Wilting in heat despite generous water
I'm having this happen with both summer and winter squash. As soon as the day heats up the leaves start to wilt. On a particularly hot day they end up looking like goners. When the sun gets low they perk right up, but the quantity and quality of fruit suffer.
The amount of water in the soil seems to have nothing to do with this. I've seen plants wilt while being drip-irrigated over a period of hours. Nor is the soil poor at retaining water; I believe it has a moderately high clay content, and is heavily amended with compost.
Any suggestions on the cause and cure of this problem?