Weeds pose a challenge to cotton production, and herbicides have been the primary means of control. However, there is growing concern over weed resistance to herbicides. To address this issue, we evaluated three cover crop species and six cotton accessions for weed suppression. The study found that hairy vetch, wheat, and B16 cotton CS line effectively suppressed Amaranthus species, while MNTN 4-15, B16, hairy vetch, and wheat were correlated with the highest cotton yield. Cover crops were also analyzed for chlorogenic acid content, with wheat, MNTN 4-15, and hairy vetch producing the highest amounts. The greenhouse tray study showed that wheat and hairy vetch cover crops were among the best treatments for weed suppression. These findings suggest that cover crops may provide effective weed control and improve crop yield.

Water level declines in the Mississippi River Valley Alluvial Aquifer (MRVAA) are attributed largely to withdrawals for rice (Oryza sativa L.) irrigation. This study was performed to determine if alternative irrigation strategies for rice could reduce withdrawal from the MRVAA without having an adverse effect on grain yield, grain quality, control of barnyardgrass, and profitability. Research was conducted in Stoneville, MS and 19 on-farm locations across the Delta region of Mississippi from 2014 through 2017 to determine the irrigation threshold for alternate wetting and drying (AWD) rice irrigation, the effect of AWD management on barnyardgrass control, and effects of irrigation water management practice, i.e., conventional flood via cascade (CONV), multiple side inlet (MSI), and MSI coupled with AWD, on aquifer withdrawal, rough rice grain yield, irrigation water use efficiency (IWUE), and net returns above irrigation costs. An AWD threshold of -20 cm below the soil surface had no adverse effect on grain yield or grain quality, reduced irrigation applied by 50%, and improved IWUE by 45% compared to a continuous flood (CF). Control of barnyardgrass in AWD was either maintained or improved compared to CF for both Clearfield and conventional rice production systems. At the production scale, up to 39% less water was applied to AWD compared to CONV and MSI. Rice grain yield for AWD was not different from either CONV or MSI, despite substantial reductions in water use. Relative to standard irrigation strategies, AWD maintained or increased net returns up to $238 ha-1 for pumping depths from 5.5 m to 122 m and diesel prices from $0.42 L-1 to $0.98 L-1. Irrigation water use efficiency was up to 59% greater for AWD relative to conventional systems due to the positive effects of the former on water use while maintaining yield. These data demonstrate that AWD can reduce withdrawal from the MRVAA while maintaining or improving yield and net returns relative to irrigation strategies currently employed across the midsouthern USA rice belt.

Optimal plant populations are critical in achieving high rice yields. The purpose of this research was to investigate yield penalties associated with inadequate, non-uniform plant populations for modern rice cultivars. Research was conducted at the Delta Research and Extension Center in Stoneville, MS, in 2019, 2020 and 2021. In one study, inbred, herbicide-resistant ‘CL153’ was drill-seeded at 73-18 kg ha-1 after being mixed with inbred, herbicide-susceptible ‘Rex’ at 0-55 kg ha-1. Likewise, hybrid, herbicide-resistant cultivar ‘CL XL7521’ was seeded at 29-8 kg ha-1 mixed with hybrid, herbicide-susceptible ‘XP753’ at 0-21 kg ha-1. At the two- to three- leaf growth stage, imazamox was applied to eliminate ‘Rex’ and ‘XP753’ in their respective studies to achieve the target plant population (TPP). Results indicate that when plant populations are reduced up to 30% in both inbred and hybrid cultivars, grain yields should be comparable if not greater than an adequate, uniform plant population.

<p dir="ltr">Cover crops and soil residual herbicides are some of the essential tools within the integrated weed management. When used at cover crop termination, residual herbicides can extend the period of weed control and reduce the selection pressure for herbicide resistance. However, previous research has indicated that the use of cover crops can increase the microbial activity of the soil which, in turn, is the primary route for herbicide degradation in the soil. In addition to the potential effect on the microbial breakdown of herbicides, cover crops can also alter the fate of herbicides by interception. Three field projects were established to (1) investigate the influence of cover crop [cereal rye (<i>Secale cereale</i> L.) and crimson clover (<i>Trifolium incarnatum</i> L.)] use on soil enzyme activities [β-glucosidase (BG) and dehydrogenase (DHA)], its effect on the concentration of residual herbicides (sulfentrazone, <i>s</i>-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue; (2) to investigate the effect of cover crop termination strategies (fallow, standing, and roller crimped 1 d prior to application) and simulated rainfall volumes (0, 4.2, and 8.3 mm simulated over 20 min; equivalent to 0, 12.5, and 25 mm h^-1) on atrazine wash off from cereal rye biomass onto the soil; (3) to investigate the effect of cereal rye termination strategies on the concentration of sulfentrazone, <i>s</i>-metolachlor, and cloransulam-methyl in the soil, weed control, and soybean [Glycine max (L.) Merr.] yield.</p><p dir="ltr">Results from the first project suggests that the use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. Furthermore, the use of cereal rye or crimson clover as cover crops did not reduce the efficacy of the residual herbicides in controlling weeds early in the growing season.</p><p dir="ltr">In regards to the fate of atrazine after simulated rainfall, the results from the second project indicated that cereal rye biomass accumulation negatively impacted the amount of herbicide reaching the soil at the time of application. Although the roller crimped cereal rye reduced the amount of herbicide reaching the soil relative to the standing cereal rye, it also reduced atrazine leaching below the 0-5 cm of soil. Furthermore, in cover cropping systems with high levels of cereal rye biomass, more than 8.3 mm of rain are required to wash most of the atrazine off of the biomass.</p><p dir="ltr">Lastly, the adoption of the planting green systems resulted in up to 84% interception of residual herbicides by the roller crimped cereal rye biomass. The use of cereal rye as cover crop did not improve the weed control relative to the fallow during the two years of field research. Soybean yield losses ranged from 10 to 44% with the adoption of the planting green system, primarily due to stand losses. However, there are strategies and proper equipment available that can be used to minimize soybean stand losses.</p>

