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Nematodes

by Karen Miller, Master Gardener Entomology Specialist

Nematodes – friend or foe? Both actually, some nematodes are beneficial and others are troublesome and harmful. Most of the thousands of species of nematodes on earth are not harmful, others are parasitic and can cause diseases in humans and animals. Also, there are many that attack and feed on living plants.

Even though nematodes are described as worm like, they are not closely related to the true worm. Nematodes are the most multi-cellar animal on earth. They are colorless, unsegmented and have no appendages.

Nematodes can be free-living, predaceous or parasitic. One handful of soil will contain thousands of this microscopic worm, many of them parasites of insects, plants or animals. Free -living species are abundant too, including nematodes that feed on bacteria, fungi and other nematodes.

Adult nematodes are made up of approximately 1,000 somatic cells and possibly hundreds of cells associated with the reproductive system. Nematodes have digestive, nervous, excretory and reproductive systems, but do not have a distinct circulatory or respiratory system. They range from 0.3 mm to over 8 meters in size.

The female will lay her eggs in masses or keep them inside her to hatch upon her death. Temperature and moisture levels determine when the eggs will hatch. The larva will not emerge from the egg until conditions are favorable for survival. The larvae are mobile in the soil and become adults after several moltings. The life cycle of the nematode is generally from three to four weeks.

Beneficial nematodes kill by releasing a bacteria that grows, feeds on and liquefy the body tissues of the pest. These nematodes are important in controlling grubs, roaches, termites, fleas, ticks and other troublesome pests. Beneficial nematodes can be purchased and used to control many pest found in the soil. They can be found in wet or dry formulations. Be sure, however, to store them according to the instructions to insure you get the maximum benefit.

The best-known problem nematodes are, of course, the root knot nematodes. They feed on plant roots and cause small galls or lesions and injured root tips. There are other destructive nematodes that live in and eat roots but do not form the knots. They are sometimes more destructive because the damage they cause is harder to detect.

There is no way to rid the soil of these pests. When nematodes become a problem it usually indicates the soil is out of balance and lacking sufficient beneficial organisms. Poor soil health is just an invitation to this unwanted pest.

Bottom line...Here are a few suggestion to help restore our soil’s balance. Humates and small amounts of sulfur help stimulate beneficial microbes in the soil. Liquid bio-stimulants are excellent for encouraging beneficial soil life.

Limited use of high nitrogen artificial fertilizers and toxic pesticides. Insects, worms and other pest are not a problem unless their populations get out of control. Spray products and fertilizers that encourage microbial and beneficial nematodes that attack and destroy plants-eating nematodes might also be recommended. Of course, crop rotation and selecting resistant or tolerant plant varieties are also suggested.

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