Currently, the Extension office has been a busy place and diagnosing tomato plant problems has been a big part of business lately. A common diagnosis for many has been Bacterial Wilt and if you are a serious gardener that loves tomatoes a diagnosis of bacterial wilt is an enough to give you a case of the blues.
Bacterial wilt is a serious disease of tomatoes caused by Ralstonia solanacenrum and unlike other plant diseases that affect tomatoes there is no cure or remedy that is going to save infected plants.  The bacterium that causes this disease survives in soil and can be viable after long periods of time.  Infections occur when the bacterium enters plants through the root system in wounds caused by transplanting, cultivating, insect damage, or through natural openings.  Disease development is favored by high temperature and high moisture levels which we have not been short on in the last few weeks.  During favorable conditions the bacteria multiplies rapidly inside the stem and plugs up the water conducting tissue with a slimy substance.  Blockage of the water conducting tissue causes a rapid wilt of the plant while it keeps a green healthy color due to the rapid onset of the disease.  Complete plant wilt/collapse will happen in just a few days.
Not all tomato plant wilting is due to this disease. So correct diagnosis is needed so that correct management strategies can be used.  There are a couple of things that a gardener can do at home to determine if bacterial wilt is causing their plants to wilt.  First examination of severally wilted plant stems that have been cut crosswise can be done. If it is bacterial wilt the inside of the stem will look brown and tiny drops of yellowish ooze may be visible.  In the early stages of infection this discoloration and ooze may be difficult to see.  For further confirmation or if discoloration and ooze are not visible in the stem, you can suspend a small section (6 inches) of the main stem in a glass of water  for a few minutes (5-10) during this time if bacterial wilt is the problem there should be a milky looking trail of ooze coming from the stem.  The stem needs to be placed with the root side of the stem down at least an inch under the water and a clear container with smooth sides is the easiest to examine for the milky ooze through.
Once a garden area has been infected with bacterial wilt it is difficult to grow tomatoes in that area again.  The best control method would be to plant tomatoes in an area that has never had tomatoes planted in it before.  If this is not possible then crop rotations with nonsusceptible crops for at least three years in between planting tomatoes will help reduce the amount of bacterium in the soil.  Nonsusceptible crops that would be acceptable for a rotation would be corn, okra, beans, peas, and cabbage.  Do not plant any peppers, potatoes, or eggplants in this rotation as these also susceptible.  When purchasing seed or transplants make sure you are getting certified disease free seed and that you only buy healthy transplants when purchasing them from a store.  There are a couple of varieties that are partially resistant to bacterial wilt and they are Neptune, Tropic Bay and Kewalo but these however are uncommon varieties and will most likely be difficult to find in local stores.
Tomatoes have a lot of diseases that like to attack them and for more information on the common tomato diseases or for help in diagnosing what is wrong with your tomatoes you can stop by your local Clemson Extension office or visit the Home and Garden Information Center online at http://www.clemson.edu/extension/hgic/.