Haskell County Oklahoma Cooperative Extension Service

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Haskell County OSU Extension
105 SE 3rd Street, Suite A
Stigler, OK 74462

Phone: (918) 967-4330
FAX: (918) 967-3290

Office Hours: 8 am-12 pm & 12:30 pm-4:30 pm 


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Haskell County Oklahoma Cooperative Extension Service

Be on the Watch for Fall Armyworms

Press Release
September 24, 2007
Brian Pugh, Haskell County Extension Educator, Ag/4-H & CED  

            Fall armyworms are caterpillars that directly damage sorghum heads, fescue and bermudagrass pastures, seedling wheat, soybean and residential lawns.  There have been reports of fall armyworm buildups in north eastern Oklahoma.  In addition, fall armyworm infestations were numerous in sorghum fields in Oklahoma during the latter part of August, and several people have commented about all of the heavy “moth flights” that are currently occurring. All signs point to the possibility that another generation will pop up in early to mid September that could cause some serious problems for grass pastures, seedling wheat and residential lawns.
            Female fall armyworm moths lay up to 1000 eggs over several nights on grasses or other plants.  Within a few days, the eggs hatch and the caterpillars begin feeding.  Caterpillars molt six times before becoming mature, increasing in size after each molt. Newly hatched larvae are white, yellow, or light green and darken as they mature.  Mature fall armyworms measure 1½ inches long with a body color that ranges from green, to brown to black.  They can be distinguished by the presence of a prominent inverted white "y" on their head.  However, infestations need to be detected long before they become large caterpillars.  Small larvae do not eat through the leaf tissue, but instead, scrape off all of the green tissue and leave a clear membrane that gives the leaf a "window pane" appearance.  Larger larvae feed voraciously and can completely consume leaf tissue.
            To scout for fall armyworm, plants from several locations within the field or pasture need to be examined.  Examine plants along the field margin as well as in the interior.  Look for “window paned” leaves and count all sizes of larvae.  OSU suggests a treatment threshold is two or three ½ inch-long larvae per linear foot in wheat and three or four ½ inch-long larvae per square foot in pasture.  An Auburn University entomologist developed an easy-to-use scouting aid for pasture by bending a wire coat hanger into a hoop and counting fall armyworms in the hoop.  The hoop covers about 2/3 of a square foot, so a threshold in pasture would be an average of two or three ½ inch-long larvae per hoop sample.
         It is crucial that you target smaller caterpillars (1/2 inches or less) for control for two reasons.  First, the caterpillars don’t cause really severe damage until they reach an inch long, and secondly, smaller caterpillars are much more susceptible to insecticide control than larger caterpillars.  Let’s hope that fall armyworm problems don’t rear their ugly heads, but keep vigilant just in case.  A final reminder; we will not be out of the woods for a fall armyworm outbreak until we get a good killing frost, so don’t let your guard down.  They can cause a lot of damage in a hurry! 

Contact the OSU Cooperative Extension Office if you have a fall armyworm outbreak or need to know what insecticide to use for armyworm control at 918-967-4330. 

     Oklahoma State University, U.S. Department of Agriculture, State and local Governments Cooperating.  The Oklahoma Cooperative extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, sex, age, disability, or status as a veteran, and is an equal opportunity employer.

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