Kendra Baumgartner,* Israel Jimenez-Luna, and Arran Rumbaugh
*USDA-Agricultural Research Service, One Shields Avenue, UC Davis, 363 Hutchison Hall, Davis, CA, 95616 (Kendra.Baumgartner@usda.gov)

Esca can cause spotting and cracking of the fruit, which typically drops before harvest. We evaluated trunk renewal as a treatment for symptomatic vines in a 17-year-old Sauvignon blanc vineyard in Kelseyville, California, in terms of presence/absence of leaf symptoms after four years and fruit chemistry. The approach is to cut away the canopy (and infected wood) and then retrain a new canopy from a sucker that grows from presumably healthy wood at the base of the trunk. In October 2017, we mapped the locations of 97 symptomatic vines, which were distributed in a randomized complete block design within three experimental blocks. Immediately after pruning in February 2018, we cut off all 97 vines above the graft union. In the freshly cut trunk wood, 96 vines had wood symptoms of Esca (black spots and/or white rot) and one vine had wood cankers, but we isolated Esca pathogens from only a small proportion of vines: Fomitiporia polymorpha in 17 vines, Phaeomoniella chlamydospora in 15 vines, and Phaeoacremonium minimum in two vines. In 2022, the status of the 97 retrained vines was as follows: 73 vines had no leaf or fruit symptoms (‘asymptomatic-retrained vines’), 23 vines were replanted (i.e., produced no sucker after the trunk was cut in 2018), and one vine had leaf and fruit symptoms (‘symptomatic-retrained’). At harvest in September 2022, we examined asymptomatic fruit from both asymptomatic-retrained vines and from healthy vines (not retrained). We also examined asymptomatic and symptomatic fruit from symptomatic vines (not retrained). Asymptomatic fruit from asymptomatic-retrained vines had the lowest levels of monomeric flavan-3-ols, compared to asymptomatic fruit from healthy vines (not retrained) or asymptomatic fruit from symptomatic vines (not retrained). In comparison, symptomatic fruit from symptomatic vines had the highest levels of monomeric flavan-3-ols, potentially indicating a plant-derived defense response to Esca.

Funding Support: American Vineyard Foundation