Hello Patrick, happy to help.

Has there been any herbicide spraying nearby recently? Even if it seemed okay when a neighboring property was treated with an herbicide, if it was windy, the spray can be carried far. If the yellowing is occurring on one side of the the plant and if other nearby plants are affected on the same side, that may indicate herbicide damage.

I'm not sure there's any kind of herbicide that would be considered food safe for produce, but if you're only growing pumpkins for use as Jack-o-lanterns, then give the plant extra watering attention until it resumes healthy growth. Refrain from any fertilizing until you see healthy new growth.

If you think that's not the issue, feel free to reply, provide an update on what you're seeing, and I'll get a veggie expert to help out.

Good-luck!

Hello again.

I'm a little wary about the spray jumping to the other side unless the breeze came around the corner of a structure or there were nearby trees that caused the wind to vary in direction; then that could happen. I'd say now, watch and see if the plant recovers. More leaves may turn yellow as the poison's effect winds down. With your added watering attention, it would be a good sign if it starts new growth.

Incidentally, I have to say that I was mistaken about not fertilizing. Feel free to fertilize as you normally do for your pumpkins (no more than the usual, though). That along with the watering (when it's not raining so much) should help your plant recover.

Best of luck!