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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, protecting beneficial insects and applying less toxic insecticides when needed. Most plants tolerate low to moderate numbers of scales.

What does scale damage look like?

• Similar to that of aphids and whiteflies
• Wet or sticky honeydew on leaves, pavement, cars, or anything else underneath the infested plants
• Black sooty mold growing on the honeydew
• Discolored, distorted, or dying leaves, twigs, or branches, especially with armored scale infestations

What do scales look like?

• Scales lack an obvious head or legs and don’t resemble most other insects.

• Adults may appear as circular, elongate, or oval discolorations or bumps on bark, leaves, or fruit. Their coverings range from 1/25 to 1/4 inch long.
• Immature scales (crawlers) are often yellow to orangish. They are called crawlers because they are the life stage that has legs and move. Once the crawlers settle down, their legs drop off and they become immobile adults.

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 for help identifying other scale species.

To reduce problems, use an integrated approach.

• Provide plants with proper 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.
• When possible, avoid broad-spectrum insecticides that kill beneficial insects.
• For infestations on 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 larger plants, 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.