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Wednesday 16 April 2014

MW seminar considers causes of sudden vine death in Burgundy

15th January, 2014 by Patrick Schmitt

Banning poisonous treatments, poor grafting techniques and electric pruning shears were all suggested as causes for the rise of esca in Burgundy during an MW seminar last week.

esca vine trunk

A cross-section of an esca-infected vine trunk shows the impact of the fungal disease.
Photo credit: UC Davis

The event, which was moderated by Berry Bros & Rudd Burgundy director Jasper Morris MW, was focused on viticulture following a similar Masters of Wine seminar last year on winemaking in the region.

While last year’s event saw a panel of prominent winemakers consider the problem of premature oxidation in white Burgundy, this year’s seminar took the same approach to a similarly complex dilemma for the region: sudden vine death due to the fungal trunk disease esca.

Introducing the issue, Morris stressed both the extent of the problem but also a worrying lack of symptoms among infected plants.

“One week the vine is fine, and then another week it is dead, and esca seems to be affecting a dangerous proportion of teenage vines,” he said.

The extent of the problem varies according to grape: Chardonnay is less sensitive to the trunk disease than Pinot Noir, according to Olivier Merlin from the domaine by the same name in the Mâconnais, who joined Morris on the panel of speakers.

However, the most susceptible variety is not found within Burgundy – Sauvignon Blanc is in fact suffering from the highest level of esca recorded Merlin.

“In some places in Sancerre producers are losing as much of 10% of their vines [to esca] each year,” he said, adding that in his Mâconnais domaine the loss due to the disease is around 1.5-2.5% of the vineyard annually.

Vine age is a further factor, with Merlin pointing out that sudden death from esca infection occurs mostly among plants which are between 15-25 years old – putting a number to Morris’s “teenage” description.

Turning his attention to possible causes for the increased incidence of esca in Burgundy, Merlin initially blamed the ban of sodium arsenite fungicides, which were historically used to kill the trunk disease.

“In the past we used arsenic, but for over 10 years it has been totally forbidden in France,” he said, stressing that he fully supported such a move because of the chemical’s destructive impact on soil life.

Continuing he described the causes of esca as “very complicated”, but said that the increased use of electric pruning shears could be one reason for the rise of the problem.

“Now we have the assistance of electric pruning shears it is easier to cut old wood, and make bigger cuts, so that may be part of the problem,” he said.

Indeed, studies have shown that extensive pruning cuts in certain vine training systems create more potential infection sites – with one Canadian study showing 0.1% esca incidence in lateral cordon vineyards, compared to 15-20% in vines trained by double Guyot.

Although the method of disease spread is not yet certain, it is thought esca infection occurs through wounds in the vine as air-borne spores become trapped in cuts and gashes, particularly when it rains.

Such a belief would go some way to explaining Merlin’s pruning theory, as well as the marked increase in vine mortality from esca during the 2012 vintage, when Burgundy suffered a particularly wet spring.

omega_grafting

Omega bench graft. Photo credit: Mercy Olmstead, University of Florida

However, a more widely proposed reason for the rise of esca is that the infection occurs during the grafting process in nurseries.

“We have a suspicion that it’s the grafting that’s inducing lots of wood disease,” said another panellist, Benjamin Leroux, who is the winemaker and manager at Domaine Comte Armand.

In particular, he blamed the omega grafting technique (pictured above), which is widely practiced in vine nurseries due to its high level of graft success.

Agreeing with Leroux, a further panellist, Dominique Lafon from Domaine des Comtes Lafon commented, “Depending on how you graft you get a different quality of seal, and we find that the omega seal is not perfect, and that may be why you get disease in the future.”

As a consequence, Lafon, along with Merlin and Leroux advocated the use of the greffe anglaise, otherwise known as the whip and tongue graft, which was historically the only recommended technique for bench grafting vines.

Nevertheless, Leroux added that even among those nurseries which use the greffe anglaise, “not many do it properly”.

It was also noted by Merlin that the best approach to ensuring a disease-free grafted vine was to join the rootstock and scion in the vineyard itself (field grafting), rather than in a nursery during dormancy (bench grafting).

In field grafting, the process normally takes places in the early spring as the sap begins to rise up the plant, and because of this, the graft fuses faster than it would do in a bench graft which is practiced indoors when the plant is dormant.

Lafon explained: “Grafting in the field is the best because you have the sap right away so after you graft it seals really well.”

However, due to the cold and wet conditions in Burgundy during the start of the growing season the success rate of field grafting is poor.

“We are not doing it in the field in Burgundy because of the climate, it is not warm enough,” continued Lafon.

While he said that some in Burgundy, such as Frédéric Lafarge from Domaine Michel Lafarge are experimenting with field grafting, he added, “They are taking a risk because only around 50% of the grafts work, so you have to redo them, and that means you have the added labour cost as well as losing half your crop – and when you replant you want a full crop as soon as possible.”

As previously reported by the drinks business before the MW seminar took place on 10 January, trunk diseases represent the next great threat for the wine industry, posing a far greater risk than phylloxera, according to consultant viticulturalist Dr Richard Smart.

Smart noted that trunk disease, a fungal pathogen that encompasses esca, botryosphaeria and eutypa dieback, “is now more widespread in the world than phylloxera”, the louse that ravaged European vineyards during the late 19th century.

Even before it eventually kills the vine, trunk disease puts economic pressure on producers as a result of the reduced yields it causes, as well as the costs of chemical preventative measures and, eventually, replanting unproductive vines.

For those more looking for more information on esca there’s a useful, brief explanation about the disease, causes and preventative measures here.

While for those searching for more information on grafting, Quinta de la Rosa has posted a clear explanation of the techniques employed at its estate in the Douro, where warm springtime conditions allow for successful field grafting, although economics favour bench grafting.

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