In my organic garden of heirloom plants here in Oregon, we have several pests: deer, raccoons, dogs, squirrels, rats, slugs, cabbage looper larvae and cutworms. Cutworms have been the most consistently damaging of the group. Typically, they sever the stems of young transplants, a preferred food of theirs. They also eat most of the plants I grow; all vegetables, but especially plants of the Brassica, Dianthus, Primula and Viola families. Here, they are a year-round pest, perhaps because of the mild weather of the region. Cutworms belong to the family Noctuidae. Note that the Latin root word here “noctu” refers to night—the time when these insects feed. They come out about two hours after dark to feast, then disappear under the soil for the day. Some cutworm eggs overwinter and hatch in spring, but others can hatch at any time after, as long as it is not too cold. Evidently there is one generation per year. The adult moths emerge in late summer and lay eggs which can hatch at varying times of the year. Several species exist: the Army cutworm, Black cutworm, Variegated cutworm, and a new species here in Oregon, which is active year round, the Winter cutworm. The first picture above shows a cutworm that appeared on heirloom petunia seedlings while they were on a bench in my greenhouse. The plants had been transplanted two weeks before, so I was surprised that the cutworm was able to climb so far! the photo was taken in May, so this was probably the variegated cutworm, which we have spring, summer and fall. The second picture shows another cutworm on the edge of a patio planter, three feet above the ground. The other three photos reveal damage on in-ground plants made by Winter cutworms in December, January and February. Cutworms typically leave black droppings on your plants; the photo of the cauliflower shows this.
An organic gardener’s best first defense against cutworms is prevention. A week before plants are to be set out, prepare your bed by cultivating heavily to dislodge and destroy any worms in the soil, then cultivate again. When you plant your transplants, place collars around the plants to make it difficult for the worms to get to your plants. Collars may be made of paper (milk cartons work well), plastic, metal or cardboard. Here it rains so frequently that I choose to use plastic milk jugs or cans with the bottoms cut out of them. After planting, spread one or more of the following sharp-edged deterrent mulches over the soil, around the plants: diatomaceous earth, eggshells, wood ashes or sharp grit. The rough surfaces of any of these will discourage cutworms from crawling to your plants. Another preventive method is to wait until two hours after dark, take a flashlight, search out the larvae and use the squish-bug technique for control. Continue to cultivate around your plants to dislodge hiding larvae. One other way to fight the battle is to attract or purchase beneficial insects to control cutworms. Ground beetles, parasitic nematodes and tachinid flies attack cutworms. Pollen-laden flowers, (don’t forget about native wildflowers) will help draw beneficial insects to your garden.
A next recourse for severe infestations is to use biological pest controls. The bacteria Bacillus thuringensis kurstaki (known as BTK) made into a liquid spray is effective in controlling cutworms as long as you do not have continuous rain, as we often do here in western Oregon. The damaged cauliflower, cabbage and primrose in the photos above show the effects of cutworms in winter, during a three month-long period of rain. Dry BTK can be mixed with moistened bran to act as a bait and will last a few days until washed away. Of course one can use the handpick squishbug method, but it might be difficult to keep up! BTK cannot be used over and over without enabling cutworms to develop resistance. Take care not to spray anything other than the very plants you need to protect when the larvae of butterflies are present. Organically approved pesticides containing pyrethrin may also be used for heavy infestations.