How high heat disrupts corn pollination
Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen. While this is a bigger problem when humidity is low, it is apparent that it is happening this year, especially on hybrids that silk quite early relative to pollen shed. Even with dew points in the 70s, when temperatures reach the high 90s to the100s, the heat can still desiccate silks and reduce silk fertility.
Heat also affects pollen production and viability. First, heat over 95°F depresses pollen production. Continuous heat, over several days before and during pollen-shed, results in only a fraction of normal pollen being formed, probably because of the reduced sugar available. In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. It’s been shown (Herrero and Johnson, see Resources) that prolonged exposure to temperatures reduced the volume of pollen shed and dramatically reduced its viability.
For each kernel of grain to be produced, one silk needs to be fertilized by one pollen grain.
Kernel Set Reduced
The net result of all this is that we are seeing a number of situations where kernel set is reduced. Usually, we see problems in the worst areas of fields, or in hybrids that are slow to silk. This year problems are even occurring in the better field areas and in some hybrids that silk rapidly ahead of pollen shed.
Some hybrids have been more impacted than others. The timing of the days of extreme heat, timing of silking versus shed of particular hybrids, and other factors are involved. Just a day or two difference in flowering, or planting, or other factors can make a substantial difference in set. While pollination issues and reduced sets are more frequent in dryland areas, this year the heat is having an impact on irrigated fields as well. We will keep you posted as we learn more about the extent of the problem. Stress during pollination and silking could result in shorter ears, increased tip back and fewer kernels per ear. All of these contribute to less yield potential.
The Forecast and Likelihood of Continued Problems
According to Elwin Taylor, Iowa State University (ISU) climatologist, and Roger Elmore, ISU crop production agronomist, we are seeing an oscillating weather pattern where above normal temperatures east of the Continental Divide are likely to persist for up to six weeks. In the past, such patterns have been consistently associated with below trend corn yields for the U.S.