|Anthracnose||Norway maple: narrrow, purple to brown streaks occur along the leaf veins. Sugar maple: large, irregular, brown or red-brown areas develop along and between the veins similar to injury due to drought and heat stress. Small, brown fruiting structures of the fungus are found near the affected leaf veins. Under very wet spring conditions, some defoliation can occur.||Discula (Gloeosporium)||Prune dead twigs and branches. Rake and destroy fallen leaves. Usually, little damage occurs and no treatment is necessary. In a nursery situation, apply a fungicidel at bud break and at 7- to 10-day intervals until the weather dries and the daily average temperature is above 65°F.|
|Bacterial leaf scorch (red maple)||Leaf margins on localized, individual branches brown in mid- to late July. The light-brown area is separated from green tissue by a dark reddish-brown band and a narrow but distinct yellow halo. Leaves may fall in August.||Xylella fastidiosa||Leafhoppers and spittle bugs carry the bacteria from tree to tree. Promote plant vigor by protecting the tree from stresses.|
|Bleeding canker||Reddish-brown cankers develop in the inner bark of the main trunk and branches. The bark over the canker becomes sunken, and reddish-brown sap oozes out. Leaves wilt and branches die.||Phytophthora cactorum||Remove the infected tree and do not replace it with a woody ornamental until the soil has been fumigated and aerated thoroughly.|
|Decline||Tree growth slows. Branch dieback progresses until much of the tree is dead.||Depending upon the site, combinations of poor soil aeration, poor soil drainage, deicing salt damage, high temperatures at the site, drought, excavation damage, soil compaction, paving close to trees, verticillium wilt, and armillaria root rot weaken and kill the tree.||Protect the tree from stresses, particularly insect defoliation.|
|Fomes root rot||A fungal fruiting structure that is hard, gray topped, hoof shaped, and 6 to 8 inches across and enlarges perennially. The underside of the “hoof” is white with tiny pores in which the spores are formed. Heart rot and dying limbs may be apparent.||Fomes fomentarius||A tree with fungal fruiting structures on the trunk 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.|
|Ganoderma root rot||Very distinctive shelf-like fruiting structures form annually on the wood singly or in overlapping clusters. They are brown to reddish brown on top with a cream to white margin, and may reach 14 inches across. The upper surface may appear to have been varnished. Branches and eventually the entire tree die as the root rotting progresses.||Ganoderma lucidum||A tree with fungal fruiting structures on the trunk, butt, or roots 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.|
|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 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||Leaf spots up to 1/4 inch in diameter with a pronounced purple border are round or irregular in shape. Tiny, black fungal fruiting structures dot the upper surface of the spots.||Phyllosticta minima||See anthracnose control above.|
|Powdery mildew||White fungal growth develops on the upper surface of leaves in the late summer and autumn.||Phyllactinia||No control is necessary since the disease begins too late to cause significant damage.|
|Tar spot||Oval to irregularly shaped, shiny, black spots up to ½ inch in diameter form on the leaves of silver or red maples.||Rhytisma acerinum or R. punctatum||No control measures are necessary.|
|Verticillium wilt||Early symptoms of verticillium wilt include heavy seed production, leaves that are smaller than normal, and browning of the margins of leaves. Frequently, the foliage on only one side of a tree wilts. The wood under the bark of wilting branches is discolored with green to black streaks. The smallest branches may not exhibit the discoloration.||Verticillium||Do not replant susceptible species where a specimen was killed by Verticillium. When a tree exhibits mild symptoms, prune out affected limbs and water to maintain tree vigor. Some trees recover. Do not fertilize heavily.|
Declining maple in mid-summer.
Verticillium wilt discoloration of xylem.
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