Organic Management Strategies for Controlling Late Blight of Potato (Solanum tuberosum L.) Caused by Phytophthora infestans in Organic Farming System

Late blight, caused by Phytophthora infestans, is considered to be one of the most destructive diseases of potato (Solanum tuberosum L.), particularly under conditions of high humidity and moderate temperatures. It leads to severe yield losses and deterioration of both foliage and tubers, posing a serious threat to food security. In organic farming systems, where synthetic fungicides are prohibited, the development of eco-friendly disease management options is essential. Our study tested several plant extracts and a biological control agent for managing late blight in organic field conditions. Our field experiment was conducted with nine treatments; Trichoderma harzianum (T₁; tuber treatment), neem leaf extract (T₂), garlic extract (T₃), tea extract (T₄), marigold extract (T₅), mint extract (T₆), turmeric extract (T₇), aloe vera gel extract (T₈), and an untreated control (T₀) for comparison purpose. Except for T₁, which was applied as a pre-sowing tuber treatment, all other formulations were applied as foliar sprays. We assessed the disease incidence and severity at regular intervals on 27 replications (5 plants from each replication) using Percent Disease Index (PDI) and 0–9 disease rating scale. Percent Disease Control (PDC) and yield (kg ha⁻¹) were also recorded. Data were analyzed using ANOVA, and S.Em. and C.D. (5 %) were computed. We found the Significant differences among treatments like; Aloe vera extract (T₈) recorded the lowest mean PDI (10.23 %) and the highest PDC (47.27 %), followed by tea extract (T₄), turmeric extract (T₇), and neem extract (T₂). The untreated control (T₀) showed the highest disease incidence (21.81 % PDI at 60 DAS) and the lowest yield. The final yield was significantly improved in T₈. Our results showed, plant-based extracts, particularly aloe vera, can effectively suppress late blight and enhance potato yield under organic farming systems.