If you have edible plants that have failed to thrive, are severely stunted, wilted, yellowed or dying for no obvious reason, then the roots of those plants might be infested with microscopic worms called nematodes. You owe it to yourself as a hard-working gardener to carefully pull up the roots and inspect them. If you see galls (enlarged, pimple-like growths) on the roots, the plants are likely suffering from root-knot nematode damage.
The problem: Not all nematodes damage plants. Some of them are beneficial. But here in Texas, and throughout the South, certain varieties of nematodes thrive in the heat — especially the southern root-knot nematode. When the soil reaches 70-85 degrees, they wake up and begin to feed and breed. These microscopic roundworms pierce the roots of some plants and lay their eggs inside the roots, robbing the plant of water and nutrients. Nematodes love the heat of Southern gardens, and in those gardens they especially love members of the solanaceous family of vegetables — tomatoes, tomatillos, eggplant, potatoes and all peppers. Get into the habit of inspecting plant roots for the characteristic galls whenever you purchase transplants or remove spent plants from the garden. If you can prevent root-knot nematode build up, you will save yourself the labor of trying to reduce their numbers.
The solution: If you discover galls on plant roots, spring into action. Comb through the soil and remove every bit of the roots you can find. Place them in the trash, not the compost pile. Secondly, solarize your soil. During the hottest six weeks of the summer (i.e. now), moisten the smoothed-out growing bed with water, then cover it with clear plastic and seal the plastic against the edges of the wet soil with stones or U-stakes. At the end of six weeks, remove the plastic and plant into the soil. Do not turn the soil after solarization. The top few inches have been cleared of nematodes and weed seeds. If the soil is turned, those two pests will be brought to the surface and the cycle will start over again.
What else can you do? Add compost to the planting holes to feed microorganisms that prey on nematodes. In the fall, plant Elbon (or cereal) rye thickly in the nematode-infested location. Allow the rye to grow until 4-6 weeks before spring soil preparation. Turn the rye into the soil (you may have to use a tiller, because it will be thickly matted). Cereal rye roots trap the nematodes. When cereal rye decomposes, it releases organic acids and feeds soil microorganisms, which further reduce the nematode population.
Prevention: Whether or not you find harmful nematodes, the North Carolina Extension Service (http://bit.ly/nematodecontrol) recommends adopting at least two of the following three measures to avoid or cut down on their numbers: rotate the position of plant families each planting season; choose resistant varieties; and use cultural practices that will discourage root-knot nematode build up.
Rotation: This refers to the practice of placing plants (mostly) in the same plant family in different parts of the garden each season. Try dividing your garden into a pie with four pieces; assign each piece one plant family (No. 1, legumes — beans, peas and potatoes; No. 2, root — onions, garlic, turnip, beets, carrots, radishes; No. 3, fruit — tomatoes, cucumbers, peppers, eggplant, squash, melon; No. 4, Leaf — lettuces, greens, herbs, spinach, brassicas [broccoli, cauliflower, Brussels sprouts, etc.], and corn. Move each quadrant one place to the right each season. If you planted legumes in quarter No. 1 in the fall, move them to quarter No. 2 in the early spring and move quarter No. 4 into No. 1. Keep a record to remind you of what goes where and when.
Resistant varieties: I’ve listed one or two varieties of several vegetables bred to resist nematode damage. For more, go to the North Carolina State web address above.
Lima bean “Nemagreen”; snap bean “Bountiful,” “Contender”; English pea “Wando”; Southern pea “California Blackeye No. 5,” “Hercules,” “Texas Cream”; bell pepper “Charleston Belle,” “Carolina Wonder”; hot pepper “Carolina Cayenne,” “Mississippi Nemaheart”; sweet potato “Jewel”; cherry tomato “BHN-968”; plum tomato “Granadero”; slicing tomato “Celebrity F1.”
Cultural and management practices: These include removing all of the roots of each crop as soon as harvest is completed; tilling the soil two to three times to destroy plant roots and expose the worms to drying of the sun and wind; incorporating large amounts of organic matter into the soil (400 lbs per 100 square feet); solarizing the soil; and inspecting transplants before setting into the garden. This is one worm we don’t want in our gardens.