Squash they will mold on the vine if the ground stays damp all the time under the large leaves. That is why I seldom water my squash unless it gets really dry, and it is best to water in the morning if you are going to do it so the surface has a chance to dry with the sun. For some reason, zucchini don't seem to do this, but I always get some yellow squash that mold. It seems to cut down on it some if you cut them off as soon as you see any mold on one and not let it get to the fully covered fuzzy stage.