What kind of deficiency?

Senescence (spelling). Plant is slowly dying toward end. Some extra N would likely help reduce that fade (bottom of plant and up yellowing and from tips in = nitrogen), but don't over do it if very close to end. The key is that a canopy of soem sort exists with soem green. Enough to finish powering it through. If you think it's fading too fast relative to when you are likely to harvest the plant, you do want to react to it, otherwise, it's normal and won't hurt you.