Rainfastness, Residue Persistence and Efficacy of Fungicides against Apple Scab (Venturia inaequalis) under Simulated Rainfall Conditions
Addafar Gulzar
*
Division of Plant Pathology, Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Tariq Rasool Rather
Ambri Apple Research Centre, Sher-e-Kashmir University of Agricultural Sciences and Technology, Pahnoo, Shopian, India.
Mohammad Najeeb Mughal
Division of Plant Pathology, Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Parveez Ahmad Sheikh
Division of Plant Pathology, Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Baby Summuna
Directorate of Extension Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Abdul Rauf Malik
Division of Fruit Science, Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Bushra Rasool
Research Centre for Residue & Quality Analysis (RCRQA), Sher-e-Kashmir University of Agricultural Sciences and Technology, Shamilar, Srinagar, Jammu and Kashmir -190025, India.
Kushboo Tariq
Faculty of Agriculture. Sher-e-Kashmir University of Agricultural Sciences and Technology, Wadura, Sopore, Jammu and Kashmir -193201, India.
*Author to whom correspondence should be addressed.
Abstract
Apple scab, caused by Venturia inaequalis (Cooke) G. Winter, is the most destructive disease of apple worldwide. Although fungicides remain the primary means of disease management, rainfall shortly after application can reduce their efficacy through fungicide wash-off. Information on the rainfastness of commonly recommended fungicides under varying rainfall conditions remains limited. Therefore, this study evaluated the persistence and efficacy of selected fungicides against apple scab under simulated rainfall conditions. Three-year-old potted plants of apple cv. ‘Red Delicious’ were treated with representative protectant and systemic fungicides and exposed to simulated rainfall (5–30 mm) at rain-free intervals of 6–36 h after application. Fungicide residues were quantified using the QuEChERS method, and disease incidence, disease severity and control efficiency were assessed following inoculation with V. inaequalis. Residue retention declined significantly with increasing rainfall but improved with longer rain-free intervals. At a 36-h rain-free interval, the trifloxystrobin and tebuconazole components showed the highest rainfastness, retaining 94.05% and 94.87% of their initial residues after 5 mm of rainfall and 74.05% and 74.87%, respectively, after 30 mm of rainfall. It also provided the highest disease control efficiency (89.6–100.0%) and the lowest disease incidence and severity across all rainfall regimes. Difenoconazole 25 EC ranked second in efficacy, whereas Dodine, Mancozeb and Captan showed progressively greater rainfall-induced loss of persistence and disease control. These findings demonstrate that Trifloxystrobin + Tebuconazole and Difenoconazole provide superior protection under rainfall-prone conditions and offer a scientific basis for optimising fungicide selection, spray scheduling and re-application decisions, thereby improving apple scab management while minimising unnecessary fungicide applications.
Keywords: Apple scab, Venturia inaequalis, fungicide rainfastness, residue persistence, simulated rainfall, rain-free interval, disease incidence, disease severity, control efficiency, fungicide wash-off