Azalea bark scale
Acanthococcus azaleae
173 host plants
Last updated
Data Coverage 2 of 6 dimensions
Inspect hawthorn and rhododendron stems closely for small flat white or grayish scales clustered along branches, sometimes covered with fine webbing. Heavy infestations coat bark with hundreds of scales, giving branches rough encrusted appearance. Look for stems exuding sticky honeydew; sooty mold often follows, blackening stems.
Prune heavily infested branches in winter when scales are dormant. Scrub stems with soft brush to physically remove light infestations. Apply horticultural oil in March or April before new growth, coating thoroughly. If populations persist, spray again in June during crawler stage when scales are mobile and vulnerable. Preserve predatory beetles and parasitoid wasps.
Quick Reference
Order
Hemiptera
Type
scale
Host Plants
173
GDD₃₂ Egg hatch/crawler
3,299
Indicator: Japanese stewartia first bloom
Azalea bark scale Egg hatch/crawler typically begins around 3299 GDD₃₂. As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂, approximately 2118 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 | 2,118 |
| Seattle / UW | 1,171 | Pre-season | Egg hatch/crawler | 2,128 |
| Kent / Auburn | 1,111 | Pre-season | Egg hatch/crawler | 2,188 |
| Olympia / Tumwater | 1,106 | Pre-season | Egg hatch/crawler | 2,193 |
| Bellingham / Whatcom | 1,101 | Pre-season | Egg hatch/crawler | 2,198 |
| Tacoma / Puyallup | 1,075 | Pre-season | Egg hatch/crawler | 2,224 |
| Sequim / Rain Shadow | 1,070 | Pre-season | Egg hatch/crawler | 2,229 |
Source: UMD IPMnet Pest Predictive Calendar (Gill & Klick, UMD Extension; base 50°F, Jan 1 biofix, mid-Atlantic Zone 7a-7b). Crawler emergence. extension.umd.edu About GDD₃₂ →
Cultural Controls
- Keep plants healthy.
- Vigorous plants are more able to tolerate scale damage.
- Several species of ladybird beetles and parasitic wasps help control scale populations.
- Avoid use of broad-spectrum insecticides which can kill these predators.
- Prune and destroy leaves or stems that are severely affected to help control minor infestations.
- Hand-picking to remove insects may control small infestations.
Host Plants (173)
Acer crataegifolium Hawthorn, Maple Adenium obesum Desert Rose, Desert Azalea, Mock Azalea Andromeda polifolia Bog Rosemary Crataegus ambigua Russian Hawthorn Crataegus autumn Crataegus autumn Crataegus columbiana Columbia Hawthorn Crataegus crus Crataegus crus Crataegus douglasii Black Hawthorn Crataegus germanica Medlar Crataegus laevigata English Hawthorn Crataegus lavallei Lavalle Hawthorn, Carrierei Hawthorn Crataegus monogyna Singleseed Hawthorn, Common Hawthorn, English Hawthorn Crataegus phaenopyrum Washington Hawthorn Crataegus punctata Dotted Hawthorn, Flat-topped Hawthorn Crataegus viridis Green Hawthorn,Southern Hawthorn Menziesia ciliicalyx var. multiflora Mock Azalea, Menziesia Menziesia ferruginea Rusty Menziesia, Fool's Huckleberry, False Azalea Pieris formosa var. forrestii Chinese Pieris, Himalaya Pieris Pieris japonica Japanese Pieris Populus alba White Poplar European White Poplar, Silver Poplar Populus angustifolia Narrowleaf Cottonwood, Mountain Cottonwood Populus balsamifera Balsam Poplar Populus canescens Gray Poplar Populus deltoides Eastern Cottonwood Populus fremontii Fremont Cottonwood, Western Cottonwood Populus grandidentata Bigtooth Aspen Populus nigra Black Poplar Populus tremula European Aspen European Trembling Aspen European Quaking Aspen Populus tremuloides Quaking Aspen Populus trichocarpa Black Cottonwood Quercus phellos Willow, Oak Rhododendron 'Purple Gem' Purple Gem Rhododendron Rhododendron airy Rhododendron, airy Rhododendron alabamense Alabama Azalea Rhododendron alice Alice Rhododendron Rhododendron anah Rhododendron, anah Rhododendron anna Rhododendron, anna Rhododendron april Rhododendron, april Rhododendron arboreum subsp. cinnamomeum Cinnamon Rhododendron Rhododendron argosy Argosy Rhododendron Rhododendron augustinii Augustine Rhododendron Rhododendron auriculatum No common name (R. auriculatum) Rhododendron beauty Rhododendron, beauty Rhododendron bibiani Bibiani Rhododendron Rhododendron blue Rhododendron, blue Rhododendron boule Rhododendron, boule Rhododendron bow Rhododendron, bow Rhododendron bric Rhododendron, bric Rhododendron bureavii Bureau Rhododendron Rhododendron campylocarpum subsp. coloxanthum Coloxanthum Rhododendron Rhododendron catawbiense Catawba Rhododendron Rhododendron cheer Cheer Rhododendron Rhododendron chevalier Rhododendron, chevalier Rhododendron christmas Rhododendron, christmas Rhododendron cinnabarinum Cinnabar Rhododendron Rhododendron concinnum Concinnum Rhododendron Rhododendron cotton Rhododendron, cotton Rhododendron crater Rhododendron, crater Rhododendron crest Crest Rhododendron Rhododendron cunninghams Rhododendron, cunninghams Rhododendron cynthia Cynthia Rhododendron Rhododendron daphnoides Daphnoides Rhododendron Rhododendron dauricum Dauricum