Anthracnose (fungus – Gloeosporium apocryptum): In rainy seasons this disease may be serious on silver maples and Japanese maples. Irregular, light to reddish-brown, or purplish-brown, dead areas occur on the leaves. Many spots occur along the veins. Areas often enlarge killing the entire leaf. Leaves partially killed appear as if scorched. Many infected leaves drop in late spring. Twigs may die back. Collect and destroy fallen leaves. Spraying with a recommended fungicide when buds begin to unfold in the spring and again in 10 to 20 days will help prevent infection.
Leaf Scorch (physiological): Light or dark brown areas along the leaf margins extending toward the mid vein. Foliage appears bronzed, dried and scorched. Causes: late spring frost; hot, drying summer winds; and drought. Water trees during summer droughts. Plant in areas protected from drying winter and summer winds.
Wilt (fungus – Verticillium albo-atrum); Sudden wilting and drying of leaves on individual branches, particularly on one side of the tree. New leaves may be reduced in size and turn yellow. Infected trees may die slowly or suddenly. An olive-green discoloration may develop in the sapwood. Other fungi can also cause this discoloration. The disease does not spread rapidly from tree to tree. Infection takes place most commonly through the roots because the fungus lives in soil. Some infections take place above ground through wounds caused by insects or by pruning. Trees showing general wilting of the entire tree cannot be saved. Recently infected trees with only a few wilted branches may possibly be saved by adequate fertilization and watering. It is thought that leaf growth is stimulated, in turn enabling the rapid formation of a thick layer of sapwood, which seals in the infected parts of the trees.
Crown Gall (bacterium – Agrobacterium tumefaciens): Rough, irregular, swollen galls at the base of the trunk or on the roots. (See section on Crown Gall)
Ganoderma Rot (fungus – Ganoderma lucidum): Rapid decline and death of tree. Large, reddish, and varnish-like mushrooms form at the base of the infected tree. No control known for this type disease.
Powdery Mildew (fungus – Uncinula circinata): White fungus growth on leaves. Rarely serious enough to use control measures.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): Silver maple is rated as highly susceptible to Phymatotrichum omnivorum).
Mushroom Root Rot (fungus – Armillaria (Clitocybe) tabescens): (See section on Mushroom Root Rot)
Trunk Rot (fungus – Fomes sp., Hydnum sp., and Polyporus sp.): Refer to section on Wood Rots and shade trees.