Tim Gibb and Douglas Richmond, Department of Entomology, Purdue University
Sod webworms may cause damage to closely mowed turfgrass early in the spring. Damage, similar to that depicted in these photos, may be seen on golf tees and greens.
The overwintered caterpillars become active when the temperatures warm up in the spring and begin to tunnel and feed. They are mostly active at night, so they often elude inspection. The absence of an obvious insect makes the diagnosis difficult, - but look for patches of close-cropped turf as well as the tiny trails or tunnels in the thatch. Often the soil (and sand top-dressing material) in these trails is bound together with silken material to create a cover or cap, hence the name “webworm”. Along with the damage, these tunnels help provide evidence of sod webworm activity. A soap flush is a sure method of verifying sod webworm presence.
To flush suspect areas, mix one full tablespoon of lemon scented Joy dishwashing liquid in two gallons of water and dispense the solution through a sprinkling can over 1 square meter of turf. It is best to mix the detergent into the proper amount of water by hand in order to minimize the formation of foam which can make it much more difficult to find emerging insects. After 10-15 minutes the sod webworms present will appear on the surface as the soapy water penetrates the silk-lined tunnels these insects create. This will allow you to decide whether the numbers present require treatment.
Healthy and vigorously growing turfgrass will often ‘outgrow’ damage from sod webworms, however if damage is extensive pesticide treatments may be needed
Click image to enlarge
Damage from sod webworm on turf
Dead sod webworm larva