Oystershell scale
Lepidosaphes ulmi
155 host plants
Last updated
Data Coverage 4 of 6 dimensions
You will see small brown or gray oyster or mussel-shaped scales about one-eighth inch long covering trunks, branches, and twigs of maples, birches, elms, and other deciduous trees. Scales may be elongated and slightly curved. Heavy infestations create a silvery, crusty appearance on bark. The pest is common on stressed trees.
Scrub branches lightly with a plastic brush to remove scales manually. Apply dormant oil before bud break in late winter to target overwintering eggs beneath scales. Monitor crawler emergence in early summer and follow with contact sprays if populations are heavy. Natural enemies including parasitoid wasps, mites, and birds control many populations. Maintain tree vigor to reduce susceptibility.
Quick Reference
Order
Hemiptera
Type
scale
Host Plants
155
GDD₃₂ Egg hatch/crawler 1st gen
1,958
Indicator: Tuliptree first bloom
Peak Activity
Crawler emergence mid-May, coinciding with lilac full bloom
Oystershell scale Egg hatch/crawler 1st gen typically begins around 1958 GDD₃₂. As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂, approximately 777 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 1st gen | 777 |
| Seattle / UW | 1,171 | Pre-season | Egg hatch/crawler 1st gen | 787 |
| Kent / Auburn | 1,111 | Pre-season | Egg hatch/crawler 1st gen | 847 |
| Olympia / Tumwater | 1,106 | Pre-season | Egg hatch/crawler 1st gen | 852 |
| Bellingham / Whatcom | 1,101 | Pre-season | Egg hatch/crawler 1st gen | 857 |
| Tacoma / Puyallup | 1,075 | Pre-season | Egg hatch/crawler 1st gen | 883 |
| Sequim / Rain Shadow | 1,070 | Pre-season | Egg hatch/crawler 1st gen | 888 |
Source: Herms (OSU) phenological tables: 363 GDD₅₀ egg hatch, Dow Gardens MI 1985-1989 (Table 3); 497 GDD₅₀ Secrest Arboretum OH 1997-2001 (Table 4). MSU Extension, UMN Extension, UMD IPMnet (486 GDD₅₀) corroborate. Profile range 350-500 brackets both Herms sites. Updated 2026-04-03. About GDD₃₂ →
Monitoring & Action
How to Monitor
Double-sided sticky tape on infested twigs starting when lilac begins to bloom. Check weekly with hand lens for tiny crawlers.
What Damage Looks Like
Direct tissue damage from cell-content feeding. Heavy infestations cause twig and branch dieback. No honeydew or sooty mold (armored scale). Camouflage makes early detection difficult.
Cultural Controls
- Keep trees healthy to enable them to tolerate some damage.
- In minor infestations, it may be possible to wipe scales off branches.
- Where practical, prune and destroy heavily infested branches.
- Natural enemies of scales help control populations, but usually not soon enough to prevent damage to plants.
- Avoid use of broad-spectrum insecticides which kill beneficial insects.
Host Plants (155)
Acer buergerianum Trident Maple, Three-toothed Maple Acer campestre Hedge Maple, Field Maple, Common Maple Acer capillipes Red Stripebark Maple, Red Snakebark Maple, Hakkoda Maple Acer carpinifolium Hornbeam Maple Acer circinatum Vine, Maple Acer coriaceifolium Leatherleaf Maple Acer crataegifolium Hawthorn, Maple Acer davidii David Maple, Père David's Maple Acer freemanii Freeman Maple, Hybrid Red Maple Acer ginnala Acer ginnala Acer glabrum Rocky Mountain Maple, Rock Maple, Douglas Maple, Dwarf Maple Acer glabrum var. douglasii Douglas Maple, Dwarf Maple, Rocky Mountain Maple Acer grandidentatum Bigtooth Maple, Western Mountain Sugar Maple, Rocky Mountain Sugar Maple Acer griseum Paperbark Maple Acer henryi Henry's Maple Acer japonicum Fullmoon Maple Acer macrophyllum Bigleaf Maple Acer maximowiczianum Nikko Maple Acer miyabei Miyabe Maple Acer monspessulanum Montpellier Maple Acer negundo Boxelder Manitoba Maple, Ash-leaved Maple Acer nipponicum Nippon Maple Acer oblongum Evergreen Maple, Smooth Leaf Maple Acer oliverianum Oliver Maple Acer opalus subsp. obtusatum Bosnian Maple Acer palmatum Japanese Maple Acer palmatum var. dissectum Dissected Japanese Maple Acer pensylvanicum Striped Maple, Moosewood Maple Acer pentaphyllum Acer pentaphyllum (no common name) Acer pictum Painted Maple Acer platanoides Norway Maple Acer pseudoplatanus Planetree Maple, Sycamore, Maple Acer rubrum Red