Trunk diseases

New approaches to tackling a global concern
6 min

It's not often that a wine gets named after a vine disease, but one of Australian wine’s most celebrated Shirazes, D’Arenberg’s Dead Arm, is named after a fungal disease. Dead arm is the colloquial name for a disease called Eutypa, which is currently the cause of a lot of concern in vineyards around the world. I remember when I was first getting into wine, Dead Arm was a favourite of mine, and the back label explained how in many of their older vineyards some of their ancient vines had an arm that was non-productive because they'd been attacked by Eutypa.

One of the interesting things about this disease is that it doesn't affect the vine’s ability to produce quality wine, just its yield. And the way it was described on the back label was that although the affected vines produced lower yields, the grapes they did produce had intense, concentrated flavours.  So, in the Australian focus on quality over quantity, these ancient – yet diseased – vineyards were preserved.

What are trunk diseases?

Eutypa is a type of trunk disease, caused by fungus attacking the permanent wood of the vine. There are others, notably Esca, which is a huge problem in Europe at the moment, as well as Botrosphaeria (also known as Black Dead Arm). Trunk diseases have been around for a long time, but at the moment they seem to be a particular issue. Some winemakers are even referring to trunk diseases as the new Phylloxera, such is the seriousness of the situation.

But why are they such an issue if the wine’s quality is unaffected, you may ask. Well, it's because of economics. If you are getting $70 a bottle for your wine, you can tolerate lower yields. But for many producers, low yields make a vineyard non-viable.

I was recently in the Loire Valley, and in many of the famous vineyards of Sancerre and Pouilly-Fumé there were lots of gaps in the rows where vines had succumbed to trunk diseases. If a vineyard is making expensive wine, then the time and effort required to replant vines to fill these gaps is worthwhile. But for many vineyards it isn't and the entire vineyard has to be replanted, which costs a lot.

In Europe, trunk diseases used to be prevented by using arsenite as a fungicide when Eutypa was a problem, but Esca and Botrosphaeria were hardly talked about. Then, in the 1990s, arsenite was withdrawn for health reasons, and suddenly Esca and Botrosphaeria emerged as serious problems.

How do trunk diseases spread?

The fungus that causes trunk diseases can be common in the vineyard, but it is pruning wounds that present a route into the wood. Fungal spores land on the wounds while they are still damp and germinate. The fungus then colonises the vascular tissue of the plant – the xylem and phloem vessels that spread water, sugar and nutrients through the vine. Gradually the wood becomes infected and dies, but the fungus also produces by-products that negatively affect the vine's physiology. Eventually, the vine dies. The spread of fungus is worse when the pruning cuts are larger, or are made in the rain, when the fungal spores are most prevalent.

The sector has been hunting for solutions. One of the leading scientists in the fight against trunk diseases is Dr Mark Sosnowski at the South Australian Research and Development Institute (SARDI) in Australia; he recently completed a term as chair of the International Council of Grapevine Trunk Diseases.

In early July, many of the leading names in the research field gathered in Reims for the 10th International Workshop on Grapevine Trunk Disease to exchange research results and ideas. There were 220 delegates from 29 countries in attendance, with 150 research abstracts presented. Dr José Ramón Úrbez-Torres of Agriculture and Agri-Food Canada led the session on ‘Pathogen Characterisation and Identification’ and Prof Laura Mugnai of the University of Florence led the session on ‘Epidemiology’. Prof Florence Fontaine of the University of Reims, who was also the workshop convener, led the session on ‘Plant-Pathogen Interactions’ followed by Dr Stéphane Compant of the Austrian Institute of Technology, leading the ‘Microbial Ecology’ session.  The final and largest session of the workshop ‘Disease Management’ was led by Dr David Gramaje of the Spanish Institute of Grapevine and Wine Sciences, together with Dr Mark Sosnowski. Such a gathering of academics and thought-leaders just goes to show how seriously this issue is being taken by the wine sector worldwide.

A remedial approach in France

Dr François Dal, at the Centre Loire has worked with growers in the Loire to devise a remedial treatment for vines that are affected. This is an approach that requires year-round vigilance and prompt action. The protocol they have devised is called ‘curettage’.

Curettage works like this. When a vineyard worker spots the first symptoms – the leaves of the vines are showing signs of struggling – they examine the trunk, and using a small hand-held chainsaw they carefully cut out the infected wood, just as a dentist removes the decayed part of a tooth before filling it. Usually, the vine recovers when this is done in a timely fashion, because the fungus attacking the wood is releasing by-products, and these are eliminated by the cutting. One of the growers I spoke to in the region has carried out this process on around 1,000 vines and has lost just 5, but he emphasised that if you want this sort of success rate you have to be monitoring the vines throughout the growing season. Dal has also issued instructions on training and pruning methods that ensure an even sap flow through the vine, which reduces the risk of trunk diseases.

The nature of the pruning cuts can also increase or decrease the disease risk: the adoption of electric-powered pruning shears has potentially contributed to the problem by making it easier to make deeper cuts, raising the risk. Another contributing factor is believed to be the grafting that has been practised in many of the French nurseries, as poorly grafted vines are thought to be more susceptible. The advantage of the curettage approach is that it is compatible with organic viticulture: it isn't a chemical solution. The disadvantage is that it is labour intensive.

Proactive action in Australia

In Australia, Mark Sosnowski and his colleagues at SARDI, The National Wine and Grape Industry Centre and the University of Adelaide have been working hard on a solution for Eutypa and Botryosphaeria dieback, which are the main trunk diseases affecting the local sector. Some of the practical advice they can give from the research is don’t prune in wet weather, which reduces the chance of the fungus spreading to pruning wounds, and for vines that have been affected, cutting out the dead material and re-training the vine from shoots below the infected zone. In addition to taking the infected wood, they also recommend removing an extra 10–20 cm of healthy-looking material to make sure the infection is fully removed.

Sosnowski has also been looking at topical treatments that can be used to treat pruning wounds. In the past, the benzimidazole fungicides benomyl and carbendazim were effective, but they have been withdrawn. This meant that for a long time, the only products registered for post pruning wound dressing were Vinevax (which is a trichoderma-based product that is OK for organics), Greenseal and Garrison Rapid (paints containing the fungicides tebuconazole and cyproconazole, respectively). Sosnowski and his colleagues have been trialling alternatives, and have found three effective fungicides. On the back of this work, two products, Emblem and Gelseal, have been registered for post pruning treatment of wounds, with a third in the process and hopefully available by next winter. Significantly, they showed that fungicides could be applied by spray machinery, rather than painted on by hand. This is important because for many vineyards, the labour required to apply fungicide by hand to every pruning wound would just be too expensive, and this would mean pruning wounds would go unprotected and the disease would continue to spread.  This looks like it will be a real breakthrough in controlling trunk diseases.

Trunk diseases remain a concern for viticulture in wine regions around the world, but this combination of remedial and preventive approaches holds promise for overcoming the worst effects of these fungal ailments.

Jamie Goode is leading British Wine Writer and the author of the Wine Anorak


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