SW MN IPM Stuff 2022 Issue 5

Volume 25 Issue 5 | May 13, 2022

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

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 http://swroc.cfans.umn.edu/weather.  

Crop Progress

Statewide planting progress continued the slowest since 2013. However, since last weekend many growers made progress in planting and areas through southern Minnesota now vary greatly in planting progress. Unfortunately, recent rain has put a temporary halt to planting in many areas. Some areas saw very heavy rains and damaging winds Wednesday and Thursday. In addition to any potential yield effects to from planting delays, some fields smoothed by tillage and planting fields were affected by heavy rainfalls with some areas needing replanting.

Germinating seeds and emerging seedlings may drown where standing water persists, particularly when temperatures are high. Prolonged wet soils can also lead to a greater incidence of seed and seedling diseases, even where fungicide seed treatments were applied.

There may be areas of fields where downpours caused significant erosion to newly planted fields. At the soil surface, pounding rains cause soil structure changes and can increase wind erosion and crusting. Rolled soybean fields may be at higher risk. The new high-speed planters might help satisfy an urge for fast driving but remember, rotary hoes too work best when run fast. You might benefit from using one this spring.

Small grains

Winter cereals

Cereal rye growth has been excellent this spring. The first aster leafhoppers showed up when sweep-netting rye on 5/09. I have not found any cereal aphids yet.

Spring wheat and oats and barley

The SWROC research plots for spring cereals finally went in on May 11. The amount of yield reduction for late planting will depend on the weather. Late-planted grains may be at a higher risk from cereal aphids migrating from the south.

There has been a change in the economic thresholds for cereal aphid (English grain, bird cherry-oat, and greenbug) for wheat, oats, and barley. Yield loss from aphids is most likely when heavy aphid infestations occur from vegetative to heading stages. However, three studies (Johnson and Bishop, 1987; Voss, et al., 1997; and Larsson, 2005) showed aphids can impact yield into the early dough stage. Aphid economic thresholds now reflect the potential for yield losses past heading along with the reducing risk later in crop development. Don’t base an insecticide decision on a single area of the field or the most heavily infested plants you find. Sample several stems at multiple random locations through the field, count the number of aphids, and determine the average number of aphids per stem.

Crop stage(s)

Average #  aphids/Stem

Vegetative through head emergence


Complete heading through the end of anthesis


The end of anthesis through medium milk


Medium milk through early dough


Source: 2022 North Dakota Field Crop Insect Management Guide


Stripe and other cereal rusts

Dry weather has limited the development of stripe rusts in the Great Plains. This means that currently there is little inoculum to move north. Of course, that can change with changes in weather patterns. The success of any rust spores arriving here will be favored by moisture and moderate temperatures.


Although behind in development, the younger stands I’ve checked still look good. However, there are older stands with problems in parts of southern Minnesota ( https://blog-crop-news.extension.umn.edu/2022/05/winterkilled-alfalfa.html)

Alfalfa insect populations at the SWROC are still very low but warmer weather and southerly winds may soon change that.

Alfalfa weevil

I picked up the first SWROC adult weevil of the season on 5/10 - A single specimen in several hundred sweeps. No larvae were observed. Alfalfa weevil populations may be higher in areas where populations were high in 2022 and where there was good snow cover last winter. It is still early but adults should move into fields soon and give us a better idea of the risk this insect poses to 2022 alfalfa crops. Degree day models can roughly predict the stage of development of alfalfa weevils. Like most models, they are not 100 % accurate. See: https://vegedge.umn.edu/alfalfa-weevil

As of 5/10/22 Tarnished plant bug (lygus) populations in SWROC alfalfa were very low, as were overwintering pea aphids. Potato leafhoppers have not yet been detected.

Avoid insurance insecticide applications to alfalfa. You risk flaring pea aphid populations some of which have been suspected to be resistant to pyrethroid insecticides. Remember – you no longer have chlorpyrifos to fall back on.


I just received my first picture of emerging corn. The corn was planted on April 29 and the photographer cleverly avoided answering questions by including a measuring device in the picture. Darn close to 2 inches deep. Thanks, Keith.

Start scouting stand-reducing insects as soon as corn can be rowed. Finding stand problems early allows more time for rescue treatments or replants.

Black cutworm

There have been several significant flights into SW Minnesota. Larvae from this flight should start producing visible leaf-feeding next week. Larvae will be large enough to cut corn around the 1st week of June. For more information, see Black Cutworm Facts and 2022 UMN Cooperative Black Cutworm Reporting Network Reports at: https://swroc.cfans.umn.edu/research/ipm/bcw-network

In a few weeks, you should be starting to scout winter cereals and corn planted into a rye cover crop for true armyworms. Several weather systems have brought moths into Minnesota this spring.

