Lawn grasses may be damaged by several species of sod webworms,
which are the larval stage of lawn moths. On cool-season turfgrasses,
the species commonly encountered are the bluegrass sod webworm, Parapediasia teterrella (Zincken); larger sod webworm, Pediasia trisecta (Walker); striped sod webworm, Fissicrambus mutabilis (Clemens); silverstriped webworm, Crambus praefectellus (Zincken); western sod webworm Pediasia bonifatellus (Hurst). Some of these species may also be present in areas where warm-season grasses are grown. The tropical sod webworm, Herpetogramma phaeopteralis (Guenee) is the most damaging species infesting warm-season turfgrasses.
The most common sod webworms are the crambid types, which rest as
adults on grass blades and nearby shrubbery during the day and fold
their wings around the body in a tubelike appearance. Tropical sod
webworm moths do not roll their wings around the body when at rest.
Female moths deposit their eggs randomly over the turf during nocturnal
flights. The ribbed eggs of crambid types of sod webworms are dropped
into the turf, while tropical sod webworms attach their flat,
scale-like eggs to blades of grass. Eggs hatch in 7 – 10 days. Larvae
of all species may vary from gray or light green to tan or brown. Most
have dark spots scattered over their body. The newly hatched sod
webworm larva is about 1/25 inch long with a brown to black head. The
body ultimately reaches a length of ½ to 1", depending on species.
Sod webworms differ from armyworms and grass loopers both in size and
in their feeding habits. Although all lawn caterpillars have chewing
mouthparts, sod webworms feed primarily at night and rest in a curled
position on the soil surface during the day. They are smaller when
full-grown than the 1 ½ inch-long armyworms and loopers. In addition,
the other lawn caterpillars usually have stripes along their sides in
contrast to the spots of sod webworms. Sod webworm pupae are usually
enclosed in cocoons made from debris, soil particles and fecal pellets.
They are reddish brown and about ½ inch long and may be found in the
soil and thatch. There are usually two or three generations per year
for most species of sod webworms, but tropical sod webworms are present
at all stages throughout the year south of Gainesville, Florida.
Turf damaged by sod webworms appears grayish and the damaged area is
usually only two to three feet across. Initial feeding skeletonizes the
grass blades, but there is little visible damage until the webworms are
almost full-grown. The nighttime feeding habit of this pest explains
how serious damage often occurs before it is noticed. Blades are eaten
back unevenly and may even be completely stripped off in patches. These
close cropped areas soon become yellowish or brown. Larger crambid
larvae may cut grass blades and pull them into the silken tunnels that
they construct. Large tropical sod webworm larvae chew notches in the
margins of the leaves, which gives the turf a ragged appearance.
Webworm damage is sometimes confused with chinch bug damage. However,
the lawn area damaged by webworms lacks the surrounding yellow border
that is typical of chinch bug damage. Another likely indication of
caterpillar damage is the persistent return of flocks of birds to a
lawn area. About 12 caterpillars per square foot will cause serious
A good way to find and identify sod webworms is to use the
disclosing solution (soap flush) technique that is also effective for
mole crickets, beetles and cutworms. Two table-spoons of liquid
detergent in a gallon of water is sprinkled evenly over a square yard
of turf. It is also possible to part the grass and look at the soil
surface for the small green caterpillars or their green pellets of
frass (excrement). Nighttime inspection with a flashlight allows one to
see the webworms feeding in the grass canopy.