Weed Science

Inventions are the agents of change and have been the driving force behind the paradigm shifts that occurred throughout human history. There have been several paradigm shifts in the field of weed science too. The first one was the birth of modern weed science seven decades ago in 1944 when 2,4-D became commercially available. Since then, hundreds of newer organic herbicides have been developed and these became the mainstay of weed management in cropping and non-cropping systems around the world. The second paradigm shift was the evolution of herbicide resistance in 1968 when Senicio vulgaris was found resistant to 2,4-D. This was followed with hundreds of reports till today.  The  third paradigm shift in weed science occurred in 1994 when transgenic herbicide resistance crops, beginning with the approval of bromoxynil-resistant BXN cotton developed by Calgene and Rhône-Poulenc and glyphosate resistant soyabean developed by Monsanto, both in USA. These paradigm shifts has led challenges to India and Indian weed scientists too. This paper presents the various research challenges  required to be worked, both directly and indirectly by the Indian scientists.

Field experiments were carried out in wetland farm at Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu during 2012-13 to study the weed density, weed seed bank, yield and economics of rice under rice based conservation agriculture system. The main plot consisted six treatments with two crop establishment methods and three tillage practices over the seasons. Sub-plot treatments were having three weed management practices. Significantly minimum total weed density, weed seed count and higher grain yield, net returns were recorded in transplanted rice with conventional tillage in CT-CT-ZT system with pre-emergence treatment (PE) of butachlor 1.0 kg/ha for Kharif, pretilachlor 1.0 kg/ha PE for Rabi + inter crop with daincha (Sesbania) incorporation and mechanical weeding on 35 DAT during Kharif 2012, Rabi 2012-13 and Kharif 2013.

A field experiment was conducted at Zonal Agricultural Research Station, Mandya, Karnataka to study the shift in weed flora of different weed species due to application of pre-sowing, pre-emergence and post-emergence application of herbicides in comparisons with hand weeding and mechanical weeding. The effect of combination of herbicide bensulfuron-methyl + pretilachlor as well as mono-herbicide butachlor  and their post-planting application were evaluated for their bio-efficacy either alone or combination with pre-planting application of non-selective glyphosate application. The treatment comprised of eight different weed management practices were laid out in randomised complete block design with three replications. The results revealed that application of glyphosate (15 days before transplanting of rice 0.75 kg/ha) in combination with bensulfuron methyl + pretilachlor  applied at 5 DAT recorded higher grain yield of 7.02 t/ha and found significantly superior over other treatments due to reduced weed population and biomass of weeds (10.30 g/m2) and higher weed control efficiency (64.97%) when compared with weedy check. There was more than 36% reduction in the grain yield of rice due to competition with weeds in weedy plots. The rice yield and weed control efficiency of herbicide combination was at par with recommended practice of hand weeding twice at 20 and 40 DAT. Sequential herbicide application is promising and effective in control of weeds as compared to single herbicide application in rice-based cropping system

A field experiment was conducted during the Kharif season of 2011 and 2012 at G.B.Pant University of Agricultureand Technology, Pantnagar to find out the efficacy of bispyribac-sodium in managing weeds in direct-seeded rice. Among the treatments, bispyribac-sodium 20 and 25 g/ha applied at 1-3 leaf stage or at 4-6 leaf stage of the weeds was found the most efficient having lowest weed density and biomass during both the years. Rice grain yield and yield attributing characters (tillers/m2 and grains/panicle) were influenced by the effectiveness of the treatments. The highest grain yield of rice was recorded with weed free (4.03 t/ha) which was at par with bispyribac-sodium 20 and 25 g/ha.

