How to Watch Out for Scale Insects This Fall

What are scale insects and why should you keep an eye out for them this fall?

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Photo courtesy of Garden Gate magazine

Article courtesy of Garden Gate Magazine

They’re small, armored and dangerous. Fall is a great time to look for scale insects on trees and shrubs because they’re easier to spot without foliage in the way.

Scale insects are a large group of sap-sucking insects that feast on nearly all woody plants. Since they don’t move around, their waxy shells, or armor, protect them while they feed and grow. They can be white, like the ones on the euonymus in the photo above. Or they may be tan, gray or brown. In small numbers they weaken the plant, but in larger numbers they can kill. Gardeners often find sooty mold on the leaves before they discover the scale insects. Sooty mold looks like black dust, but it’s actually a fungus that is growing on honeydew excreted by the insects.

This fall, inspect the trunks and branches of your trees and shrubs, especially the ones in the list below. Since scale insects are so tiny, you may need a magnifying glass to spot them. For heavy infestations, prune out the affected branches first. Then use a high-pressure jet of water to knock some of the scale insects off the plant. Next, spray horticultural oil on the plant until it begins to drip off the branches. Multiple applications may be necessary to get rid of this pest, so plan a second spray for early spring before the leaves emerge.