Manjitinder Singh Deol*, A.S. Chandel and K.K. Deol Evaluation of different herbicides on weed control in soybean [Glycine max (L) Merrill]   Manjitinder Singh Deol*, A.S. Chandel and K.K. Deol *(manjitinderdeol@gmail.com) G.B. Pant University of Agriculture and Technology, Pantnagar, Uttaranchal 263145, India

INTRODUCTION In India, soybean is mainly grown in the rainy season when occurrence of weeds is high. Chandel (1989) reported that weed infestation in soybean resulted in 54-65 per cent reduction in seed yield. Mechanical weed control can be done only when weeds attain sufficient vegetative growth. Mechanical weeding becomes difficult in rainy season due to uncertain monsoon rainfall. In view of above facts, there is an immense need of chemical weed control in soybean. Hence, the present investigation was carried out to study the comparative effect of some new pre-emergence as well as post-emergence herbicides on weeds and yield of soybean.

MATERIALS AND METHODS Experiment was conducted at G.B. Pant University of Agriculture & Technology, Pantnagar, India, on clay loam soil with pH 7.1, organic carbon 0.9 per cent, high in available phosphorus (27.16 kg/ha) and medium in available potassium (183.96 kg/ha). Field was under soybean-wheat rotation for the last several years. Ten treatments Alachlor, Clomazone, Pendimethalin and Clomazone + Pendimethalin, all applied as pre-emergence, Quazilofop-ethyl, Chlorimuron ethyl and Imazethaphz + Imazamox, all applied as post-emergence. Clomazone+ hand weeding at 30 days and two hand weeding at 30 and 45 days were tested in Randomized Block Design with three replications. Narrow leaved, of determinate growth Soybean variety PK-1024 was grown using 100 kg di-ammonium phosphate/ha was applied as basal. Plant protection measures were applied by spraying two times the mixture of Endosulfan 35 EC (0.1%) + Methyl-O-demanton (0.1%) solution in ratio of 1:1 at 60 and 75 days after planting.

RESULTS AND DISCUSSION Weed parameters The major weed species at 45 days in weedy check plot were Celosia argentea (24.4%), Cyperus rotundus (18.3%), Oldenlandia diffusa (12%) and Echinochloa colona (10.1%). At 60 days dominant weed species were Celosia argentea (32.9%), Oldenladia diffusa (24.9%) and Echinochloa colona (13.8%). Highest density of Celosia argentea was recorded at all stages due to emergence of its several flushes and fast growth as compared to other weeds. Similar results were reported by Akanksha (2004). Density of Oldenlandia diffusa had increased from 12% at 45 days to 24.9% at 60 days because this weed had emerged about a month late after sowing in the field. At 45 days (Table-1), maximum reduction (75.9%) in weed dry matter was observed due to two hand weeding. Under Pantnagar conditions beneficial effects of two hand weedings were also reported by Singh et al. (1990). Among herbicides at 45 days, highest weed dry matter reduction (48.6%), was observed with Pendimethalin + Clomazone @ 0.750 + 0.375 kg ai/ha. Mixture of two herbicides was more effective possibly due to broad spectrum of mixture for weed control. Pendimethalin cause phytotoxicity by the unchanged herbicide, binding to tubulin protein that polymerizes to form microtubules. Clomazone reduces or stops the accumulation of plastid pigment in susceptible species inhibiting an enzyme of terpenoid pathway resulting in white yellow or plate green plants (Dube and Paul, 1986). But at 60 days (Table-1), among herbicides Imazamox + Imazethapyr @ 100.0 g ai/ha was most effective in reducing (69.7%) weed dry matter as compared to weedy check because it killed all types of weeds and thereafter weeds did not reemerged. Similar results were also reported by Vyas (2000) at Sehore. This herbicide was effective many days after application because these compounds i.e. Imazethapyr and Imazamox act by killing plant very slowely by inhibiting acetohydroxyacid synthase in plant meristematic tissues after absorption through roots and foliage, but injury symptoms did not appear for 1-2 weeks or longer, Meristematic regions slowly become chloratic, followed by slow foliar chlorosis, then necrosis and finally death of weeds.

