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Serving: IA
Drought conditions have reduced the yield potential on this Clay County, Iowa, corn-on-corn field. Paul Kassel
DRY TIMES: Drought conditions have reduced the yield potential on this Clay County, Iowa, corn-on-corn field.

Drought impact deepens across Iowa

This year is the 11th-driest on record for Iowa, with rainfall averaging 10 inches below normal.

Despite some spotty light showers this week, drought conditions are persisting in western Iowa and have expanded further into central and north-central Iowa. Common issues reported by Iowa State University Extension field agronomists stationed around the state include poor grain fill and fast reproductive development in corn. Also, there are increasing disease pressure in some cornfields, concerns regarding off-target movement of dicamba, and a variety of insect issues. The insect pests include corn rootworms, potato leafhoppers, Japanese beetles, two-spotted spider mites and white flies.

Here are reports from ISU Extension field agronomists on what’s happening in different regions across the state:

 Northwest Iowa,  Paul Kassel (Region 2). “Abnormally dry conditions, moderate drought and severe drought cover most of the area that I serve, according to the July 30 U.S. Drought monitor. The area of severe drought is mostly confined to Sac County. Crop conditions have deteriorated because of this lack of rainfall. Many areas in Sac, Clay, Buena Vista and Palo Alto counties are showing large areas of moisture-stressed crops in fields that have deep, productive soils.”

Crop development is progressing rapidly, Kassel says. It is common to see corn in the R4 or dough stage — which is about a week ahead of schedule. “This increase in the rate of crop development may signal a response to the dry weather,” he says. “This is also likely an indication of reduced dry matter accumulation and reduced crop yields. Soybean aphids can be found in area fields, but they are at low levels. Farmers and agronomists are encouraged to keep checking fields for soybean aphids through the R6 or full bean stage of soybean development.”

North Central Iowa, Angie Rieck-Hinz (Region 3). “Lack of rain is causing more of the north-central Iowa area to show up on USDA’s weekly drought monitor map. “Generally, rains were very spotty the week of July 27 through Aug. 3, with the town of Humboldt reporting 0.2 inches, and all other locations reporting lesser amounts, if any, rain.”

Isolated showers on Aug. 1 produced up to 0.3 of an inch between Gowrie and Callender. Crop stress is starting to show up in Cerro Gordo and Worth counties, too. “Most corn is at R4, or dough stage,” she says, “but occasionally, I’ve found fields starting to dent or are at R5 growth stage, so we are pushing maturity with the high temperatures and lack of precipitation to assist with grain fill.”

Soybeans are mostly R5 or beginning seed. There are a few reports of low-level soybean aphids. Both corn and soybean disease pressure remain low in north-central Iowa, Rieck-Hinz says.

See a July 27-Aug. 2 precipitation map of Iowa.

Central Iowa, Meaghan Anderson (Region 7). “Most of central Iowa got some much-needed rain in the last week, though much of Dallas, Polk, Jasper, Madison and Warren counties received less than 0.5 inch. Corn is mostly in the R4 stage of growth in the area, though I’ve noticed a handful of kernels beginning to dent in some fields. In areas that have received more rainfall, corn looks mostly excellent but gray leaf spot pressure is increasing in some fields.”

0803F2-1641B.jpgCHECK FOR INSECTS: Two-spotted spider mite injury is evident along the edge of a soybean field in Dallas County. (Meaghan Anderson)

Soybeans are primarily in R4 to early R5 growth stage. Some waterhemp patches are beginning to show up in soybean fields. “While most of my central Iowa area is considered abnormally dry or in moderate drought, the most significantly affected areas are western Boone County, western Dallas County and far northwest Madison County,” Anderson says. “Soybeans are beginning to show significant moisture stress and corn ear development. Grain fill is extremely variable. Two-spotted spider mites are prevalent in many fields in these counties.”

She adds, “Common phone calls this week were about off-target dicamba injury to soybeans, weed identification, fungicide application decisions, potato leafhoppers in alfalfa and white flies in soybeans.”

0803F2-1641C.jpgKERNELS MISSING: Drought conditions caused significant tip-back of kernels on ears in this Dallas County continuous cornfield. Photo credit: (Meaghan Anderson)

East Central, Southeast and South Central, Virgil Schmitt (Region 9). “Rainfall last week was generally less than 1 inch. Temperatures last week in the counties I cover, along with temperatures statewide, were near normal,” Schmitt says. “Most cornfields are at R3 to R4 growth stage and generally looking good, except for storm-damaged fields. Gray leaf spot, a corn foliar disease, is increasing.”

Soybeans are mostly in the R3 to R4 stage of growth, he says. “In general, the soybean crops also look good, again except storm-damaged fields. White flies are abundant in some fields. Corn rootworm trait failure [in continuous corn], Japanese beetles, white flies, dealing with storm damage to crops, fungicide and/or insecticide applications, and dicamba drift were common topics of discussion last week.”

See a July 27-Aug. 2 temperature map of Iowa with departures from 1981-2010 normal temperatures.

South Central, Josh Michel (Region 11). “Scattered showers provided some relief to parts of south-central and southeast Iowa, with areas receiving anywhere from 0.25 to 1 inch of rain over the past week. Corn is generally in the R2 to R4 growth stage now, with many fields still looking good despite limited rainfall. Symptoms of heat stress are still occurring in areas with poor soils.”

Gray leaf spot continues to be found throughout the Southeast and South Central region of Iowa, along with some minor reports of corn rootworm damage and southern rust.

“Soybeans are generally now in the R3 to R5 growth stage, and are also looking pretty good,” Michel says. “The majority of the soybean field calls I’ve received have centered around insect feeding and weed escapes, especially with soybeans planted on 30-inch row-width rows. Alfalfa continues to grow very slowly, with many reports of moderate to severe insect feeding, mostly due to potato leafhoppers and grasshoppers. Forages in pastures have been growing very slowly as well. Recent cooler temperatures and small amounts of rainfall are expected to slightly improve crop conditions.”

Get your questions answered by your local ISU Extension field agronomist. Find the field agronomist's name and contact information

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