Cottony maple scale
Pulvinaria innumerabilis
45 host plants
Last updated
Cottony maple scale produces distinctive white, cottony egg sacs along maple branches and twigs in spring, creating very visible fuzzy growth on the tree. You will see the scale insects embedded beneath these waxy coverings throughout spring and summer, feeding on sap. Heavy infestations cause yellowing of leaves, wilting of new growth, and dieback of twigs. Excessive honeydew secretion attracts wasps and promotes sooty mold growth beneath infested trees.
Conserve black lady beetles, particularly Hyperaspis signata, which feed in egg sacs and on nymphs; avoid insecticides that kill these predators. Prune heavily infested branches. Spray insecticidal soap or horticultural oil for crawler nymphs in early summer. Improve tree vigor through proper irrigation.
Quick Reference
Cottony maple scale Egg hatch/crawler typically begins around 3061 GDD₃₂. As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂, approximately 1880 units before the expected threshold.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | Pre-season | Egg hatch/crawler | 1,880 |
| Seattle / UW | 1,171 | Pre-season | Egg hatch/crawler | 1,890 |
| Kent / Auburn | 1,111 | Pre-season | Egg hatch/crawler | 1,950 |
| Olympia / Tumwater | 1,106 | Pre-season | Egg hatch/crawler | 1,955 |
| Bellingham / Whatcom | 1,101 | Pre-season | Egg hatch/crawler | 1,960 |
| Tacoma / Puyallup | 1,075 | Pre-season | Egg hatch/crawler | 1,986 |
| Sequim / Rain Shadow | 1,070 | Pre-season | Egg hatch/crawler | 1,991 |
Source: Herms (OSU) phenological tables: 930 GDD₅₀ egg hatch, Dow Gardens MI 1985-1989 (Table 3). MSU Extension (872 GDD₅₀), UMN Extension, UMD IPMnet (872 GDD₅₀) corroborate. Profile range 870-930 spans extension estimates to Herms field data. Updated 2026-04-03. About GDD₃₂ →
Monitoring & Action
Visual inspection for conspicuous white cottony egg sacs on bark in late spring. Double-sided sticky tape on twigs to detect crawlers.
Honeydew excretion leads to sooty mold on foliage and surfaces below canopy. Heavy infestations cause premature leaf drop, twig dieback, and yellowed or stunted leaves. Stressed and over-fertilized trees are more susceptible.
Cultural Controls
- 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.