Answer: I can't say for sure which diseases affected your plants, but one of the most common problems for tomatoes is septoria leaf spot. It's almost impossible to avoid septoria on in the best of times, since the spores linger on infected plant debris and tomato seeds in the soil. But you can improve your chances by cleaning up plant debris, and by treating your plants regularly with a spray of compost tea. Compost tea is teeming with microbes that somehow (perhaps through competition for resources, or by stimulating plants' immune response) reduces the incidence of fungal disease. To make compost tea, mix one part mature compost that contains some manure with 5 parts water. Let the mixture sit for 2 weeks, then filter and spray at 2-week intervals. You can also mulch the soil in the containers to reduce the likelihood of spores splashing from soil to leaf surfaces during rain/watering. And be sure the containers have excellent drainage.
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