Some of my vegetables (melons, squash, pumpkins) and my marigolds are dying. The leaves are kind of discolored, dull looking like they have dust on them. They just dry up like they have burned from lack of water. Any ideas from the description and is there anything I can do to stop this? They are planted in different areas of the yard and the marigolds are watered with culinary water. The vegetables are watered with irrigation water. The vegetables etc I planted last year in the same areas did fine. The only thing I changed is the addition of some compost and a little fertilizer. The tomatoes I planted with the same compost and fertilizer are doing good.
This sounds like powdery mildew. It may be worse this year because you are growing a different variety. Powdery mildew is difficult to control on melons after it has covered the tops of the leaves. (It starts as small lesions on the bottoms of the leaves.) Most plants, like marigolds, can get powdery mildew.
Here is some more information on powdery mildew on melons and ornamental plants and how to control: