Pest nematodes cause the leaves of some vegetables to become wilted and yellow. These stunted plants may not develop edible fresh vegetables and may die prematurely.
After these symptoms, the plants should be carefully pulled or dug up for examination of their roots. A sample of the garden soil can be tested for nematodes.
The Southern root-knot nematodes (Meliodogyne incognita) attack the roots on tomato, lettuce, okra, pepper, bean, eggplant, potato, squash, carrot and many other vegetable crops.
The pest nematodes are microscopic worms that live in moist soil and eat the inside of roots. As they damage the roots, nodules form that restrict the water and nutrients from moving up to the stems and leaves of the plants. They lay eggs and move to another location on garden tools, transplants, ants, etc.
Generations of their life cycle are continuous and are most active in warm soil. They overwinter as adults or eggs. If the roots are stunted with many nodules that shelter the nematodes, the plants and lumpy roots should be trashed as a control.
During the summer, soil solarization is an effective method of controlling pest nematodes. After that, a thick layer of organic mulch should attract other earthworms and good nematodes to the area.
During the hot days of summer, you could till the soil each week or two as deep as the roots from the previous crop. The dry/hot soil and sunlight will kill many nematodes. It will probably destroy many earthworms and good nematodes. But, a thick layer of organic mulch should attract other earthworms and good nematodes to the area.
During the fall season, Elbon rye may be sown as a trap crop for the nematodes. The pest nematodes will become trapped in the roots and die. During January, the rye crop should be mulched on or tilled into the bed to improve the organic matter of the soil. Then vegetable crops may be started.
The infected crops should be rotated with resistant crops or varieties on a three-year plan.
Vegetable selections that resist nematodes (“N” on plant label) are Atkinson, Beefmaster, Celebrity and Nematex tomatoes; Wando peas; Bountiful and Tender Pod beans; also Apache, Hopi and Nemagold sweet potatoes.
To control extreme cases, consult a pest control professional about soil fumigation.
Beneficial nematodes are an essential part of the soil food web that transforms organic matter into nutrients that the roots need, especially nitrogen. Good nematodes are almost as important as earthworms in a healthy soil. Predatory nematodes may be available at garden centers or by ordering.
The application of beneficial predatory nematodes is very precise for the following problems:
• Apply Steinernema fetiae to suppress the Southern root-knot nematodes, ring nematodes and sting nematodes.
• Apply S. carpocapsae to combat cutworms, armyworms, corn rootworms and fire ants.
• Apply Heterorhabditis bacteriophora to reduce problems with cabbage root maggots, Colorado potato beetle larvae, white grubs and root weevils.
Elmer Krehbiel is a gardener with the Texas A&M AgriLife Extension Service. Email him at firstname.lastname@example.org.