A stretch of roughly two weeks of 90-degree plus weather with lots of humidity, occurring in the last half of July, has many people wondering and asking questions about corn pollination and development. Normally, it's the tail end of the critical period for corn. This year, because planting was delayed, it hit at the heart of pollination and fertilization for many fields. There are still fields yet to pollinate, especially in eastern Indiana. If you want to know where the younger, shorter corn is we talk about from day to day, head east of Indianapolis 30 miles or so, then drive north or south, take your pick, and it won't be long before you find those fields, either just pollinating or yet to pollinate.
To understand the total effect on this year's crop, go back to a near-record wet April, which delayed planting. May and June were also cool. Crops planted in May were often planted between storm systems, usually in soils that were slightly wetter than you would prefer. Now in mid-summer comes extreme heat and drought. How is corn being affected by this environment?
Obviously, Mother Nature is not being kind to this year's corn crop. The heat helps the late corn catch up, but temperatures higher than 86 degrees F actually cause stress, not more growth. That's why 86 degrees is the maximum allowed in the growing degree days formula that attempts to estimate how fast corn will develop during the season.
The fields which were planted earlier are shedding or did shed pollen in the heart of the heat wave. They are also silking. Extreme heat and drought can delay silk emergence. If the delay is too long, pollen may be gone before the silks emerge. Cases of this have not been reported so far, but it is a possibility in this kind of summer.
Leaves will roll up. That's actually a good thing. It is a defense mechanism of the corn plant to reduce the amount of water loss by evaporation from the leaves during the day. Some hybrids that don't roll their leaves, or don't roll them as much, may get sun-burnt. Use this as an opportunity to select hybrids with heat and drought stress for the future. Certainly don't knock down a hybrid just because the leaves roll up.
In extreme heat and drought, plants may run from optimum grain yield production to a survival mode. The plant's goal is to make as many kernels (with embryos, ie babies) as possible. If this happens expect the ears to start aborting kernels at the tip first. The plant is trying to make sure the remaining kernels become fully developed with a viable embryo.
For every three aborted kernels, yield my drop about one bushel per acre. Let's hope for cooler weather, but not too cool, plus rain so we end up with decent crops. (Nanda is director of genetics and technology for Seed Consultants, Inc. Reach him at Nanda@seedconsultants.com or 317-910-9876.