Sod Web Worms

Sod webworms can be serious pests of home lawns, sports fields, golf courses and other turfgrass areas. The larvae (caterpillars) are gray or tan with dark spots on the body. Sod webworms seem to prefer new, vigorous lawns and they increase in importance when many new lawns are being established. Adults are gray to tan moths, about 1/2 to 3/4 inch long with snout-like projections on the head. At rest, moths fold their wings around the body giving them a aerodynamic appearance.

 

 

Sod webworms overwinter as partially grown larvae in silky tunnels in the thatch and soil. In most cases, the larval activity starts in April or early May. Webworms complete development, pupate, and emerge as adults from mid-May to early-June. The adults rest in the turf and on shrubbery during the day and randomly scatter their eggs over the grass in the late afternoon and early evening while flying in a zigzag fashion just above the turf surface. The moths have a wingspan of less than 1 inch. Since they do not eat they only live a few days.

Sod webworm larvae feed at night on grass blades and stems. They drag the blades into silken tunnels that they construct on the soil surface. Webworm-damaged areas take on a ragged or scalped appearance. The turf first appears as brown trails or small irregular brown spots in the lawns. As the larvae grow the trails expand, becoming large brown areas of injured grass. An above-normal amount of bird feeding activity on the lawn may alert you to an early infestation. There can be several generations of webworms each season with the most severe damage usually occurring in mid to late summer.

 

There is a simple test you can do to determine if webworms are present in your lawn. Mix 1/4 cup powdered laundry detergent in 1 gallon of water. Apply the entire mixture at the edge of both damaged and undamaged areas. Remember that there won't be any worms in the middle of the dead areas (since no food is left) and there may not be any in a totally green area. The worms will come to the surface within 10 minutes. Diagnostic kits are available for commercial licensed operators. This test also works with cutworms and armyworms

Sound cultural practices, especially proper irrigation, will usually allow your turf to outgrow light to moderate webworm injury. If fifteen or more webworm larvae are present per square yard in reasonably healthy turf, an insecticide application may be needed. For a complete list of both organic and inorganic chemicals, come to our Insecticides page.

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