Fall Armyworm is a common pest in hay, especially bermudagrass varieties (Coastal, Tifton 44, Midland 99, etc.) and can decimate a crop if left unchecked.
Some years, Fall Armyworm numbers remain relatively low, causing minimal damage. Other years, populations build-up and can cause serious yield reduction in various crops. This pest is one that hay producers and pasture owners usually have on their radar in late August but reports of damage has come in as early as July. Typically, Fall Armyworm does not over-winter outside of southern Texas and Florida but warm winters can allow Fall Armyworm to over-winter which contributes to an early Armyworm migration in North Carolina. In 2021, experts estimated that Fall Armyworm damage in the southern U.S. was the worst in nearly fifty years. The question many hay producers are asking, “Will this year be another bad year?”. Because of the migratory nature of the Fall Armyworm, it is difficult to predict exactly when they will arrive. So far, NC has had a relatively uneventful hurricane season which often brings moth migrations from the south. I suspect we will begin to see some populations of Fall Armyworm develop in the next couple of weeks so hay producers should begin to scout their fields regularly. Below are some tips for identifying and managing Fall Armyworm in hayfields and pastures.
Fall Armyworm Identification: To determine if a field has an infestation, look for caterpillars with dark heads that are usually marked with a distinct, pale, inverted “Y” on top. Typically, you will find a black stripe down each side of their body and a yellowish-gray stripe down their back. Fall armyworms come in a variety of colors including, green, brown or black which can make identification difficult.
Before managing Fall Armyworms, it’s important that we understand this pest’s lifecycle. Fall armyworms are the larvae (or caterpillars) of the Ash-gray moth. Like butterflies, the Ash-gray moth starts out as a caterpillar before going through metamorphosis. This moth has white wings with light gray spots. Female moths lay eggs at night and lay up to several hundred that hatch within 2 to 4 days. What hatches from these eggs are what we call Fall Armyworms.
Development from egg to fully grown Fall Armyworm requires about 2 to 3 weeks. At this point, armyworms burrow down into the soil and form pupae. In about 10 to 14 days, the moths emerge and the metamorphosis process is complete.
While this article concentrates on pastures, note that Fall Armyworms will attack centipede and bermudagrass lawns. Armyworms feed just about any time, day or night, but are most active early in the morning or late in the evening. These caterpillars will march like an army across your fields eating plant matter along the way. They tend to start from a field edge and work their way across to adjacent farms. In severe infestations, leaves will be completely eaten with only stems left behind. Scout your fields regularly so that you can implement a control measure in a timely manner. Because they are active in the morning, this is a great time to scout your fields.
Should I spray? Most research has shown that an average of 3 medium to large armyworms (about ¾ of an inch) per square foot is enough to cause significant damage to your hay crop or pasture and justifies a control measure, such as an insecticide treatment. If your bermudagrass is within a week or two of cutting or at least a foot tall then it’s more economical to harvest the hay a little early.
What can I spray? If you do choose to apply an insecticide, read the label carefully to ensure it is safe to apply on hay and/or pasture! There are numerous insecticide options available so choosing the right product can be a bit overwhelming. Several pyrethroid insecticides, such as Mustang Maxx and Karate are effective against Fall Armyworm but are restricted use and can only be purchased with a pesticide license. Other products, such as Dipel and Intrepid Edge are worm-specific insecticides and are not restricted use but may be higher in cost. No matter what product you choose, be sure to abide by all label specifications, calibrate your sprayer and pay attention to grazing or haying restrictions!
If you have any questions concerning pasture or hay management please contact the Richmond County Extension office at (910) 997-8255. Visit our website at Richmond.ces.ncsu.edu and follow us on Facebook.