SW MN IPM Stuff 2019 Issue 12

08/9/2019

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

A print-friendly version of this newsletter is available to download here: SW MN IPM STUFF 2019-12

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

As of August 5, we are about three days behind on growing season degree-days (1657 degree-days compared to a 1580 degree-day long-term average from May 1.) However, locally, this overestimates corn development slightly as early May weather was cool and most corn was not planted until mid to late May. 

We have had a more than a week of rain-free weather. At 14.01 inches of precipitation since May 1, we are now 2.23 inches above long-term average. Of course, on your farm, your mileage may vary. 

Sweet corn harvest is underway. 

Field corn stage ranges from silk to blister. Some early planted or short season hybrid fields may have roasting ears. Cooler temperatures will not delay maturity to any great extent and can help with grain fill.   

Soybeans, for the most part, are about a week behind where they typically are at this calendar date. Depending on planting date and maturity group, most soybeans are R3-R4 (beginning pod to full pod) stage. Some, particularly where planted early, are now at R5 (beginning seed stage). Soybean aphid populations respond to these changes in soybean development.

CROP PESTS

Corn

European Corn Borer (ECB)

ECB degree-day development models can be found at VegEdge Degree-day Models & Forecasts. Second generation moth captures in the SWROC light trap have been low. Scouting for 2nd generation should be underway in southern MN.

If you have fields without above ground Bt traits that you would be willing to let us examine for fall survey please contact me at bpotter@umn.edu. We are looking for statewide infestation levels and are collecting larvae to check for parasitism and percent single generation biotype (univoltine).

Soybean

Soybean aphid watch

Use scouting and available economic thresholds to make effective and economical insecticide decisions. Use the correct product, correct rate and read the insecticide label.

Soybean developmental stage and drier weather have allowed aphid populations to increase over the past week. Most fields still have very low populations. In the note on soybean aphid populations earlier this week, I mentioned some fields with higher populations were found near bodies of water. There could be several reasons for that including: field size, soil type, microclimate, and vegetation-including buckthorn. While my intent was not to recommend a particular insecticide but rather present an update on 2019 aphid populations, the comment on bodies of water triggered a request from the Minnesota Department of Ag. They wanted to make sure that I mentioned the following  setbacks for chlorpyrifos insecticide applications: 

MN regulations for applying insecticides containing chlorpyrifos (e.g. Lorsban, generics and mixes) - If you use products containing the active ingredient chlorpyrifos (found in Lorsban, Warhawk, Cobalt, and more), please remember to maintain setbacks from the edge of surface water:

  • Ground application: 25 ft
  • Aerial: 150 ft

Surface waters include permanent water bodies such as rivers, streams, lakes, reservoirs, natural ponds, marshes, and commercial fish ponds, and ditches if they have water flowing throughout the year.

*Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement is implied.

SCN

Female soybean cyst nematodes are visible on soybean roots in southern MN now (Figure 1). Suspect SCN where soybeans are yellowed, stunted or rows are slow to close.

soybean roots with soybean cyst nematodeFigure 1. Although this soybean root looks relatively healthy and is well nodulated, there are several small, white, lemon shaped female SCN visible.

Soybean Gall Midge

soybean field with dead soybean plants on the edgeFigure 2. Faribault Co, MN gall midge infestation. Plant disease may have contributed to the severity of the damage in this case.

While you are out scouting for soybean aphids spend a few minutes on field edges near 2018 soybean fields. Look for wilting or lodged soybeans, some of these may be under the canopy of healthy plants. Infested plants may appear healthy other than a dark discoloration and or callous on the lower stem.  Sometimes larger areas of infested plants can be found, perhaps associated with disease (Figure 2).

Some of these 2nd generation larvae are located higher on the plant than first generation (Figure 3) and some may be found inside the stem. Check for the white to orange midge larvae under the epidermis and in the pith.

So far in 2018, Yellow Medicine, Jackson, Faribault and most recently Lac Qui Parle and Lyon Counties have been added to the list of Minnesota counties with known soybean gall midge infestations.

soybean stem infested with soybean gall midgeFigure 3. Second generation soybean gall midge larvae may be found higher on the plant and inside the stem pith.

Frenchy Belicot and Clint Shindler found several infested fields in Lac Qui Parle and Frenchy found midge in Lyon county while scouting fields for their clients.

Fortunately, the infestation rates have been very low in most of these MN sightings.

Determining the extent of  infestations of this insect occurs is one of the first steps in management. Please let me know if you suspect this insect in your fields!

Brown Marmorated Stink Bug

You might want to keep an eye out this insect in SW and other areas of Minnesota too! Read: Be on the lookout for brown marmorated stink bug in soybean in southeast Minnesota

Happy trails,

Bruce Potter