The 2012 growing season, with mid-season conditions that favored kernel set followed by conditions that favored plant stress, was ideal for the development of stalk rots, says University of Illinois extension educator Angie Peltier.
"Stalk rots increase lodging potential, which can decrease harvestable yield and leave much of it on the ground," she explains. "Corn plants are top-heavy, and stalk rots increase the chances that plants will fall over, or lodge, due to gravity or wind and weather events."
Many of the fungi that cause common stalk rots in Illinois survive in corn residue. Agricultural practices, such as continuously planting corn and conservation tillage, increase the amount of residue on the soil surface and the risk of stalk rot. Plants on high-nitrogen and low-potassium soils are at increased risk for the disease.
At the Northwestern Illinois Agricultural Research and Demonstration Center, north of Monmouth, early planting, residual soil moisture, and a 2-inch rain on June 30 resulted in successful pollination and the potential for large ears. After pollination, however, plants received only 0.09 inches of rain in July. This, along with temperatures that were more than 5 degrees above normal, led to water- and heat-stressed plants.
Kernels place a very high demand on the plant for sugars. Stress slows photosynthesis, thereby reducing the amount of sugars that the plant is able to produce.
Many different stresses can reduce the rate of photosynthesis in the crop: too much or too little moisture; nutrient imbalances; plant injury (for example, from hail, insects, diseases); excessive plant populations; and even long periods of cloudy weather. If the plant is unable to keep up with kernel sugar demand, it may rob sugars from stalk tissue, predisposing it to stalk rots.
Symptoms of anthracnose stalk rot were observed at NWIARDC, both inside and outside the stalks. External symptoms included shiny, black discoloration of the rind.