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Crop stress, stalk rots, and insect feeding in ear shanks are the major causes for dropped ears. High temperatures during silking (R1) may result in a weak shank attachment. Ears which are too heavy for the weak shank are likely to fall to the ground. Drought stress can result in ear shanks being cannibalized for carbohydrates to help grain fill which can lead to reduced shank strength and possible ear drop. Any disease causing premature plant death or tissue deterioration, such as Fusarium or Diplodia stalk rots, may result in shanks that are unable to hold the ear. Insects, such as European corn borer (Ostrinia nubilalis), (as evidenced by a hole and frass at the entry point) can tunnel into an ear shank, reducing its overall integrity. Ear drop problems can vary by planting date, soil type, corn product, and other agronomic factors. Therefore, problems with specific corn products may not occur every year and are affected by factors other than genetics.
A reduction in yield potential is the greatest concern from dropped ears. However, volunteer corn can be a potential concern in the next crop, particularly if the volunteer corn has resistance to glyphosate, glufosinate, or both. Volunteer corn can be an economic concern because of removal cost and the potential for yield loss from competition. To estimate potential yield loss prior to harvest, measure a 1/100th acre area in standing corn based on row width (Table 1). For example, 30-inch row corn to be harvested with an 8-row combine head, measure a distance of 21’ 10” in one row and move across the 8-row area counting the number of full- and smaller-size ears on the ground. Each full-size ear (around 3/4 lb each) represents about 1 bu/acre yield loss.1 Three smaller ears (about 1/2 lb each and 8 inches long) represents a loss of about 2 bu/acre.
Fields determined to be problematic for dropped ears and weak ear shanks should be harvested as soon as possible. Weak shanks can give way during harvest and result in lost ears. Combine operators should run the corn head as high as possible while adjusting ground and header speed for maximum ear retention. Operating the corn head higher than desired and leaving some lodged plants often results in more yield than trying to get every plant into the header. Future plans may need to be made to control potential volunteer corn. Also for subsequent seasons, planting corn with trait protection against above-ground insects, such as European corn borer can help reduce the risk of ear drop.