The field experiment was conducted to assess the residual effects of sulfosulfuron (25, 37.5 and 50 g/ha) and mesosulfuron + iodosulfuron (12, 18 and 24 g/ha) herbicides applied to wheat on maize (Zea mays L.) grown in sequence at Ludhiana, Punjab (India). None of the sulfonylurea herbicides (sulfosulfuron and mesosulfuron + iodosulfuron) applied to wheat at different doses affected the emergence of maize crop during both the years. But the effect was evident on growth characters and yield during 2005 whereas in 2004, plant height and dry matter at all stages of maize was not affected significantly. This might be due to difference in rainfall received at different stages of the crop growth in both the years. The rainfall received from April to June (optimum sowing time) was 137 mm and 54.2 mm in 2004 and 2005, respectively, however, in July rainfall was more in 2005 but the earlier status of rainfall was more responsible for the residual effect in 2005 as the reduced rainfall presumably left the soil dry for long time and might have resulted in slow dissipation rate of the herbicides. Again in August, rainfall was more in 2004 (+45.7 mm departure from normal rainfall in 2004) than 2005 so this might have enhanced the movement of the herbicide to lower surface  and thus no residual effect was observed on the crop. Hence, it is not safe to grow maize in rotation after application of these sulfonylurea herbicides on wheat, as significant effect on the growth and yield of maize was recorded during the years of less rainfall.

Field studies were conducted at Research Farm of CCS Haryana Agricultural University, Hisar, during Kharif 2006 and 2007 to find out the effect of sowing time (10th May, 25th May, 10th June and 25th June) and weed control measures consisted weedy, weed free, pendimethalin 1.0 kg/ha as pre-emergence (PE) fb  HW at 60 DAS, trifluralin 1.0 kg/ha as pre-plant incorporation (PPI)  fb  HW at 60 DAS and  HW at 30 and 60 DAS), in pigeonpea (Cajanus cajan L.). Results revealed that density and biomass of weeds increased with the corresponding advancement in crop growth and delay in sowing time from 10th May to 25th June. Pendimethalin 1.0 kg/ha as PE and trifluralin 1.0 kg/ha as PPI each followed by (fb) one hand weeding (HW) at 60 days after sowing (DAS) provided better weed control than  HW up to 60 DAS but at 90 DAS, these three treatments were statistically at par. Trifluralin fb HW had an edge over pendimethalin fb HW up to 60 DAS. In general, yield and yield parameters of pigeonpea were superior when crop was sown on 10th and 25th May compared to delay in sowing (10th and 25th June) during both the years. Performance of crop was similar when sown on 10th and 25th May. Among weed control treatments, trifluralin 1.0 kg/ha (PPI) fb 1 HW at 60 DAS, being at par with 2 HW, had an edge over pendimethalin 1.0 kg/ha (PE) fb 1 HW at 60 DAS in respect of yield attributes and ultimately yield of pigeonpea.

A field experiment was conducted during Kharif season of years 2011 and 2012 at Norman E. Borlaug crop research centre of Govind Ballabh Pant University of Agriculture & Technology, Pantnagar (U.S. Nagar), Uttarakhand. Fluazifop-p-butyl + fomesafen controlled grasses and non-grassy weeds effectively and recorded 29.3 weeds/m2  in 500 g/ha against (171.17/m2) in untreated check. However, the grain yield was highest (2.21 t/ha) in the treatment of weed free followed by fluazifop-p-butyl + fomesafen applied 313 g/ha as post-emergence (2-5 leaf stage of weeds). Biomass of weeds was also lowest in fluazifop-p-butyl + fomesafen  313 g/ha treated plots. However, total weed density was lowest in fluazifop-p-butyl + fomesafen 500 g/ha treated plot but this dose showed toxic effects on crop. Weed index was lowest (7.8%) in the treatment of fluazifop-p-butyl + fomesafen 313 g/ha and highest in untreated (63.5%).

