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ISSUE 7  June 14, 2001



Throughout the region, several different caterpillars are creating management concerns. Moth flights about three weeks ago brought the moths into the region. The different caterpillars now feeding are: Armyworm, Variegated cutworm, Diamondback moth, and Thistle caterpillar.

As mentioned last week, armyworms are being found in eastern North Dakota and NW Minnesota. Most of the fields so far reporting armyworms are corn fields. The corn crop is still young, and armyworms feeding inside the whorl may cause growth problems. Scouting for these insects is strongly recommended. Armyworms notch leaves while feeding and litter the plant with dark colored, soft frass. There have been only a few reports of armyworms in small grains (mostly barley fields). It would be wise to check grassy field margins for worms. These areas may have been more attractive for egg laying than most fields. Armyworms prefer to feed at night and hide during the day in cracks or under clods in the soil. Scouting for these caterpillars is difficult. If feeding damage but no larvae are seen, examine the soil around the base of the plant. In addition, trap reports from southern MN detected another flight this week. This could mean more damaging armyworms in another three weeks.

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Variegated Cutworm
The most recent problems with this cutworm occurred in 1999. Another migrating moth, variegated cutworm are feeding on sugarbeets. In 1999, they were also found in alfalfa, sunflower, potato, corn, flower beds and gardens. The larvae are dark gray caterpillars with a lighter stripe along the side and four light colored spots on the top of the body. Variegated cutworm have a climbing habit, moving up onto the plant in the evening and feeding. Leaves are chewed from the margins, smaller larvae may feed on the interior of the leaf, creating holes. Damage can be confused with grasshopper feeding . . . except no grasshoppers.

You may or may not find anything above ground during the day. The cutworms retreat to the soil during the daytime. They feed above ground at night (although they can be found feeding in the day as well) and prefer young plant tissue. When scouting for Variegated Cutworm on the plant, examine the base of the stems, under leaves, and within curls. They may be under the soil surface during the day.

Diamondback moth
Larval feeding in canola has been reported for the past two weeks by Jan Knodel, NDSU Plant Protection Specialist-Minot (see additional comments in Around the State). DBM larvae have been reported from all canola production areas of ND north into Canada. Insecticide treatments have been made to some fields where numbers and damage were judged to be damaging.

Though an economic threshold in young canola has not been determined, John Gavloski, entomologist, Manitoba Agriculture and Food, has provided some insight. His comments are:

Look for the small green larvae on the leaves, as well as the feeding damage. Although no economic thresholds have been established for diamondback moth in canola in the seedling stages, with flea beetle defoliation we consider somewhere around 25% defoliation to be the threshold. Since canola tends to compensate better for diamondback moth feeding than it does flea beetle feeding, a nominal threshold for diamondback moth feeding in canola in the seedling stage is probably somewhere between 1/4 and 1/3 of the plant material eaten or damaged, and larvae still present on the plant. Although there is no direct research to back this up, this is a best guess at what a threshold would be based on available information, however, realize that it is a nominal threshold (a best guess) and open to feedback that might suggest different. Canola that has diamondback moth feeding on the seedlings should be checked often since damage can progress rapidly.

Source: Manitoba Insect Update – June 7, 2001
John Gavloski, extension entomologist
Manitoba Agriculture and Food

Thistle Caterpillar

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The painted lady butterfly/thistle caterpillar is indigenous to the southern United States and migrates annually to the northern US and Canada. The painted lady breeds in the North Central States and Canada, migrates south for the winter and returns to the northern areas in early June. The black, spiny-haired larvae feed on Canada thistle, wild and cultivated sunflower, soybeans, and numerous other host plants. At the moment, most have been reported on thistle, but canola has been one crop where some feeding was occurring in and around patches of thistle. A big concern is weed control operations killing the weeds, moving the caterpillars on to the crop in fields.

If planning herbicide treatments for controlling canada thistle, check caterpillar numbers. If populations are large, the addition of an insecticide appropriate for the crop may be considered. Such treatments may be confined to the thistle patches. For more comments regarding a situation in Divide County, see Around the State.



Sunflower beetle adults are on the move. Movement to new sunflower fields has been very noticeable the past week. Some reports of large numbers in the central and northcentral counties have been received.

Scouting Method: Sampling should be 75 to 100 feet from the field’s edges. Adults and/or larvae should be counted on 20 plants at each of 5 sites along an X pattern for a total of 100 plants. The average number of adults and/or larvae per plant should be determined.

Economic Threshold: Adult - one to two per seedling. Larvae - 10 to 15 per plant will cause approximately 25 to 30% defoliation if allowed to continue feeding. Control is advised if average defoliation reaches the 25 to 30% level.

Insecticides Approved for Sunflower Beetle

Trade Name


Dosage (lb AI/acre)

Asana XL*

1.45 - 5.8 fl oz

0.0075 - 0.03


1.6 - 2.8 fl oz

0.025 - 0.044



1.5 - 2

Furadan 4F*

0.25 - 0.5 pts

0.125 - 0.25

Lorsban 4E*

1 - 1.5 pts

0.5 - 0.75

Scout X-tra*

0.71 - 1.42 fl oz

0.005 - 0.01


1.28 - 2.56 fl oz

0.01 - 0.02

*restricted use insecticide



The IPM field scouts are submitting scouting reports from small grains around the state. During the past two weeks over 100 fields have been checked for various insects and diseases.

We haven’t spoken much about grasshoppers this year. In general, numbers have been down. Most fields have zero to very few in field margins. All reports have numbers below threatening levels. The graphic provides an overview of where the greatest numbers were found.

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Next week predictions for midge emergence will appear in the Crop and Pest Report. Degree days in the southeast will be reaching the 1100 DD level, the point when adult males are first found.

To keep up with degree day accumulations for wheat midge in your area, view maps at:


Phillip Glogoza
Extension Entomologist

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