Are Nematodes Bad For Vegetable Gardens

Nematodes under microscope

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While most of the thousands of nematode species on Earth are not harmful, some cause diseases in humans and other animals or attack and feed on living plants. Luckily, there are ways to deter these pesky pests from disrupting your garden soil.

The few parasitic species of these translucent, unsegmented worms measure about 1/50 inch long and cause root knots or galls, injured root tips, excessive root branching, leaf galls, lesions or dying tissue, and twisted, distorted leaves. Plants most commonly attacked at the roots include cherry tomatoes, potatoes, peppers, lettuce, corn, and carrots. Plants that sustain leaf and stem system injury include chrysanthemums, onions, rye, and alfalfa.

What Are Nematodes?

Often referred to as roundworms, nematodes are not closely related to true worms. They are multicellular insects with smooth, unsegmented bodies. The nematode species that feed on plants are so tiny that you need a microscope to see them. The adults often look long and slender, although some species appear pear-shaped. These plant parasites are not the same roundworms as the filarial nematodes that infect the human body, spread diseases, and wreak havoc on the immune system.

Some nematodes feed on the outer surfaces of a plant while others burrow into the tissue. Soil-dwelling nematodes are the most common culprits, but some species can damage plant roots, stems, foliage, and flowers.

No matter where they feed, these tiny worms can seriously damage to crops with their sharply pointed mouths by puncturing cell walls. The real damage occurs when a nematode injects saliva into a cell from its mouth and then sucks out the cell contents. The plant responds to the parasitic worms with swelling, distorted growth, and dead areas. Nematodes can also carry viruses and bacterial diseases inject them into plants. The feeding wounds they make also provide an easy entrance point for bacteria and fungi.

Beneficial nematodes that enrich the soil may feed on the decaying material, insects, or other nematodes.

What Nematodes Look Like

Unlike most other disease-causing organisms, plant-parasitic nematodes seldom produce any characteristic symptoms. Most of the symptoms that do appear are vague and often resemble those caused by other factors — such as viruses, nutrient deficiencies, or air pollution. Nematodes feeding aboveground may cause twisted and distorted leaves, stems, and flowers.

Root nodules invaded by nematodes.

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If nematodes are feeding on the roots, a plant may look yellowed, wilted, or stunted and infected food crops will usually yield poorly. If you suspect worm injury to roots, carefully lift one of the infected plants and wash off the roots for easier inspection. If nematodes are causing damage, you may see small galls or lesions, injured root tips, root rot, or excessive root branching.

How They Spread

Whether they feed above or below ground, most nematodes spend at least part of their life cycle in the soil. While they can't move very far under their own power, they can swim freely in water and they move more quickly in moist soil — so it's a good idea to keep your soil well-drained. They also spread by anything that can carry particles of infested soil, including tools, boots, animals, and infected plants.

What About Beneficial Nematodes?

Beneficial nematodes can range from 1/25 inch to several inches long and have slender, translucent, unsegmented bodies. Their roles in the garden vary. Some are soil dwellers that break down organic matter, especially in compost piles. You can easily spot these 1/4-inch-long decomposers.

These types actually combat a variety of pest species, including weevils, clearwing borers, cutworms, sod webworms, chinch bugs, and white grubs. Nematodes attack and kill these insects by either injecting deadly bacteria or entering the host, parasitizing, and then feeding on it.

Whenpurchasing and applying them to your garden, it is very important to select the right species because different kinds of nematodes are effective against different pests. In addition, nematodes require moist, humid conditions and fairly warm soil to do their job well. Water all application sites before and after spreading nematodes and follow application instructions carefully.

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