Field experiments were conducted during Rabi and Kharif season of 2012 and 2013 at northern block of Cotton Research Station, Veppantattai, Tamilnadu, to study the effect of tillage and weed management methods on weeds dynamics and yield of sunflower under irrigated conditions. The experiments were laid out in strip plot design with three replications. Main plot treatment consisted of three tillage methods, viz. conventional tillage, minimum tillage and zero tillage. Five weed management methods, viz. pre-emergence application of pendimenthalin 1.0 kg/ha followed by hand weeding on 40 DAS, pre-emergence application of pendimethalin 1.0 kg/ha followed by power weeding on 40 DAS, hand weeding twice on 20 and 40 DAS, power weeding on 20 and 40 DAS along with an unweeded check for both the crops were included in the sub-plot treatments. The sunflower hybrid seed ‘Sunbred’ were sown on 60 x 30 cm spacing. The results revealed that conventional tillage combined with pre-emergence herbicide application of pendimethalin 1.0 kg/ha followed by hand weeding on 40 DAS recorded lower weed density, weed biomass and higher yield attributes and yield.

A field experiment was conducted at Mahatma Phule Krishi Vidyapeeth, Rahuri, Maharashtra, India  for two consecutive Rabi seasons 2011 and 2012 to find out most suitable and efficient combination of different pre-plant and post-emergence herbicides to control weeds in onion seed production crop. Experiment was conducted in randomized block design with 9 treatments and three replications consisting of pre-plant application of pendimethalin, post-emergence application of oxyfluorfen and quizalofop-ethyl and their different combinations. The pre-plant application of pendimethalin 0.750 kg/ha followed by post-emergence application of oxyfluorfen 0.250 kg/ha mixed with quizalofop-ethyl 0.050 kg/ha resulted in effective control of various broad-leaf and grassy-weeds and recorded lower weed density, weed biomass, weed index and higher weed control efficiency. This treatment also produced higher number of umbels per plant, plant dry matter, number of seeds per umbel, seed weight per umbel, 1000 seed weight and longer flowering stalk, and diameter of umbel. It also produced higher seed yield (439.30 kg/ha), gross return (` 329,475/ha), net return (` 192,450/ha) and B:C ratio (2.40) over all the other chemical weed control treatments. 

A field experiment was conducted to study the influence of various herbicidal treatments on the growth and productivity of garlic (Allium sativum L.) during 2012-13 and 2013-14 on sandy loam soils of SKUAST, Chatha. The experiment involved two genotypes of garlic replicated thrice in factorial randomized block design. The weed density, weed dry matter accumulation and weed control efficiency varied significantly with the stage of the crop showing a declining trend,  being  highest at 60 days after sowing and lowest at the time of harvesting.  Significantly lower weed density, weed dry matter accumulation, weed index and relatively higher weed control efficiency were recorded in large segmented cultivar (SJKG-01) with weed free plots followed by treatment with pre-emergence application of oxadiargyl 90 g/ha fb post-emergence application of quizalofop-ethyl 50 g/ha, at 2-3 leaf stage of weeds.  The average bulb weight (26.73 g), bulb diameter (3.96 cm.) and bulb yield (4.83 t/ha) were also more in large segemented than the smaller one (SJKG-02).  Among herbicidal treatments, the weed free plots in both the cultivars produced plants with more average bulb weight, bulb diameter and bulb yield followed by the plots with pre-emergence application of oxadiargyl fb post-emergence application of quizalofop-ethyl, applied at 2-3 leaf stage of the weeds.  From  economics point of view, the weed free plots resulted in higher cost of cultivation and net returns followed by the treatment combination of oxadiargyl  90 g/ha pre-emergence  fb quizalofop-ethyl as post-emergence 50 g/ha applied at 2-3 leaf stage of weeds yielding a B: C ratio of 5.70 in small segmented and 6.73 in large segmented garlic respectively.

A simple technique to germinate Orobanche in the presence of live host seedlings under controlled conditions was developed. Surface sterilized seeds were preconditioned separately in Petriplates and were transferred on a bed made of sterilized sand, cotton and filter paper kept on a 1000 ml beaker. Host plant (mustard and tomato) seeds were germinated in Petriplates and transferred to the beaker containing the preconditioned Orobanche seeds. The beakers were then incubated at room temperature for 10 days and observed under stereo binocular microscope. This technique may be useful in many ways including quantification of the weed seed bank in the infested fields, screening of contaminated seed lots from infested areas for the purpose of quarantine and seed certification. Use of live host seedlings instead of synthetic stimulants, both reduced the cost and made it possible to use this technique. 

