The low yield of groundnut in our state as well as in the country can be attributed to many factors, among them many folds losses caused by weeds is of serious nature. Competition of weeds with the crops was observed to be very high during 50 to 60 days period. This period was found to be critical period for crop weed competition (Mahadkar et al., 1993). Weeds when allowed to compete till harvest depleted 162.8 kg N, 21.7 kg P₂O₅ and 141.8 kg K₂O per ha. Herbicides and hand weeding significantly brought down the nutrient removal by weeds and enhanced the uptake of nutrient by groundnut crop (Yadav et al., 1986). Hence, the present experiment was conducted to find out the effect of post emergence herbicide application in groundnut in order to control weed infestation (Table 1).

Present investigation was carried out during summer seasons of 2010 and 2011 at district seed farm, kalyani under Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal to study the effect of post emergence herbicides on summer groundnut in new alluvial zone of West Bengal. The soil of the experimental field was alluvium sandy loam in texture with content of organic carbon 0.79%, total N 0.07%, available phosphorus 24.65 kg/ha and Potassium 189.59 kg/ha. The pH of the soil was 6.81. The experiment was laid out in randomized block design with eleven (11) treatments and three (3) replications. The treatment details are as follows: T₁= Un-weeded control; T₂ = Weed free check; T₃ = Pre-emergence application of pendimethalin at 1.0 Kg a.i. /ha + one hand weeding; T₄ = Post emergence application of Quizalofop Ethyl at 50 g a.i./ ha 20 DAS ; T₅= Post emergence application of Quizalofop Ethyl at 75 g a.i./ ha 20 DAS ; T₆= Post emergence application of Quizalofop Ethyl at 100 g a.i./ ha 20 DAS; T₇ = Post emergence application of Imizethapyr at 50 g a.i./ ha 20 DAS ; T₈ = Post emergence application of Imizethapyr at 75 g a.i./ ha 20 DAS ; T₉ = Post emergence application of Imizethapyr at 100 g a.i./ ha 20 DAS ; T₁₀ = Pre-emergence application of pendimethalin at 1.0 Kg a.i. /ha + T₄ ; T₁₁= Pre-emergence application of pendimethalin at 1.0 Kg a.i. /ha +T₈ ; T₁₂ = farmers practice (one hand weeding + one intercultural operation). The recommended dose of N: P₂O₅ and K₂O was 20:60:40 kg /ha and gypsum at of 400 kg /ha was applied uniformly in all the treatments. The variety TAG 24 was sown in 27^th and 30^th January during 2010 and 2011 respectively.

Herbicide application to groundnut had the significant influence to increas the groundnut yield. Results indicated that all the herbicidal treatments as well as weed free check resulted in significant increase in yield and yield attributing characters of groundnut along with reduction in the weed population and weed biomass production, compared to un-weeded control.

 

Effect on weed population and weed dry matter

        

Best herbicidal response to weed density and weed dry matter production was recorded from T₃ that is, pre-emergence application of pendimethalin at 1.0 Kg a.i. /ha along with one hand weeding. Among the post-emergence herbicidal treatments, best response was observed from application of Imizathapyrat 100 g a.i./ha at 20 DAS (T₉) and application of quizalofop Ethyl at 100g a.i./ha 20DAS (T₆) at 45 DAS and at 75 DAS ,respectively regarding total weed density and weed dry matter production. Best results of weed density and weed dry matter production was found when pendimethalin as a pre-emergence along with quizalofop Ethyl as a post emergence was applied at 20 DAS. Murthy (1982) and Yadav et al. (1983) observed that pendimethalin was most effective in checking most of the monocot as well as dicot weeds and thus by improved the yield components like number of pods per plant, shelling percentage and test weight. Application of pendimethalin at1.5 kg  a.i  perha showed equal performance in pod yield (16.51 q/ha) with hand weeding at 15 and 35 days after sowing (18.4 q/ha) and was found better in controlling grassy weeds in groundnut (Kondap et al., 1989).

 

 

Effect of different herbicidal treatments on yield and yield attributing characters of groundnut was found to be significant, except in case of 100 kernel weight. Among all the herbicidal treatments, T₃ that is, pre-emergence application of pendimethalin at 1.0 Kg a.i./ ha along with one hand weeding, recorded highest pod yield (2675 Kg/ha), haulm yield (3123 Kg/ha), number of pods/plant (17.3), shelling % (71.3) and SMK % (91.4) as compared to post emergence herbicidal treatments. This might be due to application of pendimethalin as a pre emergence suppresses the weed growth at early stage of the crop as a result of better crop stand. Among the post-emergence herbicidal treatments pod yield, haulm yield and yield attributes of groundnut was found maximum with the treatment received post emergence application of quizalofop Ethyl at 100 g a.i. /ha i,e T_6, which was significantly superior to T₇ and T₈ ( treatments received Imizathapyr at 50 and 75g a.i./ ha at 20 DAS respectively) but statistically at par with T₉ ( Imizathapyr at 100g a.i./ ha at 20 DAS). Among the combinations of pre and post emergence herbicide application, the treatment T₁₀ (Pendimethalin at 1.0 kg a.i. / ha and Quizalofop Ethyl at 50 g a.i./ha) and T₁₁ (Pendimethalin at 1.0 kg a.i./ha and Imizathapyr 75 g a.i./ha) was statistically at par among each other. From the Table 2 it was found that weed free check (T₂) gave the highest pod yield (2871 kg/ha) as compared to rest of the treatments except T₃ (treatment received pre-emergence application of Pendimethalin at1.0kg a.i./ha and one hand weeding) and T12(one hand weeding and one intercultural operation), those were statistically at par with T₂ .Practices of weed control by chemical and/or mechanical(T₂ to T₁₂) gave the significantly better pod yield of groundnut as compared to un-weeded control (T₁) and pod yield of groundnut was decreased even up to 26 to 47% in un-weeded condition . Groundnut being a deep rooted legume crop proliferation of the root at early stage is essentially required to establish the sufficient numbers of nodule and better crop growth for pegging. Weed growth is faster than crop growth at early stage so controlling of weeds at early stage reduced the crop weed competition and thus providing nutritional security to the crop as result of better pod yield. Maximum gross return (Rs.86130) , net return (Rs.60505) and B:C ratio (3.36) were recorded in the treatment T¬2  thatis, weed free check and among herbicidal treatments maximum gross return (Rs.80550), net return (Rs.55937) and B:C ratio(3.27) were recorded in T₃  that is, pre-emergence application of pendimethalin at 1.0 Kg a.i./ ha along with one hand weeding.  So it can be revealed that application of quizalofop ethyl at 50 g a.i. / ha can be more effective than imazethapyr at 100 g a.i. / ha in groundnut as post emergence herbicide to control different narrow leaved and broad leaved weeds.

The author(s) have not declared any conflict of interest.