In all my experience in working with corn, I have found it increasingly difficult over the last few years to get an accurate early August yield estimate of corn by counting rows and kernels. I attribute this difficulty to improved hybrids with robust genetic traits that allow them to add depth and weight to kernels long after the seed number has been set. That said, while I have some expectations for somewhat shorter than average ears in areas of the Cornbelt where we have experienced an excess of moisture, there is still reason to look forward to good yields.
Although we have focused on foliar disease in corn over the last few weeks, as we look towards harvest our final hurdles will be ear and kernel diseases and a potential for reduced stalk strength. Since both of these obstacles are related to hybrid characteristics as well as local weather conditions, it will be important to scout crops for potential problems. It’s still a bit early to test for stalk strength, but I can sometimes get an idea of the relative strength of a stand’s stalk strength the first week in August by pushing on the stalks to the breaking point and comparing it to what I find from several fields. Certainly any weakness I find using the standard means of testing is likely to translate into more serious problems closer to harvest.
The month of August is also a good time to evaluate the stand for ear and kernel rots. Diplodia is one of the more common rots that tends to show up early and can often be identified by the tell-tale early necrosis of the tissue surrounding the ear shank and lower husk. When the husk is stripped, the kernels may be covered with white or gray mycelium. Other rots include: Aspergillus (green or greenish-yellow), Gibberellin (redish in color), Fusarium (light pink to lavender), and Penicillium (green to bluish green). Most of these ear and kernel diseases tend to start at the tip of the ear and will require you to remove the husk to identify. Insect injury to the ear tip, or a foreshortened husk, is often a prelude to infection by these pathogens.
Although I have not yet had reports of these diseases come in from the Midwest, you should keep an ear to reports from your state as prevailing weather conditions can favor their development. Unfortunately the only remedies for ear and kernel diseases are either an early harvest or money spent drying the grain.