SW MN IPM Stuff 2020 Issue 12

Volume 23 number 12   7/08/2020

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

This newsletter is also available in a print-friendly pdf format: PDF iconSW MN IPM Stuff 2020-12


For the most part, the crop in SW (and much of Minnesota) looks pretty good. It could always be better but so far this one looks pretty good.

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.

Captain Obvious reported that “It’s been very warm with some areas of drier conditions, some areas with excessive rainfall.” There is a good crop in many areas. Some issues with down corn in SW MN after the July 6th weather.

Foliar fungicide decisions in corn and soybean

by: Bruce Potter, Dr. Dean Malvick, Travis Vollmer, and Dr. Angie Peltier

As corn begins to tassel and soybeans near the R3 stage some may still be deciding whether a fungicide application to their fields will be helpful. 

Over the past several years we have been conducting a study on potential yield benefits from insurance application of fungicides. These studies were conducted from 2016-19 (soybean) and 2017-19 (corn) and located at University of Minnesota Research and Outreach Centers.

The studies were based on the premise that over time, a network of standardized fungicide studies can provide Minnesota farmers and their advisors information to better understand yield impacts from disease and return on pesticide investments.

At each study site and year, two fungicides were applied to several corn hybrids and soybean varieties at approximately the VT and R3 growth stages respectively. The fungicides were applied to rotated corn and soybeans. Unlike most pesticide efficacy studies, the sites were not selected based on anticipated crop disease pressure.

Briefly summarized, the results are:

  • Disease pressure was low to moderate at all site-years.
  • For corn, only 1 of the 11 site-years for corn showed a significant yield response for foliar fungicide application.
  • For soybean, 9 of 17 site-years showed significantly higher yields where fungicides were applied, 8 of these were in southern Minnesota.
  • Not all of the yield responses observed would have been economical
  • Moisture differences may be influencing the yield responses for both crops and these effects might change with harvest timing.

It is unlikely that applications of foliar fungicides on an insurance basis can overcome poor variety selection and other agronomic decisions. These results do not reflect the results expected when effective fungicides are appropriately applied to fields where significant disease occurs.

Suggestions to improve the odds of return on a fungicide investment include:

  • Disease has been observed when scouting.
  • Short and long-term weather forecasts are favorable for disease.
  • The hybrid/variety is susceptible to an observed or expected fungal pathogen (e.g. northern corn leaf blight, gray leaf spot, frogeye leaf spot).
  • The timing for adding a foliar fungicide to a post-emerge herbicide application is seldom optimal. Adding an insurance insecticide to a fungicide application can produce undesirable results.

More details on these studies and an estimate of the probability of return on investments can be found on our Research Results webpage:

These studies were funded, in part, by the Minnesota Corn Research and Promotion Council and Minnesota Soybean Research and Promotion Council and their respective checkoffs.


Tassels are beginning to emerge in many fields.

Degree day accumulations indicate that scouting should be underway for Univoltine corn borer in southern MN.

Corn rootworm beetles are starting to emerge. There are some reports of significant damage to both conventional and RW Bt-traited corn. I would appreciate hearing about problem fields and am curious what sticky traps will find for beetle numbers ad species.


The hot weather and heavy rainfalls have slowed soybean aphid populations in some of the indicator fields I have been looking at. The majority of the aphid populations have left one of my indicator spots at the SWROC, leaving behind some frustrated ants.

Although new vegetation is still being produced at the top of the plants, some aphids are now found lower in the canopy, perhaps a response to heat and storms.

If you want to play with projecting aphid populations this aphid day calculator spreadsheet might be of use.

Potato leafhoppers are abundant but not expected to cause yield issues on these larger soybeans.


Watch the pea aphid and potato leafhopper populations.

Happy trails,

Bruce Potter