Rhododendron Rhododendron davidsonianum Davidsonianum Rhododendron Rhododendron day Rhododendron, day Rhododendron deciduous Rhododendron, deciduous Rhododendron defines Rhododendron, defines Rhododendron delaware Rhododendron, delaware Rhododendron dora Rhododendron, dora Rhododendron dreamland Dreamland Rhrododendron Rhododendron el Rhododendron, el Rhododendron elisabeth Rhododendron, elisabeth Rhododendron elizabeth Elizabeth Rhododendron Rhododendron falconeri subsp. falconeri Falconer Rhododendron Rhododendron fantastic Fantastic Rhododendron Rhododendron formosum var. formosum Formosum Rhododendron Rhododendron forrestii subsp. forrestii Forrest Rhododendron Rhododendron fortunei subsp. discolor Fortune Discolor, Discolor Rhododendron Rhododendron frilly Rhododendron, frilly Rhododendron gartendirektor Rhododendron, gartendirektor Rhododendron girards Rhododendron, girards Rhododendron goldflimmer Goldflimmer Rhododendron Rhododendron grace Rhododendron, grace Rhododendron groenlandicum Labrador-tea, Labrador Tea Rhododendron haematodes subsp. haematodes Haematodes Rhododendron Rhododendron hallelujha Hallelujah Rhododendron Rhododendron hanceanum Hanceanum Rhododendron Rhododendron hardijzer Rhododendron, hardijzer Rhododendron harry Rhododendron, harry Rhododendron hino Rhododendron, hino Rhododendron hinode Rhododendron, hinode Rhododendron hippophaeoides var. hippophaeoides Hippophaeoides Rhododendron Rhododendron hodgsonii Hodgson Rhododendron Rhododendron honourable Rhododendron, honourable Rhododendron horizon Rhododendron, horizon Rhododendron hotei Hotei Rhododendron Rhododendron irroratum Irroratum Rhododendron Rhododendron jock Jock Rhododendron Rhododendron johnstoneanum Rhododendron, johnstoneanum Rhododendron keiskei Keiskei Rhododendron, Keisuki Rhododendron Rhododendron ken Rhododendron, ken Rhododendron kiusianum Kiusianum Azalea, Kyushu Azalea Rhododendron lacteum Lacteum Rhododendron Rhododendron lees Rhododendron, lees Rhododendron lems Rhododendron, lems Rhododendron lights Rhododendron, lights Rhododendron loderi Rhododendron, loderi Rhododendron luteiflorum Luteiflorum Rhododendron Rhododendron lutescens Lutescens Rhododendron Rhododendron luteum Pontic or Pontica Azalea Rhododendron macabeanum Macabeanum Rhododendron Rhododendron macrophyllum Pacific Rhododendron Rhododendron moonstone Moonstone Rhododendron Rhododendron mrs Rhododendron, mrs Rhododendron mucronulatum Rhododendron, mucronulatum Rhododendron myrtifolium Myrtifolium Rhododendron Rhododendron niveum Niveum Rhododendron Rhododendron northern Rhododendron, northern Rhododendron occidentale Western Azalea Rhododendron orbiculare subsp. orbiculare Obiculare Rhododendron Rhododendron orchid Rhododendron, orchid Rhododendron oreotrephes Oreotrephes Rhododendron Rhododendron oudijks Rhododendron, oudijks Rhododendron pachytrichum Pachytrichum Rhododendron Rhododendron peekaboo Peekaboo Rhododendron Rhododendron pink Rhododendron, pink Rhododendron pioneer Rhododendron, pioneer Rhododendron pjm P.J.M. Rhododendron Rhododendron point Rhododendron, point Rhododendron ponticum Rhododendron, ponticum Rhododendron president Rhododendron, president Rhododendron prinophyllum Roseshell Azalea, Pinkshell Azalea Rhododendron prunifolium Plumleaf Azalea Rhododendron quinquefolium Quinquefolium Azalea Rhododendron racemosum Racemosum Rhododendron Rhododendron ramapo Ramapo Rhododendron Rhododendron rosamundi Rosamundi Rhododendron Rhododendron roseum Rhododendron, roseum Rhododendron rosy Rhododendron, rosy Rhododendron roxieanum var. oreonasters No common name Rhododendron rubiginosum Rubiginosum Rhododendron Rhododendron sappho Sappho Rhododendron Rhododendron scarlet Rhododendron, scarlet Rhododendron schlippenbachii Royal Azalea Rhododendron serpyllifolium Wild Thyme, Azalea Rhododendron serpyllifolium var. albifolrum White Wild Thyme, Azalea Rhododendron sinofalconeri Sinofalconer Rhododendron Rhododendron sinogrande Sinogrande Rhododendron Rhododendron smirnowii Smirnow Rhododendron Rhododendron snow Rhododendron, snow Rhododendron stenopetalum Rhododendron, stenopetalum Rhododendron taurus Taurus Rhododendron Rhododendron temple Rhododendron, temple Rhododendron thomsonii subsp. thomsonii Thomson Rhododendron Rhododendron tri Rhododendron, tri Rhododendron trilby Trilby Rhododendron Rhododendron unique Unique Rhododendron Rhododendron vulcan Vulcan Rhododendron Rhododendron wardii Ward Rhododendron Rhododendron white Rhododendron, white Rhododendron wiltonii Wilton Rhododendron Rhododendron winsome Winsome Rhododendron Rhododendron yakushimanum Yak Rhododendron Salix alba Salix alba Salix babylonica Weeping Willow Salix caprea Salix caprea Salix integra Salix integra Salix magnifica Magnolia-leaf Willow, Magnificent Willow Salix matsudana Salix matsudana Salix pentandra Laurel, Willow, Bay Willow Salix phlebophylla Skeletonleaf Willow Salix purpurea Purpleosier Alaska Blue Willow Salix scouleriana Scouler's Willow