas com densidades de 0, 3, 6, 12 e 24 plantas de A. rudis por metro quadrado sem a aplicação do produto, constituindo 13 tratamentos com 4 repetições, delineados em blocos ao acaso. O herbicida foi aplicado na dose de 80 g.ha-1, sendo adicionado à calda o adjuvante lauril éter sulfato de sódio na dose de 0,3 % base volume, e as pulverizações efetuadas nos dias 27/11/2001 e 04/12/2001. Os parâmetros avaliados foram: número de plantas, colmos e panículas por metro, altura das plantas de arroz, comprimento de panículas, número de espiguetas por panícula, número de grãos formados por panículas, rendimento de grãos, eficiência do herbicida no controle de A. rudis e fitointoxicação à cultura. Considerando-se os resultados obtidos pode-se concluir que: a) densidades de 3, 6, 12 e 24 plantas de A. rudis por metro quadrado, influenciam negativamente de forma linear, o número de colmos e de panículas por metro, o comprimento das panículas, o número de espiguetas e de grãos formados por panícula, o rendimento de grãos e o índice para colheita mecânica e não afetam o número de plantas por metro e a altura das plantas de arroz. b) o herbicida ethoxysulfuron é eficiente no controle de A. rudis nos estádios de 4 e de 6 folhas, nas densidades de 3, 6, 12 e 24 plantas por metro quadrado. c) ethoxysulfuron na dose de 80 g.ha-1, quando aplicado em pós-emergência precoce e mediana em densidades de 3, 6, 12 e 24 plantas de A. rudis por metro quadrado é seletivo para o cultivar de arroz Epagri 109, não interferindo nos parâmetros avaliados. / During the season 2001/2002, an experiment was conducted in Taubaté city, area of the Paraíba-SP valley, to evaluate the effect of Aeschynomene rudis Benth. densities on paddy rice, and the efficacy of the herbicide ethoxysulfuron applied in early and mid post emergence. The rice variety Epagri 109 and A. rudis were planted October 30, 2001 in dry soil. The treatments were four A. rudis densities (3, 6, 12 and 24 plants per square meter) and two application timings of the herbicide ethoxysulfuron in each density. The two application timings were at the 4 and 6 leaf stage of A. rudis. There were also untreated densities of 0, 3, 6, 12 and 24 plants of A. rudis per square meter without the herbicide application, resulting in 13 treatments with 4 replications delineated in randomized blocks. The herbicide was applied at 80 g.ha-1, with the adjuvant laurel ether sulfate of sodium at .3% v/v. The applications were made on November 27 and December 4, 2001. The assessed crop parameters were: number of plants, stems and panicles per meter, height of the plants, panicle length, number of spikelets by panicle, number of grains formed by panicles, income of grains, A. rudis control and crop damage. We can conclude from the results that A. rudis densities of 3, 6, 12 and 24 plants per square meter influence the crop negatively, in a linear way, the number of stems and panicles per meter, the length of the panicles, the number of spikelets and grains formed by panicles, the mechanical harvest index, and rice yield. There were no effects on the number of rice plants per meter or the height of the rice. Also, ethoxysulfuron was effective in controlling A. rudis at both the 4 and 6 leaf stage, in densities of 3, 6, 12 and 24 plants per square meter. Ethoxysulfuron at 80 g.ha-1, when applied early post or mid post emergence in densities of 3, 6, 12 and 24 plants per square meter was selective to the rice variety Epagri 109, not affecting the assessed parameters.