Iowa Field Reports: Herbicide Injury, Dry Conditions, and More

Herbicide injury on young soybeans. Photo: Iowa State University

This past week brought a range of field activities from replanting and POST herbicide applications to putting up hay and sidedressing nitrogen. Herbicide injury and carryover, dry conditions, yellow corn, and alfalfa weevils have been some of the more common issues ISU Extension field agronomists have observed in fields this week. 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 corn is ranging from V4 to V6 mostly, with some V7 as you go a little south. Some fields are struggling to establish nodal roots with the dry soil surface conditions, while the more mature fields seem to have roots utilizing the stored soil moisture.

“Daily demand of moisture with breezes, temps in the 90’s, and limited rainfall this year has created situations where rolling can be found in some fields during the afternoons. Almost all corn post-emerge treatments are completed. Soybeans are all emerged, and many seem to be at about the V2 stage. Post spraying has begun. Unfortunately, drift calls have also.

“The first alfalfa crop is harvested, and calls about alfalfa weevil have been higher than I ever remember in NW Iowa. Regrowth has been limited by alfalfa weevils in some fields, also. A note, common stalk borer migration out of brome has begun along fence rows where they are present.”

North Central Iowa

Angie Rieck-Hinz (Region 3): “Some farmers replanted soybeans and others “spiked” in more beans to compensate for stand loss due to the frost event we had on May 29. I have not heard of anyone replanting corn. Most POST applications are finished in corn in NC Iowa and POST applications in soybeans are taking place.

“Generally speaking, the hot weather is not conducive for herbicide applications so continue to monitor for efficacious weed control after spraying. Calls this past week have included questions about herbicide carryover to corn (fomesafen applications in 2020 soybeans), misapplications of herbicides—both drift and wrong products, and concerns about alfalfa growth and regrowth after first cutting due to dry conditions.

“We are pushing between a 4 and 5-inch deficit in rainfall from April 1 to June 7 in many areas, and we did not start out with a lot of subsoil moisture. I would also mention that based on what I have seen around the Humboldt area, I would think the deficit shown would be greater than what the Iowa Environmental Mesonet has listed.”

Northeast Iowa

Josh Michel (Region 5): “Overnight temperatures near freezing the end of May resulted in some light frost damage to corn and soybeans in low-lying areas, field edges and areas with moderate to high levels of crop residue. Thankfully, the most developed corn was  around V4 to V5, and the growing point was still below ground and protected.

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“Soybeans also fared better than expected, as close inspection in fields revealed that many plants, though damaged, still had green auxiliary buds, and should be able to grow out of the damage. That being said, there were some minor areas that warranted thickening up a soybean stand if the population was less than 70,000 plants per acre.

“The dry weather has allowed the first crop of alfalfa to get harvested, with reports of average to slightly less than average yields coming in. There is some concern that second crop regrowth may be slow due to dryer than normal soils. Oats continue to look good, with around 30% of the oats now heading out. Pastures are looking good, but warming temperatures and a lack of rainfall are starting to slow down the growth of many grasses.

“Recent field calls and questions have included: alfalfa management, post herbicide applications, stand assessments and replant considerations, as well as questions pertaining to frost damage to corn and soybeans.”

Southwest Iowa

Aaron Saeugling (Region 10): “Warm temperatures have helped crop progress and make up for a cool May.  Crop conditions are good to excellent in most places in SW Iowa. Area that have received rainfall look good and corn in in the V4 to V6 stage. When staging corn make sure we look at exposed collars to properly stage corn for herbicide applications.

“With the cool weather, some corn is more mature than plant hearth would indicate from a tape measure.  Remember to keep in mind that at V6 corn all leaf tissue for the year has begun initiation, however, cannot be seen without magnification.  Therefore, herbicide applications can be riskier.

“Soybeans growth has really taken off this past week with most soybeans in the V1 to V3 stage, depending on planting date and cold stress in April and May. Herbicide applications are progressing rapidly this year due to dry conditions.  Be on the lookout for increased insect activity due to hot and dry conditions as crops will have less tolerance for insect feeding.

“On the forage side of things, I have seen that alfalfa weevil damage is common and may be the worst I have seen in a long time. I have also observed aphids and a few potato leaf hoppers, so continue to scout alfalfa fields for insect activity.  Rainfall will be needed in June this season due to lower subsoil moisture conditions compared to last season.”

Central Iowa

Meaghan Anderson (Region 7): “Central Iowa continues to accumulate a rainfall deficit of about 3.5 to 5 inches since April 1. This is on top of already dry subsoil conditions that have persisted since last year. Corn is mostly V4 to V7 with the earliest planted corn already at V8. Soybeans are mostly V1 to V2.

“The northern part of my territory was hit with some frost but most of the area avoided significant affects and mostly saw the silver leaf symptom on corn leaves. Corn is still uneven when you look closely at fields but the color is beginning to even out and some fields look really beautiful. Soybeans are small but mostly healthy.

“The biggest issues have been with herbicide applications – carryover, PRE injury on soybeans, and drift onto both soybeans and corn have been the most common issues. While it is time for POST applications in soybeans for many fields, the weather is a significant cause for concern between stressed plants and hot conditions that are not ideal for dicamba applications.”

East Central, Southeast, and South Central Iowa  

Rebecca Vittetoe (Region 8): “This past week was filled with lots of field activities including sidedressing nitrogen, replanting, POST herbicide applications, and putting up the first cutting of hay. The sunshine and heat have really pushed the crops along this past week. Corn mainly falls between the V4 to V7 growth stage and soybeans are around V1 to V2.

“Corn seems to be growing out of the ugly duckling stage as the nodal roots get more developed. I have seen a few cases where the nodal roots have not developed and are causing floppy or rootless corn. I’ve also started to get calls on corn showing a response to the POST herbicide application.

“What I’ve seen so far has been cosmetic and can be related back to what was in the tank and/or the hot and humid conditions when the application was made. Overall soybeans are looking good. It’s not hard to spot fields that were impacted by the derech last year with all the volunteer corn. Many will or have started to turn their attention to POST applications in soybeans now.”

Virgil Schmitt (Region 9): “Rainfall during the last week in the counties I cover was generally less than 0.5 inch of rain south of Highway 92 and none north of Highway 92. In general, temperatures during the last week in the counties I cover were within 3 degrees of normal, with more above normal north of I-80.

“Most remaining planting was completed last week. Corn is mostly V5 +/- one collar. Most soybeans are V1 to V3. Sidedressing of corn and post-emerge herbicide applications to corn were in full swing. Hay harvest was in full swing last week and first cutting is nearly complete. Alfalfa and red clover are in full bloom and musk thistles are starting to flower.

“European corn borer moths are flying. Calls last week centered mostly around weed management, herbicide injury, herbicide drift, and sulfur deficiency symptoms in corn.”

Josh Michel (Region 11): “Scattered light rain showers delivered up to 0.10 inche of precipitation across the southern edge of the region along Highway 2. Farmers were able to take advantage of the dry weather to finish up the first crop of alfalfa harvest, start post herbicide applications, and start sidedressing nitrogen in many areas.

“Corn is generally around V2 to V3, with some early planted fields around V5 to V6. Soybean planting is pretty well finished up, with around 75% of the soybeans now emerged. Early planted soybeans are generally at V2 to V3. Oats continue to look good, with stands 30 to 35% headed out.

“Pasture growth is slowing down with warming temperatures. Recent field calls and questions have centered around post herbicide applications and forage management.”




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