Sod webworms are an annual occurrence here in the greater Houston area but some years the outbreaks are much worse than others. This year may be another bad year or on the other hand, just one with a very minor and scattered outbreaks. Residents have been calling and emailing the Extension Office with concerns about seeing small moths around their home and landscape again. There are many small tan/brown moths in nature and so you may be seeing something other than sod webworms. You can find a photo of the adult moths in a previous blog entry. Note that the wings of sod webworm moths are “held out” (like jet fighter-plane wings) when at rest.
While concerns about these pests are certainly understandable after last year’s severe outbreaks, pre-treating for the moths will generally not be helpful since the moths do not feed on the turfgrass. The moths appear in mid to late summer and lay eggs in the turf that hatch out in a week to 10 days into the larvae, the destructive stage of the insect. Products applied too soon will not be efficacious when the larvae finally hatch and start feeding. Some products such as B.t. only last a few days in the environment while others such as carbaryl (Sevin) could last a week or more.
You can scout for tropical sod webworm caterpillars by drenching the soil in a spot where you suspect the pest to be with a solution of 1 tablespoon of lemon-scented liquid dish detergent in one gallon of water. This mixture irritates the caterpillars (and other insects) and flushes them to the soil surface for collection and identification.
Approaches to management are to either: 1) wait until you are able to find the webworms through the soapy water technique or first start to see signs of their feeding and then immediately treat with an insecticide labeled for insect control in turfgrass, or 2) note when you notice the moths flying around the lawn and treat 10-14 days later. A repeat treatment 2-3 weeks after the first may be needed. Products for treatment include Bacillus thuringiensis (B.t.), spinosad, acephate (Orthene), carbaryl (Sevin), and various synthetic pyrethroids (such as bifenthrin and cyfluthrin). Always check the label for use on turfgrass and follow label instructions carefully regarding mixing and application. Liquid applications are much more effective than granular products since they cover the grass blades, which are what the larvae are consuming. Mowing removes grass blade and irrigation can wash off an insecticide, both of which may warrant retreatment to extend control.
For more information, an online publication on sod webworms can be found at the following AgriLife Extension publication.