Herbicides have contributed to substantial increase in crop yields over the past seven decades. Over reliance on herbicides for weed control has led to rapid evolution of herbicide-resistant (HR) weeds. Increased awareness of herbicide resistance and adoption of diversified weed control tactics by farmers is critical to manage HR weeds. HR weed management must include both chemical and non-chemical methods as well as the best management practices to prevent evolution and spread of HR weeds. The severity of the HR weed problem has also renewed efforts to discover new technologies. One technology will be a new generation of crops with resistance to glyphosate, glufosinate and other existing herbicides (e.g. ALS inhibitors, 2,4-D, dicamba, HPPD inhibitors, and ACCase inhibitors). These stacked-trait crops will provide new options with existing herbicides, but will not be the total weed management solution because several weeds have already evolved resistance to these herbicides. Another technology in the early stages of development that has potential to combat HR weeds is the use of RNA interference (RNAi) technology. The use of RNAi involves the topical application of double-stranded RNA (dsRNA) to interfere with the expression of herbicide resistance genes in weeds to reverse the resistance. RNAi is a revolutionary technology for resistant weed management, but is still years away from commercialization. While no new herbicides are on the horizon, in the near future, the HR management strategies must utilize an array of tools to disrupt HR weeds from evolving and spreading, with the ultimate goal of not allowing any weeds to survive and set seed.

The US Great Plains comprise the major cereal producing states in the country. In the US, wheat (winter and spring wheat) was grown in 45 million acres in 2014, with a total production of 55 M metric tons. Wheat after chemical fallow (W-F) dominates > 90% of the dryland cropping systems of the Northern Great Plains of the US, where soil moisture (< 300 mm of average annual precipitation) is often the limiting factor for continuous cropping. In the Central Great Plains of the US, wheat–corn/grain sorghum–fallow (W-C/G-F) is a common dryland rotation. An over-reliance on herbicides for weed control in these no-till cropping systems has resulted in weed shifts and escalated cases of resistance evolution in weed populations to single or multiple site-of-action herbicides. Early detection, increased awareness of socio-economic implications of herbicide-resistant weeds, and adoption of diversified weed control tactics would mitigate the further evolution of multiple herbicide-resistant weed biotypes in cereal production systems.

Herbicide resistance in weeds is evolving rapidly worldwide complicating weed management and threating agricultural sustainability and food security. Resistance has been reported to all known herbicide modes of action and no new mode of action has been marketed in the past 25 years. Though most reported cases of resistance involve a single herbicide site of action, multiple-site resistance is increasing.  As an example of the progression from single to multiple site resistance, this paper reviews the evolution and implications of herbicide resistance in kochia [Kochia scoparia (L.) Schrad.), a common and economically important weed in the North American Great Plains.

Simulation models have been instrumental in understanding the evolutionary dynamics of herbicide resistance in weeds and making informed management decisions for preventing/delaying resistance. Continued improvements in model development and analysis will be critical to address the complex interactions involved in herbicide resistance evolution Here we review current knowledge on the development of herbicide resistance simulation models using published examples and also discuss future directions.

This paper presents a systematic diagnostic approach towards the characterization of herbicide resistance in a given weed population with regards to profile (single, multiple, cross resistance), magnitude (fold level), mechanism, and related bio-physiological aspects. Diagnosing herbicide-resistant weeds can be achieved by crafting robust procedures for seed sampling, survey protocol and seed collection, seed processing and storage, germination, emergence and growth (sufficient number of representative plants), treatment conditions (i.e., discriminating dose, adjuvants, spray volume and parameters, water quality, and nutrient status), experimental design, appropriate controls including wild type/susceptible accessions, and biological parameters being measured. Understanding the processes and means by which weeds withstand labeled herbicide treatments is an important step, as well, towards devising effective herbicide resistance management strategies. Several physiological, biochemical, and molecular approaches for studying resistance mechanisms are available to researchers. The various omics approaches including genomics (DNA), transcriptomics (RNA), proteomics (proteins), and metabolomics (metabolites) will revolutionize herbicide resistance research.

