Pests in Gardens and Landscapes: Quick Tips
California red scale, an armored scale.
Brown soft scale.
Exit hole in soft scale indicating parasitization.
Scales are immobile insects that suck plant juices from many types of trees, shrubs, and houseplants. Scale infestations can cause yellowing or premature dropping of leaves, sticky honeydew, and blackish sooty mold. Plant parts can distort or die back, depending on the species and abundance of scales. Management includes proper plant care, conserving natural enemies, and applying less toxic insecticides when needed. Most plants tolerate low to moderate numbers of scales.
What does scale damage look like?
- Damage resembles that of aphids and whiteflies
- 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
What do scales look like?
- As adults, scales are immobile with coverings that are 1/25 to 1/4 inch long. Immature scales are small slow-moving bodies called crawlers that have legs which eventually drop off.
- Adults may appear as circular, elongate, or oval discolorations or raised areas on bark, leaves, or fruit.
- Scales lack an obvious head or legs and don’t resemble most other insects.
Distinguish the two most common types of scales—armored and soft.
- Armored scales are tiny and flat, have covers that usually can be removed from the body, and don’t secrete sticky honeydew. Common species include San José scale and California red scale.
- Soft scales are larger, excrete honeydew, and are more rounded and convex with covers that don’t lift off. Common species include black scale, lecanium scale, and brown soft scale.
- Consult the UC IPM website to help identify the species or family of scale insects so you can learn effective controls.
To reduce problems, use an integrated program.
- Provide plants with proper cultural care, especially irrigation.
- Monitor plants to look for scale predators such as lady beetles or lacewings and parasite emergence holes in scale covers.
- Use sticky barriers or insecticide baits to selectively control scale-tending ants.
- Consider replacing problem-prone plants. Most scales are highly specific to certain plants.
What about pesticides?
- Insecticides are not necessary unless damage from scales is intolerable.
- Avoid insecticides that injure natural enemies.
- For fruit trees and 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 may cause outbreaks of cottony cushion scale. Always read the label.
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.