Pumpkin problems

[Charlie]

Hi, total gardening beginner here! I've run into a problem with my pumpkins (first of many I'm sure lol) and I was hoping someone here would know what to do because I'm totally stumped.
Basically the more mature leaves are turning yellow from the tips and dying. Not sure if its because they're in pots still (I haven't been able to plant them out yet) or if it's something else I've done?
Any advice/ideas would be greatly appreciated!

 

[Rajesh Sethi]

Not sure looks like mildew

 

[zigs]

Looks more like sun scald, might have been the heatwave we just had.

 

[Fuzzygreenery]

I think that's just scalding from the sun. But heatwave's over, party's over

 

[Charlie]

Thanks for the responses guys! If the problem was just caused by the heat that's a big relief, so long as it doesn't get that hot again at least. I didn't even know plants could get sunburn, shows what a beginner I am!