WSU Extension

Hortsense

Maple : Cottony maple scale
(revision date: 4/11/2018)


Biology
The cottony maple scale feeds on the leaves, twigs and branches of maples and sometimes other ornamentals including dogwood, lilac, poplar, and willow. The conspicuous adults of this large scale are about 1/5" long at maturity, found on twigs and branches, and dark and flattened in appearance. The greenish-yellow crawlers (immature scales) feed on upper and lower surfaces of leaves in the summer and move to twigs in the fall. The large, white, cottony egg sacs are found on twigs and small branches. Cottony maple scale overwinters in the immature stage.
Management Options

Non-Chemical Management
  • Many natural enemies, including ladybird beetles, parasitic wasps and flies, and birds, help control cottony maple scale. Avoid use of broad-spectrum insecticides which would kill the beneficial insects.
  • Minor infestations may be wiped off by hand (when practical).
  • Prune and destroy heavily infested branches.
Select non-chemical management options as your first choice!

Chemical Management

Oils should be applied during delayed dormant period to control overwintering eggs. Use superior type oil sprays only on overwintering nymphs. Scout for crawlers and gather life history data. Insecticide applications can be effective when applied to control the immature crawlers stage, usually in late spring to early summer. Make applications from June through summer months. Do not apply acephate or acephate/fenbutatin-oxide products to sugar maple or red maple, as foliage injury may occur. NOTE: Safer Brand Insect Killing Soap Conc II is not registered for use on Japanese maple. Ortho Orthenex Insect & Disease Control is only registered for use on red maple. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Hi-Yield Dormant Spray
    Active ingredient: oil/pet distillate  |  EPA reg no: 7401-428
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
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Caption: Cottony maple scales
Photo by: R.S. Byther
Caption: Cottony maple scales
Photo by: R.S. Byther