The arrival of the warm weather is also synonymous with fungal diseases in trees. Anthracnose is sometimes found on maple, oak, and ash trees, especially after a cool and rainy spring, such as this year.
Anthracnose is a foliar disease caused by a fungus (Gnomonia spp. or Gloeosporium spp.). Early symptoms begin to appear on the leaves of host trees in hot and humid conditions. Irregular dark brown or orange-brown blotches appear on oak or ash trees. Silver maple trees, however, present black or dark brown blotches, and can affect multiple areas on leaves (see pictures). These necrotic blotches cause the leaf to wilt and fall to the ground prematurely.
But don’t worry. This fungus is usually harmless and does not damage trees.
This fungus is a normal occurrence. It appears cyclically, depending on weather conditions, so no specific action needs to be taken.
However, we do have some tips:
- Occasionally rake fallen leaves and compost them.
- Make sure that the tree’s surrounding area is moist, especially in very hot weather. - Place a drip irrigation system around the tree base.
- Avoid over-fertilizing the lawn or using chemical fertilizers that degrade quickly close to affected trees.