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Occurrence and Distribution of Soybean Sudden Death Syndrome in Iowa

Soybean sudden death syndrome (SDS), caused by blue-pigmented, slow-growing strains of Fusarium solani, is a disease recently reported in Iowa. In 1994 and 1995 the geographic distribution and status of the disease was determined at the state, local, and field levels. An east-to-west decreasing trend of SDS prevalence was found at the state level. No SDS was found in the western part of Iowa. The disease was found in commercial production fields in 4 Iowa crop reporting districts — central, north-central, east-central, and southeastern — with the greatest severity and the most frequent occurrence of SDS found in the east-central district. In two counties along the Mississippi River, disease prevalence was high; more than 50% of soybean fields had SDS in locations where surveys were conducted. Intensive surveys on a local scale were conducted in areas around the fields where the disease was first noticed. In areas where disease prevalence was low, all detected infested fields belonged to the same owners. In areas where disease prevalence was high, no such pattern was found. Disease incidence varied from field to field. Information on SDS occurrence at different geographic scales serves as baseline information to monitor the future development of the disease in Iowa.