Weed Science

Rice and wheat are the major cereals in India hence  rice-wheat system provides the staple grain supply for a large portion of the world's population and mainly this system is critically important for global food security. Twenty five per cent of the total rice area of the country is grown in rotation involving wheat, whereas 40% of wheat is grown in rotation with rice. The rice-wheat cropping system with zero tillage is the best cropping system with lower risk as it has major benefits such as improving water use efficiency, reduced cost due to saving in the fuel and labour, timely planting of crops, results in higher yield, reduced weed density and has a positive environmental impact. Hence, zero tillage are divisible nature and flexible in operation allowing farmers to benefit from than under driver situation. Tillage influences weed infestation, and thus interaction between tillage and weed control practices are commonly observed in crop production. Adequate tillage checks and delays emergence of weeds and provides a more favourable environment for early crop establishment. This paper presents current status of zero tillage in context to weed management in India.

A field experiment was conducted during the rabi seasons of 2007-08 to 2009-10 to find out the relative efficiency of weed management practices in marigold (Tagetes erecta Linn). The results indicated that a significantly higher weed control efficiency was achieved with the treatments of two hand weedings (20, 40 DAS) followed by trifluralin 1.0 kg/ha pre-plant incorporation (PPI) + 1HW. The data on yield and yield attributing characters viz., plant height stem diameter, number of leaves/plant, number of flowers/plant and flower yield were significantly influenced by various weed management treatments. The highest flower yield 29140 kg/ha was recorded with the application of two hand weedings which was at par with trifluralin 1.0 kg/ha pre-plant incorporation fb 1HW. Significantly lowest flower yield of marigold was recorded in weedy check plots.

The field experiments were conducted during kharif seasons of 2008 and 2009 at the Agronomy Research Area, Birsa Agricultural University, Ranchi on sandy loam soil to study the effect of sowing time and weed control methods on weed flora and productivity of direct seeded upland rice. Results showed that broad leaf weeds constituted 56%, grasses 40% and sedges 4% of the total weed population at 30 days after sowing. Post monsoon sown direct seeded rice produced significantly higher grain (1967 kg/ha) and straw (2967 kg/ha) yield with net return of Rs 9465/ha and benefit: cost ratio of 1.92 than pre monsoon sown crop owing to higher total and effective tillers, grains/ panicle and 1000- grain weight along with lower weed density, weed dry matter and higher weed control efficiency. Grain yield of rice was statistically at par among pretilachlor + safener 0.5 kg/ha and butachlor 1.5 kg/ha + one hand weeding at 25 days after sowing (DAS) but significantly higher than other weed control methods except weed free. Application of pretilachlor + safener 0.5 kg/ha was remunerative in direct seeded rice as it had higher net return (Rs 9459/ha) and benefit: cost ratio (1.98).

A field experiment was conducted during kharif 2008 and 2009, to study the effect of different pre-and post-emergence applications of herbicide on weed infestation and grain yield of soybean [Glycine max (L.)Merr.]. Among the different herbicides, the highest seed yield was recorded with lone application of diclosulam 18 g/ha as pre-emergence supplemented with one hand weeding at 20 DAS and application of diclosulam 18 g/ha as pre-emergence followed by haloxyfop 100 g/ha as postemergence. However, these were significantly at par with weed-free treatment. The highest weed control efficiency and the lowest weed biomass were recorded in weed-free treatment followed by application of diclosulam 18 g/ha as pre-emergence with one hand weeding at 20 DAS. Application of diclosulam as pre-emergence also performed better over the standard check either applied pendimethalin as pre- or post-plant incorporation of fluchloralin before the sowing of the seed.

