DARREL KOEHLER: The Prairie Gardener — Tomatoes And Blight

Despite the prediction this summer would be hot and dry, the opposite was the case, which didn’t bode well for some gardeners who raise tomatoes.

Early summer rains coupled with damp, cloudy weather conditions severely damaged this season’s crop. If your tomatoes were in a dry spot with lots of sunshine, you probably fared better.

According to the Minnesota Extension Service, the most common problem was blight. There are several types of blight, with septoria being the most common.

Septoria causes small, dark spots on leaves. Then, the leaves turn yellow and fall off. It usually starts at the bottom of the plant and works its way upward.

Wet and humid conditions like the kind we’ve been experiencing this summer hasten blight’s development. While you can’t deal with Mother Nature in terms of weather conditions, you can avoid overhead watering.

This disease usually does not cause damage to the fruit, but if the plant loses too many leaves, it can’t supply food to its many tomatoes.

So, we end up with two situations. If conditions have been good, you will end up with a good to bumper crop. If you have a bad blight year, you may have fewer or no tomatoes.

Besides septoria, gardeners also have had to deal with fewer cases of late or early blight. They cause larger spots to develop on leaf steams and fruit.

Protective fungicides containing Daconil can help to control blight. It must be applied at the first sign of the disease — or it will be too late.

Bacterial spot and bacterial speck have also struck tomato plants this summer. Small dark spots form on the fruit and leaves. Unlike the fungal diseases, fungicides will not control bacterial diseases.

In the case of heavy rain, tomatoes may crack. There is no remedy for this.

Here are some tips on how to deal with blight that you can file away for next season.

  • Mulch around plants early to delay onset of the disease. However, once disease is spotted, don’t bother to continue mulching.
  • Space plants a good distance apart, allowing good air circulation.
  • Staking tomato plants or encasing them with cages also helps. Purchase heavy-duty tomato cages as they will have to deal with lots of weight.
  • Don’t allow tomatoes to sit on the ground, since they will be prone to rot as well as attack from slugs.
  • Clear away plants in the fall.
  • When purchasing tomato seedlings, check to see if they are blight resistant.

Good luck!



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