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Beneficial Nematodes: An Easy Way to Begin Using Biological Control in the Greenhouse

Growers that are interested in using biological control can start by using beneficial nematodes to manage fungus gnats. They are relatively easy to use and are applied in a similar manner to conventional pesticides with some special precautions that are listed in this factsheet.

What are beneficial nematodes?

Nematodes are small, colorless, cylindrical round worms that occur naturally in soils throughout the world. Different species work best against different insect pests. Steinernema feltiae is primarily used against fungus gnat larvae and thrips pupae dwelling in the soil media. Fungus gnat larvae may be parasitized in any larval stage. Nematodes have traditionally been used against soil dwelling pests because they are sensitive to ultra violet light and desiccation.

The beneficial nematodes enter the insect host through body openings. These insect killing nematodes multiply within the host and release a symbiotic bacterium (Xenorhabdus spp.) whose toxin kills the target pest, i.e. fungus gnats. The fungus gnat larvae are killed in one to two days by blood poisoning. More than one generation of nematodes may develop in dead host insect in the growing media. The infective juveniles then exit the dead body and search for new hosts to infect.

How to use beneficial nematodes

The beneficial insect killing nematode S. feltiae is sold under the trade names of NemaShield, Nemasys, Scanmask and Entonem. All of these products are labeled as a soil drench treatment against fungus gnat larvae. Preventative applications to moist soils work best.

Unlike many traditional pesticides there is no re-entry interval (REI) (an added bonus in propagation houses).  No adverse effects have been shown against non-target organisms in many different field studies. But, beneficial nematodes are living organisms, so there are a number of precautions you need to follow for their successful use.

Check nematode viability before application

Dead nematodes are straight and still.

For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet:
Pesticide Side Effects Database
Pesticide Side Effects Database
Becker Underwood Compatibility Chart

When you receive the nematodes

 When you receive the nematodes, check to see that the cold packs are still cold.  If you must store the nematodes, store them in a refrigerator at (38-42°F). Avoid placing them in a small refrigerator where they may freeze and die!  Make sure that there is adequate circulation around each tray or package. Check the expiration date on the package for the length of time they can be stored.

Specific Tips when applying Nematodes for Use Against Fungus Gnat Larvae

Drenching nematodes at a planting line at Michaels greenhouses.

How to tell if the nematodes are working against fungus gnats

The symbiotic bacteria break down the host insect’s cuticle. The infected fungus gnat larvae rapidly disappear, so they may be difficult to locate in the growing media. Infected fungus gnat larvae are often opaque-white to light yellow in color.

Use potato disks to monitor for fungus gnat larvae. Place disks on the surface of the growing medium two days before application in order to determine the population level prior to treatment, and again 3-5 days and 10-12 days after application. Leave the potato disks on the growing media for two days in each case, before examining them for fungus gnat larval activity.

Beneficial Nematode use against western flower thrips
 
Nemasys is also labeled for use against western flower thrips. In the late 1990s in the U.K., it was reported that cut chrysanthemum growers who applied nematodes weekly as a foliar spray, noted a reduction in their thrips populations. More recent work in Canada, the U.K. and Germany showed that soil-dwelling stages of thrips (especially the pupal stages) were highly susceptible to several species of nematodes, such as Steinernema feltiae.

During the weekly sprays, a significant number of nematodes reached the growing media via runoff from the foliar sprays. Nematodes are very short lived on the foliage (significant reduction after one hour) but may persist for several weeks in the media. Mobile life stages on the plant (adults and larvae) appear to be less susceptible to attack. Thrips control noted in commercial crops may have occurred as a result of overspray and run-off into the soil after spraying. Special precautions are taken to help reduce potential desiccation: use of a non-ionic wetting agent such as Capsil, spraying in the late afternoon or evening, and the use of black shade cloth. Begin treatments with an early drench to the media and then continue with weekly sprays to the foliage making sure you have uniform coverage of the foliage and also sprench the soil.

Specific tips for use against western flower thrips (from the Nemasys label).

Grower feedback has been variable, with some observing excellent results and others less so. Efficacy will be variable depending upon the relative humidity, and temperature in your greenhouse, dose applied, frequency of application, and life stage of the thrips.  Some growers apply the nematodes with additional water in the summer months to ensure that the foliage stays wet to contact the thrips on the foliage. Depending upon the temperature, relative humidity levels and other environmental conditions, up to 2x the amount of water may be needed to keep the foliage wet for two hours. Regular monitoring, sanitation, proper spacing and judicious use of fungicides and biological fungicides may be needed to discourage foliar diseases.

References

By: Leanne Pundt, Extension Educator, University of Connecticut 2010. Revised 2012

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.



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