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Elm Tree Diseases: Symptoms, Causes, and Management Strategies

Disease Reference Table

Disease	Symptoms	Pathogen/Cause	Management
Black Leaf Spot	Small, black, slightly raised, rough spots on leaves; leaves yellow and fall prematurely.	Stegophora ulmea (formerly Gnomonia ulmea)	No control recommended for landscape trees.
Botryodiplodia Canker	Cankers on twigs/branches; sharp junction between cankered (reddish-brown) and healthy (white) wood under bark. Leaves on infected branches turn bright yellow and fall without wilting. Fungal fruiting structures roughen bark of infected twigs in autumn.	Botryodiplodia	Irrigate to prevent drought stress. Prune infected branches well below canker. Disinfest pruning tools frequently.
Dutch Elm Disease	Leaves on one/more branches wilt, yellow, fall prematurely; progressively more branches affected. Brown streaks in outer sapwood of affected branches.	Ophiostoma ulmi	See details below. Grow resistant cultivars.

Management of Dutch Elm Disease

Remove severely infected trees promptly. Peel bark off stump below soil line. Promptly burn or bury all wood >½" diameter (bark beetle larvae habitat).
If <5% crown affected: find lowest vascular streaking, prune branch ≥12 ft below that point. Inject fungicide. Maintain good elm bark beetle control.
Treating unwanted elms with cacodylic acid (herbicide; licensed arborist) kills elms, attracts beetles but suppresses brood production, reducing infested beetle numbers.

Resistant Cultivars: Accolade, Cathedral, Discovery, Dynasty, Frontier, Homestead, Independence, Jefferson, Morton Glossy, Morton Plainsman, Morton Stalwart, New Harmony, New Horizon, Ohio, Pathfinder, Patriot, Pioneer, Princeton, Prospector, Regal, Sapporo Autumn Gold, Urban, Valley Forge.

Disease	Symptoms	Pathogen/Cause	Management
Ganoderma Root Rot	Annual shelf-like fruiting structures, single or overlapping clusters, brown to reddish-brown with cream/white margin, up to 14" across; upper surface varnished. Branches and eventually entire tree die as root rot progresses.	Ganoderma lucidum	Remove promptly if in hazardous location (property damage or injury risk).
Inonotus Root Rot	Root/butt rot; trees may topple before obvious symptoms. Branch dieback, fewer yellowed leaves. Large, tough, irregular shelves at/just above soil line; light to dark brown, roughening to black with age. Cut shelf reveals reddish-brown center. Underside brown with pores.	Inonotus dryadeus (formerly Polyporus dryadeus)	Fruiting structures = sure sign of severe damage. Remove immediately.
Laetiporus Root Rot	Massive clusters of bright sulfur-yellow to salmon/orange shelves turning white with age. Form summer/autumn, fall off winter; new ones next season. Underside has pores. Bark at fruiting site depressed/cracked.	Laetiporus sulfureus (formerly Polyporus sulfureus)	Fruiting forms long after major damage. Trees prone to wind breakage before fruiting. Remove at first sign.
Leaf Scorch	Early to midsummer: marginal leaf burn/scorch on a few branches; increases later. Wavy boundary between dead/living tissue with yellow halo. Leaves fall prematurely. More branches involved in following years.	Xylella fastidiosa	Leafhoppers/spittlebugs carry bacteria. Infected trees attractive to elm bark beetles (may carry DED fungus).
Wetwood	Foul-smelling liquid oozes from branch stubs, pruning cuts, bark cracks; runs down trunk leaving gray streaks. Bark/turf where ooze lands may be killed. Affected wood water-soaked but rarely rotted.	Various bacteria	No apparent damage unless tree under other severe stress. Protect from soil compaction, excavation, drought. Avoid wounding. Do not insert pipes to relieve pressure.
Elm Yellows (Phloem Necrosis)	Leaves yellow/wilt over entire crown, fall prematurely in summer; tree dies within 1 year. Roots killed early. Inner bark (phloem) and outer xylem yellow/butterscotch with oil of wintergreen odor (fresh cut). Discolored bark in sealed jar intensifies smell. Dead phloem becomes dark brown.	Phytoplasmas	Leafhoppers/spittlebugs move phytoplasmas. Remove infected trees. Infected trees attract elm bark beetles (may carry DED fungus).

Elm bark beetle and galleries (DED); DED; DED symptoms in xylem; Wetwood ooze; Black leaf spot; Elm yellows – canopy yellowing; Elm yellows – butterscotch phloem.

Plant Disease: Assessing Elm Bark Flaking After Vine Removal; Decay Fungus in Elm After Vine Removal: Long-Term Outlook; Pecan Tree Bark Peeling: Photo Request for Rust-Colored Substance Diagnosis; Elm Tree Bark Peeling: Normal Exfoliation or Pruning Stress?; Bark Peeling and Sap Leak on Young Elm: Insect Investigation; Sycamore Bark Shedding: Normal Exfoliation, Not Disease; Bark Beetle Damage on Elm: Signs and Last-Resort Treatment; Elm 4 ft from House: Move It Before Roots & Branches Cause Damage; Beech Disease Management: Bark Disease, Bleeding Canker, and Root Rot; 'Drake' Elm Peeling Bark: Normal and Beautiful

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