| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Anthracnose | Wet weather: young leaves blighted at bud break or large dead areas between veins on lower branches. Winter twig dieback. Slightly raised brown dots (fruiting structures) on lower leaf surface and dead twigs. Often visible without magnification; magnification helps. | Apiognomonia | Only highly valued trees: fungicide to protect new twigs/leaves as they form. Otherwise: prune/destroy dead twigs/branches in dormancy. Apply fungicide to protect new leaves/twigs. |
| Armillaria Root Rot | Branch dieback. Annual honey-colored mushrooms (1.5–6" cap, 0.5–1" stem) in autumn clusters at tree base. Cap dry/slimy after rain. Spores on gills under cap. White fungal fan under bark at base. Dark brown rhizomorphs (shoestring threads) under bark or on roots/trunk. | Armillaria | Remove infected trees. Protect healthy trees from stresses, especially defoliation (gypsy moth larvae, leaf rollers). |
| Bacterial Leaf Scorch | Browning of oldest leaf margins mid-late summer on one/few branches on inner/lower canopy. Wavy reddish-brown band sometimes between brown/green tissue. Browning progresses to more leaves toward branch ends. Branches and eventually entire trees die. | Xylella fastidiosa | Leafhoppers/spittlebugs carry bacteria. Promote plant vigor by protecting from stresses. Oxytetracycline injections by professional arborist alleviate symptoms year of injection but don't cure; symptoms reappear in non-injection years. |
| Bacterial Wetwood (Slime Flux) | Dark streaks of sap (usually foul-smelling) ooze from holes/cracks in bark. Heartwood discolored dark brown. Pin oaks especially prone. | Various bacteria | Avoid wounding bark of affected trees. Care for tree normally, minimizing stresses. |
| Ganoderma Root Rot | Butt rot takes years to kill but makes tree very susceptible to wind-throw. Distinctive shelf-like fruiting structure singly on wood at/near soil line. Brown to reddish-brown with cream/white margin; brown portion varnished. Shelf grows perennially 5–10 yrs, 8–12" across. Underside light with pores; scratches turn brown (artist's conk). Infected trees slow growth, dying branches, small yellowed leaves. | Ganoderma applanatum (formerly Fomes applanatus) | Although years to die, infected tree poses hazard. Remove promptly if in hazardous location. |
| Inonotus Root Rot | Root/butt rot; trees may topple before obvious symptoms. Branch dieback, fewer yellowed leaves. Fungus reaches butt forming 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. Fruiting structures = sure sign of severe damage. | Inonotus dryadeus (formerly Polyporus dryadeus) | 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 Spot | Mid-late summer: irregular dark-brown spots between veins, enlarge to 3/8", become reddish-brown often with yellow halo. Trees with iron chlorosis/other stresses most severely affected. | Tubakia (formerly Actinopelte) | Little damage; no defoliation. No control for landscape. Nursery: fungicide at bud break. |
| Oak Leaf Blister | Spots ¼–½" diameter turn light green as young leaves expand. Leaf cells in spots multiply more → raised blister-like buckling. Aging spots: upper surface covered with buff-white fungal coating turning brown. Leaves usually don't fall prematurely. | Taphrina caerulescens | Landscape: fungicide not necessary—leaves seldom severely spotted, don't fall prematurely. Little actual damage. Nursery: fungicide late dormancy before bud break. After bud break/symptoms visible, too late to spray. |
| Powdery Mildew | White fungal growth on leaf surfaces in autumn. | Microsphaera | Develops too late for significant damage. No control recommended. Trees readied for fall sale: apply fungicide. |
| Oak Wilt | Most oaks, especially red oaks susceptible; white oaks resistant. Leaves at top brown at tips/margins, wilt, fall while still some green. Progresses down tree. Twigs/branches die. Brown streaks in outer sapwood sometimes hard to find. Trees usually die within a year. | Ceratocystis fagacearum | Remove infected trees immediately after diagnosis. Don't stack wood—insects may leave and carry fungus. Cut root grafts first, then inject mildly infected tree and neighboring oaks with fungicide. Won't eliminate fungus from roots but inhibits in twigs/branches. High-risk uninfected oaks: inject fungicide every 2 years. |
Oak leaf blister early season and summer; Anthracnose; Bacterial leaf scorch; Tubakia leaf spot; Laetiporus sulfureus; Ganoderma on oak early and well-developed; Inonotus early and late fall.
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