Continued and excessive rainfall mixed with fluctuating temperatures offer excellent conditions for seedling diseases to appear in corn and soybean fields. University of Minnesota Extension Plant Pathologist Dean Malvick says now is a “good time to check fields for seedling disease problems and efficacy of seed treatments.”
Infection of seedlings before or after emergence can result in dead plants, rotted and discolored roots, stunted and discolored plants, and wilting. The problems often occur in patches in fields. Seedling infection can also lead to damage that may not fully develop until mid to late summer, as with Phytophthora root and stem rot and sudden death syndrome. Disease can cause serious damage, but it is just one of many stresses that seedlings are encountering. Careful scouting and diagnosis are often required to identify the cause of a problem.
Seedling diseases can begin soon after the seed is planted and can continue for several weeks. One clue is reduced emergence and other clues are seedling death, yellowing, or stunting. The problems may start when soil is very wet, although they may be delayed a week or more after wet conditions occurred. Infected plants often show symptoms that can be caused by multiple pathogens or other stress, and cannot be accurately diagnosed without laboratory testing. For example, tan/brown, soft-rot symptoms on roots and stems caused by Pythium and Phytophthora are very similar. Fresh, intact plants without extensive rotting are needed for diagnosis by the University of Minnesota Plant Disease Clinic or other diagnostic laboratories.
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