Growings On: Potential for armyworm pests

Published 8:00 am Wednesday, September 27, 2023

Late summer through fall is when we have the highest potential for fall armyworms starting to move in to lawns, pastures and hayfields in Georgia. Sometimes they arrive earlier than others. It is important to stay vigilant while watching for these pesky critters.

For pastures and hayfields, damage can sometimes become severe before the worms are ever found. The grass may not be killed completely but hay yield or turfgrass production can be reduced to almost nothing.

If you are not sure if armyworms are present, pour soapy water on the grass (a half ounce of dishwashing soap/gallon water) to flush them out of their hiding place within the turf canopy. Another monitoring technique is to watch for large populations of birds feeding in a specific area as armyworms make an easy meal. Heavily-infested areas will also have visible greenish-black fecal pellets on the soil surface.

Treatment thresholds (levels at which chemical control is recommended) are three larvae (caterpillars) per square foot. Scout your fields every 3-4 days to look for signs of feeding damage. If your hay is close to being ready for cutting and baling, go ahead and do it before you spray.

It also helps if you increase your spray volume to the highest recommended, particularly if you have larger, more mature worms as they are not as susceptible to insecticides. Smaller larvae are easier to control and will have caused less damage than full grown larvae (35-55 millimeters long), which will soon pupate.

Armyworms are most active in the cool hours late in the day and at night so apply insecticides as late in the day as you can for best control. Traditional products such as Sevin are available as well as newer formulations like Baythroid, Intrepid or Mustang Maxx.

Adult moths are active at night, and females lay eggs in batches of 50 to several hundred. Eggs hatch in 2-10 days, and the young larvae will begin to feed on leaf tissue. Damage from small larvae may at first look like the leaf has been skeletonized, but as the worms grow, the entire leaf will be consumed.

Armyworms are most active in the early morning and late evening, spending the hotter hours of the day down near the soil in the shade. Larvae feed for two to three weeks before pupating in the soil, and adult moths will emerge 10-14 days later. The entire life cycle from egg to adult moth takes about 28 days.

If you have any questions, feel free to contact Brenda Jackson, the agricultural and natural resources agent for Murray County Extension, at (706) 695-3031 or bljack@uga.edu.