Information compiled by
Maggie Wolf ,
Asst. Prof., Horticulture
USU Extension Salt Lake County

Sod webworm is a common pest in lawns along the Wasatch Front.  The larvae at left have overwintered in the soil and thatch and resumed feeding in spring.  These larvae were collected April 21, 2005 from a lawn in Herriman , UT.   Larvae are about three-quarter inch long.

The classic symptom of sod webworm is an irregular spot of dead grass in the lawn, with the dead grass blades easily pulled away from the roots.  Dig a little deeper into the thatch or topsoil, and you will likely find the larvae.

This Kentucky bluegrass lawn has sod webworm damage.  This picture was taken April 21, showing the early season effect of larval feeding.  Damage isn't severe at this point, but left unchecked the pest population could increase dramatically. 

Birds, ground beetles, and other insects prey on sod webworm.  Environmental conditions must also be favorable for their population growth, although larvae are well protected under thick thatch. 

Cultural control of sod webworm includes: regular core aeration of the lawn to help reduce thatch layers.   Aerate in spring or early fall, when temperatures are favorable for quick re-growth.  Allow the cores to remain on the turf surface.

Adult sod webworm emerge in summer and fly low across the lawn in a zigzag pattern.  Females can scatter fertilized eggs as they fly.  After about 7 to 10 days, the eggs hatch and begin to feed.  Apply pesticides as larvae feed for most effective control.

Organic controls include B.t. (Bacillus thurengiensis var. kurstaki), a bacteria that kills moth and butterfly larvae.  It is available under the commercial name Dipel.  Parasitic nematodes, Steinernema carpocapsae, may also help keep webworm populations under control. 

 Chemical insecticide treatment of sod webworm is recommended only when damage is severe.  Many of the chemical controls have high toxicity to fish.  Carbaryl (Sevin), is toxic to earthworms. 

Spinosad, a new type of insecticide that is produced by a soil organism, has less non-target effects and would thus be the best choice for chemical control options.

Always follow label directions when using any pesticide, organic or not.  Apply only to crops listed for pests listed, and mix at recommended rates. 

More information about sod webworm is available at the USU Extension website http://extension.usu.edu/insect/fs/sodwebwo.htm, however, several of the chemical controls listed in the publication are no longer available.

USU Extension does not endorse any particular brand of pesticide product.  Any indication of endorsement in this webpage is unintentional.