Cutworms: it’s amazing how much damage to our vegetables
and flowers such a small insect can cause.
By Larry Hodgson
What a disaster! You make your morning rounds of the vegetable garden, in perfect condition the previous day, to find a dozen plants lying flat on their sides, cut at their base. It almost looks like someone went at them with a weed-eater! What in the world could cause this kind of damage?
That would be an insect called a cutworm. It’s the larva of a dull and unremarkable small moth. So, even though we use the term cutworm, it’s not a worm. In fact, it’s a caterpillar. There are hundreds of different species found all over the world. Anywhere you garden, there are probably a dozen or more local species. They come in all sorts of colors: brown, gray, black, yellow, green, etc., even white in the case of newly hatched cutworms. Often the caterpillars have longitudinal dark racing stripes.
Most gardeners see cutworms during daylight hours, as they sleep. At that point, they are characteristically found rolled up into a C shape.
Young cutworms simply bore holes in plant leaves or nibble at the margins. On the other hand, when they get a little bigger, they begin to chew the stems of young plants. This cuts them to the ground as the name suggests. Some at least cut a plant down and settle in to consume it. Others—the most destructive ones!—seem to prefer taking just a few bites of many plants over a single night. This leaves the garden strewn with fading plants in the morning, all of them barely nibbled on. Yet others mostly chew on roots. So, they’re very much a mixed bag.
A cutworm always does its damage at night. During the day, it takes refuge in the ground, sheltered from predators such as birds, toads and snakes. It never goes very deep, always remaining found near the surface.
Its life cycle is variable, depending on the species. Some cutworms overwinter in the soil as eggs, pupae or larvae. Others don’t survive the cold winters of northern regions. Instead, the moths of these species fly back up from the south each year as temperatures rise. They then lay their eggs soon after they arrive. Most species produce more than one generation per year.
Some cutworms are very specific as to their host, affecting only beans or only corn, for example. On the other hand, most are “polyphagous”: they attack almost any plant. By the way, they go not just for vegetables, although they are often mostly blamed for that. They also attack annuals, perennials and herbs, even young trees.
Note that several species are linked to lawns. For this reason, there is often an abundance of cutworms the year a lawn is converted to a garden through tilling. (Setting up a raised bed over a newspaper or cardboard barrier, on the other hand, prevents this problem.) Another problem: when lawns are overpopulated with cutworms, they start to migrate into nearby gardens. Leaving a 2-foot (60 cm) strip of soil free of lawn all around a vegetable garden or flower bed can therefore seriously reduce the risk of infestation.
Controlling a Cutworm Infestation
The easiest control is manual harvesting. Usually, the culprit spends the day in the ground near a plant that it mowed down the night before. All you have to do is dig in the ground looking for it, never any deeper the 2 inches (5 cm). Use a trowel or hand rake for that purpose.
Some species drag the cut plant into the ground to continue chewing on it during the day. However, in doing so they leave part of the plant exposed. That way, you know exactly where your enemy is!
Another possibility is to go out at night with a flashlight. Then a rudimentary inspection of the plants reveals the culprit: the cutworm at work on the surface of the soil or on the lower stem. Thus, you actually catch the cutworm in the act.
When you find it, drop it in a bowl of soapy water or squish it. Or feed it to the chickens.
Speaking of Chickens
You can also let chickens (or ducks) loose in the garden. They’ll seek cutworms out and eat them. Unfortunately, they may damage young seedlings as they do so. Sometimes it’s better to keep the chickens out of the garden until the plants are solidly rooted and growing.
How to Prevent Cutworms
One possible preventative treatment is to hoe the garden about 2 weeks before planting. This will kill many overwintering worms and leaves others exposed to birds and other predators.
In a vegetable patch or garden that often has a cutworm problem—perhaps one located next to a lawn—, it may be necessary to protect the plants with a barrier of some sort.
You can, for example, cover the entire garden with floating row cover starting at the beginning of the season. That’s a translucent fabric available in garden centers that allows the sun, rain and air to penetrate, but not insects. It works perfectly for cutworm moths arriving from the South to lay eggs. However, this method won’t be effective against species that overwinter in the soil.
Make sure the edges of your barrier are solidly en contact with the soil on all sides. If there are any gaps, the cutworms could worm their way in!
Or protect your plants one by one. To do this, simply cut the bottom off a few cans, plastic jars or plastic, Styrofoam or cardboard cups and glasses, making a cylinder. You can even use the tube from the center of a roll of toilet paper! Set these barriers around the young plants, sinking the lower part of the barrier 1 inch or so (3 cm) into the ground. Then let it protrude 2 to 2 ½ inches (5 to 6 cm). Cutworms are not very persistent. They’ll wander off elsewhere looking for something easier to reach rather than look for a way over or under a barrier.
Another possibility is to treat the soil with beneficial nematodes, available in garden centers.
Whatever you choose to do to control cutworms, the important thing is to start reacting quickly, as soon as you see signs of their presence, in order to limit the damage.
Apparently cutworms need to wrap themselves around the stem to eat it. I always push a nail into the soil next to the stems of transplants that won’t regrow if they are cut off, such as tomatoes. It works, although I’ve never really thought about the details of WHY it works until I read this post — they don’t like the feel of metal? They can’t wrap around the wider diameter of stem + nail?
I would guess the latter, but… I’ve never been able to confirm the “belief” that they need to wrap themselves around the stem is true. You’d think that, given the hundreds of species of cutworms, that wouldn’t be true of all of them, at least.
Skunks! (Although, I do not know how to get rid of skunks.)