Some gardeners have mentioned that their tomato leaves are starting to yellow. When this happened to me last year, I did some research and learned of about 5-7 pathogens... any of which could cause yellowing leaves. Though I learned of all the possible diseases. Properly diagnosing the disease was a bit out of my expertise and time allotment.Some diagnostic tests were extreme... even involving cutting the plant down and immersing the stem in water to look for whitish discharge. Left alone, the symptoms diminished, and my tomato eventually made it through the summer reasonable well. But from this scare, I learned the benefits of pruning in promoting plant vigor and in reducing pathogens.
For some gardeners engaged in intensive gardening, pruning also encourages strong vertical growth, giving more space to other plants ( http://www.taunton.com/finegardening/how-to/articles/pruning-tomatoes.aspx). Pruning encourages air circulation and bigger fruits. At the end of the summer the plant can easily be capped to encourage the ripening of the last few tomatoes.
There are a few drawbacks from pruning: fewer fruits, commitment to trellising, and since there is less foliage, fruits are more exposed to sun scalding.
I hope more people will consider pruning as a tool to discourage soil/plant pathogens and as a tool to manage their plots. Anyone suspecting that their plants are diseased should act responsible to contain the disease and restrict it from spreading to other plants. Diseased plant should be disposed of in the garbage - NOT THE COMPOST.
