Iowa Field Reports: Derecho Devastates State Infrastructure, Crops

Corn completely flattened in Boone County by the derecho on August 10. Photo: Meaghan Anderson, Iowa State University

While some rainfall has come to the droughty areas of the state, drought intensified to D3 (extreme) drought in parts of central and west central Iowa.

Unfortunately, a large swath of the state is now facing devastating infrastructure and crop damage after the August 10 Midwest Derecho. Our thoughts are with all Iowans as they work to assess and recover from damage.

Other issues noted by field agronomists prior to August 10 include fast maturing crops, twospotted spider mites, spotty foliar diseases, a general tapering off of some insect pests, and continued concerns about off-target dicamba movement.

Read on for more specifics for what’s happening in different regions across the state.

Northwest Iowa

Joel DeJong (Region 1): “In the NW corner of Iowa – received nice rainfall in the past week in about the southern half of the area I serve. The north half had a few tenths. We missed most of the severe wind damage, and feel for those who didn’t miss it.

“Lack of moisture remains an issue in much of the area, tip back very prominent, and it seems maturity of plants in the driest areas is speeding along quicker than I like to see. Spider mites are rather common, but soybean aphid numbers, although present in more fields, seem to be staying below thresholds in most fields.

“The waterhemp misses are becoming more visible in soybean fields, too.”

Paul Kassel (Region 2): “Corn and soybean crops continue to deal with dry soil conditions across much of the area. Parts of Sac county are now classified as D3/Extreme drought. Also, parts of Buena Vista, Pocahontas, Clay and Palo Alto are dealing with D2/severe drought.

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“Some rainfall amounts of 0.5 to 1.0 inch have occurred in parts of Kossuth, Hancock and Winnebago counties recently. Crop development also appears to be progressing rapidly as corn approaches the dent stage.

“There are soybean fields that are approaching the full bean/R6 stage of development. The amount of time from R6 stage until R7/early maturity stage is around 20 days.

“Insect pest problems have been low so far. Farmers and applicators are encouraged to check soybean fields for soybean aphid development. Soybean aphid levels have been light so far. The risk of damage from soybean aphid is reduced once the soybean crop reaches the R6 stage.”

North Central Iowa

Angie Rieck-Hinz (Region 3): “Rains continue to be spotty, but nearly every reporting station across my 9 counties reported some rain during the week of August 3 through August 10. Rainfall ranged from 0.18 inches at Rockwell City to 1.13 inches at Fort Dodge.

“Eldora and Hampton continue to see only about 20 to 25% of their average rainfall for this time of year. Rainfall reports for the storm that pushed through on August 10 are so varied that I don’t think it will do much to alleviate our drought concerns in the more severely impacted areas.

“Corn is mostly R4-R5. There continues to be little disease pressure in the majority of fields. Soybeans are R5.5 to R6. I have seen some frogeye leaf spot, but at low levels.

“I was in Rockwell City when the August 10 storm hit. A crop tour after the storm with a local farmer and seed dealer showed there was leaning corn and tattered beans in scattered places. I tracked this on my way home with scattered crop damage in southern Webster and Hamilton counties.

“I live in northern Story county and once you get east of the interstate 35, there are numerous acres of flattened corn, tattered and lodged beans and missing grain bins, plus a lot of structural damage.”

Northeast Iowa

Terry Basol (Region 4): “Just like most of the state, corn and soybeans in Northeast Iowa could use some precipitation, as all of the NE counties have entered into the category of DO (abnormally dry, according to the United States Drought Monitor).

“Most of the corn is finishing up the R3 stage (Milk) and has begun the R4 stage (dough). According to the National Agricultural Statistics Service (NASS), 77 and 59 percent of the corn as of August 9 in North Central and Northeast Iowa respectively, is in the dough stage of growth.

“The most common foliar disease so far this season that’s shown up in the last few weeks is gray leaf spot. There has been some isolated cases of tar spot reported and confirmed in the counties Floyd, Butler, Black Hawk, and Buchanan, but generally few and far between up to this point.

“Soybeans are finishing up the R4 stage and beginning the early stage of R5. This is the time period for soybeans where the seed is 3 mm (1/8 inches) long in the pod at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node.

“Japanese beetle feeding is now tapering off in most soybean fields, but continue to monitor defoliation levels, as grasshoppers are also feeding. In dry years, grasshoppers can become problematic as their normal vegetative food sources are decreased and they turn to feeding on soybeans.

“For more information on scouting and thresholds for pests that feed on soybeans, check out the ICM article titled “Scouting guidelines for soybean defoliators here. As stated earlier, we could use a good drink from Mother Nature, as we have only received 1.07 inches of precipitation at the Northeast Iowa Research and Demonstration Farm since August 1 according to the Iowa Mesonet.”

Central Iowa

Meaghan Anderson (Region 7): “Most of central Iowa received anywhere from about 0.5″ to more than 3 inches in the last week. This rain was needed, but droughty areas are still <50% of normal rainfall for the last 60 days, so most areas got a small drink compared to what is needed.

“Unfortunately, the most recent rainfall brought significant wind that impacted corn fields over nearly the entire region of the state that I serve. Corn fields that were in the R4 (dough) to early dent (R5) are now facing finishing out kernel fill with plants mostly on the ground and harvest will be especially arduous this fall.

Bob Nielsen (Purdue University) wrote a nice article in 2018 outlining the effects of severe stresses during corn grain fill that is very useful. The prospects for recovery in these fields do not seem encouraging this late in the growing season. Additionally, the storm caused significant structural damage to livestock buildings, farm sheds, homes, and grain bins (to name a few).

“Weedy areas of soybean fields continue to become more apparent and I’ve received more phone calls recently with questions about survivors of 2,4-D and dicamba herbicide applications; resistance to these herbicides has been discovered in Palmer amaranth in other states but has not yet been officially reported in Iowa waterhemp populations. Speaking of Palmer amaranth, now is a great time to be scouting for it in Iowa.

“Insect issues in both corn and soybean are mostly tapering off. Common phone calls this week were about corn recovery from wind damage, weed identification, twospotted spider mites in soybeans, and Japanese beetles in corn and soybean.”

East Central, Southeast, and South Central:

Virgil Schmitt (Region 9): “Rainfall last week in the counties I cover was generally less than 0.1 inch. In general, temperatures last week in the counties I cover and statewide were cooler than normal. Most corn fields are at R4 and generally looking good, except for storm damaged fields. Gray leaf spot lesions and occasional sightings of tar spot continue.

“Soybeans are mostly R5. In general, they also look good, again except storm damaged fields. Dicamba drift, potential dicamba resistance, late summer seedings, cover crops were common topics of discussion last week.”




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