Root Rot
Symptom category — not a single disease
182 host plants · Oomycete
Last updated
Wilting and death of canes or branches appears in early spring through late summer, often coinciding with warm, dry spells. Leaves on infected stems turn yellow or bronze, develop scorch symptoms, and wilt before the canes die. When you excavate the root system, you'll find most larger-diameter roots are dead with sharp color transitions from healthy white or bright-green wood to reddish-brown rotted tissue. In low-lying areas of plantings, you may see disease pockets where multiple plants fail together.
Root rot caused by Phytophthora thrives in poorly drained soils, so drainage is everything. Never plant in wet sites or areas with hardpan; if you must garden in heavy clay, build raised beds at least 12 inches high and amend with compost or bark mulch to improve aeration. Use certified disease-free planting stock and never reuse soil from previous plantings of small fruits. Once plants show symptoms, there's no chemical cure, so removing severely infected specimens protects healthy plants nearby.
What Should I Do?
- Improve drainage before planting. Raised beds, French drains, or soil amendment with coarse organic matter.
- Never plant deeper than the root flare. Buried crowns invite infection.
- Avoid overwatering. More plants die from too much water than too little in Western Washington.
Quick Reference
Agent Type
oomycete
Causal Agent
Symptom category — not a single disease
Host Plants
182
Spread
soil
Favorable Conditions
Phytophthora spp. are most active at soil temperatures of 59-74°F (optimum 71°F) in saturated or poorly drained soils. Zoospore release requires free water in soil pore space. Prolonged soil saturation (48+ hours) dramatically increases infection. Pythium spp. favor cooler conditions (50-65°F) and are most damaging in overwatered container stock. Armillaria root disease progresses in warm moist soils but does not require saturation. Clay soils and hardpan sites with impeded drainage are highest risk in western WA. Source: PNW Plant Disease Management Handbook; Erwin & Ribeiro (1996) Phytophthora Diseases Worldwide.
Management
Vulnerability Window
Newly planted stock and plants in poorly drained sites are most vulnerable during wet fall/winter/spring months (October-May in western WA). Summer irrigation on clay soils can extend the risk window.
What Triggers Infection
Phytophthora spp. are most active at soil temperatures of 59-74°F (optimum 71°F) in saturated or poorly drained soils. Zoospore release requires free water in soil pore space. Prolonged soil saturation (48+ hours) dramatically increases infection. Pythium spp. favor cooler conditions (50-65°F) and are most damaging in overwatered container stock. Armillaria root disease progresses in warm moist soils but does not require saturation. Clay soils and hardpan sites with impeded drainage are highest risk in western WA. Source: PNW Plant Disease Management Handbook; Erwin & Ribeiro (1996) Phytophthora Diseases Worldwide.
Cultural Controls
- Improve drainage before planting. Raised beds, French drains, or soil amendment with coarse organic matter.
- Never plant deeper than the root flare. Buried crowns invite infection.
- Avoid overwatering. More plants die from too much water than too little in Western Washington.
- Remove and destroy infected plants promptly. Do not replant the same species in the same location without addressing drainage.
- In nursery settings: use clean containers, pasteurized media, and avoid standing water on bench surfaces.
