Esca grapevine trunk disease (GTD) and the role of the Guyot-Poussard pruning system in combating it

During my recent visit to Tenuta di Trinoro, I discovered that the estate had an Esca problem and was employing a pruning system called Guyot-Poussard (G-P) to combat it. I was unfamiliar with G-P so I did some research after my visit with the intent of (i) gaining an understanding and (ii) writing a blog post on the topic.

My good intentions were derailed by a flurry of writings on the Barolo zone. That is, until my visit to Barboursville Vineyards (Barboursville, VA) where, in discussions with GM-Winemaker Luca Paschina, he also mentioned that he was battling Esca and his staff was undergoing training in order to implement the G-P system of the Italian duo Simonit and Sirch. That was a sign. I had to write this blog post. And I had to write it now.

First some background on Esca.

Esca
Grapevine pruning, arguably one of the most important viticultural practices, is employed during the vine's dormant phase and, when done properly, structures the plant such that there is balance between vegetative and reproductive growth. It is generally held that a balanced vine will allow for adequate yields and good quality fruit, assuming no deficiency in the other grape-growing parameters.

Two examples of pruning systems
(Source: pinterest.com)

One of the characteristics of traditional pruning systems is numerous large pruning wounds in the grapevine trunk with the potential for (i) intrusion of desiccated material into the interior of the trunk -- and the interruption of sap flow therein -- and (ii) serving as the infection pathway for grapevine trunk disease (GTD) fungi (Infowine).

Esca is one of the most feared of these GTDs. According to wineterroirs.com (Experimental cure of Esca in the Loire), this disease was known in ancient times but has had an alarming resurgence, especially after the banning of the carcinogen Arsenite which had been used to keep it under control. According to Jane Anson, vineyards across Europe has been losing 10 - 20% of their vines to Esca. But the disease is not limited to Europe, as evidenced by the fact that the Esca-fighting duo Siminot and Sirch have 130 customers across the world.

Esca is caused by several different fungi to include Phaeoacremonium aleophilium, Phaeomoniella chlamydospora, and Formitiporia mediterranea. Symptoms appear on mature grapevines in vineyards (Úrbanz-Torres, et al.):

• First, symptoms appear as dark red (red cultivars) or yellow (white cultivars) stripes on leaves. These eventually die and become necrotic.
• As the disease progresses, it causes:
• Gray to dark-brown speckling of berries, known as "black measles"
• Sudden wilting of the vines, including shriveling of the fruit that normally occurs in summer and is known as "vine apoplexy"
• A dieback of the entire grapevine.

"Esca vascular symptoms include primarily a white rot characterized by a yellowish spongy mass of wood, usually in the center of the trunk and/or cordons, which can be observed alone or along with dark-brown to black spots in the xylem vessels (Úrbanz-Torres, et al.). Examples of Esca symptoms are shown in the figures below.

Leaf "burning" associated with Esca
Source: http://www.ipm.msu.edu/

Wood rot associated with Esca
Source: http://www.ipm.msu.edu/

Esca-infected berries speckled with measles
Source: http://www.ipm.msu.edu/

Guyot-Poussard Training System
The principle behind the G-P pruning system (or soft pruning, as it is called in some circles) is simple: If pruning wounds are a gateway for pathogen entry into the vine, then let us seek to reduce the number and severity of those wounds. The hypothesis is that the probability of new infections would decline with a reduction in the number and size of pruning wounds.

The soft-pruning method was adopted by Lafon from a training system used in France in the early 20th century and eventually renamed Guyot-Poussard. It has been further refined and evangelized by the Italian duo of Simonit and Sirch who have traveled around the world preaching the benefits of the approach and who train practitioners of the system at their school in Italy.

The system uses small cuts in the upper portions of the cordon to promote continuous horizontal development of adjacent perennial spurs. The small cuts reduce the size of wound desiccation, minimizes the inward-facing size of the desiccation, and, through their placement on the upper part of the structure, leaves unobstructed channels at the lower part of the established structure. The system structure is depicted in the figure below.

Illustration of the Guyot-Poussard pruning system.
Note the pruning cuts st the top of the cordon
allowing the free flow of sap along the bottom
portion of the cordon (Source:marceaubourdarias.fr)

According to Infowine, this system:

• Reduces the probability of new GTD infections
• Promotes more homogenous development of phenological stages
• Promotes more balanced vegetative growth and more balanced ripening.

A 2016 study of the system as applied in a German vineyard has shown that:

• Activities such as shoot removal are more extensive and important in maintenance of the training system
• Leaf removal at flowering and fruit set requires less manpower
• A higher amount of work is required in the early years
• G-P pruning 37.7 hours/ha while traditional takes about 23 hours/ha
• Transition from a traditional to a G-P pruning system will take several years
• G-P a demanding pruning method and requires significant training before implementation.

According to Bowman, Simonit and Sirch assert that their approach will "double the life of a vineyard and dramatically reduce the incidence of grapevine trunk diseases." Bowman goes on to say that there is no scientific evidence as regards claims about sap flow but that a 2006 study by Geoffrion and Renaudin showed a 50% reduction in Esca-affected vines in G-P-pruned vines when compared to traditional Guyot-pruned vines.

G-P a la Simonit and Sirich has been implemented in a number of high-profile vineyards to include Domaine Leroy, Ornellaia, Chateau Latour, Haut-Bailly, and Louis Roederer. I have previously mentioned Tenuta du Trinoro and Barboursville Vineyards. According to Delbecque, 60% of the producers in the Sancerrois vineyard have trained their employees in this method while 80% have at least one person competent in this approach.

Adoption levels will only increase as we go forward.

Bibliography
Jane Anson, Anson on Thursday: The Prada of Vineyard Pruning, Decanter, 12/10/2015.
Sam Bowman, Pruning: The right cuts to improve vine health and longevity, Grapevine and Winemakers, winetitles.com.au.
Xavier Delbecque, The Guyot-Poussard has the wind in its sails, RéussirVigne, October 29, 2015.
Antonio Graniti, et al., Esca of Grapevine: A Disease Complex or a Complex of Diseases, Phytopathologia, 39(1), September 2006.
Infowine, Technical Data Sheet: Pruning with regard to sap flux, infowine.com.
C. Mutawilla, et al., An overview of grapevine pruning wound protection in South Africa, June 2011, wineland.co.za.
Jan van Niekerk, et al., Susceptibility of grapevine pruning wounds to trunk pathogen infections, wineland.co.za.
J.R. Úrbaz-Torres, et al., Grapevine Trunk Diseases in British Columbia: Incidence and Characterization of the Fungal Pathogens Associated with Esca and Petri Diseases of Grapevine, Plant Disease, 98(4), April 2014.

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