Powdery Mildew	Fungi that grow superficially on the leaves causing a grayish fungus layer. Resulting from a lack of air circulation.
Black Knot	Black, rough cylindrical shaped galls. Treatment – prune knotted twigs and excise knots on large branches during winter.
Tar Spot/Black Spot	Irregular, shiny black tar-like discolourations that can be up to 1/2″ in size. Treatment – rake and compost leaves.
Leaf Hopper/Aphids	Small insects that suck and chew on a variety of trees (i.e. Locust) and give the appearance that sap is dripping from the tree. The insects feed for approximately 4-8 weeks, depending on weather conditions.
Wilt	A sudden wilting or dying of leaves on individual limbs. Does not spread rapidly and lives in soil. Fertilization is the only recommended practice.
Sunscald	A drying up of the upper side of the exposed tree bark giving the tree a bleached appearance, causing slow decay.
Fungal	Many different varieties. Majority of these growths live on decaying matter that can be found on either the tree or on the ground.
Girdling Roots	A growth habit of certain roots – circular in fashion, causing slow death of trees in urban environments.
Galls	Primarily caused by a variety of mites laying eggs on upper side of foliage.
Canker	A variety of fungal fruiting bodies that can cause structural problems as they grow.
Leaf Scorch	The leaves of many deciduous trees, particularly Maples, may be scorched on warm windy days, resulting in a discolouration of the leaf surface.