SW MN IPM Stuff 2019 Issue 5

Volume 22 number 5


This newsletter and the advice herein are free. You usually get what you pay for.

A print-friendly version of this newsletter is available to download here: PDF iconSW MN IPM Stuff 2019-05

Crop Weather

Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University of Minnesota Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN, can be found at SWROC Weather.

Early-planted corn is 4 collars and soybeans V2. Crop development is well behind this in many fields.


Black cutworm

In spite of the number of significant captures, this remains a relatively quiet spring. Larvae from the early April 22 flight should be actively feeding for another week or more. While early-planted corn will soon be large enough to be safe from damage, there is plenty of small corn out there.  

Yesterday, a couple more reports came in. Austin Hopwood, found black cutworms injuring corn in Cottonwood County. Damage was still sub-economic.

Meanwhile, on the western front, Jeff Petersen sent images of Clark County, South Dakota soybeans killed by cutworm feeding. These had reduced stand to a level where yield was threatened. Because of high plant populations, economic damage from black cutworm is less common in soybeans than some other crops. There were two age classes of larvae that would match the flights detected in West Central MN on April 22, May 1, and May 13.

In both reports, some of the larvae were displaying the nasty habit of feeding on plants below the soil surface. This makes control a bit more difficult.  Pay close attention to fields where herbicide applications have killed emerged weeds or cover crops.

True armyworm

We need to keep an eye on this insect this year! On June 6th, the black light trap located at the SROC in Waseca had a one-night capture of 78 armyworm moths. This is added to some previous large captures (see VegEdge True Armyworm (TAW) Moth Flight Data). A past UMN  Extension entomologist used 60 armyworm moths/night as an indicator for problems in small grains. This number has worked well over the years I have been dealing with corn and small grain insects.

As mentioned last week, a large light trap capture indicates increased risk of economic populations of the crop damaging larval stage. Unfortunately, the light trap captures are poor at predicting where in the state the crop damage will occur.

True armyworm moths lay eggs in areas with dense grasses. A sweep net is a useful tool to detect larvae in the grasses in field borders. In corn, a rye cover crop or grassy weeds increase risk. In small grain crops, pay attention to any lodged areas.  

For more armyworm information see: Armyworm in corn


European corn borer (ECB)

Based on degree-day models and the peony bloom, the first generation multi-voltine corn borer flight should be well underway in parts of the MN River Valley and SC MN. ECB development will lag behind in other, cooler, areas of Minnesota. However, black light trap captures have been nil. Part of the reason may be cool nights have reduced moth activity.  

ECB degree-day development models can be found at VegEdge Degree-day Models & Forecasts. ECB egg laying is not complete and any eggs laid have not yet hatched. It is still too early to scout whorl stage corn for corn borer injury and insecticide decisions. That will soon change. In order to be efficient, you will want to focus efforts on the tallest non-Bt corn fields in an area. Because of the concentration of DIMBOA, a compound occurring in all corn, corn borer larvae cannot survive on any corn corn less than 15- to 18-inch extended leaf height. This could have a significant impact on corn in areas where corn was delayed. It will concentrate egg laying in those fields that were planted earlier than others. In some areas, most, if not all, corn could be too small to support ECB populations. This could have a devastating, and from an agriculturalist’s perspective welcome, effect on those local corn borer populations.

Damping off or… a million ways to die in a wet cornfield.

Several consultants are reporting damping off of South Central MN corn seedlings planted into wet conditions. Any of a number of fungi could be involved if these are disease induced. In some cases, seedling vigor may also be part of the equation. Be sure to send plants in various stages of death when you send samples to the UMN Plant Disease Clinic for diagnosis. Complete sample collection and submission instructions are available on the PDC website.

Corn rootworm

We will be coordinating a network for corn rootworm sticky trap data this year. If you would be interested in participating and sharing your data please contact me. We can supply a relatively pain-free sampling protocol and yellow sticky traps.


Toward the eastern front, “Deep throat” reported seeing a few thistle caterpillars. These are the larval stage of the migrant painted lady butterfly. They are very seldom economic abundant enough to affect yield. Based on the number of adults I have seen this spring, I doubt they are a threat. Even highly risk averse agriculturalists would be money ahead to leave them alone.


The second and third crop usually sees the most insect issues.

Alfalfa weevil populations increased over the past week in SW MN. Larvae range range from 1st to 3rd instar with the majority 2nd.

Pea aphids are enjoying the cooler, drier weather. Good soil moisture will help minimize yield effects.

Happy trails,

Bruce Potter