Preventing trunk diseases with fungicide applications to pruning wounds in Washington winegrapes

Authors: Baumgartner, Kendra; TRAVADON, RENAUD - University Of California, Davis; Fujiyoshi, Phillip; MIRELES, MARIA - Washington State University; MOYER, MICHELLE - Washington State University

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2022
Publication Date: 1/1/2023
Citation: Baumgartner, K., Travadon, R., Fujiyoshi, P.T., Mireles, M., Moyer, M. 2023. Preventing trunk diseases with fungicide applications to pruning wounds in Washington winegrapes. American Journal of Enology and Viticulture. 74. Article 074007. https://doi.org/10.5344/ajev.2022.22019.
DOI: https://doi.org/10.5344/ajev.2022.22019

Interpretive Summary: Grapevine trunk diseases in the Columbia River Basin of eastern Washington include Cytospora dieback, Eutypa dieback, and Esca. Although some of the causal fungi have been identified in the past from diseased vineyards (as Cytospora viticola, Eutypa lata, and Phaeomoniella chlamydospora, respectively), we are missing important details of how these fungi spread and when they infect vines, which makes it difficult to time management practices. The common assumption is that these pathogens infect through pruning wounds during the dormant season, as has been shown for causal fungi of some grapevine trunk diseases in California. As such, we evaluated fungicides for protecting wounds after pruning under eastern Washington conditions. In March (late winter) of 2019, 2020, and 2021, at an established (> 8-year-old) Vitis vinifera ‘Chardonnay’ vineyard in Prosser, WA, we evaluated the efficacy of protectant spray applications within 3 days of pruning of the fungicides pyraclostrobin + fluxapyroxad and thiophanate-methyl. Spores (2,000 per wound) of C. viticola, E. lata, and P. chlamydospora were inoculated to pruning wounds within 2 days of fungicide treatment, with molecular detection attempts 5 to 8 weeks later (after budbreak). Compared to water-treated spurs, there were lower detection rates of C. viticola and P. chlamydospora from thiophanate-methyl-treated spurs in all three study years. There was also lower detection of E. lata from thiophanate-methyl-treated spurs in one study year. This suggests that dormant-season spray applications of thiophanate-methyl as a pruning-wound protectant could minimize grapevine spur infection by these pathogens.

Technical Abstract: Grapevine trunk diseases in the Columbia River Basin of eastern Washington include Cytospora dieback, Eutypa dieback, and Esca. Although some of the causal fungi are known (as Cytospora viticola, Eutypa lata, and Phaeomoniella chlamydospora, respectively), basic epidemiology is not, which makes it difficult to time management practices. The common assumption is that these pathogens infect through pruning wounds during the dormant season, as has been shown for causal fungi of some grapevine trunk diseases in California. As such, we evaluated fungicides for protecting wounds after pruning under eastern Washington conditions. In March (late winter) of 2019, 2020, and 2021, at an established (> 8-year-old) Vitis vinifera ‘Chardonnay’ vineyard in Prosser, WA, we evaluated the efficacy of protectant spray applications within 3 days of pruning of the fungicides pyraclostrobin + fluxapyroxad and thiophanate-methyl. Spores (2,000 per wound) of C. viticola, E. lata, and P. chlamydospora were inoculated to pruning wounds within 2 days of fungicide treatment, with molecular detection attempts 5 to 8 weeks later (after budbreak). Compared to water-treated spurs, there were lower detection rates of C. viticola and P. chlamydospora from thiophanate-methyl-treated spurs in all three study years. There was also lower detection of E. lata from thiophanate-methyl-treated spurs in one study year. This suggests that dormant-season spray applications of thiophanate-methyl as a pruning-wound protectant could minimize grapevine spur infection by these pathogens.