In Nebraska phytophthora diseases are mainly a concern on soybean, but pythium diseases can affect soybean, corn and sorghum. In fact, as many as 14 species of pythium can infect corn, some of which are also able to infect soybean and sorghum.
Systemic seed treatment fungicides that contain mefenoxam or metalaxyl provide short-term control of pythium diseases in seedlings. Currently, more than 90% of corn seed and about half of soybean seed are treated with fungicides, some of which are a combination of products that include one of these compounds. Unfortunately, there is no known plant resistance to pythium diseases and there are no rescue treatments that are economical for use in most Nebraska crops. Pythium damage can be minimized by improving drainage in some lower lying fields and planting in warmer soil.
Diagnosis of seedling diseases can be difficult because several of them cause similar symptoms, such as stunting and chlorosis (yellowing) of upper plant parts and discolored or rotted roots. You can look for an additional symptom often accompanying pythium infection by pulling gently on a discolored root. If the outer part of the root (cortex) slips off the root, leaving the white stele in the center, then pythium is likely the cause.
Tamra A. Jackson
Extension Plant Pathologist
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