No. 8/May 15, 1998
Seedling Blight of Corn
We are receiving numerous reports of seedling blights on corn, especially corn planted in central Illinois around April 25. The major fungal pathogen isolated is Pythium, a very common seedling blight of both corn and soybeans.
Pythium thrives in cool and wet soils and is among the first plant pathogens active in the spring. Symptoms on corn roots include a soft rotting of the root tip on the seminal roots, a rotting of the mesocotyl (the attachment tissues between the seed and the base of the plant), or a general browning of large areas of the seminal roots.
Most corn seed is now treated with either Apron, Apron XL, or Allegiance to reduce losses to Pythium. However, in very wet soils or under other conditions that delay germination and emergence, the seed treatments may not last long enough to protect the seedling once it finally emerges. Designed to protect seedlings under "normal" conditions or when there areshort delays in emergence, seed treatments usually are effective for 10 to 14 days, depending on the soil environment. This year, because some of the corn seed has been in the soil for over 10 days, the seed treatments may not still be fully active. It is not a matter of the treatments' being ineffective but rather that the treatments were not designed to last 3 weeks. Each pesticide has a half-life during which some of the material is no longer fully active. The longer the delays in emergence, the more likely this will occur.
H. Walker Kirby (firstname.lastname@example.org. edu), Extension Plant Pathology,(217)333-8414