Producers choosing to implement an early corn planting management strategy often experience several yield limiting biotic and abiotic factors. Field variability, flooding, sub-optimal soil temperatures which leads to poor nutrient uptake, delayed emergence and reduced root growth can limit grain production. Three separate experiments were conducted to address some of the negative effects associated with early corn planting. Experiment 1 evaluated flooding effects on several morpho-physiological traits including root system architecture during early crop development. Hybrids (DKC 6208, Pioneer 1197) were flooded at planting (V0) and growth stages V1, V2, V3 for 0, 6, 12, 24, 48, 96 hours. Plants flooded at V0 11% suffered the steepest decline in collar height. Plants flooded at V2 10% were more susceptible than plants flooded V1 4%. Overall, there was a linear decline in nutrient concentration if flooding occurred at planting. Tissue Na levels were the most affected by flood duration and K was the least affected. Experiment 2 evaluated biologic compounds developed to increase immobile nutrients P and K to improve fertilizer use efficiency and provide slow developing roots essential nutrients. The effectiveness of microbial products (B-300, QR, Mammoth, EM-1) with/without starter fertilizer influenced yield, emergence, plant growth, and nutrient uptake. Biologic seed treatments compared to the control, resulted in a positive yield advantage for all treatments. Yields ranged from 37 to 48% higher if biologic compounds were applied. On average, yields increased from 26 to 38% after starter fertilizer was added to the biologic compounds. Phosphorus levels at VT were significantly higher for QR and K content was higher for B300, SF-B300, QR, Mamm, and SF-Mamm compared to the control. Experiment 3 addressed soil physical/chemical properties affecting plant development and there yield plant density relationship. On average, yields significantly increased 40% as plant population increased from 49,400 to 103,740 plants ha−1. Based on the quadratic model agronomically yields would be highest at 61,360 plants ha−1. Correlation analysis among yield and soil physical and chemical properties revealed positive correlations for grain yield, sand% (r2 = 0.42), soil K (r2 = 0.17) soil Na (r2 = 0.46), and soil P (r2 = 0.49).

Two field trials were conducted to determine the impact of water management on the efficacy of insecticide seed treatments against rice water weevil, Lissorhoptrus oryzophilus Kuschel, in rice at the Delta Research and Extension Center during 2011 and 2012. The performance of thiamethoxam, chlorantraniliprole, and clothianidin was evaluated when the permanent flood was established at different timings (6 and 8 weeks after planting) and the effect of flush number (0, 1, or 2) on seed treatment performance was evaluated. Seed treatment efficacy was not impacted by delayed flooding, but 2 flushes reduced efficacy of some seed treatments. Experiments were also conducted to determine the impact of reduced seeding rates found in hybrid rice production on the efficacy of insecticide seed treatments targeting rice water weevil. Efficacy was similar when comparing currently labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin with higher rates of these products.

Blackleg, caused by Leptosphaeria maculans, inflicts greatest canola yield losses when plants are infected before reaching the six-leaf growth stage. Studies were conducted to model pseudothecia maturation and ascospore dispersal to help growers make timely foliar fungicide applications. Pseudothecia maturation occurred mostly during the second half of June or in July in 2017 and 2018 in North Dakota and ascospores concentrations peaked during mid to late June in both years. A logistic regression model developed using temperature and relative humidity predicted the maturation of pseudothecia and ascospore dispersal with approximately 74% and 70% accuracy respectively. In addition, trials to evaluate the efficacy of five seed treatment fungicides were conducted under greenhouse and field conditions. All treatments reduced (P = 0.05) disease severity on seedlings in greenhouse trials, but not in field trials. Seed treatments, while a valuable tool, should not be used as the only means to manage blackleg.

