I have an heirloom variety that was passed down from a family member who immigrated from Italy. So far, they have been huge, healthy, study plants, but I noticed over the last couple days that one seems to be in trouble. It started with yellowing leaves at the bottom, and now looks like the whole plant is dying. Most of the stems are hollowing and weak. It has some huge tomatoes on it, and if it can be saved that would be best. If not, I don't want it to spread to it's neighbors. I've tried looking online, but most articles about tomato diseases or pests are vague and don't provide much detail.