Description and Symptoms
Plants affected by Diplodia stalk rot (Stenocarpella maydis) have shredded pith and die prematurely. Numerous black dots, about the size of a pinhead or smaller, can be observed in the lower internodes of the stalk. Under very wet conditions, a white mold may develop on the stalk surface. Infections occur through the crown, roots, mesocotyl, and lower nodes. Insects possibly carry the spores and introduce them into feeding wounds. Diplodia stalk rot is favored by dry conditions early in the season followed by warm, wetter conditions after silking. The disease is more prevalent in corn following corn. There are hybrids available with good resistance to Diplodia stalk rot. Rotation and tillage can reduce inoculum.
• Target fields that have had significant foliar disease.
• Target hybrids with low stalk rot and/or standability scores.
• Evaluate at least 100 plants per field (20 plants in 5 locations).
• Use the "push test" or the "pinch test" to determine standability. If 10 to 15 percent of plants lodge or are rotted, schedule an early harvest.
Fields in which greater than 10 percent of the plants have stalk and/or ear rots should be scheduled for early harvest. Identifying these diseases can also help with management for future years. Since stalk and ear rot pathogens survive in infested residue, rotation to a nonhost crop such as soybean may help reduce inoculum. Hybrid susceptibility to stalk and ear rots differs among hybrids.
Photo by Gary Munkvold