Adsorption-desorption was studied by batch equilibrium technique at 37+1 C at different concentrations of oxadiargyl and butachlor in selected soils of Andhra Pradesh. Desorption isotherms showed a considerable hysteresis which was more prominent when desorption was carried out at higher concentrations of adsorbed oxadiargyl and butachlor. Desorption isotherms at lowest level of adsorbed herbicide concentration were close to adsorption isotherms. The cumulative desorption after five desorption steps was significantly different for all the initial concentrations of adsorbed herbicide for all the soils. Desorption of these herbicides was higher in Alfisol than Vertisol, might be attributed to low organic carbon and low clay content. The variation in per cent desorbed may be due to heterogeneity involved in different soils, that vary widely in type and energy of bonding. Desorption isotherms confirmed to Freundlich's equation and the Freundlich's constants increased with increasing initial concentration of adsorbed herbicide thus confirming the irreversible nature of the adsorption of oxadiargyl and butachlor on these soils

A field experiment was conducted during kharif seasons of 2008 and 2009 at Livestock Farm, JNKVV, Jabalpur, to evaluate the efficacy of imazethapyr against weeds in groundnut. Eight treatments comprising of five doses of imazethapyr 50, 100, 150, 200 and 300g/ha alone, combined application of imazethapyr + chlorimuron (100+24 g/ha), hand weeding twice (20 and 40 DAS) including weedy check were laidout in randomized block design with three replications. The experimental field was infested with monocot weeds like Cyperus iria (44.08%) Echinochloa colona (30.51%) and Dinebra retroflexa (25.39%) at 40 DAS during both the years among the sedges and grassy weeds. The efficacy of imazethapyr at lowest rate (50 g/ha) was poor, which improved with the increase in application rates from 150 to 300 g/ha. However, combined application of imazethapyr at lower rate 100 g/ha with chlorimuron 24 g/ha paralyzed the weed growth identically (98.1%) to that of hand weeding twice (98.6%) and attained the superior values of yield attributes (13.5 pods/plant, 2.4 kernels/pod) as well as higher pod and haulm yields (12.83 and 21.21 q/ha). The latter treatment was also found more remunerative as it fetched the maximum values of net monetary returns (Rs 14096/ha) and benefit:cost ratio (1.8) and surpassed the recommended practice of weed control viz., hand weeding twice which recorded the inferior values of net monetary return (Rs 10194/ha) and B:C ratio (1.4) due to more cost of weed control.

A field experiment was conducted in rainy season of 2005, 2006 and 2007 with direct seeded line sown rice as first crop and wheat as subsequent crop in winter season at the University farm of Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh, India to understand the effect of tillage systems and weed control methods on weed flora and grain yield of rice-wheat cropping system. The weeds found in initial two year consisted of Echinochloa colona, Ischaemum rugosum, Fimbristylis miliacea, Cyperus iria, Alternanthera triandra, Cynotis axillaris and Croton bonplandianum. In third Year, Setaria glauca emerged as new weed and Fimbristylis miliacea got disappeared, whereas in wheat, broad leaf weeds like Melilotus indica and Chenopodium album dominated the weed flora. In the initial two years, the grain yield of rice was not influenced significantly due to tillage methods, but during 2007, the grain yield was significantly higher by 10.24% under zero tillage than conventional tillage. Among the different weed control practices, farmer's practice produced maximum grain yield which was significantly superior over recommended herbicide and unweeded check and the increase in yield was to the tune of 48.09 and 96.64%, respectively, in order. During dry season, significantly higher grain yield of wheat by 5.55% was recorded under conventional tillage than zero tillage. Significant variation in grain yield and yield attributes was also registered due to various weed control treatments. Grain yield of wheat was significantly higher under herbicidal treatment i.e. pendimethalin 1.0 kg/ha as preemergence followed by metsulfuron 2.0 g/ha as post-emergence by 10.0 and 31.3%, respectively, as compared to farmer's practice i.e. two hand weeding and weedy check.

