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Weather stress is a key factor when evaluating the cause of corn ear drop. Generally, the problem is most severe when extreme high temperatures occur at silking (R1 growth stage). High temperatures during silking can result in a weak shank attachment. Plants may recover from initial stress at early R1 and produce normal grain on the upper part of the ear. However, this will produce more weight on the ear tip than the weakened shank may be able to support. The result may be ear drop shortly before normal harvest would occur (Figure 1).
Drought stress and premature plant death affects shank strength. Ear shanks can be cannibalized for carbohydrates by the ear, leading to shank deterioration and eventual ear drop. Fungal infections, which develop more quickly at higher temperatures, also may lead to shank deterioration.
Insects, such as European corn borer, can tunnel into a corn shank and weaken it. A hole and frass may be found at the entry point.
Ear drop problems can vary by planting date, soil type, corn product, and other agronomic factors. Therefore, problems with specific corn products will not occur every year and are affected by factors other than genetics alone.
Preharvest losses due to ear drop can usually be estimated in less than 15 minutes. Begin by measuring the required distance behind the combine. The length of corn rows equivalent to 1/100 acre will vary by row width and number of rows covered by the corn head (Table 1). Each full-size ear (about 3/4 lb each) represents about 1 bushel/acre loss and finding 3 small ears (about 1/2 lb each) represents about 2 bushels/acre loss.1
The first step is thorough scouting. Growers should scout fields looking for weak shank attachment problems. What you see from the pickup is not indicative to what is occurring beyond the first few rows.
Problem fields should be harvested as soon as possible. Where ear drop is a problem, growers 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. If loss is significant, plans should be made to reduce the amount of potential volunteer corn. Also, planting corn with trait protection against certain above-ground insects, can help reduce the risk of ear drop by providing protection against shank-boring insects.
Sources: 1 Shay, C., L. Ellis, and W. Hires. Measuring and reducing corn harvest losses. Department of Agricultural Engineering. University of Missouri Extension. Pub G1290. (verified 8/14/14). 140814010101