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Scale insects suck plant juices and are pests of many trees and shrubs. Infestations
can cause yellow or prematurely dropping leaves, sticky honeydew, and blackish sooty mold. Plant parts may
distort or die back, depending on the species and abundance of scales. Management includes proper plant care,
conserving natural enemies, and applying low-toxicity insecticides when needed. Most plants tolerate low to
moderate numbers of scales.
Damage resembles that of aphids and whiteflies.
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- Abundant sticky honeydew excreted by soft scales and certain other species.
- Black sooty mold growing on the honeydew.
- Discolored, distorted, or dying leaves, twigs, or branches, especially with armored scales.
- Circular, elongate, or oval discolorations or raised areas on bark, leaves, or fruit.
- Immobile or slow-moving bodies or coverings 1/25 to 1/4 inch long, without an obvious head or appendages,
and not resembling most other insects.
Distinguish the two most common types of scales: soft scales and armored scales.
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- Armored scales are tiny and flat, have covers that can usually be removed from the body and do not
secrete sticky honeydew. Common species include San Jose scale and California red scale.
- Soft scales are larger, more rounded and convex with covers that do not lift off, and they excrete
honeydew. Common species include black scale, lecanium scale, and brown soft scale.
- Learn the species or family name of your scale so you can identify effective controls.
- For example, a popular systemic insecticide, imidacloprid, controls most soft scales but not armored scales,
and it causes outbreaks of cottony cushion scale.
To reduce problems, use an integrated program:
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- Provide plants with proper cultural care, especially irrigation.
- Encourage scale natural enemies. Look for predators such as ladybeetles or lacewings and parasite emergence holes
in scale covers.
- Use sticky barriers or insecticide baits to selectively control scale-tending ants.
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Consider replacing problem-prone plants. Most scales are highly specific to certain plants.
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- Do not treat unless you have an intolerable or damaging problem.
- Avoid insecticides that injure natural enemies.
- For fruit trees and for smaller plants, make a well-timed and thorough spray using horticultural
oil during the dormant season or when scale crawlers are active in the growing season.
- For intolerable soft scale problems, especially on large trees, consider soil applied imidacloprid. This material
is not effective against some scales, including armored scales, and is not for use on fruit trees.
Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal. |
