We have small green worms eating the leaves on our Boston ferns. I think it may be cutworms. Sevin Dust
doesn’t seem to deter them at all. What else will kill them?
The Gardener’s Answer
Hello, Susan in South Carolina: There are several different species of cutworms and they are hard to tell apart but in general there are a couple of different cutworms that attack ferns belonging to the Nephrolepis genus, such as the Boston ferns. The spotted and variegated cutworms are the most common caterpillars found on these ferns. They are typically black and gray in color and feed only at night. They remain below the soil surface during the day. They are named cutworms because of the way they feed on the plant foliage, and as a result it appears that the foliage has been cut in half. Control measures include hand-picking, which is quite effective but it has to be done while they are actively feeding during the dark hours. Sevin (Carbaryl) is labeled for caterpillars but it is most effective if it is applied to the base of the plant. Since these cutworms are active at night it is best to apply the insecticide during the evening hours, shortly before they emerge to feed. As with all insecticides, they are less effective as they are exposed to heat and light so the less time between the application and the feeding time the more effective they will be. So, if you have not applied the insecticide in this manner go ahead and try it again; if it does not seem to work you should take a sample of the worm to your local garden center or to your county Extension office to have it identified. The first step in controlling insects in the garden is having them properly identified. This way we know what we are dealing with and what options we have in terms of control.