SW MN IPM Stuff 2016 Issue 3

Volume 19, Issue 3 - April 27, 2016

This newsletter is available in a print-friendly pdf format: SW MN IPM STUFF 2016-03

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 Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN can be found at the SWROC weather webpage.

Corn planted the week of April 11 is spiking. For SW Minnesota, rainfall and a cool, wet remainder to the week are forecast. The recent weather has shut down planting and a nearby opportunity to "plant in the dust" now looks unlikely for a much of SW MN. We are starting to see some significant weed flushes. Pre-emerge herbicides should have the moisture to work well in those fields where corn has been planted.

Wheat & etc.

Spring-planted wheat and oats have emerged and, at this point, stands look good.  Winter rye stems are starting to elongate. 

In a rare bout with optimism, I am hoping this cool, wet weather might trigger fungal pathogen mortality in the cereal aphid populations.

The black light trap at the SWROC has been capturing low numbers of migrating true armyworm moths.


pea aphid nymph

A pea aphid nymph. The pea aphid is a larger aphid than the soybean and cereal aphids. Note the long legs and dark-tipped cornicles and pea green color. Pea aphids are sometimes pink rather than pea green in color.

Much of the alfalfa in the area is approximately 12 inches tall and in good condition.

I was expecting to find a few potato leafhopper adults had migrated in from the Gulf states but so far have been unable to do so. Your fields may be different.

In the limited alfalfa scouting I have done, pea aphids are the most abundant insect. In sweep net samples at the SWROC, these large, pea green aphids are easily found but still well below an economic threshold.

Alfalfa weevil adults are active in, mating and laying eggs in the stems of alfalfa.

alfalfa weevil adult

Alfalfa weevil adult. The antennae and mouthparts are placed at the end of the long snout. Note the dark band along the back.

Approximately 1/4 inch long, alfalfa weevils are not large insects. In spite of their small size, the long-snouted alfalfa weevils have always reminded me of the Goons in the Popeye cartoons.

Alfalfa weevils appear to have survived the winter well and their grub-like larvae should be scouted for as we get closer to first cutting. The stage of alfalfa weevil development for your area can be estimated by using a degree-day development prediction model.

Time your alfalfa weevil scouting to begin after 300 degree-days (base 48ºF) have been accumulated from January 1.

alfalfa weevil degree-day mapThe alfalfa weevil degree-day map to the right was obtained from the very handy UW Extension Ag weather site.


As soon as corn can be rowed, it is time start evaluating stands. Because of this spring’s rapid corn emergence and now planting delays from wet weather, there will be a difference in corn development stage between fields in some areas of Minnesota. While it may only be a leaf or two, it could make a difference in insects and diseases later on. Rain has produced weed flushes in some fields that can also influence insect populations.

One group of early season insects you should be scouting for are the cutworms. The black cutworm moths migrate into the state each spring. They find un-worked soybean residue and early-season weed growth particularly attractive spots to lay eggs. 

A group of volunteer cooperators have been tracking the arrival of black cutworm with pheromone traps in the southern part of Minnesota again this spring. There has been several significant flights into Minnesota this spring. Most of these have occurred on a diagonal from Rock County through Sibley County in southwest Minnesota. The first of these was March 28 in Swift County and April 12 in Rock County. Similar to many other insects, degree-days can be used to calculate the rate of black cutworm larval development. The prediction for larvae resulting from this flight to be large enough to cut 5 leaf or less corn is the third week of May.

field attractive to black cutworm laying mothsA low area in a field of soybean residue without spring tillage - an attractive site for egg-laying black cutworm moths. The early season weed populations, common lambsquarters in this case, increase the attractiveness. The moths can find these weedy areas well before the plants are large enough to see them from the road. Incorporating dense weed stands like this can create a seed corn maggot problem if tillage and planting are done when flies are active.

Over the past week, Murray and Sibley and Blue Earth County captured numerous moths. Fields most at risk are those where soybean residue that has not been worked prior to a moth flight, particularly if early season weeds are present. Small corn is more vulnerable to attack than is large corn. The Herculex and Viptera above-ground Bt traits provide protection against black cutworm attack. However, very large populations of large cutworm larvae might still damage small corn.

The planting date of corn, the size and timing of black cutworm flights detected with pheromone traps and degree-days can be used to predict risk of cutworm damage. This does not mean that you can ignore scouting as other species of stand reducing insects may be about.

For more information on risk and management, see the weekly reports and general information on black cutworms at our Black Cutworm Prediction page. Updates for the previous weeks trap captures are posted each Thursday.


I have heard some rumors have it that there have been soybeans planted. They should do just fine and if planted with proper attention to planting depth, should be emerging soon.

First generation seed corn maggot adults are still present, but degree-day models indicate fly emergence has peaked. Fields that had large amounts of organic material (manure and green manures) incorporated close to planting should be scouted for potential stand losses. Seedling diseases and mental /mechanical malfuctions can also reduce stands and should be scouted for.

Pesticide News

Most of you are already aware of the resistance to synthetic pyrethroid insecticides found in some 2015 southern Minnesota soybean aphid populations. This may limit control options for this insect in the future.

You may have also heard that the organophosphate insecticide chlorpyrifos (Lorsban and others) and the sulfoximine insecticide sulfoxaflor (Transform) used for soybean aphid control are currently facing regulatory challenges with the registration currently canceled for Transform. If you are interested in the industry perspective on these proposed regulatory changes, Dow AgroSciences has made its communication with retail customers for one of these insecticides available for public viewing. This link is presented for informational purposes only.

Sulfoxaflor: Isoclast Regulatory Update Letter

Happy trails,

Bruce Potter

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