While drought slowed down or prevented many soybean diseases in 2012, it favored others. Loren Giesler, UNL plant pathologist, says that among the problems to watch for in 2013 are Fusarium wilt and root rot and charcoal rot. Additionally, soybean cyst nematode, a root parasite, is more apt in dry years to cut into yields.
Charcoal rot plays no favorites. It can affect corn and sorghum in addition to soybeans. It is caused by a fungus that survives persistently in soils, Giesler says. Infection generally occurs at soybean emergence and early seedling stages. But the infection lays dormant until plants are stressed by drought and heat in the reproductive stages, from flowering through mature pod formation.
WESTERWARD HO: University of Nebraska-Lincoln map shows how soybean cyst nematode has spread in Nebraska.
At these stages, infected soybeans can produce flat pods, be stunted and have reduced vigor. As the disease progresses, leaves will wilt and turn brown as the plant dies. "When plants are split open, a light gray to silver discoloration will be visible in the tap root and lower stem. Black specks will be visible in the tissue of the stem and tap root."
Giesler's suggestions: "Plant varieties that are not highly susceptible to charcoal rot. You may need to plant short-season varieties that mature before drought stress. In fields with a history of charcoal rot, rotate out of soybeans for two years to reduce the pathogen."
Due to dry conditions, you may see more Fusarium diseases this year, in both seedling soybeans and later as wilt around the seed-fill stage. Several species of the soilborne fungus can affect soybean roots and cause root rot and the late-season Fusarium wilt.
Giesler says the fungi can affect plants at any stage but infection is more likely to occur when plants are weakened by drought and other stresses.