SW MN IPM Stuff 2022 Issue 8

Volume 25 Issue 8 | June 16, 2022

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 http://swroc.cfans.umn.edu/weather.  

An extreme rainfall event in parts of Cottonwood and Nobles Counties left standing water and soil erosion in its wake.

The recent and upcoming warm weather will speed crop and insect development, but the heat combined with winds will be hard on soybean aphids that are colonizing small soybeans.  

Chronic wind and the forecast hot weather will not make pesticide applications easier. Avoid drift.

Crop Progress

Early planted corn is V5 to V6.

The earliest soybeans are V3 with a few V4.

Alfalfa weevil populations in parts of WC and C Minnesota are problematic again this year. Heavier infestations may relate to areas with higher populations last year an more snow cover this winter.

In addition to earlier reports of black cutworms in corn and sweetcorn, a few reports of cutworm injury to sugarbeets have been coming in.  Problems seem focused on the Renville to Meeker County area. The cutworm populations seem to be fairly low, but they are cutting and killing beets in stands with already low populations. Cutworms have been staying below ground to cut making control difficult.  They should be still feeding larvae and should begin pupating around June 20th. Larvae from mid to late May flights will be active into July.  

Some folks appear to have hit the jackpot with respect to timing planting with seedcorn maggot adult activity. Soybeans planted late into passed 2021 sugar beets, right after cover crops and dense weeds were worked down seem to have the most problems.

On July 15, soybean aphids were found in V3-4 stage soybeans at the SWROC. The appearance of aphids in soybeans, development of volunteer or very early planted soybeans, and buckthorn reproductive stage once again appears to be closely related here. Based on the stage of the nymphs, they had been deposited A few days ago.

Buckthorn SBA
Buckthorn reproductive stage and soybean aphids on V4 stage soybeans.

Soybean aphid populations are barely detectable at this point and nowhere close to yield-threatening levels. It may be worth looking at the early planted fields, particularly those fields you often find aphids first. Tracking aphid populations in a few of those fields will start to develop a picture of how well they were able to colonize soybeans and if/how fast populations increase.

Soybean aphid populations have been low for the past few years. Some of you might miss seeing large, yield-robbing soybean aphid populations in your fields. If would like to help the aphids out, you could try tank mixing an insurance pyrethroid insecticide with your soybean post emerge herbicide. It could get sporty. This is not a recommended practice if you are trying to avoid problems with soybean aphids, and potentially other pests, on your farm.

Bean leaf beetle populations appear to have wintered well. At the SWROC populations may be higher than last year at this time (Figure 1). Their survival makes me suspicious that western corn rootworm eggs survived well too.

Bean leaf beetle and feeding injury to soybean seedlings.
Figure 1. Bean leaf beetle and feeding injury to soybean seedlings.

For more information on bean leaf beetle can be found in Minnesota Crop News.

Corn rootworm

As of 6/15 at the SWROC near Lamberton, MN  we were at 403 DD at 2" soil depth and 407 DD at 4".  Rootworm eggs should be starting to hatch.

Coincidence, or not, “Deep Throat” reported a firefly observation on 6/13 in SC Minnesota. For more information on the timing of corn rootworm egg hatch see Issue 7 of SW MN IPM Stuff.

Little yellow spiders

I’ve received a couple of photos from folks finding large numbers of small light-colored spiders in fields. They might be goldenrod crab spiders. They are harmless and beneficial.


Common whitetail dragonfly
Figure 2. Common whitetail dragonfly

There are quite a few species of dragonflies and damselflies that make Minnesota their home during the summer or year-round. See one you don’t recognize?  Minnesota Dragonfly has a handy online reference.

Happy trails,

Products are mentioned for illustrative purposes only. Their inclusion does not mean endorsement and their absence does not imply disapproval.

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