The silver maples in our front yard are developing black spots on the
leaves. Not knowing any better, I'd guess this is some kind of
fungus. How big of a concern is this?
In case the details matter:
zone 4 or 5 depending on who you believe
Thank you very much!
Black leafspots on maples that are due to fungal infections (anthracnose, tar
spot, Phyllosticta leaf spot) are usually only seen in the spring following a
period of wet weather. Fungal problems can occur at other times if there has
been a period of unusually rainy weather. They are not a great cause for
concern as they cause minimal damage to the tree.
Leaf damage this late in the season is no great concern on any deciduous
plant. The tree "gave up" on the leaves sometime in mid-September, and they
are not really contributing anything to the tree right now - essentially
just waiting to drop off at this point. If you want to try to thwart
something from starting up next spring, you could be especially anal about
collecting all the dropped leaves and getting them out of your yard. By the
way, there have been some fascinating television specials on the things
plants do to protect themselves from insects and disease. Usually, the first
juicy leaves of the season are the most productive as far as photosynthesis
goes - but as voracious insects and diseases attack them, the plants respond
by putting various kinds of poison in their leaves to thwart the pests.
Unfortunately, those additives cut back on the efficiency of photosynthesis
to a certain extent.
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