pateras

My squash plants have gotten some white substance of some sort on them. I'm assuming this is mold or something (it's too dense to be bird droppings, even though the garden is right by my bird feeder). What can/should I do about it? It spreads more and more every day, so I was thinking it might be prudent to cut off the infected leaves, though most of the plants are infected, so that seems a bit drastic.