We have a large, stately American Elm which has been the centerpiece
of our garden for years. It does not have Dutch Elm disease (we've
been treating it with injected fungicide, etc., for years). It has
always had a serious case of elm black spot (anthracnose), however.
In recent years the black spot has gotten progressively worse. It is
so bad now that the tree drops 60-80% of its leaves between June 15
and July 1. Remarkably the tree seems to remain otherwise healthy --
leafing out fully each spring. Dropping diseased leaves all over our
garden every spring and ruining the beauty of the tree is such a
drag. It has been treated with sprayed fungicide vigilantly this
year and last, but this seems to have no had no effect. Does anyone
know a more aggressive treatment?
Here are some other facts. The tree now has a very dense crown
(thanks to pruning several years ago and regular fertilization). It
leafs out very densely in April, with layered decks of leaves. Both
this year and last spring in Massachusetts has been rather wet and
cool, but not off-scale. We've made sure to remove all leaf litter
around the tree. We've heard that dense foliage inhibiting air
circulation can encourage the disease. On the other hand it's hard to
believe that thinning the crown could control such an infestation.
It took a while to track this down -- they spray is mancozeb, aimed at
black spot; the injection is Arbortech, aimed at Dutch elm disease.
Our arborist is stumped... If anyone else has an elm ravaged by black
spot, at least we could share the pain...
I don't have a clue about things, but I've read that Chives
planted around roses will help fix Black Spot problems with
roses. I don't know if it's true yet, but I've planted some
Chives... and am hoping that the chives will germinate, because
the first 6 chive seeds I've planted never germinated. Hope
it's only because I have a bad bunch of seeds.
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