Half of my Japanese tree does not grow leaves. What might be the problem?
Thank you for contacting the Toronto Master Gardeners regarding your Japanese maple tree.
There are several possible reasons that a section of the tree is not leafing out this spring. Your tree looks fairly substantial and as if it’s been there for many years. Japanese maples need sufficient water but don’t like to sit in soggy soil. They can also be susceptible to damage from harsh winter winds. The other consideration based on your picture is a fungal disease called verticillium wilt (Verticillium dahliae) that is found in soil. This fungus affects the tree’s ability to move water through its trunk and branches by blocking the passageway (xylem). It is not uncommon for only part of the tree to be affected.
Start by verifying that the branches without leaves are actually dead. Do this by checking the bare branches for signs of leaf buds, which may just be slow to emerge. Next you can prune a piece of branch and peel back the bark to see if the wood underneath has any living green tissue or is brown / black and dead. Once you have established that there are no buds and the branches are dead, then you can prune away the dead branches. Be sure to clean your pruners (shears or lopers) with disinfectant between each cut so that you don’t inadvertently spread disease to other parts of the tree. Dispose of the dead branches in the garbage – not elsewhere on your your property or in compost, to prevent spreading the fungus. The next thing to do is give your tree the best care that you can. Water the tree regularly but don’t let it get soggy. One way to do this is with a soaker hose at the base of the tree. Put 1-2 inches of compost around the base of the tree to provide nutrients. Keep the compost from actually touching the tree trunk.
There is no cure for verticillium wilt. Sometimes the remaining parts of the tree will fight off the fungus and continue to grow. It will be a matter of waiting to see what happens. For more information you can refer to this reference from the Morton Arboretum on Verticillium wilt, and this from Landscape Ontario regarding the care of Japanese Maples.
Best of luck with your tree.