We have had reports from Will County and southern Cook County of cranberry girdlers (Chrysoteuchia topiaria) causing damage to turf. There are many species of sod webworm that attack turfgrass, and most of them have similar life cycles that cause similar damage. They typically overwinter as larvae, live in silk tunnels in the thatch, come out at night to feed on grass blades by eating them off at the crown, and have several generations per year. Although the cranberry girdler is a sod webworm, its life cycle, damage, and control are more similar to that of white grubs. As the name implies, this insect is also a pest of cranberry, girdling the roots of cranberry, as well as some needled evergreens.
Cranberry girdler adults emerge from late June into August. They are similar in shape to other sod webworms, holding their wings close to the body. Their palps are long and protrude from the front of the head like a snout. However, their wings are brown and whitish, striped with silver V-shaped bands and three black dots near the tip. They are less than 1/2 inch long, with a wingspan of about 3/4 inch. While other sod webworm moths fly low over the turf, dropping eggs that fall to the soil, cranberry girdler moths land on grass blades to drop their eggs.
Eggs hatch into larvae that feed through the late summer into fall. The larvae are slender and dirty white in color, but without the spots characteristic of other sod webworms. Young larvae live in the thatch or alongside the crown of grass plants. Older larvae live in silk tunnels. They are about 3/4 inch long when fully mature. Unlike other sod webworms, the larvae feed on the roots of cool-season grasses, including Kentucky bluegrass, fine fescues, and bentgrass. As cold temperatures arrive, typically by November, they go dormant for the winter. In May, larvae that were not fully grown at the end of fall resume feeding. Later in the spring, both these larvae and those that were mature the preceding fall pupate, emerging as moths at about the same time.
Damage is caused as larvae tunnel into the grass crowns and feed on grass roots, stems, and leaves. Damage appears as small, roundish, brown areas of turf 1 to 3 feet in diameter. Brushing your hand across the turf frequently causes the grass blades to break off, and the turf easily can be pulled back, as with white grub damage.
Starlings, blackbirds, killdeer, and other insectivorous birds feeding on the larvae in the fall commonly provide all the control that is needed. Large numbers of birds feeding on turf areas in the fall can be indications of either white grubs or various sod webworms, including cranberry girdler. If grubs are not numerous and turf damage is not evident, treatment is usually not needed--allow the birds to provide the control.
Chemical control is most effective when applied a couple of weeks after heavy moth activity in the summer; however, treatment in the fall should also be effective if bird-feeding is not sufficient to prevent obvious damage. Spring treatments are usually not very effective because much of the population has finished feeding, making those larvae less susceptible to insecticide. Trichlorfon (Dylox) or halofenozide (Mach 2) should provide control. Watering in the application improves control.