Lecanium scale
Parthenolecanium spp.
255 host plants
Last updated
Lecanium scales appear as small, dome-shaped, brownish bumps on the twigs and branches of numerous ornamental and fruit trees. The female scales are immobile, shell-like structures that do not look like living insects until you examine them closely. Heavy infestations coat twigs with these bumps and produce copious honeydew that attracts ants and supports sooty mold.
Apply dormant oil in late winter or early spring before scale eggs hatch to smother overwintering females and eggs. For active-season populations, horticultural oil targets the crawler stage emerging in mid to late spring. Prune out severely infested branches. For high-value trees, a second oil application in early summer targets new generations; timing to crawler emergence is critical.
Quick Reference
Order
Hemiptera
Type
scale
Host Plants
255
Peak Activity
May-June crawler emergence; treat when crawlers visible
Damage Severity
growth-reducing
Monitoring & Action
How to Monitor
Double-sided sticky tape on infested twigs to detect crawlers. Check weekly with hand lens May through June. Visual inspection for shiny brown helmet-shaped scales on twigs.
What Damage Looks Like
Lecanium scales are shiny brown insects found on twigs. Adults are 1⁄8\" to 1⁄4\" in diameter and roughly turtle-shaped. They may have light markings or appear somewhat waxy. Crawlers (immature scales) are flatter. Heavily infested branches may be wilted, yellowish, or show other signs of stress. New growth may be stunted or lacking. Twigs and small branches may be killed. Lecanium scale is a common pest in the landscape and garden, infesting many plants including ornamentals and fruit trees. Feeding scales produce large amounts of honeydew, a sweet, sticky material which may attract ants or bec...
Cultural Controls
- Natural enemies normally keep lecanium at below-damaging densities in diverse landscapes (WSU). When populations explode, it usually means something disrupted the predator-prey balance: a broad-spectrum spray application, excessive nitrogen fertilization, or ant colonies farming the honeydew.
- Ant exclusion is the highest-impact single cultural intervention. Ants farm honeydew and aggressively attack natural enemies. Apply Tanglefoot or sticky barrier around trunk; research showed ant exclusion reduced scale by 54% after one season and 69% after two (Vanek & Potter 2010).
- Larvae of green lacewings and other insects, such as ladybeetles, are aggressive predators of lecanium scale.
- Home orchardists: Scale can be rubbed off plants by hand with a glove or toothbrush.
- Major infestations can be pruned off.
- Avoid excessive nitrogen fertilizer or water applications, as this drives soft, sap-rich growth that favors scale reproduction.
Host Plants (255)
Asimina triloba Common Pawpaw Custard Apple Atriplex hymenelytra Desert Holly Berberis aquifolium Oregon Grape, Oregon Grape Holly, Tall Oregon Grape Berberis buxifolia Berberis buxifolia Berberis darwinii Darwin Barberry Berberis emerald Berberis emerald Berberis fremontii Fremont Barberry, Fremont Mahonia Berberis gladwynensis Berberis gladwynensis Berberis jamesiana James Barberry Berberis julianae Wintergreen Barberry Berberis mentorensis Mentor Barberry Berberis nervosa Longleaf Mahonia Cascade Mahonia Berberis pinnata California