Certified GKH Gardening Expert
Unfortunately, your photo did not come through. I am unable to see the damage, but I can take a guess at the issue.
Usually, this is going to indicate overwatering, or bacterial infections. Make sure that the soil is well draining, and does not have a chance to stay wet. Ideally, there needs to be a drain pan to remove excess water.
Treat with a fungicide. This will help treat any residual infections.
Here are some articles that will help: