All my squash leaves are turning yellow! The cucumber met its end several days ago, yellowed, wilted, and ended up in the trash. Now the two different types of zucchini, and a pumpkin are following suit, leaves turning yellow, and developing little light brown spots. I'm hoping it doesn't happen to the three plants I have left--another zucchini and two cukes. I noticed in the photos I took that there is a bit of white, so could this be mildew? Overwatering? (Not me, the darn rain, what can I do...?). Bugs? I don't see anything crawling on them or any evidence of anything. Arrgh!

My raised beds are in what would be full sun, if the rain would ever quit. They are filled with brand new "garden blend" which is a mixture of aged compost, bark, topsoil-y stuff that was recommended to me by the bark and landscaping place. I did spray them with miracle grow a couple days ago, to see if that helped the yellowing, but so far, it has only progressed. The soil is ridiculously well-draining--I don't know how I will keep them moist when the heat comes on. So the plants aren't sitting in a swamp by any means, we have just had non-stop rain for several days, so...

Any ideas? I am new to gardening, so I have no idea what to do! Thanks!