Red corn leaves and stalksCorn plants in many fields are turning red and that is not a good sign. The red color is coming from a build-up of sugar in the leaves and stalks. The build-up of sugar is a result of too few kernels being developed on the ears. 
During the process of plant growth and development, a plant produces sugar through photosynthesis. That sugar is used to build new plant parts, to fuel growth and development, and to help produce seeds. Each plant will produce the sugar necessary for expected yields. When those expected yields don't happen, the sugars remain in the leaves and stalks and, eventually, turn the plants red to reddish-purple. To paraphrase a poor pun from one of my colleagues, "red corn plants are a red flag that seed development has gone wrong."
Red corn leaves and stalksThis season, a lot of corn in central Kentucky reached full height, or close to it and looked relatively healthy from the road. But, much of that corn tried to pollinate when temperatures were above 100 degrees during the day for about seven consecutive days. Heat stress during pollination was the primary culprit of red leaves in these fields. In western Kentucky, much of the corn made it through pollination, but the kernels did not make it through early seed set and aborted. In those fields, kernel abortion led to the red leaves. In either case, poor pollination or kernel abortion, the producer is left with low yields.