SW MN IPM Stuff 2021 Issue 8



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

The first part of the growing season has seen some wild temperature fluctuations. In June, there were eleven days above 90ºF and pockets of frosted corn in Meeker and Stearns County on June 22.

At the SWROC, we have had 4.66 inches of rainfall since April 1. Not a lot, but better than some areas. From last Saturday to Tuesday Minnesota was a state of haves and have nots with respect to rainfall (Figure 1), the SWROC received 0.43 inches.

precipitation map over Minnesota and surrounding states
Figure 1.

We have received less than half of average rainfall and well above average temperature accumulation. From May 1 to June 28, the SWROC accumulated 3.08 inches of precipitation compared to a 7.43-inch historical average and 938 growing degree-days compared to an 850 GDD long-term average.


Most corn is now V12 and above and rows have closed. Moisture stress is the main concern in some parts of the state, including the SWROC area, as corn needs increasing amounts of water now. Other areas are in really good shape for moisture.

Corn rootworm feeding is visible on nodal roots now. Larvae are mostly 2nds and 3rds, but as of June 30, we have not yet seen pupae at the SWROC. Others, however, have found pupae. Beetle emergence is expected to be early this year but unexpectedly early, I have already received a couple reliable 2nd hand reports of western and northern beetles in South Central Minnesota and we found a couple newly emerged beetles near Luverne today.  

For the most, high beetle populations and rootworm damage has been observed in fields that have been in long-term corn. However, I received a call this week about damage to Bt-RW hybrids in a 2nd year corn field in SW MN. Scouting corn fields for beetle populations is becoming increasingly important, particularly in areas of Minnesota where continuous corn is prevalent. I suspect there will be quite a few unexpected damage reports again this year.

We are in the process of shipping sticky traps for a rootworm beetle trapping project. We hope this project will provide data to help encourage field specific management of rootworms and understand to changes in rootworm populations and Bt resistance.

European corn borer captures have been very low this spring, but we did capture our first moth on July 1. Based on degree days this should be a univoltine individual. This year some univoltine scouting will likely be on corn still in the whorl stage. Scouting for 1st generation should be completed see: degree days for insect pests.


The earliest emerging soybeans in SW Minnesota are now V7 and above and R2 stage. SCN are active this year but otherwise things have been quiet on the disease front in drier areas.

There are some not yet diagnosed issues on soybean in an area of Waseca County that received heavy rainfall. The large areas of dying plants may be disease related or some other factor. We are trying to sort out the cause but if nothing else, I was able to add the word abiotic to Jay Zielske’s vocabulary.

Two spotted spider mites

According to Professor Ian MacRae, a few spider mites have been spotted in the drier areas of NW Minnesota. Other than a couple small areas at the edge of a corn field, I have not yet found any infestations yet this season. Soybeans are most vulnerable to spider mites during the mid-late reproductive stages so that may change quickly with high temperatures in areas that are drought stressed. The upcoming ruling on chlorpyrifos may change our pesticide options in soybeans and other crops.

Bean leaf beetle

First generation bean leaf beetles will be emerging soon. These beetles will be the progeny of the overwintering beetles that laid their eggs in soybean fields this spring. During warm years like this one, an additional summer generation can be produced with beetles present in soybean during spring, early summer, and again in late summer. Defoliation is the concern with this generation and the greatest risk might be pod feeding late in the season. Pod feeding can be more pronounced in dry years. Sorting out pod clipping caused by bean leaf beetles from stress induced pod abortion can get puzzling. Soybean fields where bean leaf beetles were most abundant this spring (usually the earliest emerging) are most likely to see problems in July through early September.

Herbicide injury

If anyone believed there would not be many soybean fields with herbicide injury symptoms this year, they are disappointed. Hot, dry, windy weather and inversions were a recipe for off-target dicamba problems.

While dicamba injury does not necessarily mean reduced soybean yield it can delay canopy closure keeping allowing higher soil temperatures, moisture loss, and late season waterhemp escapes. The first varieties incorporating a new herbicide tolerance released are often not up to snuff on disease and SCN resistance. It is a bit unfair to those who chose to plant dicamba susceptible soybean varieties.

However, do not jump to conclusions on herbicide drift. While there certainly are fields with drift, drought stress can also cause reduced leaf size and some leaf cupping. In some cases, it is not going to be easy to sort out where the herbicide came from. While playing drift detective, remember that growth regulator herbicides were applied to both corn and soybeans in June.

Some wounds are self-inflicted. Spray tank/boom contamination is a possibility in some cases. Some layered pre-emerge applications (e.g., dual, outlook, etc.) can cause leaf that can be confused with a growth regulator.

