View full sizeAdult females develop concentric rings.If you're not familiar with scale, you've probably seen it and thought it was a disease rather than an insect. When an infestation gets going, the insects can cover an entire branch and look like bumpy or crusty growth.
Here's a rundown on scale:
Latin name:
Hundreds of species belong to numerous genera, including
Quadraspidiotus
,
Aonidiella
and
Icerya
.
Common names:
Too numerous to list. Some include San Jose scale, oyster shell scale, white cottony cushion scale, black scale, brown scale and red scale.
Description:
The tell-tale sign is the protective disc-like coating that grows over these tiny insects. Varying in size from 1/8 to 1/16 inch in diameter, scales can be brown, black, reddish, gray, cream or cottony. They are classified as soft or armored. Soft scales have a leathery or waxy coating; armored ones have stiff, lacquered shells. Both types look like round or oval, scabby bumps on stems, branches, bark or leaves.
View full sizeJust emerged from eggs and the size of a pinpoint, scale crawlers move to new sites on the host plant or are blown to other plants. Monitor activity with double-stick tape wrapped around a twig. Damage:
Scale insects pierce the plant and suck sap and chlorophyll out of it while hiding under their protective shells. Leaves can become yellowed, mottled, dotted or curled, eventually dropping off. A large infestation can kill the infected plant. Soft-shelled scales secrete a sweet, sticky substance called honeydew that promotes a blackish sooty mold fungus. Ants are attracted to the honeydew and can carry scales with them from plant to plant.
What's bugged:
Lots of plants, including houseplants, fruit trees, ferns, evergreen and deciduous ornamentals.
Control:
To prevent scales, inspect plants when you buy them. Keep plants properly watered and fertilized. Wash dust off plants. Natural enemies include black ladybug, lacewing larvae, predaceous beetles and a microscopic wasp called
Aphytis melinus
. Encourage these beneficial insects by planting a range of flowering plants for nectar and pollen.
Hand-picking scales can be effective if the infestation isn't too advanced. Scales can be scraped off with a fingernail, cotton swab dipped in alcohol, nail file or, for trees, a plastic scouring pad. A light horticultural dormant oil can be sprayed on leafless fruit trees in winter. Because of scales’ tough coating, pesticides rarely kill them. If you spot them in the crawler stage, you can kill them with insecticidal soap.
Scales are tough to get rid of indoors if you let them get out of hand and natural enemies aren’t around. On houseplants, isolate the plant so that scales don’t spread. With a bad infestation, getting rid of the affected plant might be the best option.
-- Homes & Gardens staff
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