The tropical sod webworm is a caterpillar that feeds on leaf blades in grass. The insect is active in Southern Florida year round with the greatest potential for damage from April to November.
Initial damage appears as small brownish areas of close-clipped grass which enlarge and overlap with each other as the infestation progresses. Tan and gray colored moths flying just above the grass in a low zig-zag pattern in the early evening hours is an indication of tropical sod webworm activity.
Large numbers of moths can be flushed out when mowing, however this does not mean there is an impeding outbreak. Early detection of caterpillar activity is the key factor. Inspect your turf closely for chewed grass blades and caterpillars in the thatch.
An insecticide application followed by fertilization to help turf recover is the most effective treatment. Because of the long flight periods, several applications may be needed.
Predator insects and spiders play an important role in suppressing tropical sod webworm populations by as much as 75 percent. Therefore, to preserve these natural enemies, insecticide applications should use a product that is selective for caterpillars only.