Thanks for the question regarding your pumpkins.

Spotting and curling on pumpkin leaves can be caused by several factors, including pests, diseases, and environmental conditions. Based only upon the picture, I cannot give you a specific cause. However, here are some of my thoughts:

1). The condition you are observing could indicate the presence of aphids, spider mites, or squash bugs.

2). With respect to diseases, the symptoms you are seeing could be due to Powdery Mildew, Downy Mildew, cucumber mosaic virus, and/or bacterial wilt.

See the following for information about these and possible remedial actions:

https://extension.umn.edu/yard-and-garden-insects/aphids

https://vegento.russell.wisc.edu/pests/squash-bug/

https://www.gardeningknowhow.com/edible/vegetables/pumpkin/powdery-mildew-on-pumpkins.htm

https://www.maine.gov/dacf/php/gotpests/diseases/factsheets/downy-mildew-purdue.pdf

https://www.canr.msu.edu/news/viral_infections_in_traditional_pumpkin_varieties

https://www.smartgardener.com/plants/1927-pumpkin-triple-treat/diseases/782-bacterial-wilt - :~:text=The first sign of this,reduce problems with this disease.

3). Various environmental factors could also cause damage to the leaves. These include over watering, under watering, exposure to cold temperatures and/or high temperatures.

As a starting point, please look these sites over and compare the images they contain to what you are observing on your pumpkins. Perhaps you could narrow the possibilities down a bit?

Having looked these sites over, there are three routes that you might follow:

1). Do nothing. Keep the plants watered. See what happens. If things keep getting worse, then consider replanting.

2). Rip everything out now without knowing exactly what is causing your current situation.  New plants may or may not show symptoms similar to what you are now seeing.

3). Send a sample of the leaves to the Plant Disease Clinic of the University for testing. In this way you could confirm either the presence or absence of various diseases. If you go this route, contact the clinic ahead of submission for information on exactly what should be submitted. See:

https://pdc.umn.edu/

I wish that I could be more precise as to a causative agent, but the large number of possibilities precludes this.

Good Luck. Please get back to us with any questions.