Planting date, seeding rate, soil texture, and row configuration are important factors in soybean production. Each of these factors can impact overall production and yield of soybean immensely. Growers can have difficulty making decisions about how to best manage their production systems with these factors in mind. Therefore, research was conducted from 2019 to 2021 at the Delta Research and Extension Center in Stoneville, MS, to evaluate the agronomic performance, yield components, and weed control of soybean planted with different planting dates, row configurations, soil textures and/or seeding rates. Common row configurations utilized in Mississippi soybean production were compared to a triple-row configuration on raised beds. First planting dates occurred from late-April to early-May and second planting dates followed three weeks later. Each row configuration was planted at 320,000 seed ha-1 for agronomic studies. Seeding Rate Study was initiated where triple-row configuration plots were planted at 320,000, 445,000, and 553,000 seed ha-1. Total dry matter (TDM) was determined by removing a m-2 in each plot at soybean growth stage R6.5 and allowing samples to dry down and weigh them. Harvest index was determined by collecting seed from TDM samples and weighing them. Pod node-1, seed number, and node plant-1 were determined by collecting five random plants from each plot and counting the total number of pods, seed, and nodes. Soybean planted on silt loam at the first planting produced lower seed weight, seed number, and harvest index than soybean on clay soil at either planting date. Two row configurations, single- and triple-row, were planted on raised beds for weed control studies. Programs included PRE only, EPOST, LPOST, PRE fb EPOST, PRE fb LPOST, and PRE fb EPOST fb LPOST. Herbicide timings included 7, 14, 21, and 28 DA-crop emergence and each timing was followed by a sequential application 14 d after the initial application. Triple-row configuration had lower plant densities and produced lower yield than single- and twin-row configurations. Triple-row configuration soybean planted on clay soil and at 445,000 and 553,000 seed ha-1 produced greater yield than any other seeding rate or soil texture.

The lack of effective broadleaf weed control represents one of the major factors having detrimental effects on growth and yield of soybeans. Broadleaf weeds are a serious threat to soybean growers in the southeastern United States. A broad range of herbicides is being used in an effort to control broadleaf weeds in soybeans, and research is still being conducted to find new herbicides that can best work for this purpose. This study involved the use of one these herbicides. It was fomesafen, 5-[2-chloro-4-trifluromethyl) phenoxy]-N-(methyl-sulfonyl)-2-nitrobenzamide, which controls a broad spectrum of broadleaf weeds in soybeans. The experiment was conducted in the summers of 1987 and 1988. Broadleaf weed control treatments with fomesafen at rates at 0.07, 0.14, 0.28, and 0.35 kg ai/ha in single early postemergence and late postemergence applications were evaluated using the herbicide with a nonionic surfactant at 0.25% and 0.50% of the solution. All treatments were compared with a check which did not receive herbicide application. Among the most common broadleaf weeds found in the area under study during the summer of 1987 were morningglories (Ipomoea spp), redroot pigweed (Amaranthus retroflexus L.), jimsonweed (Datura stramonium L.), common lambsquarters (Chenopodium album L.), carpetweed (Moliugo verticillata L.), and prickly sida (Sida spinose L.), For the summer of 1988 the most prevalent broadleaf weeds were morningglories, horsenettle (Solanum carolinense L.), horseweed [Conyza canadensis (L.), Cronq.], and prickly sida. The results of the experiment showed no significant differences between early postemergence and late postemergence treatments. There were no significant differences in broadleaf weed control in treatments which received 0.14, 0.28 and 0.35 kg ai/ha of fomesafen for either 1987 or 1988. Poor broadleaf weed control resulted with the application of fomesafen at its lowest rate (0.07 kg ai/ha). No significant differences were found in broadleaf weed control between concentration of 0.25% and 0.50% of the nonionic surfactant added to fomesafen. Statistically significant yield variation did occur among treatments in 1987. No significant differences in yields were found between any of the herbicide treatments in 1988. Soybean yields were significantly higher in 1988 than in 1987.

