‘CL151’ a Clearfield long-grain rice cultivar, was released in 2008, based upon excellent agronomic characteristics, including excellent yield and moderately resistant rating for lodging. Further experience has indicated it’s susceptibility to lodging. Lodging can reduce harvest efficiency, yield, and cause grain quality loss. The purpose of this research was to evaluate multiple management practices such as nitrogen rates and timings, seeding rate, trinexapac-ethyl application, potassium, and fungicide application to mitigate lodging for CL151. The results of this research indicate that N rate and application timing largely influence lodging incidence and grain yield. Fungicide application decreased, but did not eliminate lodging, while potassium application did not impact lodging or grain yield. Seeding rate also has a significant impact on grain yield and lodging incidence. Trinexapac-ethyl also decreased lodging incidence, but negatively impacted grain yield which was most evident when applied at 48 g ha-1 and applied at PD +14d growth stage.

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.

Doctor of Philosophy / Department of Plant Pathology / Megan Kennelly / Large patch, caused by the fungus Rhizoctonia solani anastomosis group (AG) 2-2 LP, is the most common and severe disease of zoysiagrass (Zoysia spp). Despite the importance of this disease, few studies have examined pathogen biology, cultivar susceptibility, cultural controls, and chemical controls. The objectives of this dissertation were: (1) Characterize large patch isolates based on anastomosis pairing, in-vitro mycelial growth rates, nuclear counts, virulence, PCR, and amplified fragment length polymorphism (AFLP); (2) Determine the effects of cultivation (aerification, verticutting, and sand topdressing) on disease severity; (3) Evaluate different fall and spring applications of the fungicides flutolanil, azoxystrobin, and triticonazole; (4) Evaluate the susceptibility of fifteen new zoysiagrass germplasm lines from parental crosses including Z. japonica, Z. matrella, and Z. pacifica. All the R. solani isolates from large patch-infected zoysiagrass from Kansas belonged to AG 2-2 LP. Variations were observed among the isolates in their average number of nuclei per cell, mycelial growth rates and virulence. There was also variation in the amplified fragment length polymorphism (AFLP) DNA fingerprints, suggesting possible underlying genetic differences of biological significance among members of AG 2-2 LP. Cultivation did not affect soil moisture or temperature. Cultivation also did not reduce patch sizes, nor influence turf recovery rate from large patch. From 2009 to 2011, spring and fall N fertility was consistently associated with lower percentages of diseased turf in both cultivated and non-cultivated plots at Manhattan and Haysville. In general, two fall applications of fungicide did not reduce disease compared to one fall application. Fungicides applied in the fall when thatch temperatures ranged from 17.8oC to 23.2oC reduced disease compared to untreated controls. Early spring applications reduced disease compared to later spring applications. In germplasm screening studies, all progeny had similar disease levels compared to Meyer in the growth chamber, but only 6 consistently had disease levels as low as Meyer in the field. Growth chamber results did not correlate to field results.

No description available.

Differences in pea (Pisum sativum L.) and chickpea (Cicer arietinum L.) microbial compatibility and/ or their associated farming practices may influence root fungi of the following crop and affect the yield. The main objective of this research was to explain the difference in durum wheat (Triticum turgidum L.) yield the year after pea and chickpea crops through changes in the functional diversity of wheat root fungi. The effect of fungicides used on chickpea on the root fungi of a following durum wheat crop was studied using plate culture and pyrosequencing. Pyrosequencing detected more Fusarium spp. in the roots of durum wheat after fungicide-treated chickpea than in non-fungicide treated chickpea. Plate culture revealed that the functional groups of fungi responded differently to fungicide use in the field but the effect on total community was non-significant. Highly virulent pathogens were not affected, but antagonists were suppressed. More fungal antagonists were detected after the chickpea CDC Luna than CDC Vanguard. Fungal species responded differently to the use of fungicides in vitro, but the aggregate inhibition effect on antagonists and highly virulent pathogens was similar. The effect of chickpea vs. pea previous crop and different chickpea termination times on root fungi of a following durum wheat crop was studied. The abundance of Fusarium spp. increased after cultivation of both cultivars of chickpea as compared to pea according to pyrosequencing and was negatively correlated with durum yield. Plate culture analysis revealed that fungal antagonists were more prevalent after pea than both cultivars of chickpea and chickpea CDC Vanguard increased the abundance of highly virulent pathogens. The abundance of highly virulent pathogens in durum wheat roots was negatively correlated to durum yield. Early termination of chickpea did not change the community of culturable fungi in the roots of a following durum crop. It is noteworthy that Fusarium redolens was identified for the first time in Saskatchewan and its pathogenicity was confirmed on durum wheat, pea and chickpea. The classical method of root disease diagnostics in cereals is based on the examination of the subcrown internode. I evaluated the method by comparing the fungal communities associated with different subterranean organs of durum wheat. The fungal community of the subcrown internode was different from that of roots and crown, suggesting cautious use of this method.

No description available.