August, 13, 2004
White Mold and Sudden Death Syndrome Widespread in Soybeans
White mold is caused by the fungus Sclerotinia sclerotiorum, which overwinters in the soil and plant residue as sclerotia. Sclerotia are dark, hard structures that look like mouse droppings. Infection of the soybeans occurs during flowering and is favored by cool temperatures and high soil moisture. Infected plants now have a mass of cottony white fungal mycelium and dark sclerotia on the stem. The herbicide Cobra and several fungicides are labeled for white mold, but these need to be applied during early flowering to be effective. There is nothing that can be done now to fields that have white mold. Tactics to reduce the problem in the future include; clean harvest equipment between fields or harvest white mold infected fields last, plant tolerant soybean varieties, and plant in wider rows.
Soybean sudden death syndrome is caused by the fungus Fusarium solani, which overwinters in soil and plant residue. Cool, wet conditions early in the growing season result in greater levels of plant infection. Symptoms usually do not show up until early August, when leaves show yellowing and death between the veins, with the veins remaining green. Often it occurs in fields where soybean cyst nematode is also present. It is sometimes confused with brown stem rot. To distinguish it from this disease, split the stem lengthwise. With brown stem rot the center (pith) of the stem is brown. With sudden death syndrome the pith is white but the rest of the stem is discolored. There is nothing that can be done now for fields with sudden death syndrome. It is common to see more of the disease in parts of the field that have poorer drainage or more soil compaction, such as near the edge of fields. Tactics to reduce the problem in the future include; plant more tolerant varieties, plant later, improve soil drainage, and use practices that reduce soybean cyst nematode. For more information about white mold and sudden death see“ Soybean Sclerotinia Stem Rot” (Pm-1519) at http://www.extension.iastate.edu/Publications/PM1731.pdf and the August 2 2004 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2004/8-2-2004/plantdis.html.
Late Summer Seeding of Forages
target date to have forages seeded by for the best chance of establishment in
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