Undervine weed management

We have done a lot of work in this area, including investigating herbicide reduction, nonchemical weed management, and ways to maintain yield while cultivating under vine for weed control.

Weed control method comparison 2013-16

This trial compared undervine mowing, undervine cultivation, and undervine herbicide in terms of vine performance and productivity. All management practices other than weed control were done identically across the whole block. Undervine mowing consistently reduced yield by about 30% compared with herbicide, beginning in the first year. Undervine cultivation saw no yield loss for the first two years, but in year three productivity fell to levels similar to undervine mowing.

Herbicide reduction 2017-2020

Following on the heels of our original undervine work, we wanted to see we could at least reduce herbicide use while maintaining yield at comparable levels to completely bare ground all season. A single early-season spray, followed up with either undervine cultivation or undervine mowing, was compared with a standard multi-spray herbicide regime aimed at keeping the undervine bare all season. For all three years of the study, yields of the one spray treatment were not significantly reduced compared with the control. This consistent finding suggests that the obsession for maintaining a clean bare earth undervine all season is not necessary to maximise yield. However, juice from the reduced herbicide treatment had consistently lower YAN, which could require supplementation in the winery.

Yield maintenance employing undervine cultivation 2017-21

Another spin off project from our original undervine work looked at ways to maintain vine performance and yield in undervine cultivated vineyards so as to avoid the drop off in productivity seen in the original study. Additions of small amounts of compost (10 tons/Ha) every other year or a midrow winter cover crop mix to be mown and thrown under the vines were compared with cultivation with no additional inputs. . No consistent benefit was seen from either treatment, but the four year time frame for the project may have been too short to see benefits, especially for the cover crop treatment. Other benefits might have been gained, for example improved soil health, that were not measured in the study, which focused on the grapevines themselves.

Mechanical shaking to reduce bunch rot at harvest

Previous work in New Zealand has shown that lightly shaking the vines around pea sized berries (EL stage 31), to remove abscised floral parts and unpollinated berries trapped in the developing bunches, reduced rot seen at harvest by about 50%. We looked at the timing of shaking in order to assess the window of opportunity to get a positive result. Benefit could be gained from shaking soon after set (peppercorn sized berries-EL stage 29) all the way through until bunch closure (EL stage 33), indicating that the window of opportunity for shaking is wider than previously thought. This eases the logistics of growers wanting to shake large areas with limited machinery. Our work also showed that the shaking induced tougher skins in the fruit, reducing their susceptibility to infection from Botrytis, which might help explain the results from previous studies.

Subsurface Irrigation 2019-21

Movement of the irrigation lines 30 cm underground and 30 cm off the vine row was compared with traditional in-row above ground dripline. All vines received the same water/fertigation, only the location of the dripline was changed. Subsurface lines were installed in several rows of a block to be compared in terms of canopy growth, water status, fruit development, and yield. There were no consistent negative effects of moving the lines underground, and by so doing the weeds encouraged by irrigation water were moved from the difficult to control undervine area to an area where they can be mowed with a regular midrow mowing pass. This reduces the need for herbicide and/or slow mechanical weeding passes in the vineyard. It also protects the irrigation infrastructure from damage by machinery and grazing animals. Subsurface irrigation also offers the possibility of more efficient irrigation by reducing evaporative loss from the soil surface.

Irrigation Optimisation 2018-21

Irrigation of grapes using stem water potential thresholds was compared with traditional irrigation scheduling using visual signs and soil moisture probes. In white wines (Sauvignon blanc and Chardonnay), the aim was to maintain yield but use less water during the season. In reds (Pinot noir and Merlot), mild water stress was imposed after set to reduce yield to target by manipulating berry size, obviating the need for hand crop thinning. The quality of wines was assessed by wine professionals. Water savings as large as 700,000 L/Ha were achieved by simply measuring the vines and watering only when they need it, rather than guessing vine water status based on soil moisture and visual observations of the vines. Differences in canopy thermal characteristics were large enough to be seen in satellite NDVI images of the trial plots. In reds, higher yields of better quality wines were produced by limiting water without hand crop thinning, compared with over irrigation and artificial crop manipulation. In all vineyards, undervine weed growth and the need for trimming was reduced when irrigation was only applied as needed. More efficient water usage increases vineyard profitability by reducing farming costs, increasing income, and improving fruit quality.

Hemp as a cover crop in vineyards 2019-22

Industrial hemp (cannabis sativa) was sown as a cover crop in the midrows of a Sauvignon blanc vineyard located in Marlborough, New Zealand. Midrow hemp in the vineyard did not negatively affect vine canopy growth, water relations, nutrition, or yield. Midrow soil from the hemp treatment had higher organic matter, especially at 40-80 cm. Juice from the first year of the trial (2019) had a much higher yeast population from the hemp treatment than from the control. The winemaking team felt the wines were better from the hemp treatment, and that there was no noticeable taint imparted to the wines from hemp growing next to the fruit. All together, these findings show the benefit of hemp as a cover crop to sequester atmospheric carbon, improve soil organic matter, increase vineyard biodiversity, and improve wine quality, without negatively affecting the vines.

Cover crops, soil health, and carbon sequestration 2022-present

Cover crops offer many benefits to vineyards, including nitrogen fixation, increasing soil organic matter, fostering beneficial insects, and atmospheric carbon sequestration. Cover crops also improve soil structure, water infiltration, alleviate soil compaction, and increase water holding capacity. Undervine cover crops can displace weeds and eliminate the need for undervine management completely. Traditionally, cover crops have been sown each year, and each sowing required either spraying out or tilling the midrow prior to planting. This method does not accumulate organic matter as quickly as a system with full groundcover all year round. Our current work involves testing a new paradigm to midrow cover crop management, where mowing and tillage are not regularly practiced, but rather the cover crops are managed by rolling them down using a roller-crimper when they get too tall so as to interfere with vineyard operations or increase frost risk. We are also looking into permanent undervine cover crop species with an aim to eliminate the need for herbicide or undervine soil disturbance.

Cool Climate Syrah Improvement 2019-21

Syrah is a challenge to grow in a cool climate that receives summer rainfall, like Hawke’s Bay, New Zealand. Shoot vigour can be very high, necessitating early trimming and the encouragement of lateral growth. This makes it a challenge to keep the fruit zone open for airflow and light penetration. Syrah also needs long hangtime to develop ripe flavours, and thus issues with bunch rots can be a challenge, especially in wet years. Several vineyard manipulations were tested in order to improve the quality of Syrah fruit for winemaking, including: deficit irrigation to improve fruit quality, early root pruning to reduce vigour at the start of the season and delay the need for trimming, and bunchline calcium chloride sprays to strengthen skins. Deficit irrigation actually led to slower sugar accumulation and lower Brix at harvest, but did not reduce (or improve) wine quality. Root pruning at budburst had no effect on subsequent canopy growth. Calcium sprays increased the skin toughness, and thus could potentially be used to allow longer hangtime. No effects of calcium sprays on rot incidence or severity could be seen, but the three years of the trial were extremely low Botrytis pressure years, and in 2020 COVID 19 shutdowns precluded the gathering of harvest data from some sites. The strengthening of the skins is suggestive that a more significant result might be seen in a more typical year.

Defoliation timing as a tool for cool climate viticulture 2010-2012

Cool, maritime climates, such as those in New Zealand, often receive rain around harvest. This rain encourages bunch rots to grow on the fruit, which reduces wine quality. Growers must remove infected fruit, which adds to farming costs and reduces yield. Red wine growers in cool climates remove leaves in the bunch zone to increase airflow and light penetration to the fruit, they often also remove crop during the season to ensure the remaining fruit fully ripens in order to optimize wine quality. We tested early leaf removal, before flowering, to purposely reduce berry number on the bunch compared with later leaf removal timings at set and bunch closure. Early defoliation reduced crop and created a more open bunch, allowing for airflow and reducing berry-to-berry spread of rots if they became established in the bunch. This technique worked well, reducing bunch compactness and rot significantly with no further manipulations needed to reduce yield to desired levels for red wine making.