What are nematodes? What do they do to my plants?

NematodeA nematode is a unsegmented roundworm. It is related to the round heartworms that sometimes harm people and pets.  Nematodes live in practically every environment in the world: in the oceans, in our lakes and rivers, in the soil, inside plants and animals. Only a few nematodes can kill your plants.  Nematodes in the soil or in plants are microscopic.

There are good and bad nematodes. Some of the good ones eat bacteria and fungus and prey on some insect pests. For example, there is a nematode that kills mole crickets (an insect that destroys bahaigrass). The bad nematodes are plant and animal parasites. When nematodes infect a plant, you will see the plant wilting, turning yellow, smaller or thinner that other similar plants, or the plant just dies. Often the damage will be in sections or small parts of the plant rather than the entire plant. In that case, only that section of the plant dies. Other times, they infest and destroy the entire plant and it dies.

Lance nematodeThree Basic Types of Harmful Nematodes

  • Nematodes on the outside of the roots
    These nematodes eat the roots of your plants. You cannot easily tell they are there except by the plant getting sick or dying.
  • Root Knot nematodes
    These small worms get into the roots of plants. They then interfere with the proper functioning of the roots which either weakens or kills the plant. It is very hard to tell if they are in your plants without digging up the roots and looking at the hard little knots on those roots.
  • Nematodes in the stem or leaves
    Some of these nematodes get into your plant and stay in one place; others move around the plant causing damage as they go. It is very hard to tell they are there even after the plant is dead.

Nematodes effect some plants more than others. They effect vegetables, bedding plants, and sometimes shrubs. Tomatoes are especially susceptible.

What can I do about nematodes?

First, if you can, use a lot of organic matter such as compost in your plant beds. This organic matter will help prevent the nematodes from migrating to your plants.

Once there are nematodes in your soil, the only thing you can do is replace or solarize your soil. This is best done in the hot summer months. The solarization process is as follows:

  • Clean all plant matter and other debris from the area to be solarized.
  • Place two layers of clear plastic over the soil.
  • Between the layers of plastic, place a divider such as a 1" plastic pipe.
  • Seal the edges of the plastic with soil.
  • Let the sun beat down on the plastic and soil for a couple of months.
  • After a couple of months remove the plastic and enjoy growing plants in the nematode free soil.

This process will kill pretty much everything in the soil down to the depth of about one foot. Plants or turf can now be re-introduced to the area.