I have a long (8ft+) butternut squash vine that seems to be healthy (green leaves) and producing both male and female flowers. It grew all summer and is still alive and healthy. I see many nice female flowers (the baby fruit part is 2--3 inches long) get pollinated; I even hand-pollinated a few flowers myself. However, after pollination, they all turn slightly yellow, shrivel, and rot (see below).
I live in zone 9b and it's starting to become cooler, so I don't have much hope for this season. What can I do better?