Powdery mildew is a rare fungus type in that it doesn't need, or like wet leaves. The spores will actually burst if forced to soak up water. Peeing on the leaves at night may well work as it keeps the leaves wet over night. Then again one might be just as successful spraying the plants with water after sunset.

People have long suggested various controls for powdery mildew that seem to work OK for some and not at all for others. Water plus milk, water plus baking soda, water plus oil, water plus soap, water plus...

It may be it's the water that actually has the effect on it.

Most all organic control, especially the homebrew stuff, works before the mildew shows up by hindering it's ability to get to the plant.

After the fact application for control may slow, but it's usually too late for proper control by then.

There have been studies with water/milk/oil homebrews, but almost all of them show limited/spotty value and generally only as a preventative measure, not a solution to something already happening. Also, then tend to have to be applied many times per week for maximum effectiveness.

Not a fan of the stinkiness of urine or milk sprays for PM. Peeing on the compost pile is actually pretty useful though. Marking your territory with urine usually just ends up with the animal peeing over your scent to show that it is challenging your ownership.

Best way to control PM seems to be planting resistant cultivars and as noted, spraying as a preventative. I've given up on melons here in LA because PM always strikes before I can ripen them and I germinate squash ever 6 weeks or so in summer because PM will always take down the vines within a few months.

A professor at Cornell developed a product called Green Cure. It's potassium bicarbonate instead of sodium bicarbonate (baking soda) with some proprietary wetting agents. It's approved for organic production and said to control downy and powdery mildew as well as anthracnose,botrytis,alternaria/cercospora/septoria leaf spot, scab, phytophthora, botrytis, fusarium wilt, and blight. Baking soda works on powdery mildew but this stuff is supposed to work better and the plants like the added potassium and with salt sensitive plants you don't have the issue of the sodium.