Palmer amaranth and kochia are major problem weeds in many cropping systems in the United States. Wide acceptance of glyphosate tolerant crop technology has resulted in extensive use of glyphosate, consequently, a number of weeds including Palmer amaranth and kochia evolved resistance to glyphosate throughout the US. Within a span of 5-7 years the glyphosate resistance in these weeds has spread extensively, devastating several major crops. Understanding the mechanisms of herbicide resistance is valuable to determine the level of resistance as well as how the resistance spreads in the populations. Glyphosate resistance mechanisms in Palmer amaranth and kochia have been investigated extensively. Although resistance to glyphosate has evolved as a result of amplification of 5-enolpyruvylshikimtate-3-phosphate synthase (EPSPS), the target site of glyphosate, but the distribution and configuration of amplified copies of EPSPS gene in the genomes of these two species is different. The EPSPS gene amplification may have possibly mediated by transposons in Palmer amaranth and whereas, likely to have resulted because of unequal recombination in kochia. These findings suggest that the EPSPS amplification can occur via different mechanisms in different weeds. Evolution of glyphosate resistance as a result of EPSPS gene amplification is a threat to long-term sustainability of glyphosate-resistant crop technology.

In recent times, biotechnology has been widely used for crop improvement. Today, about 2 billion hectares of global area is planted with genetically modified (GM) crops. In India, the first GM crop to be introduced was Bt cotton. The current acreage planted with Bt cotton is 93% of the total cotton acreage. However, the average yield is lower than that of other countries suggesting an opportunity to increase yield further. One of the major factors affecting yield is weed competition which reduces yield by 50 to 85%. Effective weed control is achieved by Integrated Weed Management (IWM) which includes adoption of transgenic herbicide tolerant crops (HTCs). The major transgenic HTCs grown in the world are soybean, cotton, corn and canola and the yield increase due to effective weed management is significant. In cotton, glyphosate and glufosinate tolerant systems have been used successfully across the globe and are being tested at the moment in India. Over reliance on single MOA (mode of action) rather than a diversified IWM system with multiple, complementary herbicide MOAs can lead to emergence of herbicide tolerant weeds. Therefore, there is a need to use diversified management practices for sustainable weed control in cotton.

Field experiments were conducted during the rainy seasons of 2011 and 2012 in Odisha, India to evaluate the efficiency of different tillage practices at beausaning on weed flora and yield of direct-seeded rice (Oryza sativa L.). Two passes of ploughing at 5 cm depth and 15 cm spacing with country plough at ‘beausaning’ showed the highest yield of grain (4.06 t/ha) and straw (4.66 t/ha), which was associated with higher weed control efficiency, effective tillers/hill, panicle length, number of filled grains/panicle, 1000-grain weight and with lower number of non-bearing tillers/hill and sterile spikelet/panicle. The lowest value of all parameters was found in 1  and 2 passes with tractor.  Two passes by power tiller was as good as 2 passes by country plough in controlling weeds and achieving higher yield. Though 1 and 2 passes with country plough and power-tiller showed statistically identical result, but the B:C ratio (2.25) was more in later treatment than the former (2.10).

Field experiment was conducted to evaluate the performance of weed management and biofertilizer on productivity of transplanted rice variety ‘MTU-7029 (Swarna)’. Experiment was laid out in factorial randomized block design with 24 treatments, comprising of twelve weed management practices and two nutrient management practices viz. No biofertilizer and biofertilizer (Azotobacter + PSB), replicated thrice. All the herbicidal treatment resulted in significant reduction in total weed dry weight and weed population than weedy check. The higher grain and straw yield was recorded in the plot where pendimethalin 0.75 kg/ha fb bispyribac-sodium 50 g/ha was applied. In case of grain yield, it was statistically at par with application of pendimethalin 0.75 kg/ha fb bispyribac-sodium 25 g/ha and weed free check during both the years. The highest net returns and benefit-cost ratio was realized under the application of pendimethalin 0.75 kg/ha fb bispyribac-sodium 25 g/ha and also in biofertilizer applied plot.

Field experiment was carried out to study the effect of integrated weed management in aerobic rice (Oryza sativa L.) for consecutive two Kharif seasons in 2011 and 2012 at Karaikal, Puducherry Union Territory with seven treatments in three replications. Grassy weeds dominated the weed flora, with Echinochloa colona as the major weed. Weed free condition maintained throughout the crop growth recorded significantly lower weed density, dry weight and higher weed control efficiency. Though the highest gross monetary returns ( 56,000/ha) and net returns ( 25,360/ha) was recorded in weed free condition, maximum B: C ratio (1.94) was recorded in pre-emergence application of pendimethalin 1.0 kg/ha along with a hand weeding at 30 days after sowing (DAS). Uncontrolled weeds accounted for 86.3% yield loss in aerobic rice under coastal ecosystem of Puducherry UT, India.

