I've got fall tomatoes planted in my unheated high tunnel and some plants are developing a disease that I've never seen before. It sounds similar to what you are describing. Several plants have some spots on leaves, but seem otherwise pretty healthy. A few had stems that rotted all the way to the base, and I've found some fuzzy mold on some of those stems. My two cherry tomato plants had it the worst so I removed them. As I cut the plants apart, I noticed a brown ooze in some of the affected stems. I've been on a weekly spray schedule of Serenade, an organic fungicide. This week I sprayed liquid copper instead, which I think might be more effective if I'm dealing with a bacterial disease. I'm including a link to an article I found that describes a stem rot disease found in greenhouse tomatoes. This may be what both of us are dealing with. Lack of circulation, high moisture and temps 60-70 help this fungus survive. Those are the exact conditions on my high tunnel right now. I'm glad to have this little fall crop of tomatoes, because my main season crop this year was so bad, but I figure my tomatoes' days are numbered. I'll be lucky if I get another few weeks out of them. I'm still getting some very good tasting tomatoes, so I'm going to keep them alive as long as I can. Here is a link that might be useful: Stem rot in greenhouse tomatoes

I have only been growing tomatoes for 5 years or so, but the yellowed plant reminds me of some plants I had that were put in overly damp soil... they look generally sick, but no clear signs of one plant disease or another (i.e. oddly shaped splotches, mold or similar markings). From my limited experience and what I have read here and elsewhere online, this kind of thing (general yellowing, greyish purple veins, etc) seems to be due to environmental issues such as low temps or damp soil. Is it possible that more water is draining into that corner of the bed? Also some varieties handle tough conditions better than others, so that alone might account for the difference between plants. Maybe someone with more experience can find signs of other problems.

Where? What zone/time frame? Are the plants salvageable? Sure. Are they in containers or the ground? If containers what mix are they in? If in ground, how well does your soil drain? What have you fed and how often? They may just need a good feeding. More info please. Dave

Leaf compost is carbon based and has very little nitrogen which would be there if the green portion of compost were added. However the leaf compost will be good for the soil in the long run. Try adding nitrogen to your soil.Lawn fertilizer is high in nitrogen. I don't know if it will solve your oroblem but it;'s worth a rtry