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  • Writer's pictureMark Krasnow

Don’t Undermine Your Undervine

For the first post in our research inspiration series let’s start with the ground directly under the vines. Undervine management in conventional vineyards worldwide largely relies on herbicide applications to control weeds that can have negative impacts on vine growth and wine quality. While herbicides can be a great tool in vineyard management, over use and/or reliance solely on chemical weed control is not a long-term sustainable answer for vineyards, regardless of its acceptance in many sustainable certification standards. In NZ and abroad, weed species have developed resistance to herbicides, and whether you believe there is merit in it or not, there is growing consumer awareness of herbicides and pushback against them. Whether your goal is to reduce or eliminate herbicides, we have, and will continue to, investigate tangible solutions.  


Past Research

Herbicide reduction IS possible even in high production blocks. We’ve done work in NZ Sauvignon Blanc vineyards showing no yield loss when herbicide applications were cut by up to 66%. In this study traditional herbicide undervine management (2-3 applications/season) was compared to one application of herbicide before bud burst followed by mechanical weed management in season. While herbicides were successfully reduced with no statistical difference in vine performance, this technique does require additional machinery (undervine cultivators or mowers) to be successful, which can be cost prohibitive for some.


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Left - Weed growth with traditional irrigation in vine row. Right - Weed growth over subsurface irrigation line shifted into tractor row

We have done quite a lot of research looking into installing the irrigation drip line underground, similar to how fibre optic cable is installed. The major reason growers have started working with subsurface irrigation in New Zealand was to reduce evaporation, and thus increase irrigation efficiency. However a side benefit, and one that I believe outweighs the benefits in terms of water savings, is a clear reduction in weed growth under the vines. Traditional irrigation line is run along the trellis system which puts it is as close as possible to the vine trunks. When the vines are watered so are the weeds in the undervine strip, which then need to be managed chemically or mechanically. In our subsurface irrigation trial, the lines were put in 30 cm (12 in) below ground and 30 cm off the vine row. While some weeds were still able to access water from the subsurface line, their growth was now positioned in the tractor row, where they could be mowed when the rows were mowed, leaving the undervine area clear. Lines could theoretically be plowed in further from the vines rows, or even in the row middle, which could allow for irrigation of a mid-row cover crop sward to keep soil biology going year round. A vineyard in Central Otago has done this to grow clover to fix nitrogen in a region where mid-row crops dry up early in the season. Subsurface irrigation is certainly a tool that I think deserves further investigation because of the dual benefits in terms of weed/cover crop management and improved irrigation efficiency.


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Mid-row subsurface irrigation supporting cover crop growth in tractor row

What Else Can We Do?

Perhaps another way forward for the judicious use of herbicides is to establish a cover crop of selected species undervine. If we can coax the undervine seed bed towards these species, we can work towards an undervine that does not require any subsequent management after a pre-bud burst herbicide spray, or maybe even no herbicide sprays at all.  Work has already started in the undervine cover crop space, however the ultimate challenge comes down to species identification which requires local R&D. An undervine crop needs to be practical to seed (commercial techniques still under investigation), persistent year after year, displace problematic weeds, and not devigourate vines. We anticipate a largescale movement towards this management regime by those wishing to reduce reliance on herbicides in an economically sustainable way. However, gaps in the research, specifically around species selection, is a large hurdle for many vineyards to start trying undervine cover crops on a commercial scale. 

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Undervine calendula in Napa Valley in 2023. Calendula is growing as a weed in the area, so it’s unlikley it was sown by the manager. However, its growth habit and propensity to take over the seed bed can be taken advantage of in vineyards as long as there is no negative effect on the vines or wine quality.

Can it Work in the Real World?

I have seen evidence of this paradigm in the real world, albeit likely not purposefully done by the manager, with an undervine calendula crop in Napa Valley. This crop had pretty much colonised the entire undervine, had terminated its vertical growth well below the fruiting zone, and definitely did not seem to be holding the vines back in any way by their appearance.


In Australia there has been much research in undervine species that do not require management in season, with several candidate species and species mixes shown to be effective in South Australia (Penfold et al., 2018; Penfold et al., 2019; Ball et al., 2020) and in the Mediterranean (Guerra et al., 2022)). Both studies included several local “weed” species as undervine crops, and we want to do the same. Here in NZ, we have a “weed” called scrambling speedwell (Veronica filiformis) that has a spreading growth habit and is the one of the first species to colonise recently tilled ground, we just don’t know how competitive it is with vines if allowed to take over the undervine, or if it even will do so when left to compete against other species for the growing space. Vineyards in NZ have had varying levels of success with volunteer stands of medic and clovers undervine, but the legitimate fear of devigouration/yield loss keeps many from doing trials in this space, and no one here has done a large scale replicated study. We aim to fill this knowledge gap, ideally with sites all around new Zealand because crops that succeed in one climate may be poorly suited to another, and there will likely be regional differences in the “ideal” undervine crop.


Closing Thoughts

We already know, at least in the New Zealand context, that allowing undevine cover to become established under the vines later in the season does not necessarily affect productivity when managed. If we don’t need a bare undervine all season to maintain productivity in New Zealand, why do we do it? I suspect we’re not alone in being able to get away with this, any region that can irrigate/fertigate can likely get the same results as we did in terms of yield. A major impediment, maybe THE major impediment, to moving away from bare ground under the vine, is aesthetics. It has nothing to do with wine quality, and in fact, we may be reducing quality by reducing biodiversity in a “pretty” vineyard. 


To too many people’s eyes the straight lines of herbicide strips and neatly hedged vines look like good management, because the point of comparisons are gardens. This preference for “order” and “neatness” has reduced the plant biodiversity of our vineyards (sometimes to a single species), and almost certainly negatively affected the below ground communities that depend on this diversity. We’re excited to explore alternative undervine management strategies, and hope research in this space can produce viable options for people to try wherever their vineyards are located. 


If you have established ground cover/cover crops under your vines we’d love to hear about it. Leave a comment below, or shoot us a message at thoughtfulviticulture@gmail.com.


References:


Guerra, J. G., Cabello, F., Fernández-Quintanilla, C., Peña, J. M., & Dorado, J. (2022). Use of under-vine living mulches to control noxious weeds in irrigated mediterranean vineyards. Plants11(15), 1921.


Penfold, C., Howie, J., Weckert, M., & Nordblom, T. (2019). Under-vine cover cropping-a source of vine medication. Australian and New Zealand Grapegrower and Winemaker, (671), 34-38.


Penfold, C., Weckert, M., Nordblom, T., Howie, J., & Norton, M. (2018). Development of a low-input under-vine floor management system which improves profitability without compromising yield or quality.: FINAL REPORT to WINE AUSTRALIA, Project Number: UA 1303.


Ball, K. R., Baldock, J. A., Penfold, C., Power, S. A., Woodin, S. J., Smith, P., & Pendall, E. (2020). Soil organic carbon and nitrogen pools are increased by mixed grass and legume cover crops in vineyard agroecosystems: Detecting short-term management effects using infrared spectroscopy. Geoderma379, 114619.

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