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Improving Success with Beneficial Nematodes

March 27, 2013

Many growers rely on beneficial nematodes to control various greenhouse pests. Products containing the beneficial nematode Steinernema feltiae are used to control fungus gnat larvae and Western flower thrips pupae.  Another nematode species, Steinernema carpocapsae, can be applied to control shore fly larvae.

Beneficial nematodes work by actively seeking out the life stages of the pests that live in the growing mix. Once they enter the host, the nematodes molt and release a symbiotic bacterium which multiplies and rapidly kills the pest.  The nematodes feed on the host's tissues and continues their lifecycle, reproducing a new generation of nematodes which attack additional pest pupae or larvae in the growing mix.

Application Rates of Beneficial Nematodes

To properly control fungus gnats, it is very important to apply beneficial nematodes at an appropriate rate and application frequency.  The application rates vary with the pest population and should be determined by the weekly scouting results (namely sticky card counts).  

Controlling Fungus Gnats Using Steinernema feltiae

The best results are obtained when the fungus gnats first become apparent and the pest pressure is low.  Multiple applications are usually beneficial. The best control is obtained when nematodes are applied at 7 to 10 day intervals. When the fungus gnat populations are low, the application interval can increased to 10 to 14 days.  Applying beneficial nematodes more than 14 days apart usually results in inadequate levels of fungus gnat control.

Light Pest Levels
250 million nematodes per 8,500 square feet (approximately 29 million per 1000 sq ft)

Moderate Pest Levels
250 million nematodes per 5,500 square feet (approximately 45 million per 1,000 sq ft)

Many growers elect to apply a higher application rate initially and use lower rates for the subsequent applications unless their scouting activities indicate the pest levels are not decreasing or have increased since the previous application.

Scouting should occur at least on a weekly basis. The frequency of the application can be determined by the pest levels observed. When the pest levels begin to increase, apply beneficial nematodes more frequently using higher rates; conversely, when the pest levels are decreasing, the application interval and application rates can be decreased.  Even when an appropriate quantity of nematodes are applied, an unacceptable levels of control may be obtained if the applications are applied too infrequently.  

Controlling Western Flower Thrips Using Steinernema feltiae

Steinernema feltiae can also be used to disrupt the portion of the life cycle of Western flower thrips which occurs in the growing mix (the pre-pupae and pupae stages).  The same application rates and guidelines used to control fungus gnat larvae can effectively be used to control Western flower thrips.

Controlling Shore Flies Using Steinernema carpocapsae

Steinernema carpocapsae can be applied by itself or in conjunction with Steinernema feltiae.  Many growers primarily apply Steinernema feltiae to control fungus gnats and add Steinernema carpocapsae when the shore fly populations begin to rise and omit them altogether when the shore flies are not present or are at very low levels.  A common practice for controlling shore flies once they become present is to use a high rate (250 million per 3,000 square feet) and make 3 consecutive applications at 7 day intervals.

To enhance the effectiveness of beneficial nematodes, it is best to practice the following guidelines:

  1. Keep in mind that the applications are targeting the generations that occur in the soil – not the foliar life stages.  
  2. Moisten the growing mix prior to applying nematodes. Wetting the foliage just prior to application will help the nematodes move into the growing mix as well.
  3. Apply at dusk or during cloudy weather conditions to increase the time the foliage remains wet – this improves the migration of the nematodes into the growing mix. Avoid applying in direct or intense sunlight.
  4. Apply using a hydraulic sprayer, injector, boom irrigation or hose-end sprayer. Remove any filters or screens from spray equipment or irrigation systems.  Continuously agitate the solution containing the beneficial nematodes during the application.  Use course spray settings (minimum 0.5 mm or 35 mesh).  Apply with pressures below 300 psi.  
  5. Apply within one hour of mixing.
  6. Using an wetting agent or surfactant increases the nematodes ability to move into the soil and find the target pests.
  7. Lightly wetting or rinsing the foliage following the application is an effective method of moving the nematodes to the growing mix.  Avoid excessive irrigation at this time.
  8. Avoid large wet dry cycles following application. Maintain uniform moisture levels.
  9. Beneficial nematodes are going to be active at the same temperatures as the larval and pupal stages of the pests they control (more active during warm days and less active with cooler conditions). Nematodes are active when the temperatures are 50 to 86° F (74° is optimal).

Paul Pilon
Perennial Solutions Consulting

The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.


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