Just what the corn grower ordered

Rain, heat make the crops grow

By Jean Caspers-Simmet

Northern Iowa crops progressed rapidly in the past couple of weeks thanks to plenty of moisture and heat.

Hot, humid conditions also brought storms with isolated areas of hail, high winds and heavy rain.


The Iowa Department of Agriculture and Land Stewardship's July 7 crop report noted some corn grew 16 inches in the preceding week.

"It amazes me each year to see how rapidly corn grows, and I think this year it is even faster than normal,'' said Joel DeJong, Iowa State University Extension crops field specialist in LeMars. "Elwynn Taylor, ISU Extension climatologist, has said that 92 degrees, not 86 degrees, is the peak growing temperature for corn if no other stresses like moisture are occurring. As I watched these fields develop in recent weeks, I think that is probably true.''

"The corn has been growing fast, but it better be growing fast," said George Cummins, ISU Extension crops field specialist in Charles City.

Northern Iowa is about 100 heat units behind for May 1 to July 6, Cummins said. On top of that, a lot of corn was planted late.

"We like to see the reproductive phase of tasseling and silking taking place between July 20 and Aug. 1,'' Cummins said. "A lot of corn is going to be pushing that Aug. 1 date this year.''

Warm weather and moisture in late June have been excellent for rapid corn development.

"I say if it's difficult to sleep at night without air conditioning, it's ideal for corn growth and development,'' Cummins said. "We certainly had that kind of weather.''

Brian Lang, ISU Extension field specialist for crops in Decorah, said crops are doing OK in his area.


"We've had spotty hail all over the place, but overall corn and beans look fine,'' Lang said. "They're a little behind, but then most were planted behind normal this year.''

Crop specialists said farmers should look for corn rootworm damage. Larvae have been feeding since early June and adults are emerging.

First-generation bean-leaf beetles have started emerging and farmers should be scouting. Those spotting soybean mosaic virus should treat fields as soon as beetles emerge. For physical damage control, scout first-generation beetles to determine if the second generation needs to be treated.

While scouting for bean-leaf beetles, farmers should look for soybean aphids. A field near Decorah where Lang has a soybean aphid research plot was at threshold level last week.

"You have to scout,'' Lang said. "There could be other fields at threshold level, but that doesn't mean all fields are. Neighboring fields to our plot have very low aphid levels.''

Now is also a good time to scout for soybean cyst nematode. If there are areas with yellow stunted soybean plants, look for evidence of the pest on roots.

"If you have SCN, you'll never get rid of it, but you can reduce the problem by managing for it,'' Lang said.

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