By Sharon Omahen
University of Georgia

Most garden pests can be seen crawling and nibbling their way across plants. But tiny subterranean pests could be attacking your garden without you knowing it.

“Nematodes are microscopic non-segmented worms,” said Jim Crawford, a University of Georgia Cooperative Extension agent in Jefferson County. “The ones we are concerned with live mostly in sandy soils and have a stylet or mouth-spear that resembles a hypodermic needle.”

Nematodes live in the soil and feed on plant roots preventing them from providing nutrients to the plant. Tomatoes, okra, cantaloupe, watermelon and squash are the most susceptible garden plants.

The most common nematode is the southern root-knot nematode, which causes roots to gall or swell. “These knots are very obvious,” Crawford said.

The stubby-root nematode “stubs off roots” so they appear short and thick, Crawford said.

No matter which nematode attacks, the resulting swollen roots cause the plant’s vascular system to shut off so the root doesn’t transport water and nutrients.

How do you know if your plants are under attack from nematodes? Look for “unthrift, stunted or deformed plants,” he said. Due to their lack of nutrients, nematode-infested plants will appear wilted even when they have plenty of moisture.

Homeowners can also have their garden soil tested to see if nematodes are present. “This is similar to the soil samples taken for fertility testing except this sample would be tested for the presence of nematodes,” he said.

If you have nematodes in your garden, the good news is they don’t move very fast or very far. “It’s been estimated that they can only move about three feet per year by themselves,” Crawford said. “They can, however, be moved with garden tillers or brought in with fill dirt or on infected transplants.”

Row-crop farmers are accustomed to fighting the tiny critters. They attack crops, stopping or reducing yields and, as a result, profits.

“Farmers can choose from a few products specifically formulated to kill nematodes,” said Crawford. “Unfortunately, home gardeners are unable to use these products.”

There are currently no chemical products labeled for use on nematodes found in home gardens, he said.

So, what can home gardeners do to control nematodes? One way to kill nematodes in your garden plot is to use the sun as your weapon.

“Solarization must be done in the summer months on fallow ground that will be a garden the next year,” Crawford said. “It involves spreading plastic over the ground and letting the sun’s heat kill the nematodes that live below.”

Crawford finds another control method “relatively effective” although it hasn’t been tested by UGA Extension.

“Adding chitin to the soil is a simple, legal, safe and affordable approach,” Crawford said. “It’s crushed marine shells, but to nematodes it’s razor-wire. When viewed under a microscope it looks very sharp and jagged.”

Available at most lawn and garden supply stores, chitin should be mixed into the top eight inches soil at a rate of one pound per two square feet of affected area. After harvest, remove all roots and till the soil well to dry out and kill any surviving nematodes.

“Homeowners shouldn’t expect this to solve their problems in heavily infested areas,” he said.

To prevent nematodes, UGA experts recommend rotating your garden plants each year.

“Try rotating the most susceptible plants, like tomatoes and okra, to a different place in the garden,” he said. “If you’re using transplants, select bigger ones since they’re not as likely to be attacked.”

Planting resistant varieties also helps. Nematode-resistant varieties are often designated as such by the acronym VFN on their labels. “Nematodes can’t reproduce on the roots of these plants thus controlling the population,” Crawford said.