|I have 1 large Big Boy plant and it has grown large and has lots of tomatoes on it. All of a sudden the top leaves are wilting and turning yellow and then dieing. What do I need to do?|
|Your plants could be suffering from either early or late blight, which are caused by different fungi. Early Blight is caused by the Alternaria fungus. It overwinters on infected plant material, even seeds, so it's hard to completely remove the spore reservoir from the garden by cleaning up all the vines and fruit. Early Blight works slowly, whereas Late Blight (caused by the Phytophthora fungus) may kill plants within a week. The fungus is always growing somewhere and releasing spores into the air, which moves on wind currents, eventually coming to a rest on your plants.
There are other disease and pest problems that may be affecting your crop, such as Verticillium wilt and Fusarium wilt. Fusarium wilt is a fungal disease that chokes the vessels in the plant stem and prevent moisture and food from moving through the plant. Unfortunately, once the disease sets in, there's nothing you can do to cure your plants. As a last ditch effort you might try pruning off the affected stem. This might help your plant ripen the fruit it has set.
If you are growing tomatoes in the same site every year, the soil could use a break from constant monocropping, but if you don't have room for a second plot, I suggest loading up the soil with good compost. Compost contains lots of helpful organisms which can work against disease organisms. Work a few inches into the existing soil, and then spread several inches on top of the soil as a barrier mulch. Once your tomatoes are planted, mulch with straw as well. Keep your plants healthy so they'll be in top condition to resist disease. Stake or cage them, and keep the lowest leaves from coming in direct contact with the ground.
Good luck with your tomatoes!