November 8th, 2011

Knotty Tomato Roots

I just pulled my tomato plants out and the roots are a mass of ugly bumps and warts. They were planted in new raised beds with a mix of soil and compost from the city. What am I dealing with, and how do I correct the problem?

blog-dougWhat you describe sounds like the galls of root-knot nematodes. Nematodes are small soil-dwelling roundworms; when they parasitize or feed on plant roots, crop yields suffer. It’s possible that the tomato transplants you purchased were infected. Destroy the infested tomato plants—don’t add them to your compost pile.

There are thousands of species of nematodes, and most are beneficial. Good nematodes are part of the soil “food web” in which nutrient components of organic matter are released in forms that plants can use. Other beneficial nematodes prey on cutworms, beetle larvae, and destructive nematodes.

Even though many vegetable crops are susceptible to nematodes, each is parasitized by different nematode species, so crop rotation helps to minimize the damage. Plant your tomatoes in a place where tomatoes or related vegetables (peppers, eggplants, potatoes) have not grown for at least three years. Another control tactic is to fortify your soil with plenty of compost, which feeds the beneficial microbes that keep root-knot nematodes in check.

Next spring, look for nematode-resistant tomato varieties, or invest in grafted tomato plants, which are grown on a vigorous rootstock that is resistant to nematodes and soil-borne diseases. If these efforts fail, consider solarizing the soil by covering it with a sheet of plastic for 6 to 8 weeks in summer. Because solarizing kills beneficial microbes as well as pests, consider it your option of last resort.  —Doug Hall

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