Parthenium hysterophorus, one of the “worst weeds”, is an erect and much branched annual or ephermeral herb causing colossal loss in terms of economic, environmental, animal and human health hazards. A survey on occurrence of the natural enemies of P. hysterophorus L. was conducted in Kurukshetra and its adjoining areas, Haryana, India. The Parthenium population at different places during different seasons were found to have various diseases. The native pathogens of Parthenium hysterophorus were studied and compared on the basis of pathogenicity by Koch’s postulates. A total of twenty six pathogenic fungi, P1-P26 were isolated from different diseased Parthenium plants. All the isolates were preliminarily identified on the basis of cultural and morphological characteristics and it was observed that all of them belongs to the fungi imperfecti except isolates P19, P20 which belongs to Ascomycota. On the basis of pathogenicity, the isolates P2, P5, P7, P9, P12, P17 and P23 were selected and the effect of different media on the growth and sporulation of selected pathogens was tested. This study will help to develop mycoherbicides by using these fungal pathogens in combination or single.

Study was done on impact of invasive alien weeds Chromolaena odorata and Parthenium hysterophorus on native naturalized flora of few selected sites in Mysore, Karnataka. Total six sites were selected for the study. Of which, at 3 sites C. odorata and P. hysterophorus were present (sites 1, 2 and 3) while at other 3 sites C. odorata and P. hysterophorus were absent (sites 4, 5 and 6). At sites 1, 2 and 3, frequency, density and abundance of the native flora were low than the sites 4, 5 and 6. There was 30, 24 and 12% reduction of native flora at sites 1, 2, and 3, respectively. There was a constant fear of losing many medicinally and economically important plants due to invasion of these weeds.

A field trial was conducted during Kharif 2012 at Agricultural Research Farm, Institute of Agricultural sciences, Banaras Hindu University, Varanasi, Uttar Pradesh (India) to study effect of rice establishment and integrated weed management practices on weed growth and grain yield. Pendimethalin 1.0 kg/ha fb azimsulfuron 17.5 g/ha + bispyribac 25 g/ha 15 DAS fb 1 HW significantly reduced weed density and weed biomass in comparison to oxadiagryl 50 g/ha fb metsulfuron-methyl 2 g/ha + chlorimuron-ethyl 2 g/ha 20 DAS fb 1 HW. Rice grain yield in CT paired row was statistically at par with CT normal spacing, CT square planting and RT paired row. It was significantly higher as compared to RT square planting. Amongst weed management practices, pendimethalin 1 kg/ha fb azimsulfuron 17.5 g/ha + bispyribac 25g/ha fb 1HW recorded higher rice grain yield attributing characters viz. number of panicles/m2, number of grains/panicle, test weight and grain yield and it was found significantly better than oxadiagryl 50 g/ha fb metsulfuron methyl 2g/ha+ chlorimuron-ethyl 2g/ha fb 1 HW.

An experiment was conducted at Kole lands in Thrissur district, Kerala to study the efficacy of various post-emergence herbicides in wet-seeded rice. The results showed that cyhalofop-butyl + chlorimuron-ethyl+ metsulfuron-methyl, fenoxaprop-p-ethyl + chlorimuron-ethyl+ metsulfuron-methyl and bispyribac-sodium were best treatments with a lower weed biomass as well as high grain yield and B:C ratio. Maximum weed control efficiency of 97.1% was obtained in hand weeded plots followed by bispyribac-sodium (93.6%). The highest grain yield of 6.13 t/ha was recorded in hand weeded plot which was at par with cyhalofop-butyl + chlorimuron-ethyl + metsulfuron-methyl and fenoxaprop + chlorimuron ethyl+ metsulfuron-methyl (5.8 t/ha). From this study it can be concluded that, cyhalofop-butyl with a follow up spray of chlorimuron-ethyl + metsulfuron-methyl or fenoxaprop-p-ethyl with a follow up spray of chlorimuron-ethyl + metsulfuron methyl or bispyribac sodium alone can be recommended for effective post emergence weed control and higher yield in wet seeded rice. If grasses are the predominant weeds, cyhalofop-butyl or fenoxaprop-p-ethyl alone without follow up spray of chlorimuron-ethyl + metsulfuron-methyl can also be recommended.

