Hi friend of Baikal.
I have used hydrogen peroxide for powdery mildew on the recommendation of a friend. It has to be applied frequently to work well.
Here is a link to a chart with dilution rates.
http://www.using-hydrogen-peroxide.c...-peroxide.html
And here is a thread on this topic I found by searching this forum when I had problems.
http://www.tomatoville.com/showthread.php?t=33102