Pensacola News Journal

For: Saturday, Jan. 3, 2004

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Control Mature Scale Insects on Shrubs

Infestations by armored scale insects were more numerous last year than in the past. Extension Agents across the state agree that it was the worst year that most can remember. Though we aren’t sure why, some believed that a wet summer led to more scale problems.

Many of those same scales that infested ornamental plants last summer are still alive and remain as over-wintering adults on shrubs. Uncontrolled, they will begin reproducing in early spring and even more heavy plant damage next year is possible.

Early scale infestations go largely unnoticed in the landscape except by the most observant gardener. Beginning populations are usually low and symptoms are not seen until several generations and high populations are present.

Controlling armored scale insects is easier once the life cycle of these unique insects is understood. There are dozens of different kinds of armored scales and they are somewhat specific as to the kinds of plants that they infest. Tea scale for example, is common on Camellias but rarely infests other common landscape plants except a few species of holly.

The general life cycle of armored scales that infest some species of ornamental plants is as follows: After over-wintering under this hard covering or “armor,” adults produce eggs. Egg laying and hatching of the immature scales usually coincides with the spring flush of new plant growth.

While the scales are young they have legs and are known as “crawlers.” They leave the older growth and move up to the more tender new growth. Once a good spot on the new stem or leaf is found each baby scale inserts its needle-like beak into the plant tissue and begins feeding by sucking plant sap.

Soon after feeding has begun, each immature scale sheds its legs, becomes immobile and begins secreting a waxy substance that forms the armor over its body. Once this covering is formed, control becomes more complicated.

Gardeners are advised to check landscape plants this winter, determine which are infested and apply control measures before spring. While inspecting plants it will become obvious that not all species are prone to scale problems. Some that are commonly infested include Camellia, holly, sago, peach, mulberry, privet and euonymus. Euonymus is so susceptible in fact, that I rarely see one that is not infested by Euonymus scale.

Some mature scales are large and easy to see, while others are small and difficult to detect. Florida wax scale for example, appears as a small light colored blob that is about the size of a match tip. Tea scale is easily seen on the underside of Camellia and Burford holly leaves. Holly pit scale on the other hand, is difficult to see. It blends in well with plant stems and they appear bumpy. It took twenty years for me to learn to identify this scale species as a problem on Japanese hollies.

Sprays containing horticultural oil emulsion can be used to control over-wintering adult scale insects. This product contains a petroleum based oil plus an emulsifier which allows the oil to mix with water. Properly used, this special oil is safe and controls scales by coating and suffocating them.

Follow label instructions carefully when using horticultural oils. Plant damage can result if some oils are used during extremely hot or cold periods. The label will provide the safe temperature range for that particular product. Since oils control scales by suffocation, complete spray coverage is required.

Note: There are several other insecticides that can be used for scale control, including at least one new product that is a systemic. These will be discussed in a future column. Horticultural oil is suggested because it is an old standby that is effective, normally applied during the fall or late winter, relatively safe and is readily available.