Features Agronomy
Beneficial nematodes and their impact on grubs in turf

NEMATODES (also called entomo-pathogenic or beneficial nematodes) are
microscopic roundworms, or tiny worm-like parasites that lack any
appendages. They are found in products that are classified by the
government as bio-pesticides since they contain living organisms. The
product acts as a biological turf insecticide that, at this time, is
not yet registered as a pest control product in Canada.

The term “entomo-pathogenic” comes from two Greek words: entomon which means insect, and pathogenic, meaning causing disease.

Classification of entomo-pathogenic nematodes

Entomo-pathogenic nematode products are considered as low-risk, green alternatives to conventional insecticides. They have been classified or described in a multitude of ways. Here are some examples:
• beneficial nematode product
• bio-control of insect pest
• biological control agent
• biological insecticide
• bio-pesticide
• bio-suppression of insect pest
• commercial nematodes
• entomo-pathogenic nematodes
• exotic nematodes
• infective juvenile nematodes
• low or reduced-risk pesticide
• microscopic worms
• natural insecticide
• natural organism
• nematode product
• parasitic nematodes

Canadian regulatory management of entomo-pathogenic nematodes

In Canada, pest control products, or pesticides, are federally regulated and registered by Health Canada under the Pest Control Products Act, and are among the most stringently regulated substances in Canada. The Pest Management Regulatory Agency (PMRA) is the branch of Health Canada that administers the act on behalf of the Minister of Health. The primary objective of the PMRA is to prevent unacceptable risks to people and the environment from the use of pest control products.

Here is the federal definition of a “pest control product:"

“Pest control product” means a product, an organism or a substance, including a product, an organism or a substance derived through biotechnology, that consists of its active ingredient, formulants and contaminants, and that is manufactured, represented, distributed or used as a means for directly or indirectly controlling, destroying, attracting or repelling a pest or for mitigating or preventing its injurious, noxious or troublesome effects.

Current regulatory policy concerning nematodes

According to the Pest Management Regulatory Agency of Health Canada, in a meeting held May 22 and 23, 2008, with a document entitled “Pest Management Advisory Council (PMAC) — Meeting Report,” in a segment called “Overview of Some Current PMRA Policy Development Projects.” Here are excerpts from that report:

• This overview was intended to prompt Council members in providing advice on areas where they consider there may be a need for PMRA to either develop new policies or review existing ones. (…)

• To a concern expressed on the process to register biopesticides, PMRA pointed out that Canada and the U.S. have harmonized their requirements, and reminded stakeholders that PMRA can work with a U.S. package for assessment, although Europe is different. (…)

More explanations on regulatory policies are found in the following excerpts from the 2002 book, “Entomopathogenic Nematology”:

• Commercial development of entomopathogenic nematodes in the U.S.A in the early 1980s was aided by an exemption from registration (…)

• Canada followed and adopted a similar approach a few years later. (…)

• Little was known about the risks associated with the introduction of entomopathogenic nematodes and concerns eventually arose about the considerable exchange of nematode germplasm occurring between laboratories. (…)

• The issues for entomopathogenic nematodes (…) sparked a rethinking of the mechanisms by which the U.S.A. should regulate exotic natural enemies of pests. (…)

• In the U.S.A., there are now complex regulatory procedures and safeguards in place for the introduction of exotic nematodes. (…)

Reduced-risk pest control products in Canada

Entomo-pathogenic nematode species are listed as a reduced-risk chemical active ingredient by the PMRA in a Jan. 7, 2008 document entitled, “Update on Reduced-Risk Pesticides in Canada.”

