The Boston fern (Nephrolepis exaltata “Bostoniensis”) is a variety of sword fern desirable for its ease of care and long, gracefully arching fronds. Because they are so hardy, Boston ferns are often grown indoors as houseplants. For that reason, they can sometimes suffer from common indoor insect infestations. Outdoor ferns can also be plagued by insects.
Mealybugs and Scale
These insect pests can damage or even kill a Boston fern if the infestation is severe enough. Mealybugs appear as white, fuzzy masses of insects that often gather where the leaf meets the stem of the frond. They also cluster on the undersides of the fronds. Scale insects, which range in size from tiny dots to ovals 1/16 inch wide, also feed on the tender leaves of Boston ferns. They can appear brown, black or almost white. Wilting of the plant, the presence of honeydew (a sticky substance secreted by the bugs) and stunted growth are all symptoms of an infestation. Control mealybugs and scale by drenching the soil with an insecticide. Make sure the insecticide is able to drain freely from the pot once applied.
Caterpillars usually infest Boston ferns that are grown outdoors. Although many different types of caterpillars can infest ferns, one in particular, the Florida fern caterpillar, is especially troublesome. These insect pests are the larvae of moths. The moths lay their eggs on the fronds of the ferns. Once the larvae hatch, they start feeding on the leaves. This is easily noticeable as the leaves will appear ragged on the edges, or contain holes. If the infestation is minor, simply pluck the caterpillars off by hand and drop them into a bucket of soapy water to drown them. Severe infestations will require an application of insecticide. Move your Boston fern outdoors, and spray the plant thoroughly following the instructions on the package, as per the size and age of your plant.
Fungus gnats are most often seen on indoor plants that are overwatered. The larvae feed on the roots of the fern. If the roots are damaged enough, the plant will wilt, suffer stunted growth or even die, although such cases are rare. Adult gnats are small, black insects that are commonly seen flying erratically around the plant. Larvae can be controlled with soil drenches, while chemical sprays or yellow sticky traps will kill the adults. Do not keep the soil saturated with water, but let it dry out a bit between waterings.
Snails and Slugs
Snails and slugs are two more pests that can affect outdoor Boston ferns. Like caterpillars, they feed on the juicy green leaves of the plant. Snails and slugs usually feed at night, when it is cooler. During the day, they hide from the hot afternoon sun. For that reason, you are more likely to notice the damage in the morning when you go to water your ferns. If you stay up late enough to catch them, you can pluck snails and slugs off your fern fronds by hand. Otherwise, surround your ferns with a barrier of slug and snail bait.