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Army cutworms marching into Great Plains wheat fields
Like soldiers marching across the battlefield, army cutworm larvae are munching through green fields in Texas, Oklahoma, and Kansas.
The two crops most affected are alfalfa and wheat, but canola can also be significantly affected, according to Jeff Whitworth, Extension entomologist at Kansas State University.
“Alfalfa and wheat are vulnerable because these crops have green, succulent plants during the fall when the moths are ovipositing,” Whitworth says.
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However, late-planted wheat fields may escape infestation if plants hadn’t germinated when the moths were flying around seeking oviposition sites. Each female can produce 1,000 to 2,000 eggs, which hatch in the fall. The small larvae then start feeding on any nearby leaf tissue, and will do so all winter any time the temperature is over 45°F.
The easiest way to detect an army cutworm infestation early is to take notice of any feeding by animals (birds, skunks, possums, etc.) in wheat or alfalfa fields. Next, go out to that area and dig around the base of the plants looking for the dusky, soil-colored, usually curled up, small cutworms that have faint lateral stripes.
“Sample a field by stirring or digging the soil to a depth of 2 inches at five or more locations. The cutworms will be greenish-grey and will probably curl up into a tight ‘C’ when disturbed,” says Tom Royer, Extension entomologist at Oklahoma State University.
This feeding will probably continue for another month or two, depending upon the weather. The larvae will then pupate, emerge as adult moths (often called Miller moths), then migrate back to the Rocky Mountains for over-summering until heading back to the Plains next fall to start the cycle all over again.
It is better to control army cutworms when they are small (½ inch long or less). Army cutworms are very susceptible to pyrethroid insecticides. At this time of year, an insecticide application can be combined with a late winter topdress nitrogen application, Royer says.
Under good growing conditions, treatments should not be necessary unless there are four to five larvae per square foot in wheat – even more if the wheat is growing well and is well tillered. In seedling alfalfa, probably one to two larvae per square foot may justify treatment, but it will take probably at least four to five larvae per square foot in established fields, Whitworth says.
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However, if treatment is warranted, there are a number of options available. Baythroid (beta-cyfluthrin), Cobalt (chlorpyrifos + gamma-cyhalothrin), MustangMaxx (zeta-cypermethrin), Stallion (chlorpyrofos + zeta-cypermethrin) and Tombstone (cyfluthrin) all are effective against army cutworm. More treatment information can be found on this link from Oklahoma State University.