Myclobutanil is Nova. I suspect your timing wasn't so good as Nova is a systemic and only needs about an hour drying to be waterproof. Sulfur is for synthetiphobes and really has no place in my disease control programs here in the humid northeast. Great for reducing pH though. You've already done some research so you know that sulfur is only a preventive and must be on the plant before it rains and reapplied after. On wet years this is almost impossible. The SIs like Nova will usually irradicate an infection if you get there within a couple days. When was your first application last year? I only need a couple of applications of Nova to control all my grape issues. The first I make 2 weeks after my apples have lost their petals and the next 2 weeks later. All I use is Nova unless I have blossum worms (not real name). The little worms that fit between the leaves of emerging shoots which can eat the blossums. Coffee hasn't clicked in and I'm to lazy to look up.

From what I am reading, one of the types of powdery mildew actually prefers hot and dry conditions and hates to get wet. This year would be the perfect conditions, since it never rains. http://westernfarmpress.com/powdery-mildew-melons "P. xanthii prefers dry conditions, with relative humidity of 50 percent to 90 percent for spore production. Although relative humidity doesn�t often reach those levels consistently in the desert, dense foliage and irrigation may create microclimates that favor powdery mildew development. However, presence of water on the plant surface may wash off and/or inhibit the germination of the fungal spores. P. xanthii grows on the outside of leaves, first appearing as a small white growth, eventually becoming a layer of white fluffy mycelium and spores on the upper or lower side of leaves. P. xanthii does not grow systemically (able to spread through the inside of the entire plant), instead this fungus prefers to produce mycelium on the outer surface, and penetrate the leaves with specialized feeding cells called haustoria. The fungus will then produce spores in the absence of free water; spore production gives the leaves the characteristic powdery appearance. The spores are spread to new infection sites by wind. After the fungus has extracted nutrients, the plant cells die, causing the leaves to become brown and papery. Fruit produced by the plant may accumulate less sugar, have reduced yield, and shortened production times."

This is why people should never read medical texts. Pretty soon, you convince yourself that you have every disease mentioned. Baldo should be helpful with this, but I can tell you that the marks of downy mildew are more commonly bordered by the veins in the leaf, so that you get something of a Stained Glass effect (of course, eventually the leaf DOES turn yellow and fall off). On the canes, the discolorations are most commonly a sort of purple-ish color, darkening to black, and eventually becoming necrotic. I'm not saying it's not possible -- but from our experience here, I think it is unlikely. But -- just suppose it WAS downy mildew. Would that be a death sentence for the plant? Not necessarily. When, in the early 90's (I think) we did have downy mildew here, we rushed out and bought the recommended chemical. It was to be used as a drench. Extremely powerful stuff! You used about a tablespoon-full in something like 30-G water. The stuff melted the surface of the plastic measuring spoon, and the first roses we used it on died very quickly. We then re-thought the problem, and in the end used what the avocado farmers here were doing for the closely-related fungal organism that causes avocado root rot. Fresh manure, piled around the infected plant, out to the drip line. THAT brought the situation under control. I suppose it WILL always remain in the plant, but the plants appeared to strengthen to the point where they were able to fight off the effects. And I'd far rather deal with a little horse poo, than with a chemical that melts plastic spoons. Jeri

You must not be very far from here, and we've had awful weather this growing season... more than 8" of rain in June. I lost half my tomato seedlings before I could get them in the ground -- and naturally it's the first year I didn't grow lots of extra plants! :( My cukes are growing better than ever, however, so go figure. Read this and you should feel better: dealing with downy mildew If it were me, I'd trim away the BAD leaves and just try to keep water off the leaves in general. I'd allow the leaves w/ minimal damage to stay because they're still feeding the plant and shading the fruit as they are now. The DM won't survive our winters, so even if you keep the plants and they fail miserably, at least you don't have to worry about any residual holding over until next year. All you risk is your watermelons -- but you're at risk as long as the wet weather continues. Good luck! I lost all my beautiful cukes to bacterial wilt last year, so know the pain. PS: I try to stay organic too. One of the nicest homemade organic fungicides is cinnamon spray... man that smells good. lol!