IMPACT OF SELECTED CROP ROTATION PRACTICES ON THE INCIDENCE OF INSECT PESTS IN PADDY FIELDS AT DINHATA, WEST BENGAL, INDIAGobinda Chandra Roy, Kaushik Chakraborty and Siddharthasankar Banerjee
To evaluate the influence of crop rotation practices on the prevalence of four significant paddy insect pests, studies for three consecutive years (2012-2014) were conducted at Dinhata, Coochbehar, and West Bengal, India. Grossly 26 types of crop rotation practice and four major insect pests were distinguished in this area. The pests are yellow stem borer (YSB), brown plant hopper (BPH), gall midge (GM) and paddy bug (PB) correspondingly. Paddy-green manure, maize-paddy, jute-paddy, vegetable-paddy and pulses-paddy are more commonly practiced out of the all renowned crop rotational practices. Incidence of pest number (individuals/hill) and the extent of crop damage viz., dead heart (DH) + white head (WH) for YSB, damaged leaf area (DAL%) for BPH, silver shoot (SS%) for GM and unfilled grains (UG%) for PB under five selected crop rotation practices were compared with that of the result of monoculture field having two or three paddy crops in a year. Side by side incidence of pest population was also noted in fallow-paddy circumstance. Damage due to pest infestation was determined after assessing the number of infested hills (for YSB and GM), infested leaf (for BPH) and shockingly filled grains (for PB). Maximum number of pest individuals (7.14 YSB/5 hills, 19.68 BPH/hill, 14.81 GM/10 hills and 3.12 PB/hill) and the level of damage (7.16% DH +4.18% WH, 29.04% DAL, 40.1% SS and 40.31% UG) were noted in field having three consecutive paddy crops in a year. The least pest incidence (1.80 YSB/5 hills, 4.68 BPH/hill, 2.15 GM/10 hills and 0.98 PB/hill) with lowest level of damage (2.18% DH +2.50 WH, 10.14% DAL, 5.01% SS and 16.12% UG) was registered in field where paddy was grown after green manure production. Maximum yield (q/ha) with highest cost: benefit value (C: B) was registered in green manure-paddy (33-35q/ha) as the least was scored from the field with three successive paddy crop in a year (23-25q/ha).