Controlling Sod Webworm aka “Lawn Moths”

sod webworm damage to grass along driveway
Sod Webworm damage

Sod webworms, Often referred to as “lawn moths”, are buff-colored and about 1/2 to 3/4 inches long when adults. At rest, they fold their wings around the body, giving them a cylindrical or cigar-shaped appearance, but when disturbed in late afternoon they fly. Sod webworm larvae (caterpillars) are gray to tan with small dark spots on the body and brown heads. They reach 3/4 to 1 inch when fully grown. Most of the damage is done by the larvae.

Infestation occurs fast. Though it often starts in spring it mostly shows up in summer when the grass is going through stress. It seems to be most prevalent on new sod installations. The summer of 2018 has seen some of the worst infestations ever according to experts in the field.

An early sign of potential infestation is if you see small bugs zig-zagging over the turf at dusk. If a sod webworm infestation is suspected, closely examine the turf for evidence of insect activity. Small patches of grass will be chewed off at ground level. Fresh clippings and green fecal pellets are also usually present. Examine the thatch layer and top inch of soil for larvae, silken tubes and webbing.

If insecticides are used, the turf should be mowed and the clippings removed before treatment to enhance insecticide movement into the turf canopy. A thorough irrigation (1/2 to 3/4 inch) prior to application will move the webworms closer to the surface. For best results, apply insecticides in the late afternoon or early evening when larvae are active. Following application, the treated area should be lightly irrigated (1/8 inch), but delay heavy watering for 24 to 48 hours unless irrigation is indicated on the insecticide label. Granule applications also should be lightly irrigated immediately after application to wash granules off grass blades and activate the insecticide. Always follow instructions on the chemical label, do not overdose thinking this is better. Most likely you will have to do several applications timed at 7 day intervals to kill adult, larvae and eggs.