Here is so more sites that could help you.
http://www.ca.uky.edu/agc/pubs/id/id67/id67.htm
"Raleighgirl" wrote in message
m...
I've been so worried about my dogwoods b/c they have this powdery
mildew and two of them are LARGE, old trees. In case anyone else
is interested, here's what I found out about it (from
http://www.ca.uky.edu/agc/news/1999/May/pmildew.htm):

The most severely affected trees could be wilted and brown by
late summer and the youngest leaves may be distorted and curled.
"Although it would appear to weaken trees," Hartman said.
"Powdery mildew does not appear to be lethal. We have observed
that under high disease pressure, flower production is decreased
the following year."So, what can Kentuckians do to help out the
dogwood's plight? Hartman said to avoid cultural practices that
stimulate succulent growth, such as applying nitrogen fertilizer,
heavily pruning and excessively irrigating. Also, apply mulch
over the root system, prune out dead branches, and provide good
air movement and light penetration by judicious pruning of nearby
vegetation.

So, I may wait until early spring next year to spray the affected
trees. I hate that they won't bloom tho.

Jw