Household composters: beware of dead leaves with black stains!

Some dead leaves mostly from maple trees are covered by black stains called tar stains; they can be harmful to the potting soil that you’re making with household compost.

In the last few weeks, several residents were enquiring about black stains – or tar stains – as they are called. Even if they appear mostly in August and September, the infection can start as early as spring. The fungus hibernates in the stains of these dead leaves. In the spring, the fungus produces spores that settle on young leaves causing new infections. This is how the infection cycle continues from one year to the next.

The disease affects the aesthetic nature of trees and the damage is rarely significant. But in more serious cases, there is an unusually large number of fallen leaves, which diminishes the leaf’s ability to undergo photosynthesis.