I have a variety of tomatoes (Sweet 100's, Celebrity, Mr. Stripey, some yellow variety, etc.) and all of them are succumbing to some sort of disease that is destroying the bottom leaves. The tops of the plants look beautiful, but the bottom leaves are dropping off one by one. I took a picture today so posters could get an idea of the problem. I did some reading and Celebrity is supposed to be disease resistant. What is the problem and what can I do to repair the problem?