SW MN IPM STUFF 2017 Issue 12


This newsletter is also available in a print-friendly pdf format: SW MN IPM STUFF 2017-12

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 SWROC Weather.

While the cooler weather has been good for corn pollination, it has further slowed soybean development. Soybeans in many parts are still R4 or less and behind where they would normally be this time of year.

Cool weather will slow down pest development down. Heavy dews and rain combined with cool temperatures will favor some pathogens if inoculum is present and crop genetics are susceptible. Insects have fungal and bacterial pathogens that can be favored by these conditions as well.


Corn Rootworm

Western corn rootworm egg–laying is underway in research plots at the SWROC. Populations in this heavily infested area are starting to decline as crowded females leave and males are starting to die.

The northern and western corn rootworm problem fields that I have heard of are all on corn without a rootworm trait, some with and some without insecticide. Multiple years of corn without a Bt-RW trait are most common but extended diapause northern corn rootworm populations are still present.

Bacterial leaf streak

If you observe this disease you can help us try to understand the distribution and factors influencing this disease in Minnesota. Dean Malvick (dmalvick@umn.edu). Dean’s lab will confirm the presence of bacterial streak.

U of M Plant Disease Clinic sample submission instructions and forms can be used when you submit samples. For the week of August 6th, submit your samples to the U of M Plant Disease clinic.  Samples submitted after August 13th should be sent to:

Dean Malvick

495 Borlaug Hall

1991 Upper Buford Circle

St. Paul, MN 55108


+1 612 625 5282

Including the following information on the form will be helpful in understanding the epidemiology. Hybrid information will be helpful in understanding if there is a genetic component to infection. Location information will be used to generate maps but field specific information will not be published.

  • Location
  • County & GPS Coordinates
  • Disease information
  • Hybrid(s) affected (if known)
  • Describe incidence (% of plants with symptoms/field wide or localized)
  • Describe severity of symptoms (percent of corn leaf area affected/individual leaves or most of the plant)
  • Any weather events that may have infected disease (hail, high wind flooding)
White mold mycelia and developing sclerotia on soybean stem.Figure 1. White mold mycelia and developing sclerotia on soybean stem. Photo: Deep throat.


Drying and dead plants symptomatic of white mold are showing up in some fields. Cooler, wet weather in the forecast and soybean still blooming will favor this disease. Dense canopies from high fertility and high plant populations favor this disease.

Watch for SCN symptoms - Last week I forgot to mention water-logged soils as another, abiotic cause for yellow soybeans. Most of you with yellow beans standing in water have already figured this out.

The 2nd round of thistle caterpillars are very abundant (several/plant) in some soybean fields. Larger plants can tolerate more larvae before reaching a 20% defoliation threshold.

Soybean aphid watch 2017

Over the past week pocket of soybean aphids reaching economic threshold began to appear in SW MN. As always, not having to treat a field is preferred but not always economically viable. Because soybean development in many fields is behind that in most years, the longer you can wait to treat, the better. Watch for re-infestation of insecticide treated fields or late developing economic populations. Fields with that are late planted or otherwise later maturing deserve extra attention.

Soybean aphids attacked by fungal disease.  Figure 2. Soybean aphids attacked by fungal disease. Note discolored aphids.

While the cool weather will slow soybean development, it might have a positive effect on aphid management.  Most aphid fungal pathogens are most effective in cool, wet weather. Look for gray to brown dead aphids. Fungal diseases can cause the rapid collapse of aphid populations. Soybean aphids develop slower but will produce more young in cool weather.

Some of you may have been hearing about a carbamate (Group 1A) insecticide methomyl (e.g. lannate, nudrin) as a control for soybean aphid.

These insecticides are labeled but for aphid control in soybeans. However, methomyl has a high acute toxicity to humans! Many of you are not used to handling or otherwise dealing with insecticides this toxic. Pyrethroid resistant aphids or not, safer insecticide options are available. 

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

We have a Pest Management Field Day planned for August 9th from 9:30 AM to 12:30 PM. The event will cover soybean aphid management and aphid resistant varieties, soybean agronomics and SCN, corn insects, and weed management. After the tour stops and a lunch, there will be the opportunity to discuss future research and education needs. This field day is sponsored, in part, by Minnesota Soybean.

The event will be held rain or shine. Since the event includes a noon meal we need a reasonably accurate head count. If you plan to attend please remember to Pre-register online here to help us plan for lunch.

Happy trails,