Walking Rows 2025: ISA agronomist update – June 5

June 5, 2025 | Kriss Nelson

Iowa Soybean Association agronomists are urging farmers not to wait on weed control, as herbicides may lose effectiveness once weeds grow too tall.

Alex Schaffer - Central/South Central Iowa

Over the past couple of weeks, post-emergence herbicide application and side-dress nitrogen application began across the state. I have observed beans at growth stages V1-V3 and corn from V2 in the later-planted fields to V5 in the fields planted in mid-April. I think the crop still looks pretty good, with some unevenness appearing in certain corn fields. Most of the unevenness appears to be in compacted areas on field edges and in places that remained too wet for an extended period.

In walking some trials over the past two weeks, the cooler weather last week slowed crop progress, especially soybeans. It seemed like the crop needed the heat over the weekend to get some trifoliate leaves unfolded. The rain was welcome after a period of some dry, hot weather. The other thing I'm noticing when walking some corn fields is surfactant burn from the recent post-applications. Nothing really to be concerned about here as it comes with the territory, but it is helpful for an agronomist walking fields to be able to tell if and when a corn field was sprayed.

Be on the lookout in your bean fields for dicamba damage. Fortunately, at this early growth stage, research indicates that yield loss is unlikely, and there is little that can be done about it afterward. Just be on the lookout, and more importantly, if you are spraying Status or another dicamba product, please be aware of weather conditions and consider the impact on surrounding neighbors.

Shane Beck – Northeast/Northern Iowa

Last week was filled with finishing up planting and replanting some corn that had poor emergence. In my area, soybean emergence shows variability from fields planted early to mid-April. Recent soybean stand counts as part of our seeding rate trial showed a 30-40% reduction in final stands compared to the number of seeds planted, particularly in April-planted soybeans. This trial has four different seeding rates: 80,000, 110,000, 140,000, and 170,000 seeds per acre.

May-planted soybeans have better emergence and only a 15-25% reduction in final stands compared to seeds planted.

The 170,000 seeds-per-acre soybean population took the most significant hit in terms of the percentage of seeds that emerged compared to the number of seeds planted in April with a final stand of anywhere from 120,000 to 140,000 plants per acre.

Fields planted no-till with heavy residue also experienced stand issues, especially where residue was blown to areas of the field, leaving a residue pile of 6 inches or greater.

Spraying is also occurring across the countryside when we can find a light enough wind to make that happen. There are a few fields that are becoming overrun with waterhemp and grass. One thing to remember is to target those weeds when they are less than the size of a pop can or 4-6 inches in height.

I have heard that some people are waiting for more weeds to emerge before they spray. I would caution that if the weather turns wet for a few days or a week, those weeds may grow beyond the ideal height, and our post-emergent herbicides won't control them sufficiently.

 Ensure you are including the  correct adjuvants to enhance the performance of your herbicides. Different adjuvants are better suited for specific purposes. For example, non-ionic surfactants (NIS) help spread the spray droplets out on the leaf of the weed, allowing for better coverage. Whereas crop oils are used to help penetrate the waxy cuticle, which helps protect the plant. This allows for the herbicide to be more effective at killing the weed. Overall, the best way to determine what and how much of different adjuvants to include is to read the label of the herbicide before applying it to the field.

Mikaela Connelly Southwest/West Central Iowa

Planting is mostly complete in this area, and it’s a busy time of year for scouting.

Post-emergence herbicide applications have been occurring as weather conditions allow. With the rising temperatures and increased moisture, weeds are emerging for a second time. The warm weather over the past couple of weeks has allowed the corn to take off, so I’ve seen corn at the V8 growth stage. For soybeans, I’ve seen around V3/V4 growth, but the cooler temperatures and cloudy days last week didn’t allow for much growth. The rain this week was much needed across the western side of the state, but dry conditions persist.

While out scouting some of our trials, I have seen bean leaf beetles and green cloverworm. Pressure has not been heavy enough to cause significant injury to the soybean plants, but I advise farmers to be aware that these pests are present.

Soybean gall midge has been reported in Nebraska, so be on the lookout for it in your fields, particularly if you have had issues in the past.

Craig Woods – Northwest Iowa

Soybean and corn emergence is looking solid across northwest Iowa, thanks to consistent moisture, except in areas that received significant rain and ponded. Soybeans vary from the V1 to V3 growth stages, while corn ranges from V2 to V3. Growth appears to be somewhat slow due to the limited heat units across the region, despite the wide range of planting dates. With slower growth rates slowing future canopy closure, it will be crucial to manage weeds effectively over the following weeks.

With post-emergence applications, it is essential to remember that applying in good conditions and with a targeted approach will be paramount. The ideal temperatures for most post-emergence herbicides are between 65 and 85 degrees. If possible, try to scout and target areas that were drowned out the year before, as weed pressure is likely to be higher due to either replanting or being left fallow. These conditions would allow for a weed seed bank to have formed. Try to prioritize areas that have weeds that have yet to reach 4 inches, as they are less likely to survive the herbicide application.

Scouting sprayed fields about a week after application will help determine the efficacy of the application and whether another application of a different herbicide would be worth making a second pass on the field.

Evan Brehm - Southeast/Eastern Iowa

Soybean planting is almost finished across eastern Iowa. Soybean growth stages range from planting to the V3 stage. Corn was planted in early April, and replanted acres were completed in mid-May. Growth stages are pushing V7, and some fields that were replanted are V2.

Small grains, such as cereal rye and winter wheat, intended for harvest, are at an early stage of flowering. These small grains are generally used for livestock and ryelage, but interest in relay cropping is increasing in small grain acres.

Farmers should be scouting for bean leaf beetles, especially in areas with high-residue fields that have not received insect treatment.

Cutworms and armyworms aren’t a concern with later-staged corn; however, continue to scout for evidence of cutting. I have not heard of any economic threshold fields for those pests, however, for this season.

Weeds have been emerging after pre-emergence herbicide applications, with post-applications occurring due to the drier weather on both corn and soybeans. Weeds I have seen in fields include waterhemp, lambsquarter, foxtail and giant ragweed.

A large number of alfalfa first cuttings have been completed over the past two weeks. While no insect pressure has been reported yet, regular sweeping and scouting for potato leafhoppers is advisable as the season progresses.

Ag retailers and farmers have been pleased with field conditions for split applications of nitrogen. Sidedressing has primarily wrapped up as ag retailers are now topdressing urea. This is an excellent practice for farmers as it splits their nitrogen sources. It gives corn a boost during the growing season and it’s a fantastic environmental practice that reduces nitrate runoff.

I recently walked a field with Alex Schaffer, ISA senior regional agronomist, in East Central Iowa. This field was planted with soybeans in mid-April into wheat. Soil conditions were ideal, but with a thick cover of a cover crop, this attracted early-season insects and emergence issues. Deer also found a salad buffet of soybeans and chewed off the first trifoliate. The field across the fence was a similar practice but planted three weeks later. Those soybeans look great planted into a rye cover crop. The good news is that soybeans are resilient. They've begun to shoot trifoliate leaves and branch out. These are 7.5-inch rows and will be able to canopy and shade the rows. Recent rain on June 3 and forecasted warmer temperatures will assist in recovery. At this time, it appears that early-planted soybeans with cooler temperatures are struggling.

Written by Kriss Nelson.

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