A field experiment was conducted to evaluate the bioefficacy of some potent low dose herbicides of sulfonylurea group in conjunction with other traditional recommended herbicides for control of broad spectrum of weeds in transplanted rice (Oryza sativa L) during the wet season of 2012 and 2013. Pretilachlor 750 g/ha as pre-emergence (PE) fb ethoxysulfuron 18.75 kg/ha as post-emergence  or pretilachlor 750 g/ha followed by metsulfuron-methyl + chlorimuron-ethyl 4 g/ha or pyrazosulfuron 20 g/ha (PE) followed by manual weeding were better options for efficient weed control, higher grain yield and B:C ratio in transplanted rice.

An experiment consisting of five establishment techniques in rice-wheat cropping sequence with different combinations of conventional tillage (CT), zero-tillage (ZT) and minimum tillage (MT) viz. CT-CT, ZT-CT, CT-ZT, ZT-ZT and MT-ZT) was conducted during 2003-2007 at the farm of a farmer in Haryana on a larger plot size of 0.4 ha under each treatment. During first year, grain yield of wheat did not differ significantly among different treatments but during 2004-05 to 2007-08, grain yield of wheat in ZT method of planting was either higher or at par with conventional ploughed method of planting but CT transplanting of rice was significantly more than ZT transplanted treatments except during first year when rains were very good at transplanting time. Weed dynamics after 4 years revealed that in rice crop, weed density of Echinochloa colona, E. crusgalli, Leptochloa chinensis,Cyperus spp. and broad-leaf weeds such as Ammania baccifera and Eclipta alba was more when rice was transplanted under ZT or MT conditions but in wheat, weed density of grassy weed Phalaris minor was less under ZT-ZT or MT-ZT treatments. After 4 years of continuous ZT in both rice and wheat crops, weed flora changed in favour of broad-leaf weeds. Bulk density of soil did not vary after 5 years of ZT-ZT conditions. Soil temperature of root zone in wheat crop planted under ZT conditions was more (0.7-1.7 OC) in first week of February and less (2.1-.3.8 OC) in first week of April as compared to conventional CT-CT practice of rice and wheat crops resulting in more grain yield of wheat due to temperature moderation and also due to a bit addition of organic matter in ZT conditions. Grain yield of rice planted under ZT or MT conditions was less mostly due to more weed infestation and it also consumed 4.8-184% more water as compared to CT method of puddle transplanted rice.

Field experiments were conducted in three successive seasons (Rabi 2010–11, 2011-12 and 2012–13) to evaluate the efficacy of clodinafop-propargyl formulations (wettable powder and emulsifiable concentrate) applied as post-emergence against Phalaris minor in wheat crop. All formulations of herbicide reduced the density of Phalaris minor over the weedy check however treated plots yielded below than the state average yield of wheat crop. These new clodinafop formulations/brands failed to provide effective control of resistant P. minor prevailing in wheat field during all years, and gave only 27-32% control of Phalaris minor over the weedy check. These new formulations also yielded similar to clodinafop-p-propargyl applied as standard check. Per cent control of Phalaris minor was found to be reduced from 60 to 40% over unsprayed check with delay in application time of clodinafop from 35 to 60 DAS.

Field experiment was conducted under organic farming for three consecutive years during 2008-09 to 2010-11 to study the effect of different non-chemical weed management practices on productivity and weed infestation in maize in mid altitude (950 m MSL) of Meghalaya, India. Total eight treatment in three replication were evaluated on maize. Grain weight/cob of maize was maximum under mulching with fresh Eupatorium sp. biomass after earthing up at 30 days after sowing (DAS). The highest maize yield was recorded under mulching with fresh Eupatorium 10 t/ha, but it was statistically at par with two hand weeding (HW) at 20 and 40 DAS, weed free check and soybean green manure incorporation in situ + one HW. Two HW, soybean green manure incorporation + one HW and mechanical weeding (20 DAS) + one HW (after earthing up) were found to be effective in weed reduction in maize. Weed control efficiency was recorded maximum under two HW which was at par with mechanical weeding (20 DAS) + one HW. Available N, P, K and soil organic carbon concentration after 3-croppoing cycles were maximum under mulching with fresh Eupatorium 10 t/ha treatment followed by soybean green manuring + one HW (45 DAS) than those under other weed management practices. Thus, mulching with fresh Eupatorium (after earthing up) and soybean green manuring + one HW were the recommendable options for sustainable organic maize production under high rainfall hill ecosystem of North-East India.

