July 31, 2003 at 4:05 p.m.
I'm no expert but I've had my share of tomato problems and the type of weather we have had this summer, I'm sure some of them will appear.
About the time those first tomatoes are beginning to form, a fungal disease called septoria leaf spot begins to infect the lower leaves of your tomato plant. Check the lower leaves for circular spots about 1/8 inch in diameter with a light center and dark margins. Spores produced in these lesions quickly spread up wet plants infecting all green tissue.
The best control for septoria leaf spot is to pinch off and dispose infected leaves when they first appear in mid to late summer, and hope for drier weather. If you planted an early variety, you may be able to harvest some fruit before it becomes a problem. Mulching to keep the soil from splashing onto the plants can help. The cool spring and early summer is ideal for the verticillium wilt. This is a cool season fungal disease that attacks tomatoes, potatoes, eggplants, peppers, strawberries and raspberries. Symptoms first appear on the oldest leaves, which wilt and show marginal yellowing. These areas eventually turn brown and the leaves fall off. A clue that it is verticillium wilt is that the leaves often turn yellow and dry up without any evident wilting beforehand.
Fusarium wilt, on the other hand, is a warm season fungal disease that only attacks tomatoes. As with verticillium wilt, the lower leaves of tomato plants will turn yellow. However, the yellowing is often confined to one side or the other of the midrib. Eventually, the entire plant wilts, yellows and dies.
Another potential tomato problem this summer could be early blight. The symptoms are that the leaves and stems develop large dark spots, with each spot having many narrow, concentric rings. Similar dark sunken blotches also appear on the fruit, usually beginning at the end of the stem. There doesn't seem to be much one can do about preventing the wilt or early blight. You can remove infected leaves or the entire plant to control spreading. If you do remove any part of the plant, destroy it rather than compost it. There may be some home remedies that work or fungicides that may help control the diseases. If they work and are safe, go for it.
If you get through the summer without these diseases, you still may have to deal with late blight. You may have read about the Irish Potato Famine in the 1840's. Well, that is the same blight that attacks our tomatoes. There have been some blight-resistant potatoes developed but so far that is not the case for tomatoes, at least for the late blight. Although late blight can occur at any time during the growing season, it is more likely to be seen in late summer or early autumn. Under favorable conditions, which are cool, rainy weather, this disease can spread quite rapidly and can destroy plants in a few days.
Fruits infected by late blight show gray/green water soaked spots. A white cottony fungus develops on the fruit during wet conditions. The best control is to remove infected area or the entire plant and keep the plants dry with good air flow. Again, if you can find a good, safe, fungicide, use it.
I have given symptoms of tomato diseases, in this piece, with very few answers. Nobody asks me the question I know the answer to concerning tomatoes. The question is: Are tomatoes a fruit or a vegetable? The Supreme Court ruled that tomatoes are a vegetable. It was based on the fact that they are more likely served with dinner and also fruits generally grow on woody plants.