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Blackspot/Powdery mildew treatment

Several questions have come up regarding the treatment of these diseases.
  Both of these fungi must grow for several days to several weeks before
becoming visible - by the time you can see the damage, it is already to
late! A spraying program, to be truly effective, should be started before
any evidence of the problem is visible. Even then, it is possible that the
disease has already established itself on the leaves, but is not yet
visible - such leaves may still succumb to the disease. This is one reason
why many people become frustrated with spraying.
 Once the leaves have been damaged by either organism, it is impossible to
reverse the damage - blackspot/powdery mildew cannot be "cured" in the sense
that existing damage can be repaired. Most of the fungicides on the market
do not even kill existing fungi, the merely prevent new spores from
establishing themselves when the germinate. This is another source of
frustration for beginners. However, once a good spraying program is begun,
new growth should be disease free. Because of the reasons mentioned above,
it often takes several weeks for the results of a good spraying program to
become evident - be patient.
 Many sprays are labeled as "systemic." This means that the active
ingredients are absorbed by the plant tissues, and remain effective over
some period of time. The good news is that this means you don't have to
reapply the spray when it rains. The bad news is that although the material
is absorbed, it does not travel throughout the plant's "bloodstream."
Whenever you spray, you MUST cover the entire plant's surface for the
treatment to be effective - top & bottom of all leaves, all stems, etc.

Hope this helps,

Dave Amorde
dave_amorde@msn.com
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