The frequent and plentiful rains throughout this season have helped to produce some very large ears and rather small roots in many healthy corn fields. The frequent rains resulted in either surface compaction or sidewall compaction at planting in some fields, which greatly restricted root growth. However, the rains masked that compaction and allowed those corn plants to produce large ears. Whether healthy corn or corn with root restrictions from compaction, the combination of large ears, shallow roots and a prolonged drydown period increases the risk for corn plants to fall over. Stalk strength is good in many fields, but we have observed some late outbreaks of diseases, such as Gray Leaf Spot. Diseases like this could compromise stalk strength.
As corn approaches black layer, it would be wise to walk through the fields and check stalk strength. You can do this by reaching out at shoulder height and grabbing corn stalks. Pull corn stalks about 18 inches off of center, release and the healthy plants will bounce back into a fully upright position. If the stalks break, or fall over, then stalk strength is weakened and corn needs to be harvested sooner. Repeat this process several times in a field and avoid end rows or areas where high traffic normally occurs. We would expect those areas to have more compaction and be more compromised than the majority of the field.
(Source – http://www.farms.com/news/heavy-ears-and-shallow-roots-at-corn-harvest-66387.aspx)