Question
I would like to ask for a second opinion.  You helped me out about two months ago as I was over watering my tomato plants.  Now several of the plants (different varieties planted in pots) have the stems rotting, making the leaves turn yellow and the fruit is dropping off!  Very frustrating.  From looking at pictures on the web it looks like I might have blight.  If so is there anything I can do to stop it?  Is it contagious to the other tomato plants nearby?  The weather two weeks ago was foggy and overcast but I am not sure if that can cause whatever problem I am having.  Thanks for your help...

Answer
I would suspect one of three fungus diseases; late blight, verticillium wilt, or fusarium wilt.

The bad news is that none of these diseases are usually reversable. Once the plants are infected, the problem gradually gets worse. You can, however, potentially halt the disease and prevent it from spreading by spraying the plants with a copper-based fungicide. These are sold in all garden centers. It can never be guaranteed that this will curtail the disease; it will all depend on how advanced it is.

When the season is over, you definitely want to discard the soil. Do not compost it or dispose of it in the garden. Most tomato diseases are soilborne and will survive the winters.

Attached are two great websites; one that describe tomato diseases in detail and one that gives photos.

http://www.extension.iastate.edu/Publications/PM1266.pdf

http://www.avrdc.org/photos/tomato_diseases/index.html

In the future, be sure to use sterile potting mediums. Never use soil from the garden. Be sure to wash the pots thoroughly if you plan on reusing them with a ratio of one gallon of water to 3 tbs. of bleach.  I also would purchase disease resistant varieties. Examples of these hybrids are in the link below:

http://www.parkseed.com/gardening/AS/commonname/Tomato

Good luck. I hope the fungicide works so that you will be able to get some harvest from your plants this year.

Regards,

Mike