your YEWPINE is virtually pest and disease free, so what that is I have not got a clue, I surgest that you PM Bluespruse after christmas , he is our expert on this sort of thing,and will proberly put your minde at rest, by the way you proberly know that it is common for them to grow to 20 feet and they can grow to 30 or 40 feet unless you have maki which dose not grow quite as big or quit as fast,but do allow Bluespruse to have his christmas befor you contact him, all the best.

Sounds like algae? This would normally be brought about if the plant was in high humidity or at least a conservatory with dampness.