Control of Blumeriella jaapii and determination of fungicide residues in sour cherry fruits

Blumeriella jaapii represents a widely distributed and a significant pathogen of sour and sweet cherry. Chemical control is the most effective and indispensable in the control of this pathogen in these fruit species. The objective of this study was to evaluate the efficacy of fungicides in control of B. jaapii in sour cherries, as well as to determine their residues in fruits. The experiment was conducted during 2015 at the locality Merošina (Niš) in the sour cherry orchard (cultivar 'Oblačinska'), using standard EPPO methods. The orchard was three years old, with a growth form of enhanced pyramid. Applied fungicides were dodine (650 g a.i. kg^‑1), in a concentration of 0.1%, dithianon (700 g a.i. kg^‑1), in a concentration of 0.075% and mancozeb (800 g a.i. kg^‑1), in a concentration of 0.25%. The treatments were carried out by foliar application, with a backpack sprayer and water consumption of 1000 L ha^‑1. During the field trials two assessments of the fungicide effects were performed. The first evaluation was during the occurrence of first symptoms in control variant. The presence of a pathogen, its development and the percentage of the affected leaf area was observed. The second evaluation was performed 4 weeks after the first and the percentage of fallen leaves was determined according to the scale (1 - without fallen leaves, 2 - 25% of fallen and 3 - more than 25% of fallen leaves). The efficacy (E%) of fungicides was calculated according to Abbott. The results indicated the greatest efficacy of applied fungicides during the first assessment in the variant in which the fungicide was applied on the basis of dodine (99.1%), dithianon (95.9%) and mancozeb (94.4%). The second evaluation showed that the control variant lost over 25% of its leaves, while in the other treatments fallen leaves were either not registered or only in a very low percentage. In order to determine residue levels and dissipation dynamic of dithianon fungicide in sour cherry fruits, samples were randomly collected immediately after the application and every second day during the preharvest interval. For sample pre-treatment, QuEChERS procedure was used, followed by HPLC-DAD analysis.