Temporal progression and effective chemical control strategies for apple blotch disease in Brazilian orchards

Abstract Apple blotch disease (ABD), caused by the fungus Diplocarpon mali , identified as the teleomorph of Marssonina coronaria , has been increasing in major cultivars such as Gala, Fuji, and Eva within Brazilian apple-producing regions since the 2001/2002 season. The factors contributing to the increase of ABD severity remain unclear, but research suggests that elevated temperatures and increased humidity during summer, attributed to climate change, may be fostering pathogen growth, thereby intensifying the disease globally. Investigations into the disease's epidemiology and chemical control hold promise for enhancing orchard management practices. This study aimed to evaluate the temporal progression of ABD in economically significant national cultivars (Gala and Eva) and to assess the efficacy of seven active ingredients in chemical control within 'Princesa,' a cultivar highly susceptible to ABD. Results indicate that the maximum ABD asymptote and disease progress rate were higher in 'Princesa' than in 'Gala' and 'Eva.' Defoliation commenced earlier and was more severe in the Princesa cultivar, revealing a strong correlation between ABD symptom severity and early apple tree defoliation. ABD symptoms were effectively managed by propineb (FRAC#M03), tebuconazole (FRAC#3), and trifloxystrobin+tebuconazole (FRAC#11 and #3), resulting in a 55%, 76%, and 80% reduction, respectively, in the area under the disease progress curve compared to the untreated control during the 2019/2020 season. Furthermore, these treatments demonstrated consistent efficacy in the 2020/2021 season, achieving reductions of over 90% in disease severity.