Fall armyworms continue to threaten forage crops in South Central Missouri. Recent rainfall has caused many types of forage to green up which may provide additional feeding areas for the armyworm.
Last month Bermuda grass and alfalfa fields were hardest hit by armyworm; recently, fescue fields have had some damage from the pest. Farmers need to be scouting their fields for fall armyworm activity; more areas may become infected as the season progresses.
Multiple generations can exist in one season, scouting should continue until late October.
Scouting is best done in the early morning hours before the heat drives the larvae into sheltered areas. Fall armyworm can be identified by the appearance of four black spots forming a square on the eighth abdominal segment and the presence of a pronounced inverted Y shaped white mark on the head (Figure 1).
If fall armyworms are found in pasture or hayfields, the best option is to graze or harvest as soon as possible to minimize damage. Spray decisions depend on the value of the crop and the stage of crop growth. If there are four or more half grown or larger worms per square foot the economic threshold has been reached and spaying may be warranted.
For more information on control options for fall armyworm contact MU Extension Regional Agronomy Specialist Sarah Kenyon at (417)778-7490 or kenyons@ missouri.edu. More information can be found from the MU guide sheet G7115 Management of the Armyworm Complex in Missouri Field Crops.
