SW MN IPM Stuff 2019 Issue 4

Volume 22 number 4


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: PDF iconIPM Stuff 2019-04

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.

In some parts of southern and western Minnesota, good corn and soybean planting planting progress was made over the past week. Where planted into good conditions, corn and soybeans are emerging rapidly and stands are good. Corey Sinn called to mention that, across southern MN, there are emergence issues with corn planted into wetter soils on May 16-17 compared to other dates. This matches what I have seen in a field that was planted on the 17th. While attempting to beat a forecasted heavy May 17 rain, most understood the risk. Some parts of these fields will need to be replanted. There are also soil crusting issues in some soybean fields.

On 6/4-6/4, heavy rain and hail affected the upper Minnesota River Valley with rain spreading south and east along the valley into SE MN. Many of these areas in west and central MN were already suffering from excess moisture and planting delays. Frenchie Bellicot reported that, fortunately, emerged corn was only V1 stage and should be OK. I have not heard if any wheat or sugarbeet crops were affected by hail. The 1.5 to 2-inches of rain put a crimp in planting and scouting. Fortunately, much of the SW corner of the state missed the heavy rain.

The benefits of pattern tiling are obvious this tough, wet spring. Curt Burns called to point out that fact and briefly discuss the difficulty of intensively managing crop inputs without good drainage. He’s right...effective crop and pest management needs to start at the start.

Crop pest management focus is on weed control now. But don’t ignore other pest issues while scouting. 

black flyBlack fly

Another issue brought on by the high precipitation and stream levels in 2018 and now in 2019 is a bumper crop of black flies, a.k.a. gnats, a.k.a. buffalo gnats, aka. turkey gnats, a.k.a. annoying little bloodthirsty #@!s. Unlike mosquitos, the aquatic larvae and pupae live attached to rocks and other substrates in unpolluted, running water. Also unlike mosquitoes, the adults are active during daylight hours. For a couple weeks now, adults have been emerging. The appearance of the adults follows water temperatures and progresses upstream. After emergence, adults can be found quite far from water. Male blackflies feed on nectar, but the females use a blood meal to develop their eggs, which are deposited in streams. Different species prefer particular hosts for a blood meal. When populations are very high, stress and blood loss caused by blackflies can kill animals. Birds can be suffocated from black fly clogged nostrils and nasal cavities. In 2018, black flies caused mortality to raptor chicks in Iowa. Jay Zielske mentioned chickens had succumbed to black flies this spring. Well, if there’s a bright spot, it’s that I suppose this means many of the streams in MN are not too polluted. 


Black cutworm

So far it has been quiet this spring. Larvae from the late-April flights should be at or near 4th instar and will be actively feeding until late June. The 4th-6th instars do the bulk of the larval feeding and large larvae can kill up to 5-6 leaf corn by cutting below or into the growing point. Last week, I observed leaf feeding in two Rock County strip-till fields. Steve Commerford reported leaf feeding and a few cut plants in a SC MN corn field and C MN sugarbeet field.

True armyworm

Blacklight and pheromone traps have been picking up a rather large influx of true armyworm moths over the past week. On June 3rd, the SROC trap in Waseca had a three-night capture of 106 armyworm moths, and the SWROC trap in Lamberton had a 35-moth capture over the same period. If the large Waseca capture occurred over just one or two nights, this could be a crop threatening migration. We will continue to monitor flights of this insect over the next few weeks. Light trap captures can indicate that a migration into Minnesota has occurred but not where problems will arise.

True armyworm moths lay eggs in areas with dense grasses. In a couple weeks, pay close attention to corn in fields with dense grassy weeds and corn planted into a rye cover crop. This morning Brian Weller sent a photo of a mid-stage armyworm caterpillar from an earlier flight. It was found this in a field with a rye cover crop. Lodged wheat, barley, oats, and rye and field borders with lodged grass are also good areas to scout for the presence of armyworm larvae with a sweep net.

European corn borer

1st generation multi-voltine European corn borer should be hatching soon in much of the southern part of the state. UMN researchers picked up the first male moth in a Rosemount ROC black light trap on 6/03. While I usually count on seeing the first corn borer moths within a few days of peony blooms opening, there is another method. See UMN Vedge Edge for corn borer degree-day development models (Figure below). The degree-day models can help with timing of scouting efforts. 

degree day development model map of MN

Corn rootworm

I looked at a few degree-day models. They indicate that egg hatch is delayed this spring. In fields with high populations, unlike 2018, June planted corn could still be at risk of injury this year.

We will be coordinating a network for corn rootworm sticky trap data this year. If you would be interested in participating and sharing your data please contact me. We can supply a relatively pain-free sampling protocol and a number of yellow sticky traps.


Second generation seedcorn maggot fly activity should peak next week over much of southern MN. These insects could impact soybeans planted very late. If planting into fields with incorporated livestock or green manures (including dense weeds); see UMN Vedge Edge or degree-day predictions.  

We do have fields in Minnesota with emerged soybeans. These fields will be the ones to watch early on for how well soybean aphids colonized soybeans. Early soybean emergence and dry conditions can contribute to good soybean colonization success. Areas of Minnesota where aphids do well early in the season will help determine and drive the 2019 aphid populations.

It looks like these soybean gall midge may be more widespread in MN than I previously hoped - see the MN Crop News update on soybean gall midge for more details.

potato leafhopperPotato leafhopper


As the first cutting is underway, here is a reminder of some insects to watch for in 2nd cutting.

As of June 3, potato leafhoppers have arrived at Lamberton. They are at very low populations here but southerly winds may have brought higher populations to other areas.

alfalfa weevilAlfalfa weevil larvae

Alfalfa weevils range from adult to 2nd instar. Larvae are still hatching in SWROC alfalfa. Watch 2nd crop regrowth in fields with higher populations.

Variegated cutworm are relatively abundant this year. High populations of both these and alfalfa weevils can cause damage under windrows if they lay in the field too long.

variegated cutwormVariegated cutworm

Pea aphids numbers are increasing but it takes very high numbers and often a lack of soil moisture to reduce yield. Insecticide applications that kill beneficials can flare pea aphid populations.

For thresholds and scouting information on alfalfa insects see: Alfalfa insect scouting and action thresholds.

Happy trails,

Bruce Potter