I have squash and zucchini growing - they are about 3 weeks old from planting. They have several true leaves, but half of them (the older leaves) turned yellow yesterday. The weather was 95 degrees yesterday, and I watered them in the morning in anticipation of the heat.

They are planted in raised beds, with a loose soil with plenty of organic amendments (worm castings, compost, decomposed manure). While I had one inch of mulch already on the soil, I decided (when I got home yesterday) to spread out more mulch to help protect the roots better. Does this sound like the plants just got too hot? They leaves aren't sagging, just yellow and curling on the edges. I've also noticed white trails left on the cotyledons - I assume left by slugs?