Afflictions Of Late Summer
Tree Leaves Only Skin Deep
Being an arborist, I’m of course very
mindful of complexion. Things like
bruises and blemishes catch my eye,
in addition to scabs, cuts, and even those
out-of-place whiskers that appear out of
nowhere. It sounds like a description of
my aging skin, but I’m talking about
blotches, warts and cuts that accumulate
on tree leaves over the summer.
I suppose if we had to stand outside day
and night all season, our skin would
develop issues too. Those who work o
r play much outdoors need to be
concerned about skin spots that
suddenly show up. With tree leaves,
that’s not the case – even the ugliest
“skin” condition is generally no cause
for concern.
and night all season, our skin would
develop issues too. Those who work o
r play much outdoors need to be
concerned about skin spots that
suddenly show up. With tree leaves,
that’s not the case – even the ugliest
“skin” condition is generally no cause
for concern.
One of the more alarming leaf
disorders is called tar spot, whose
symptoms are black blobs that often
show up in late summer or early fall.
Tar spot affects Norway, silver, red
and sugar maples, in order of
severity. The spots, which really do
look like drips of roofing tar, seem
to appear overnight, and sometimes
cover much of the leaf. While it may
look like a serious affliction, it’s
really just a cosmetic issue
(meaning if you’re good with
cosmetics you can probably make
your tree look pretty again).
disorders is called tar spot, whose
symptoms are black blobs that often
show up in late summer or early fall.
Tar spot affects Norway, silver, red
and sugar maples, in order of
severity. The spots, which really do
look like drips of roofing tar, seem
to appear overnight, and sometimes
cover much of the leaf. While it may
look like a serious affliction, it’s
really just a cosmetic issue
(meaning if you’re good with
cosmetics you can probably make
your tree look pretty again).
Unlike the tar sands of northern
Alberta in Canada, though, tar
spots can’t be processed into
crude oil. As disappointing as
that may be, at least tar spot is
not a problem. Spots are caused
by several different species of
fungi in the genus Rhytisma,
which I mention because some
of you play Scrabble.
Alberta in Canada, though, tar
spots can’t be processed into
crude oil. As disappointing as
that may be, at least tar spot is
not a problem. Spots are caused
by several different species of
fungi in the genus Rhytisma,
which I mention because some
of you play Scrabble.
If your tree’s leaves have sprouted
tiny spindle-shaped structures
that make it appear that the leaves
need a shave, don’t worry. These
are tiny galls, formed when a
minute arachnid called an
eriophyid (go for a triple score
on that word) mite laid an egg,
along with a dose of a plant
hormone which directed the leaf
to grow a little home for her
young one.
tiny spindle-shaped structures
that make it appear that the leaves
need a shave, don’t worry. These
are tiny galls, formed when a
minute arachnid called an
eriophyid (go for a triple score
on that word) mite laid an egg,
along with a dose of a plant
hormone which directed the leaf
to grow a little home for her
young one.
Depending on the species of mite,
these galls can be green, yellow,
red or pink. Some are squat and
thick, resembling a wart, but they
are all completely harmless.
Good thing, too, because galls
shield the mites from anything
you could spray on them anyway.
these galls can be green, yellow,
red or pink. Some are squat and
thick, resembling a wart, but they
are all completely harmless.
Good thing, too, because galls
shield the mites from anything
you could spray on them anyway.
Believe it or not, scabs are caused
by a disease called scab. I think it
was late on a Friday when scab
and tar spot were named, probably
by a new intern who was later
reprimanded for “making sense.”
It affects apple, crabapple,
hawthorn, juneberry and other
trees in the rose family. Scab
causes affected leaves to drop
early, and is much worse in wet
seasons when it can defoliate a
tree by mid-summer.
by a disease called scab. I think it
was late on a Friday when scab
and tar spot were named, probably
by a new intern who was later
reprimanded for “making sense.”
It affects apple, crabapple,
hawthorn, juneberry and other
trees in the rose family. Scab
causes affected leaves to drop
early, and is much worse in wet
seasons when it can defoliate a
tree by mid-summer.
It’s a serious problem for
orchardists because it causes
scab-like blemishes on fruit in
addition to weakening the tree,
so they routinely spray fungicides
beginning at bud break.
Other ways of managing scab
include proper pruning,
increasing air flow and access
to sun, and buying scab-resistant
varieties.
orchardists because it causes
scab-like blemishes on fruit in
addition to weakening the tree,
so they routinely spray fungicides
beginning at bud break.
Other ways of managing scab
include proper pruning,
increasing air flow and access
to sun, and buying scab-resistant
varieties.
High winds, especially early-
season
events, can tatter leaves, a
condition called “leaf tatter.”
(Same intern, don’t you think?)
Japanese beetles, caterpillars,
sawflies and other insects chew
on leaves over the summer,
while leaf-cutter bees remove
perfectly scribed circles.
All in all, many trees look
bedraggled by September.
Should you be worried?
season
events, can tatter leaves, a
condition called “leaf tatter.”
(Same intern, don’t you think?)
Japanese beetles, caterpillars,
sawflies and other insects chew
on leaves over the summer,
while leaf-cutter bees remove
perfectly scribed circles.
All in all, many trees look
bedraggled by September.
Should you be worried?
Here’s a secret: by late summer,
trees don’t “need” their leaves
any more. While this is true, it’s
akin to saying you don’t need
another five bucks at the end
of the year. It would be nice,
but it’s not going to change
the big picture. A deciduous
tree expends a huge amount
of energy investing in new
leaves each spring, and its
leaves have to make enough
sugar from sunlight to “repay”
the tree, plus a little extra for
rainy days. By early August,
trees have recouped their
investment along with a pile
of interest.
trees don’t “need” their leaves
any more. While this is true, it’s
akin to saying you don’t need
another five bucks at the end
of the year. It would be nice,
but it’s not going to change
the big picture. A deciduous
tree expends a huge amount
of energy investing in new
leaves each spring, and its
leaves have to make enough
sugar from sunlight to “repay”
the tree, plus a little extra for
rainy days. By early August,
trees have recouped their
investment along with a pile
of interest.
Late-season disorders are
superficial and no cause for
concern. But if you’re
embarrassed by your tree’s
appearance come late summer,
you can always try cosmetics.
superficial and no cause for
concern. But if you’re
embarrassed by your tree’s
appearance come late summer,
you can always try cosmetics.
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