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They usually come out at night, but the day is not off limits.

June 28, 2011

Like some other creepy creatures, cutworms come out after the sun is down, and especially when they need something to eat.    

“They are usually going to be in the grass,” says Stanley Swier, extension professor in entomology at the University of New Hampshire. “Most of them are nocturnal but however, when they get larger and they run out of food they may be active during the daytime, particularly on a cloudy day.”

But your customer doesn’t really care when they do their damage, they just want the problem solved. Lawn & Landscape spoke with Swier about the pest and how to keep them permanently in the dark.

Identification. Cutworms can be fairly large caterpillars and when fully grown, they can be a couple inches long. They have three sets of legs behind the head that you’ll be able to easily see, Swier says. Usually, they are striped along the back or on the sides. The exception is the black cutworm, which tends to be more of a solid brownish-black color.

Cutworms can be misidentified as the fall armyworm or the common armyworm.  They can be distinguished by differences in striping on the head and body. Cutworms may also be mistaken for sod webworms, a common lawn pest. Sod webworms can be identified by the rows of rectangular spots down the top of the body.

“Armyworms tend to have different feeding habits, in that, when they get large, they will  march across a lawn and mow down the grass,” Swier says. “When that lawn gets chewed and there’s nothing left, they march on and look further for other food sources.  Cutworms get their name and reputation because they chew off the base of the plant and then go on to another plant and are less likely to march across in uniform army style.”

While most cutworms stay near the base of a plant, they can be up on the foliage when they are young because the eggs can be laid on the foliage. The young larvae feed on the foliage and when they get older, drop down and get closer to the soil.

Lifespan and location.  The lifespan of a cutworm depends on the location and the type.
“The individual cutworm only lives a month or so, but there are several generations. Each generation produces new adults that lay eggs which hatch into more larvae,” he says. Swier says the adults will live a week or two  laying the eggs.
Bronze cutworms produce one generation a year, and are tolerant to cooler weather and will overwinter as eggs.
“Sometimes the eggs can hatch underneath the snow and the caterpillars will feed under the snow,” Swier says.
You may see some feeding in the spring, but most of the feeding will be in May or June. They will spend the summer as a pupa, the stage between the caterpillar and the adult, and then emerge as an adult in the fall and die after laying their eggs back down on the turf.
Black cutworms, which are another grass feeder, will overwinter in the South and are blown North by spring winds from the Gulf of Mexico. They can have five or six generations in the south, but only one to two in the North. They will land on lawns as adults in April or May, and that’s when they  deposit their eggs on the turf.

“The black cutworm, because it comes up in early spring, will do most of its damage by early June for the first generation in the north and the second generation in late July and early August,” he says.  The black cutworm does most of its damage on short cut grasses on golf courses and is not a serious problem on home lawns.  

Variegated cutworms, much like black cutworms, overwinter in the south and get blown north, and there are two generations a year in north, but five to six in the in the south, and they can live year round in the extreme south

Control. There are two strategies to handling cutworms.
If you are dealing with a lawn that has a history of caterpillar damage, you can go with a preventative strategy where you put your material down before you see any serious damage.

“This is based on previous history. You know this particular lawn has had a problem. You can put on a preventative application of a chemical,” Swier says.

You would apply the chemicals before you expect damage. In the North, that would be early to mid-May, but earlier in the South.   

The second strategy would be treating a lawn when the caterpillars are present, but you need to find out if you have them. Birds probing your lawn are a good indication you have caterpillars because they are an excellent food source for them.

You can also use a soap solution to inspect for any cutworms. Use one tablespoon per gallon of water, and spread it out over a square yard of the lawn where you think you might be seeing damage. Within a couple of minutes, the caterpillars will rise to the surface, Swier says.

“They get irritated by the soap and they will crawl to the surface, usually within a few minutes,” he says.
If you have them, you could use chemicals including, chlorantraniliprole,  pyrethroids such as bifenthrin, deltamethrin and lambda-cyhalothrin, or the botanical pesticide neem.  

If you aren’t interested in using chemicals, you can use the nematode, Steinernema carpocapsae or the bacterium Bacillus thuringiensis kurstaki,  but Swier says to make sure you use them properly. Both work best if applied to small caterpillars. Nematodes need light watering after application to get them off the foliage and to protect them from heat and sunlight.  The bacterium is also subject to degradation by sunlight and should be applied in early evening. L&L

The author is associate editor at Lawn & Landscape. He can be reached at