Hot & dry: Stress on the corn crop escalates
However, if the drought continues and crop condition worsens, this estimate would quickly become outdated. For comparison, statewide grain yield for the drought years 1988 and 1991 were 31% and 27% below trend yield, respectively.
Much of the state's corn crop will enter the critical pollination phase over the next two or three weeks. Continued lack of adequate rainfall during this period will place undue stress on the crop. Forecast excessive heat during the same time period will only amplify the stress; resulting in delayed silk emergence, premature pollen shed, tassels failing to emerge from whorls, potentially inviable silks or pollen, poor synchrony between exposure of silks and availability of pollen, incomplete pollination success, or abortion of newly developing kernels. Yield loss per day during pollination due to severe stress is often estimated to be 5 to 10 percent. Yield loss for any given field could easily approach 100 percent with continued drought/heat stress due to complete failure of the pollination process.
Assessing Drought Effects on Yield
Growers who elect not to abandon drought-stressed fields prior to pollination will be wanting to assess the yield potential of their fields prior to harvest in order to estimate the potential loss of net income and/or to revise their grain marketing strategies for this fall. Assessing yield potential for an individual field cannot be done with any accuracy prior to pollination, but rather depends on assessing kernel set later in the grain filling period. The challenge with assessing yield potential of drought-stressed fields is that of obtaining ear samples that adequately captures the variability of the yield potential throughout a damaged field.
Immediately following pollination
Given the severity of the drought stress in some fields, growers may want to assess the success of pollination itself within the first week after pollen shed by sampling ears and conducting the so-called "ear shake" test. This assessment simply gauges the degree to which pollen successfully fertilized the ovules on the ears via the silks, but does not predict the risk of kernel abortion in the few weeks following pollination or estimate grain yield. However, the test will at least give you an idea whether pollination was an absolute failure or was moderately successful. Unfortunately, there will be fields that appear to be only moderately stressed according to windshield surveys that, in fact, are severely stressed to the point that pollination will be a near or total failure. Better to find out the bad news soon rather than be totally shocked later in the season.