On Wed, 23 Apr 2003 10:59:57 -0700, paghat wrote:

sniped
Good advice but a few plants, such as beebalms, clean-up & trimming just
won't stop powdery mildew, & a little "preventative" spraying of dilute
milk or of neem oil seems to be the only thing that assures these plants
are as beautiful at their seasons' end as they were at beginning & middle.
I've found skim milk effective in stopping powdery mildew from showing up
in the beebalms.
sniped
"New succulant growth" is a common phrase in overviews about powdery
mildew. But I never see this problem except toward autumn when humidity
rises & plants are no longer putting on as much new growth. It's
wearing-down deciduous leaves or die-back perennials that are most
susceptible (I don't grow things like squashes & cucumbers, so perhaps
those have earlier "new succulent growth" problems, I dunno, but for my
plants it's exclusively something seen at the end of growing seasons). In
my garden at least the only plants ever effected have been beebalm,
honeysuckle, & the very lowest leaves of just one of our deciduous
azaleas. The azalea requires no treatment at all, as the powdery mildew
attacks only the lowest branches that touch the ground, & only at the time
the leaves are about to fall anyway; when I'm industrious I pluck them to
discard just before they fall, but even that doesn't seem to be essential.
The beebalms are another matter. I can get an extra month of beauty out of
the beebalms that will bloom into autumn if I treat them preventatively.
If I can keep the beebalms from getting mildew, then there is none to
spread to the honeysuckles which were never afflicted before the beebalms
were planted. When a gardener seems to have excellent "preventative" luck
there's always the possibility there never would've been mildew anyway,
but it really seems to me that if beebalms are milk-sprayed very
occasionally leading up to autumn, the mildew just never appears. And by
now there are several horticultural station findings that make this happy
outcome proven to be more than random gardeners' luck & lore.
sniped
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.

Dr. Bettiol in Brazil used diluted whole milk, but other studies used
either whey or 1% milk, all with excellent outcomes. Last year I used skim
milk very effectively, but when I later saw the actual published studies,
they found that a little milk-fat improved the effect (though milk whey
was the greater factor). Last year, Peter Crisp of the University of
Adelaide (with follow-up studies at Cornell, by Dr Wilcox et al) seems
definitively to shown that dilute milk is the superior treatment for
powdery mildew (Crisp's study was on vineyards). Crisp said that milk fed
the organisms that stopped the development of mildew spoors; other papers
say it is changing the pH range just enough to retard the spoors. For
other sorts of funguses such as black-spot on roses, the Cornell study
shows that milk was not a good choice, but what did work best was
horticultural oil mixed oil with a tiny bit baking soda. This was highly
effective for BOTH powdery mildew & blackspot. But because neem oil harms
bees & ladybug larvae, I prefer milk, & I don't grow much of anything that
is susceptible to blackspot except a single large rose that I hand-pluck
for any blackspot, easily done when it's the only plant that ever gets it
even a little.

Most alleged values of compost teas have been wildly exaggerated by a new
industry designed to suck money out of gullible gardeners' pockets,
selling them all kinds of crapola that while functional is NOT more
effective or better than actually cost-effective techniques, & the
targetting recipes for narrowly derfined purposes are 95% flimflam
designed to to sell easy marks even more unnecessary crapola. But finally
some credible research is indicating that compost teas sprayed all over
plants (as opposed to in soils) feed the bacteria that compete with & eat
mildew spores in much the same way as does milk & whey. All the studies
are so new that this information really only reached the larger gardening
community between 2001 & 2002. More horticultural station studies are in
progress right now, but there's already firm agreement everywhere that
milk works extremely well without altering the flavor of crops & by
adhering to organic gardening practices. The newest question seems to be:
is a dousing of compost tea even better (at feeding the beneficial
microorganisms that devour & outcompete the mildew spoors). Crisp by the
way said that many Average Gardeners had been using milk for many years
for this purpose (long before the first revealing Brazillian study) but
until it reached university horticultural station researchers it was just
one of those unproven Lore things. Crisp didn't even mention the Dr.
Bettiol's earlier study, but knew of the milk treatment as used by people
with houseplants. Crisp seems instead to have made a list of ALL the
existing alleged treatments for powdery mildew, even those recommended by
folksy practitioners, & tested them all. Milk was the hands-down out-front
winner.

Powdery mildew spores are not highly competitive & ultimately just about
ANY treatment works to some degree (except sulfur at low temperatures).
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 only got to try the milk treatment last year. When the beebalms became
mildewed I cut them to the ground, discarded the foliage, & as they're
fast growers they rapidly grew back with me giving them preventative
sprayings of dilute milk. The mildew did not return. Because of the
Brazillian, Cornell, & Adelaide studies, I'm convinced that my good luck
was not just one-time-random-good-luck, so I am using milk as a
preventative this year, with the expectation that I may not see the mildew
at all.

This is great information. Thanks for clarifying this for me. I have a few
customers who would like to try such a spray but I've never been able to
find concrete evidence on it's effectiveness and use. Have these studies
been published on the net? If so, could you point me to them? Thanks for
your time....
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