How to manage sod webworms

Sod webworm (Photo: Quali-Pro)
Sod webworm (Photo: Quali-Pro)
Sod webworm (Photo: Quali-Pro)
About a 1/2 inch in length, sod webworms are caterpillars that feed on turf. (Photo: Quali-Pro)

The sod webworm hasn’t really evolved in the past few decades, but how lawn care operators (LCOs) identify and manage this insect has changed and become more accurate.

What do moths mean?

Getting a clearer picture of this insect has made proper identification easier in recent years. A sod webworm is a caterpillar about a 1/2 inch in length in the juvenile stage of a moth. This fact often leads to the misidentification of this pest because customers will tell their LCOs they have sod webworms if they see moths on their lawn when that might not be the case, says Ian Rodriguez, Ph.D., technical services manager for Quali-Pro.

“It’s a very simple pest to understand, but there’s a lot of misconception about it,” Rodriguez says. “You treat when you have the damage. You can’t judge an infestation by the mere presence of adult moths flying around.”

Even if there is damage where moths are present, it could be from drought stress, grubs, chinch bugs or other causes that would require a different approach. However, there aren’t other pests that chew leaves like they do, Rodriguez says.

Signs of sod webworms

Brown patches about the diameter of a tennis ball in the grass where blades might be missing, but not necessarily dead, are good indicators of sod webworms. The grass will look scalped with only the stem left.

Bright green fecal pellets also can be signs of sod webworms. The presence of these pellets, which are found where larval feeding has recently occurred, is also a good way to distinguish sod webworm damage from other reasons turfgrass may turn brown, like dog urine, drought, disease or herbicide injury. Having flocks of birds pecking small holes in the turf to find the larvae may be an indicator of sod webworms, as well.

As the infestation grows, so will the size of the brown turf. Taking a closer look at these areas will show a grazed or scalped appearance because the larvae chew off leaves and stems just above the crown of the plant, says Matt Giese, technical services manager for Syngenta.

Sod webworm damage (Photo: FMC)
Brown patches of turf with missing blades can indicate a sod webworm problem. (Photo: FMC)

To determine if sod webworms are present, he suggests mixing two tablespoons of liquid dish soap into 2 gallons of water and evenly pouring the soapy solution over a marked-off, 1-square-yard area.

“This solution irritates the caterpillars, and they will move to the surface within five to 10 minutes and will provide valuable information about the level of infestation,” Giese says. “Most turf entomologists agree that 10 to 15 sod webworms per a 1-square-yard area may warrant treatment on an as-needed basis.”

If you use chemical treatments, Giese adds, apply them in the late afternoon or evening because sod webworms are actively feeding near the surface at that time.

Change in control methods

A lot has changed over the years when it comes to managing sod webworms.

“In the past, there’s been a lot of reliance on chemical control — not just with sod webworms, but how pests have been managed in the past overall,” says Rakim K. Turnipseed, Ph.D., product development manager, insecticides, FMC. “We’ve learned that you need more than chemicals. You need an integrated pest management approach when dealing with sod webworms, in addition to the chemicals you use.”

That includes cultural practices like avoiding excessive fertilization and overwatering, which can cause thatch to build up, he adds.

“Insecticides, in general, have evolved from a very broad spectrum to a more targeted species approach,” Giese says. “Today’s products, such as Acelepryn (chlorantraniliprole), can now select for control of webworms and yet have a minimal impact on beneficial insects in that same ecosystem. That wasn’t the case 25 years ago.”

Other products commonly used for sod webworm management include Conserve SC (spinosad), Orthene (acephate), Sevin (carbaryl), Talstar (bifenthrin) and Tempo SC (beta-cyfluthrin), according to a University of Georgia Extension bulletin.

LCOs and their customers should determine what’s an acceptable level of damage before making a treatment plan.

“It’s not a pest like chinch bugs where you have to buy new sod because they will kill it,” Rodriguez says. “Sod webworms eat the blades, and a week after they are sprayed, the grass looks fine because the leaves grew back. They aren’t hard to kill, and they don’t typically cause turf loss.”

Where to find them

Sod webworms are generally found in the Southeast, which has remained the case over the years. However, other species of this insect, including the burrowing sod webworm, are now present in areas they weren’t found previously. This burrowing species was originally contained to the Midwest but can now be found in the Northeast.

Climate change also has caused sod webworms to emerge a little sooner than they did in the past, Turnipseed says.

“Whether it’s warm- or cool-season turfgrass, webworms seem to be more prevalent because turf managers are actively scouting for them, rather than misdiagnosing the damage as a different causal agent,” Giese says. “We also probably know more about the life cycles of these insects now and what the damage thresholds are for initiating control measures.”

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