Phytic acid (PA) accounts for up to 75% of the P in soybean (Glycine max L. Merr.) seeds, but it is indigestible by mono- and agastric animals resulting in economic and environmental detriment. Soybean lines with genetically reduced PA contents have been developed using three distinct mutant alleles at the MIPS1, LPA1, and LPA2 genes resulting in up to a 75% reduction in PA. Low PA (LPA) soymeal-based feeds have been tested on several agricultural species and shown to reduce the P in the animal effluent, but they have not been tested on any aquacultural species. However, LPA soybean lines often exhibit low field emergence making them commercially inviable. The cause of this phenomenon is widely debated with possibilities ranging from increased disease pressure to decreased seedling vigor. The objectives of this research were to 1) enhance field emergence of LPA soybean varieties through pre-planting seed treatments, 2) study the impact of the LPA mutant alleles on agronomic, quality, and seed composition traits, and 3) design a low-error method for studying the effect of LPA soymeal-based feeds on aquatic animals using Pacific White Shrimp (Litoenaeus vannamei). These results describe a variety of agronomic and genetic strategies with which the low field emergence of LPA soybeans can be addressed, reveal a heretofore not reported interaction between the mips1 and lpa2 alleles to further increase the digestibility of soymeal, and a possible method for studying LPA soymeal based feed on aquacultural animals. / Master of Science

Seedling blight of maize has significantly influenced field crop stands and seedling vigour over various localities and seasons. The extent of the problem is influenced by a number of factors which includes soil temperature (generally below 13 °C), waterlogged soils, inadequate fertilization, herbicide damage and fungal pathogens. The fungi generally causing seedling damping off are often involved in a complex and succession over time varying in importance depending on the field circumstances at a given time. These generally include the Pythium spp., Rhizoctonia spp. and various Fusarium spp. These have been recorded in a number of studies conducted by local researchers in the late 1980’s and early 1990’s on sorghum but to a lesser degree on maize. Uncertainty regarding the status of the etiology of maize seedling blights as maize production practices have changed dramatically in the last 10 years with increased plant populations, reduced tillage, increased crop rotation options and new short season maize hybrids. It is therefore essential to determine the present status of seedling blights in South Africa to confirm the necessity of fungicide seed treatments to ensure adequate plant densities and seedling vigour. Cob and tassel smut caused by Sphacelotheca reiliana is a disease of maize that was a problem in the 1970’s. Due to improved fertilisation, fungicide seed treatments and hybrid resistance this disease was reduced to such levels that the disease was only found to occur on research farms where seedlings were inoculated. Since 2007, the disease was reported to reach epidemic proportions on the heavy clay soils in the Standerton area. This disease has since spread over the last seven seasons to a range including northern KwaZulu/Natal, namely as far as Underberg/Swartberg, the Witbank, Ermelo, Middelburg and Delmas area in Mpumalanga and to Harrismith in the eastern Free State maize production area. This may be due to susceptible hybrids coming onto the local market or the inability of traditional fungicide seed treatments to contain infection. New and unregistered seed treatments available will be tested for their ability to control cob and tassel smut in two fields over two seasons. The aims of this dissertation were to determine the extent of the seedling blight problem in commercial fields throughout the maize industry. To determine the efficacy of fungicide seed treatments for the control of maize seedling blights using both field and greenhouse studies, and to determine the efficacy of fungicide seed treatments for the control of cob and tassel smut of maize in field trials. A total of 101 localities were sampled throughout the maize producing region of South Africa with root discolouration varying from 0 to 90 % root discolouration. Seventy different fungal species were isolated from the maize seedlings roots which include species such as Aspergillus, Clonostachus, Fusarium, Trichoderma and Penicillium. The most commonly isolated fungi which included Aspergillus niger, Fusarium solani, Fusarium verticillioides and Fusarium oxysporum were evaluated in glasshouse studies to determine their pathogenicity. Pathogenicity differed between isolates of the same fungal species, which were