Spring rains bring root rots to Missouri field crops

  • Published: Wednesday, June 23, 2021

COLUMBIA, Mo. – Frequent spring rains in Missouri set the stage for seedling and root rotting diseases that can lower yields.

Pythium species usually infect the roots of corn, soybean and wheat, especially in the northern half of the state, says University of Missouri Extension plant pathologist Kaitlyn Bissonnette.

Infection by Pythium favors cool, wet weather, which Missouri saw in large amounts in April and May. As soil temperatures rise, infection slows and eventually ends, says Peng Tian, director of the MU Plant Diagnostic Clinic.

Stand loss from seedling diseases in corn and soybean is concerning, says Bissonnette. Fields may have seed rotting in the ground or young plants that emerged but started to die back after several weeks of slow growth.

Even with a seed treatment, prolonged exposure to cool, moist soils can still result in seedling disease, especially when disease pressure is high, she says.

Farmers may consider replanting when stand loss occurs, especially in soybean. An MU Extension guide to replant decisions, written by soybean specialist Bill Wiebold and economist Ray Massey, makes these calls easier with spreadsheets to estimate dollar gain or loss from replanting. The guide, “Corn and Soybean Replant Decisions,” is available for free download at extension.missouri.edu/g4091.

Winter wheat production has not been left out of the game this year when it comes to root rotting diseases, says Bissonnette. Some winter wheat fields have quickly begun to show symptoms of stunting and white heads in patches or in strips across the field.

Upon closer examination, roots showed signs of not only Pythium species but also Rhizoctonia and Fusarium, Tian says.

Since these diseases infected plants during the grain fill period, affected areas will produce little to no grain. Infection risk will decrease as temperatures rise and soils dry. Because these diseases are in the soil, it is unlikely infection will move to other fields before harvest. Field assessments should rely on percentage of acreage affected and severity of root rot symptoms.

If you suspect seedling diseases in corn or soybean or fields, or root rots in your wheat field, contact the MU Plant Diagnostic Clinic at [email protected] or 573-882-3019.

Photos available:

Soybean seedlings, one rotten and one slow to emerge, from a field with extensive stand loss due to seedling disease. Photo by Kaitlyn Bissonnette.

Wheat field with symptoms of root rot. Blank heads and early maturing plants in patches appear. Photo by Kaitlyn Bissonnette.

Symptoms of sharp eyespot, caused by Ceratobasidium cereale (Rhizoctonia cerealis), at the base of a wheat plant. Photo by Kaitlyn Bissonnette.

Writer: Linda Geist

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Kaitlyn Bissonnette

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