Now is the time to start assessing corn stands, says Iowa State University plant pathologist Alison Robertson.
Doing stand counts involves more than just counting the number of seedlings that have emerged, Robertson says. Seedling health should also be assessed.
Iowa State Extension field agronomists Virgil Schmitt and Mark Carlton have reported that seedling rots are prevalent in southeast Iowa.
Rotted seedlings may result from fungal infections, anhydrous ammonia injury, wireworms and cold injury, Robertson adds. Seedling susceptibility to fungal infection increases the longer the seed sits in the ground, and the more stress germinating corn undergoes. Wet and cool soil conditions (less than 55 F) predispose seedlings to infection by a number of fungi.
Corn germinates well at soil temperatures above 68 F. When soil temperatures are below 55 F, germination is greatly retarded. This growing season, soil temperatures across much of the state were above 55 F from April 13 through April 23, when temperatures dropped below 55 F for two (central and northwest Iowa) to five (southeast Iowa) days.
"As you evaluate corn stands, remember to dig up seedlings and check for symptoms of seed rots and seedling blights," Robertson says. "This will also give you an opportunity to evaluate the effectiveness of the seed treatment that was applied to the seed planted.
"If you have significant seedling rot, you may have to replant."