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Findings from Perennia’s Nova Scotia nematode project

June 11, 2024  By Matt Peill, acting vegetable specialist, Perennia


Close up of a root-lesion nematode as seen under a microscope. Photo courtesy of Perennia Food and Agriculture.

In 2021, Perennia Food and Agriculture partnered with the Nova Scotia Department of Agriculture (NSDA) to complete a three-year project to address the increasing threat of nematodes in Nova Scotia. Plant parasitic nematodes are microscopic roundworms that feed on roots and can significantly impact crop production. Feeding can also cause damage by creating entry points for soil-borne pathogens and transmitting viruses. Preliminary sampling in Nova Scotia showed high populations of plant parasitic nematodes in horticultural crops.

The project’s objectives were to determine the diversity and distribution of plant parasitic nematodes affecting horticultural crops in the province, and to develop and adapt management practices for the region. To do this, a nematode survey involving systematic sampling was performed across the province, along with on-farm management trials.

The nematode survey sampling was completed during the 2022 and 2023 seasons, with 151 soil samples collected from 56 farms across Nova Scotia to determine nematode presence and distribution. Several types of plant parasitic nematodes were identified from sampling, but root-lesion, root-knot and dagger nematodes were determined to be of greatest concern due to their wide host ranges and potential to damage crops.

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Root-lesion nematodes were the most prevalent nematode type identified and were present in 92 per cent of samples. Of the sites sampled, 36 per cent had root-lesion nematode populations above or approaching economic threshold for most crops. Root-lesion nematodes are important pests, as they cause damage directly by feeding and create openings for soil-borne pathogens to infect roots. They have also been implicated as a component of disease complexes, such as apple replant and strawberry black root rot disease.

Root-knot and dagger nematodes were less prevalent than root-lesion nematodes, with both only being identified in 16 per cent of samples. But both are still of concern due to their potential to damage crops. Root-knot nematodes can be highly damaging to a wide range of crops grown in Nova Scotia, but especially carrots, and are the most important genus of plant parasitic nematodes globally. Dagger nematodes are also important; they do not generally cause direct damage to plants but are vectors of nepoviruses (e.g. tomato ring spot virus). However, nepovirus-related diseases are currently uncommon in Nova Scotia.

On-farm management trials were initiated as part of the project in 2021-2022 to assess cover cropping and chemical nematicides as management strategies. The information would drive decision-making to maximize productivity for horticulture crops. Trials were monitored and evaluated through to 2023 to assess the resulting crop parasitism associated with the treatments.

Our work to date has shown that brown mustard cover crops can unintentionally support root-lesion nematodes if not implemented correctly. Brown mustard can be used as a biofumigant to control nematodes when mowed and incorporated, but serves as a nematode host while it is growing. Additionally, it needs to be grown intensively to reach sufficient biomass to provide nematode control, as well as incorporated correctly. Therefore, brown mustard may not be a practical approach to managing nematodes in horticultural crops if it is not carefully managed.

A pearl millet cover crop prior to crop establishment discourages root-lesion presence and multiplication but does not reduce the population in the short-term. Chemical nematicides that were investigated did not show clear promising effects for management of root-lesion nematodes, but the lack of efficacy could have been a distribution or timing issue that could be explored further.

We also conducted sampling to evaluate root-lesion nematode population patterns and fluctuations during the season in Nova Scotia. We identified a natural cycle beginning with small populations in spring influenced by winter die-off, followed by magnification of the population by fall as the nematodes feed on the host plant. We conclude that spring nematode samples are misrepresentative of the actual carrying capacity of root-lesion nematodes in a horticultural system. Fall soil samples represent the highest population and provide the most valuable information for decision-making.

Plant parasitic nematodes continue to be a difficult pest to control, but this project was a major step in addressing the issue in Nova Scotia. Funding for this project was provided through the Canadian Agriculture Partnership (CAP) and the Sustainable CAP programs. Additionally, with the completion of the project, Perennia’s Plant Health Lab will now be offering nematode diagnostic services.

Thanks and acknowledgements to Michelle Cortens (Perennia tree fruit specialist), who co-led the project, Kristen Cue (Perennia agricultural research technician), who led the field work on the project, our nematode advisory committee (NSDA and AAFC representatives) and farm collaborators.


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