The Q&A Archives: Preventing Fungal Diseases On Tomatoes

Question: Last August we went on a five-day vacation -- just in time for a five-day deluge. When we returned, we found our porch garden half-drowned. Despite our best efforts, the plants were never quite the same. The tomatoes were especially affected -- the foliage became stippled with brown spots that seemed to affect the undersides of leaves and spread rapidly.

I'm getting ready to start this year's garden, and I'd like to know how to avoid letting the spores that I'm sure are everywhere on my deck get the better of my young plants. I'm sterilizing all my pots and sweeping my pressure-treated wood deck, but the dense clouds of gray dust raised by my efforts are starting to make me think my deck is ground central for fungal diseases of all kinds, and anything I plant will be doomed. Any advice?

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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