Pumpkin Question

We have pumpkins growing (that we didn't even plant!) and would like to see them grow. However, we have noticed a mold/mildew looking white growth that is killing the leaves. I know this isn't a great explanation but any ideas on what we could do? The pumpkins are growing out of my brush pile on the back of our property. It seem the leaves with the problem do not get as much sun as the rest of the plant. [img]/forums/images/icons/confused.gif[/img]