By Angie Peltier
Stalk rots can reduce yields. Stalk rots can decrease harvestable yield - literally leaving some ears on the ground. Corn plants are top-heavy and stalk rots increase the chance that plants will fall over (lodge) due to a combination of gravity and weather.
Conditions that favor stalk rots. Mid-season environmental conditions that favor kernel-set followed by conditions that favor plant stress increase the risk of stalk rot disease. Kernels place a very high demand on the plant for sugars. Stress reduces the rate of photosynthesis, thereby reducing the amount of sugars that the plant is able to produce. If unable to keep up with kernel sugar demand, the plant can rob sugars from other plant parts, including stalks. Many different stresses can reduce the rate of photosynthesis in the crop: too much or too little moisture; nutrient imbalances; leaf injury (ex.: hail, insects, diseases); high plant populations; and even long-periods of cloudy weather. Low stalk sugar content can increase susceptibility to stalk rot pathogens. Many of the fungi that cause common stalk rots in Illinois survive in corn residue and continuous corn and conservation tillage can increase the risk of stalk rot.
The hail that fell in the Monmouth area in June bruised stems, potentially providing a point-of-entry for stalk-rotting pathogens.
Scouting for lodging potential. Scouting for stalk rots is essential to minimize harvest losses. Begin scouting fields now or just before physiological maturity (black layer) when grain moisture is between 30 and 40 percent. Walk each field in a zigzag pattern, checking random plants from multiple areas of each field. To check a plant for stalk strength, either pinch it or push it. For the pinch test, pinch stalks toward the bottom, below the lowest node, checking for firmness. For the push test, at waist height push the plant 30 degrees from vertical to see if it returns to an upright position and the stalk remains intact (Figure). With either test, there is a significant lodging potential if 10 to 15 percent of the plants fail your particular test.
Harvesting first those fields with the greatest lodging potential reduces the chances of having to harvest lodged corn. Remember to drive slowly and harvest against the grain in lodged corn.
The next corn crop. Hybrids vary in their susceptibility to common stalk rots. Look into purchasing seed with good 'stalk rot', 'lodging', or 'standability' ratings.