The critical period for avoiding stress in corn is during the two weeks before and after tassel emergence. The most important time is about eight days after tassels emerge.
Drought and heat stress around tassel emergence can affect pollination success and the number of kernels per ear.
How heat and temperature stress affects corn
Heat stress generally impacts corn less at pollination than water stress. It does not occur until the temperature exceeds 86 degrees Fahrenheit with dry soils or 92 degrees with adequate soil moisture and high humidity.
With high temperatures, corn plants require more energy to maintain themselves. Temperature and/or water stress before pollination can reduce the number of potential kernels per row, while a combination of temperature and water stress shortly after tassels emerge can cause exposed silks to desiccate and not be receptive to pollen.
When corn pollinates during high temperatures but is not under severe moisture stress, it accesses water deep in the soil profile through its roots. In this situation, the high temperatures’ direct impact on pollinating corn will likely be low. Instead, the amplified loss of soil moisture with the high temperatures will likely have a greater impact on the crop.
How water stress affects corn
Water stress before pollination affects the number of potential kernels per row. It can cause pollen shed and silk emergence to get out of sync, as water stress slows silk emergence and elongation while either speeding up pollen shed or not affecting it at all.
This can result in poor kernel set and ears with missing kernels. You can evaluate the kernel set’s success during and soon after pollination. Carefully unwrap husks and gently shake ears, as silks detach from the ear within a couple days after successful pollination.
Water stress after successful pollination is more common in Minnesota, and will likely be the main result of dry conditions. This causes the ear tips to lose kernels, but this can occur in other patterns on ears if water stress is intense enough or combined with other stresses.
Persistent dry conditions could affect the success of pollination, but losing kernels after pollination is the most likely result. The amount of kernel loss at this stage will depend on soil moisture levels and future rainfall.
Reviewed in 2021