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What’s the deal with webworms?

June 14, 2019 -  By
Sod webworm (Photo: FMC Professional Solutions)

Photo: FMC Professional Solutions

As adults, sod webworms are long, brownish-gray moths with a wingspan of about 22 millimeters and a snoutlike projection on the front of their heads. Keep an eye out for the adults because it could mean larvae, and they’re the ones who do the real damage.

Sod webworm larvae are small, only about 1-13 millimeters in length, and range from green to beige or brown/gray in color. Rows of darker spots run lengthwise along their bodies.

The first three to four instars damage turf by feeding on the outer layer of leaf tissue and leaving a scraped appearance on the leaf’s surface, says Brian Mount, insecticide technical manager at FMC. Later instars will notch leaves or cut them off completely.

Sod webworm larvae damage thins turf, sometimes forming small straw-colored patchy areas that can coalesce into larger patches, says Doug Richmond, Ph.D., associate professor of turfgrass entomology at Purdue University. The worst damage usually occurs between July and August, according to Penn State University.

Fine fescue, Kentucky bluegrass and other grass species are susceptible to the larvae, the university adds.

Soap flushes can help identify areas of sod webworm activity and allow for more focused treatment, Mount says. According to Penn State, the soap solution irritates the body of the insect, forcing it to the surface. If 10 to 15 larvae are present in about a square yard of turf, treatment may be warranted.

One suggested control alternative to chemicals is using an endophyte-enhanced turfgrass, according to the university. Fungal endophytes produce alkaloids, which enhance resistance to insects and disease.

According to Richmond, sod webworms are relatively easy to control with contact insecticides such as pyrethroids, oxadiazines, organophosphates and carbamates.

They can also be controlled with certain systemic materials including clothianidin, thiamethoxam, chlorantraniliprole and cyantraniliprole. Because sod webworms are a sporadic pest, preventive strategies are not usually warranted, but scouting and monitoring are useful tools, he adds.

This is posted in 0519, Turf+Ornamental Care

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