Here are excerpts from that report:

• Health Canada’s Pest Management Regulator Agency (PMRA) recognizes the need to encourage registration of new reduced-risk pesticides and has acted upon a government commitment to pursue harmonization as one of the key means of achieving efficiencies and facilitating access to new lower-risk technology. To facilitate the registration of reduced-risk pesticides, the PMRA, the United States Environmental Protection Agency (USEPA) and pesticide regulatory agencies in Mexico collaborated to establish the Joint Review Program for Reduced-Risk Chemicals in 1996, under the NAFTA Technical Working Group on Pesticides. (…)

• The reduced-risk desgination does not imply that a product exhibits no risk. A reduced-risk pesticide may have a slightly improved risk profile when compared to other registered pesticides with the same use pattern. (…)

• Registration of a pesticide is considered only if the health and environment risks are acceptable and if the product is effective. (…)

List of reduced-risk pest control products in Canada

In Canada, the list of active ingredients that fall under the classification “Reduced-Risk Chemical Active Ingredients, End-Use Products and Uses Registered in Canada — Commercial Products” does not just include the “green alternatives” to conventional pest control products.

Here are some of the products listed, as of Sept. 30, 2007, in a Jan. 7, 2008 document entitled, “Update on Reduced-Risk Pesticides in Canada,” issued by Health Canada:

• acetic acid
• azoxystrobin (Heritage)
• bacillus thuringiensis
• boscalid (Cadence)
• corn gluten meal
• diatomaceous earth
• glyphosate (Roundup)
• sclerotinia minor
• soap
• trifloxystrobin (Compass)

Canadian manufacturers’ position regarding bio-pesticides

In April 2009, CropLife Canada issued a public letter to the Ontario Ministry of the Environment.
CropLife is the trade association representing the manufacturers, developers and distributors of plant science innovations—pest control products and plant biotechnology—for use in agriculture, urban and public health settings.

Here are excerpts from the letter:

• The description used in Class 11, “certain bio-pesticides and naturally-derived pesticides,” does not constitute scientific criteria. There is no scientific merit for the differentiation between naturally-derived and synthetic products. This type of arbitrary designation perpetuates the misconception that “natural” automatically means “safe.” We know of numerous examples of substances that are naturally-occurring—such as arsenic, lead and nicotine—that would clearly not be appropriate for this class. The active ingredients listed here certainly do not encompass the full range of innovative, low-risk products that have been made available by members of CropLife Canada. CropLife Canada requests that the Ministry provide its rationale for the definition of Class 11. (…)

• We would suggest that the Province of Ontario consider the Health Canada model, which bases all pesticide assessments on science and the inherent properties of all products—both natural and synthetic—as part of the risk assessment. (…)

Ontario regulatory management of entomo-pathogenic nematodes

Here is the Ontario definition of a “pesticide.”

“Pesticide” means any organism, substance or thing that is manufactured, represented, sold or used as a means of directly or indirectly controlling, preventing, destroying, mitigating, attracting or repelling any pest or of altering the growth, development or characteristics of any plant life that is not a pest and includes any organism, substance or thing registered under the Pest Control Products Act (Canada); (“pesticide”)

In order to implement the 2009 Cosmetic Pesticides Ban Act, the Ontario Ministry of the Environment developed a new classification framework that includes 11 classes of pest control products.

Here is a summary of the Ontario classification of pest control products:
• Class 1 — Manufacturing concentrates used in formulations.
• Class 2, 3 and 4 — Commercial or restricted (non-domestic) products that may continue to be used by farmers and exterminators. Examples include 2,4-D, Acclaim, Aliette, Arrest, Banner, Benvel, Captan, Compass, Cygon, Daconil, DeltaGard, Diazinon, Gramoxone, Heritage, Instrata, Killex, Orthene, Proturf Fungicides, Quintozene, Ramik, Roundup, Senator, Sevin, Waxed Mouse Bait.
• Class 5 and 6 — Domestic products, including bio-pesticides and lower-risk products allowed for cosmetic use.
• Class 7 — Domestic products for non-cosmetic use.
• Class 8 — Domestic products that are prohibited.
• Class 9 — Active ingredients prohibited for cosmetic use. Examples include 2,4-D, Acephate, Captan, Carbaryl, Chloroneb, Chlorothalonil, Deltamethrin, Diazinon, Glyphosate, Imidacloprid, Iprodione, Myclobutanil, Propiconazole, Quintozene, Thiophanate-methyl.
• Class 10 — Products to be used under the health or safety exception.
• Class 11 — Certain bio-pesticides and naturally-occurring pesticides.
Of particular interest is Class 11, which is described as follows:
Class 11 lists ingredients that are biopesticides or lower-risk pesticides. Licensed exterminators (applicators) that use Class 11 pesticides are required to post a green notice sign to provide public notice of the use of these pesticides.

