Critical timing of fungicide application for pruning wound protection to control grapevine trunk diseases

Background and Aims Grapevine trunk diseases, caused by fungal pathogens that infect pruning wounds, pose a major threat to the sustainability of vineyards throughout the world. Pruning wound protectants can control infection, but little is known about the optimal timing of application of protectants following pruning. In this study, the timing of fungicide application to pruning wounds was evaluated to assess curative and preventative effects. Methods and Results To assess curative control, on the day of pruning, wounds were inoculated with ascospores of Eutypa lata or conidia of Neofusicoccum luteum followed 1, 3 or 6 days later by application of the fungicides tebuconazole, pyraclostrobin or fluazinam. To assess preventative control, fresh pruning wounds were treated with the same fungicides, then inoculated 1, 6 or 14 days later. The fungicides provided curative control of both pathogens for up to 6 days and preventative control of E. lata for up to 6 days and of N. luteum for up to 14 days. Conclusion These results indicate that fungicides can provide control of trunk disease pathogens when applied up to 6 days after wound infection, and continue to protect wounds for up to 14 days after application. Significance of the Study Current recommendations to protect grapevine pruning wounds from trunk disease pathogens are to apply protectants within 24 h of pruning. This study suggests that a single application of the fungicides tested 6 days after pruning may provide up to 3 weeks of wound protection, thereby offering improved flexibility in managing grapevine trunk disease.