SW MN IPM STUFF 2017 Issue 10

07/24/2017

This newsletter is also available in a print-friendly pdf format: SW MN IPM STUFF 2017-10

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

Crop weather

windmill with missing bladeFigure 1. The area around Hendricks, MN has been hit with a couple big storms this year. This windmill was probably rougher running than a stalk chopper with missing knives. Photo: Chad Estabo - Centrol.

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.

Most corn tasseling to pollination. Most soybeans are R2-3. Small grains are ready and harvest has started.

Welcome rain in many areas last week. Unwelcome wind and hail and reports of tornados in others. Lodged and green snapped corn.

Corn

Univoltine biotype of the European corn borer moth. So far light trap numbers continue to be low: https://www.vegedge.umn.edu/moth-data/ecb-info. However, I had one report of probable a probable univoltine corn borer infestation from Central MN. 

suspected bacterial leaf streakFigure 2: Suspect, not lab-confirmed, bacterial leaf streak. Note irregular wavy edges. Many times there is a yellow halo like in this backlit photo. Photo: Dan Coffman

Since the last newsletter we have received several heads-up for bacterial leaf streak of corn in southern MN and it has been confirmed to be in the state. If you suspect you are seeing symptoms, contact Dean Malvick (dmalvick@umn.edu). Dean’s lab will confirm the presence of bacterial streak. We are trying to determine the distribution and potential yield impact of the pathogen in Minnesota. Might even make a distribution map at the end of the season if there are enough samples coming in to the lab.

aerial view of crop rotation's effect on western corn rootworm injury and lodgingFigure 3. Effect of crop rotation on western corn rootworm root injury and lodging.

Corn Rootworm

Western corn rootworm populations are definitely higher than previous years in some SW MN continuous corn fields.

6-day sticky trap with corn rootworm beetle captures Figure 4. A six–day rootworm beetle capture from 2017 research plots at the SWROC.

At Lamberton, and several other locations, both CryBb1 (VT3) and corn hybrids without a Bt-RW trait have severe root damage and are producing very high numbers of beetles. Here, northern corn rootworm beetles are present but at very low levels, at least currently.

What does this mean for corn rootworm beetles in your area or fields? Nothing, other than impressing the need to scout populations to determine risk for 2018 corn. Remember, after a non-corn crop in a field’s rotation, it may take several years of corn for western corn rootworms to rei-infest and reach economically damaging populations.

volunteer corn in soybeansFigure 5. Live volunteer corn, this late in the season, is not an effective crop rotation.

Start scouting now! Don’t assume lodged corn is due to rootworm without checking the roots.

Soybean

The painted lady butterflies can be seen in large numbers. These quick and nervous fliers can be seen drinking nectar from flowers and moisture from water puddles. While painted ladies very agile fliers, they fly low to the ground and susceptible fast moving vehicles. They are thick enough to plug a radiator in some areas. There could be a second generation produced on soybeans but these butterflies have erratic migration patterns and large numbers may move to other areas.

painted lady butterflyFigure 6. Painted lady butterfly

We will start to see larvae in August. Scout for these as you are scouting for soybean aphids and other defoliators, combining defoliation for those species actively feeding when determining economic risk. Other lepidopterans in soybeans now include green cloverworm and alfalfa caterpillar. I am also starting to see a small amount of flea beetle feeding. Nothing I have seen or heard seems threatening.

Diseases are relatively minor at this point. The occasional bouts of tropical weather we have been experiencing in many parts of the state may change that, but I wouldn’t get too excited until significant fungal disease is observed. If you’re planning on a fungicide, there is no reason to rush it.

Soybean aphid watch 2017

lady beetle larvaFigure 7. Allowing beneficial insects, like this lady beetle larva, to control soybean aphids is just one of the reasons you are encouraged to wait until aphids are at economic threshold before insecticide applications.

Most of the action is currently centered in some, but not all areas of NW MN. Aphid populations are present across the state but have not built to threatening levels in most.

A network of underground informants shared excellent information on soybean aphid populations. There have been a few scattered insecticide applications in parts of central MN and a very few further south. Most of these have been in small fields with wooded areas, and presumably buckthorn, nearby.

two spotted spider mitesFigure 8. Flaring other pests, like these two spotted spider mites for example, with an insecticide application is always a concern when an insecticide is applied. Don’t push your luck.

In much of Southern MN, aphid populations are low and early season colonization appeared somewhat slower than typical. Populations have built over the past week and in some areas of SC and SW MN populations have been very uniform in infestation rates and aphid age classes. This lack of hot spots indicate these fields were colonized relatively late by large numbers of immigrating aphids. It is unknown if these were produced in nearby fields, but they could have come from anywhere a large number of winged aphids were produced.

weedsFigure 9. Why you are encouraged to kill weeds early and why they are small.

Weeds

Waterhemp, and a few other species, are starting to make their appearance above soybean canopies. For future management, remember the problem fields. Pollinating waterhemp and ragweed are very attractive to corn rootworm beetles, however, we do not believe that MN populations lay eggs only in corn.

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. Pre-register online here to help us plan for lunch.

Other UM SWROC Events

Happy trails,

Bruce