At least 110 million landmines have been planted since the 1970s in about 70 nations, many of which remain in place today. Some risk of detection may be mitigated using currently available remote sensing techniques when vegetation is present. My study focused on using plants as phytosensors to detect buried explosives. I exposed three species representing different functional types (Cyperus esculentus (sedge), Ulmus alata (tree), Vitis labrusca (vine)) to 500 mg kg-1 of Composition B (Comp B; 60/40 mixture of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT)), a commonly used explosive mixture, and measured functional traits and reflectance over a nine-week period. Cyperus esculentus was not a good indicator for the presence of explosive compounds. Comp B treatment woody species, U. alata and V. labrusca, exhibited changes in pigment content, leaf area, specific leaf area, dry leaf biomass, and canopy reflectance. The efficacy of plants as landmine detectors is species and/or functional group dependent.

Doctor of Philosophy / Department of History / James E. Sherow / This dissertation contributes to the environmental, agricultural, and technological history of the modern United States by examining pesticide use and the debates surrounding them in the Great Plains from the 1940s to the 1980s. Specifically, it addresses the relationships among aerial sprayers, farmers, agriculturalists, and grassroots concepts of toxicity that emerged from mid-century technological and environmental changes. It argues that pesticides as well as a variety of weeds and insects actively transformed the tools, attitudes, and regulatory policies of their users. Historians of agricultural chemical use in America have focused on the political debates over DDT, the social activism against pesticides that Rachel Carson inspired with her best-selling book Silent Spring (1962), the growth in federal regulatory policy in the 1970s, and the contentious reactions by the chemical and agricultural industries. This study offers a new, ground-level history of pesticides by showing how aerial sprayers, farmers, and agriculturalists developed custom chemical applications and conceptualized toxicity as each related to the technological and environmental changes in the region. Drawing on multiple sources, including agricultural experiment station reports, scientific studies, government documents, farm journals, landowner and aerial spray pilot correspondence, and oral histories, this study explores how local producers changed with their chemicals, spray planes, and pests to develop an environmental ethos that understood toxicity as a synthetic and natural danger. Although opposition to pesticides became central to modern environmentalism, debates around pesticides‘ effectiveness and dangers did not come only from activists or government regulators. Beginning just after World War II, landowners and spray pilots in the fields and rural airstrips of the Great Plains took the hazards of agricultural chemicals seriously, critiquing how and why pesticides were used for decades after. By viewing chemicals, spray planes, and pests, as well as landowners, pilots, and agriculturalists as equal forces in the regional transformation of farming landscapes, this dissertation highlights a new history of pesticides, agriculture, and the environment. Farmers and custom applicators did not simply follow the economic goals of agribusiness. Nor did they dismiss the dangers of pesticides. Rather, they constructed their own standards of injury and environmental risk that stressed accuracy, regulation, and a reasonable certainty of safety—a result of the equally transformational influences of chemicals, pests, and the region. This study finally offers new insights into the creation of national chemical policy and the regulatory debates over pesticides during the 1960s and 1970s.

Most managed turfgrass species require frequent inputs to maintain an acceptable level of quality. Among these inputs, nitrogen (N) fertilization is usually the most limiting in terms of growth and development. However, N fertilization is also linked to non-point source (NPS) pollution. White clover (WC) is known for its ability to provide N when mixed into stands of turfgrass, and does not pose a threat for NPS pollution. Two field studies were designed to investigate the effects of WC inclusion in stands of cool-season turfgrasses. In the first field study, three cultivation techniques were examined for establishment of WC into preexisting turfgrass stands at three different seasonal timings. Scalping during the summer was seen as providing the highest WC populations, although scalping treatments also caused the most initial damage to the turfgrass. In the second field study, mixed stands of turfgrass and WC were examined for response to several weeks of traffic simulations, with WC withstanding the traffic events. Additionally, a greenhouse study was implemented to examine the effects of several commercial broadleaf herbicides on two WC varieties. Only 2,4-D was shown to be safe for application to both WC varieties, although Microclover did show tolerance to quinclorac applications.

The control and eradication of the invasive biennial herb garlic mustard (Alliaria petiolata) and the restoration of invaded forest habitats present important linked challenges to land managers in North America. Removing garlic mustard by hand and by glyphosate herbicide application have both been used as eradication strategies with mixed results. Each method has advantages and disadvantages, but they are rarely compared for effectiveness and community impact across multiple years of management. Some previous studies have shown improvements in species diversity and plant community composition following management, while others have found no differences. To better understand both garlic mustard population and native plant community responses to these two methods across a broad geographic range, we tested these two management methods for four years in seven northern hardwood forests in Massachusetts and New York State. We found that pulling juvenile and adult garlic mustard plants for four years significantly reduced adult abundance, while spraying had no effect compared to invaded control plots. In the plant community, we found no negative impacts of garlic mustard on species diversity nor increased diversity in managed plots following three consecutive years of management. Our results suggest that increased diversity should not be the primary goal of garlic mustard management at these sites and plant community monitoring at the site-specific scale should be explored. This study highlights how complicated decisions can be for managers when deciding which invasions to prioritize and how to measure plant community recovery.