new growth dying
when new growth comes in half dead
Certified GKH Gardening Expert
This appears to be a fungal infection. Since it is in container, the cure is a little easier to manage. Just mix 1 tablespoon of hydrogen peroxide per cup of water the next time you water. Do this once a week for 2 or 3 weeks, and then it should subside. This treatment will only need to be done when it shows signs of infection.
Make sure to only water once the soil is dry down to 2 or 3 inches if there are drainage holes. If there are not, consider repotting or adding drainage holes. Overwatering is the most common cause of plant disease, so it is necessary to be very certain to only water when necessary to ensure that this is prevented in the future.