Japanese maple (Acer palmatum) is a sturdy little ornamental tree, popular for its graceful shape, deep fall colour and delicate, lacelike leaves. Occasionally, Japanese maples are troubled by aphids, scale or powdery mildew, but these are easily treated and seldom kill the tree. Serious problems like wood rot, leaf scorch and leaf scorch are often fatal unless immediately addressed. Diagnose the problem before pursuing a course of action.
Check the soil drainage around the Japanese maple. Dig a 15-cm (6-inch) deep hole 60 cm (2 feet) from the trunk. Pour a few cups of water into the hole. If water is still standing in the hole 15 minutes later, the tree may be dying from root rot.
Carefully dig the tree out with a shovel. Examine the roots. If they are black and mushy, prune them back to healthy tissue. Amend the soil in 1.2-by-1.2-metre (4-by-4-foot) area with equal parts peat, sand and organic compost. Replant the tree in the amended soil.
Look at the leaves of the dying Japanese maple. If they are curled, yellowing and dropping, your problem is leaf scorch. Japanese maples require some shelter from wind and sun in winter. Transplant the tree to a sheltered area, near a building or other trees. Keep the tree well watered as winter approaches, because a dehydrated tree is much more susceptible to leaf scorch.
Prune out dead and wilted branches as you see them, leaving 13-mm (1/2-inch) downward-slanting stubs that will drain moisture. Flush or horizontal cuts will only provide a collecting place for moisture, which will cause more problems. An angled stub lets moisture drip off, allowing the wound to heal faster.
Fertilise the dying tree in early spring with a 10-10-10 nitrogen-based fertiliser, following instructions on the package for the size and age of the tree. An extra boost of nutrients at the start of the growing season will give it the best chance for survival.
Collect seeds from the dying tree if you think it cannot be saved. These seeds can be cold-stratified and planted in place of the old tree. Choose a different site for planting in case soil pathogens were the problem, because they will remain in the soil for several years.
Always clean pruning equipment before and after use to prevent fungus, bacteria and insect eggs from being transmitted from a sick tree to a healthy one. Simply wipe the blades with a soft cloth dipped in rubbing alcohol.
Do not fertilise sick Japanese maples late in the growing season. It will cause a flush of late growth that will die off in winter, leaving the tree even more weakened.