Barberry, California Holly Grape Berberis pruinosa Pruinosa Barberry Berberis repens Creeping Mahonia Berberis replicata Evergreen Barberry Berberis stenophylla Rosemary Barberry Berberis thunbergii Japanese Barberry Berberis thunbergii var. atropurpurea Purple (Red) Leafed Japanese Barberry Berberis triacanthophora Threespine Barberry, Wisley Barberry Berberis verruculosa Warty Barberry 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 Corylus americana American Hazel, American Filbert Corylus avellana Common Filbert Daphne burkwoodii Burkwood Daphne Daphne caucasica Caucasian Daphne Daphne cneorum Garland Daphne, Rock Daphne, Rose Daphne Daphne genkwa Lilac Daphne Daphne laureola Spurge Laurel Daphne lawrence Daphne, lawrence Daphne mezereum February Daphne, Mezereon Daphne odora Fragrant Daphne, Winter Daphne Eucalyptus cinerea Silver Dollar Eucalyptus, Silver Dollar Gum Argyle Apple 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 Grevillea aquifolium Holly, Grevillea Heteromeles arbutifolia Toyon Christmasberry California Holly Ilex aquifolium English Holly Ilex attenuata Ilex attenuata Ilex cornuta Chinese Holly, Horned Holly Ilex crenata Japanese Holly Ilex glabra Inkberry Inkberry Holly, Gallberry, Evergreen Winterberry Ilex latifolia Lusterleaf Holly Ilex meserveae Meserve Hybrid Holly Ilex paraguariensis Yerba Matá, Maté, Paraguay Tea Ilex verticillata Winterberrry Winterberry Holly, Michigan Holly, Christmas Berry Black Alder Malus 'Indian Magic' Indian Magic Crabapple Malus 'Prairifire' Prairifire Crabapple Malus 'Snowdrift' Snowdrift Crabapple Malus atrosanguinea Carmine Crabapple Malus brandywine Brandywine Crabapple Malus floribunda Japanese Flowering Crabapple Malus fusca Pacific Crabapple Malus hupehensis Tea Crabapple Malus pumila Apple Malus robusta Cherry, Crabapple Malus sargentii Sargent Crabapple, Pigmy Crabapple Malus transitoria Transitoria Crabapple Olearia macrodonta Daisy, Bush, New Zealand Holly Osmanthus heterophyllus Holly Osmanthus Holly-leaf Osmanthus, Holly Tea Olive Prunus americana Wild Plum American (Red) Plum August Plum, Goose Plum Prunus armeniaca Apricot Prunus avium Sweet Cherry Prunus besseyi Sand Cherry, Western Sand Cherry Prunus blireiana Blireiana Plum Prunus caroliniana Carolina Cherrylaurel American Cherrylaurel Prunus cascade Prunus cascade Prunus cerasifera Cherry, Plum Prunus cistena Purpleleaf Sandcherry Redleaf Sandcherry Cistena Sandcherry Cistena Plum Prunus dream Prunus dream Prunus emarginata Bitter Cherry, Wild Cherry, Quinine Cherry Prunus first Prunus first Prunus fruticosa Steppe Cherry, European Dwarf Ground Cherry, Mongolian Cherry Prunus glandulosa Dwarf Flowering Almond Prunus ilicifolia Hollyleaf Cherry, Holly-leaved Cherry Prunus laurocerasus Cherry, Laurel Prunus lusitanica Portugal Laurel Prunus maackii Amur Chokecherry Amur Cherry, Manchurian Cherry Prunus mume Japanese Flowering Apricot Prunus newport Newport Flowering Plum Prunus okame Okame Flowering Cherry Prunus padus European Birdcherry Common Birdcherry Prunus prostrata Rock Cherry, Mountain Cherry Prunus sargentii Sargent Cherry, Sargent's Cherry Prunus serotina Black Cherry, Rum Cherry Prunus serrula Birchbark Cherry, Paperbark Cherry, Tibetan Cherry Prunus serrulata Japanese Flowering Cherry Prunus snow Prunus snow Prunus subcordata Klamath