Could this split, soft pumpkin stem be squash vine borer damage?

It’s a reasonable suspect, especially if you see small holes or damp, sawdust-like frass around the damaged area. Check along the stem for fresh frass and eggs, which can be laid singly on stems. A split or mushy patch by itself isn’t proof, though, so look closely before cutting.

If you find a larva, you can make a small, careful lengthwise opening near the damage and remove it. Try not to cut through the stem. Then cover a healthy section of vine at a node with soil, which may help it form extra roots. A badly damaged plant can still decline, so keep an eye on the leaves and fruit.

Don’t assume the pumpkin is lost just because one section looks rough. If the vine is still firm beyond the damaged spot and the leaves stay healthy, it may keep feeding the fruit. If you do find a larva, removing it may help, but opening the stem too much can cause more damage, so keep any cut small.

Fruit that is intact and has no rot or soft, spoiled spots is generally fine to eat. If the vine wilts or dies before the pumpkins are mature, the fruit may not finish ripening normally.

For next season, rotating squash to another area and clearing out old vines and plant debris can help reduce the chance of pests carrying over, but neither is a guarantee. Row covers can protect plants while they’re young, though they need to come off for pollination unless you’re hand-pollinating. Check stems regularly for eggs and remove any you find.

If the damage is only on one part of the vine, you can also watch for roots at nodes farther along. A plant with healthy rooted sections may be less dependent on the injured part.