Sod Webworms cool-season

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Typical sod webworm larva in turf thatch. Note green frass (fecal) pellets
Larger sod webworm adult, Pediasia trisecta
Typical sod webworm trail in surface of short-cut turf
  • Scientific Name: Crambidae (formerly, subfamily Crambinae of the Pyralidae): Lepidoptera (numerous species) The most common species are: bluegrass webworm, Parapediasia teterrella (Zincken); larger sod webworm, Pediasia trisecta (Walker); striped sod webworm, Fissicrambus mutabilis (Clemens) and silverstriped webworm, Crambus praefectellus (Zinchen); and, western lawn moth, Tehama bonifatella (Hulst). Common, but less damaging species are: paneled crambus, Crambus laqueatellus Clemens; corn root webworm, Crambus caliginosellus Clemens; pretty crambus, Microcrambus elegans (Clemens); and, vagabond crambus, Agriphila vulgivagella (Clemens).

  • Common Names: sod webworm, lawn moth, snout moth

  • Climatic Zone: Temperate and subtropical

  • Geographic Distribution: North America, Europe

  • Damaging Stage: Larvae

  • Hosts: All grasses may be attacked, but turf with endophytes is generally resistant.

  • Damage Symptoms: Large populations (30 to 50 larvae per square meter) can cause general thinning of high-cut turf especially during periods of drought and slow growth; short-cut turf of golf greens and tees may have frass and topdressing covered silk-lined trails visible on the surface.

  • Description of Stages: Sod webworms are the larvae of small moths, and thus, they have complete life cycles with egg, larval (caterpillar), pupal and adult stages.

Eggs: The eggs are usually barrel-shaped, with distinct longitudinal rows of depressed squares over the surface; they are approximately 3/64 inch long by 7/128 inch wide (1.58 by 1.35 mm).

Larvae: Larger sod webworm larvae are characterized by having light tan to light burgundy-colored bodies with diagnostic rows of darker, squarish spots running down the body. The larvae undergo five to six instars and usually attain a mature length of 1/2 to 1 inch (13 to 25 mm). Larvae are difficult to identify to species.

Pupae: The pupae are tan to reddish-brown 3/8 to 5/8 inch (8 to 14 mm) long. The antennae, wing pads and legs are firmly joined together, but the abdomen is free to twist around if the pupa is disturbed.

Adults: The adults are generally tan to gray and have various markings that help in identifying each species. All sod webworm adults have prominent, snout-like mouthparts that extend forward from the head. When at rest, all the species have the habit of rolling the wings around the abdomen. In turf, adults usually rest upside down with the wings and abdomen extending at an angle from a grass stem. This camaflauges them to look like a dead grass blade. They range from the small elegant sod webworm with wing span of less than 3/8 inch (10 mm) to the larger sod webworm with a wing span of 7/8 to 1 3/8 inch (22 to 35 mm).

  • Life Cycle and Habits: Sod webworms generally have two types of life cycles: multiple generations per year or a single generation. The paneled, corn and vagabond sod webworms have one generation with adults emerging in the spring, summer or fall, respectively. All the rest have two to three generations in cool-season turf zones. All sod webworms overwinter as partially or nearly mature larvae.

The bluegrass webworm is a common example of a species with multiple generations per season. Half grown larvae overwinter curled up in a silk lined cell, called a hibernaculum, one to two inches in the soil. As warmer spring temperatures return, these larvae exit their hibernacula and dig a tunnel to the thatch surface. This tunnel is also silk lined. At the thatch surface, the larvae may extend their silk tubes along this surface, from which they emerge at night to feed on leaf margins. Some literature reports that the larvae snip off pieces of leaves to pull back into their burrows for feeding during the day. The larvae have a habit of depositing their dark green fecal pellets, called frass, along the opening of their burrows.

By mid- to late May, the larvae have matured and they form their pupae within the top layer of soil or within the thatch. The pupae take five to 15 days to mature, depending on temperatures. Adults emerge after dark, expand their wings, and usually mate in the middle of the first night of emergence. Some couples may remain together after sunrise, but most finish mating by daybreak. Those who have not mated the night of emergence usually accomplish this task the following night. Males die within a day or two of emerging while females live five to seven days.

Females begin laying eggs the night after mating by hovering over the turf. They rarely fly more than two feet high. Maximum egg laying occurs about an hour after sunset and may continue for a couple of hours. A female may lay 200 eggs before expiring. Since the eggs have no adhesive covering, they tend to work into the thatch. The eggs hatch in five to six days at 70°F (21.1°C) or above, but take longer at cooler temperatures. The larvae hatch by breaking open the end of the egg and soon spin some webbing across a leaf blade. Within this webbing, the larvae eat the surface tissues, and after a molt or two, drop to the ground to form their larger tubelike silken tunnels. The larvae take about 40 to 50 days to complete development in the summer. The bluegrass webworm normally undergoes two generations at the level of Pennsylvania to Iowa, but three generations occur during extended summer temperatures. Larvae present in October dig into the soil to form hibernaculae.

The annual sod webworm species (i.e., a single generation per year) tend to have larvae that develop more slowly during the season, or they may form resting pupal stages for extended periods. The corn root webworm develops slowly, overwinters in a typical hibernaculum, and feeds into mid-June before pupating. The vagabond sod webworm appears to feed in the fall, form a hibernaculum, finish feeding in early spring, and then forms a pupa that remains dormant for June, July and August before the adults emerge in September.

  • Control Approaches:

Cultural Control -

Mechanical Control -

Chemical Control -