The experiment was conducted at the farmer’s field of sadar upazila of Patuakhali district, Bangladesh to screen mungbean varieties against major insect pests i.e., leaf folder (Cnaphalocrocis medinalis), gram pod borer (Helicoverpa armigera) and legume pod borer (Maruca vitrata) of mungbean and their yield performances during late Robi season 2016.
2.1 Experimental location: It was located in between 22°14' and 22°29' North latitudes and in between 90°12' and 90°28' East longitudes (BANGLAPEDIA:National Encyclopedia of Bangladesh, 2015). It is adjacent to the Bay of Bengal and this area lies at 0.9 to 2.1 metre above mean sea level (Iftekhar and Islam, 2004).
2.2 Experimental layout and fertilizer application: Experiment was laid out in Randomized Complete Block Design (RCBD) with three replications. Each replication represented a block which was divided into 15 unit plots. There were 45 unit plots altogether in the experiment. Each unit plot (4 m x 2.5 m) was made ready as per treatment design. The distance from block to block and from plot to plot was 1.0 m and 0.5 m, respectively. The fertilizers were applied as per fertilizers recommendation guide (BARI, 2011). Urea, triple super phosphate (TSP) and muriate of potash (MoP) were applied in the field uniformly @ 50, 85 and 35 kg ha-1, respectively during the final land preparation. The fertilizers were then properly mixed with the soil by spading and the plots of the experimental unit were leveled.
2.3 Planting materials and sowing of seed in the field: 15 mungbean varieties viz., BARI Mung-1, BARI Mung-2, BARI Mung-3, BARI Mung-4, BARI Mung-5, BARI Mung-6, BINA Moog-4, BINA Moog-5, BINA Moog-6, BINA Moog-7, BINA Moog-8, BU Mug-1, BU Mug-2, BU Mug-4 and Patuakhali local Mung were used as study materials. The seeds of these mungbean varieties were collected from Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur and Patuakhali local Mung variety collected from farmers’ of Patuakhali district, Bangladesh. The seeds of mungbean were sown on the 29th January, 2016 at the rate of 30 kg ha-1 (BARI, 2011). In rows, the seeds were sown continuously at a depth of 6-7 cm and covered by loose soil by hand. The distance from row to row was 30 cm.
2.4 Data collection of insect pests: The plants were exposed to natural insect pests’ infestation and insecticide was not applied during the experimental. Population of leaf folder, gram pod borer and legume pod borer were recorded at an interval of 7 days commencing from first incidence. All plants from each unit plot were observed individually and the number of leaf folder, gram pod borer and legume pod borer were recorded at early in the morning (6.30 a.m.-9.00 a.m.). Data on insect pests were recorded at 18, 25, 32, 39, 46 days after sowing (DAS) for leaf folder and at 51, 58, 65 DAS for gram pod borer and legume pod borer. During experimental period meteorological data on temperature and relative humidity (RH) were collected from the Weather Observatory, Meteorological office, Patuakhali.
2.5 Statistical analysis: The collected data was statistically analyzed through the analysis of variance using Web Agri Stat Package (WASP 1.0). Means were separated by critical difference (CD) values at 5% level of significance. The insect population data were transformed to square root (√x + 0.5) values.