This summer I grew the ugliest carrots you’ve ever seen.  They had multiple forks and lots of bumps like little tumors.  The carrot in this picture is handsome compared to mine, but it clearly represents my problem:  Root knot nematodes.    Nematodes are not insects.  They are microscopic animals that look like little worms, and many live in the soil.  Some kinds help the gardener by destroying grubs and maggots. [Some kinds are parasites on humans, like pinworms, hookworms, trichinosis, and whipworms.]

The nematodes that are parasites on plants can do a lot of damage to almost any part of the plant.  The root knot nematod lives in the roots and causes knot-like swellings on the root system.  In addition to carrots, they can infect many other plants.

Control of root knot nematodes is done by many of the good-gardening habits that we hear about from garden friends:  Keeping garden beds clean and free of dying plant matter, applying compost, rotating planting, mulching.   If you suspect nematodes in your plants, you should remove and destroy the infected plants. Letting the land lie fallow for a year is not reasonable in our garden, but buying resistant varieties of plants would help. Stone and I plan to try two more drastic measures:

1. Sterilization:  After removing dead plant material and turning the soil over, cover it with clear plastic, weighing the sides down with bricks.  Four to six weeks of this solar treatment should sterilize the soil of most of the nematodes, but also of the good fungi and bacteria too.
2. Using marigolds as a cover crop:  After the sterilization, we will plow under our marigolds in the area concerned.  The chemicals released into the soil by the marigolds cannot be tolerated by the nematodes.

Then mulching should help introduce new good organisms to the soil.

-AnneT

References:  Picture from Flint, M L. Pests of the Garden and Small Farm, 2nd ed.  Los Angeles, CA: U of CA Press, 1998

Info abt. nematodes from Deardorff, D & Wadsworth K.  What’s Wrong With My Plant? (And How Do I Fix It?) A Visual Guide to Easy Diagnosis and Organic Remedies.  Portland:Timber Press,2009.

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