Maple Tree Diseases With White Spots on the Bark

Maple Tree Diseases With White Spots on the Bark

When white spots appear on the bark, you realize something is amiss with the maple (Acer) tree. Numerous ailments affecting maple trees may cause discolorations on the tree bark. These disorders may lead to serious issues such as defoliation, branch dieback and death of this maple tree. After you have determined the reason for the white spots, take the necessary actions to control the illness.

Valsa Cankers

A maple infected with valsa cankers will develop superficial cankers on its branches, bark and stems. These cankers will include many small, white or grayish pimple-like bumps. This disease happens when the fungal pathogen enters through injured bark caused by mechanical damage or pruning cuts. Valsa cankers also lead to wilting and discoloration of the leaves, and branch dieback. Valsa cankers are most prevalent during periods of high humidity and humidity, and trees that are stressed and unhealthy are more prone to valsa cankers. There is no cure for valsa cankers and management measures rely on ethnic care. Provide enough water to the tree during periods of drought and make sure that the roots have proper drainage. Immediately eliminate and remove branches with cankers in the tree. Prune pine trees in the spring during dry conditions and disinfect pruning shears after each cut.

Armillara Root Rot

Also called shoestring rot, armillaria root rot results in stunted growth and poor leaf production. Branch dieback and girdling will begin to occur and the life of this maple tree is endangered. Armillara root rot spreads via rhizomorphs, which look similar to dark shoestrings and are attached to infected stumps and roots. These rhizomorphs spread across the soil and soften stressed or damaged walnut trees. Loose bark will reveal white fan-shaped spots underneath and honey-colored mushrooms will grow in clumps at its base. Water stressed trees are vulnerable to armillara root rot, so always provide enough water to the maple during periods of drought. No chemicals are available to control or cure this respiratory disease. However, it is possible to prevent it from spreading by eliminating and destroying all infected areas of the tree. Be sure to sterilize the cutting edge instrument after each cut.

Bacterial Wetwood

Also referred to as slime flux, bacterial wetwood is a disorder that leads to yellowish-brown wood discoloration and also foul-smelling slime to ooze from the bark. The slime may be clear or white and frothy. After the slime dries, it leaves a white or grayish crust on the bark of this maple tree. Sap beetles and flies are a few insects that will feed on the slime, but mercifully, they’re not proven to spread the germs. The bacterium that causes slime flux enters through division and root wounds. Wetwood infections can be controlled by opening wounds to prevent liquid from building up under the bark. Another choice is to drill a hole from the bark and also add a tube to drain the excess fluid and decrease the pressure.


Numerous species of annoying insects may appear as white spots on the bark of pine trees. As winter nears, the female walnut mealybugs will crawl into crevices in the bark and generate a white casing that protects them during the winter. These white casings may be seen from the bark of this maple tree. Cottony maple scale form egg masses in early summer that are covered in a protective wax covering that looks like spots of white cotton. Dormant horticultural oil implemented in early spring will help control mealybugs and scale. Some species of maples, such as sugar maples, can be more sensitive to oils so care has to be taken when applying the insecticide.

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