Help - my tomatoes are turning brown on the bottom. This one plant out of 15. It's not every tomato on this plant. Maybe 1/3 have this problem. t's an heirloom, brandywine. I am in zone 9b. This just happened in the last couple of days. I have a drip system and all my other tomatoes are doing well. But we have had a sudden heat wave of 100 plus days for the last 3 days. Is it disease or a heat/water issue? Should I quarantine? It is in a fabric pot so I can move it.