Weed control efficiency (%) Table 1 : Effect of different herbicides on weed dry weight (g/m2) and weed control efficiency Treatment Weed dry weight (g/m2) Weed control efficiency (%) 45 DAS 60 DAS Alachlor 2.0 kg ai/ha 244.3 245.3 22.0 63.7 Two hand weeding at 30 & 45 DAS 75.2 101.3 75.9 85.0 Quizalofop ethyl @ 50.0 g ai/ha 249.6 357.9 20.3 47.1 Chlorimuron ethyl @ 9.0 g ai/ha 288.0 436.8 8.10 35.4 Clomazone + Pendimethalin @ 0.375 g ai/ha + 0.750 g ai/ha 160.8 283.1 48.7 58.2 Clomazone @ 1.0 g ai/ha 282.5 582.5 9.8 13.9 Pendimethalin @ 1.0 kg ai/ha 250.2 402.9 20.1 40.4 Imazamox + Imazethapyr @ 100.0 g ai/ha 258.4 205.1 17.5 69.7 Clomazone 1.0 kg ai/ha + hand weeding at 30 DAS 130.1 87.6 58.0 87.1 Weedy check 313.3 676.4 0.00 CD (P = 0.05) 70.3 149.4 – DAS – Days after Sowing

Effect on soybean All the treatments gave grain yield significantly higher than weedy-cheek. Two hand weeding at 30 and 45 days after sowing yielded 192.5% higher grain than weedy check, which was significantly higher than all other treatments. It was because of higher number (88.9) of pods/plant associated with maximum 000’ grain weight (Table-2). Similar were reported by Akanksha (2004) at Pantnagar. Alachlor@ 2.0 kg ai/ha resulted in 113.7% higher grain yield than weedy check, which was due to higher plant population associated with higher number (71.7) of pods/plant. Pendimethalin + Clomazone @ 0.750 + 0.375 kg ai/ha resulted in 100.5% higher grain yield over weedy check and was on par with Alachlor @ 2.0 kg ai/ha. Imazamox + Imazetapyr @ 100.0 g ai/ha resulted 88.7% higher grain yield than weedy-check and was on par with Alachlor @ 2.0 kg ai/ha, resulted lowest (95.3 g) thousand grain weight. Seed/pod and branches/plant did not differ significantly (Table-2).

Yield increase over weedy check (%) Table 2 : Effect of different herbicides on yield attributes and grain yield of soybean cv. PK 1024 Treatment Yield attributes Grain yield (q/ha) Yield increase over weedy check (%) Branches/ plant Pods/ plant Seeds/ pod 000’ grain weight (g) Alachlor 2.0 kg ai/ha 4.4 71.1 2.53 98.1 22.01 113.7 Hand weeding at 30 & 45 DAS 5.9 88.9 2.47 103.9 30.13 192.5 Quizalofop ethyl @ 5.0 g ai/ha 5.1 56.5 99.4 18.19 76.6 Chlorimuron ethyl @ 9.0 g ai/ha 4.9 56.6 98.9 15.83 53.7 Clomazone + Pendimethalin @ 0.375 g ai/ha + 0.750 g ai/ha 3.2 102.1 20.65 100.5 Clomazone @ 1.0 g ai/ha 52.9 2.20 103.2 18.07 75.4 Pendimethalin @ 1.0 kg ai/ha 4.7 59.7 99.9 17.19 65.7 Imazamox + Imazethapyr @ 100.0 g ai/ha 4.8 71.6 95.3 19.44 88.7 Clomazone 1.0 kg ai/ha + hand weeding at 30 DAS 5.2 55.2 101.1 18.44 79.0 Weedy check 4.2 51.9 2.40 10.30 – CD (P = 0.05) NS 21.5 6.84 4.15 DAS – Days after sowing

Conclusions Thus, it is concluded that two hand weddings were found to be best to reduce weed infestation and increase grain yield. Among pre-emergence herbicides combination of Pendimethalin @ 0.0750 kg ai/ ha + Clomazone @ 0.375 kg ai/ ha and among post-emergence Imazamox + Imazetapyr @ 100.0 g ai/ ha are some of the potential herbicides for weed control and increase in the grain yield in Trai region. References Chandel, A.S. 1989. Soybean productivity constraints in north Indian plain. An agronomist view. In: fourth world soybean research conference held at Buenos Aires, Argentina, March 5-9, 1989, vol I, pp. 672-676. Dube S. and Paul R N. 1986. Effects of diamethazone on chloroplast development. I. Ultrastructural effects in cowpea primary leaves. Pestic. Biochem. Physiol., 25 : 1-10. Gupta A. 2004. Integrated weed management in soybean. M.Sc. Agriculture Thesis. Submitted to G. B. P. U. A. & T. Pantnagar, Uttaranchal, India. Singh D, Sharma, K C and Singh D. 1990. Effect of variety, row spacing and weed control treatments on yield and quality of soybean seed. Annals of Agricultural Research 1(2) : 211-214. Vyas M D, Singh S and Singh PP. 2000. Weed management in soybean. Annals of Plant Protection Sciences 8(1) : 76-78.