Leaf Spots on Boston Ferns

Spore

• Unlike most other plants, ferns reproduce by spreading spores rather than seeds. These spores are produced every year on the underside of Boston fern leaves. The spores appear in uniform brown clusters evenly lining the underside of the plant. They are commonly mistaken for insect eggs or disease. These spots are completely natural on the Boston fern plant and are no cause for concern.

Insects

• Though usually not pestered by insects, Boston ferns occasionally host to a few bugs, including thrips and shore flies, each of which can cause spotting on the plant. Thrips are carriers of tomato spotted wilt virus, which infects the Boston fern. The virus causes yellow spotting on the plant’s leaves, which can cover the entire leaf, killing it. Shore flies do not actually damage ferns, but they defecate on the plant leaves, leaving unsightly dark green-and-black spots. Manage these pests with insecticidal soap or horticultural oil.

Environment

• Improper care causes spotting on the plant's leaves. Hard water causes white spots on the leaves. These spots can simply be wiped off the leaves, but they do decrease the plant’s aesthetic value. If the plant is in an overly humid area, brown spots may begin appearing on the plant leaves and can grow covering the entire leaf. Changing the plant’s environment can solve both spotting issues.

Aerial Blight

• Aerial blight is one of the few fungi that commonly attack Boston ferns. The fungus is evidenced on the plant by patterns of brown spots and webbing along the plant leaves and stems. If not cared for, the fungus overwhelms and kills the plant. Excessively hot temperatures and overwatering encourage aerial blight. Changing cultural practices helps prevent the fungus from overwhelming your plant. If symptoms do not disappear after changing the fern’s environment, a liquid copper fungicide kills the fungus.