Sod webworms
Description of this pest
Adult sod webworms, called lawn moths, are typical snout moths: they have sensory appendages
called labial palps that extend in front of the head. The moth holds its wings close to
and over its body at rest, giving it a slender appearance. When disturbed, the moth makes
a short
flight close to the grass. At night, these moths drop their eggs indiscriminately on to
turf. The creamy larvae have a distinctive double row of brown or black spots down their
backs,
located at the base of long bristles. The Lucerne moth larva is somewhat larger than the
other sod webworm larvae. During the day larvae reside in silk-lined burrows, writhing
when disturbed. At night they emerge to feed.
Susceptible Species
Bluegrasses and bentgrasses often suffer the most damage, while perennial ryegrasses and
turf-type tall fescues infected with endophytes (symbiotic fungi) and warm-season turfgrasses
are more
resistant.
Damage
First instar sod webworm larvae are leaf skeletonizers. Later instars notch or cut off leaf
blades and pull them into the burrow. Heavily infested turf (more than 100/sq yd) quickly
appears moth eaten, with irregular patches of brown grass or bare areas. Significant damage
can occur on drought-affected bluegrass and on bentgrass green and tee areas. Lucerne moths
are primarily a problem where clover and dichondra are mixed with turfgrass.
Management
When sod webworms are present, dethatching the turfgrass may help. Monitor to determine
if treatment is needed. Treatment choices include parasitic nematodes and Bacillus thuringiensis
(BT).
Biological Control
Natural enemies include a parasitic tachinid fly and two parasitic
braconid wasps, along with earwig, rove beetle, robber fly, paper wasp, ant, and vertebrate
predators. The
extensive soil or thatch contact of sod webworms makes Steinernema carpocapsae nematodes
a valuable control measure. Bacillus thuringiensis subsp. kurstaki (BT), a microbial insecticide,
can be used but it breaks down rapidly in sunlight, washes readily off leaves, and is ineffective
against late instar larvae.
Cultural Control
Thatch removal can assist in removing sod webworm habitat, although larvae
do not require a thatch layer to be present in very high numbers. Control of clover and dichondra
may help
minimize damage.
Monitoring and Treatment Decisions
Monitor for these pests from June to early October. Consider
treating only when a drench test (see section on MONITORING) indicates
there are more than 5 larvae
per square yard on stressed greens or 15 larvae per square yard in other situations. If
Bt is used, apply it when there are predominantly early instar larvae. Other materials should
be effective on both small and large larvae.
Mow and irrigate the site before applying insecticide and do not mow or irrigate the turfgrass
for at least 24 hours after treatment unless nematodes were applied, in which case apply a
post-treatment irrigation. When BT is applied, do not irrigate for 2 days after treatment.
Threshold: 15 per sq. yard
