Effect of fungicides on different stages of the apple scab pathogen

Apple scab (Venturia inaequalis (Cooke) G. Winter) remains one of the most damaging diseases, limiting the productivity of apple orchards in the Central Region of Russia. This study aims to experimentally validate an integrated protection scheme based on the sequential application of the contact fungicide Merpan, SP (500 g/kg captan) (FRAC M04) and the systemic fungicide Znatok, VDG (500 g/kg trifloxystrobin) (FRAC 11), compared to a standard treatment program involving difenoconazole (FRAC 3). The research was conducted in 2024-2025 in the Solnechnogorsk district of Moscow Oblast on the Mantet and Lobo cultivars. Disease incidence and severity were assessed visually using a 4-point pictorial scale, and biological efficacy was calculated using Abbott’s formula. Additional assessments included the morphology of conidia and conidiophores using scanning electron microscopy, as well as the viability of ascospores on overwintered leaves. The results showed that on Mantet trees, the incidence of scab symptoms on leaves following three applications of captan and two of trifloxystrobin did not exceed 43 % by August, compared to 79 % in the control. On Lobo trees, leaf infection in the experimental scheme remained at 15 % by the end of the season, while reaching 80% in the control. On fruits, disease development in the captan and trifloxystrobin treatment did not exceed 20 % for Mante and 3 % for Lobo, which was 2-5 times lower than the control values. The biological efficacy of the tested scheme was 62-73% for Mantet and 69-89 % for Lobo, significantly exceeding the efficacy of the standard treatment program. Furthermore, a reduction in the viability of V. inaequalis ascospores to 2.0-3.9 % was established, which is 1.6–3 times lower than the control values. Moreover, pronounced morphological damage to conidia and conidiophores was observed. The combination of captan and trifloxystrobin demonstrated high stability of protective action and promise for use in integrated apple scab management programs in the Central Region of Russia.