Lawrence Akutagawa wrote:

Well...just in case you don't know...if you just let peroxide after being
opened sit around unused (like for a year or so), it turns into plain
ordinary water and loses all its potency. Whence it needs renewing (like
every year or so)....





Hydrogen peroxide is used commercially for fungus/mildew/bacterial
control on plants. There are two formulations (trade names) available:
Oxidate and Zero-Tol. Oxidate is labelled for vegetable crops and
Zero-Tol for ornamentals. I don't see much difference between the
formulations in the listing of ingredients. They're basically 27%
hydrogen peroxide with some peroxyacetic acid added as a stabilizer. It
comes in 2.5 gallon containers (smallest size I've found, about $120).
One of the demonstrations of the product is a fish tank with an 0.1%
solution and fish (live). Don't try that with your bottom feeders,
because it kills algae, which is a good part of what they're eating.

For use on plants, it is diluted by a factor of 100 to 300. The stuff
you can get in the grocery store is about 3% concentration, so it should
be diluted by a factor of about 10. If you go to a discount
grocery/pharmacy, a quart of the 3% stuff costs around 75 cents, for
about $3/gallon, significantly cheaper than the original post. At that
price, it's cheaper than the commercial stuff. Commercial users, however
don't have to deal with the 100 quart bottles for the equivalent of
their 2.5 gallon container, and that (plus the stabilizing additives)
is worth the price difference.

I have used it for several years and one container lasts me about 2-2.5
years before I've used it up. It is easy to check the activity just by
adding some full strengh liquid to an organic soil. It will fizz. (I
occasionally check this accidentally by spilling a bit during mixing).
(This is of course a qualitative test, not quantitative). I have not
noticed any degradation of the product after the 2.5 years of storage.
(This is the commercial stuff, not the home-use stuff; the home-use
stuff is so cheap you can afford to buy a new bottle each year. Use the
leftover stuff on your teeth.)

The product is effective against powdery mildew and anthracnose. An
advanced case of powdery mildew takes several applications. A really
advanced case might not be worth curing, since the plant is probably too
heavily damaged by that point.