this is my 3 year old key lime plant which showing burns . New growth come fine but as leaves become older they start having burn spots . This thing only appears on older growth , new growth comes fine . As you can see plant is pushing new growth , but when these leaves become big they start to have this problem . This thing happening from this year only , Plant is potted in large laundry tub having fabrics on side and bottom par having tiny tiny holes everywhere to improve drainage and air circulation . I reside in zone 11 New Delhi , India . Temps these days easily cross 45 C /115F so i put it under 50 percent shade cloth from past 3 months , but same thing is happening under shade .3 other plants are grown in same container , Reaper Carolina , Ghost Pepper and orange Habs , they all are doing fine. I fertilize it every month with organic fertilizer only (equal parts of bone meal , neem cake , vermicompost , cow manure and tsp of seaweed granules ) . I repeat new growth comes fine but as soon as leaves become old they have these burn marks