Thank you for your question. I am unable to find any research on a darkening of bark on ficus. I’m afraid the photo is not clear enough to see whether it is a fungus, which might exhibit spores. What happens when you ‘wash’ it with a damp paper towel? Does anything come off? Could you send a photo of the entire plant, as well as a closeup of the stem? Thanks!
Thank you. Well, they might be fungal spores. We’d have to examine under a microscope to see clearly. Your tree looks otherwise healthy. I would suggest getting some Neem oil, and spray it on the gray tissue. Apply per package directions. It is a fungicide (and an insecticide and miticide), and will not injure the plant. If the discoloration continues, you can take some samples to the Extension offiice once they are again open to the public. Good luck!
Thanks for your advice and for your unbelievably quick response!
You’re welcome! I’m retired—but quarantine doesn’t hurt, either!
MG Jean Natter suggests the plant has scale (which I cannot see!) Here is an Extension article about this pest and how to control it: https://aces.nmsu.edu/ces/yard/2003/090603.html Neem oil is a horticultural oil, but you might want to try the cotton swan physical removal as well. Good luck!
I read info on the link you sent, however, nothing is sticky. Could it still be what was suggested in that article?
Without being able to see it more closely, we’re limited to a triage of the most common pests. There are several families of scales, and it would require far higher resolution to tell which your plant has. Each secretes different amounts of honeydew. You can read about the variations here: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html
Jean was able to enhance your photo to show the scale. She says: “Look for the 2 tan oval shapes, the young scale - the largest is shown in profile just left of the “Y” in the green twig, the other is a bird’s eye view and is farther to the left.” “They’re literally sucking the life out of the tree.” What you wiped off is the sooty mold that grows on the honeydew.