Many eastern Corn Belt cornfields planted in mid-April when farmers got off to an early start have started to show symptoms of seedling blights, says Kiersten Wise, a Purdue Extension plant pathologist. Symptoms include uneven stands, stunted seedlings or reduced plant vigor. They can be caused by a number of scenarios, such as damage from cold temperatures, nutrient deficiencies, herbicide or anhydrous ammonia injury, wireworms or "wet feet," but also could be caused by seedling blights from fungi or fungal-like organisms.
"Seedling blights are prevalent when cool, wet soil conditions persist after planting," says Wise. "These conditions favor germination and infection by many of the organisms that cause soil-borne diseases. Cool, wet soils also slow plant growth and development and give diseases more time to infect and damage the seedling."
Most farmers planted into dry soils this year, but the mid- to late-April cool-down lowered soil temperature and slowed corn emergence. Rain in late April and early May likely increased the stress and allowed fungal organisms to infect and damage seedlings, Wise says.
Many different types of soil or seed fungi can cause seedling blights. They can cause seeds to rot after germination, either preventing emergence or stunting root development in plants that do emerge.
"Roots of infected plants may be brown and discolored and can be soft or mushy," Wise says. "Infected plants may also have brown discoloration on the mesocotyl."
Because it can be difficult for corn growers to determine the diseases in their fields, Wise says it's often necessary to submit a sample to a lab for accurate diagnosis.
But growers can assess the level of seedling blight damage in their fields. If enough of the stand is lost, fields might need to be replanted.
Before making replanting decisions, however, farmers need to think about replant timing, costs and expected yields. A free Purdue Extension publication provides more information about those considerations and offers a worksheet for growers to go through the process step by step.