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In the mountains south of Cache Valley, and only by
perfect timing, did I happoen to find the destruction of these maple leaves so beautiful.
Tar spot, as this fungus is commonly called, is most prolific
when the leaves stay unusually wet, such as a lot of rain, mist,
fog, shade, or anything that keeps the leaves from drying out.
It is the chlorophyll produced in the leaves that give them
their green color, but when it gets cold the trees suck the
chlorophyll in from the leaves and drop them to the ground. It
is in the abscence of the chlorophyll that we get our fall
colors, such as yellow, orange, and red. The fungus that you see
on the leaves above usually starts to grow in June and first
appears as small yellow dots. As the spots grow bigger they
begin to develop black spores which you see in the center of the
circles. This tree has already sucked its chloropyll in and the
leaves have turned yellow, but the fungus prevents the
chlorophyll from leaving which is why you see green circles
around the spores. The spores will be released into the wind and
spread the disease to other trees. Even after the leaves fall to
the ground and get covered by snow the spores can survive on the
leaves through winter and be released into the air the following
year. Enough of the fungus can cause the leaves to turn brown
and fall to the ground prematurely, but most trees are healthy
enough and have enough internal reserve to survive even such an
assault. The fungus usually creates only a cosmetic issue and
rarely kills the tree, but if you have trees in your yard and
you are trying to clear of them of this blight the best approach
is to clean up all the fallen leaves and burn them (where
allowed,) send them to the city compost, bury them under and
inch of soil, or cover them with grass clippings. Spraying
fungicide on the infected tree is not recommended because it is
very expensive and it might be impossible to reach every leaf
anyway. In the meantime, as seen above, I hope you enjoy
the idea that even an ugly parasite like "tar spot" can have its
moment of beauty.
(Photo: Sept. 19, 1992
Film: Kodachrome 64) |
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