The present study revealed that weeds cause a rice yield loss of about 90% in dry-seeded rice and the integrated approach to control weeds based on PE application of pendimethalin 1.0 kg/ha  fb  POE bispyribac-sodium 25 g/ha + ready-mix chlorimuron + metsulfuron 4 g/ha 30 DAS fb one HW 60 DAS was found to be best with WCE of 82%. Increase in rice seed rate from 10 to 32.5 kg/ha resulted in decrease in weed density and weed biomass but the rice yield increase beyond 17.5 kg/ha seed rate was non-significant. Therefore, rice seed rate of 17.5 kg/ha was found optimum for DSR, however it needs further investigation and confirmation. 

Ten on-farm trials (OFTs) were carried out at farmers’ fields in participatory mode during the Rabi season of 2007-08 to 2008-09 in selected adjoining villages to the Krishi Vigyan Kendra, Azamgarh of eastern Uttar Pradesh. The main objectives of activities were to evaluate the performance and profitability of zero tillage and herbicides on weed control and productivity of wheat crop under rice-wheat cropping system. Zero till sown wheat was found much effective in suppression of weed density and population of Phalaris minor in comparison to conventional tillage. A drastic reduction in weed density was obtained with the application of sulfosulfuron + metsulfuron methyl 75 WG at 40 g/ha ready-mix under both method of wheat sowing. The higher average grain yield and monitory returns were also achieved under zero tillage sown wheat combined with sulfosulfuron + metsulfuron methyl as post emergence. However, grain yield obtained under zero tillage was almost comparable to conventional tillage with fenoxaprop-p-ethyl 10 EC at 1000 ml/ha.

The present study was conducted to quantify the effect of different weed control treatments alone or in combination with each other on weed growth and grain yield of transplanted rice during Kharif season of 2012 at G.B. Pant university of Agriculture and technology, Pantnagar, Uttarakhand. Different weed species responded variably to tested weed control treatments. The dominant weeds in experimental plots were Echinochloa colona, E. crusgalli, Leptochloa chinensis, Ischeamum rugosum among grasses and Ammania baccifera, Alternanthra sessilis and Ceasulia axillaris among broad-leaf weeds and Cyperus difformis was the only sedge. Pre-emergence application of pretilachlor 750 g/ha without water stagnation in the field up to one week fb post-emergence application of bispyribac-Na 20 g/ha was found superior to rest of the treatments.

The bio-efficacy of clodinafop-p-propargyl 60 g/ha was better against Avena ludoviciana Dur. and Pharalis minor Retz. to that of sulfosulfuron 25 g/ha, penoxsulam + cyhalofop 105 g/ha, penoxsulam + cyhalofop 150 g/ha and carfentrazone 25 g/ha but it was poor against broad leaved weeds. However, the mesosulfuron-methyl + iodosulfuron-methyl sodium 12 g/ha, sulfosulfuron + metsulfuron-methyl 40 g/ha and combined application of clodinafop-p-propargyl + 2,4-D (60+500) g/ha gave effective control of grassy and broad leaved weeds. Use of pinoxaden 60 g/ha or clodinafop 60 g/ha a brought about a reduction in infestation   of grassy weeds. Presently, some new herbicide ready mix combination of mesosulfuron-methyl + iodosulfuron-methyl sodium 12 g/ha, sulfosulfuron + metsulfuron-methyl 40 g/ha and tank mixture herbicides clodinafop + 2,4-D (60+500) g/ha appeared to be more profitable and efficient over other treatments.

