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July 8, 2020

Worrisome Forecast for Corn in Eastern Corn Belt

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

The forecast is worrisome especially for the eastern Corn Belt. The corn condition is still a little better than average, but if the forecast verifies, the corn yield estimates will probably decline on a weekly basis going forward. How much it declines will depend on the weather of course.

There were some showers around the Midwest last week especially in the far northwestern Corn Belt, but for the most part it was hotter than normal and dryer than normal. All eyes are on the forecast for this week which is also generally hot and dry. There will be widespread 90's across the Midwest this week with the hotter temperatures later in the week. There are improved chances for rainfall later in the week, but most of the rainfall this week will be in the northwestern Corn Belt.

Nighttime temperatures are also forecasted to be quite warm, which can result in increased levels of what is called "dark respiration." When nighttime temperatures stay above 72-73-74 degrees, the corn plant must expend energy to maintain cellular functions instead of "resting" at night. This is more important when the corn is filling kernels because it uses some of its energy to maintain cellular function instead of using that energy to fill the kernels.

The soil moisture declined last week and it's going to decline a more this week. The driest soils are now in the eastern Corn Belt states of Indiana, Ohio, Illinois, and Michigan. There are also dry pockets in the western states of Kansas, Nebraska, and western Iowa.

The condition of the crop declined 2% last week to 71% rated good to excellent. The corn silking is now 10% compared to 7% last year and 16% average. Later this week, corn pollination will accelerate across most of the Midwest and it will continue for the next 2-3 weeks. Pollination is actually a little slow compared to average which I attribute to the cold snap we had in mid-May.

Moisture Stress and Corn Pollination - There are always a lot of questions concerning the type of weather that can negatively impact corn pollination. If a corn plant has adequate soil moisture, temperatures in the mid-90's alone probably would not cause too many pollination problems. If the temperatures get extreme, let's say 100 degrees or hotter, there could be pollination problems even if there is adequate soil moisture.

If a corn plant is already suffering moisture stress, temperatures of 90 degrees could cause pollination problems. If a corn plant is already suffering moisture stress and then there are temperatures of 100 degrees or hotter - that could be catastrophic.

When corn plants are under moisture stress, the timing of silking and pollen shed may be out of sync, which is called the "nick." The silks grow slower if the plant is under moisture stress whereas the timing of the pollen shed is not affected as much by moisture stress. If there is significant moisture stress, the pollen shed may end before all the silks emerge resulting in poor nick and poor pollination.

Under extreme drought, it is possible that nearly all of the pollen grains will have been released from the tassels by the time most of the silks have emerged. This results in a few kernels being produced on an ear rather than the normal 600. Most of the yield loss from poor nick is permanent because corn has little capacity to compensate for small seed number by increasing seed size - even if adequate precipitation returns after pollination.

Continued moisture stress after pollination can result the abortion of kernels at the tip of the ear, which is called tip-back. Significant moisture stress prior to pollination when the ear size is being determined, can result in shorter than normal ears with fewer than normal rows of kernels.