Hi, this year for the first time, we are experiencing a number of tomatoes, Burpee's Early Girl and Big Girl, developing soft bottoms that turn black and slightly flattenend, most of which fruit cannot be salvaged. We carefully dipose of it in the trash so as not to infect our compost pile. Any clues as to cause/cure? Ron, Van Nuys, CA USDA 9b, Sunset 20