Pictures would help, it's easy to say they are too wet but the reality is that the information provided is insufficient for proper analysis; In ground or containers? Soil amendments? Fertilizers? Sun or shade? Geographic area, swampy, coastal or highlands? Watering habits? Insecticides or pesticides? Mulch etc....

On the zucchini, the blossoms do not fall of of zucchini as quickly as they do yellow squash. You may have to go out and pick them off when they fade, and put a little baking soda on the ends of the fruit to keep them from getting end rot.

If the fruit is rotting from the blossom end, add some calcium to your soil. Spray them with a tablespoon baking soda to a gallon of water with a squirt of dish soap (to make it stick to the plant). That should kill most of the fungus.

Squash are hard if you have a wet spell. They don't like the humidity.