Corn rootworm

An open winter in much of SW MN may have reduced the survival of egg populations slightly. Next week, I’ll start looking at degree days to estimate egg hatch.

I had a call from a crop consultingt friend asking about post-plant insecticide options for corn rootworm larvae. There are no good (i.e., simple, safe, and effective) options. In the past, carbofuran and chlorpyrifos were occasionally used with varying success but they are no longer options. Counter, Thimet, and Force 3G have post-plant cultivation as an application option but, they have issues. All need to be directed toward the base of the plant and incorporated by cultivation. Some are only available in closed handling systems that would need to be modified and attached to a cultivator toolbar. The organophosphates Counter and Thimet are toxic, and Force’s low solubility will need rainfall.  Finally, there can be interactions with organophosphate insecticides and some herbicides. Read the label!


Soybean aphid eggs should be hatching as buckthorn buds open. Low 2021 aphid populations on soybean, undetected overwintering populations on buckthorn in the fall, and brief periods of bitter cold winter temperatures may indicate another low aphid year. Ultimately, good success when colonizing soybeans in the spring and the weather in late May and June can still develop large aphid populations. By late June or early July we will have an indication of 2022 soybean aphid potential.

Watch degree-day models for seedcorn maggot ( https://vegedge.umn.edu/degree-days-midwest-insects/seed-corn-maggot) if planting into fields that have had livestock or green manure incorporated. Adjust planting dates and/or use an appropriate insecticide if your planting coincides with fly emergence.

Bean leaf beetle populations might have been impacted in areas that had little snow cover. Portions of WC Minnesota have seen economic populations of this insect the past two seasons. Overwintered beetles will be attracted to the earliest emerging soybeans. Fields infested early can see defoliation and pod feeding from 1st generation beetles.

Some folks have been finding white grubs while checking planting depth and seedling emergence. Use a high rate of a labeled seed treatment or at plant insecticide.  Fields with white grub infestations tend to have problems in future years. White grubs and seedcorn maggots sometimes can get past soybean and corn insecticide seed treatments.


Start scouting black (and other) cutworms next week. Pay close attention to low lying areas and areas that had weed escapes last fall.

Pest forecast models

Disease forecasting

North Dakota Ag Weather Network (NDAWN) (Crop Growing Degree Day Models and some wheat, sugarbeet, and potato disease models. NDAWN does not cover all of Minnesota but does have numerous stations in NW and Central MN). https://ndawn.ndsu.nodak.edu/

Insect forecasting

NDAWN has an option to calculate degree-days for several base temperatures. All accumulations start March 1st

UMN VegEdge  Website has insect degree-day development models for MN and WI. Mainly vegetable pests but does include alfalfa weevil, seed corn maggot and European corn borer. https://vegedge.umn.edu/degree-day-models-select-insect-pests-midwest-region

Insect ID

If you look at enough pictures, you’ll find the right one. The problem is there are many thousands of species. Also, there are numerous species that look similar, even to highly trained professionals. Many insects would benefit from professional ID, particularly if causing crop damage. Here are some Internet available resources that I sometimes use that are available on the internet.

BugGuide (Insects, spiders, and other arthropod adults and immatures) https://bugguide.net/node/view/3/bgpage

Moth photographers group (Moth adults and locations found) https://mothphotographersgroup.msstate.edu/

Butterflies and Moths of North America (Butterfly and moth adults, caterpillars, and locations found) https://www.butterfliesandmoths.org/

Cutworm Pests of Crops on the Canadian Prairies (Pictures and life histories. Not every cutworm but most MN pest species are included. Note: True armyworm are listed as Armyworm cutworm in this excellent publication. PDF) https://prairiepest.ca/wp-content/uploads/2019/05/Cutworm-booklet-Final-EN-May1-2017.pdf

Field Guide to Common Western grasshoppers (an excellent reference on ID and biology of short-horned grasshoppers (Acrididae). Only a few cause crop damage in Minnesota but there are more species than you might suspect. PDF file.) https://www.ars.usda.gov/ARSUserFiles/30320505/grasshopper/Extras/PDFs/FieldGde.pdf

Bugwood Image Database System (Pictures are available for non-profit use but they should be cited when used. There are also some weed and disease pictures) https://images.bugwood.org/

Happy trails,