I live in Riverdale in Toronto, and the Manitoba Maple in my front yard has been losing leaves the past few years. This year is the worst with many of the leaves curling, turning black and falling off. Is there anything that I can do?
The symptoms you describe could have a number of possible causes. Black curled leaves are often a symptom of a fungal disease, such as anthracnose that attacks foliage and young stems. This year’s wet cool spring has provided the perfect conditions for fungal diseases in trees and other plants. Manitoba maples (Acer negundo) are also susceptible to a root fungal disease that can lead to leaf drop and decline. Typically, mature trees are not permanently damaged by fungal diseases that attack foliage, unless there is a sustained infection that causes significant leaf drop over a number of years. You mentioned there has been leaf drop for the past several years, so this may be a concern, although from your photo the tree looks quite vigorous with the exception of the curled leaves.
Fungal diseases in mature trees are not readily treatable once they are apparent. However, you can adopt some good practices to reduce the likelihood of spread in subsequent years. Many fungal pathogens can overwinter in dropped leaves and twigs. Be sure to remove leaves that drop prematurely and to thoroughly rake and bag leaves in the fall. If you have close neighbors with trees displaying similar symptoms, you may want to encourage them to do the same, as fungal spores can travel a fair distances carried by rain and wind. If there are prolonged dry spells later in the summer, make sure the tree is well watered along the drip line (edge of the canopy) to help the tree stay as vigorous as possible.
Urban trees are subject to a number of stresses, including disease, insects, pollution, road salt, poor growing conditions and competition from other trees, that can lead to decline. If you continue to be concerned about the health of your tree, you may want to contact a certified arborist who can perform a detailed inspection, and provide advice about maintenance. You should be able to find an appropriate expert by consulting the following websites:
- Landscape Ontario, which has contact information for tree specialists and arborists; and
- The Ontario chapter of the International Society of Arboriculture (ISA).