Although some maple varieties, such as paper bark maple, shed their bark as a normal part of growth, Japanese maples generally do not. A Japanese maple tree may lose its bark due to sun scald, borer infestation or even squirrels or cats. The two problems of insects in the branches and shedding may or may not be related. A bit of detective work is necessary to find a solution.
Identify the Insects
Catch a few of the insects and take them to a county extension agent for identification. Aphids, scales and Japanese beetles are the most common insects that infest the branches. Aphids are small, green, brown, red or grey insects, usually less than 1/4 inch in length. They secrete a sticky substance known as honeydew on the leaves, bark and soil. Japanese beetles are round beetles with iridescent bodies. They eat the foliage, leaving a skeletonised leaf behind. Scales form in small masses on the branches of Japanese maple, sucking the sap from the twigs and branches.
Survey the Damage
Look for other damage in addition to peeling bark to determine the cause. Aphids and scales usually cause yellowing, wilted leaves and branches, while Japanese beetles quickly defoliate a tree. Boring insects may cause the bark to shed as they tunnel through the wood, but you may also notice small holes in the wood, piles of sawdust around the trunk, rough or knotted wood on the branches or a wet, sappy area on the trunk. Look for signs of suncald, such as discoloured bark, particularly on the south or southwest side of the tree. The bark may be red, yellow or silvery. Watch for signs of squirrel activity as well.
Peeling Bark Treatment
The most likely cause of shedding bark is sunscald. Plant Japanese maples in partial shade, especially if you live in a climate with long, hot summers. Paint the affected trunk area with latex paint diluted with water, or wrap the tree with a tree wrapping during the winter. Avoid excessive pruning, which reduces the canopy, and makes the tree more vulnerable to sunscald. Water the tree frequently in the summer and occasionally in the winter during dry weather to keep it healthy. Watch for signs of borers. These destructive insects often attack Japanese maples that have sunscald. To prevent damage from squirrels and animals, wrap chicken wire loosely around the trunk of the tree to prevent climbing and plant Japanese maples away from fences and structures.
Once you've positively identified the insect, you can decide on a treatment option. Unless the insects are causing severe damage, the tree might not require any treatment at all. Spray Japanese maples in late winter with a dormant oil to treat for aphids and scales. Other options include insecticidal soap and neem oil applied during the growing season. Birds, ladybirds and lacewings eat aphids and may control them without the use of pesticides. Treating for borers is difficult because the insects are inside the tree, where the chemicals do little good. The best solution is to prune out infected wood and keep the tree healthy so it doesn't become infested. Pyrethroid and carbaryl pesticides are labelled for treating Japanese beetles.
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