collected from different geographical regions, in the glasshouse studies. Field trials for seedling blight disease showed significant differences between the localities (P < 0.001) the trials were planted at, and between seed treatments. Significant season (P < 0.001) and locality (P < 0.05) differences were also found for cob and tassel smut trials planted at Potchefstroom, North-West province and Greytown, KwaZulu/Natal Province respectively. Fungicide seed treatments also showed significant differences for cob and tassel smut regarding plants infected (P < 0.001) and yield loss (P < 0.05). Overall seed treatments can be seen as an effective controlling agent for the control of seed- and soil-borne fungi on maize. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Seedling blight of maize has significantly influenced field crop stands and seedling vigour over various localities and seasons. The extent of the problem is influenced by a number of factors which includes soil temperature (generally below 13 °C), waterlogged soils, inadequate fertilization, herbicide damage and fungal pathogens. The fungi generally causing seedling damping off are often involved in a complex and succession over time varying in importance depending on the field circumstances at a given time. These generally include the Pythium spp., Rhizoctonia spp. and various Fusarium spp. These have been recorded in a number of studies conducted by local researchers in the late 1980’s and early 1990’s on sorghum but to a lesser degree on maize. Uncertainty regarding the status of the etiology of maize seedling blights as maize production practices have changed dramatically in the last 10 years with increased plant populations, reduced tillage, increased crop rotation options and new short season maize hybrids. It is therefore essential to determine the present status of seedling blights in South Africa to confirm the necessity of fungicide seed treatments to ensure adequate plant densities and seedling vigour. Cob and tassel smut caused by Sphacelotheca reiliana is a disease of maize that was a problem in the 1970’s. Due to improved fertilisation, fungicide seed treatments and hybrid resistance this disease was reduced to such levels that the disease was only found to occur on research farms where seedlings were inoculated. Since 2007, the disease was reported to reach epidemic proportions on the heavy clay soils in the Standerton area. This disease has since spread over the last seven seasons to a range including northern KwaZulu/Natal, namely as far as Underberg/Swartberg, the Witbank, Ermelo, Middelburg and Delmas area in Mpumalanga and to Harrismith in the eastern Free State maize production area. This may be due to susceptible hybrids coming onto the local market or the inability of traditional fungicide seed treatments to contain infection. New and unregistered seed treatments available will be tested for their ability to control cob and tassel smut in two fields over two seasons. The aims of this dissertation were to determine the extent of the seedling blight problem in commercial fields throughout the maize industry. To determine the efficacy of fungicide seed treatments for the control of maize seedling blights using both field and greenhouse studies, and to determine the efficacy of fungicide seed treatments for the control of cob and tassel smut of maize in field trials. A total of 101 localities were sampled throughout the maize producing region of South Africa with root discolouration varying from 0 to 90 % root discolouration. Seventy different fungal species were isolated from the maize seedlings roots which include species such as Aspergillus, Clonostachus, Fusarium, Trichoderma and Penicillium. The most commonly isolated fungi which included Aspergillus niger, Fusarium solani, Fusarium verticillioides and Fusarium oxysporum were evaluated in glasshouse studies to determine their pathogenicity. Pathogenicity differed between isolates of the same fungal species, which were collected from different geographical regions, in the glasshouse studies. Field trials for seedling blight disease showed significant differences between the localities (P < 0.001) the trials were planted at, and between seed treatments. Significant season (P < 0.001) and locality (P < 0.05) differences were also found for cob and tassel smut trials planted at Potchefstroom, North-West province and Greytown, KwaZulu/Natal Province respectively. Fungicide seed treatments also showed significant differences for cob and tassel smut regarding plants infected (P < 0.001) and yield loss (P < 0.05). Overall seed treatments can be seen as an effective controlling agent for the control of seed- and soil-borne fungi on maize. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

