Milky patches of sticky substance in my plant

Hello, I hope this is the right forum for this post.

Last winter I cut this plant practically to the ground because it was invaded by this same critter (fungus?). Before doing that I used a product containing Potassium salts of Fatty Acids (Safer Brand for Organic Gardening) to try to kill whatever was ailing it, and did not succeed. By the way I freaked out at the warning label, really? For Organic gardening? Lots of warnings of all kinds...  Now, almost six months later, with lots of healthy new growth on it, I realize there are leaves at the very bottom that have this powdery/sticky substance (picture attached).
I have not been able to see any bugs or critters crawling on the plant, someone had mentioned thrips but I was never able to identify them. I live in Northern California. Any suggestions? Thanks in advance.

How dry is your climate? My first thought is powdery mildew, which can be dealt with in a few different ways. Unfortunately I cannot find the threads talking about it. I think in one case, you spray milk on it. Another option I think was using aspirin. I'll see if I can find them and link them here. You can see if you think it matches the symptoms

I expect it is probably powdery mildew, but it reminded me of this thread on crystals on sweet potato leaves: https://permies.com/t/108402/Sweet-potato-leaf-weirdness which apparently is oxalates crystalising on the leaves. Is it just on the older leaves? Does it wash off with water?

Here is my recipe that I had great success with for powdery mildew:

https://permies.com/t/93537/toxic-Fungicide#1423936

Grape vines here have problems with powdery mildew, so I went looking for possible solutions, having heard of spraying with soap.water or something similar:-  Make sure to test on a small area before going full on!