what are these spots on my grape vine?
I planted this thing, which i believe is a thompson seedless, probably 15 years ago on a whim and have not cared for it at all, despite this it has grown fantastically. A few years ago i noticed these spots on the leaves (could have been going on longer and I just never noticed). The grapes always turned out fairly small and a large number of them would seemingly just turn into raisins before they were done growing. My best guess was some sort of powdery mildew so this winter I tried to actually start caring for it and pruned it back for the first time. For the first few months of this growing season it looked like the spots were gone however they seem to have developed again. Anyone know what it could be and or how to fix it?
it is planted on (and has essentially consumed) a trellis on a south facing wall in southern California so it gets about as much sun as it could possibly want.
as for watering, I think I sprayed it with the garden hose once a decade or so ago, and there is a sprinkler probably 10 feet away that sprays within a few feet of the base of the vine for probably 10 min a day.
the soil is just the dirt in the ground, i'm no expert but based on what i've read it seems like I have a pretty good type of soil for grapes here. As a testament to that the vine has seemingly self propagated twice.