Wallaces Farmer

Forecasters warn hot temperatures and minimal rain will stress corn in its critical stage of pollinating.

Rod Swoboda

July 7, 2020

4 Min Read
Closeup of tassels on corn
SILKS EMERGING: As of July 5, the weekly survey shows 5% of Iowa’s corn crop is silking, a week ahead of last year but two days behind the five-year average. Rod Swoboda

Hot, sticky weather is greeting the corn crop in Iowa and the Midwest this week, as corn enters the critical pollination stage. Corn pollinates better when you get normal rains and normal temperatures. These above-normal temperatures with minimal rainfall will stress the corn if this hot, dry weather continues over the next couple of weeks.

“Having above-normal daytime temperatures isn’t the only thing that can stress a corn crop,” says Dennis Todey, climatologist with USDA’s Midwest Climate Hub at Ames. “Overnight temperatures have been consistently above normal as well due to very high dewpoints. In June, we had warm weather and relatively dry conditions for the Midwest. In July, we’re seeing hot weather and higher humidity. However, areas that have received recent rainfall and have reserve soil moisture will be able to manage the heat.”

Highest temps mid- to late July

The highest temperatures on average typically occur around the second and third weeks of July throughout much of the Corn Belt, Todey says.

“Last week Iowa had above-normal temperatures across the state continuing the recent trend of rapid crop development. Some corn is now tasseling across Iowa,” notes Iowa Secretary of Agriculture Mike Naig. “Short-term forecasts favor warm temperatures with dry weather across much of the state. Some pockets of Iowa are already experiencing moisture stress from the dry weather, as crops and pastures are feeling the heat, although much of Iowa continues to have ample subsoil moisture.”

The complete weekly Iowa Crop Progress and Condition report is available on USDA’s site at nass.usda.gov/ia.

Crop report

Little to no rain for much of Iowa allowed farmers six days suitable for fieldwork during the week ending July 5, according to the latest weekly survey by USDA’s National Ag Statistics Service. Fieldwork activities included applying fertilizer, spraying, harvesting hay and hauling grain.

As a statewide average, topsoil moisture is rated 3% very short, 19% short, 76% adequate and 2% surplus. Subsoil moisture is rated 2% very short, 14% short, 81% adequate and 3% surplus.

There were reports of corn silking across much of the state, with an average of 5%, almost one week ahead of the previous year but two days behind the five-year average. Corn condition is rated 85% good-to-excellent. Soybean blooming reached 37% of the crop, almost two weeks ahead of last year and six days ahead of average. There were scattered reports of soybeans beginning to set pods. Soybean condition is rated 84% good-to-excellent.

Iowa’s oat crop that’s headed progressed to 94%, five days ahead of last year. Oats turning color reached 36%, four days ahead of last year but two days behind the average. Oat condition rated 85% good-to-excellent.

Alfalfa hay second cutting reached 38%, 11 days ahead of last year and two days ahead of the average. Hay condition rated 77% good-to-excellent. Pasture condition rated 69% good-to-excellent. There were reports of heat stress affecting cattle, as well as continuing issues of pinkeye for cow-calf producers.

Weather summary

Unseasonably warm and dry conditions persisted through the end of June into early July across the majority of Iowa. “The warmest conditions were found in eastern Iowa with temperatures of up to 6 degrees warmer than normal,” says Justin Glisan, state climatologist at the Iowa Department of Agriculture. “The statewide average temperature for the seven days ending July 5 was 77.4 degrees F, 4.3 degrees above normal.”

Measurable rain was reported across most of Iowa, though only extreme southeast Iowa reported above-normal totals for the week. Portions of north-central Iowa reported deficits of up to an inch.

Weekly rainfall totals ranged from no accumulation at multiple stations in north-central Iowa to 3.37 inches at Keokuk Lock and Dam (Lee County). The statewide weekly average rainfall was 0.35 inch, while normal is 1.09 inches. Bellevue Lock and Dam (Jackson County) reported the week’s high temperature of 94 degrees on the July 3, which was 9 degrees above normal. Mapleton (Monona County) reported the week’s low temperature of 61 degrees on July 4, 1 degree below normal.

U.S. corn, soybean ratings drop

Looking at the national crop picture, USDA’s weekly crop progress report shows a slight decline in corn ratings and a slowdown in development. USDA estimates the corn crop moved from 73% in the good-to-excellent category a week ago to 71% in that category as of July 5. The survey shows 10% of the nation’s corn is now in silking stage, a little behind the five-year average of 16%.

USDA’s survey shows 31% of the nation’s soybean crop is now blooming ahead of the five-year average of 24% for this date and well ahead of 2019’s pace of 8%. And 2% of the crop is now setting pods, versus 1% at the same time last year and 4% for the prior five-year average. USDA estimates the current soybean crop rating at 71% in good-to-excellent category, the same as a week ago.

About the Author(s)

Rod Swoboda

Rod Swoboda is a former editor of Wallaces Farmer and is now retired.

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