paghat wrote:

...I think I'm on solid ground suggesting that horticultural oil or diluted
milk are best for effectiveness against powdery mildew, & the least
chemically invasive. Milk diluted to as weak as 1 parts milk to 9 parts
water were AS GOOD as fungicides in the 1999 Brazillian study that first
proved milk was excellent for stopping powdery mildew. In stronger
concentrations (diluted to one-fifth to one-half) the efficacy increased
-- hence was vastly superior to even the best outcomes ever seen from
copper-based & sulfur-based fungicides....
(snip)...
...The trick is to increase the healthful bacteria on & around the plant. Any
chemical treatment that intends to toxify the environment against fungal
development is less effective than treatments that increase the healthful
microorganisms overall. That would be milk or compost tea. Copper &
sulfur fungicides interfer with fungal enzymic activity -- but also
interfer with the enzymic acitivity of healthful soil funguses & other
microorganisms which are the greater factors in keeping mildew at bay...





I have heard these things (milk, baking soda) as garden lore for some
time but I'm happy to see that someone has taken the time to do a real
test and that it looks promising. For the last couple of years I have
been treating my zinnias with ZeroTol, a commercial fungicide (basically
hydrogen peroxide, an oxidizing agent, acceptable to the organic
community). However, this year I will be trying milk on some plantings
and ZT on others to try to compare the result. The powdery mildew can
also be a problem on late zucchini and other cucurbits. Given the amount
of time I (don't) have to keep records (I can just barely keep my spray
log up to date), I doubt that this will be a real scientific study, but
I hope at least to get an overview of whether it works or not for me.

Email me next fall and ask me how it went.