Field study was conducted at Dryland Farming Research Station in Bhilwara, Rajasthan during Kharif seasons of 2010 and 2011 to study the weed control efficiency of different weed management practices including pre- and post-emergence herbicides in blackgram [Vigna mungo (L.) Hepper]. Among herbicidal weed control treatments, the lowest weed density and dry matter, and highest yield attributes, seed yield and economic return with B:C ratio was recorded with quizalofop-ethyl 50 g/ha 30 DAS and it was statistically at par with interculture at 15 DAS fb imazethapyr 100 g/ha 30 DAS, interculture at 15 DAS fb quizalofop-ethyl 50 g/ha 30 DAS, imazethapyr 100 g/ha 20 DAS and weed free. Whereas, highest weed control efficiency was recorded with alachlor 1.0 kg/ha PRE fb imazethapyr 100 g/ha 30 DAS. All herbicidal treatments reduced weed biomass and improved seed yield and yield attributing parameters as compared to weedy check. Weedy check registered the highest values of weed count and biomass and lowest seed yield and yield attributing characters. Rainfall was directly related to weed count and weed dry matter accumulation with the coefficient of 0.65 and 0.61, respectively.

Pre-mix combination of imazethapyr + pendimethalin at 1000 g/ha had maximum weed kill efficiency over alone application of herbicides applied as pre- or post-emergence. Similarly, the maximum grain yield (1.38 t/ha) was achieved with pre-mix combination of imazethapyr + pendimethalin at 1000 g/ha plot followed by its lower dose applied at 900 g/ha and both doses were found significantly superior over other herbicidal treatments. Supremacy of this treatment was proved by increment of grain yield to the tune of 63.3% over the weedy check and only 3.7% lesser than the hand weeding (20 and 40 DAS). Pre-mix combination of imazethapyr + pendimethalin also proved to be effective in improving other parameters like plants/m2, pods/plant, seed/pod and 100 seed weight (g).

A field experiment was conducted during Rabi season of 2011-12 and 2012-13 at Raipur, Chhattisgarh to find most effective herbicides for weed management in lentil. Best result was found in hand weeding twice at 20 and 40 DAS closely followed by pre-mix application of pendimethalin + imazethapyr 1.0 kg/ha as pre-emergence wherein lowest weed dry weight was recorded at 60 DAS with  maximum weed control efficiency, tallest plant, maximum branches/plant, highest plant dry matter accumulation, highest pods/plant, seeds/plant, test weight, maximum grain and stover yield, maximum net return and B:C ratio over all the treatments.

Field and pot culture studies were conducted at Bengaluru to study the influence of three tillage practices, viz. conventional tillage (3 ploughings + 3 inter cultivations), reduced tillage (2 ploughings + 2 inter cultivations) and minimum tillage (1 ploughing + 1 inter cultivation) and three nitrogen management practices, viz. 100% N through Urea, 100% N through integrated supply (50% N through urea+ 25% N through FYM+ 25% N through Glyricidia) and 100% N through organic source (50% N through FYM+ 50% N through Glyricidia) on live weed seedbank and yield of fingermillet (Eleusine coracana L.) under rainfed pigeonpea-fingermillet system in Alfisols. The results showed that conventional tillage reduced the infestation of Borreria articularis, Cynodon dactylon and Cyperus rotundus compared to other tillage practices. However nitrogen management practices didn’t influence live weed seed bank significantly. Among tillage practices, conventional tillage recorded significantly higher fingermillet yield (3.03 t/ha) compared to other tillage practices and among nutrient management practices integrated supply of N recorded higher yield of 2.67 t/ha compared to other nutrient management practices. More live weed seeds were distributed in upper 10 cm soil depth in minimum tillage whereas in conventional tillage live weed seed distribution was more or less uniform in the soil profile studied.

Experiment was conducted to investigate the effects of imazthapyr and quizalofop-ethyl in different doses (50, 75 and 100 g/ha) with two interval (20-25 and 30-35 DAS), hand weeding twice (20 and 40 DAS) in comparison to unweeded control on yield and yield components of French bean during Rabi season of 2009 to 2011 under irrigated condition on Inceptisols. Among herbicides, application of imazethapyr at 100 g/ha at 20 DAS produced lowest weed index and highest weed efficiency and seed yield (1.24 t/ha). Imazethapyr at 100 g/ha at 20-25 DAS gave more economic profit (28869/ha) followed by imazethapyr at 100 g/ha at 30-35 DAS (27780/ha). None of the herbicides showed phytotoxicity to crop and was compatible with French bean. Imazethapyr and quizalofop-ethyl at lower concentration did not provide satisfactory weed control in rajmash field.

