This year we have received many calls concerning tropical sod webworms, a common late summer to fall pest of turfgrass here in the Houston area. Callers say that numerous moths are flying out of the turfgrass when they walk across their lawns. There are numerous species of small moths in the landscape so this characteristic alone is not an identifying factor for diagnosing a sod webworm infestation.
There are several species of sod webworms in Texas but it is the tropical sod webworm that is the most damaging to our lawns. The adults are tan to brownish moths about ¾” in size. They hold their wings out alongside their body when at rest, giving them a triangular shape.
The adult moths do not feed on turfgrass but rather lay clusters of eggs on grass blades stems and thatch from which tiny caterpillars hatch in about a week. The larvae feed on the turfgrass blades primarily feeding at night. They then hide in the thatch during the daytime. The larvae eventually pupate and emerge as adults to repeat the life cycle. Several generations of tropical sod webworms can occur during the year but it is generally the late summer to fall generations that are the most numerous and damaging to our lawns.
Areas of injury are usually spotty at first but can quickly grow in size as caterpillars migrate outward in search of food. In addition to identifying the adult moths the larvae can be forced to come up out of the thatch by sprinkling soapy water on the turf, causing them to crawl up on grass blades. Larvae are usually light green from having consumed grass blades, with numerous dark, raised spots along the length of their body.
The turfgrass usually recovers in time but if already in a weakened state may die in some areas. Recovery of St. Augustine is especially slow especially when damage occurs in the fall. If three to four sod webworm larvae are found within a 6-inch-square section of dying sod, then chemical treatment is recommended. There are several products including synthetic pyrethroids and the organic product Spinosad that are effective in controlling tropical sod webworms. However, finding an over-the-counter product labeled for sod webworm control in turf can be challenging. It is important to spray early in an infestation before much damage has occurred.
For more information on tropical sod webworms see the following web sites: