Quelle Surprise – Soil Borne Pests Present in Vineyards When Looked For

Mark Krasnow

Last week I was alerted to a recently published paper from Lincoln University and Plant and Food Research in which the authors reviewed nematode population analysis from soil samples collected across ten sites in Marlborough in 2018. While nematodes are nothing new in the global viticulture scene, this paper comes as a timely reminder for those looking to replant, that pre-planting choices can be as critical as post planting management.

As a Viticulturist trained in California, plant parasitic nematodes in vineyard soils have always been of concern for me. I know firsthand how devastating they can be in large populations, and so am acutely aware of how important it is to choose appropriate rootstocks to your site, including the biological component of the soil. After all, it was the introduction of Phylloxera, a soil-borne pest, that required vineyards to need rootstock in the first place. When I arrived in New Zealand in 2010, I was surprised by the narrow range of rootstocks used in vineyards as compared to California, particularly given the soil texture of many growing regions. While rootstock variety is getting better, there is still an alarmingly large proportion planted and replanted to 3309, which is known to be quite susceptible to certain species of nematodes.

Adult root lesion nematodes inside roots (UCIPM - Nematodes - Jack Kelly Clark)

The Vineyard Ecosystem

Over the years, nematodes did not come up as a pest of concern during my time in New Zealand, but when an opportunity to test fell into my lap I couldn’t ignore it.  NZ Winegrowers funded a long term project investigating the effects of herbicide use on vineyard biology, and as part of that, DNA sequencing of soil microbes was assessed. The trial was carried out in the two largest wine regions in New Zealand, Marlborough and Hawke’s Bay, with a dozen vineyards in each region being included. After the study, I queried the DNA database for nematodes, and was not surprised to see that there was DNA for root knot nematode (Meloidogyne sp.), root lesion nematode (Pratylenchus sp.), and Dagger nematode (Xiphinema sp.). DNA from one or more of these nematodes were present in 14 of the 24 vineyard soils at some point in the study.

Since this was only DNA sequence data, populations could not be established, but it was enough to alarm me. After seeing this, I reached out to Dr. Knight at the University of Auckalnd, whose lab did the original sequencing, to see if we could arrange a wider sampling of the Marlborough and Hawke’s Bay regions as well as the rest of the country. At the same time, Dr. Kularathna (a nematologist) and I applied for funding to do precise population analyses of these country-wide samples. Unfortunately, we could not obtain research funding for the population work, but given the potential implications of nematode presence on the long term planting and redevelopment plans of the industry we approached industry members to gauge interest and collect samples for analysis anyways – because as Aldous Huxley has been quoted “facts do not cease to exist because they are ignored.” Unsurprisingly, there was interest from many willing to support this work, and soils are currently at Auckland Uni for semi-quantitative DNA analyses.

Preliminary survey of plant-parasitic nematodes associated with grapevines in Blenheim, New Zealand (Moukarzel, R. et. al., 2024)

Thresholds for damage from plant parasitic nematodes in vineyards (Reprinted from Nichol et al,. 1999)

Back to the paper - grapevine parasitic nematode population analyses of ten of the same Marlborough vineyards from the soil DNA sequencing work were undertaken in 2018. Their results were in equal measure interesting, unsurprising, and alarming. The study found the most prevalent nematode in vineyard soils to be pin nematode, present in seven of ten vineyards. In four of those vineyards, populations were over the threshold likely to produce damage to vineyards planted on susceptible rootstocks (that's 40% of the assessed vineyards!). This is a species that did not turn up in the DNA sequences mentioned earlier, but this could easily be explained by differences in testing methodology.

In the original soil DNA sequencing work, the most prevalent nematode seen in the trial vineyards in Marlborough was the root lesion nematode, whose DNA sequence was seen at some point in five out of the twelve vineyards. This species was only in two of the ten vineyards in the new study, but was above the damage threshold in both. Dr. Kularathna told me in a conversation once that this species is very common in paddocks in the South Island, and it is mentioned in the literature from “pasture” (Knight et al., 1997), so I had assumed it would have been found in a higher proportion since that is the previous land use of most vineyards here.

So What Now?

My team and the team in Dr. Sarah Knight’s lab are working on the semi-quantitative sequencing data that will start to answer questions about species ranges across the country. Samples were collected from Gisborne, the Wairarapa, North Canterbury, and Central Otago, in addition to a wider geographical sampling of Marlborough and Hawke’s Bay. With around 100 samples, this survey should help add to the story. While there has been limited nematode research conducted in New Zealand wine grapes, there are plenty of publications on nematodes, and about farming strategies that have been investigated. If you have concerns about your vineyard, or are in the process of redevelopment planning, reach out if you’d like to discuss options. However, given the importance of this topic I am obliged to provide some free advice, which I have noted before:

Choose your rootstocks wisely and ask more questions from your nursery representatives.

We also need to start thinking about the potential biosecurity issue of spreading nematodes from one site to another.

We certainly can’t ignore the issue and hope it goes away, because history has shown that to be a losing strategy every time. Farming around nematodes is the definition of an uphill battle, so identification, quantification and rootstock selection can help define your defence.

Literature cited

Ferris, H., Zheng, L., & Walker, M. A. (2012). Resistance of grape rootstocks to plant-parasitic nematodes. Journal of nematology, 44(4), 377.

Knight, K. W., Barber, C. J., & Page, G. D. (1997). Plant-parasitic nematodes of New Zealand recorded by host association. Journal of Nematology, 29(4S), 640.

Moukarzel, R., Ridgway, H. J., Jones, E. E., & Kularathna, M. (2024). Preliminary survey of plant-parasitic nematodes associated with grapevines in Blenheim, New Zealand. New Zealand Plant Protection, 77, 43-48.

Nicol, J. M., Stirling, G. R., Rose, B. J., May, P., & Van Heeswijck, R. (1999). Impact of nematodes on grapevine growth and productivity: current knowledge and future directions, with special reference to Australian viticulture. Australian Journal of Grape and Wine Research, 5(3), 109-127.

Rahemi, A., Peterson, J. C. D., & Lund, K. T. (2022). Grape rootstocks and related species. Springer.

Other Helpful Resources:

Notes from the Underground: Rootstock Selection. Thoughtful Viticultrue Blog. 6 May 2024 https://www.thoughtfulviticulture.com/post/notes-from-the-underground-rootstock-selection

Agriculture: Grape Pest Management Guidelines Nematodes. UCIPM. Accessed 15 October 2024. https://ipm.ucanr.edu/agriculture/grape/nematodes/#gsc.tab=0