Southwest MN IPM Stuff - Issue 7

​Volume 25 Issue 7 | June 9, 2022

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  

Crop Progress

Early planted corn is V4 -V5.

The earliest soybeans are V1 and pushing V2.

Winter rye is headed and flowering, early winter wheat varieties are starting to head.  Aphids and thrips are present at low levels. On small infection focus presumed to be barley yellow dwarf virus was observed on winter wheat.

Many production fields have been cut. Alfalfa weevil populations at the SWROC are relatively low this year and potato leafhoppers have not yet shown up. Your mileage may vary.

European corn borer

I start expecting to see the beginning of the 1st generation European corn borer (Ostrinia nubilalis) flight on the opening of common peony (Paeonia lactiflora) blooms in the area. The cool weather in late May and early June has delayed peony bloom and the emergence of corn borer adults. The peonies in my yard started to open on 6/08. Coincidence, or not, we captured the first corn borer of the season, a single corn borer at the SWROC the same day.

For those wishing to use a more high-tech approach to moth prediction, you can check out the bivoltine degree-day maps that are updated once a week.  For scouting and management tips see European corn borer in Minnesota field corn.

Corn rootworm

We typically think of rootworm eggs hatching around the first week of June. The cool spring has likely delayed that a bit.

Some agriculturalists gauge the timing of rootworm egg hatch by the appearance of one of the Midwestern firefly species. Others use degree-day accumulatios to predict rootworm hatch.

One of the often-used predictive models indicates that western corn rootworm eggs begin to hatch at 377 degree-days, base 54.9 F, and 50% of the eggs have hatched between 684 and 767 DDs (base 52F).  Looking for larvae and root injury will be most productive after peak egg hatch. These results were based on IL rootworm eggs.

There are several temperature-dependent models for northern corn rootworm egg hatch. Using the same 52 F base, egg hatch starts between 300 and 400 2 to 4-inch soil temperatures, and 50 % hatch occurs around 530 DDs.

Temperature-dependent predictive models for below-ground insects have several challenges because of insect location within the soil profile, crop residue, crop canopy,  and soil type on temperature. Also, be advised that there are several studies in the literature that indicate that the local populations might vary in development base and degree-days required for development with those adapted to northern geographies needing slightly less heat.

As of 6/6 at the SWROC near Lamberton, MN  we were at 233 DD at 2"soil depth and 232 DD at 4".

A few of the older works on the topic

  • Apple, J. W., E. T. Walgenbach and W. J. Knee. 1971. Thermal requirements for Northern Corn Rootworm egg hatch. J. Econ. Entomol. 64: 853-856.
  • Chiang, H. C., and V. Sisson. 1968. Temperature relationships of the development of Northern Corn Rootworm eggs. J. Econ. Entomol. 61: 1406-1410.
  • Levine, E., H. Oloumi-Sadeghi, and C. R. Ellis.1992. Thermal requirements, hatching patterns, and prolonged diapause in western com rootworm (Coleoptera: Chrysomelidae) eggs. J. Econ. Entomol. 85:2425-2432.
  • Wilde, G., H. C. Chiang, E. T. Hibbs, and D. E. Lawson. 1972. Geographic variation among populations of western and northern com rootworms. J. Kans. Entomol. Soc. 45: 256-263
  • Davis, P. M. Davis, N. Brenes, and  L. L. Allee.  1996. Temperature dependent models to predict regional differences in corn rootworm (Coleoptera: Chrysomelidae) phenologyEnviron.  Entomol. 25:  767–775.

Tiny, black, humpbacked bugs

Recently, I’ve had two different reports of tiny, humpbacked black insects in fields with heavy residue. Based on verbal descriptions and some fuzzy photos they appear to be a globular springtail of some sort. I do not have a clear photo or specimen but based on the dangerous assumption that my preliminary diagnosis is correct...

Springtails are arthropods but not insects and belong to the taxonomic class Collembola. They are very small arthropods ( < 1/8th inch)  that need damp conditions and most desiccate rapidly in dry conditions. Most species feed on decaying organic material, fungi, bacteria, and a few are predatory on smaller organisms. Rarely, some species will feed on plants causing damage. The snow fleas that you might notice upon the snow in late winter are collembolans rather than fleas.

Globular springtails (the name is based on their shape) are in the order Symphypleona. Most springtails, including globular springtails, are harmless, but the garden springtail, (Bourletiella hortensis, is one of the rare species that has been documented to cause crop damage. This may be the species that people are reporting but it is not likely they will cause yield-limiting damage. I could not find a public domain image of a globular springtail but BugGuide has pictures of one of them, the garden springtail

The same damp, high residue situations that favor springtails will also favor slugs and millipedes that might take bigger bites. Do some detective work.

Seedling diseases

Yes, they are present in some corn and soybean fields, with or without fungicide seed treatments. Pythium is a pathogen that causes seedling damping-off in cool and wet conditions but there are others as well. The University of Minnesota Plant Disease Clinic can provide diagnostic services and sample submission instructions.

Rye cover crop

Be vigilant for insects and other pests in corn and soybean crops planted into, or adjacent to, a cereal rye cover crop. Armyworms, cutworms, and slugs are on the shortlist of culprits, the latter particularly favored by no-till.  A way to get across a field thoroughly and quickly, and a sweep net are your friends.

Happy trails,


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