The photo was taken last week. Platanus x Hispanica is a white banana. The target is also called "oidium." It's mostly a spring disease. Seeing the disease in force indicates that we still have a spring environment. It originates from a fungus that needs some moisture, but especially when heat and drought and rain de-heat each other. It's a white mold that spreads on the leaf superficially. If you see this somewhere, you're being given the alarm for the orchard: watch out there the pumpkins, zucchini and pickles, they're the same white ones. Treat with sulfur, propolio, dairy or bicarbonate.