Mrs. Doodlepunk wrote:
My tomatoes are doing really well except for the past week, the lowest branches on each plant have spots on the leaves and are now turning yellow. I took off the spotted branches but now others have it too.
I wonder what thoughts others will have on this. I'm kind of biased toward thinking it's a virus/fungus, because that's a problem I've run into quite a bit in the past myself. Removing the lower branches was exactly the right thing to do, but it sounds like it's moving up into the other branches anyway.
I have a "biofungicide" from Gardens Alive that seem to work on some kinds of problems like this--it worked very well on some sick pumpkin plants last year, for example. It's called Plant Guardian, and I think it's a microbial that establishes itself in the plant to fight & prevent fungus. It smells kind of yeasty. I haven't used it on tomatoes, though, myself. It's possible that once the disease takes hold it can't really be stopped but you might be able to stall it long enough to allow the plants to put out new, healthy growth. (Kind of like the toenail process in humans!) That is one reason I started planting 'indeterminate' tomatoes, which keep putting out new growth all season--in order that they could outgrow the virus or wilt diseases afflicting the lower leaves!
My Rodale's organic gardening encyclopedia lists garlic spray, compost tea and baking soda as possible anti-fungals, but I can't vouch for these myself. Sulfur and lime are what our ancestors used but these have drawbacks, like being somewhat toxic both to people and plants. Personally I think that good healthy compost at planting time does tend to give you healthier plants from the outset, but even so you can still get these diseases. They tend to be regional and seasonal. For example, one year when I lost most of my tomatoes to some sort of virus, everybody else that I talked to around here had lost theirs too. The following year, all was well again.