Vol. 18 No. 3
Integrated management of Alternaria blight caused by Alternaria spp. in rapeseed (Brassica rapa var. toria) under field conditions
Author(s): R. CHAKRABARTY, H. KALITA, 1M. CHAKRAVARTY, 2M. BASUMUTARY, 3B. BHATTACHARYYA AND 4B. MEDHI
Field trial was conducted during rabi, 2017-18 and 2018-19 at Nagaon, Assam to identify effective and economic agro-technique (s) for management of Alternaria blight caused by Alternaria brassicae (Berk) Sacc. and A. brassicicola (Schw) Wiltshire in rapeseed (Brassica rapa var. toria L.). Mancozeb 75 WP @ 0.2 % spray at 45 days after sowing (DAS) followed by propiconazole 25 EC @ 0.05 % at 60 DAS with the lowest disease severity of 16.05% on leaves at 70 DAS and 7.25 % on pods at 75 DAS accrued in the highest disease reduction (56.91 % on leaf at 70 DAS and 54.11 % on pod at 75 DAS) and increase in seed yield (73.6 %) over control. This treatment accrued in a net return (NR) of Rs. 16237 ha-1 and benefit-cost ratio (B:C) 1.71. Seed treatment with mancozeb 75 WP @ 0.2 % in combination with foliar application of propiconazole 25 EC @ 0.05% at 45 DAS followed the former treatment with 55.97 % disease reduction on leaf, 47.47 % on pod and 69.4 % yield increase. However, this management practice recorded the highest NR (Rs 16860 ha-1) and B:C (1.79). The biological management practice involving soil application of biogreen @ 2.5 kg ha-1, seed treatment with biogreen @ 5 % and biogreen foliar spray @ 5 % at 45 DAS also emerged to be promising claiming the third position with 53.29 % disease reduction on leaf, 43.04 % on pod, 63.1 % yield increase and a B:C of 1.50. In comparison to the latter two treatments, the former could avoid 2.4 and 6.1 % yield loss, respectively. Under on-farm testing through KVKs in four agro-climatic zones of Assam, mancozeb 75 WP @ 0.2 % at 45 DAS + propiconazole 25 EC @ 0.05 % at 60 DAS resulted in 40.5-54.7 % disease reduction on leaves and 39-52.1 % on pods with 38.3 - 69.2 % yield increase and B:C ranging from 1.55 to1.87. Disease reduction on leaves was 25.4 - 31.1 %, on pods 22 - 36.6 %, yield increase 31.1 - 45.8 % and B:C 1.28 - 1.75 under the biological control measure was recorded using biogreen as soil treatment @ 2.5 kg ha-1, seed treatment @ 5 % and foliar spray at 45 DAS @ 5%.