Plum, Sierra Plum, Pacific Plum Prunus subhirtella Higan Cherry Prunus subhirtella var. autumnalis Autumn Flowering Higan Cherry Prunus tai Prunus tai Prunus virginiana Prunus virginiana Prunus virginiana var. demissa Western Chokecherry Prunus virginiana var. virginiana Common Chokecherry, Eastern Chokecherry Prunus yedoensis Yoshino Cherry, Somei-yoshino Cherry, Tokyo Cherry Quercus ilex Holly, Oak, Holm Oak Rhododendron 'Alice' Alice Rhododendron Rhododendron 'Anah Kruschke' Anah Kruschke Rhododendron Rhododendron 'Anna Rose Whitney' Anna Rose Whitney Rhododendron Rhododendron 'Argosy' Argosy Rhododendron Rhododendron 'Bruce Briggs' Bruce Briggs Rhododendron Rhododendron 'Capistrano' Capistrano Rhododendron Rhododendron 'Carmen' Carmen Rhododendron Rhododendron 'Cheer' Cheer Rhododendron Rhododendron 'Cilpinense' Cilpinense Rhododendron Rhododendron 'Crest' Crest Rhododendron Rhododendron 'Cunningham's White' Cunningham's White Rhododendron Rhododendron 'Cynthia' Cynthia Rhododendron Rhododendron 'Dora Amateis' Dora Amateis Rhododendron Rhododendron 'Dreamland' Dreamland Rhododendron Rhododendron 'Elizabeth' Elizabeth Rhododendron Rhododendron 'Fantastica' Fantastica Rhododendron Rhododendron 'Gibraltar' Gibraltar Azalea Rhododendron 'Girard's Fuchsia' Girard's Fuchsia Azalea Rhododendron 'Glacier' Glacier Azalea Rhododendron 'Goldflimmer' Goldflimmer Rhododendron Rhododendron 'Gomer Waterer' Gomer Waterer Rhododendron Rhododendron 'Hallelujah' Hallelujah Rhododendron Rhododendron 'Hino-Crimson' Hino-Crimson Azalea Rhododendron 'Horizon Monarch' Horizon Monarch Rhododendron Rhododendron 'Hotei' Hotei Rhododendron Rhododendron 'Jock' Jock Rhododendron Rhododendron 'Klondyke' Klondyke Azalea Rhododendron 'Lee's Dark Purple' Lee's Dark Purple Rhododendron Rhododendron 'Lord Roberts' Lord Roberts Rhododendron Rhododendron 'Mandarin Lights' Mandarin Lights Azalea Rhododendron 'Moonstone' Moonstone Rhododendron Rhododendron 'Mother's Day' Mother's Day Azalea Rhododendron 'Nancy Evans' Nancy Evans Rhododendron Rhododendron 'Nova Zembla' Nova Zembla Rhododendron Rhododendron 'P.J.M.' P.J.M. Rhododendron Rhododendron 'Peekaboo' Peekaboo Rhododendron Rhododendron 'Percy Wiseman' Percy Wiseman Rhododendron Rhododendron 'Pohjola's Daughter' Pohjola's Daughter Rhododendron Rhododendron 'Purple Gem' Purple Gem Rhododendron Rhododendron 'Ramapo' Ramapo Rhododendron Rhododendron 'Rosamundi' Rosamundi Rhododendron Rhododendron 'Roseum Elegans' Roseum Elegans Rhododendron Rhododendron 'Sappho' Sappho Rhododendron Rhododendron 'Solidarity' Solidarity Rhododendron Rhododendron 'Stewartstonian' Stewartstonian Azalea Rhododendron 'Taurus' Taurus Rhododendron Rhododendron 'The Honourable Jean Marie de Montague' Jean Marie Rhododendron Rhododendron 'Trilby' Trilby Rhododendron Rhododendron 'Unique' Unique Rhododendron Rhododendron 'Vulcan' Vulcan Rhododendron Rhododendron 'Winsome' Winsome Rhododendron Rhododendron 'Yaku Prince' Yaku Prince Rhododendron Rhododendron 'Yaku Princess' Yaku Princess Rhododendron Rhododendron alabamense Alabama Azalea Rhododendron arboreum subsp. cinnamomeum Cinnamon Rhododendron Rhododendron augustinii Augustine Rhododendron Rhododendron auriculatum No common name (R. auriculatum) Rhododendron bibiani Bibiani Rhododendron Rhododendron bureavii Bureau Rhododendron Rhododendron