(Printed with permission from Jim Conrad. Visit his website for more great content!)
NATCHEZ NATURALIST NEWSLETTER
Issued weekly by Jim Conrad from the forest and fields
of the Sandy Creek Watershed 12 miles ESE of Natchez,
Mississippi
August 1, 2004
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DOG-DAY LEAF-TATTERS
The annual or "dog-day" cicadas have begun droning
high in the trees lately and that's as good a sign as
any that summer is getting on. Leona in the Missouri
hill country tells me that walnut leaves up there are
turning yellow. Around here the lower leaves of Winged
Sumac are crimson red, though everything else,
including the walnuts, remain lush and deep-summer
green.
However, if you look closely at tree leaves you'll see
that they're starting to show their age. Just about
every one is splotched with fungal infections and
has been nibbled on by bugs.
On the one hand it's astonishing that leaves have so
many enemies beating up on them all summer, yet, on
the other hand, you wonder what's to keep the fungi
and bugs from just eating up everything. If a bug can
eat leaf material, then why doesn't it eat the whole
thing, or why aren't there so many bugs that all the
leaves get eaten?
Of course sometimes that does happen. This spring a
Black Cherry tree next to the barn had every single
one of its newly emerged leaves eaten by tent
caterpillars, and sometimes fungi do kill weakened
trees. However, that isn't the way it commonly is.
Usually fungi and insects are evident, but they don't
overwhelm their host.
All plants, not just trees, have evolved ways to
defend themselves. Among higher plants the main
defense is often provided by chemicals inside the
plants.
Buttercups with their pretty yellow blossoms in spring
contain ranunculin, a toxin causing diarrhea and
vomiting. Lily of the Valley contains convallarin,
which causes irregular heartbeat. Leaves of the common
yew planted around many suburban houses contain
taxine, which can cause sudden death. For many other
examples like this you can review the lecture notes
for a class at the University of Maryland on
"Poisonous & Allergenic Plants" at
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