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How to keep sod webworms at bay

March 13, 2023 -  By
Sod webworm caterpillars are the most damaging part of the turf pests’ life cycle. Most damage occurs when the caterpillars reach peak maturity. (Photo: Envu)

Sod webworm caterpillars are the most damaging part of the turf pests’ life cycle. Most damage occurs when the caterpillars reach peak maturity. (Photo: Envu)

Sod webworms are an equal-opportunity turf pest, says Jesse Benelli, Ph.D., green solutions specialist for Envu. The sod webworm will feed on just about any type of turf, making it a tricky pest to manage for lawn care operators (LCOs), especially those in the southeast.

Benelli shares with LM what LCOs need to know about one of the green industry’s most widespread pests.

Know when and where to look

LCOs should look for adult moths first because they’re easier to spot, according to Benelli, despite the fact that moths are not the damaging part of the life cycle.

“You don’t want to find these when you already see the damage, and you’re looking at mature caterpillars because as they become larger, they are more difficult to control,” he says.

Benelli says that LCOs will most likely find adult moths on the turf during the day. Caterpillars will be tougher to see as they are mostly burrowed during the daytime.

“This is slightly easier said than done,” he says. “The adult moths tend to come out at night, and the caterpillars themselves usually won’t feed during the daytime. If you’re in an area with a chronic history of sod webworms, once you start to see adults, then you can make a preventive application.”

Moths are slender and are off-white to light yellow in color. Their most unique characteristic is a pronounced snout, which Benelli says is a dead giveaway that sod webworms are present.

“The other thing is how they hold their wings when they’re resting on the turf,” he says. “(A sod webworm) holds them very tight to its body, so they look very slender.”

What damage looks like

According to Benelli, there are two different times in the growing season when sod webworms will cause damage: in the early spring and summer.

“They can overwinter as caterpillars,” he says. “Then, in the spring, the caterpillars will start feeding in the upper root system and the lower plant stems. So they’re essentially cleaving off roots and the stem of the plant.”

As a result, LCOs will see sunken depressions of dead turf that could be similar to several other diseases, such as dollar spot. One way to confirm webworms as the culprit, Benelli says, is through a soap flush.

“You’re taking some water and dish soap and pouring it onto the turf during the day,” he says. “After a while, the caterpillars will come to the surface because the soapy water has irritated them.”

In the second generation of webworms, which appear in the summer, damage appears to be thinning and irregular patches of turf because the pest feeds more on the leaf tissue as opposed to the root system.

Have a preventive approach

Recommendations for sod webworm control have shifted in recent years, Benelli says, with a preventive approach becoming the most popular.

“In an area where you’ve seen multiple generations of sod webworms, I would put down an insecticide that has residual activity,” he says. “Ideally, you’ll want something that will work both right away and provide some residual control.”

Historically, Benelli says, the preferred method of control among LCOs was contact insecticides. That’s still a valid course of action to control as many webworms as possible if you see active damage. 

“In a perfect situation, you would put down an application if you’re concerned about the overwintering caterpillars in the early spring,” he says. “Then six to eight weeks later, you’ll get the second generation of caterpillars that feed in a different way. So you’re looking at another application there around mid-July.” 

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