All our young maples have tar spot this year, which hasn't been a problem in the past. We imported a lot of organic materials, included bagged leaves from a neighbor down the road and wood chips (with maple) from an arborist. I'm guessing that we imported the tar spot fungus with the leaves.
Although the disease does not compromise the tree's health, apparently, it cannot be a particularly good thing either. They say to rake up the leaves and thoroughly compost religiously for several years to knock back the amount of fungus that overwinters on the fallen leaves. **Any other control strategies (for lazy gardeners) would be welcome.**
And just a word to the wise: shortcuts to accumulating organic matter (like bringing in bagged leaves from neighbors) can have unexpected consequences.