Efficacy of Pruning-Wound Protectant Fungicides for the Management of Botryosphaeria Canker and Dieback of Apple Trees in Maule Region, Chile

Botryosphaeria canker and dieback is an important fungal disease caused by Botryosphaeriaceae spp. that affects the productivity of apple orchards in Chile and worldwide. In the field, studies on the management of this disease are focused on the protection provide by fungicides applied on pruning wounds. However, in Chile, information about the protection and efficacy of fungicides on apple trees against twig and branch pathogens is scarce. Therefore, in this study, we evaluated the efficacy of fungicides to control fungal trunk pathogens causing Botryosphaeria canker and dieback in apple trees using in vitro, greenhouse, and field trials. Isolates of Diplodia mutila, D. seriata, Neofusicoccum arbuti, and Lasiodiplodia theobromae obtained and characterized previously in Chile from apple trees with canker and dieback symptoms were used in this study. In vitro tests showed that benomyl, fluazinam, difenoconazole, and tebuconazole exhibited the lowest EC50 values, with means of 0.08, 0.09, 0.12, and 0.18 μg/ml, respectively. This study demonstrates that infection caused by D. mutila, D. seriata, L. theobromae, and N. arbuti can be significantly reduced using single-sprayed fungicides. The most effective in reducing infection on pruning wounds of apple trees by Botryosphaeriaceae were benomyl (66 to 76%), tebuconazole (47 to 68%), thiophanate-methyl (68 to 71%), boscalid + pyraclostrobin (47 to 63%), fluxapyroxad + pyraclostrobin (54 to 57%), and thiophanate-methyl + tetraconazole (63 to 74%). To our knowledge, this is the first study reporting the control of Botryosphaeriaceae causing canker and dieback in apple trees through the use of commercially available chemical fungicides, with different active ingredients and modes of action.