Beneficial Nematodes

- Tiny worms that kill soil pests -

Summary: Beneficial nematodes are microscopic worms that infect and kill certain soil insect pests. Some of these nematodes can now be artificially produced and applied like a pesticide against a variety of landscape pests including root weevils, white grubs, mole crickets and fungus gnats.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

What are beneficial nematodes?

Nematodes are microscopic worms (see photo right) that live in all soils. Most species feed on soil bacteria but some species are plant pathogens that cause plant disease, and a few are insect pathogens. The species that attack insect pests are the so-called beneficial nematodes.

Naturally occurring beneficial nematodes are generally not present in high enough numbers to completely control soil pests like root weevils, white grubs, and mole crickets. However, some species can now be mass-produced and applied to soils much like a conventional pesticide. These nematodes are non-toxic and will not harm you or your plants.

entomopathogenic nematode

A beneficial nematode worm, highly magnified.

Using nematodes for insect control can be a bit tricky however. The most important considerations are (1) selecting the strain (species) of nematode that is intended for your target pest; (2) maintaining adequate soil moisture, (3) proper soil temperature, and (4) ensuring product viability. Follow package instructions carefully to have the best chance of success.

Nematodes actually live on a thin film of water that covers soil particles so nematodes are essentially aquatic organisms. Because of this the correct soil moisture is important. If the soil is too dry then the nematodes can't swim, too wet and they may be washed away.

There are several different types of nematodes made for soil insect control.  Be sure to select the correct species and follow instructions exactly. Remember, beneficial nematodes are living organisms that must be handled correctly to be effective. Pay particular attention to proper soil moisture and soil temperature. Optimum soil temperature varies but generally temperatures above 50 deg. F. are needed.

Are the nematodes you bought still viable (alive)?

Finally, and this is very important, you should always do a viability test before applying nematodes to be certain they are alive and able to function. If the packaged nematodes are not handled properly during shipment they can arrive dead and therefore useless. Be sure the supplier ships quickly and packages include a cold pack.

To conduct a viability test mix the nematodes as per package instructions, wait 30 minutes then place a drop or two on a flat piece of glass or clear plastic. Carefully examine the drop under good light with a hand lens or microscope. You should be able to see the tiny nematodes wriggling or bending back and forth. If they are stiff and not moving, they may not be viable. If you receive non-viable nematodes contact the supplier immediately to get a replacement.

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