Q. What can I do about cottony cushion scale?
Cottony cushion scale (Icerya purchasi) is a scale insect that feeds on many woody plants and is particularly fond of citrus. The mature insects lay white, squishy egg sacs containing hundreds of red eggs on twigs and branches.
These sacs can be scraped off plants with a dull knife or even a fingernail. A swab dipped in rubbing alcohol is also effective, as long as the alcohol contacts the insects. Spray infested plants with a mixture of 1 cup of isopropyl alcohol and 1 tablespoon of insecticidal soap in 1 quart of water. (If your insecticidal soap is already mixed with water, add 1 tablespoon of alcohol to a pint of the diluted soap.) Spray every three days for two weeks. The soap kills newly hatched nymphs (called crawlers), while the alcohol penetrates adult insects' shells.
Light horticultural oil, also called superior horticultural spray oil, is also effective. This oil is lighter and less viscous than traditional dormant oil, and so less toxic to plants. Use a 2-3 percent solution. Spray directly on the scale insects, as it works by suffocating them.
In late winter or early spring, spray your plants with dormant oil to smother overwintering adults and eggs.
Usually birds will help control these insects, but maybe not completely.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service