The scene is gruesome – even the strongest may turn their gaze: young plants cut down, their bases firmly embedded in the soil, but their dismembered tops strewn about the ground. It’s the work of cutworms…and there are many different species responsible for such damage.
Cutworms feed on the base of plants, then leave their wasteful calling card: a chopped down plant.
Photo Credit: Tom Weissling
A plastic cup makes a good and easy collar to keep cutworms away. Just remove the bottom of the cup and push it into the ground about 2 inches.
Photo Credit: Tom Weissling
This cutworm larva is in its typical resting position.
Photo Credit: ©2008 Buglady Consulting
But before we start pointing fingers, let’s clear a few things up: While rebellious in their youth, adult cutworms are innocent of any assault on plants. The adults are nocturnally active moths that fly about, sipping on flower nectar, if they feed at all. That said, they’re not completely innocent. In late summer, these moths emerge from the soil, where they had metamorphosed from a caterpillar into the winged creatures they become. Once they’re out and about, they mate, and the females go off to look for grassy or weedy areas to lay their eggs. These eggs, sometimes hundreds per female, are laid on plant stems or in the soil. And so a new generation of cutworms begins…
Soon after they’re laid, the eggs hatch, and very tiny cutworm larvae go off in search of food. At this point they’re so small (and the plants are so big), that their munching damage goes unnoticed. But they’re out there – feeding and chewing on the base of plants…or on the leaves or perhaps even below the soil surface. (Feeding preference is really related to species. Army cutworms, for example, prefer grasses – especially certain wheat cultivars. In other words, few plants are safe.)
Most feeding stops when fall temperatures are too cold for activity and the caterpillars seek a place to spend the winter, such as under leaf litter, in clumps of grass or even in cells made in the soil. There they wait until spring temperatures warm them up and promote plant growth. They’re very hungry by spring, so seedlings or transplants are at risk.
The pests hide in the soil during the day and come out to feed at night. Most cutworm species chew on the base of plants right at, or just below the soil line, felling the plant. But they only feed on the base, wasting the rest of the plant. This dangerous feasting continues until midsummer, when the fattened caterpillars then crawl into the soil to change into the adult stage.
As I said, there are many species of cutworms. The good news is they can be easy to spot. Most larvae are smooth and plump, varying in color from brown to pink, to green or gray. Their coloration may be solid, spotted or even striped. The adults are stout brown or black moths with a variety of markings on the wings.
As you walk through your garden on a sunny spring or early summer morning and stumble upon the ugly sight of plant tops strewn about, you vow to prevent this from occurring again. But how?
Well, there are steps you can take to reduce or eliminate the impact of cutworms in your garden. Frequent cultivation around plants – digging lightly around your planting beds – is an effective way of exposing cutworm larvae. Once exposed, larvae are vulnerable to a variety of predators and parasitoids. And you, too, can act as a predator…only you don’t have to eat the worms. Rather, you can crush them, drown them in a bucket of soapy water or toss them over to nearby birds.
Your transplants can be protected, too, with a variety of “collars” placed around the stems. Collars are typically constructed of cardboard or a plastic cylinder – even foil. Make sure the stem is in the center of the collar, then just push the collar a few inches into the soil, making sure the entire piece is long enough to cover several inches of the plant stem. This will effectively keep cutworms away from your plants.
Parasitic nematodes applied to the soil around plants are generally very effective at killing cutworm larvae without chemicals. If applying nematodes, just remember to keep the soil moist. Also, bait applications (bran or oats) containing Bt (Bacillus thuringiensis var. kurstaki) can be effective at killing cutworm larvae if the pests ingest enough of the toxin. If insecticide application is your control of choice, contact your county Extension educator or a knowledgeable staff member at your local garden center for recommendations.
While cutworm larvae can be very damaging to plants, they can be managed. As with all pests, you just need to get to know them and learn their biology – then you’ll be better equipped to fight them…and cut them down!