15-Year Rosemary Sudden Decline: Hard Prune or Accept Old Age

Established rosemary (15 yr, San Bernardino, CA) dying fast; low branches have thick brown crust (grey/powdery when dead). No insects. Owner cut affected branches.

Advice

Severe rejuvenation prune: cut back ~50%. If new growth is clean, the plant had a fungal canker or age-related decline that pruning resets. Few fungicides labeled for rosemary. At 15 years, woody herbs often simply senesce—replacement may be easier.