Sounds like bacterial wilt disease, which is partial to vining crops and which has been the bane of my melon patch this summer as well. Actually it eventually got most of my melons, cukes, and pumpkins since I had them so close together on the same trellis. There's not really much you can apply that is safe for vegetable gardens. About the only thing you can do is prune affected branches and destroy them. Also, try not to handle your plants when they are wet, as this tends to spread the disease. If a plant ever gets sick enough to die completely, remove it ASAP. Make sure to dispose of diseased branches and plants in the garbage, not the compost pile, and in a plastic bag if possible. For next year, try to find a disease resistant variety if possible, and make sure to rotate your plantings; don't plant your pumpkins in the same spot again next year.