A survey of weed flora of cotton and clusterbean in south-western Haryana revealed that a total of 22 species were found to infest cotton crop, out of which 7 were grassy, one was sedge and 14 were broad leaf weeds. On the basis of IVI values, Trianthema portulacastrum, Dactyloctenium aegypticum, Echinochloa colona, Digera arvensis and Cyperus rotundus were found highly associated with cotton crop in all districts. T. portulacastrum alone constituted 48.7-56.8% of total weed flora with IVI values of 58.1-72.7 in all the districts, was the most dominant weed of cotton crop. Similarly cluster bean crop was found to infest with 25 major weeds of which 9 were grassy, 2 were sedges and 14 were broad leaf weeds viz., Digera arvensis, Cleome viscosa T. portulacastrum, Cyperus rotundus, Physallis minima, D. aegypticum, Corchorus tridens, Mollugo verticillata and Cucumis callosus. Digera arvensis constituting 43.2 to 69 % of total weed flora alone was the most dominant weed of cluster bean crop in all the districts except Bhiwani and Mahender Garh where C. viscosa was the most dominant weed with a relative density of 34.4 and 27.9 % and IVI values of 41.4 & 33.3, respectively. Among grassy weeds, Dactyloctenium aegypticum was the major grassy weed in all districts except in Mewat where Echinochloa colona was the most dominant weed with IVI value of 27.9. Mollugo verticillata, a weed of loamy sand soils showed its presence in Bhiwani, Mahender Garh, Jhajjar and Rewari only

A field experiment was carried out to study the effect of doses and stage of application of various herbicides namely sulfosulfuron, isoproturon and metribuzin during rabi 2003-04 and 2004-05 at Pantnagar. All the herbicides reduced dry matter of weeds at 60 days more effectively when they were applied at higher rates and after first irrigation. Annual weeds and total weeds were higher in conventional tillage than zero tillage under weedy situation while perennial weeds were more in zero tillage. Under zero tillage, sulfosulfuron at 25 g/ha after first irrigation recorded highest grain yield viz., 4431 kg/ha and 3924 kg/ha during 2003-04 and 2004-05, respectively. Weed control efficiency (94% during both experimental years) too was highest in this treatment. However, two hand weeding at 30 and 45 days stage under conventional tillage recorded highest yield among all the treatments. Use of herbicides under zero tillage fetched higher net returns than hand weeding at 30 and 45 days after sowing.

To study the effect of weed control methods on weed seed bank and composition of weed flora in wheat and rice under wheat-rice system, a field experiment was conducted at crop research center of GBPUAT, Pantnagar during rabi and kharif of 2001-02 and 2002-2003. The weed seed bank studies revealed that application of herbicides has no significant effect on the weed seed bank of soil. Weed control treatments isoproturon + hand weeding in wheat and butachlor + hand weeding in rice recorded less number of weed seeds (14450, 3800 and 605 of Phalaris minor, Chenopodium album and Melilotus alba, respectively in wheat and 2650, 2048 and 4265 of Echinochloa colona, Echinochloa crusgalli and Paspalum scrobiculatum, respectively in rice). Under the influence of different weed management practices, there was significant negative relationship of grain yield with weed dry weight and weed seed bank in both wheat and rice. Among herbicide treatments, isoproturon (1.0 kg/ha) + hand weeding; butachlor (1.5 kg/ha) + hand weeding followed by isoproturon (1.0 kg/ha) +2,4-D (0.5 kg/ha); butachlor (1.5 kg/ha) fb 2,4-D (0.5 kg/ha) + organic matter through Sesbania aculeata were found effective in reducing total weed population, weed dry matter and weed seed density there by increasing yield of wheat and rice.

The experiment comprising 12 weed management practices with different herbicidal doses and hand weeding was conducted on light textured soil of S.G. College of Agriculture and Research Station, Jagdalpur, during kharif season of 2004, 2005 and 2006. Digitaria sangunalis, Eleusine indica, Setaria gluaca, Cyperus rotundus and Echinochloa colona among monocot and Celosia argentea, Commelina benghalensis, Spilanthus ecmela and Euphorbia geniculata among broad leaf weeds were dominant. Irrespective of weed management practices, density and dry weight of weeds and weed control efficiency were higher in pre-emergence application of oxyfluorfen 0.50 kg/ha + one hand weeding at 20 DAS (60.18) over weedy check. The control was highest under oxyfluorfen 0.50 kg/ha + two hand weeding at 30 and 45 DAS, followed by oxyfluorfen 0.25 kg/ha + two hand weeding at 30 and 45 DAS.

