Q.Tibouchina Dying One Stem At A Time
Hi: I have T.urvilleana that have thrived in plastic pots in full sun in Houston until about a month ago. They’re in an azalea mix, and I’m careful with the water. Yet, the plants are dying, but it’s not uniform. One entire stem dies slowly, while the others keep growing and blooming for now. I’ve seen this happen with this species in the ground as well. What the hell can I do? Please post Dave Sherron in Houston

Certified GKH Gardening Expert
Typically, this is attributed to two different diseases. Phytopthora root rot and Verticillium wilt will be most common. Here are some articles that will help you to deal with these situations:
https://www.gardeningknowhow.com/plant-problems/disease/what-is-phytophthora.htm
https://www.gardeningknowhow.com/plant-problems/disease/verticillium-wilt-treatment.htm