The list of active ingredients that fall under Class 11 basically includes all the “green alternatives” to conventional pest control products.

Here are some of the Ontario Class 11 bio-pesticide products listed, as of March 4, 2009:
• acetic acid
• Bacillus thuringiensis
• Borax
• corn gluten meal
• fatty acid
• iron (ferrous or ferric) sulfate
• lime sulphur
• Sclerotinia minor
• Soap
• Sulphur

Target insects suppressed by entomo-pathogenic nematodes

Specific types of nematodes may suppress only specific insects. Nematodes do not suppress all insects. Here are some examples of entomo-pathogenic nematode species that are considered virulent against certain insect pests of turf. Some reports of suppression may be anecdotal only:

• annual bluegrass weevil (hyperodes weevil) larvae — Heterorhabditis bacteriophora and Steinernema carpocapsae.
• Ants — Steinernema feltiae.
• Billbug larvae — Steinernema carpocapsae.
• Chinch bugs — Steinernema carpocapsae. To date, entomo-pathogenic nematodes have not been thoroughly tested for the suppression of chinch bugs. Some nematode species may be effective in suppressing chinch bugs under moist to wet thatch conditions, but they may not be recommended.
• Cutworm larvae — Steinernema carpocapsae.
• European chafer larvae — Heterorhabditis bacteriophora, Heterorhabditis megidis and Steinernema scarabaei.
• Japanese beetle larvae — Heterorhabditis bacteriophora, Heterorhabditis zealandica, Steinernema glaseri and Steinernema scarabaei.
•â€ˆLeatherjacket larvae — Heterorhabditis bacteriophora and Steinernema feltiae.
• Nematodes (naturally-occurring species that are plant-parasitic to turf) — Steinernema carpocapsae and Steinernema riobrave.
• Sod webworm larvae — Heterorhabditis bacteriophora and Steinernema carpocapsae.

Mode of action of entomo-pathogenic nematodes

With the appropriate environmental conditions, entomo-pathogenic nematodes will seek the insect larvae and pupae in the soil. The infective juvenile nematodes enter natural body openings of the insect larvae, such as the anus, mouth and spiracles. They release a symbiotic bacterium in the body cavity that causes rapid infection of the internal tissues, leading to death in one or two days. The nematodes then feed and reproduce inside the insect cadaver, and subsequently release a new generation of hungry little nematodes that disperse and attack other larval victims. Some reports indicate that suppression of larval populations may sometimes last for one to two years after the application.

Target insect response to infective nematodes

When an insect has been killed by entomo-pathogenic nematodes, the body becomes flacid and changes to a conspicous colour. As a rule, larvae killed by certain nematode species will change into the following colours:
• Heterorhabditis bacteriophora — reddish-brown cadaver colour.
• Steinernema carpocapsae — yellow cadaver colour.
The nematodes then feed on the bacteria and the dead insect, and move on to consume and contaminate new target insects.
Conserving entomo-pathogenic nematodes in the soil
Suppression of larval populations may sometimes last for one to two years after the application of entomo-pathogenic nematodes. In order to properly conserve nematodes once they are in the soil, the following factors must be considered:
• Extremely dry soil conditions are detrimental to nematodes.
• Presence of the target insect is important. If it has been absent for an extended period of time, the nematodes may not be able to suppress it later.
• Conventional insecticides may have minimal impact on beneficial insects such as nematodes. Nonetheless, nematode manufacturers recommend that pest control products be avoided.

