Karen Cambre, Sharpe, Kenneth W.
News article for October 22, 2018
I have had a number of reports of large areas of grass damage in lawns over the past few weeks. The areas appear as large, somewhat circular spots with lots of missing grass, but weeds are untouched.
Tropical sod webworms are the problem. I have seen reports from around the state that they are active. Sod webworms are caterpillars that like to feed on grass, much like armyworms. One of the unique features about them that makes it hard for people to find the culprit is that sod webworms feed at night, unlike armyworms that feed during the day.
If you are seeing missing pieces of grass blades that appear to have been chewed, yet no worms are present, you should suspect sod webworms. Another clue will be the worm’s castings. Castings are the digested grass that has passed through the caterpillar and appear as dark green pellets at the base of grass plants.
Observing your lawn early in the morning while the dew is still present is also helpful. If you have sod webworms, you will see extensive webs left in the grass by sod webworms. The webs are visible in the morning as the water droplets attach to the webs. This is where they get the name sod “web” worms.
To further confirm the theory, you can look down in the thatch layer of the grass during daylight hours and you can usually find the caterpillar. He will be hiding from the sun and will be a small emerald green worm, about 1 inch long, and about half the diameter of a pencil.
Do not be too discouraged if you do not see the worms or very few. They are hard to find, but circumstantial evidence will lead you to the correct conclusion.
You might also notice a lot of moth activity coming out of the grass and from under trees. If you turn on the outside lights right after dark you can attract a lot of sod webworm moths if they are present in the area. Sod webworm moths are going to be relatively small, only ½ to ¾ inches long and a wing span of about 1½ inches wide. They are tan to gray in color and have a snout like projection on their foreheads.
Use an insecticide with bifenthrin or Sevin to spray the lawn to control sod webworms. If you have a yard that is too big to spray, just treat the spots infested and expand out 3 to 4 feet past where you see browning. Continue to monitor your yard as moths are constantly laying eggs when active and you can have a new hatch ready to eat in 7 days. Cooler weather does slow down the generation interval and will help to slow damage, but it will not kill worms already infesting your lawn.
Moths do not feed on grass and will not be controlled by the spray. Concentrate on caterpillars, they are causing the damage.
In my experience sod webworms seem to have a preference for carpet grass, followed by St. Augustine grass.They will also eat centipede and Bermuda, but usually not first.
Last year we had a lot of sod webworm damage in newly planted ryegrass pastures, so be aware.