There are some fields where dicamba and 2,4-D choline injured but did not kill waterhemp. I looked at a field last night where injured survivors were developing new roots, and some are likely to survive. If not for the surrounding dead waterhemp plants, it would be easy to blame these escapes on environmental conditions.

This is the same dance that we went through with glyphosate resistance. Partially because of performance, and partially because of resistance to other chemistries, we are now using growth regulator herbicides in corn and soybeans, often in the same fields. The loss of growth regulator herbicides will tighten the noose. Weed management is going to get a lot more complicated. Maybe herbicide tolerant crops were not such a good idea.

Soybean gall midge

Adult captures in emergence cages have shut off after a week of activity. There was a bit of rain at the Rock County research site last weekend but it did not trigger any additional emergence. Orange 3rd instar larvae are the predominate stage now. We are finding a high percentage of plants infested on the field edge.

SGM injury symptoms on stems are present now and we are just starting to see wilting and dying plants on field edges. Damage looks to be much less than previous years but by next week, I will have a better feel on how this year’s infestation compares to 2020 and 2019.

See my soybean gall midge scouting video for early season scouting tips.

Please contact me if you find soybean gall midge in your Minnesota soybean fields.

Soybean aphid watch

soybean aphids on the underside of a soybean leaf
Figure 2. Soybean aphids parasitized by wasps. Photo: Gabe Schumacher

Soybean aphid populations remain low, likely lower than most years at this time.

At the SWROC, there have been some high rates of wasp parasitism (Figure 2) of isolated, larger aphid. Several consultants have reported none to few aphids in areas that traditionally have early season aphid populations.

Soybeans are under significant moisture stress will not support large aphid populations. Unfortunately, they will still be vulnerable to two-spotted spider mites.

After July 4th, you might want to check some of your known aphid hotspots to get a feel for 2021 risk.

As always, I like to hear your observations on soybean aphid populations.

Small grains

This weekend’s heat will not be helpful on fields that still have some potential to fill grain.

Aster leafhopper nymph populations have declined as crops mature. This insect can transmit the aster yellows phytoplasma disease. There are some reports of aster yellows symptoms on garlic. Several other crops such as lettuce, carrots, and many ornamentals are more susceptible to damage from the aster yellows.

Cereal aphids will be moving from what is left of the small grains to corn and other hosts. In MN corn most aphid populations tend to build after pollination and decline as the crop reached dough stage. However, in dry areas, aphid movement may have been triggered early and any documented yield impacts of cereal aphids on corn have been from heavy populations on drought-stressed corn before pollination. 

Things that go bump in the night


On June 24, a Faribault County black light trap found 100 armyworm moths, a very large single night capture! Thanks to Suzanne Wold-Burkness for the heads-up!

Armyworm moths were abundant around New Ulm last weekend also. There have also been some larger captures in pheromone traps near grass seed production fields in Roseau and Marshall Counties. These could be locally produced moths although, they could also be immigrants produced elsewhere. I need to do some more checking, but I did not notice any obvious weather systems conducive to migration into that part of MN near the 24th. Moths from this flight may not have stayed in the area where the large capture occurred and laid their eggs elsewhere in Minnesota.  

It will be worth looking for the larvae from this moth flight in two to three weeks. There are some areas where rains caused grasses to lodge. These are good spots to run a sweep net through. 

Hot, dry weather and drought stressed plants will not favor armyworms (they leave Texas and other southern areas in the spring for a reason). While this type of weather reduces risk from armyworms, it does not eliminate risk.

Army cutworm

One of the moths we look for in black light trap captures in July is the western bean cutworm. While we have not yet captured any western bean cutworms, the black trap located at the SWROC captured a look-alike over the past few days. Several army cutworm moths were blown off course on their way to summer habitat in the Rocky Mountains. This insect is not a typical pest in Minnesota.

The western bean cutworm is a significant corn pest in some areas. They can be distinguished from the army cutworm by a broader white band on the leading edge of the forewing. For those running western bean cutworm pheromone traps, be advised that they can capture other moth species, particularly yellow-striped armyworms.


Most economic infestations this year have been observed in NW Minnesota, but I have heard of one field in WC. While we often think grasshopper populations starting from the field edge, red-legged grasshopper species like to lay eggs in alfalfa and both red-legged and differential grasshoppers often lay eggs in soybeans. Infestations in crops planted after alfalfa and soybeans can start within the field.

Meetings and other topics of interest

Have a great Independence Day holiday and happy trails,

Bruce Potter