Activity of entomo-pathogenic nematodes in the soil

Different entomo-pathogenic nematodes species will differ in their type of activity against different insect pests. These differences are determined by the nematode behaviour and by the number of symbiotic bacteria carried by nematodes. Here are some examples:
• Heterorhabditis bacteriophora — Cruising activity, allowing this species to prey on insects that are less mobile in the soil, such as white grubs.
• Steinernema carpocapsae — Ambush activity, allowing this species to prey on insects that are mobile close to the soil surface and thatch, such as the larvae of billbugs, cutworms and sod webworms.
• Steinernema glaseri — Cruising activity.

Application of entomo-pathogenic nematodes

Applications of nematodes may be performed using conventional liquid sprayer equipment, with eight to 20 litres of water per 1,000 square feet. Ideally, the nematode product should not remain in solution for more than two hours after it has been mixed with water. Labels usually state that the solution must be used immediately after mixing.

Most labels will also indicate that nematode products should not be tank-mixed with other products. Some of the following products may be suitable for tank-mixing with nematode products, depending, of course, on the manufacturer’s directives:
• Azoxystrobin (Heritage)
• Benomyl (Tersan 1991)
• Carbaryl (Sevin)
• Chlorothalonil (Daconil)
• Deltamethrin (DeltaGard)
• Iprodione (Rovral)
• Primer 604 wetting agent
• Propiconazole (Banner)
• Thiophanate-Methyle (Senator)

Storage of entomo-pathogenic nematode products

Once entomo-pathogenic nematodes have been purchased from commercial suppliers, they must be used within a short space of time. Most suppliers will ship directly to the end user, using next day or second-day delivery service. During transport, the nematodes may be kept cool with ice packs. The shelf life of nematodes is limited, and the label may recommend that this product be stored in a refrigerator at plus 5 degrees Celsius (40 degrees Fahrenheit).

Efficacy of entomo-pathogenic nematode products

Laboratory and field tests indicate that the best species provide up to 50 to 65 per cent control or suppression of the damaging insect population.

Additionally, some studies have indicated that, under ideal conditions, some species of nematodes can be as effective as some conventional insectides.

Conditions favouring suppression by entomo-pathogenic nematodes

When utilizing entomo-pathogenic nematodes, their control efficacy can be maximized by the manipulation of environmental conditions. The following conditions have proven to affect the results when using nematode products:

• Aeration by coring before an application of nematodes is recommended by some professional lawn care companies. In theory, soil aeration can be instrumental in making it easier for the nematodes to get down into the soil where the grubs are located.

• Irrigation must be performed as a soil drench immediately after application with at least 13 millilitres (half-inch) of water in order to rinse the nematodes off the foliage and move them into the soil and thatch. Maintaining soil moisture at an optimum level following the application will help to enhance the nematode activity and suppression of insect pests.

• Soil conditions must be moist. Nematodes require moist soil conditions for optimal activity. If the soil is too dry, turf may require irrigation prior to application. Irrigation must be performed prior to applying the nematodes under dry soil conditions.

• Soil type may also be a factor for good results. For instance, nematode activity and survival appears to be lower in heavy clay soils when compared to sandy-loam soils.

• Sunlight must be avoided…especially direct sunlight. Nematodes are extremely sensitive to direct sunlight as well as heat. It is preferable to perform applications early in the morning, or late in the evening, or during days that are overcast.

• Temperatures need to be above 13 degrees Celsius or 55 degrees Fahrenheit. Otherwise, insects will not be affected by nematodes. Soil temperatures of 13 to 27 degrees Celsius (55 to 80 degrees Fahrenheit) are deemed to be good for nematode survival and activity. Additionally, higher temperatures will tend to diminish the survival of nematodes.

• Timing is important for the effective suppression of certain insects with nematodes. Nematodes must be applied preventively, before larvae become a problem. This means that for the suppression of many white grub species, the nematodes must be applied in the fall. However, for ants, a curative application is recommended when they are present.

