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Fall armyworm on the march!

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David Marburger

David Marburger

Since April 2016, I have served as the Small Grains Extension Specialist at Oklahoma State University. My research and extension efforts focus on delivering science-based recommendations in order to increase small grains production and profitability for stakeholders throughout Oklahoma and the southern Great Plains.

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by: Tom Royer, OSU Extension Entomologist

Fall armyworms are active this fall. I checked a field of wheat this past weekend with significant damage from fall armyworms that averaged 6-7 fall armyworms per square foot. Scout for fall armyworms by examining plants in several (5 or more) locations in the field. Fall armyworms are most active in the morning or late afternoon. Look for “window paned” leaves and count all sizes of larvae.

Fall armyworm damage is characterized by window panning on wheat leaves. Injury can sometimes be greater in field margins as armyworms sometimes move in from adjacent road ditches or weedy areas.

Fall armyworm damage is characterized by window panning on wheat leaves. Injury can sometimes be greater in field margins as armyworms sometimes move in from adjacent road ditches or weedy areas.

Fall armyworms are generally most active early in the morning or late in the evening. Spray when 2-3 armyworms per linear foot of row are present.

Fall armyworms are generally most active early in the morning or late in the evening. Spray when 2-3 armyworms per linear foot of row are present.

Examine plants along the field margin as well as in the interior, because they sometimes move in from road ditches and weedy areas. The caterpillars were widely distributed in the field that I checked, suggesting that they were the result of a large egg lay from a recent adult moth flight. The suggested treatment threshold is 2-3 larvae per linear foot of row in wheat with active feeding. We won’t get relief from fall armyworms until we get a killing frost, since they do not overwinter in Oklahoma.

Consult the newly updated OSU Fact Sheet CR-7194 Management of Insect and Mite Pests of Small Grains for control suggestions.


7 Comments

  1. Kenneth Rose says:

    What do you recommend for treatment and timing?

    Kenneth Rose, Cimarron County

    • osuwheat says:

      As far as timing, go ahead and spray when the 2 -3 armyworm larvae per linear foot of row is reached. This is not a problem that I would utilize preventative spraying, but once you hit threshold don’t delay treatment.

      Regarding which product to use, there are several products that work well for control of armyworm. I would consult the linked fact sheet for a listing of products and then check with your local ag retailer regarding prices.

      • Tom Royer says:

        Jeff is correct. Eggs hatch in 2-4 days at these temperatures. Egg lay from moths occurs over several days after crop emergence. The best advice is to wait until thresholds are reached and rely on residual activity of the product you use for control (probably 7-10 days of residual). That way, you will get some later hatched larvae.

        Don’t ignore the field after treatment; check regularly to make sure you obtained good control and that you don’t have a resurgence.

  2. Ron Butler Garfield County says:

    Where in the state are they the worse?

    • Tom Royer says:

      I have received reports from Payne county and Washita County. We have had several moth flights this summer beginning in early July, so I believe they are probably statewide (not predictable). The bottom line is to watch your fields after seedlings emerge and treat when thresholds are reached.

  3. D. Chad Cummings says:

    Where across the state are you encountering threshold level populations? Statewide or in pockets? Heavier in the south?

    • Tom Royer says:

      See above. Flights have been so widespread and early this year, that any field that is “green” will be at risk. The bottom line is to watch your fields after seedlings emerge and treat when thresholds are reached.

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