We like growers to plant their corn early, however, we want them to wait until the ground is ready and soil temperatures are 50 degrees and above. When you have a lot of area to cover, you have to plant when the weather will let you. But this can create opportunities for disease organisms and insects to attack the newly emerging plants. This year after planting, it turned cold and the seedling blights had their chance to invade. There have been several reports of seedling root-rot in corn fields. Some of the causes for seedling blights are as follows:
• Seedling diseases are favored by wet and cool soil conditions (50-55 F) after planting. Corn planted early or in no-till ground is more susceptible to these diseases. Recent cool and wet periods were ideal for the pathogens that cause seedling blights.
• The disease organisms that infect corn seedlings are species of Pythium, Fusarium and Rhizoctonia. These fungi over-winter in the soil or plant debris.
• These fungi can infect a substantial portion of the developing root system, including the mesocotyl which attaches the primary roots of the seed to the developing seedling, the primary or seminal roots.
• The seeds of infected plants start rotting and become mushy and the seedlings turn to brownish color. Survival of seedlings depends on healthy germinating seed. Seedlings should remain firm and mesocotyl should be white.
• Seedling blights are more severe in cold, wet soils, in low lying areas of the fields or in soils that have been compacted and remain wet for an extended period.
• Crop rotation may be helpful in reducing inoculum levels; however, some fungi can affect both corn and soybeans. Use of the best seed treatments available can help in defending the young seedlings and is strongly recommended if you are going to plant early since it can turn cold.