Spray technique affects nematode rates

Spraying nematodes in your greenhouse for fungus gnats, shoreflies, or thrips?  Then check out this article published in the January 2015 issue of Hort Matters (OMAFRA’s Horticultural newsletter):


Researchers realized that nematodes can “stick” to the inside of spray tanks, reducing the number of nematodes coming out of the nozzle as you spray.  This is unlikely to be a problem using backpack sprayers (since the volume is so small), but could be an issue if you use a towed sprayer on wheels.

What’s the solution? Agitation, agitation, agitation.

To keep your nematode numbers consistent throughout the application, do your best to keep nematodes in suspension.  And, if you have any concerns about your application technique, it’s easy enough to assess if you have a microscope (or have a friendly neighbourhood OMAFRA agent with one).

Nematodes (S. feltiae) preparing to enter an adult western flower thrips.
Nematodes (S. feltiae) preparing to enter an adult western flower thrips. Photo by R. Buitenhuis (Vineland).

Nematodes are around 0.5 mm long, and can be easily seen using the low magnification setting on a scope.  A black background makes them easier to see. Live nematodes are usually serpentine or “J” shaped, and often wiggle slightly.  Dead nematodes are stick straight.

By counting the number of live nematodes in a small volume of your original spray solution (1 mL should do it), you can compare this to the number of nematodes in the same volume (1mL) from the nozzle dribble at the end of your application.  Seeing a huge reduction here?  Then you may have a problem.

To ensure nematode health, also follow these other tips:

  • Air temperature should be less than 30 C at application time
  • Apply during low light levels since nematodes are UV sensitive
  • Nematodes can be stored in a refrigerator (4C) but should be used within 4 weeks of receipt
  • Do not apply nematodes though sprayers that exceed 300 psi
  • Use a nozzle aperture of more than 0.5 mm


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