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When the Armyworms Come Marching In

When the Armyworms Come Marching In

This has truly been a hot summer at times! We did get significant rain in late August, which provided cooler temperatures and some needed moisture. It will be interesting to see what this month will bring. Hopefully it will be cooler temperatures! The late rains in August did, however, lead to an outbreak of fall armyworms.

Fall armyworms cause the most problems in home landscapes. They have four life stages: egg, larva, pupa, and adult. The adult is a moth that can lay a cluster of 50 or more small eggs that are covered with grayish, fizzy scales. The eggs are rarely seen and are laid at the base of the host plant.

The larva has a dark head capsule which is marked with a distinct, inverted “Y”. Long, black stripes can be found along each side of its body. On the middle of its back is a yellowish-gray stripe with four black dots on each segment. Once it becomes full grown, the larvae will enter the soil and form the pupal stage. The adult moth will emerge from the pupae. Typically the life cycle from egg to adult takes 28 days. Several generations occur each year.

Armyworms feed on the foliage of the warm-season turfgrasses. High populations of the worms can cause excessive damage. Examine your grass blades closely. Small larvae will chew and feed on the green layer of the leaf blade. Armyworms actively feed early in the morning or late in the evening.

It is best to control the larvae when they are small. This can be done by using Bt products (Dipel or Javelin) which will not harm beneficial insects. Large armyworms can be controlled by using insecticides that contain bifenthrin (Ortho Bug-B-Gon Max Lawn & Insect Killer) or gamma-cyhalothrin (Spectracide Triazicide Insect Killer for Lawns & Landscapes). These can be purchased at any of your garden centers or nurseries. Please read and follow the directions on the label.

Unfortunately, I know firsthand the damage armyworms cause because they visited my Bermuda lawn. I woke up one morning to find them feasting away on my turf, damaging about 15% of it. I did not use any chemicals to control them, so as to learn a little more about their habits. They did eventually move on.

No need to worry, my grass is already growing back. It is bermuda grass you know! Now if they would have just feasted on that crabgrass!

Until next time, happy gardening!

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