SW MN IPM STUFF 2017 Issue 7


This newsletter is also available in a print-friendly pdf format: SW MN IPM STUFF 2017-06

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

GDD comparison graph

SWROC growing degree days comparison. Source: U of MN SWROC weather

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.

There have been 862 degree-days and 8.68 inches of rain accumulated from May 1-June 30, the latter above average.

Hail and crop pest management

early bacterial blight lesions on soybean

Early bacterial blight lesions on soybean.

Another large hail storm went through parts of Lincoln and Lyon Counties and into South Dakota on June 22. Some growers fell victim to big hail stones and significant crop loss.In areas that have received hail, look for Goss’s blight and wilt to appear on susceptible hybrids later. In areas where Goss’s occurs it needs to be considered in future hybrid selection. Common smut of corn and soybean bacterial blight are also more common after hail. None of these diseases are controlled with fungicide.

Captures of true armyworm moths in the black light trap at Lamberton dramatically increased after the hail event and the moths have been common since. This morning there were 50 moths in the trap, enough to raise some concern for small grains and corn crops. In areas near hail, I would spend some time scouting for armyworm for the next two weeks. The moths prefer to lay eggs in dense grass vegetation and the larvae feed primarily on grasses. Grassy areas, particularly when lodged, near corn and small grain fields and lodged small grain crops are good places to focus initial detection efforts. A sweep net is a very good tool to find small larvae.

early instar true armyworm larva

An early instar true armyworm larva. Note the longitudinal stripe pattern and the net-like pattern on the head. They're so cute when young.

Corn herbicides and replanting after hail

Even replanting short season corn for silage corn at this time of year is not likely to turn out well, so soybean, sorghum, millet or other cover crops may be considered.

If the re-plant is not harvested or grazed, rotational restrictions for crop tolerances are not a concern, but they still can impact the chances of successful crop establishment. The following references may provide some help in deciding whether soybeans or cover crops can be planted after corn. From U of M Extension: Using herbicides and cover crops in corn and soybean (includes additional references) and from Penn State: Herbicides Persistence and Rotation to Cover Crops

Maintaining weed control (waterhemp in particular) in hailed out areas is important for long-term weed management and avoiding fallow syndrome in following crops.


Early planted corn is up to 12 collars. Most of the crop is looking good.

shotholing caused by feeding of young first generation corn borer

Shotholing caused by feeding of young first generation corn borer.

Scouting for first generation corn borer in corn without a Bt corn borer trait should be underway and wrapping up in the southern part of the state soon. Damage from 1st generation corn borer is easily seen in the whorl. Scouting guidelines and economic threshold guidelines can be found at: Corn pest Management. This publication is in need of an update but still useful. The 80% efficacy might be a bit optimistic.

A bit of corn borer nostalgia from 1927.  Some of you might find this interesting: European Corn Borer from the UMN Conservancy.

Volunteers wanted

We are looking for growers that are willing to let us survey corn borer in their corn field this fall for more information see: Assistance with European corn borer survey requested.

Other insects in corn

I have been seeing a few armyworm and common stalk borer out there but have not heard of any significant problems.


Early planted soybeans are now blooming. Some herbicide is still going on. It is getting late! We will soon know how careful we all were with drift and tank cleanout for dicamba and other herbicides. There are already some reports of drift of corn herbicides to beans.

yellow bear caterpillar in soybean

Yellow bear in soybean. Photo by Matt Wordes, SW MN IPM

Soybean fields are looking better with drier fields. Iron deficiency chlorosis (IDC) is an issue is some fields. IDC tolerant varieties can get show iron deficiency symptoms. Soybean cyst nematode (SCN) resistant varieties can be damaged by very high SCN populations or SCN populations virulent on resistant varieties.

However, while some level of SCN can be found in most southern MN soybean fields, just seeing IDC symptoms does not mean it is caused by SCN.

Soybean aphid watch 2017

Some of the early colonies have dispersed, colonizing new plants and fields. I am seeing aphids in plots where soybean seed was treated with a neonicitinoid insecticide.

While soybean aphid populations are still currently low, it would be prudent to start scouting efforts after July 4th. Practice always improves performance, aphid scouting is no exception.

thistle caterpillar

Thistle caterpillar. Photo by Adam Hass, SW MN IPM

Painted lady larvae (thistle caterpillars) are fairly common, but not economic this season. We could find some that survived hail at the hail clinic in Lincoln County yesterday. You might even find some of their tan pupa with gold spikes.

White, hairy caterpillars in soybean are present this spring. These are yellow bears, the larvae of the Virginian tiger moth. I doubt that they would be numerous enough to be economic. Treat them the same as other general defoliators.

Pest Management Field day at the Southwest Research and Outreach Center August 9

We have a pest management field day planned for August 9th. Details will follow next week.

We typically need rain about this time of year. My scheduling a pest field day should help.

painted lady/thistle caterpillar chrysalis

Painted lady/thistle caterpillar chrysalis

Other U of MN SWROC Events

Additional Extension events you might be interested in include:

  • Field school for ag professionals (St. Paul Campus) 
  • Corn and soybean weed management tour (Rochester)

 Happy Trails,