What Are Cutworms and How Do I Get Rid of Them?
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These insatiable pests munch your grass, leaving unsightly bald patches. Here's how to spot them and eliminate them.
A nuisance to homeowners and farmers, cutworms feed not only on lawns, but also on vegetable plants, ornamentals and farm crops. Found across the globe, they are known to cause significant damage once they’ve taken up residence.
“These non-discriminate feeders attack a wide range of plants,” says lawn expert Dave Holmes of The Grounds Guys. “All common turfgrasses are susceptible to damage by the larvae that feed at night.” Here’s how to spot these ravenous pests and send them packing before they cut your yard to shreds.
What Are Cutworms?
Cutworms are the larvae of the cutworm moth, which lays its eggs in clusters in grass at night from spring through fall, depending upon the type of moth. The adult moths are attracted to light, so cutworm invasions often happen on lawns surrounding well-lit homes when the eggs hatch a few weeks after they’re laid.
Cutworms chew turfgrass at the crown — the pale section at the base where the shoot and root meet — until the blade is severed. This habit of gnawing has earned the caterpillar its name and its reputation as a particularly destructive invader.
Types of Cutworms
There are several species of cutworms found in North America. Holmes says the two most common are the Black Cutworm (dark colored with brown to black spots running the length of its back and sides) and the Variegated Cutworm (various colors with a pale white line and/or yellow dots along its back). Other types you may encounter, depending on where you live, include:
Pale Western Cutworm.
What Are the Signs of Cutworms?
During the day they hide in underground burrows or under thatch near the surface of the soil, so they’re hard to spot. You’ll more likely know you have cutworms based on the damage they cause.
The most common sign of cutworms? Patches of grass that look like they’ve been sliced off at the base. “Depending on the species, damage typically occurs in early summer through the fall,” Holmes says.
You can also sometimes catch the larvae themselves above ground in the early morning or late evening. “If you brush your hand across the surface of the soil, you may notice them if they curl up,” says Drew Wagner of Sod Solutions. “They typically make a ‘C’ shape when they’re disturbed.”
Also, according to Holmes, “Watch out for a large number of birds scratching and pecking at your lawn, as this can indicate a large cutworm population in the grass.”
Finally, you can check for droppings around damaged plants. They’re tiny and black, found on plant bases near the soil surface.
How To Get Rid of Cutworms
Luckily, Holmes says these insatiable pests are relatively susceptible to insecticides, as well as some biological control agents. “The key to successful control is to apply treatments when most of the caterpillars are small,” he says. “For best results, make control applications 14 to 21 days after peak adult moth flight activity.”
Biological control agents: BT (Bacillus thuringiensis) is a natural biological control option that the University of California Integrated Pest Management Program recommends using during the young larval stages. Avoid irrigating for two days after treatment to optimize results. Releasing nematodes that feed on cutworms in the soil is another natural biological control option, according to Holmes. You can also spread DE (diatomaceous earth), a natural powder that is made up of razor-sharp particles that will kill the larvae.
Physical control: “If you spot them and don’t want to use chemicals, grab them and throw them into a bucket of soapy water to kill them,” Wagner says. They are easiest to cull at night when they are actively feeding.
How To Prevent Cutworms From Coming Back
“There is no pre-emergent treatment you can apply to a lawn to prevent cutworms,” Holmes says. “But there are some things you can do to limit or stop their damage before it kills your lawn.”
Control thatch: “Cutworms like to hide in the thatch layer during the day, so controlling thatch can help prevent cutworm infestations,” Holmes says. Dethatch when needed to limit the level in your lawn.
Lawn care: Cutworm moths tend to lay eggs in high grass and weeds, so mowing regularly can deter an invasion.
Vigilance: “Although cutworms are primarily a problem in early and late summer, they can harm lawns all through the growing season,” Holmes says. Keep up on your lawn care tasks all year to keep these pests at bay.