I did a search for "Southern Blight" because I’m not familiar with it. I thought it might be similar to our early blight or late blight but from the information I found it looks like it isn’t something we wouldn't see here in Zone #5. Your county agent is correct that it is a soil-borne disease and similar to the blights we have here; it is hard to get rid of. From the information I found there are some things that you can do to reduce your susceptibility to the disease. I suggest you go to http://www.google.com/ and do a search for +"Southern Blight" +tomatoes (type it in just as I have it including the +’s). There were several approaches mentioned on the sites listed but some of them seem way too harsh to me, such as “Soil fumigation with methyl bromide”. The site: http://www.aginfo.fvsu.edu/teletips/insects_diseases/216.htm offered some ideas that I would consider trying.

For the blights I’m familiar with, early blight and late blight, the first approach we use is to mulch around the tomatoes to minimize to possibilities of soil-borne disease being splashed onto the plants from rain and overhead watering. We are using drip irrigation so rain would be our only concern.

I hope some of this information is helpful to you. We would be very hurt if we had a disease that wiped out our tomatoes.

John Franklin