Host Plants (182)
Ceanothus centennial Centennial Ceanothus Ceanothus concha Concha Ceanothus Ceanothus cuneatus Narrowleaf Buckbrush Common Buckbrush, Wedgeleaf Ceanothus, Greasewood Ceanothus dark Ceanothus, dark Ceanothus delilianus Ceanothus, delilianus Ceanothus gloriosus Point Reyes Ceanothus, Glorymat Ceanothus Ceanothus griseus var. horizontalis Carmel Creeper Ceanothus Ceanothus impressus Santa Barbara Ceanothus Ceanothus sanguineus Redstem Ceanothus, Buckbrush, Oregon-tea Ceanothus thyrsiflorus Blue Blossom Ceanothus velutinus Snowbrush, Cinnamon Bush, Tobacco Bush, Shiny-leaf Ceanothus Cedrus libani subsp. brevifolia Cypress Cedar, Cyprian Cedar Chamaecyparis lawsoniana Port Orford Cedar Chamaecyparis obtusa Hinoki Falsecypress, Hinoki Cypress, Japanese Cypress Chamaecyparis pisifera Sawara Falsecypress, Sawara Cypress Chamaecyparis thyoides White Cedar, Atlantic Whitecedar, Whitecedar Falsecypress Cistus ann Cistus ann Cistus corbariensis White Rockrose Cistus crispatus Cistus crispatus Cistus dansereaui Cistus dansereaui Cistus doris Cistus doris Cistus elma Elma Rockrose Cistus florentinus Cistus florentinus Cistus grayswood Cistus grayswood Cistus hybridus White Rockrose Cistus ladanifer Common Gum, Rockrose Cistus oblongifolius Oblongifolius Rockrose Cistus pulverulentus Cistus pulverulentus Cistus snow Cistus snow Cistus victor Cistus victor 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 Cupressus arizonica Arizona Cypress, Rough-bark Arizona Cypress Cupressus bakeri Baker Cypress, Modoc Cypress Cupressus dupreziana Saharan Cypress, Tassili Cypress, Duprez Cypress Cupressus glabra Smooth Arizona Cypress Cupressus guadalupensis Guadalupe Cypress Cupressus lusitanica Mexican Cypress Cupressus macrocarpa Monterey Cypress Cupressus sempervirens Italian Cypress, Mediterranean Cypress Daphne caucasica Caucasian Daphne Daphne cneorum Garland Daphne, Rock Daphne, Rose Daphne Daphne laureola Spurge Laurel Daphne lawrence Daphne, lawrence Daphne mezereum February Daphne, Mezereon Daphne odora Fragrant Daphne, Winter Daphne Gaultheria miqueliana Miquel's Spicywintergreen Miquel's Wintergreen Gaultheria mucronata Chilean Pernettya Gaultheria procumbens Wintergreen Gaultheria tetramera Si lie bai zhu (Chinese) Hebe emerald Hebe, emerald Hydrangea anomala var. petiolaris Climbing Hydrangea Hydrangea arborescens Hydrangea, arborescens Hydrangea macrophylla Bigleaf Hydrangea Hydrangea paniculata Panicle Hydrangea Hypericum androsaemum Tutsan Hypericum hidcote Hidcote Hypericum Hypericum kouytchense Kouytchense Hypericum, Large-flowered St. John's Wort Juncus ensifolius Daggerleaf Rush Lonicera ciliosa Western Trumpet Honeysuckle, Orange Honeysuckle Lonicera fragrantissima Winter Honeysuckle, Sweet-Breath-of-Sping January Jasmine Lonicera hispidula Pink Honeysuckle Hairy Honeysuckle, California Honeysuckle Lonicera involucrata Twinberry, Black Twinberry, Inkberry Lonicera maackii Amur Honeysuckle, Bush, Honeysuckle Lonicera nitida Box Honeysuckle Lonicera pileata Privet, Honeysuckle Lonicera tatarica Tatarian Honeysuckle, Tartarian Honeysuckle Magnolia acuminata Cucumber Magnolia, Cucumbertree Magnolia, Mountain Magnolia Magnolia liliiflora Lily Magnolia Photinia ×fraseri Red Tip Photinia Photinia davidiana var. undulata Wavy-leafed Chinese Stranvaesia Photinia glabra Japanese Photinia Photinia serratifolia Chinese Photinia Taiwanese Photinia Photinia villosa Oriental Photinia Ribes aureum Golden Currant, Buffalo Currant Ribes cereum Wax Currant Ribes davidii ge ye cha biao zi (革叶茶藨子) (Chinese name) Ribes divaricatum