Managing Esca in susceptible ‘Sauvignon blanc’ wine grapes through trunk renewal

Trunk renewal was evaluated as a treatment for highly susceptible ‘Sauvignon blanc’ wine grapes with moderate leaf and wood symptoms of the trunk disease Esca, in a 17-year-old vineyard, seven years after symptoms first appeared. The trunk was cut above the graft union, removing all woody parts of the vine above it, including infected wood. Then a new trunk was retrained from a shoot off presumably healthy wood, at the base of the trunk. Prior to trunk renewal, we detected Esca pathogens from 26% of 97 symptomatic vines. Five years after trunk renewal, 72 retrained vines were still asymptomatic, 24 were replanted (i.e., did not produce a shoot after trunk renewal), and one had leaf and fruit symptoms. Chemical composition of asymptomatic fruit from asymptomatic-retrained vines (RV-AF) was compared to that of vines that were not retrained, the latter of which included asymptomatic fruit from asymptomatic vines (AV-AF), and both asymptomatic fruit (SV-AF) and symptomatic fruit (SV-SF) from the same symptomatic vines. Given the high proportion of asymptomatic retrained vines after five growing seasons, trunk renewal was an effective cultural practice. Although there were no differences in chemistry parameters used to make harvest decisions (total soluble solids, pH, titratable acidity), SV-SF was unique in having the highest concentrations of the flavonoids catechin and epicatechin, and the lowest concentrations of the volatile-aroma compounds hexanal and 2-hexanal. These findings in all three blocks, among fruit with visible spots, may reflect a host-defense response and/or the effect of Esca on fruit ripening.