Pruning-wound protectants for trunk-disease management in California table grapes

Authors: BROWN, ALBRE - University Of California, Davis; TRAVADON, RENAUD - University Of California, Davis; LAWRENCE, DANIEL - University Of California, Davis; TORRES, GABRIEL - University Of California - Cooperative Extension Service; ZHUANG, GEORGE - University Of California - Cooperative Extension Service; Baumgartner, Kendra

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2020
Publication Date: 1/22/2022
Citation: Brown, A.A., Travadon, R., Lawrence, D.P., Torres, G., Zhuang, G., Baumgartner, K. 2022. Pruning-wound protectants for trunk-disease management in California table grapes. Crop Protection Journal. 141:105490. https://doi.org/10.1016/j.cropro.2020.105490.
DOI: https://doi.org/10.1016/j.cropro.2020.105490

Interpretive Summary: In California’s Mediterranean climate, management of grapevine trunk diseases (Botryosphaeria dieback, Eutypa dieback, Phomopsis dieback, Esca) focuses on protecting vines during the dormant season, when the vines are pruned each year and are susceptible to infection by spores of the fungi that cause trunk diseases (‘trunk pathogens’). Applying protectants (fungicides, toxic barriers, sealants, biocontrol agents) after pruning can minimize infection of pruning wounds. For the dormant seasons of 2017 to 2019, in a 2-year-old Vitis vinifera ‘Scarlet Royal’ vineyard in the southern San Joaquin Valley, we evaluated tractor-spray applications of the following protectants labeled for table grapes: fluopyram+tebuconazole, pyraclostrobin, thiophanate-methyl+myclobutanil, and Bacillus amyloliquefaciens. A comprehensive set of virulent and widespread trunk pathogens, including Diaporthe ampelina, Eutypa lata, Neofusicoccum parvum, and Phaeomoniella chlamydospora, were inoculated to pruning wounds post-application, with detection attempts 3 to 4 weeks later (before budbreak). Consistently high efficacies of pyraclostrobin (68 to 100% and 56 to 100%, respectively) and thiophanate-methyl+myclobutanil (64 to 77% and 91 to 100%, respectively) against Botryosphaeria-dieback pathogen N. parvum and Phomopsis-dieback pathogen D. ampelina suggest spray applications of these protectants could minimize infection of California table grapes. However, because of pyraclostrobin’s low efficacy against P. chlamydospora (12 to 56%), this fungicide alone may not protect vines from this Esca pathogen. Low detection rates of Eutypa-dieback pathogen E. lata, even from water-treated spurs (8% detection in culture, 28 to 44% via qPCR), made it difficult to identify an effective protectant. With no one protectant providing uniformly high efficacy, combining protectants is a good strategy to help protect California table grapes against the broad taxonomic range of trunk pathogens.In California’s Mediterranean climate, management of grapevine trunk diseases (Botryosphaeria dieback, Eutypa dieback, Phomopsis dieback, Esca) focuses on protecting vines during the dormant season, when the vines are pruned each year and are susceptible to infection by spores of the fungi that cause trunk diseases (‘trunk pathogens’). Applying protectants (fungicides, toxic barriers, sealants, biocontrol agents) after pruning can minimize infection of pruning wounds. For the dormant seasons of 2017 to 2019, in a 2-year-old Vitis vinifera ‘Scarlet Royal’ vineyard in the southern San Joaquin Valley, we evaluated tractor-spray applications of the following protectants labeled for table grapes: fluopyram+tebuconazole, pyraclostrobin, thiophanate-methyl+myclobutanil, and Bacillus amyloliquefaciens. A comprehensive set of virulent and widespread trunk pathogens, including Diaporthe ampelina, Eutypa lata, Neofusicoccum parvum, and Phaeomoniella chlamydospora, were inoculated to pruning wounds post-application, with detection attempts 3 to 4 weeks later (before budbreak). Consistently high efficacies of pyraclostrobin (68 to 100% and 56 to 100%, respectively) and thiophanate-methyl+myclobutanil (64 to 77% and 91 to 100%, respectively) against Botryosphaeria-dieback pathogen N. parvum and Phomopsis-dieback pathogen D. ampelina suggest spray applications of these protectants could minimize infection of California table grapes. However, because of pyraclostrobin’s low efficacy against P. chlamydospora (12 to 56%), this fungicide alone may not protect vines from this Esca pathogen. Low detection rates of Eutypa-dieback pathogen E. lata, even from water-treated spurs (8% detection in culture, 28 to 44% via qPCR), made it difficult to identify an effective protectant. With no one protectant providing uniformly high efficacy, combining protectants is a good strategy to help protect Califor

Technical Abstract: In California’s Mediterranean climate, management of grapevine trunk diseases (Botryosphaeria dieback, Eutypa dieback, Phomopsis dieback, Esca) focuses on protecting vines during the dormant season, when pruning coincides with rain-induced spore dispersal of the causal fungi (‘trunk pathogens’). Applying protectants (fungicides, toxic barriers, sealants, biocontrol agents) after pruning can minimize infection of pruning wounds. For the dormant seasons of 2017 to 2019, in a 2-year-old Vitis vinifera ‘Scarlet Royal’ vineyard in the southern San Joaquin Valley, we evaluated tractor-spray applications of the following protectants labeled for table grapes: fluopyram+tebuconazole, pyraclostrobin, thiophanate-methyl+myclobutanil, and Bacillus amyloliquefaciens. A comprehensive set of virulent and widespread trunk pathogens, including Diaporthe ampelina, Eutypa lata, Neofusicoccum parvum, and Phaeomoniella chlamydospora, were inoculated to pruning wounds post-application, with detection attempts 3 to 4 weeks later (before budbreak). Consistently high efficacies of pyraclostrobin (68 to 100% and 56 to 100%, respectively) and thiophanate-methyl+myclobutanil (64 to 77% and 91 to 100%, respectively) against Botryosphaeria-dieback pathogen N. parvum and Phomopsis-dieback pathogen D. ampelina suggest spray applications of these protectants could minimize infection of California table grapes. However, because of pyraclostrobin’s low efficacy against P. chlamydospora (12 to 56%), this fungicide alone may not protect vines from this Esca pathogen. Low detection rates of Eutypa-dieback pathogen E. lata, even from water-treated spurs (8% detection in culture, 28 to 44% via qPCR), made it difficult to identify an effective protectant. With no one protectant providing uniformly high efficacy, combining protectants is a good strategy to help protect California table grapes against the broad taxonomic range of trunk pathogens.