Doug fir disease
Diagnosing this may take some back and forth Q&A.
It appears to affect only the current season's growth, correct?
Do you see it on larger trees, higher up in the crown?
Have you applied herbicides in the area around affected trees?
Branch tip dieback can be caused by Douglas-fir twig weevils. If it is twig weevil, the twig as well as needles will be dead and there will be signs of weevil entry/exit or grubs in the center of twig. See p. 37 in:
Other signs to look for would be some indication of problem on the twig at the transition from living to dead foliage. Possible cause would be stem cankers. Sign of this is a distinct live to dead twig transition (dead twig is hard and dark brown, live twig softer, green to cream colored when you scratch with blade or thumbnail).
Feel free to continue the inquiry with answers to questions above. Or contact me directly via email.