Field experiment was conducted to evaluate the bio-efficacy of ametryn 73.15% + trifloxysulfuron 1.85% W.G for the management of grasses, sedge and broad-leaf weeds in sugarcane. The experiment consisted of nine treatments laid out in randomized block design with three replications. Cyperus rotundus, Ipomoea spp, Brachiaria reptans, Echinochloa colona, Digitaria sanguinalis and Dactyloctenium aegyptium were observed as major weeds. Among herbicide treatments, the lowest density of total weeds was observed with ametryn + trifloxysulfuron at 1500 g/ha though the differences were non-significant when compared with its lower dose i.e. 1250 g/ha at 15 and 45 days after application (DAA). Application of ametryn + trifloxysulfuron 1250 and 1500 g/ha recorded significantly lower weed dry weight over any other herbicidal treatment at 15 and 45 days. Highest weed control efficiency of total weeds at both 15 and 45 DAA were recorded with the application of ametryn + trifloxysulfuron 1500 g/ha which was closely followed by 1250 g/ha. The highest cane yields (9.04 t/ha and 10.51 t/ha) were recorded from weed free plot being at par with hand weeding thrice at 30, 60 and 90 DAP.

The experiment involved nine treatments replicated thrice in randomized block design. Significantly lower density and dry matter of weeds were recorded with weed free followed by oxyflurofen 0.30 kg/ha before planting fb one hand weeding of 40-60 DATS after transplanting  and combined application of oxyflurofen at 0.30 kg/ha before planting + quizalofop-p-ethyl 0.05 kg/ha at 30 days after transplanting. The average bulb weight, plant height, marketable bulb and total bulb yield were also highest in weed free while it was at par to oxyflurofen at 0.30 kg/ha before planting fb one hand weeding of 40-60 days after transplanting and oxyflurofen at 0.30 kg/ha + quizalofop-p-ethyl 0.05 kg/ha at before planting and 30 days after transplanting. The maximum B: C ratio of 2.31 was obtained in combined spray of oxyflorfen and quizalofop-p-ethyl at before planting and 30 days after transplanting of crop.

 Field experiment was conducted at Bikaner for two consecutive years during Kharif seasons of 2012 and 2013 to test the efficacy of different weed control measures against weeds in clusterbean Cyamopsis tetragonoloba (L.) Taub. The experiment consisting of seven treatments, viz. imazethapyr 40 g/ha, quizalofop-ethyl 37.5 g/ha, fenoxaprop-p-ethyl 50 g/ha, imazethapyr + imazamox 40 g/ha, pendimethalin 0.75 kg/ha as pre-emergence (PE), hand weeding twice at 20 and 40 DAS and weedy check. Among herbicids, post-emergence application of imazethapyr + imazamox (ready mix) 40 g/ha applied at 3-4 leaf stage (around 20 DAS) recorded lowest weed density and dry weight of both grassy and broad-leaved weeds with maximum weed control efficiency (88.1%). Application of imazethapyr alone at 40 g/ha applied at 3-4 leaf stage (around 20 DAS) significantly reduced the density and dry weight of broad-leaved weeds but not effective significantly against grassy weeds. Yield attributes i.e pods/plant, seed and straw yields, net return and B: C ratio were also superior with imazethapyr + imazamox 40 g/ha applied at 3-4 leaf stage (around 20DAS).

The mile-a-minute weed, Mikania micrantha, is a highly problematic and widespread invasive weed in the moist forests of the Western Ghats and in the north-eastern states in India causing significant damage to natural forests as well as to plantation crops, including tea, coffee, bamboo, coconut and teak. The microcyclic rust fungus, Puccinia spegazzinii, was identified as a potential classical biological control agent to replace the unsustainable or even hazardous conventional control methods. Following a successful risk analysis under quarantine at CABI (UK), a pathotype of the fungus (IMI 393067) from Trinidad and Tobago was imported into India. Prior to its release in the open field, the rust was further evaluated under strict quarantine conditions to ascertain the susceptibility of M. micrantha populations from three regions in India where the weed is invasive, and to confirm the safety of economically important plant species and indigenous flora. Results of host-specificity screening of 90 plant species belonging to 32 families ensured that the Trinidadian pathotype of P. spegazzinii was highly host- specific and could not infect any of the test plant species, though it was highly pathogenic to most of the target weed populations from Assam, Kerala and the Andaman and Nicobar Islands. The rust was released in Assam and Kerala but failed to establish at the time.  However, due to the apparent success of this rust at controlling M. micrantha in the Pacific region, further releases in India are recommended.

