Only experienced hay producers will readily recognize what is going on in this photo. Fall armyworms! Fall armyworms are important pests of home lawns and sports fields, but they are especially threatening to bermudagrass hay fields. From now until the end of the growing season, hay producers need to check maturing fields two or three times per week in order to avoid losing yield and income to fall armyworms. There are many effective insecticides for controlling fall armyworms, but insecticides will only help protect yield if they are applied before serious damage occurs. Treatment is recommended when populations exceed 3 caterpillars that are ½ inch or longer per square foot. Once caterpillars reach ½ inch in length, there is a good chance they are going to survive to pupation, but they have only eaten a small fraction of the grass that they are going to eat in the next few days.
During the summer it takes about 14 days for fall armyworm caterpillars to grow to maturity and be ready to pupate. However, as with many other caterpillars, they do 80 to 90 percent of their eating in the last two or three days of their life. This explains why a bermudagrass hay field that is lush and pretty when the farmer drives by to see if the field is ready to cut can be severely defoliated two days later when he returns with the mower. Fall armyworms can also damage home lawns, especially newly established bermudagrass lawns, and bermudagrass sports fields just as quickly. “Coach, we can’t practice out here with all these caterpillars crawling around!”
See Extension Publication 2717, Fall Armyworms in Hayfields and Pastures, for a list of recommended insecticides, application rates, pre-grazing intervals, and pre-harvest intervals. Information on scouting and thresholds is also included here.
See Pages 12 and 13 of Extension Publication 1858, Insect Control in Commercial Turf, for information on fall armyworms in commercial turf. Before treating sports fields be sure to verify that the product you plan to use is specifically labeled for use on sports fields and carefully check the re-entry interval.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service. The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.