All the pestilence that’s fit to print

Volume 23 number 6
This newsletter and the advice herein are free. You usually get what you pay for.


For the most part, the crop in SW Minnesota and much of Minnesota looks pretty good, so far.

In-person meetings are expected to be restricted for some time because of Covid-19 virus fears. I’ll try to do more videos on scouting and research plot treatments.

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.

Looks like a stretch of warm weather on the way and crop growth should will be rapid over the next week.

It might involve looking at the label but remember the growth stage restrictions for herbicide applications.

Things that go bump in the night

The larvae from black cutworm moth flights into Minnesota are feeding on leaves with those from the earliest flights large enough to cut corn. Compared to 2019, few flights were large enough to cause concern for economic damage. However, several early and mid-May flights detected by the network of pheromone trap cooperators indicate scouting should still be worth the effort. After June 6th, these later flights should be large enough to cut small corn plants. Corn larger than 5 leaves is usually too large for cutworms to cut below the growing point and kill. Somewhat larger corn might still be injured if large black cutworm larvae tunneling into the growing points.

Although I am not aware of any large captures, some of the black light and pheromone traps have detected prolonged, moderate activity of true armyworm moths. These moths are attracted to areas of dense grass vegetation to deposit eggs. These grasses can include live rye or wheat cover crops, lodged grains or grasses in field borders. This spring, I’ve seen some cornfields where dense grass weeds have not yet been controlled – these areas may attract armyworm moths.


Early planted corn in the area is 2 to three collars. There is likely some larger corn out there, particularly near groves and other sheltered areas. With the forecast heat and good soil moisture we may see some five-leaf corn by the end of next week. As corn reaches the five to six leaf stage, growth becomes more rapid and growing point moves above the soil. Issues with poor root development tend to become visible at this time. 

Damage from white grubs has been reported from several parts of Minnesota and will become more visible as stunting and wilting as greater root mass is needed to support growing corn.

Pay special to stand reducing insects and slugs when scouting corn planted into grass cover crops or weedy 2019 prevent plant fields.

Common stalk borer will soon be moving to corn from field borders and where giant ragweed has been recently killed.

Based on the peony bloom, we should start to see the start of 1st generation European corn borer in parts of southern Minnesota as early as next week.  Degree-day predictions https://www.vegedge.umn.edu/ecbddmulti agree with my peonies.


Some early soybeans are working on the first trifoliate. Many are late VC.

Scout your fields. The comments on white grubs in the corn section are appropriate for soybeans also. Remember, no insecticide, fungicide or nematicide seed treatment can make your soybean, corn or other row crop “immune” to attack from seed and seedling insects, disease or nematodes.

Soybean gall midge adults should begin emerging within the next few weeks. We are monitoring emergence in Rock and Yellow Medicine Counties.

Buckthorn is pollinating in SW and SC MN. Based on previous year’s observations in SW Minnesota, soybean aphids move to soybean when buckthorn berries are approximately 1/8”, or a bit more, diameter. At that time, the earliest emerging soybeans (sometimes volunteers) are usually late V2 or V3 stage. How consistent is the relationship of buckthorn stage, soybean stage and spring movement of aphids to soybean? I’d appreciate your help if you are scouting soybean fields that are typically colonized early in the year that have buckthorn nearby. Let me know when you see your first aphid, the soybean bean stage and the berry development on nearby (female) buckthorn plants.  Another potential benefit of these reports would be an early look at which areas of Minnesota aphids have had good success in colonizing soybeans.

This will be well before aphids reach economic threshold. For early-season detections, focus on the earliest planted fields or volunteer soybeans.  Look for ants and lady beetles as they often find the infested plants first. Initially, a very low percentage of soybeans will be colonized but in the southern part of Minnesota any winged aphids moving from buckthorn to drop off nymphs should find plenty of suitable early-planted plants to choose from. 

Wheat, Oats, Rye, Barley

Bird-cherry oat and English grain aphids are present in low numbers in SWROC winter wheat and cereal rye. For those of you scouting spring grains – scout for aphids before heading. I am seeing very little disease at this time.

The bright orange pustules of oat crown rust is now present on buckthorn. Spores from these infects will infect oats.


There is a lot of hay going down.
There were some problems with frost heaving, particularly in some areas that got the cold but not the snow cover in April. Most of what I have seen looks OK.

1st instar alfalfa weevil larvae are active in southern MN now. Watch these in second cutting.

Pea aphids are the predominate pest but below economic levels at the UM SWROC. 

I have not yet found potato leafhoppers at the SWROC. They will get here eventually.

Happy trails,

Bruce Potter
Extension IPM
University of Minnesota Southwest Research & Outreach Center
23669 130th Street                                                                                          
Lamberton, MN 56152           

Phone: 507.752.5066 
Cell:  507.276.1184
Fax:  507.752.5097
E-mail: bpotter@umn.edu


Facebook: https://www.facebook.com/swroc
Twitter: https://twitter.com/SWMNpest

Products are mentioned for illustrative purposes only. Their inclusion does not mean endorsement and their absence does not imply disapproval. 
© 2020, Regents of the University of Minnesota. All rights reserved. The University of Minnesota Extension is an equal opportunity educator and employer. For University of Minnesota Extension crop production information: http://www.extension.umn.edu/agriculture/crops/