My maple tree
has black spots on most – if not all – of its leaves.
Can you tell
me what this is and if I should be concerned about it? I would hate
to lose this tree since it is the only one in my front yard.
A: The writer enclosed a leaf sample that had large
black spots on it, typical of a common fungal disease appropriately
called maple tar spot. Despite affecting an alarming percentage of
the leaves on a tree, maple tar spot is a cosmetic problem rather
than anything life threatening. This disease has been prevalent this
season, probably because the wet conditions in spring as maples were
leafing out created very favorable conditions for maple tar spot to
Life Cycle of Maple Tar Spot
The disease is
caused by the fungus Rhytisma and overwinters on fallen leaves.
Infection occurs in the spring as new growth starts and spores are
blown from those old leaves onto the tender new foliage. Maple tar
spot first appears as very small yellow spots that enlarge to an
inch or so in diameter through the growing season. In late summer,
those spots turn black as the fungus matures and produces
Maple tar spot
Photo: Sandy Feather
Maple tar spot
generally does not cause premature leaf drop, and it occurs so late
in the growing season that it does not impact the overall health of
affected trees. They have already formed next year’s buds, and those
leaves will fall soon anyway.
Spray for Control?
are not recommended to control maple tar spot. The best
recommendation is rake up and destroy fallen, infected leaves to
reduce the amount of fungal spores around next spring.
Trees have value
Where does landscape
mulch come from?