Answer: It sounds like your tomatoes are suffering from either early blight or septoria leaf spot, or both. These fungal diseases impossible to eradicate from the garden, but you can work around them well enough to get a good crop. Start by planting disease-resistant varieties. Rotate crops so that you don't plant tomatoes in the same spot more than once every 3 or 4 years, since the spores of septoria remain viable on dead plant material and seeds that linger in the soil. The spores of the early blight pathogen, Alternaria solani, are always floating around in the air and dust, so these measures won't help much there. Copper is used as a fungicide, but it wouldn't be effective in the planting hole. It needs to be mixed according to label instruction sprayed upon the leaves to prevent infection. Use a heavy layer of organic mulch on the soil to prevent spores in the soil from splashing on leaves, and water in the root zone of the plants, avoiding getting moisture on the leaves, since the fungi need moist leaf surfaces in order to grow. Some people report good results using fungicidal soaps and neem oil sprays.
Best wishes with your tomatoes!
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