Two of my pumpkin vines have developed a disease that strongly resembles downy mildew on the upper side of the leaves. There are yellow patches that initially appear, the centers of which turn brown, and as they spread the leaves die. Also noteworthy is the fact that the edges of the leaves curl upward. Uncharacteristic of downy mildew however, there isn't any white patches underneath the leaves . . .

Any input would be appreciated