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Beneficial Nematodes
- Tiny worms that kill soil pests -
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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.)
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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.
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A beneficial nematode worm,
highly magnified.
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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.
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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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using least-toxic methods.
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