Have several nice squash plants going. They are flowering beautifully and there are several small sqaush forming. For a few days they look perfect; great color, firm, plump. Then when they get to be about thumb size they begin to get squishy feeling, turn brown on the end away from the plant and shrivel up. The plants themselves look great. There have been a few small slugs but putting out some beer seem to help get rid of the. There are no other signs of bugs or diease. Any idea what I can do to stop this?

Thanks in advance.