Chemical management of Phytophthora blight of colocasia in mid hills of Himachal Pradesh.

摘要

A study was conducted to evaluate the commonly used and new fungicides for their efficacy against Phytophthora blight (P. colocasiae) of C. esculenta and to develop an effective and economic disease management spray schedule. Five fungicides, i.e. ridomil MZ (metalaxyl 8+mancozeb 64 WP), Blitox (copper oxychloride 50 WP), Dithane N-45 (mancozeb 75 WP), Kavach (chlorothalonil 75 WP) and Antracol (propineb 70 WP), were evaluated during 2007-08. Three sprays of the fungicides were given at an interval of 10 days for protectant and 15 days for systemic with the first spray given at the appearance of the disease. All the fungicides significantly reduced the disease compared to the control. Individually Ridomil MZ (metalaxyl+mancozeb) at 0.25% was the best treatment, resulting in only 7.36 (15.67) percentage disease index (PDI) and provided 84.27% disease control (PDC). Its efficacy in controlling the disease during both years was also significantly higher than all the other fungicides. Amongst the different spray schedules, schedule IX (Ridomil MZ-Ridomil MZ-Ridomil MZ) was found highly effective as indicated by low PDI (6.40) and high PDC (86.63) values followed by schedule I (Ridomil-Blitox-Blitox) and schedule II (Ridomil-dithane-dithane) with PDI 12.90 and 14.00, PDC 71.83 and 69.43, respectively. The PDI and PDC under schedule I and II were statistically at par with each other indicating thereby the importance of application of combination of systemic and protectant fungicide at the initiation of the disease. High corm yields under schedule IX (201.40 q/ha), I (160.04 q/ha) and II (148.16 q/ha) showed their better efficiency, which was further supported by their high cost:benefit ratio (1:6.05, 1:6.80 and 1:7.45, respectively). The cost:benefit ratio was higher in schedule II and I compared to schedule IX, but the yield and PDI were significantly lower than schedule IX. The schedule X (farmers' practice) have shown low yield (114.86 q/ha) and cost:benefit ratio of 1:5.71. Therefore, it can be concluded that foliar spray of Ridomil MZ at 0.25% at 15 days interval is the most effective in managing phytophthora blight of colocasia under field conditions followed by Blitox at 0.20% in Dithane M-45 at 0.25% out of 10 spray schedules tested for their comparative efficacy the schedules 9 (Ridomil-Ridomil-Ridomil) followed by schedule I (Ridomil-Blitox-Blitox) and II (Ridomil-Dithane M-45-Dithane M-45) were found the most effective in the management of Phytophthora blight.