I have a Big Max pumpkin plant that sprouted in late June and has since taken off, with a lot of leaves, flowers, and pumpkin buds. I have been fertilizing it fairly often with a pretty balanced fertilizer (little less N than P or K, I don't remember the exact ratio).
I live in central New Mexico. This plant did fine with the hot temperatures in early July, then we had two weeks of cooler temperatures with the monsoon, and now that highs are in the 90's (Fahrenheit) again, starting around 11 am the leaves get limp and shriveled as seen in the picture below. It starts with the leaves at the end of the main vine, then leaves at the ends of the other vines, then the central leaves get a little droopy too.
With the leaves behaving this way, I now water in the morning, at noon, and in the evening. The leaves return to normal in the evening and are normal throughout the night through the next morning.
With how many pumpkin buds and flowers my plant is producing (way more than I want; I pruned things a couple of days ago), and how large it has grown, I have very recently switched to a 0-10-10 fertilizer.
What can I do for my plant to keep the leaves from getting so droopy and limp in the afternoon? The dirt around it is always at least slightly muddy with the watering schedule I give it. I notice no difference in the leaves after the noon watering. Is the plan just too large for the roots? Should I prune some of the vines?