Nematodes are tiny, microscopic, un-segmented, threadlike worms that swim in the soil moisture surrounding both soil particles and plant roots. Many nematodes are beneficial, preying on other nematodes that actually attack plants and other pests. They live in moist soil, decaying organic matter, water and inside of plants and other animals.
There are thousands of species of nematodes. Although “worm-like” they are not related to actual worms.
Parasitic nematodes lay eggs on plant roots that hatch into tiny larvae. The larvae molt a few times and then mature into adults. They puncture plant cell walls, inject a body fluid and suck out the plant cell’s contents. Some species feed on the outside of plant roots and others enter the roots and live inside the plant, slowly destroying it. Symptoms include reduced growth, wilting and just an overall, unhealthy look. They can also attack leaves.
Root knot nematodes are very common, especially in lettuce, beans, tomatoes, potatoes, peppers and corn.
Good organic matter in the soil helps to prevent nematodes as it promotes populations of beneficial fungi that feed on the nematodes. Also, companion plants such as marigolds repel them. Susceptible crops should always be rotated.
Beneficial nematodes, available in most garden centers, kill soil dwelling and boring insects such as weevils, grubs, beetles, maggots and cutworms. More than 230 different species of insects can be destroyed. They also hasten the decomposition of organic matter in compost. Once they attack an insect, they release bacteria that paralyze and kill the insect within a couple of days and feed on it.
Since nematodes travel in a moist environment, the area to be treated should be well watered before application and again, after application for a few days. Keep them out of direct sunlight which will kill them. Evening or very cloudy conditions are the best time to apply.
As temperatures drop in the winter, they travel deeper into the soil to hibernate. In spring, warmer temperatures allow them to move closer to the soil surface. Since their return lags behind the earlier arrival of spring pests, they should be reintroduced every year.
In areas where nematodes are common in the soil, plant susceptible crops as early as possible or very late to take advantage of lower soil temperatures. Most nematodes are unable to penetrate plant roots when the soil temperature is below 64 degrees.
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