Sounds like the lack of rain before and possible the competition from tree roots could be the cause.* I used to have Virginia creeper too, but in my small garden it began to take over and I had to eliminate it.* It's lovely though, especially in fall.* Glad to hear you aren't going to try and save that tree.* Don't forget to use it for pruning practice.* :)*
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.