The first biannual Viticulture Technical Conference organised by the WineGB Viticulture Working Group (VWG), under the leadership of Stephen Skelton MW, was held at the Denbies Estate in late November. Over 150 delegates represented a wide range of vineyards across the country. The event was well-received, possibly because it allowed plenty of break-out time between formal presentations. This enabled delegates to catch up after the amazing 2018 harvest and view research posters from Plumpton College and NIAB EMR, and to visit trade stands in the Denbies cellars. Next year, WineGB will organise a Winemaking Technical Conference and a Business and Marketing Conference and the intention is that the two will alternate.
Dr Martin Lukac, Professor of Ecosystem Science at Reading University, wanted to widen the view of fungi in the vineyard. His research on the interaction of roots and mycorrhizal fungi has led to his view of vines as a ‘super-organism’. The relationship between plants like vines and their associated mycorrhizal fungi is complex, involving a host of positives for both organisms. Vine growers need to be aware that soil biodiversity contributes to system stability.
Arbuscular mycorrhiza (AM) particularly, with their hyphae attached to roots of higher plants, can facilitate the amount of major and minor nutrients available to the plant in exchange for sugars to feed the fungus. AM may limit the growth of the plant in the short term while the relationship builds, but later there are positive effects on growth when maximum colonisation is reached. Amongst these are an increase in the rate of photosynthesis, minimising drought effects and possibly delivering induced resistance to pest species like Armillaria– honey fungus and ectoparasitic nematode species. This symbiotic relationship between AM and vines is, in Martin’s opinion, “most likely a key part of terroir”.
When asked how to encourage AM in the vineyard, Martin considered that herbicides and fungicides were likely to be harmful, but glyphosate was possibly okay. Cultivating the rows for weed control will change the species of AM present, as it will get rid of those that don’t cope with disturbance. The composition of the species of AM in the vineyard will change over the life of the vines. To find AM species specific to vines needs research.
Dr Glen Creasy has experience of working in viticulture research in the USA, Australia and, before moving to France in 2018, at Lincoln University in New Zealand. He reported research in New Zealand on the effect of site, soil and season on Pinot Noir vine performance and wine quality. Using sites in the Waipara Valley north of Christchurch on the South Island as a test bed, Glen’s findings range across vine responses between sites and irrigation regimes and they also consider grape and wine composition changes. Conclusions from the research show that vines are very elastic and can adapt to new situations. A reduction in applied water had a relatively small effect on the fruit, but wine colour and particularly ester-related aroma compounds were most affected by site and irrigation treatment.
Sensory analysis suggested that site and vintage have larger effects on wine compared to reduced irrigation. His overall message was that vines can adapt to short-term stresses, but he had a warning for growers wanting to maximise yield in a very cool climate like the UK. A slightly high crop-load may mean that the vines are pushed beyond their capacity to adjust, because they’ve used up carbohydrate stores in the whole plant to ripen a big crop. The next year there will have been no recovery time after the previous harvest, so over-cropping should be avoided.
Dr Moustafa Selim has been working on grapevine fungal diseases, mainly downy mildew and botrytis, at Geisenheim’s viticultural research centre. His presentation covered the prediction, control and detection of grapevine diseases downy mildew, botrytis and esca, with innovative methods under a changing climate. The climate-change trial at Geisenheim is helping to increase our understanding of what we can expect and how to prepare. There is a possibility that by 2040 vine growing will be possible throughout Germany.
One effect of rising temperatures has been earlier bud-break and shorter seasons. This has led to more compact bunches and more fungal problems. Harvest in the local area is earlier and shorter, down from 27 days to 13 days. So how can we delay ripening? There are several answers: by reducing leaf area, delaying winter pruning, increasing trunk height and, of course, if planting new vineyards by using later clones, varieties and/or rootstocks.
In the climate-change trial, increased levels of CO2 are being pumped into the vineyard. This has already shown that the plant response is to grow leaves with more stomata, which allows 20 per cent more photosynthesis. However, the downside is that there are more openings into the leaf for the downy mildew fungus to gain entry. The spores of this disease can remain dormant in soil for ten years and primary infections occur in the splash zone up to 80cm from the soil surface. Botrytis susceptibility may also be affected by climate change. Harvests are getting earlier and experience much high temperature periods than in the past. Early harvests in dry years will escape, but not in a combination of wet and hot weather. The CO2 trial has shown that bunch architecture is changed by increased CO2; a cultivar like Riesling with a compact bunch showed increased bunch length and berry number, resulting in more disease.
Dr Julien Lecourt, head of viticulture research at NIAB EMR, is well qualified to give an overview of what the various elements of precision agriculture can offer viticulturists. Precision viticulture is a management concept based on measuring and adapting growing practices to inter- and intra-vineyard variability in yield and quality. Research is needed to define decision-support systems. The cross-effects of the climate and plant physiology on berry and wine quality need to be measured to optimise growing practices for the UK climate.
We are in the age of ‘big data’, and Julien stressed that it is easy to end up with too much data and the problem of storing it. What the research must do is decide what is valuable to measure and what are manageable zones; we certainly need to build decision-support maps of vineyards to show trends over several years, as a snapshot is of no use for a perennial crop. An obvious goal would be increased wine quality by zoning the vineyard between premium and lower quality. This could better link the vineyard with the winery.
Julien will be using precision viticulture technologies as a tool for research. But he emphasised that you can try to measure symptoms with the physiological status of the plant, but what does this tell you? The symptom could be due to many things. It’s a ‘support tool’ not a ‘decision tool’. New skills will be needed to interpret all the data, and a cynic will know that the mathematicians and statisticians required will be more attracted by salaries in financial services than scientific research.
Spotted Wind Drosophila (SWD)
Rob Saunders is member of the WineGB viticulture working group, an agronomist with Hutchinsons and a board member of AHDB Horticulture. SWD was less of a problem for UK vine growers in comparison with 2017, but Rob wanted to update vineyard managers on current findings, future implications and control strategies for this relative newcomer to the UK.
In a survey of vine growers, 60 per cent admitted that they would not be able to identify SWD. Rob was keen to give growers the tools to get control of the pest, beginning with all the resources on the AHDB website, including a very helpful video. He warned that female SWD, which can lay eggs in unripe fruit, unlike any other fruit fly species, can lay up to 300 eggs in a lifetime. SWD like humidity and the middle of the canopy is the best area to look for them, by testing fruit for eggs and larvae. The combination of hope and denial by vine growers, even though there had been a lot of warnings, was obviously a poor strategy as the early harvest in 2017 caught many out. SWD egg-laying is suppressed at temperatures over 30C, so 2018 wasn’t so bad as 2017, but the survey showed that 40% of growers had applied Tracer. Damage by the fly allows botrytis and sour rot to gain entry. Research in Bordeaux has shown that if SWD was controlled there was less sour rot. Multiple approaches to control, from crop hygiene to monitoring and early trapping around the edge of vineyards, are the only answer, targeting the fly all-year-round.
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