The development of sudden death syndrome (SDS) in Iowa soybean production has progressively increased since being first observed in 1993. Movement of the disease from the Southern United States has brought along with it the agronomic recommendations for management of SDS, however these recommendations have not been investigated in Iowa. This research is part of a number of studies focused on developing agronomic recommendations for the management of SDS in Iowa. The particular studies in this work are focused on the management of the causal organism of SDS Fusarium virguliforme. Chapter two is a literature review of past SDS research. The research reported in this thesis is divided into three manuscripts encompassing chapters three, four and five.

Chapter three addresses the response of soybean seed quality to sudden death syndrome disease development. Early planting in Iowa is important to maximize soybean yield, however environmental conditions such as cold soil temperatures observed with early planting are also conducive for infection of F. virguliforme. Seed of reduced quality has been observed to have troubles germinating and emerging from cold soil conditions. The resulting combination of reduced seed quality and prolonged emergence could allow for increased pathogen infection resulting in greater SDS disease symptoms and soybean yield loss. Therefore our objective was to determine the impact of soybean seed quality on SDS disease severity.

Chapter four addresses the effect of planting depth by planting date interaction on the development of SDS symptoms and severity. Previous research has shown early planted soybean express greater foliar symptoms of SDS. This response is believed to the result of cool soil temperatures observed during early planting conditions allowing for increased infection of F. virguliforme. However no research has concluded these results in a field setting. To our knowledge no previous research has been published studying the interaction of planting date and planting depth on the development of SDS symptoms and disease severity.

Chapter five evaluates the use of various fungicide seed treatments on the development of sudden death syndrome. Current management practices to prevent infection of soilborne pathogens occurring at planting include host plant resistance and use of fungicide seed treatments. Fungicide seed treatments have shown to increase plant stands and reduce infection of early season soilborne pathogens and diseases. Research of the literature has shown no published results observing if fungicide seed treatments do in fact impact F. virguliforme infection and SDS symptomlogy. Therefore our objective of this study was to measure the impact of seed treatment against the onset of F. virguliforme.

The three manuscripts contained in this thesis are the first to attempt to understand the effects of soybean seed quality, planting depth interactions, and fungicide seed treatments in the presence of F. virguliforme and the resulting progression of SDS disease symptoms on soybean yield. From the information provided in this thesis, recommendations for the management of F. virguliforme and SDS can be provided to producers in Iowa and the upper Midwest. This thesis provides a reference point for further investigation of F. virguliforme and SDS research related to seed quality, planting depth, and fungicide seed treatments.