Product safety and toxicity

Entomo-pathogenic nematode products are considered lower-risk green alternatives to conventional turf insecticides. Nonetheless, they may cause mechanical irritation of skin and eyes after prolonged or repeated contact. Prolonged inhalation may lead to respiratory tract irritation.  No information is available regarding the LD50 of nematode products, or the symbiotic bacteria associated with them.

Material safety data sheets

Work has yet to be done in order to improve the information contained in material safety data sheets for entomo-pathogenic nematodes. It may be only a matter of time before the environmental movement demands more information regarding the safety of nematodes, as well as their symbiotic bacteria.

Here are some adapted examples of statements found during a review of the material safety data sheets produced by some manufacturers or distributors of entomo-pathogenic nematodes:
• Ingestion is not an intended route of exposure for this nematode product.
• Inhalation is not expected with this nematode product.
• Irritation may develop with this nematode product, causing itching and redness.
• No data is available regarding the eco-toxicity of this nematode product.
• No data is available regarding the environmental fate of biodegradation of this nematode product.
• Repeated or prolonged exposure to the nematode product, at a concentration above the exposure limits, may cause sensitization leading to eye and skin irritation.
• Short-term harmful effects of this nematode product are not expected.
• The composition of this nematode product is a trade secret.
• The information provided by the Material Safety Data Sheet is for information only.
• There is no known chronic toxicity of this nematode product.
• There is no known developmental toxicity by this nematode product.
• There is no known mutagenic effect by this nematode product.
• There is no known teratogenic effect by this nematode product.
• This nematode product does not require a Material Safety Data Sheet.
• This nematode product has no reportable quantities of hazardous ingredients.
• This nematode product is not considered dangerous.
• This nematode product is not considered hazardous.
• This nematode product is not considered to be a hazardous substance as defined under government regulation.
• This nematode product is not expected to have any deleterious eco-toxic effect.
• This nematode product may upset the gastro-intestinal tract.

Conclusion

 In those regions affected by prohibitions of conventional pest control products, and in those same regions invaded with damaging turf insects such as white grub larvae, entomo-pathogenic or beneficial nematodes are an effective option available for the professional lawn care industry as well as the do-it-yourself-homeowner. The fact that such products are not registered as pest control products in Canada is something that should be corrected quickly in order to guarantee that this kind of product remains available in the marketplace. 

This is regardless of the situation whereupon the best nematode species provide moderate control of damaging insect populations. The manufacturers themselves are providing high-quality products, but those suppliers who import entomo-pathogenic nematodes into Canada must take a pro-active approach before the demands for registration begin. The market longevity of entomo-pathogenic nematodes is at stake.

 It has been repeatedly pointed out that the use of many green alternatives, such as beneficial nematodes, are reduced-risk and safer for health and the environment. It is time that such products be federally registered to fully support these claims.

A precedent was set with another bio-insecticide, Bacillus thuringiensis, which was once embraced by the environmental movement but has since been deemed unacceptable from a safety standpoint.

About the principal author

William H. Gathercole holds a degree in horticulture from the University of Guelph and another pure and applied science degree from McGill University. He has worked in virtually all aspects of the green space industry, and has overseen or managed tens of thousands of turfgrass locations, including golf courses, sports fields and residential home lawns. He has been a consultant and instructor for decades. He is a contributing columnist for Turf & Recreation.

Personal note and disclaimer

In sickness or in health, with the help of his entourage, we still hope to keep all of our readers entertained and informed. William continues to recover from his serious motor vehicle accident. Well wishers may send a personal note to Bill by way of this magazine or by email to whg007@gmail.com. By the way, the opinions expressed in this article, even though from an independent perspective, may not reflect those of Turf & Recreation.

References

Although every item found within this article has been carefully researched, there is no exhaustive list of references since this is not a scientific journal. Besides, the sheer number of references and documents that were used to support this article are far too numerous to list within the confines of this magazine. However, the authors will provide references to any reader who requests them. Please send your request to whg007@gmail.com.