Root-Knot Nematodes

root-knot nematodes

Have you ever pull up a troubled plant and found knots on the roots? Most likely root-knot nematodes are the root of your problems.

Nematodes are microscopic roundworms that live in the dirt. Many of them are actually beneficial and are used to control pests including grubs, fleas, aphids, beetles, fungus gnats and other pests that inhabit the soil.

Unfortunately there is one type of nematode that attacks and eats the roots of plants and although there are other nematodes that cause plant damage, the root-knot nematode causes the most damage worldwide. Infected plants produce less basically because the knots prevent water and nutrients from getting to the leaves and fruit.

Root-Knot Nematode Symptoms

Because nematodes are so small, you can’t really see them and you must look carefully for symptoms of their existence. Stunted growth, yellowing leaves, thinning plants, damage in patches and premature wilting all can be symptoms of nematode infestation. Of course these symptoms are also symptoms of many other problems.

Most nematodes cannot be diagnosed by looking at the plant so if you suspect you have them, take a soil sample to your agricultural extension office for analysis and diagnosis. You will need a special nematode testing kit which you should be able to get at your extension office.

Root-Knot Nematode Prevention

  1. Low tech and easy soil solarization can reduce the nematode population and has the added benefit of eliminating weeds. Lay a transparent plastic sheet over moist soil in the planting bed and anchor the sheeting with bricks or boards. Leave it for 6 to 12 weeks (the warmer the outside temperature, the less time it takes).

  2. Plant resistant varieties such as Park’s Whopper Improved, Better Boy, Celebrity (large varieties) or Supersweet or Golden Cherry (small fruit) there are many other resistant varieties. Look for VFN on the tag. Plants carrying this designation will be resistant to Fusarium wilt and root knot nematodes.

  3. Practice integrated pest management techniques and destroy all plant debris after harvest. Destroy any infected plants as soon as you see them and don’t use pond or ditch water for irrigation because it may contain harmful nematodes. Rotate your plants and remember to rotate all of a similar variety. For example, tomatoes are nightshades so you should rotate all nightshades (peppers, eggplants).

  4. Reduce stress on your plants by providing enough water and nutrients.

  5. Add organic matter to the soil. This will make the water and nutrients more available to the plants and healthier plants will tolerate more nematode damage!

  6. There are no chemical controls registered for homeowner use!

Destructive nematodes will affect other plants too and cause an overall reduction in your harvest. Good cultural control and Integrated Pest Management are your best defenses.

Comments from Other Gardeners
  • Julie says:

    I have had problems with nematodes in the past and have used all of the above listed controls. Another very important thing you must do to control and prevent nematodes is to clean up all plant debris after the growing season and to keep plant beds weed free. I do this and then cover the bed with oak leaves which I then till into the soil a month or so before planting.

  • Theresa says:

    I see that you mention several ways to prevent nematode infestation but what can you do if you get it? Is there a way to get rid of them, or do they die off when the weather gets cold in most parts of the country? I ask because this sounds like something that I would have to worry about here in Florida.

    Thanks in advance!

  • Paul Guzman says:

    What about beneficial nematodes? I work in a retail garden nursery and have sold hundreds of beneficial nematodes(they eat the bad ones). Most of our customers say they work well. I would recommend anyone who has this problem to research “beneficial nematodes for plants”.

  • Lin says:

    I am plagued with root knot nematodes in my raised beds. I believe they arrived in the very sandy “topsoil” I ordered and added to the beds.
    I tried solarizing one year with good effect, but they returned the following year, and are spreading. I have obtained some thyme oil concentrate to apply as a drench in spring, and am again solarizing. Would it help to pour boiling water onto areas of slight infestation, to keep the worms from spreading throughout the beds?

  • Deanie Edwards says:

    I too have had a terrible experience with nematodes. I tried the beneficial nematodes, but it came a cold spell and it did not work. I visited with my county agent and he told me to try planting cereal elbon rye grass. I did plant it and I have a nice crop of it. My plot is 20 x 30 feet. When it dies he said to plow it under. It is supposed to attract the nematodes. I will be anxious to find out. I had nematodes in the okra, squash and tomatoes last year. Beastly little critters.

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