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There have been a few fields where topramezone – the active ingredient in Impact and Armezon – carried over from an application last June – and is injuring this year’s soybean crop. Other agronomists have reported carryover of other Group 27 herbicides on soybean this year (mesotrione, isoxaflutole).

Spotty rainfall across the state, herbicide drift, “Rapid Growth Syndrome” in corn, and shorter beans were common issues or concerns that ISU Extension Field Agronomists saw and heard about this past week. Read on for more specifics about what’s happening in different regions across the state.

Northwest Iowa

Many farmers and agronomists are noticing short soybean this spring. Some are pondering if there is something that can be done to spur some additional growth as flowering is fast approaching, if not already begun. The surprise with short soybean is that planting was timely. The unfortunate situation after planting was the onset of cool, wet, cloudy conditions.

Over the weekend there have been several reports of bacterial leaf streak (BLS) of corn in eastern Iowa.  The infections also appear to be quite severe (Figure 1).

Figure 1. Symptoms of bacterial leaf streak observed on corn in eastern Iowa in June 2020 (Photo courtesy of N. Stecklein, Bayer).

How do I recognize BLS?

There have been reports of flowers in the earliest planted soybeans, and I observed them in NW Iowa late last week. That means these beans are entering the R-1 stage of development.

Temperature Inversions

It is never recommended to spray a pesticide when a temperature inversion exists, and many labels provide guidelines to follow in order to avoid applications during one. This blog will discuss what temperature inversions are, why they can be dangerous for pesticide applications, and how to identify when temperature inversions are happening.

Today, with Ashley Dean and Angie Rieck-Hinz, I met Warren Pierson at FEEL to look for corn rootworm larvae. I predicted peak corn rootworm egg hatch for central Iowa this week based on accumulating degree days. We had no trouble finding larvae in refuge corn, ranging from ¼ to ½ inches in length. They were very active (wiggly) today. I came up with a few guidelines for corn rootworm scouting:

The growing season is in full swing, and as Iowa growers and gardeners move along toward the Fourth of July, it is important to remember that the COVID-19 precautions continue to alter operations at the Iowa State University Plant and Insect Diagnostic Clinic (PIDC).

Reports of soybean gall midge adults emerging, rainfall or lack of rainfall, weed management concerns, and herbicide drift were some of the common issues or concerns that ISU Extension field agronomists saw or heard about this past week. Read on for more about what's happening in specific regions across the state.

Northwest Iowa

Radiation is down up to June 1 according the latest FACTS extrapolations.

The springtime decreases in radiation—especially in May—could have caused yellowing corn leaves and slowed down leaf appearance rates (radiation and moisture play a role in phenology, even though temperature is the main driver). The cooler temperatures means lower soil N mineralization, slower plant growth and lower soil water evaporation.

Today, ISU entomology graduate student, Mitchell Helton, captured the first adult soybean gall midge in Iowa. Just a few hours later, cooperator Lauren Botine (Corteva Agriscience), collected another adult. Currently, our traps are placed in fields infested with soybean gall midge in 2019. There was an earlier report of adults captured in Nebraska this week. This is approximately the same time as the first adult detections in 2019.

Sidedressing nitrogen, post emergence herbicide applications, and putting up hay were the main field activities that took place over this past week across the state. Some of the issues ISU Extension and Outreach field agronomists saw this past week ranged from dry conditions in the western part of the state, thistle caterpillars in soybeans, alfalfa weevils and aphids in alfalfa, isolated hail damage in parts of the state, and discoloration issues in corn.

Yellowing of corn plants early in the season can be confusing to diagnose. And in some conditions there may be a period of time after corn emergence where small corn just does not look good. There can be a number of causes for plant yellowing. An example is the description in a recent ICM Blog by Alison Robertson (Anthracnose leaf blight prevalent in corn fields).

One important benefit of cover crops to our production system is providing an alternative selection pressure on weed populations. Cereal rye has the best potential to suppress weeds because it accumulates more biomass than other cover crop species.  Weed suppression is closely related to the amount of biomass at the time of termination (Figure 1). 

Numerous herbicides registered for postemergence use on Xtend soybean have excellent activity on important weeds of Iowa’s soybean fields. Unfortunately, herbicide resistance in waterhemp is widespread to the herbicide groups active on this weed: Group 2 (ALS inhibitors), 9 (glyphosate) and 14 (PPO inhibitors).

Earlier this week I was out in corn fields "helping" my lab crew collect disease data.  The corn was not looking great but hopefully it has perked up with the past few days of sun and warmth. I know I have!

The trapping season for true armyworm (TAW) and black cutworm (BCW) has come to an end. We appreciate our cooperators for tirelessly checking traps the last two months and reporting their captures so we can provide the most accurate scouting information for these pests. To recap, we had 36 cooperators participate from 34 counties in Iowa. A total of 78 traps (39 of each species) were placed and monitored during April and May.

The crops have really started to take off this past week with the warmer temperatures. While rainfall limited field activity in parts of the state, where fieldwork could be done many got started on sidedressing, post herbicide applications, and putting up hay.

Although there is no evidence of widescale problems with carryover injury to corn or soybean, ISUEO field agronomists have received a few reports. The potential for carryover injury is determined by several factors, including: 1) persistence of the herbicide, 2) herbicide rate, 3) soil characteristics, 4) amount of rainfall during the season following the application, 5) length of interval between herbicide application and planting the rotational crop, 6) sensiti

In order to keep up with any changes and updates on pesticide uses and restrictions from year to year, it’s important to thoroughly read the label before any applications are made, even if the same product was used the previous year. If nothing else, it helps to refresh our memory on the particulars of specific products that are applied to ensure optimum pest control and environmental protection.