Floriculture Greenhouse Update

Entomopathogenic Nematodes

Tuesday, 19 January 2010 09:41

Nematodes are small, colorless, cylindrical round worms that occur naturally in soils throughout the world. Different species work best against different target pests. Steinernema feltiae is primarily used against fungus gnat larvae and thrips pupae in the soil. 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.

The nematodes enter the insect host through body openings. They multiply within the host and release a symbiotic bacterium whose toxin kills the fungus gnats. The 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 media. The infective juveniles then exit the dead body and search for new hosts to infect

The nematode S. feltiae is sold under the trade names of NemaShield and Nemasys. Both of these products are labeled as a soil drench treatment against fungus gnat larvae. Preventative applications to moist soils work best.  Apply nematodes with a sprayer (remove screens and filters), injector, hose end sprayer or even a watering can. If using an injector, set the dilution to 1:100. Remove all filters or screens on the intake tube. Remove pump filters. Use a small battery powered submersible pump to keep the solution agitated.

Unlike many traditional pesticides there is no REI (an added bonus in propagation houses), nor possibility that the target pest will develop resistance. 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 viability before application. To do this, place a small amount of the product in a small container or petri dish. Add 1 or 2 drops of room temperature water; wait a few minutes and look for actively moving or swimming nematodes. Use a dark black background and a hand lens or field microscope to see the small (0.6 mm or 0.02 inches in length) nematodes. Apply in the evening or at dusk or on a cloudy, overcast day. (Nematodes are very sensitive to UV light and desiccation).

Nematodes are compatible with a number of different pesticides. However, they are generally not compatible with organophosphates, carbamates, and nematicides.   However, do not mix nematodes with your fertilizer solution!  

For more detailed information on pesticide compatibility: consult with your supplier or with the following resources on the Internet:

- Pesticide Side Effects Database – www.koppert.com

- Pesticide Side Effects Database - www.biobest.be/

Apply immediately after receiving them, if possible.  If you must store the nematodes, store in a refrigerator (38-42°F). Avoid placing in a small refrigerator where they may freeze. Check expiration date on the package for how long you can store them.

Specific Tips for Use Against Fungus Gnat Larvae. 

• Treat as soon as possible (2 to 3 days) after sticking cuttings, planting plugs or starting seeds. 
• Apply as a media drench to target the fungus gnat larvae.
• Media temperatures should be above 50° F but avoid applying when soil temperatures are above 80°F. Optimum media temperatures are between 60-70°F. (Use a soil thermometer to monitor temperatures).
• Water the growing media before and after application. (Nematodes need moisture for movement). But, avoid over watering, so they aren’t washed out of the container.
• Apply in the evening or at dusk or on a cloudy, overcast day. (Nematodes are very sensitive to UV light and desiccation).
• Repeated applications are often needed. Reapply in 2 to 4 weeks under moderate to heavy infestations. For longer term crops, apply at the beginning and at mid crop.

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

In addition, the product Nemasys is also labeled for use against western flower thrips. Specific tips for use against western flower thrips (from the Nemasys label).

• Nematodes require moist conditions to enhance effectiveness.
• If plants are dry, provide light overhead irrigation prior to nematode application.
• Ensure good foliar coverage of spray mix to enhance contact with the target pest.
• Use of a wetting agent or surfactant will enhance wettability of the spray mix and encourage nematode movement.
• Following application, ensure that the crop remains wet for at least two hours.
• Do not apply in direct sunlight.

Note: the nematodes will dessicate after about one day.  Growers who have had success with this application method, apply the nematodes on a weekly basis, and target the young growing point where thrips tend to hide.

For more information on Steinernema feltiae:

NemaShield- BioWorks
Nemasys - BeckerUnderwood
Searchable Database on Insect Parasitic Nematodes: Ohio State University

Leanne Pundt, University of Connecticut