Maple Tree Diseases With White Spots on the Bark

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Maple trees are recognisable for their bright fall foliage and prized for their sap, which may be tapped and turned into syrup. Whether the tree is meant for food or decoration, no one wants to see their maple become the victim of a potentially deadly disease. Identifying the problem is crucial to treating it. Maple tree diseases involving white spots on the bark may arise from a number of problems; pinpoint yours to start treatment.

Preventing Disease

Preventing and treating maple tree diseases go hand-in-hand. Trees that become targeted by various diseases are in danger precisely because they are already weakened by environmental factors. Maple tree diseases strike trees that are weather-damaged or suffering from poor cultivation. The best way to treat maple tree diseases is to prevent them by growing maples in well-drained, rich, healthy soil. Protect the trees from sun and cold damage to keep them healthy, and you will be identifying a lot fewer diseases that create white spots on the bark, as well as other symptoms.


Canker is a common tree disease; valsa canker is particularly prone to damaging maple trees of all types. Elliptical cankers appear on the branches and stems of maple trees when the disease is present. The cankers are extremely small and grey or white in colour. Canker is the most common type of fungus, and it rarely affects any but the smallest branches that measure less than 4 inches in diameter. Valsa canker is not generally fatal and will rarely kill maple trees until extreme weather, such as severe drought and extreme heat, is also present over the course of a year. Treat canker by pruning away the damaged branches.

Shoestring Rot

Canker is not the only fungus that may affect maple trees. Shoestring rot may also occur. The fungus is localised to the roots and collar of the tree, usually affecting only bark under the ground. Shoestring rot will eventually kill the tree by attacking the roots. Foliage growth will be severely and visually affected by shoestring rot. Dwarfed leaves may appear on branches, if anything grows on them at all, when shoestring rot is present. Shoestring rot is so named for the long, thin black ropes of fungus that appear on the lower trunk of the tree. Small, fan-like white growths will also appear inside loose bark along the trunk of the tree. Shoestring rot generally attacks mature maples that are stressed by drought conditions, but it only lasts 30 days. Keep the tree well-watered to prevent shoestring rot.


Many maple tree pests have white markings on them. The Asian long-horned beetle is capable of killing an entire population of maple trees. Females burrow into the bark and wood of the tree to lay eggs, which hatch into tree-eating grubs. Adult Asian long-horned beetles have glassy bodies with white spots. Forest tent caterpillars also attack hardwood trees to feed. The brownish bodies blend in well to the surrounding bark of the maple tree, but the single white line and dual white spots on each body are easy to see.

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