In this study the population and dry matter of weeds was significantly more under under ZT than CT. Seed yield of soybean was the highest under CT–raised-bed, followed by ZT-raised-bed, CT–flat-bed and ZT-flat-bed. Application of pendimethalin + HW and pendimethalin + chlorimuron-ethyl resulted in almost similar weed control efficiency and gave equal seed yield. Uptake of N, P and K by grain was maximum under pendimethalin + HW, which was significantly more than rest of treatments. It was concluded that soybean can be grown under permanent raised-bed with pre- and post-emergence herbicides for realizing higher productivity.

A field experiment was conducted at the Punjab Agricultural University, Ludhiana to study the effect of post-emergence herbicides imazethapyr at 25, 40 and 55 g/ha 25 or 35 DAS and quizalofop-ethyl at 30 and 50 g/ha 25 or 35 DAS along with unweeded check and two hand weedings at 30 and 60 DAS on weeds, growth and yield of lentil (Lens culinaris Medikus). Imazethapyr caused phytotoxicity to lentil but with time the crop recovered. Imazethapyr at 25 as well as 40 g/ha and quizalofop-ethyl at 30 g/ha, both at 25 and 35 DAS, did not adversely affect nodulation. Imazethapyr at 25 as well as 40 g/ha at either 25 or 35 DAS showed promise in improving the grain yield of lentil.

The benefits of tillage are multifaceted as it loosens soil, enhance release of nutrients from soil for plant growth, kill weeds and regulates the circulation of water and air through soil which lead to an enhanced nutrient uptake and better yield of crops. Weeds creating competition for nutrients, space, water etc. reduce the crop yield and deteriorate the quality of produce hence, reduce the market value of the turnout (Arif et al. 2006). The response of weed flora to different weed control methods also vary depending upon field situation. Tillage affects the weeds by uprooting, dismembering and burying them deep enough to prevent emergence by changing soil environment and so inhibiting weeds germination and establishment, thereby creating favorable soil environment for plant growth (Sawanton et al. 2000). Soybean is a miracle crop which is mainly grown for oil and is a good source of protein, used in cattle feeds. Weed infestation in soybean results in a loss of yields to the extent of 30-80 per cent (Yaduraju et al. 2002). Hence, an experiment was conducted to identify ideal method of weed management in soybean-wheat cropping system.

A field experiment was conducted at PGI farm, M.P.K.V., Rahuri during Kharif, 2012. The experiment was laid out in randomized block design with three replications and nine treatments consisted of different weed control treatments, viz. weed free, weedy check (control), pendimethalin 1.0 kg/ha (PE) fb 1 HW at 45 DAT, oxyfluorfen 0.150 kg/ha (PE) fb 1 HW at 45 DAT, quizalofop-ethyl 0.05 kg/ha at 21 DAT (POE) fb 1 HW at 45 DAT, pendimethalin 1.0 kg/ha(PE) fb oxyfluorfen 0.25 kg/ha at 45 DAT (POE), pendimethalin 1.0 kg/ha(PE) fb quizalofop-ethyl 0.05 kg/haat 45 DAT  (POE), pendimethalin 1.0 kg/ha(PE) fb quizalofop-ethyl 0.037 kg/ha+ oxyfluorfen 0.18 kg/haat 45 DAT (POE), quizalofop-ethyl 0.037 kg/ha+ oxyfluorfen 0.18 kg/haat 21 DAT (POE) fb 1 HW at 45 DAT. The onion, cv. ‘Baswant-780’, was transplanted on ridges and furrow. The lowest weed population, weed biomass, weed index and higher weed control efficiency were recorded in weed free check and were at par with application of quizalofop-ethyl 0.037 kg/ha+ oxyfluorfen 0.18 kg/ha at 21 DAT (POE) fb 1 HW at 45 DAT which was followed by spraying of pendimethalin1.0 kg/ha (PE)  fb quizalofop-ethyl  0.037 kg/ha + oxyfluorfen 0.18 kg/ha at 45 DAT. Pendimethalin1.0  kg/ha (PE) fb quizalofop-ethyl 0.037 kg/ha + oxyfluorfen 0.18 kg/ha at 45 DAT proved to be the most remunerative weed control treatment, which recorded the highest benefit: cost ratio (3.48). However, the highest net monetary returns (` 1,67,839/ha) was recorded quizalofop-ethyl 0.037 kg/ha + oxyfluorfen 0.18 kg/ha at 21 DAT (POE) fb1 HW 45 DAT with benefit:cost ratio of 3.39.

