Charlene, the waitress down at the Chat 'n Chew Cafe, tells me that the boys have complaining royally the past couple of weeks about the poor manner in which their corn crops are filling the ears. It seems that pollination didn't go so well and quite a few ears have a lot of blanks up and down the cob where kernels should be. Incomplete kernel set in corn can be caused by a number of different things, but let's concentrate on the likely culprits in 1995.
The lion's share of the state's corn crop pollinated during some fairly hot days in late July and early August. While I am still not convinced that the heat by itself did much damage to corn pollen, the excessive temperatures could easily have slowed silk elongation and/or decreased silk receptivity due to rather large evapotranspiration losses by the plant. Temperatures in the mid- to high 90's can cause short-term moisture deficits in corn even if soil moisture is technically adequate for crop growth. For more information on drought and heat stress on pollination, see my article in P&C Newsletter, 7/14/95.
A lot of folks reported corn rootworm beetles or Japanese beetles clipping silks during pollination (R. Edwards' article in P&C Newsletter, 7/28/95). In some fields, the clipping by itself probably caused the incomplete pollination and subsequent incomplete kernel set. In other fields, the combination of silk clipping and slow silk elongation probably worked together to cause the problem.
In addition to pollination problems, some of the incomplete kernel set being observed may be caused by kernel abortion due to severe stresses immediately following pollination. Examples of such plant stress include cloudy weather, severe heat/drought stress, severe leaf disease (e.g., grey leaf spot), severe leaf defoliation due to hail, and severe nitrogen deficiency.
Usually, tip kernels are most likely to abort because they are the youngest on the ear. Kernel abortion occurs most easily during the blister and early milk stages of grain development (grain fill stages explained in P&C Newsletter, 7/28/95). You can distinguish between aborted kernels and unpollinated ovules by the fact that aborted kernels will be visible as shrunken, shriveled remnants while unpollinated ovules will simply be blank.
For more information, see my article on stress during grain fill in the P&C Newsletter, 8/4/95.