We have several very large Maples in our backyard. This year the leaves have black spots and eventually the black covers the entire leaf which falls off. The tree still produced keys. We have 3 maples in our back yard and 2 of these have the same problem.
Thank you for contacting Toronto Master Gardeners.
Anthracnose is a fungal disease that tends to attack plants in the spring, primarily on leaves and twigs. Anthracnose fungi overwinter on fallen leaves and twigs that were infected the preceding year. Cool, rainy weather creates the perfect conditions for the Anthracnose spores to spread. Dry and hot weather stop the progression of the disease that may begin again once the weather conditions become optimal. The problem can be cyclic but is rarely fatal.
To reduce the spreading of the disease:
- Collect and destroy infected leaves as they fall.Infected leaves and twigs that remain in the vicinity are a source of spores for new infections in the spring.
- Prune out dead branches.Be sure to clean all garden tools to avoid the spread of the disease. A 1–part bleach to 9–part water solution can be used to dip tools into between cuts.
- Promote air circulation.Thin out excessive twig and branch growth. This will reduce the period of time that leaves are wet and vulnerable to inoculation.
- Keep trees growing vigorously.Supply 1–2 inches of water weekly only during dry periods. Fertilize early in the spring or in late fall.
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