SW MN IPM STUFF 2018 Issue 5

Volume 21 number 5

5/31/2018

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

A printer-friendly pdf version of this newsletter is available to download here: SW MN IPM Stuff 2018-05

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.

In addition to a chronic rain issue in SW MN, some areas, including the SWROC have received small hail.

Things that go bump in the night

We are still picking up a few black cutworms in pheromone traps but it is late enough in the spring that we have now stopped trapping.

Harmless, mosquito-like midges (Chironomidae) and May beetles are dominating the black light trap captures at Lamberton. Biting gnats (Blackflies) are dominating the insect fauna in my yard near the Minnesota River. The first mosquito adults were observed on Memorial Day. They will have to compete with gnats for blood this spring.

We captured a single European corn borer female on May 30, the first of the year. It is interesting because we have not yet captured any males, which tend to emerge first. Timing is not that far off degree-day wise and peony flower buds are opening in my yard, the latter is usually timed close to corn borer moth emergence.

Some things to consider right about now

Alfalfa

In between rain events, 1st crop harvest has started in SW MN. Potato leafhoppers have arrived. We started picking up adults on May 30.

Alfalfa weevil in 2nd-3rd crop alfalfa

Re-scout stubble fields within 4-5 days of cutting. When scouting early second crop, pay close attention to fields with 1st cutting damage and higher alfalfa weevil populations.

alfalfa weevil cocoonsAlfalfa weevil cocoons

Second cutting thresholds vary by state but weevil damage to second crop results can result in yield loss through delayed re-growth. Are alfalfa weevil larvae still numerous (8 or more adult and larvae/square foot), do 50% of the crowns show weevil feeding, or is the presence of weevils and their feeding the reason re-growth is delayed? If so, an insecticide is recommended.

Switch to the number/stem sampling method (see last issue of IPM stuff) when the size of the re-growth allows.

Depending on cutting schedules and weather, AW larvae can sometimes still be found early in the 3rd crop. Carefully consider whether weevil larvae pupating before treating the 3rd crop for alfalfa weevil.

Insecticide applications

Always read and follow insecticide label directions. Avoid insurance insecticide treatments to alfalfa as most insecticides will kill beneficial insects and can flare other insect problems; pea aphids, for example.

Do not apply insecticides unless the alfalfa weevil has reached economic threshold numbers and avoid treating fields in bloom or with flowering weed species.

If an insecticide treatment to flowering alfalfa does become necessary:

  • Make application in early morning or late evening when fewer bees will be foraging in the field.
  • Follow pesticide label precautions concerning bee safety.
  • Use insecticides that are as safe as possible for honey bees.
  • Notify area beekeepers so they can move or confine bees during the insecticide application.

Selected references:

  • Pellissier, M.E., Z. Nelson, and R. Jabbour. 2017. Ecology and Management of the Alfalfa Weevil (Coleoptera: Curculionidae) in Western United States Alfalfa. Journal of Integrated Pest Management. 8(1): 5; 1–7
  • Peterson, K.D., S.D. Danielson, L.G. Higley. 1993. Yield Responses of Alfalfa to Simulated Alfalfa Weevil Injury and Development of Economic Injury Levels. Agronomy Journal. 85:595-601.

Wheat

Scout for cereal aphids, early season foliar disease symptoms.

Pay attention to the base of tillers and leaf sheaths for cereal aphids.

Herbicide applications should be starting on spring wheat in SW MN.

Remember to check the herbicide label for weed and grain size restrictions. If you call me about this topic and hear typing or paper shuffling, that’s likely what I’m doing. If you hear some accompanying mumbling about print format and layout, you can be sure.

Corn and soybean

Scouting stands and evaluating pre-emerge herbicide performance (I know you all got one down) and scheduling post emerge herbicide applications should be occupying our time. As you scout fields, pay close attention to stand-reducing insects and diseases.

Black cutworm

Information on black cutworm trap captures and predictions of when and where cutting is most likely to occur can be found in weekly reports at MN Cooperative Black Cutworm Reporting Network. Scouting tips, cutworm ID (important with cutworms in corn) and thresholds and other management advice can be found in the magnum opus black cutworm facts

The most recent projections on cutworm larval development are available at 2018 MN Black cutworm reporting network report #5. Scout now! Larvae are at or close to a size where they can cut small corn plants. In addition to the previously reported leaf feeding, on May 30, I received a report of cutworms cutting leaves of small corn above-ground in Dakota county – thanks, Stephan and Tom! None of these sightings have been confirmed to be black cutworm.

There are several insects out there that can produce holes in crop and weed leaves. While cutworms are not all that hard to control, make sure you know what you are aiming at before you pull squeeze the trigger on an insecticide application. By the way, damage from small hail stones can look very similar to insect feeding, particularly on soybean. Early season scouting fatigue has been documented (by me) to produce an increase in hallucinations involving insect pests.

overwintered bean leaf beetle on a soybean leafOverwintered bean leaf beetle on soybean

Bean leaf beetle

I have been receiving a number of photos of bean leaf beetles from agriculturalists in eastern South Dakota.

These beetles have overwintered. They may currently be in emerged soybean, alfalfa, and volunteer soybean in corn or other crops. 

If you are seeing many of these insects in Minnesota, let me know. It is possible this insect is seeing a resurgence.

Soybean aphid watch 2018

Just for the sport of it, in the next issue of IPM stuff, I’ll start sticking my neck out with some bold predictions for 2018.

Happy trails,

Bruce