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Heat stressing corn crop in places, agronomists say

While yield loss from heat stress has the attention of the markets, opinions of Midwest agronomists vary on whether the crop is in danger.

For corn, yield loss occurs with unsuccessful pollination, and just after pollination when young kernels are setting. Also, under drought stress, kernel abortion can occur. Following that period, the weight of the kernel will decide yield potential, agronomists said.

Because more yield potential can be lost per day during pollination than any other growth stage, the concern of the heat in this week's weather forecast is not to be taken lightly, agronomists said.

Len Nelson, University of Nebraska professor of agronomy, said heat of this week's magnitude is never a good thing.

"Once we get past 86 degrees, the crop can go backwards, especially if it is without moisture," Nelson said. "In Nebraska, the rain-fed fields run out of moisture very rapidly in heat like this. Irrigation is just too expensive to continually pour on the crop."

With Nebraska's corn just starting to pollinate, the extreme heat is a big concern, Nelson said.

"I don't think anybody knows what level of damage will be done to this crop, but it's not going to be good," Nelson said. "Until we get past pollination and look at the ear formation, we won't know if we got hurt by it (heat stress) or not."

Corn yields in Minnesota will be significantly lowered from the potential yield that was developing, according to Dale Hicks, agronomist with the University of Minnesota Extension Service.

However, Hicks stated in a press release that it's too early to assess the effect weather conditions will have on corn yields in any one field. In Minnesota, corn is beginning to tassel now and ear shoots are also due to emerge in the next few days.

"It's too early to think about any action other than to hope for rainfall
soon," said Hicks.

For most of the state, corn plants are under some level of low moisture stress, according to the press release.

"The corn crop can best be described as extremely variable, even within
fields," Hicks said. "The parts of the fields with coarser textured [sandy]
soils have low water-holding capacity, and plants on those field areas are
extremely stunted; leaves tightly rolled, dying, and or dead, while other
areas in the same field have corn that is under stress but will fully
recover if rainfall occurs soon."

Hicks said the very high temperatures predicted for the next few days will
cause plant conditions on all parts of these fields to deteriorate quickly.

Bob Neilsen, Purdue University agronomist, said the heat stress to the Indiana corn and soybean crops is limited.

"There are exceptions, of course," Neilsen said. "However, we are going to come out of pollination fairly successfully. We went into this heat period with very good rainfall."

Neilsen said Indiana has had temperatures in the low 90's. With ample soil moisture and temperatures in the 90's, the stress has been minimal, he said.

"I was out in my corn plots all weekend, last night, and this morning, and the plants look good with pollen-shed occurring," Neilsen said.

While yield loss from heat stress has the attention of the markets, opinions of Midwest agronomists vary on whether the crop is in danger.

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