Courgettes, Squashes, Pumpkins etc

I have quite a few of these growing away in the greenhouse, around half of them have dried out leaves..look scorched..dry and whitish.

The greenhouse maintains a good temperature is ventilated daily to allow air circulation and to keep it cool in hot sun the plants are neither over of under watered. The plants are in direct sunlight, should they be perhaps shaded a little or placed somewhere so they only get half a days sunlight?

Steve...

 

The plants sound as if they are scorched Steve.
I think they would do much better outside.
I'm in Perthshire and they get on fine outside for me.

 

I think it might be that too; I have a pumpkin that I've started off inside near the windowsill. It's been fine but after these last few hot, sunny days the leaves are going lighter colours and don't look so happy (especially the young leaves).