campylocarpum subsp. coloxanthum Coloxanthum Rhododendron Rhododendron catawbiense Catawba Rhododendron Rhododendron cinnabarinum Cinnabar Rhododendron Rhododendron concinnum Concinnum Rhododendron Rhododendron daphnoides Daphnoides Rhododendron Rhododendron dauricum Dauricum Rhododendron Rhododendron davidsonianum Davidsonianum Rhododendron Rhododendron falconeri subsp. falconeri Falconer Rhododendron Rhododendron formosum var. formosum Formosum Rhododendron Rhododendron forrestii subsp. forrestii Forrest Rhododendron Rhododendron fortunei subsp. discolor Fortune Discolor, Discolor Rhododendron Rhododendron groenlandicum Labrador-tea, Labrador Tea Rhododendron haematodes subsp. haematodes Haematodes Rhododendron Rhododendron hanceanum Hanceanum Rhododendron Rhododendron hippophaeoides var. hippophaeoides Hippophaeoides Rhododendron Rhododendron hodgsonii Hodgson Rhododendron Rhododendron irroratum Irroratum Rhododendron Rhododendron johnstoneanum Rhododendron, johnstoneanum Rhododendron keiskei Keiskei Rhododendron, Keisuki Rhododendron Rhododendron kiusianum Kiusianum Azalea, Kyushu Azalea Rhododendron lacteum Lacteum Rhododendron Rhododendron luteiflorum Luteiflorum Rhododendron Rhododendron lutescens Lutescens Rhododendron Rhododendron luteum Pontic or Pontica Azalea Rhododendron macabeanum Macabeanum Rhododendron Rhododendron macrophyllum Pacific Rhododendron Rhododendron mucronulatum Rhododendron, mucronulatum Rhododendron myrtifolium Myrtifolium Rhododendron Rhododendron niveum Niveum Rhododendron Rhododendron occidentale Western Azalea Rhododendron orbiculare subsp. orbiculare Obiculare Rhododendron Rhododendron oreotrephes Oreotrephes Rhododendron Rhododendron pachytrichum Pachytrichum Rhododendron Rhododendron ponticum Rhododendron, ponticum Rhododendron prinophyllum Roseshell Azalea, Pinkshell Azalea Rhododendron prunifolium Plumleaf Azalea Rhododendron quinquefolium Quinquefolium Azalea Rhododendron racemosum Racemosum Rhododendron Rhododendron roxieanum var. oreonasters No common name Rhododendron rubiginosum Rubiginosum Rhododendron 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 stenopetalum Rhododendron, stenopetalum Rhododendron thomsonii subsp. thomsonii Thomson Rhododendron Rhododendron wardii Ward Rhododendron Rhododendron wiltonii Wilton Rhododendron Rhododendron yakushimanum Yak Rhododendron Sambucus nigra subsp. cerulea Blue Elderberry, Blueberry, Elder Taxus baccata English Yew Taxus brevifolia Pacific Yew Taxus canadensis Canadian Yew, American Yew, Ground Hemlock Taxus cuspidata Japanese Yew Taxus media Hybrid Yew, Anglojapanese Yew Tilia americana American Linden, American Basswood Tilia cordata Littleleaf Linden Tilia euchlora Crimean Linden Tilia europaea European Linden, Common Linden Common Lime European Basswood Tilia mongolica Mongolian Linden, Mongolian Basswood Tilia tomentosa Silver Linden, Silver Basswood Vaccinium angustifolium Lowbush Blueberry Vaccinium corymbosum Highbush Blueberry Vaccinium crassifolium Creeping Blueberry, Thick-leaved Whortlberry Vaccinium moupinense Himalayan Blueberry Vaccinium ovalifolium Oval-leaf Blueberry Vaccinium sikkimense Sikkim Blueberry Viburnum dilatatum Linden, Viburnum, Linden, Arrowwood
Sources & References
Primary: PNW Insect Management Handbook
Data Maturity Structured Multiple sources. Expert review underway.