Oak Diseases

Disease	Symptoms	Pathogen/Cause	Management
Anthracnose	During wet weather, young leaves are blighted as bud break occurs or large dead areas form between the leaf veins primarily on lower branches. Winter twig dieback may occur. Tiny, slightly raised, brown fungal fruiting structures form on the lower surface of leaves and on dead twigs. Magnification helps greatly in finding these small structures.	Apiognomonia (sexual stage)	Only highly valued trees should be treated with a fungicide to protect new twigs and leaves as they form. Otherwise, prune and destroy dead twigs and branches during dormancy. Apply azoxystrobin, chlorothalonil, or mancozeb.
Armillaria Root Rot	Branches die back. A fleshy, firm, honey-colored mushroom forms annually in the autumn in groups of a few up to 100 or more at the tree base. The cap of the mushroom is dry, 1 1/2 to 6 inches in diameter, slightly depressed center and may have brown, scale-like spots. Stems are 1/2 to 1 inch thick and 2 to 6 inches long. Spores are formed on flat, plate-like structures on the underside of the cap. A white fan of fungus is found under the bark at the base of the tree. Dark brown, shoestring-like threads may be found under or on the surface of the bark.	Armillaria	Remove infected trees. Protect healthy trees in the area from stresses, especially insect feeding (gypsy moth larvae) that results in defoliation.
Bacterial Leaf Scorch	Browning of oldest leaves along their margins begins mid to late summer on one branch or a few branches on the lower portion of the tree. A wavy reddish-brown band sometimes develops between the brown and green tissue of the leaf. Symptoms progress upward to include more leaves and toward the ends of branches.	Xylella fastidiosa	Infected trees may survive for years. Severely affected trees should be removed.
Bacterial Wetwood (Slime Flux)	Dark streaks of sap, usually foul smelling, ooze from holes or cracks in the bark. The heartwood is discolored dark brown. Pin oaks are especially prone to wetwood.	Various bacteria are involved.	Avoid wounding the bark of affected trees. Care for the tree as normal, minimizing any stresses.
Ganoderma Rot	A butt rot may take several years to kill the tree but makes the tree very susceptible to windthrow. A very distinctive shelf-like fruiting structure forms singly on the wood at or near the soil line. It is brown to reddish brown on top with a cream to white-colored margin. The brown portion appears to have been varnished. The shelf grows perennially for 5 to 10 years and may reach 8 to 12 inches across. The underside of the shelf is light colored and has millions of tiny pores in which the spores are formed. The underside turns brown when scratched and forms an interesting drawing surface, thus the common name "Artist's Conk." Infected trees slow in growth rate, have branches dying, and their leaves are small and yellowed.	Ganoderma applanatum (formerly Fomes applanatus)	Although it may require several years for the tree to die, an infected tree poses a hazard. A tree with fungal fruiting structures on it should be removed promptly if it is in a location where property damage may occur or where people or pets could be struck by falling limbs or the falling tree.
Inonotus Root Rot	A root and butt rot develops. Trees may topple before any obvious symptoms are noted. Infected trees often have a branch dieback, and fewer than normal leaves that are yellowed. Although the root rot begins well out on the root system, the fungus eventually reaches the butt of the tree where it forms large, tough, irregularly shaped light to dark brown shelves at or just above the soil line. With age, these become very rough and dark brown to black. Cutting the shelf reveals a reddish-brown center. The underside of the shelf is brown with millions of tiny pores in which the spores are formed. A sure sign of severe damage to the tree is the presence of the fruiting structures.	Inonotus dryadeus (formerly Polyporus dryadeus)	Infected trees should be removed immediately.
Laetiporus Root Rot	Massive clusters of bright, sulfur-yellow to salmon to bright orange shelf-like fruiting structures that turn white with age initially form in the summer or autumn on the wood of the tree but fall off during the winter. The underside of the fruiting structure has millions of tiny pores in which the spores are formed. New shelves form on the wood the following summer and autumn. The bark where the fruiting structure forms is slightly depressed and cracked.	Laetiporus sulfureus (formerly Polyporus sulfureus)	Fruiting structures form long after most of the damage has been done. Infected trees are very prone to wind breakage even before the fungus begins to form fruiting structures and should be removed at the first sign of infection.
Leaf Spot	In mid to late summer irregular, dark brown spots form between the leaf veins and enlarge up to 3/8 inch in diameter and become reddish brown often with a yellow halo. Trees with iron chlorosis and those under other stresses are most severely affected.	Tubakia (formerly Actinopelte)	Little damage results from this disease. No control action is recommended for landscape situations. Mancozeb or propiconazole can be applied in the nursery beginning at bud break.
Oak Leaf Blister	Spots, 1/4-1/2 inch in diameter, turn light green as young leaves expand. Leaf cells in the spots multiply more than surrounding cells and a buckling of the leaf results. As the spots age, their upper surfaces become covered with a buff-white coating of fungal growth that later turns brown. The leaves usually do not fall prematurely.	Taphrina caerulescens	Fungicide application in the landscape is not necessary because the leaves are seldom severely spotted and do not fall prematurely. Although infections may be extensive some years, little damage actually results. In the nursery, chlorothalonil or mancozeb must be applied late in dormancy prior to bud break to prevent spotting. Once bud break has occurred and symptoms are visible, it is too late to spray.
Powdery Mildew	White fungal growth develops on the surface of leaves in the autumn.	Microsphaera	This disease develops so late in the year, no significant damage occurs. No control is recommended. Where trees are being readied for fall sale, apply azoxystrobin, triadimefon or myclobutanil.,
Oak Wilt	Most oaks but especially red oaks are susceptible. White oaks tend to be resistant. Leaves at the top of the tree turn brown along the tips and margins, wilt, and soon begin to fall while there is still some green color left in them. This progresses down the tree. Twigs and branches die. Brown streaks often observed in the outer sapwood is sometimes difficult to find. Trees usually die within one year after infection.	Ceratocystis fagacearum	Cut a trench between oaks that are within 50 feet of one another in order to sever root grafts. Remove infected trees and soon as the diagnosis is made. Do not stack the wood since insects in it may leave and carry the fungus to neighboring trees. Propiconazole injection can protect trees.

COMMON NAME	TRADE NAME
azoxystrobin	Heritage
chlorothalonil	Daconil 2787
mancozeb	Dithane, Mancozeb
myclobutanil	Systhane
propiconazole	Alamo, Banner
triadimefon	Bayleton, Strike