Penoxsulam at 22.5 and 25.0 g/ha was found effective to control weeds in transplanted rice on the basis of vegetation analysis. However, based on economic analysis, penoxsulam at 22.5 g/ha could be adjudged as the best treatment for effective and economic weed management.

Application of bispyribac-sodium 25 g/ha at 15 DAT recorded significantly lower total weed population  and higher grain (6.47 t/ha) and straw yield (7.66 t/ha) as compared to pretilachlort 750 g/ha at 5 DAT. The nutrient uptake by weeds for N,P and K was significantly higher with unweeded check (12.32, 2.78 and 20.28 kg/ha, respectively). Whereas the lowest uptake was noticed with bispyribac-sodium 35 g/ha at 15 DAT (1.02, 0.21 and 1.62 kg/ha, respectively). The nutrient uptake by rice for N, P, and K was significantly higher with bispyribac-sodium 25 g/ha at 15 DAT (122.66, 15.74 and 164.51 kg/ha, respectively) as compared to unweeded check (78.24, 9.99 and 105.58 kg/ha, respectively). Similar trend was observed with net returns and B:C ratio.

Four tillage systems viz. (i) zero–zero tillage (ii) zero-conventional tillage (iii) conventional-zero tillage (iv) conventional–conventional tillage systems were evaluated on the survival and growth of free living nitrogen fixing bacteria, total phosphate solubilising bacteria, soil biomass carbon, soil respiration, per cent root colonization and enzymic activities in rhizospheric soil. Among weed control measures, comparative effects of hand weeding and recommended herbicides (isoproturon at 1.0 kg/ha + 2,4-D + 1 HW (45 DAS) were tested along with weedy check. The results revealed that tillage systems did not influence microbial soil health. The maximum growth of different micro organisms was observed in zero tillage system, whereas minimum was in conventional tillage system. There were no adverse effects of recommended herbicide use on soil microbial health. Application of isoproturon + 2,4-D had no adverse effect on rhizosphreric soil health of wheat crop.

Weed free treatment produced highest seed yield which was at par with pendimethalin 1.0 kg/ha as pre-emergence (PE) + hand weeding at 30 DAS and oxyfluorfen 0.18 kg/ha PE + hand weeding at 30 DAS. However, among the other treatments, pendimethalin 1.0 kg/ha as PE + hand weeding at 30 DAS was found superior in controlling weeds and increasing seed yield. 

Trifluralin as PPI, pendimethalin as pre-emergence and imazethapyr at 55 g/ha either applied as PPI or PRE provided excellent control of weeds up to 25 DAS. At 100 DAS and at harvest, post-emergence application of imazethapyr (55/ha) significantly reduced the weed population over other herbicidal treatments. Maximum dry matter accumulation by the crop, yield and yield attributes were recorded in weed free plots which was significantly higher over all herbicidal treatments. Maximum weed control efficiency (69%) was observed with post-emergence application of imazethapyr 55 g/ha.

All the weed control treatments significantly reduced the density and dry weight of weeds compared to weedy check at 60 DAS (Table 1). Among the treatments, the lowest weed density, dry weight and highest weed control efficiency (WCE) of 65% was observed in the sequential treatment with pre-emergence application of pendimethalin 0.75 kg + paraquat 0.5 kg/ha fb post-emergence application of 2,4-D amine 0.58 kg/ha and was at par with other sequential treatments and hand weeding at 20 and 40 DAS, but significantly superior to pre-emergence application of herbicides. The lower weed growth in these treatments was mainly due to effective control of weeds in the early stage by pre emergence herbicides and at later stage by post emergence herbicides. Maximum weed growth was observed in unweeded check. In general, sequential treatments were found to be superior to one time application of herbicides. Similar observations reported in normal sown sorghum by Sharma et al. (2000).

 Leaching potential of metsulfuron-methyl herbicide was evaluated under laboratory conditions in Mollisol soil of Pantnagar, Uttarakhand with simulated rainfall. Metsulfuron- methyl was applied at recommended dose (4 g/ha) on 60 cm long soil columns. After seven days of experiment, maximum concentration was observed in 30-35 cm column depth and some amount of herbicide leached out and was detected in leachates. Study indicated high mobility of metsulfuron-methyl under saturated moisture conditions which may pose significant ground water contamination.