Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
Although corn is still undergoing grain fill in many Delaware fields, estimates of yield can be performed right now. The University of Kentucky has several methods for estimating yield, depending on the amount of information you have on hand: http://www2.ca.uky.edu/agcomm/pubs/agr/agr187/agr187.pdf. Since these methods involve counting kernels and rows on a few ears, you will need sharp eyes and the ability to keep your place.
Our variety trials in Georgetown were planted on May 2nd, so they have gone through the deluge of rainfall, as well as the droughty conditions during pollination. The earlier maturing varieties (110 days) were tasseling a little ahead of the later maturity (115 days) in the trials, during higher night and daytime temperatures. There could be many variables besides temperature that explain yield loss, including fertility, compaction and flooding. Actual ear size is determined during the vegetative stages, and also needs to be considered. However, by scouting fields right now, you can at least determine if you had some issues during the reproductive states. Tipback will be common (see the image below), where kernels were either not pollinated or aborted. Pollination occurs at the bottom of the ear first, so the most likely loss of kernels is at the tip.
Based off counting rows and kernels, we did observe a difference in potential yield between the earl, mid and late maturing varieties. The early and mid-maturities (110-112) both had yield estimates of 150-240 bu/acre, while the later maturity (115) was statistically higher at 185-290 bu/acre. Again, temperature alone does not explain the difference; it could also just be the hybrids. If weather is the issue, it is hard to control, but if it turns out fertility, disease or hybrid selection was the issue, we have a little more control when planning for next year.