Corn across the Dakotas and Minnesota looks much better than elsewhere in the Cornbelt, but we're in a critical period. Water and heat stress two weeks before and two weeks after tassel emergence can can affect the success of pollination and the number of kernels per ear, says Jeff Coulter, University of Minnesota Extension agronomist.
The most important period is eight days after tassel emergence.
Heat stress generally has less of an impact on corn at pollination than water stress, and does not occur until temperatures exceed 86 degrees F with dry soils, or 92 degrees F with adequate soil moisture and high humidity, he says. With high temperatures, corn plants require more energy to maintain themselves.
What can happen
Temperature and/or water stress before pollination reduces the number of potential kernels per row, while combined temperature and water stress shortly after tassels emerge can cause exposed silks to desiccate and not be receptive to pollen.
Water stress before pollination can also cause silk emergence and elongation to slow while hastening or not affecting pollen shed, resulting a mismatch between pollen shed and silk emergence. This can result in poor kernel set and ears with missing kernels.
Water stress following successful pollination shows up as a loss of kernels at the tips of ears, but kernel loss can occur in other patterns on ears if water stress is intense enough or combined with other stresses.
How to check now
The success of kernel set can be evaluated throughout and soon after the pollination period by carefully unwrapping husks and gently shaking ears, as silks detach from the ear within a couple days after successful pollination, Coulter says.
"Current dry conditions …will more likely result in the loss of kernels following pollination. This loss of kernels following successful pollination could be a little greater than normal this year, but will depend on current soil moisture levels and future rainfall."
Source: U of M Extension