Why is this topic important?

• Maples dominate urban forests (50-90%), so their problems attract a lot of attention.
• It is important to learn to recognize serious problems, and ignore inconsequential ones.

• Yes. Late summer is a good time to view stress in trees because its effects are so visible in the canopy, and winter is a good time to see structural defects.

• branch dieback
• early fall coloration
• leaf scorch
• reduced terminal growth
• large seed production
• signs of specific insects or diseases

                                                    Bladder gall on maple, a disfiguring but minor disease

• Drought - Reduced water supply during summer months means more water is being given off than is being taken up. Maples will often exhibit leaf scorch (browning of leaf edges). Repeated leaf scorch often indicates restriction, smothering, or death of the roots.
• Girdling roots - These roots circle trunks, often below grade, constricting sugar transport to the roots and slowly killing them. Norway maples seem particularly prone. Symptoms: center crown death or early fall coloration. Inspect roots of new stock carefully.
• Included bark - Branch attachments on maples often have included (embedded) bark between branch and trunk, or co-dominant stems. This weak union is a common point of failure on older maples. Inspect suspicious unions showing swelling, plants, or leakage.
• Maple decline - Decline or dieback of sugar maples is becoming more common. Probable cause is a combination of internal factors aggravated by environmental conditions. Symptoms: premature fall color, smaller leaves, and branch dieback. There is no permanent solution.
• Verticillium wilt - This destructive disease attacks through the roots, causing the xylem to plug up. Symptoms: wilting of leaves on one limb, reduced growth, gray-green streaks in sapwood. Prune out affected limbs. Avoid wounding roots, and water new trees. If replacing with another tree on the same site, select a resistant species.

• Tar spot - This is a fungal leaf disease occurring on Norway, red and silver maples. Early light yellow-green areas later turn into black, raised, tar-like spots on upper leaf surfaces. Damage is ugly, but usually only cosmetic. Raking up and removing infested leaves reduces infection.
• Powdery mildew - Here is another fungal leaf disease. It shows up as a thin layer or patches of grayish white powdery material. Infected leaves may turn yellow and drop early. A cosmetic problem only. 
• Maple gall mites - These tiny mites produce very visible warty or spindle shaped galls on the leaves of maples. Usually noticed in April and May, they can be very unsightly. This is a cosmetic problem that does not affect the overall health of the tree.

Miller, H. C., and S. B. Silverborg.  1973.  Maple Tree Problems.  Syracuse NY: SUNY ESF.  (To order, call 315-470-6644)  George Hudler, 1984.  Diseases of maples in eastern North America.   For other information, advice and help on this topic, call offices of your State Urban Forestry Coordinator or University Extension service, visit urban forestry web sites.