Corn crops don't like the heat, either!

This week's heat wave is stressing crops in Winneshiek County and Northeast Iowa.

The latest statewide crop report showed corn production increased rapidly last week in Northeast Iowa due to warm and humid conditions. 58 percent of the corn crop is now tasseling—right around normal.  

Decorah Extension Office crop specialist Brian Lang says "This week's weather pattern will put us ahead of normal, but that's not really a good thing."

ISU Extension Corn Production Specialist Roger Elmore says maximum corn water use occurs at tasseling.  Current hybrids can handle the stress of hot temperatures better than the older hybrids did, but they still are stressed.

When stress occurs during pollination and silking, it could result in shorter ears, increased tip back and fewer kernels per ear. All of these contribute to less yield potential.

Elmore says the heat wave may have a double impact on the crop. The first is the increase in rolling of corn leaves in response to moisture deficiency.  The second is a decrease in yield.  Says Elmore, "When soil moisture is sufficient (as it in Northeast Iowa) the crop does not have a measurable yield response to one day of 93 degrees or above temperatures.  However, the fourth consecutive day with a maximum temperature of 93 degrees or above results in a one percent yield loss in addition to that computed from the leaf rolling. the fifth day results in an additional two percent loss; and the sixth day an additional four percent loss."

Lang sums up the situation by saying, "Corn production does better with cooler than normal July weather to avoid stress and extend plant development."