By Alison Robertson, Department of Plant Pathology
When corn reaches black layer, the crop should be scouted for stalk and ear rots. Anthracnose stalk rot is apparent in many fields across the state and Diplodia ear rot has been reported.
The incidence of corn ear rot should be determined before harvest since ear rot diseases can reduce yield and quality of the corn harvest. Furthermore, some of the fungi that infect corn ears may produce mycotoxins, which are harmful, and can be fatal, to livestock.
At least 100 plants, scattered throughout the field, should be assessed. Look for visible symptoms of ear rot by stripping back the husks. For a description and photographs of ear rots you might encounter in the field see corn ear rots. If more than 10 percent of the ears have significant mold that is greater than 25 percent of the ear, the corn should be harvested in a timely manner and dried to below 15 percent moisture as quickly as possible to prevent further mold growth and, in some cases, mycotoxin accumulation.
For stalk rot, at least 100 plants, scattered throughout the field, should be assessed. Test stalk firmness at the lower internodes with thumb and forefinger. If more than 15 percent of the stalks are rotted, schedule for the earliest possible harvest because significant lodging is possible. Scout different hybrids and fields with different tillage, rotation, or fertilization histories separately.
Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases.