NDSU Crop and Pest Report

Entomology


ISSUE 1   May 6, 2004

ARMY CUTWORM WAKE UP IN SOUTHWEST NORTH DAKOTA

With last weeks warm temperatures, the army cutworms have come out of hiding and begun feeding aggressively on alfalfa, wheat, and barley. This cutworm overwinters as partially grown larvae and becomes active when soil temperatures reach 40 F. There were reports of army cutworm activity back in March from Kansas, and just recently from Montana. (See Southwest Report in Around the State)

Treatment Thresholds for Cutworms by Crop:

Canola 1 per square foot
Small grain 4 to 5 cutworms per square foot
Corn 3 to 6% of plants cut and small larvae less than 3/4 inch present
Sugarbeets 4 to 5% of plants cut
Soybean/Drybean 1 or more larvae per three feet row or 20% of plants cut
Sunflower 1 per square foot or 25 to 30% of plants cut
Forage 4 to 5 or more per square foot (new stands may only require 2/sq. ft)

Insecticides labeled for treating the above crops for cutworm control include:

Canola
Wheat
Corn
Sugarbeets
Soybean
Dry Bean
Sunflower
Alfalfa
Capture, Warrior
Lorsban 4E, Mustang, and Warrior
permethrin (Ambush, Pounce), Asana, Lorsban, Mustang, Sevin, and Warrior
Asana, Lorsban, Mustang, and Sevin
Asana, Lorsban, Mustang, Pounce, Scout X-tra, Sevin and Warrior
Asana, Mustang, Sevin, and Orthene
Asana, Baythroid, Lorsban, Sevin, and Warrior
permethrin (Ambush, Pounce), Baythroid, Lannate, Lorsban, Mustang, Sevin, and Warrior

 

WHEAT MIDGE OUTLOOK FAVORABLE

The wheat midge risk map for 2004 was released in February. Estimated populations of overwintering midge continue to be low overall based on the North Dakota Wheat Commission sponsored survey.

There was little detection of wheat midge from the soil samples this year. Very good news for the growers in the state. Unlike previous years, we did not even have a few samples with high numbers of larvae that, due to parasitism, were reduced to significantly lower levels. None of the 200 fields sampled in the survey had healthy, overwintering populations of wheat midge larvae exceeding 1,200 larvae per square meter. This level of midge has been critical in past seasons.

There was a comment from Benson county Extension Agent, Scott Knoke, that is worth noting. He reports a few growers in the northern part of that county who spotted midge larvae crawling from filled grain trucks that were parked in the field over night. We have seen this before. It indicates that midge larvae had not dropped from the wheat heads due to lack of rain. The midge numbers are hard to quantify in this situation, since they have all been concentrated in a small area.

You will also notice that Ramsey County was not included in this year's survey. Due to county staffing changes that developed there during the time for collecting soil samples, the county was not surveyed. We hope to have the county back in the survey by next year.

As a reminder, the map is presented your reference. You can also find the map and keep track of degree day accumulations at the NDSU Entomology Updates, found at:

www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/index.htm

 

NORTH DAKOTA GRASSHOPPER OUTLOOK FOR 2004

We still have some areas of the state where grasshoppers will be of great concern this season. In particular, there were areas in the north central counties and the south central counties where adult numbers regularly exceeded 8 adults/square yard during late summer surveys in both crop and range settings. Dry conditions in the south and west could favor grasshopper survival and enhance outbreaks. A summary of adult surveys from 2003 is provided as a forecast for this season. Two highlighted areas should have the greatest risk. There were other, smaller areas scattered throughout the region that should also be noted.

Grasshopper treatment guidelines are:

 

Nymphs (Young hoppers) per square yard

Adults per square yard
Rating

Margin

Field

Margin

Field

Light

25-35

15-23

10-20

3-7

Threatening

50-75

30-45

21-40

8-14

Severe

100-150

60-90

41-80

15-28

Very Severe

200+

120

80+

28+

Whenever grasshopper populations reach the threatening level, feeding damage to crops should be anticipated. Directing control efforts at nymphs in hatching sites is recommended to minimize the total area requiring insecticide treatment, permits lower insecticide rates for effective control of small nymphs, and minimizes the potential for future crop damage.

If you are further interested in the rangeland situation, the USDA-APHIS-PPQ rangeland grasshopper survey map can be viewed in color at:

http://www.sidney.ars.usda.gov/grasshopper/Extras/map04.htm

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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