The largely hidden threat of esca: including a conversation with Christophe Mesliard
Esca is a vine fungal disease that usually over time kills the infected vine. It is becoming an increasing threat to the vineyards of France and other parts of Europe.
Reports on vintages tend to concentrate on how a particular year’s climate has impacted on the quality and quantity of wine made in a particular year. This includes factors like frost, hail, the amount of rain and sunshine etc.
Vine diseases and their effect on reducing yields are rarely mentioned. Esca now appears to be the most prevalent vine disease in France and has become a constant for producers with a varying number of their vines killed every year. The level of mortality appears to be depend upon the climate in a particular year and may well be related to the amount a vine is stressed during the growing season.
Loss of leaves
The latest figures for the Loire from the Grapevine Trunk Disease Observatory are frightening. In 2017 they studied 17,250 vines – Cabernet Franc, Chenin Blanc, Melon de Bourgogne and Sauvignon Blanc. They found only 79.7% of these to be completely health and fully productive. The last survey was in 2014 when 86.1% of the vines surveyed were found to be healthy. Much of this sharp decline in vineyard health is ascribed to Esca and Black Dead Arm, (BDA).
The Observatory found that the vines most affected were planted between 1996 and 2000. There was a lesser incidence in vines planted before 1993 and even less for those vines planted between 2008 and 2012 – only 2.8%. However, unfortunately the figure for vines planted after 2008 doesn’t mean a great deal as Esca normally strikes vines when they are 15 years old or more. Given this it is very concerned that even these young vines (2.8*%) are already showing evidence of infection.
Lost leaves – shrivelled grapes
Some grape varieties are more susceptible to Esca than others. For instance Sauvignon Blanc, Cabernet Sauvignon, Ugni Blanc are particularly susceptible, Melon de Bourgogne and Chardonnay is quite prone to infection, while Cabernet Franc, Chenin Blanc, Gamay and Syrah are more resistant.
2017 has been a particularly bad for Esca with a wettish spring followed by a summer with some hit heat spikes, especially in June, putting vines under stress. There are reports of mortality rates around 10% compared to around 3% in 2016.
Christophe Mesliard, vineyard manager at the Domaine de la Taille aux Loups in Montlouis (Loire Valley) explains: “Esca attacks the trunks of vines and their delicate root systems cutting off the sap. A vine may have esca for several years before it dies. The end is frequently brutally short. Often it is as though a vine has suffered an ‘apoplectic seizure‘ or a very severe stroke. In as little time as 48 hours all the leaves fall off and grape bunches become shrivelled and bitter to taste. Esca has deprived the vine of its life giving sap.”
Several infected vines
Replacing dead vines every year is the standard practice. This is expensive as Christophe Mesliard, vineyard manager at the Domaine de la Taille aux Loups in Montlouis (Loire Valley) explains. “A standard vine will cost 1.30€ but we choose vines that have been both treated against Esca that also have a bacteria that fights off the Esca microbes. These vines cost 2 euros each. Add in the work to remove the dead vine and replace it with a new plant, the cost rises to between 6-8€.”
Christophe went on to explain: “Whereas a vine planted in an all new parcel will start to properly produce fruit in its third year, when co-planting – replacing dead vines in an already existing vineyard it can take six years and more before the vine is back in production.”
Christophe continues: “There are alternatives to replanting. Re-grafting is one possibility if the Esca is not too advanced. If successful your vine is back in production within one or two years. However, the success rate varies from between 0% to 90%. For us the success rate has been between 20%-40%. In Sancerre the success rate has been 90%. Re-grafting is also time consuming – only around 40 re-grafts can be done in a day.
The economic cost of Esca is immediately apparent. Assuming a producer with 10 hectares of vines with a planting density of 5500 vines per hectare loses 10% of their vines through Esca, the cost of replacement at 7€ per vine will be 38,500 €. This doesn’t take any account the loss of harvest from the dead vines or the time it takes for the replacement vines to come back into production.
Sodium arsenite is an effective treatment against Esca and other fungal vine diseases. However, in 2001 the French Government banned its use on public health grounds on fears that it is a carcinogenic.
What with the perennial threats of frost, hail, mildew etc. producers really don’t need Esca as well!