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Weed & Pest

Army Cutworms likely culprit in pasture die-off

Written by Dallas Mount
Goshen County – A group of natural resource professionals gathered in northern Goshen County on July 16 to tour and investigate pasture die-off that occurred this spring.
    The group gathered first on the ranch of Doug DesEnfants near Prairie Center.  A few pastures in the area failed to green-up or show any signs of growth this spring and the DesEnfants contacted Dallas Mount, with the University of Wyoming Cooperative Extension Service. “I was completely baffled by it.  I knew I needed to get a group together to assess this situation and make recommendations to Doug as well as address the ecological concerns this will create.  The affected pastures seemed to be irrespective of ownership or management, this was something environmental causing the damage,” said Mount.
    The group included employees of the Natural Resources Conservation Service, the Southeast Wyoming Resource Conservation and Development Council, conservation districts and the University of Wyoming Cooperative Extension Services as well as interested neighbors that had similar conditions in their pastures.
    “We talked about drought, funguses, herbicide even considered aliens,” laughed Mount. “The most likely explanation seems to be army cutworms that caused the damage by feeding on the rangeland plants either last fall, or early spring.  The cutworms work at night, or even underground and can do their damage completely unnoticed until the plants show signs of stress.”
    UW Extension Entomologist Scott Shell took soil samples back to Laramie for testing to see if he could find pupal casings that would likely be left behind by the cutworms when they turn into the familiar miller moths that pester homes in the spring.
Mike Smith, UW Extension Rangeland Specialist said that during his 30-year career this is the first time he has seen anything like this.  “Likely you all will never see it again,” said Smith to the affected ranchers. Shell explained that once the cutworms affect an area that area is unattractive to them in the near future because they feed on the healthy plants.  
The main question for the landowners now is do they reseed the affected areas or just defer grazing to allow the perennial grasses to repopulate the area naturally.  Some ranchers seemed to think the reseeding would be necessary to speed recovery of the land, while others thought simply deferring grazing would be enough.  The Goshen County conservation districts will be made aware of the situation and NRCS expressed an interest in using some EQIP funding to assist the ranchers in either reseeding and/or grazing deferment to help the areas recover.
    “If ever there was a need for conservation dollars to be put to work, this is an ideal situation,” said Mount.
    For questions concerning the army cutworm damage contact UW Extension Educator Dallas Mount at 307-322-3667 or This email address is being protected from spambots. You need JavaScript enabled to view it..