Hi there Norman,
I find the leaves can go like this if water dries on them, it could be scorched, or the other watering problem of mildew. It won't effect your pumkins unless botrytis is present.

Happy gardening.

Thanks, will try only watering the roots in future..don't think botrytis is present cos of the number of marrows the plants are throwing out....any tips on growing eNormous marrows???

All plants, not just produce, should be watered on the ground/on the soil/on the roots because to water over the top of the foliage invariable causes various different problems.
Also, watering the soil means less water consumption and in these days of rising utilities that can only be good !