Nematodes that “eat” corn rootworms for lunch are a hot topic in Northeast winter meetings, especially with growing evidence of rising rootworm resistance to Bt corn. The Steinernema nematode species, propagated to manage alfalfa snout beetles in northern New York, also eats rootworms for dinner and — yes — breakfast.

The nematode species, developed and grown to manage alfalfa snout beetles, shows strong potential for managing corn rootworm, affirms Elson Shields, Cornell University entomologist and research leader on the project funded by the Northern New York Ag Development Program. “We have very compelling field data from the 2016 field season showing that the biocontrol nematodes used against alfalfa snout beetle controlled corn rootworm larvae at Aurora [western New York] at the same level as the different CRW Bt toxins,” he adds. “The biocontrol nematodes were applied in the plot in 2014.”

Shields’ research in northern New York indicates the ASB nematodes persist, even increase, at effective populations over multiple years when fields are rotated to corn or soybeans for four to five years. “That strongly suggests the nematodes are reproducing in corn rootworms attacking the corn. Even in continuous corn, the ASB nematodes completely protected non-Bt rootworm corn at the same level as rootworm Bt corn,” he notes.

First evidence of it arose several years ago in northern New York cornfields rotated from alfalfa. The fields previously had been “seeded” with the entomopathogenic (insect-attacking) nematodes grown to control snout beetles.

Questions remain
The biggest question is: Is the impact of biocontrol nematodes on corn rootworm significant enough to eliminate the need for Bt-rootworm seed corn or soil insecticide — and for how long?

Two persistent Steinernema species native to New York and effective for controlling ASB were cultivated by the Shields Lab at Cornell. Then they were made available to growers. The one-time applications required two to four years for full effectiveness, depending on the application method. But effectiveness on ASB may last five years or more, he speculates.

Persistence under New York conditions was a key development component. “That’s why we use native nematodes.”

Shields hesitates to recommend commercial biocontrol strains already on the market. Commercial suppliers want to sell these biopesticides every year. One-time establishment in the soil profile for long-term pest suppression isn’t their focus.

That’s why Cornell Extension cultivated a farmer-friendly nematode rearing and application technique. Producers can purchase starter cups from the Shields Lab, then rear their own nematodes for application.

Protocols for growing them are simple. For details, visit alfalfasnoutbeetle.org/index.php/shields-lab.