Sweet corn (Zea mays L. var. Saccharata Sturt), is a variety of maize with a high sugar content. It is  also called Indian corn, sugar corn and pole corn. Nature of weed problem in Rabi maize is quite different from that of the rainy season maize. In the rainy season, emergence of maize and weed start simultaneously in which first 20-30 days are most critical looking to crop-weed competition while in winter maize, weeds emerge most often after the first irrigation. However, wider row spacing and liberal use of irrigation and fertilizers lead to more growth of weeds (Porwal  2000). Therefore, the study was carried out to find economically effective method of weed control for realizing higher productivity and profitability of sweet corn.

Fenugreek is one of the most important condiment crops of country in general and Rajasthan in particular. The state contributes the major share of India’s production, accounting for almost 80%. The state accounts for 82.35 thousand ha area with production of 87.38 thousand tones and the productivity of 1.06 t/ha (National Horticultural Board 2011-12). It is a winter season crop having multiple uses and its every part is consumed in one or the other form. The crop is used as a spice, as a vegetable for human consumption, as forage for cattle and to some extent for medicinal purposes.Weeds have been identified as a serious drawback in achieving its potential yield. Weeds reduce grain yield of this crop upto an extent of 86% (Tripathi and Singh 2008). Scarcity of labour and their increasing wages compel the farmers to opt the alternative of manual weeding. Therefore, the present investigation was under taken to find out the most effective weed management practice in fenugreek.

The present study was undertaken to determine the persistence and residue of oxyfluorfen in tea and sandy clay loam acid soil with a pH of 4.3 and organic carbon content of 4.1%. Results showed that, the application of oxyfluorfen at 200 g /ha persisted in soil up to 10 days while up to 25 days at 400 g/ha and 50 per cent degraded from the soil before 30 days. Within 3 hrs of application, 6.9 to 35.8% of the oxyfluorfen dissipated from the soil. More than 80% of the applied oxyfluorfen degraded from soil before 10 days of its application under 200 g/ha, while it took 25 days at 400 g/ha. Oxyfluorfen residue was not detected in tea leaves upto 50 days. It is concluded that the waiting period of 75 days should be implemented for plucking the tea leaves after the application of oxyfluorfen or else there will be a chances for the herbicide to enter the food chain due to bioma-gnification.

Lack of glyphosate translocation to the site of action (growing apex) is the limitation for effective control of purple nutsedge (Cyperus rotundus L). Glyphosate is used for weed control in wasteland, zero tillage, directed spray in plantation crops and on quarantine weeds. Senescence of leaf is programmed cell death involving degradation of macromolecules viz. proteins, nucleic acids and lipids and during later stage of this process, essential nutrients are remobilizes to the growing apex. Pre-treatment with ethephon (5000 ppm) induced the leaf senescence and reduced callose accumulation in phloem which enhanced 2,4-D and glyphosate translocation and thus their efficacies (Devendra et al. 1996). Senescence period of 48 h, induced by glyphosate (1.3 kg/ha) enhanced the efficacy more than 24 or 72 h senescence period (Dhanraj et al. 2012). Senescence was found to increase the activity of low affinity (Pht 2,1) phosphate transporter (Daram et al. 1999) and high affinity (PhPT1) phosphate transporter (Chapin and Jones 2009). Glyphosate being phosphate having molecule, compete with phosphate with transporter which led to enhanced phloem mobility.