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Problems Growing Tomatoes - Fusarium Wilt

Scott Aker, Washington Post
Saturday, July 28, 2007

Q: How should I reduce the effects of fusarium wilt in my tomato plants?

A: Generally, fusarium wilt is controlled by planting tomato varieties that are resistant to the fungus that causes the disease. Most modern tomato cultivars are bred with good resistance to fusarium wilt and other diseases, but if you are growing heirloom tomatoes, you may find the plants susceptible.

Crop rotation is a great tool for controlling the disease as well, but it's difficult if you have limited space because the spores may persist as long as six years in the soil. You may not be able to avoid planting crops that play host to the fungus, including eggplant, peppers, potatoes, strawberries and raspberries. Many weeds also may host fusarium wilt, so keep your garden weed-free.

Commercial growers often resort to soil fumigation to eliminate fusarium wilt. Although you can't fumigate your garden soil, you could potentially solarize it to much the same effect without the use of harmful chemicals. That is best done in May before tomato season, but it could be done in late summer and early fall for the next year's crop.

Till the soil, making sure it is first moistened. Place bricks or aluminum cans at regular intervals over the soil to be treated, and dig a trench at the perimeter of the area. The bricks or cans will act as spacers for the sheet of clear plastic that is laid over the area. Bury the edges of the sheet in trenches. The greenhouse effect will heat the soil to a temperature of 140 degrees or higher, killing the fungal spores that cause fusarium wilt, along with many other diseases, nematodes and weed seeds. It is most effective near the soil surface, so all remnants of plants previously growing in the garden should be removed rather than tilled into the soil before you solarize it. In the heat of May, keep the sheet in place for three weeks. If you do it in early fall, keep it down longer, especially if the weather is cool or wet.

Scott Aker is a horticulturist at the U.S. National Arboretum.

Palo Alto, California

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