Hard Brown Bumps on Plants

Characteristics

• Armored scale insects secrete a waxy coating that dries to a hard, brown bump. They feed, mate and grow underneath this covering, which is usually circular or oval and about the size of a pencil eraser. A scale infestation can kill a plant, so scale needs to be controlled as soon as you notice it. Another symptom, besides the brown bumps, includes yellow spots on the leaf tops.

Life Cycle

• Scale insects lay their eggs under the already-formed coating, and the eggs hatch over a period of several weeks. The newly hatched scales are called crawlers, because they leave the covering and move to a fresh part of the plant to feed. This is the only period when an insecticide spray is useful, while the insects are unprotected. Under the protective covering, scale insects overwinter on plants or plant debris, so dispose of infected plants in the garbage.

Pesticides

• Shake the plant over a piece of white paper to determine whether there are any crawlers. Spray weekly with an organic pesticide, such as insecticidal soap. Even if there are no live insects underneath the brown scales, the scales remain on the plant, and are generally impervious to pesticides.

Oils

• The protective coating and the insects under it can be smothered with horticultural oil or neem oil during the dormant season, when the coating is more vulnerable. The oil should be applied in late winter or early spring, when crawlers are beginning to hatch.

Hand Scrubbing

• You can scrape scales off with your fingernail, a toothbrush or a kitchen scrubbing pad if the plant isn’t too large to make this impractical. The exposed eggs or insects die without their protection.