Turf managers can tell what type of larvae are invading their turf by the unique physical characteristics of the damage caused. Sometimes larvae damage can be mistaken for disease or distress, so it’s important to know the differences between types of larvae for effective detection and control.

One common larvae, sod webworms, typically attack Kentucky bluegrass, perennial ryegrass, fine fescue and bentgrass through late September. Bobby Walls, Ph.d., turf product development manager for FMC Professional Solutions, offers the following information for detection and control.

Sod webworm larvae vary in color from gray or light green to tan or brown. A physical characteristic that sets them apart from other species is their spotted backs. These larvae will grow to reach a length of approximately 1 inch.

Areas of damaged turf first appear as small brown patches. These patches often will run together causing large and irregular-shaped damaged areas. The pests burrow in tunnels in thatch during the day and emerge at night to feed. The nighttime feeding habits of the sod webworm explains how serious damage often occurs before it’s noticed. The pest eats back blades unevenly and may even completely strip off patches of turf. Another common indicator is large flocks of birds gathering on the turf area to feed.

A disclosing solution (soap flush) technique is a useful tool for monitoring and detecting these pests. Sprinkle a mixture of 2 tablespoons of liquid detergent and a gallon of water evenly over a square yard of turf. The soap will irritate the worms causing them to crawl to the surface. The recommended treatment threshold for these pests is typically 10 to 15 worms in a square yard, after observing obvious damage to turf.

Walls recommends that lawn care professionals control sod webworms with an insecticide containing the active ingredient bifenthrin.