You could try spraying the biological antagonist Serenade, which in my experience works pretty well against powdery mildew even as a curative agent so it would definitely work as a preventative. It's less effective against more aggressive fungal diseases like white mould.

I know the answer to this!!!! I am soooo excited!!!!! :D :D :D Ok, milk. You want to dilute the milk so it is about 10-20% of what you have, definitely less than 30% or it will make something else bad that you don't want to happen happen, and spray it on every week or two (don't do it too often or the plants will be unhappy), and this will prevent a lot of powdery mildew. It is more of a preventative measure but you can try it if you see just a little, well, you might as well try it when you see a lot, but it's better to start before you see it at all. This is probably the only answer I will ever know, thank you so much :D

g'day slashy, manage is about the best way to treat it, that management can start with the planting conditions and position as well ie.,. in well drained medium and in full sune with plenty of aur movement breezes etc. it also starts with your watering regime wetting the foliage at watering time makes for ideal p/m conditions as does watering too later in the day so that any moisture on the plant can dry off before nightfall. water on the root zones only. my zuce's and similar can get some p/m toward the end of their life when they are at a low ebb, suppose like us that is to be expected, so good healthy soil will mean a good healthy plant for as long as possible, the health of the soil comes from the trace elements and all we can do in that department is to feed the soil encourage earth worms (not desirable in pots/containers) and soil oraganisms. as said it is an air borne thing that needs good moist conditions to thrive, try the milk spray (we have a recipe on our site), ther is a product out all organic that helps with the plants trace elements, you would need to e/mail me for the link (commercial links not allowed here), that could help a lot with container plants? i compost all my plants p/m or not once it is covered (in our case we just break the plant up and mulch it right where it stood cover it well with mulch and it breaks down in a couple of weeks or so. we continually feed our soil by using green type mulches ie.,. sugar cane mulch and spoilt pasture grass/lucerne mulch, as well we feed all our rottable kitchen scraps to the gardens so the worms and bacteria can process it right where the plants need it. it amy help to remove affected leaves as they occur? len Here is a link that might be useful: len's garden page

what is milstop MilStop is a broad spectrum, contact foliar fungicide that controls a variety of diseases on plants. You can search it by name to find vendors. Other similar products are also available at most garden centers. I also linked below an excellent resource guide on p. mildew that offers additional info on prevention and controls. Hope it helps. Dave Here is a link that might be useful: Powdery Mildew on Vegetables