Role of indigenous plant products in the sustainable management of major insect pests of cabbage under Imphal valley agroecological situations

A field experiment was conducted at the College of Agriculture, Iroishemba, Imphal during Rabi,  2020-21  to  study  the  bio-efficacy  of  certain  aqueous  indigenous  plant  extracts  against  the Diamond  back  moth(DBM),  Plutella  xylostella  Linnaeus,the  Cabbage  butterfly(CB),  Pieris  brassicae Linnaeus  and  the  Cabbage  aphid  (CA),  Brevicoryne  brassicae  Linnaeus  and  their  toxic  effect  on  the population  of  predatory  coccinellid  beetle,  Coccinella  septempunctata  Linnaeus  in  cabbage  crop  var. Pride of  India‖.  There was  moderate incidence of P.  xylostella, P.  brassicae  and  B.  brassicae  in  the experimental crop var. ―Pride of India‖. The insects maintained mean incidence of 14.42 to 22.80 % leaf damage, 9.51 to 16.14% leaf damage and 37.33 to 77.35 aphids/plant, respectively. Thus, these pests were considered as the regular and major pests of cabbage during the investigation. The results on the efficacy of bio-rational insecticides against P. xylostella, P. brassicae and B. brassicae revealed that 
all the insecticidal treatments resulted in significantly suppression of both the pests‘ incidence. The pooled results based on three applications of insecticide indicated that Margosom (Azadirachtin 300 ppm) @ 0.3% spray conc. followed by Melia azedarach, extract applied at the spray conc. of 5.0% were quite effective in reducing the population of the insect pest of cabbage with a record of lower mean leaf damage of  6.92 and 7.61 per cent, respectively and did not  differ significantly between them. Against  P.  brassicae  also  Margosom  (Azadirachtin  300  ppm)  @  0.3%  spray  conc.  registered significantly  the  lowest mean  leaf damage  of 7.65  per cent  as against 14.73% in  untreated  check, closely  followed  by  Melia  azedarach  extract  @  5.0% spray conc.(8.10%  LD) and  Artemisia  nilagirica extract@  5.0%  spray  conc.(8.37  %  LD)  which  had  none  significant  difference  one  another.  The significantly highest mean leaf damage incidence (12.33% LD) was noticed in the plots treated with aqueous extract of Solanum conyzoides when applied @ 5.0% spray conc. Of the aqueous indigenous plant extracts field evaluated against the butterfy, M. azedarach proved the most effective treatment in suppression the pest incidence with minimum mean leaf damage. The results on the effectiveness of various insecticidal treatments against B. brssicae, further showed that Margosom (Azadirachtin 300 
ppm) @ 0.3% conc. also maintained its superiority to other treatments in suppression of the aphid population recording the lowest mean population of 9.43 per plant as against 36.46 aphids/plant in untreated control. It was at par with the mean population recorded in the treatments with Ageratum conyzoides  (11.97  aphids/plant),  Solanum  xanthocarpum  (12.01  aphids/plant),  Mariandra  bengalensis (12.46 aphids/plant) and Artemisia niligirica (12.69 aphids/plant). While, M. azedarach extract exhibited its  inferior  performance  in  controlling  aphid  with  highest  mean  population  of  14.04 per  plant.  The plots treated  with  Margosom (Azadirachtin 300 ppm) recorded maximum  cabbage yield of 22.38 t ha-1 follower by M. azedarach extract treated plots (19.93 t ha-1) with increase yield over control of 6.50 t ha-1 and 40.93 per cent, and 4.05 t ha-1 and 25.50 per cent, respectively but deferred significantly from each other as per the yield harvested from the plots of these insecticides is concerned. The minimum mean yield (18.00 t ha-1 ) was obtained from the plots treated with A. nilagirica  with  increase  yield  of  2.12  t  ha-1  and  13.35  per  cent  over  control  ,but,  did  not  differ significantly  from  that  of  rest  insecticidal  treatments  except  yield  of  Plectralthus  ternifolius  extract. However, it is amply clear that all the plant extracts were superior in controlling DBM, CB and CA in comparison  to  untreated  control.  The  extent  of  avoidable  yield  loss  due  to  the  incidence  of  P. xylostella, P. brassica and B. rassicae was estimated to be 29.04 per cent in untreated control which was reduced to 10.95- 19.57 per cent. Minimum being recorded in M. azedarach and maximum in Artemisia nilagarica extract. Further, the pooled mean data of three observation periods‘ revealed that among the  test  insecticides  M.  azedarach  @  5%  A.  nilagirica,  Cinnamomum  tamala  and  Aralia  armata  each applied at the spray concentration of 5.00%, proved to be the safer extracts to the predatory beetle C. septempunctata with their corresponding mean beetle population of 1.56, 1.41, 1.32 and 126 per plant as against 3.27 in untreated control which did not show significant difference from one another. The lowest beetle population (0.79/plant) recorded in the plots treated with Margosom (Azadirachtin 300 ppm) @ 0.30% conc. closely followed by Solanum xanthocarpum and Meriandra bengalensis extracts @ 5.00% conc. with the mean beetle population of 0.89 and 0.92 per plant, respectively.