Drought, heat and potential effects on corn pollination
Coming into this spring, it looked like the drought was continuing unabated. However, during April and May, many parts of Nebraska, especially the eastern half of the state, received rain. The amounts were fairly generous, but should be viewed in terms of the accumulated deficit over 2012. These rains extended our planting season over four or more weeks, resulting in corn that's in multiple stages of development.
Sufficient plant water is critical to two aspects of the corn pollination process. Corn silks are largely composed of water; thus, a lack of plant water can affect their growth rate and timing of emergence. It takes one silk and one pollen grain to make a kernel of corn, and they need to function simultaneously. Also, corn that is rolled and wilted does lots less photosynthesis, leaving the developing ears short on sugars. The supply of sugars to the developing ovules/kernels from a week before to a week after pollination is critical to obtaining good kernel set on ears and to preventing kernel abortion. Consistent silking and the timing of silking with respect to pollen shed are critical.
The earliest planted corn, in most areas, is in the best shape. It had the advantage of developing with the best moisture/temperature conditions. Over the last few weeks, there have been areas of corn fields (those with the poorest soil resources, most compaction, slopes, etc.) that have rolled and suffered, while corn in better areas looked quite good. In most regions of the state, the corn recovered normal appearance by morning, and development continued fairly normally. Those stressed areas have struggled to silk, however, leading to pollination concerns.
While we have had some hot days, the night-time temperatures have cooled fairly well, resulting in much better pollen production this year than we had in 2012. And, we have not had the continual heat—it seems that every week we have had a little break in the high temperature. The issues this year will be with silking and silk timing.
Rainfall has been nearly absent for the last five weeks in many areas, leaving the crop extremely vulnerable. The later developing fields in most regions, rainfed corn in areas from south central Nebraska westward, and corn on less than ideal soil types are suffering severe stress. It is likely that kernel sets will be less than optimum and, where pollinated, will continue to suffer from kernel abortion during development, if this dry spell continues.
Nebraska’s irrigated corn continues to look quite good. With less heat damage, and adequate water and fertility, it is possible that yields will be even better than last year. Certainly, the range of development in some areas—from early to later planting—is a concern, and may leave some of the later developing fields in danger of later heat stress and early frost. However, the heat impacts have been much less in 2013 than in 2012.