Coast Black Gooseberry, Straggly Gooseberry Ribes gordonianum Gordon's Currant Ribes malvaceum Chaparral Currant Ribes nevadense Mountain Pink Currant, Pink Sierra Currant, Sierra Currant Ribes odoratum Golden Currant, Missouri Currant, Clove Currant, Buffalo Currant Ribes roezlii Sierra Gooseberry, Roezl's Gooseberry, Mountain Gooseberry Ribes sanguineum Red-flowering Currant Rubus allegheniensis Allegheny Blackberry Rubus armeniacus Himalayan Blackberry Armenian Blackberry Rubus calycinoides Crinkle-leaf Creeper Creeping Raspberry Yü-shan raspberry Rubus dicolor Himalayan Blackberry Armenian Blackberry Rubus hayata Rubus hayata Rubus laciniatus Evergreen Blackberry Cutleaf Blackberry Rubus leucodermis Blackcap, Western Raspberry Rubus lineatus Silky-leaved Berry Rubus odoratus Flowering Raspberry Purple-flowering Raspberry Rubus parviflorus Thimbleberry Western Thimbleberry Rubus rolfei Creeping Raspberry, Crinkle-leaf Creeper Rubus spectabilis Salmonberry Rubus tricolor Creeping Bramble Korean Raspberry Rubus ursinus Trailing Blackberry Western Blackberry California Blackberry Dewberry 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 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 Thuja orientalis Chinese Arborvitae, Oriental Arborvitae Thuja plicata Western Redcedar Vaccinium angustifolium Lowbush Blueberry Vaccinium corymbosum Highbush Blueberry Vaccinium crassifolium Creeping Blueberry, Thick-leaved Whortlberry Vaccinium macrocarpon Cranberry American Cranberry Vaccinium membranaceum Big Huckleberry, Mountain Huckleberry Thinleaf Huckleberry Vaccinium moupinense Himalayan Blueberry Vaccinium ovalifolium Oval-leaf Blueberry Vaccinium ovatum Box Huckleberry, Evergreen Huckleberry Vaccinium parvifolium Red Huckleberry, Red Whortleberry Vaccinium sikkimense Sikkim Blueberry Vaccinium uliginosum Bog Blueberry, Bog Bilberry Vaccinium vitis Vaccinium vitis Veronica American Brooklime or American Speedwell Viburnum × bodnantense Bodnant Viburnum, Dawn Viburnum Viburnum awabuki Sweet Viburnum Viburnum bracteatum Bracted Viburnum, Limerock Arrowwood Viburnum Viburnum burkwoodii Burkwood Viburnum Viburnum carlesii Koreanspice Viburnum Viburnum cassinoides Witherod Viburnum, Northern Wild Raisin Viburnum cinnamomifolium Cinnamon Viburnum Viburnum davidii David's Viburnum Viburnum dentatum Arrowwood Viburnum Viburnum dilatatum Linden, Viburnum, Linden, Arrowwood Viburnum edule Mooseberry Highbush Cranberry, Moosewood Viburnum, Squashberry Viburnum ellipticum Oregon Viburnum, Western Wayfaring Tree Viburnum farreri Fragrant Viburnum Viburnum juddii Judd Viburnum Viburnum lantana Wayfaringtree Viburnum Viburnum lantanoides Hobblebush Viburnum lentago Nannyberry Sheepberry Viburnum nudum Possumhaw Smooth Witherod Northern Wild Raisin Viburnum opulus var. americanum American Cranberrybush Viburnum Viburnum opulus var. opulus European Cranberrybush Viburnum, Guelder-rose Viburnum opulus var. sargentii Sargent Viburnum Viburnum plicatum var. plicatum Japanese Snowball Viburnum Viburnum plicatum var. tomentosum Doublefile Viburnum Viburnum pragense Prague Viburnum Viburnum prunifolium Blackhaw Viburnum Viburnum rafinesquianum Downy Arrowwood Viburnum, Rafinesque Viburnum Viburnum rhytidophyllum Leatherleaf Viburnum Viburnum rufidulum Rusty Blackhaw Viburnum, Southern Blackhaw Viburnum setigerum Tea Viburnum Viburnum suspensum Sandankwa Viburnum, Sandanqua Viburnum Viburnum tinus Laurustinus Viburnum trilobum American Cranberrybush Viburnum
Sources & References
Data Maturity Structured Multiple sources. Expert review underway.