Sod Webworm Control in Gulf Coast Lawns
Edited by Marv Keenan, Ph.D., Retired Entomologist & Master
Gardener Carol Brouwer, Ph.D., County Extension Agent – Horticulture
There are several genera of
sod webworms in Texas. The native species in the genus
Crambus are widespread, whereas the tropical sod webworm, Herpetogramma
phaeopteralis is less cold tolerant, thus is confined to areas along the Gulf
Coast. The tropical sod webworm has caused extensive damage to St. Augustine
lawns in the Houston area. The adult
moths are similar in size with ¾” (20mm) wingspread, but differ in that the
Crambus sp. Fold the wings around the body at rest, the tropicals spread their
wings, giving a triangular appearance.
The adult Crambus vary in color from white to gray, the tropicals are a
dull brown.
The slender
caterpillars of both groups reach ¾” in length, usually light green from the
grass consumed, with numerous raised dark spots in rows along the length of the
body. They differ in their feeding
habits with the Crambus severing the leaves, then consuming these on the ground
or in silken tunnels in the thatch; the tropicals feed on the leaves while
attached. Both groups feed primarily at
night.
Sod webworms spend the winter months as
partially grown larvae, several inches below the soil surface. During spring,
the larvae mature and transform into the adult moth stage. After mating, the
moths deposit eggs that hatch in about one week. The young, developing
larvae may feed for one to two weeks before transformation to the pupal and
adult stages. Two or three generations may be completed within a year.
Tropical sod webworm Moth, Herpetogramma phaeopteralis
Guenée (Lepidoptera: Pyralidae), adult. Photo by G. McIlveen, Jr.
Damage
Sod webworm larvae feed primarily at night and
prefer areas in lawns that are hot and dry during daylight hours. As a result,
steep slopes, banks and other areas difficult to water properly are subject to
larval damage. Heavily shaded areas are seldom attacked by the larvae.
During the
summer months, sod webworm larvae live on the soil surface in silken tunnels
constructed in the thatch of' the grass. Lawn damage occurs as the larvae chew
off grass blades and retreat into their protective silken tunnels to consume
the foliage. Injury first appears as small brown patches of closely clipped
grass. Lawns are particularly susceptible to larval damage during the months of
July and August when the temperatures are hot and lawns are not growing
vigorously. Large lawn areas may be damaged rapidly if controls are not
applied.
Control Measures
The need for sod webworm control can be determined
by close examination of the grass and thatch. If three to four sod webworm
larvae are found within a 6-inch-square section of dying sod, then chemical
treatment is recommended. Larvae are most active on cloudy days or at night.Insecticides can be applied in either spray or
granular form. Spray solutions can be applied with a garden hose sprayer or
compressed air sprayer. Apply at least 15 to 25 gallons of insecticide-water
solution to 1,000 square feet of grass. Watering the lawn before application
will aid penetration into the turf. If
the damage is from the tropical sod webworm, a liquid spray applied to the
leaves is suggested.
Granular insecticides are easier to use and
generally provide more thorough coverage. This type o£ insecticide can be
applied with a fertilizer spreader. Following application, the lawn should be
watered for about an hour to wash the granules into the matted turf. Use
insecticides containing acephate (Orthene®),
bendiocarb (Dycarb® or Turcam®), carbaryl (Sevin®), or the microbial
insectices Bacillus thuringiensis ssp. Kurstake (B.t.k.) and ssp.
Aizawai (B.t.a).
The microbial insecticides are specific for
caterpillars thus do hot harm non-target arthropods or animals. Consult the directions given on the container
label to determine the approved rate of insecticide application.
Sod Web Worm . Caterpillar. Photo by G. McIlveen, Jr.
Note... many other articles stress using a combination of a hose end liquid insecticide and a granular. Sod webworms and cutworms are both readily controlled by most liquid insecticides approved for turfgrass — bifenthrin, malathion or any of the synthetic pyrethroids or carbamates out there. However, these are short-residual materials, and repeat applications are required to control the next generation. Just as in controlling chinch bugs, three applications of liquid insecticide spread over two weeks usually does a great job of breaking the egg cycle. The eggs hatch in 7-10 days.
Precautions
Children and pets should be kept off treated turf
until insecticide has been watered and turf has dried. Follow directions on
insecticide labels and observe all safety precautions. Pesticides should be
stored out of reach of children and pets.
Suggested
pesticides must be registered and labeled for use by the U.S. Environmental
Protection Agency and the Texas Department of Agriculture. The status of
pesticide label clearances is subject to change, and may have changed since
this publication was printed. County Extension agents and appropriate specialists
are advised of changes as they occur
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