We’re not absolutely positive on this so we’re double checking with a tomato specialist. Will get back to you if we find out more. This might be bacterial spot, a disease that affects foliage in humid, wet growing seasons. It starts 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.