Tropical Sod Webworm
There are quite a few pests and diseases that can damage your Florida lawn, and tropical sod webworm (Herpetogramma phaeopteralis) is one of those pests. While they prefer St. Augustinegrass, these very hungry caterpillars also munch on bermudagrass and zoysiagrass. They are most active from spring to fall, although in South Florida they can be found year-round.
You may notice the signs of their destruction in your lawn before you see these critters—they feed at night and rest during the day, curled up below the blades. Signs of damage include areas of ragged grass blades that are shorter than other areas of the grass, thinning of the lawn (fewer leaves), and eventually brown patchy areas. Many gardeners report that the damage to their lawn seems to have occurred overnight.
The moths of tropical sod webworms are another sign of these caterpillars in your landscape. These light tan-colored moths will flitter and scatter as you walk through the grass. But it's not the moths causing damage; it's their offspring—the caterpillars—damaging the turf. This larval stage is the most damaging of the tropical sod webworm’s life-cycle. Mature caterpillars are ¾ to 1 inch long and grayish-green. (Interesting fact: the caterpillars will appear greener the more grass they have eaten.)
As in so many things, the best way to address damage is to actively work to prevent it in the first place. A healthy, well-maintained lawn will be less susceptible to tropical sod webworm damage. You can help keep your lawn healthy by properly mowing and, if you choose to, irrigating and fertilizing correctly.
While being told to prevent damage is all well and good, that doesn’t help you if you are already dealing with a pest problem. You may read that in some cases your lawn will recover just fine from tropical sod webworm damage. That is true—as long as your lawn is not suffering from any other type of stress. However, in other cases your lawn may not return to its desired health. If you choose to treat your damaged lawn, be sure to verify that you are in fact dealing with tropical sod webworms. Then select a pesticide labeled for this particular pest; there are a number you can buy at your local garden store. You can use the proper pesticides to spot-treat the affected areas following label instructions.
Speaking of identifying tropical sod webworms…
If you are an active Master Gardener we need your help.
In studying tropical sod webworms, UF Entomology graduate student Ethan Doherty sees the important role citizen scientists can play in his research. Doherty is studying how St. Augustinegrass diversity affects the development of tropical sod webworm (TSWW) caterpillars. He is also looking into the moth’s distribution throughout Florida. He is hoping that his research will help develop best practices for controlling this landscape pest. Contact your Master Gardener coordinator for more information about this project.
If you are interested in becoming a Master Gardener contact your local county Extension office.