In the warmer areas where humidity is high, powdery mildew and other fungal and bacterial diseases will grow on everything that has matte leaves or is hairy like tomatoes, cucumbers, squash, beans, pumpkins, and most of the western vegetables. It depends on where you live. If you do live in a humid place then you need to choose cultivars that have the disease resistance you need and have a regular fungicide program for when the weather conditions exist that encourages fungal growth. The spores are in the air, so it is hard to avoid it. Your location is not indicated but if you are in the U.S. you can look up cultivars recommended for your location. It is also a good idea to include your location and zone in your profile.
Happy gardening in Hawaii. Gardens are where people grow.