Root Rots and Stalk Strength

Many growers are beginning to wonder about the standability of their corn crop this fall, particularly if there will be challenges in getting the crop out of the field. With the type of season most of us have experienced this year, we might expect such problems to occur since there are several weather related factors that can affect stalk strength and root rots.

Stalk strength is directly related to carbohydrate accumulation and utilization. Conditions which favor carbon exchange from the atmosphere (adequate sunlight, adequate soil water, adequate levels of N, P, & K) will contribute to good standability. Cloudy skies, drought stress, and a deficiency of a nutrient brought about by restricted root growth can be expected to reduce standability. Something we may not think about that is directly related to stalk strength is the demand that the ear and kernels put on the stalk for nutrients.  Recall that in order to fill the ear the plant will scavenge carbohydrates from stalk, leaf, and roots to complete the task. This process starts soon after pollination and won’t be complete until black layer.

Many hybrids, especially those with a characteristic large ear, are quite efficient at pulling photosynthates out of the stalk. For these hybrids the tug-of-war between stalk and ear will be heavily weighted in favor of the ear.  If you have planted a hybrid with a particularly susceptible stalk you should perhaps be planning on an early harvest of those fields.

Of course root and stem diseases also contribute to weak stalks. Not only do diseases reduce overall plant health, thereby reducing overall plant carbohydrate pools, but they can break down cell walls, weakening the plant structure. Early ear drop and ear loss is quite possible with diplodia, a disease that often starts at the shank and expands towards the tip of the ear and then into the stalk. With the wet season so many growers experienced in June and early July, diplodia is expected to be present in many fields throughout the Midwest.

Scouting fields now is an ideal time to test for stalk strength. Recommended procedures include pinching the stalk between thumb and forefinger to determine if the stalk collapses. Another procedure is to push stalks over about 30 to 40 degrees. If they snap or break, it suggests there may be problems with that field. While scouting the whole field is the recommended practice, if you are short on time you may confine such tests to known weak spots in the field to get an estimate of the worst you might be facing at harvest.