Greenkeeper Scholar: American study: wild, native nematodes appear to remain effective against white grubs longer than commercial strains

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MARKET & CURRENT AFFAIRS

Hein van Iersel, Wednesday 17 September 2025

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Greenkeepers and field managers have long used nematodes (EPNs or entomopathogenic nematodes) against grubs and leatherjackets. These are commercially cultured nematodes applied in high doses. This approach has disadvantages: the costs are high, the application is labor-intensive, and effectiveness generally declines quickly because the number of nematodes in the soil decreases rapidly.

White grub of cockchafer (photo Henk Vlug)

Rutgers University in New Jersey tested an alternative under the leadership of Albrecht Koppenhöfer: the use of 'wild,' native nematodes originating from local turfgrass. The idea is that these nematodes are already adapted to local conditions and therefore remain active longer. Moreover, they have not lost important traits that support long-term survival in the topsoil. Commercial strains are expected to have lost these traits due to mass production. This idea is not entirely new. In agriculture, there are several comparable applications, for example against wireworms in sweet potato, but also against insect infestations in corn, strawberries, and cranberries.

Albrecht Koppenhöfer, Rutgers University

Trial setup on two golf courses

In Koppenhöfer's study, test plots were established on fairways and roughs at two golf courses in New Jersey. The researchers isolated two nematode species from local turf: the surface-active Steinernema carpocapsae and the deeper-working Heterorhabditis bacteriophora. They compared four treatments: water only, Steinernema carpocapsae only, Heterorhabditis bacteriophora only, and finally a combination of both species.

Application

The nematodes were applied in June 2020 at relatively low doses. The plots were monitored for three years for the presence of nematodes and various pest species, including the annual bluegrass weevil, the beetle Ataenius spretulus, and several other white grubs. The annual bluegrass weevil is an American beetle that mainly targets annual bluegrass.

Results: long-term pest suppression

The native nematodes quickly established themselves in the treated plots. Steinernema carpocapsae remained present at high levels throughout the study. Heterorhabditis bacteriophora declined after half a year but remained detectable at low densities. In the combination treatment, both species were recovered, albeit at slightly lower densities than with single applications.

The combination provided the broadest and most consistent pest suppression:

Larvae and pupae of the annual bluegrass weevil were reduced by 59% on the fairway in 2021, and adult beetles even by 74%.
White grubs of the beetle Ataenius spretulus decreased by 43-62% in 2021.
Larvae of various grass and sod webworms disappeared completely in the rough after treatment with Steinernema carpocapsae and decreased by 75% on the fairway.
Larvae of various cutworms were reduced on the fairway by 75-88% by Steinernema carpocapsae or the combination.
In 2022, the effects were less pronounced but in many cases still present.

Why do native nematodes work longer?

According to the researchers, there are three reasons for the success:

The applied nematodes were already accustomed to the soil and pest insects at the site.

The wild nematodes had not been cultured in a laboratory for years, so traits for long survival in the field were preserved.

Cooperation: Steinernema carpocapsae is active in the upper soil layer and mainly targets caterpillars and above-ground stages; Heterorhabditis bacteriophora penetrates deeper into the soil and is more effective against white grubs.

Practical significance

For practice, this means that greenkeepers and field managers may achieve multi-season effectiveness with one well-planned application of wild native nematodes, especially when two species are combined. This may save costs in the long run, as repeated annual applications are not always necessary. It may seem complex to culture nematodes in this way, but according to Koppenhöfer this is not too difficult. In the US, there is a company that has been culturing and selling such nematodes for several years: Persistent Biocontrol.com. This company produces nematodes that are locally isolated. It has developed a successful method for maintaining nematode colonies.

Greenkeeper scholar

Greenkeeper Scholar is a new initiative by the trade journal Greenkeeper, in which we make articles from a scientific journal accessible to an audience that normally does not read such journals. We do this by translating and popularizing one article per issue.
This time it concerns a study by Albrecht M. Koppenhöfer and Ana Luiza Sousa of Rutgers University in New Brunswick (USA), under the title Long-term suppression of turfgrass insect pests with native persistent entomopathogenic nematodes.
This article was originally published in Journal of Invertebrate Pathology 204 (2024) 108123.

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