Protect your plants and trees from scale infestation

One insect problem on trees and shrubs that seems to go unnoticed until it is almost too late is scale. It goes unnoticed because the signs are not always evident during the growing season. So fall and winter is a good time to check plants for scale.

Scale is a class of insects that have an interesting life cycle. They spend most of their life under a "roof" that they form. This roof gives the appearance of a scale that you might find on your skin if you have a skin ailment. The "roof" may have a hard surface or it may be soft. It may have a white appearance or different earth tones, to almost black.

The mouth of the scale insect is shaped like a hypodermic needle. They puncture the surface of plant leaves and twigs and suck out plant sap, their food. Obviously when a plant loses a lot of its sap over a long period of time the tree or shrub will slowly decline in vigor and eventually die.

There is only one scale insect that lives under each roof. When it is time to mate (usually one to three times per year, depending upon the species) the adult emerges from under the roof and crawls around until a mate is found. This is obviously called the "crawler stage."

After mating, females lay their eggs on plant twigs or leaves. The eggs hatch and the resulting larvae find a suitable home, the "scale" is produced and the life cycle begins again.

Tree and shrub systemic insect drench, left, broad-use insecticide, center, and horticultural oil spray can be used to rid plants of scales.

There are two different time periods within which to control for scale. The first occurs when the adults are "crawling" and mating occurs. At this time, during the spring and summer months, you can spray the infested plant using any contact insecticide such as permethrin or malathion. The most difficult aspect of this method of control is the timing of the application. You have to inspect the infested trees or shrubs continually until you find the adults actually crawling around on the plant.

One of the easiest ways to control for scale during the dormant period (late fall to early spring) is to spray the infested shrub with horticultural oil. This oil forms a film over the scale, and the insect suffocates. I prefer to use refined horticultural oil rather than dormant oil because you have a much larger window for application during the year.

If your infested plant is a large tree such as tulip poplar, spraying the entire plant can be difficult. In this case I suggested you use systemic insecticide such as imadicloprid for control. Mix the insecticide with water and pour the solution around the base of the tree and out to the drip line. The insecticide will move up into the plant. Then as the scale insect is feeding they will ingest some of the insecticide and die.

Although different species of scale can attack a wide range of plants, I find most of the scale problems in the Heartland associated with tulip poplar, euonymus varieties, mugo pine and holly. If you have any of these plants in your landscape, now is the time to make an inspection for scale. If you do find scale, I would suggest an application of the dormant oil or systemic insecticide to control the problem and to ensure you have a vigorously growing tree or shrub next growing season.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699, Cape Girardeau, MO 63702-0699 or by email to news@semissourian.com.