Impact Assessment Of Different Sowing Dates On Maize Aphid, Rhopalosiphum Madis Infestation In Bangladesh
Md. Jewel Alam, Most. Khairun Nahar, Mst. Khadija Khatun, Md. Harun-or Rashid, Kazi Shahanara Ahmed
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Maize (Zea mays L.) is attacked by many insect-pests which are the principal limiting factor for its productivity all over in Bangladesh. The maize aphid, Rhopalosiphum maidis is one of the most destructive pests of maize as second important cereal crop after rice. The present investigation was set up at the Entomology Field Laboratory, Department of Entomology, Bangladesh Agricultural University (BAU), Mymensigh during Rabi season of 2016-17 in order to assess the impact of different sowing date on maize aphid infestation under field condition and it’s also effect on morphological, phenology, yield attributes and yield of maize. The experiment was laid out in randomized complete block design (RCBD) having three replications. Maize var. BARI Hybrid Butta-09 variety was used as experimental crop. Nine sowing dates viz. 3rd(S1) & 4th(S2) week of October, 1st(S3), 2nd(S4), 3rd(S5) & 4th(S6) week of November and 1st(S7), 2nd(S8) & 3rd(S9) week December were used as treatments. To assess the impact of different sowing dates, different data were collected from randomly selected five plants from each replicated plots at different growth stage i. e. vegetative, inflorescence and cob formation stage at least three times based on three main parameters such as entomological features (healthy & infested plants, inflorescences & cobs; body length(mm), number of aphid per plant and inflorescence), morpho-physiological characters (Plant height, cm) and yield attributes & yield (number of cob plant-1, cob length without husk (cm), diameter of cob without husk (cm), number of grain cob-1, grain weight cob-1(g) and grain yield, t ha-1). The results revealed that 1st week of November (S3) as sowing date was found the best for suppressing the maize aphid, and morpho-physiological characters, yield attributes and grain yield was also the best compared to others sowing dates due to ensuring the lowest percentage of infested maize plant at vegetative stage (36.91%), inflorescence stage (43.12%), cob formation stage (20.53%) & average the lowest percentage of infested maize (33.52%), and the highest plant height (223.66cm), number of cob plant-1 (1.73), cob length without husk (23.23cm), diameter of cob without husk (16.17cm), number of grain cob-1 (641.21), grain weight cob-1(235.16) and maximum grain yield (10.56 t ha-1). Furthermore, based on average aphid infestation, the increasing order of infestation due to different sowing date were S4<S9<S1< S2< S7< S8< S5< S6, and thereby to yield, the increasing order of yield were S4<S5<S6< S7< S8< S9< S2< S1. Besides, a matter of correlation between different parameters, considering to the different sowing dates, average aphid infested plants (%) and yield of maize; firstly, the present study showed that strongly significant positive correlation was found between sowing dates with aphid infested plants, and secondly, very strongly significant negative correlation between sowing dates & grain yield of maize, and finally, very highly significant negative correlation was observed between average infested plants (%) with grain yield of maize. Henceforth, on the basis of body length, among different growth stages of maize production, the minimum (2.10mm) body length of aphid was recorded at inflorescence stage than vegetative (2.32mm) and cob formation stage (2.51mm), which is why; less damage of pollen as well as produced higher yield. On the other hands, based on body size, among the different sowing dates, the tolerable body length (2.34mm) was found sown on 1st week of November where the highest yield occurred than others sowing dates due to less damage of pollen as well as occurred maximum fertilized of pollen. However, considering the incidence of aphid, among different sowing dates, the minimum tolerable no. of aphid per plant (280) and inflorescence (470) was recorded sown on 1st week of November where the maximum grain yield occurred than others sowing dates. Sowing date of 1st week of November (S3) was the best because all environmental factors are more suitable for producing of maize and suppressing or combat against aphid as well as yield with better quality. In addition, we have also found that the sowing date of 2nd week of November (S4) performed second best. Therefore, considering all facts, 1st week of November as sowing date could be recommended to the maize grower for the most effective for suppressing the maize aphid, R. maidis. Hence, in addition, 2nd week of November could also be suggested for second best effective sowing date for suppressing incidence of aphid where second crop of cropping pattern is not available or not apply in the field.