Maple Acer rufinerve Redvein Maple, Honshu Maple Acer saccharinum Silver Maple Acer saccharum Sugar Maple Acer sempervirens Cretan Maple Acer shirasawanum Shirasawa Maple Acer spicatum Mountain Maple, Moose Maple Acer tataricum Tatarian Maple, Tartarian Maple Acer tataricum subsp. ginnala Amur Maple Acer tegmentosum Manchurian Stripebark Maple, Manchustriped Maple Acer triflorum Three Flowered Maple Acer truncatum Purpleblow Maple, Shantung Maple Acer velutinum Velvet Maple Betula alleghaniensis Yellow Birch Betula davurica Asian Black Birch, Dahurian Birch Betula glandulosa Dwarf Birch Bog Birch, Scrub Birch Betula lenta Sweet Birch, Cherry Birch, Black Birch Betula maximowicziana Monarch Birch Betula nana Dwarf Birch, Bog Birch Betula nigra River Birch, Black Birch Betula occidentalis Water Birch, Western Birch, Red Birch, River Birch, Black Birch Betula papyrifera Paper Birch Betula pendula European White Birch Betula platyphylla Asian White Birch, Manchurian Birch Betula populifolia Gray Birch, Fire Birch Betula pubescens Downy Birch, Moor Birch Betula utilis Himalayan Birch, Bhojpatra, Indian Paper Birch Betula utilis subsp. albosinensis Chinese Paper Birch, Chinese Red Birch Betula utilis subsp. jacquemontii Whitebarked Himalayan Birch Buddleia davidii Butterfly Bush, Summer Lilac Cornus alba Tatarian Dogwood, Tartarian Dogwood Cornus alternifolia Pagoda Dogwood Cornus amomum Silky Dogwood Cornus canadensis Bunchberry Cornus capitata Evergreen Dogwood, Bentham's Cornel, Himalayan Strawberry Tree Cornus controversa Giant Dogwood Cornus drummondii Rough-leaved Dogwood Cornus eddies Cornus eddies Cornus elwinortonii Cornus elwinortonii Cornus florida Flowering Dogwood Cornus kousa Kousa Dogwood Cornus mas Corneliancherry Dogwood Cornus nuttallii Pacific Dogwood Cornus officinalis Japanese Cornelian Dogwood Korean Cornelian Dogwood, Chinese Cornelian Dogwood Cornus porlock Porlock Dogwood Cornus racemosa Gray Dogwood, Red Panicle Dogwood Cornus rutgersensis Cornus rutgersensis Cornus sanguinea Bloodtwig Dogwood Cornus sericea Cornus sericea Cornus sericea subsp. occidentalis Western Dogwood, Creek Dogwood Cornus stolonifera Redosier Dogwood Cornus torreyi Western Dogwood, Creek Dogwood Cornus venus Venus Dogwood Daphne genkwa Lilac Daphne Fagus grandifolia American Beech Fagus sylvatica European Beech Fagus sylvatica f. pendula Weeping European Beech Fraxinus americana White Ash, American Ash Fraxinus anomala Singleleaf Ash, Dwarf Ash Fraxinus excelsior Euopean Ash, Common Ash Fraxinus latifolia Oregon Ash Fraxinus ornus Flowering Ash Fraxinus oxycarpa Fraxinus oxycarpa Fraxinus pennsylvanica Green Ash Fraxinus quadrangulata Blue Ash Fraxinus sieboldiana Siebold Ash, Japanese Flowering Ash, Chinese Flowering Ash Malus 'Indian Magic' Indian Magic Crabapple Malus atrosanguinea Carmine Crabapple Malus brandywine Brandywine Crabapple Malus floribunda Japanese Flowering Crabapple Malus fusca Pacific Crabapple Malus hupehensis Tea Crabapple Malus prairifire Prairifire Crabapple Malus pumila Apple Malus robusta Cherry, Crabapple Malus sargentii Sargent Crabapple, Pigmy Crabapple Malus snowdrift Snowdrift Crabapple Malus transitoria Transitoria Crabapple 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 Pyrus calleryana Callery Pear Pyrus communis Common Pear Pyrus fauriei Pyrus fauriei Pyrus salicifolia Pyrus salicifolia Quercus phellos Willow, Oak 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 Syringa chinensis Chinese Lilac Rouen Lilac Syringa hyacinthiflora Early Flowering Lilac, Early Hybrid Lilac Syringa josikaea Hungarian Lilac Syringa laciniata Cutleaf Lilac Syringa meyeri Syringa meyeri Syringa microphylla Syringa microphylla Syringa patula Syringa patula Syringa pekinensis Peking Lilac Chinese Tree, Lilac Syringa prestoniae Preston Lilac, Canadian Lilac Syringa reticulata Japanese Tree Lilac, Giant Tree Lilac Syringa vulgaris Common Lilac Ulmus americana American Elm Ulmus davidiana David Elm Ulmus davidiana var. davidiana unknown Ulmus davidiana var. japonica Japanese Elm Ulmus glabra Ulmus glabra Ulmus hollandica Dutch Elm, Holland Elm, Hybrid Elm Ulmus parvifolia Lacebark Elm, Chinese Elm Ulmus pumila Siberian Elm