Angelo & Yvette wrote:

Peter Cundall, the presenter of Gardening Australia, also presents a
radio show. Below is a link to a story on that radio show regarding home
made white oil.
http://www.abc.net.au/brisbane/stories/s780287.htm

Also try http://www.thewaterwisegarden.com/bicarb.htm
Water wise garden has a recipe to treat powdery mildew and blackspot, plus
one for white oil.

I've tried the bicarb and it does help, but I read somewhere it's not a
good idea to use it a lot because of the sodium it adds to the soil.

Jane