Answer: There are many problems that can beset tomatoes. The best defenses are to select varieties such as Big Beef or Celebrity and others with inbred wide disease resistance and then to grow them as healthy as possible.
First off, purchase only healthy plants.
Follow good sanitation practices and do a thorough garden clean up at the end of the season. Remove and destroy tomato plants, do not compost them.
Rotate your crops so that you do not grow tomatoes or their relatives (eg peppers and eggplants and potatoes) in the same place each year. Three years in between is a suggested minimum.
Prepare your soil with ample amounts of organic material, especially good quality compost if you can get it or alternatives such as old rotted leaves, well aged stable amnure and bedding, etc. Healthy soil is one of the most important defenses against diseases.
Test your soil so you can add amendments such as fertilizer and/or lime in appropriate amounts as indicated by the results of the test. You do not want to overfeed them as this can cause fast but soft growth more prone to disease.
Water your plants if needed to keep the soil evenly moist. Use your fingers to dig down into the soil to see if and when you need to water. Avoid wetting the foliage when you water as this can encourage disease. It is better to encourage deepr rooting by watering deeply less often than to water lightly daily.
Use an organic mulch to help keep the soil moist; it will also keep down weeds and will eventually feed the soil as it breaks down in time.
Space the plants far enough apart that they have good air circulation and place them in a full sun all day location. Avoid working around the plants if they are wet from rain or dew as this can spread disease from one plant to another.
Finally, if a plant shows signs of trouble, identify the problem and if necessary remove it immediately to try to limit spread of the problem to other plants. For the same reason, remove and destroy (do not compost) any infested plants including their roots and any foliage that may have fallen off.
Your county extension or knowledgeable nursery personnel should be able to help you identify the specific problem you are having, if it happens again. Once you know what it is, there may be additional steps you can take. With any luck however following the above guidelines will help you to avoid further situations. All the best with your tomatoes this year!
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