Diseases are very challenging to identify from photographs, but this might be bacterial spot, a disease that affects foliage in humid, wet growing seasons. It starts as dark brown or black spots surrounded by yellow halos. On the edge of the leaf, turns it white and then brown, and spreads inward, usually on new growth. To minimize spread, water early in the day with drip irrigation. Overhead watering may spread the disease by splashing pathogens. If disease is not extensive, snip off affected foliage and dispose in the trash. When more leaves are affected, cut off as much of the damage as you can and place the pots farther apart. The disease can spread on clippers and other tools, so prepare a solution of 1:10 bleach:water and dip your clipper in it between plants.