Brown scale can be difficult to detect

Q. My house plant is covered with a sticky residue and small brown bumps — Miguel, Kingston

A. Your anthurium has a scale insect infestation.

Scale can be hard to detect. The brown soft scale (Coccus hesperidum L.) is one of the most common soft scales. It is a pest in greenhouses and on houseplants in our part of the country.

The brown soft scale is a rather flat insect, oval in shape, often broader at the hind end, and variable in color, but usually yellowish brown, sometimes with a green tint. The adult scales are about 3-4 millimeters long and 2 millimeters wide.

The scale insects infest both the leaves and the stems of the host plants, and feed by inserting needlelike mouthparts into the plant tissue and sucking out plant sap. Feeding injury may result in poor growth and stunted plants.

As the scales feed, they excrete droplets of a sweet sticky liquid known as honeydew. The honeydew gives the leaves a shiny appearance, and they are sticky to the touch. A black fungus, sooty mold, often grows on honeydew, and it may inhibit photosynthesis by blocking light.

The result of sooty mold is that the aesthetic qualities of the plant are greatly reduced because of the dirty or sooty appearance, and the leaves may exhibit yellowing (chlorosis) under the sooty mold.

Heavily infested plants are often best discarded. Clean up the area around the plant to remove honeydew droplets as well as any unseen crawlers that might infest a nearby plant.

If only one or a few plants are affected, gently washing with a dilute mixture of detergent and water may be a practical way to remove scale insects, using a soft brush or cloth to help dislodge them and wash off honeydew.

Wash the stem as well as leaves, because the crawlers (generally too small to see), older nymphs and adults may be present on either.

Handpicking may also be effective for one or a few plants. Remove scales using a toothpick, or tweezers, or a cotton swab that has been dipped in rubbing alcohol. Repeat every few weeks as needed.

If you are not getting control, there are commercial houseplant insecticides registered for scale insects, including insecticidal soap, hydrophobic neem oil, and horticultural oil preparations, which may be used according to the manufacturer's directions. Read and check the label carefully to be sure the product is labeled for use indoors, and that the plant you want to treat is listed. Some plants are sensitive to certain products.

Insecticidal sprays are most effective against the crawler stage. It will require some monitoring with a hand lens or magnifying glass to tell when crawlers are active.

The key to eliminating scale is to treat even the ones that you cannot see. That means thoroughly drenching all leaf and stem surfaces until they are dripping wet.

It is also best if you repeat this treatment all over again in five to seven days to catch any crawlers (the translucent young ones) that you missed the first time. After that, you should check your plant weekly to see if they return.

Dona M. Crawford is the Master Gardener coordinator at Cornell Cooperative Extension of Ulster County.S