Why all the polka dot trees?
As this fall comes to an end have you been noticing the black marks on the leaves in your neighbourhood, either on the trees or as you have been raking?
It is called Tar Spot and it is a fungal disease most common to Maples, Oak, Willow and Tulip Trees.
The fungi infect the leaves of the trees and cause raised, black spots to form on upper leaf surfaces that resemble black tar. Tar Spot is not serious enough to affect the health of the trees although when covered extensively the trees can be unsightly. And heavy infections can cause premature leaf drop.
It reoccurs year to year because fallen leaves bearing the tar spots will overwinter. With the warmer weather in spring, the black spots begin to produce spores internally. After extended rainfall or prolonged wetting, the black spots absorb moisture, and the spores are then carried by wind to newly expanded maple leaves. There are no fungicides available to treat Tar Spot on the trees.
The only recommended method of control is reducing the amount of leaves that overwinter in your yard and neighbourhood, which can prove to be challenging. All infected leaves should be collected and left at the curb for city collection. Mulching leaves and distributing in your garden encourages the overwintering of the fungicide and may start to affect perennials and vegetables. Also back yard composters will not get to the temperature required to kill the fungal spores. Complete disposal of the leaves is very important.
You can help your trees to become more resistant to contracting the disease and minimize the problems due to Tar Spot. Reducing stress on trees to make them more resilient, that can be done in the following ways:
• Soil aerating
It is important to spread the word about Tar Spot to encourage others to deal with it in their own yards and to encourage everyone to take care of the trees in their yard as well as the trees on their boulevard.