Fall armyworms and other armyworm species have made a return to hay fields and pastures in Jenkins County. Usually we observe worm pressure mid-August and early September, but this year is different. This year armyworms seem to have made their presence earlier. Damage from armyworms seems to come in “waves,” about two weeks apart. This is because moth activity and egg laying peak periodically, even though there is substantial overlap between generations. As with any pest, the key to managing armyworm problems is early detection and continual monitoring.

Scouting

Scouting pastures and hay fields can help detect armyworm infestations before they cause economic damage. How many times have you heard people say, “I saw flocks of cow birds in my pasture”? If you see flocks of birds in your fields, that is a very good indication of a worm infestation. As you check fields, check for leaf damage and live larvae. Sometimes it is necessary to flap the hay leaves with your hand. This will knock any worms to the ground where they can be identified.

The decision to treat for armyworms depends on the amount of the armyworms detected and the timing of the next hay cutting. The basic threshold is 4-5 armyworms per square foot. In other words, if you see above 4-5 per square foot, then it is most likely time to treat. As with other pests, timing is critical. If infestations are detected too late, the damage may already be done. Smaller armyworms are much easier to kill than larger ones.

Control

If your hay field is close to cutting, then this is the most practical means of control. Once the hay is cut, the moisture levels quickly drop thus making the hay not attractive. However, if your cutting is a couple of weeks out, then treating with an insecticide will be necessary. Several insecticides are available for armyworm control. The cheapest and quickest insecticides are the pyrethroids Mustang Max, Asana, Karate, etc. These insecticides are the cheapest but do not provide a long window of residual activity. Insecticides, such as Intrepid and Tracer, are more expensive but provide much more residual activity than the pyrethroids. It is very important to spray with at least 15 gallons of water per acre. This allows for more thorough coverage and will help the chemical penetrate into the canopy.

Armyworms in hay fields and pastures are a very serious problem, with economic damage happening in a short period of time.

If you have any further questions, please do not hesitate to call the extension office.

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