SW MN IPM STUFF 2017 Issue 6

6/16/2017

This newsletter is also available in a print-friendly pdf format: SW MN IPM STUFF 2017-06

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

There have been 648 degree-days and 7.77 inches of rain accumulated from May 1-June 16, the latter above average. The big weather news was the hail across parts of Minnesota on June 11.

Alfalfa

Alfalfa weevil activity is starting to wind down in southern MN. Some fields reached economic levels. This year, cutting followed by hot, dry weather was hard on larvae.

Potato leafhoppers are now present in alfalfa. New seeding alfalfa often has higher populations and is more susceptible to damage. Use a 15-inch sweep net to sample new seeding, 2nd and 3rd crop alfalfa for potato leafhoppers. Nymphs indicate a reproducing population in the field. To assess populations, take 3-5 sets of ten pendulum sweeps (http://www.extension.umn.edu/agriculture/forages/pest/#insect) making sure the interior of the field is sampled. The economic threshold is based on numbers of leafhoppers and size of alfalfa. It basically works out to 0.1 leafhoppers/sweep/inch of alfalfa height for alfalfa 12” tall or less.

Alfalfa heightPotato leafhoppers/sweep
< 3"0.3
3-7"0.5
8-12"1.0
>12"2.0

Corn

Some folks are done and some folks trying to finish up herbicides. Good broadleaf weed control in soybeans starts with good broadleaf weed control in corn.

Early-planted, narrow-corn has closed canopy and thirty-inch rows are not far behind. Early planted corn is V8 now and most early-planted corn has the growing point above-ground now. 

Where soils remained saturated for a period of time and emergence was delayed, there are some stand issues from corn seedlings damping off at the two–three leaf stage. Hot dry soils, sometimes exacerbated by shallow planting, have produced rootless corn syndrome in some fields. Recent moisture should help with future nodal root development.

Corn rootworm hatch should be underway but wet soils have prevented verifying that in research plots here.

The EPA has recently approved conditional registration for Monsanto’s SmartStaxPRO corn. These hybrids add mRNAi to Bt proteins for corn rootworm control. The mRNAi trait does not yet have export approval and remains regulated. For more information see: https://www.epa.gov/pesticide-registration/epa-registers-innovative-tool-control-corn-rootworm.

European corn borer moths

Figure 1. European corn borer moths (female)

Things that go bump in the night

The black light trap at the SWROC has been catching a few European corn borer moths for the past week - at low numbers but more than we have been seeing for the past few years. I am not sure we are at the peak of this flight yet. Don’t assume that the moths you are seeing in the headlights are corn borer. All other locations are reporting low numbers as well.

For trap captures see: https://www.vegedge.umn.edu/moth-data/ecb-info.

Begin to scout for 1st generation corn borer feeding next week.

There are several larger moth species you may be observing as you drive at night or around yard lights. Most have nothing to do with crops.

Virgin tiger moth, Virginia tiger moth, Isabella tiger moth, and big poplar sphinx

Figure 2. Top to bottom: Virgin tiger moth, Virginia tiger moth, Isabella tiger moth, and big poplar sphinx

There are several species of Sphinx moths out and about now, the big popular sphinx is probably the most impressive specimen visiting lights at this time. You can probably guess one of the hosts for the larva.

There are several species of tiger moths active now as well. The brightly colored Virgin tiger moth has been flying for a couple weeks and is one of the more common species in the light trap at the SWROC. The flight of the white Virginia tiger moth is starting to taper off. This is the adult of the yellow woolly bear caterpillar that can occasionally be found in soybean.

The Isabella tiger moth is the adult of the black and orange banded woolly bear caterpillar that, based on the width of the black bands, folklore suggests can predict the severity of winter. Woolly bear coloration data would probably need to be triangulated with the height of muskrat mounds and date of redwing black bird migration to provide acceptable accuracy. Anyhow, the Isabella tiger moths seem less common than usual this year.

Forage looper moth

Figure 3. Forage looper moth

The drab, delta-winged forage and clover looper moths will be found for most of the season in southwest MN. They are found in grassy areas and field edges. Occasionally, you will find their very slender larvae in soybean and alfalfa. While somewhat similar in shape to European corn borer, forage loopers are much larger.

For those of you who enjoy nocturnal Lepidopterans, a very good internet picture reference is: http://mothphotographersgroup.msstate.edu/. Though it’s probably better on butterflies, there are some great photos on https://www.butterfliesandmoths.org/ also.

Soybean

Crusting caused stand issues in many fields planted just before the heavy rains. Fields worked a bit on the wetter side seem to have a few more problems.

The earliest emerging soybeans are V4 now.

IDC symptoms are starting to appear. Often these are associated with SCN.

Thistle caterpillar on soybean

Figure 4. Thistle caterpillar on soybean

The recent rain has produced a flush of weed emergence and with the warm temperatures, weeds are growing fast. Err on the early side with herbicide applications.

We are seeing a few thistle caterpillars (painted lady butterfly larvae) and their shelters constructed in in soybean leaves. They seldom become numerous enough to cause economic concern.

Soybean aphid watch 2017

Soybean aphids are being found in soybean in both southern and Northwest Minnesota. Most reports are from the area of southern MN where aphid populations were higher in 2016. They have also been observed in Wisconsin, Iowa, Indiana, and are likely present in other upper Midwest states as well.

Soybean aphids tended by ants and increasing on V4 soybean

Figure 5. Soybean aphids tended by ants and increasing on V4 soybean. Photo: Adam Hass

At the SWROC, aphids are easy to find in isolated, early emerging soybean plots. Based on the presence of new nymphs being produced on V1-2 SWROC soybean on June 8th, the move from buckthorn probably occurred between June 2-5.

Focus any early soybean aphid scouting to locate indicator fields on the earliest emerging fields. General scouting won’t begin until July.

For more information on soybean aphid scouting see: http://www.extension.umn.edu/agriculture/soybean/pest/soybean-aphid/scouting-soybean-aphid/

There's gold in them thar bindweeds!

The gold tortoise beetle population seems to be doing unusually well at the SWROC this spring. The larvae feed on members of the morning glory family (Convolvulaceae) and we find the adults near field bindweed.

Gold tortoise beetle

Figure 6. Gold tortoise beetle

The spiny larvae use frass (insect poop in lay-terms) and cast skins as a protective covering. 

Like little beetle mood rings, golden tortoise beetles are able to change their metallic coloration at will. Sadly, the golden hues of these insects disappear when the beetles die.

-Bruce Potter