Heirloom Expert: Managing Tomato Blight

How do you prevent or treat early blight and septoria leaf spot in tomatoes?

| Fall 2015

My tomatoes took a beating this year, we had tons of rain in the spring and summer too. They got some kind of blight. The leaves started turning yellow on the bottom and the disease worked its way up the plant. I got tomatoes, but not nearly the amount I’m used to harvesting. Do I need to do something to the soil to prevent the same problems from happening next season? — Gary from Pennsylvania

I feel your pain, Gary, as I experienced the same weather and problems.

You probably were dealing with early blight or septoria leaf spot, neither are usually fatal to the plants, but do slow production. The spores are soil borne and are always there; it’s tough to eradicate them.

The early diseases start the way you describe, with bottom leaves turning yellow and blotchy, eventually drying to brown and dropping off the stems. Then the disease works its way up the plant. Most of the time tomatoes can survive and produce fruit, but not as well as healthy plants.

The first thing you can do next season is to give the plant everything it needs at planting time and plenty of space between plants (five feet if possible). A planting hole filled with compost will keep the plants strong and it’s also a natural fungicide.

Another line of defense is a layer of mulch, which provides a barrier between soil-borne spores and plants. Removing some lower leaves helps too; spores thrown up by splashing rain will have farther to go. Leaves which stay wet for a day or so invite infection. That’s why you should always water tomatoes in the morning, to give the foliage time to dry out.

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