No description available.

Roughly 79-100% of maize in the United States (US) is treated with a neonicotinoid seed treatment (NST), and transgenic (GMO) maize, Zea mays L. (Poaceae), that produces insecticidal toxins by way of genes derived from Bacillus thuringiensis (Bt), occupies more than 75% of maize acreage. Among a variety of secondary pests targeted by NSTs, the primary soil-dwelling pest targeted by Bt maize is the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). Transgenic Bt technology has dramatically reduced insecticide use for WCR, and insect resistance poses the greatest threat to its utility. To delay resistance to Bt traits, in 2010 the US Environmental Protection Agency (EPA) approved a "refuge-in-a-bag" (RIB) insect resistance management (IRM) strategy, where 5% of seeds do not express Bt toxins (i.e., "refuge" maize). The RIB strategy is intended to preserve Bt trait effectiveness if mating between 'resistant' insects from Bt plants and 'susceptible' insects from refuge plants occurs at a high enough frequency. Investigations into the effectiveness of RIB for WCR have shown that beetles emerged from Bt plants tend to vastly outnumber beetles emerged from refuge plants, which contributes to low rates of mixed mating. Large proportions of Bt beetles is one of several factors that contributes to resistance development, and resistance to all currently-available WCR-Bt traits has been documented. I conducted field experiments in two regions (Indiana and Virginia) comparing refuge beetle proportions in NST-treated (NST+) and NST-untreated (NST-) 5% RIB maize, to determine whether NSTs may be limiting refuge beetle emergence. To assess advantages of combining use of Bt and NSTs, I compared stand, root injury rating, and yield between NST+, NST-, Bt and non-Bt maize in both states. I also measured neonicotinoid residues in soil, water, and stream sediment within and surrounding fields of maize, to study the off-site movement and soil residence time of these compounds. I found that 5% seed blends did not produce large populations of refuge beetles in any site-year, and that NSTs showed inconsistent effects on refuge beetle populations. Treatment comparisons showed inconsistent benefits of NSTs when combined with Bt traits. I detected neonicotinoid residues in soil matrices throughout the growing season (range: 0 – 417.42 ppb), including prior to planting, suggesting year-round presence of these compounds. My results suggest that, while the effects of NSTs on Bt IRM may be inconsistent, the benefits of universally applying NSTs to Bt maize for soil pests may not be worth the ecological costs of doing so in all cases. / Doctor of Philosophy / About 75% of maize planted in the United States is encoded with genetic traits allowing them to manufacture insecticidal proteins which are toxic to key pests. These insecticidal proteins, known as "Bt toxins," are highly specific to targeted insects, and are virtually non-toxic all other animals and non-target insects. One target insect is the western corn rootworm (WCR), which feeds on and damages maize roots. In the past, WCR was controlled by applying millions of kilograms of chemical insecticides every year, at ever-increasing rates, to compensate for reduced effectiveness due to pest resistance. "Bt" plants, were released for commercial use in the late 1990s; they reduced the need for growers to apply chemical insecticides for managing key pests. The Environmental Protection Agency established regulations aiming to maintain the effectiveness of Bt technology, which they declared have "provided substantial human health, environmental, and economic benefit." This Insect Resistance Management (IRM) strategy, also known as the "refuge" strategy, is meant to preserve Bt-susceptible insects so they can pass on their Bt-susceptible genes to successive generations. The refuge strategy works by incorporating a certain percentage of non-Bt plants per every field of Bt plants; if enough insects survive on these "refuge" plants to outnumber "resistant" insects, population-wide Bt-susceptibility may be maintained. While this strategy has been effective for other key maize pests, it is failing for WCR, evidenced by WCR populations that have developed Bt-resistance. We know current refuge configurations aren't producing enough refuge-WCR to mix sufficiently with resistant WCR, likely due to insufficient refuge sizes. I wanted to know whether the refuge strategy could be improved, if increasing refuge proportions is not an option. Considering that Bt toxins are only effective against a narrow range of insects, seed manufacturers always coat seeds with an insecticide to protect seedlings against other insects. These coatings, or neonicotinoid seed treatments (NSTs), are included on nearly all seed, including those reserved for Bt refuges. I conducted two years of field trials to investigate whether removing NSTs from refuge seeds would improve WCR-IRM by providing an insecticide-free "refuge." My results suggest that removing NSTs may increase refuge beetle proportions, however my results also show that refuge plant proportions are simply too small to support large enough refuge-WCR populations to delay resistance, regardless of whether NSTs are present or not. While NSTs may provide extra comfort to growers at little additional cost, questions regarding their necessity at current use patterns have been raised. Several studies have shown inconsistent benefits, and others have shown longer-than-expected persistence in the environment, movement into streams and groundwater, and even alterations to insect and non-insect animal communities associated with their use. I conducted research comparing their relative effectiveness against WCR and non-WCR insect pests in fields of Bt maize. Additionally, I scouted for their residues in soil collected in field margins, forests buffering streams, and in water collected from agricultural ditches and waterways neighboring fields. I found that, while NSTs produced higher plant populations, they rarely resulted in greater yields. I detected neonicotinoid residues in soil matrices throughout the growing season, including prior to planting, suggesting year-round presence of these compounds. My results suggest that, while the effects of NSTs on Bt IRM may be inconsistent, the benefits of universally applying NSTs to Bt maize for soil pests may not be worth the ecological costs of doing so in all cases.

No description available.