Heirloom Expert: Managing Tomato Blight

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

Tomatoes

Early blight and septoria leaf spot are common tomato problems in wet years.

Photo by Fotolia/akiyoko

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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.

Keep the plants off the ground too. Grow them in cages or up stakes. At planting time, I surround mine with a homemade cylinder of concrete reinforcing wire 5 feet tall. A tomato stake attached to the cage stops a huge tomato plant from toppling the cage in August.

One of the best ways I’ve found to avoid fungal issues is succession planting. After the first crop is planted, find space for some more plants to be added every week, all the way until July 1 in my zone 5 garden.

When choosing plants for later plantings, go with varieties that are bred to ripen early. Cherry tomatoes, ‘Early Girl’ and patio tomatoes are all good choices.

Serenade is a great, easy to find organic fungicide that is effective in combating many fungal issues. It’s a biological control which targets the spores themselves and stops them from reproducing. It’s a safe alternative to chemical fungicides. 

Another way to deal with fungal problems is to choose many different tomato varieties to grow. Each one reacts differently to diseases.

If plants contract one of the early diseases, remove the infected foliage and treat with the Serenade. They usually put on fresh growth where those yellow leaves were and should keep producing.  Crop rotation is also important; don’t plant tomatoes in the same place every year. In my garden, there’s only one place with enough sun for the plants. I add lots of compost, and then plant, mulch, cage and hope for a dry “Italian summer.” The weather is really the most important factor in keeping tomatoes healthy. A hot, dry summer is what tomatoes love and also gives fruit the best flavor.