Effect of tillage methods and weed management practices on weed infestation and yield of wheat was studied during 2002-2003 and 2003-2004. Density and dry weight of total weeds recorded lower under zero till and bed planting system as compared to conventional tillage for initial year. In second year, it was again recorded lowest under zero tillage, but increasing trend was observed under bed planting situation. Number of spikes as well as grain yield was not influenced by tillage methods during first year, but was found maximum under zero till situation in the next year. Excellent suppression of weeds and thereby higher yields were obtained under two hand weeding under conventional system. Under weedy situation, zero till system was found better because of lesser weed emergence.

A field experiment was conducted during kharif 2007 at the Main Research Station, University of Agricultural Sciences, Hebbal, Bangalore, under irrigated conditions to know the pattern of dry matter production in maize using empirical models under weed management practices. Empirical models simulated the crop growth (dry matter production) of maize by 98% indicating that competition of weed types did not alter the pattern of growth of maize, but cumulatively affected the total dry matter at harvest, where as, the linear function predicted the crop growth by 92 to 94%. Differentiating quadratic and linear functions indicated that dry matter production efficiency (DMPE) were improved by 34 to 46% in hand weeding or atrazine treatments due to elimination of weed competition over unweeded control. Competition of grassy weeds (in 2,4-D EE treatment) lowered the DMPE by 24% over atrazine treatment with less weed competition, while competition from broad leaf weeds and sedge lowered the DMPE by 22%. Thus grasses showed higher competitive ability, followed by broad leaf weeds and sedges.

A field experiment was conducted during kharif seasons of 2008 and 2009 at the research farm of Birsa Agricultural University, Ranchi with the objective to study the effect of establishment and weed control methods on weed dynamics and productivity of rice. Results indicated that transplanting of rice recorded reduced weed population as well as dry matter with higher weed control efficiency resulting in higher grain yield. Among weed control methods, application of pyrazosulfuron as pre emergence 20 g/ha + mechanical weeding (40 days after sowing) with lower weed population and weed dry matter had higher weed control efficiency as well as grain yield. Transplanting associated with application of pyrazosulfuron + mechanical weeding produced maximum and significantly higher grain yield (4244 kg/ha) of rice.

A Survey of weed flora of Indian mustard (Brassica juncea L.) in south-western Haryana conducted during 2004-05 revealed that a total of 29 species were found to infest mustard fields, out of which 3 were grassy, 26 were broadleaf weeds. Asphodelus tenuifolius Chenopodium album, Melilotus indica, Trigonella polycerata, C. murale, Cynodon dactylon, Orobanche aegyptiaca, Carthamus oxycantha, Avena ludoviciana and Convolvulus arvensis were found highly associated with mustard crop in all districts. Asphodelus tenuifolius was the dominant weed in all districts except Hisar where relative density (R.D.) of C. album was more. Malwa parviflora a robust dicotyledonous weed which was considered to be weed of non cropped areas has also shown its presence in Jind, Jhajjar, Hisar, Rohtak and Mewat districts. Infestation of parasitic weed Orobanche aegyptiaca was more in Bhiwani, Rewari, Mahender Garh, Jhajjar and Gurgaon districts where crop is grown in light textured soils( loamy sand) and irrigated by sprinkler.

Management of risk by a pest in agriculture is one of the major concerns of the decision makers and policy planners. There is always risk of introduction of alien weed seeds along with the imported cereals. This study revealed that how much cost may be involved in management of an alien introduced weed in due course mentioning example of Parthenium which got introduced into India in 1955 along with imported cereals. Initially Parthenium was a problem in waste and vacant land. Reports started to appear about its infestation in field crops after 1980. In general, about 35 million hectare land has been estimated to be infested with Parthenium currently. The increase of Parthenium infestation in crop area in recent past is alarming. For the management of Parthenium, two hand weeding or two chemical sprays are essentially required to get complete relief. It was estimated that 182000 or 18200 crores will be required per year to mitigate the problem by manual labour and Rs 119000 million or 11900 crores are required to manage the weed by Chemical method besides Rs 880 crores for treatment of health and about 10 crores on researchable issues related to biological control in particular and integrated management in general including people awareness programmes. Therefore, since 1955, it would have cost Rs 2067160 million or 206716 crores to manage the parthenium in India by manual labour The losses caused by this weed may be much higher if we take into consideration the cost involved in restoration of biodiversity and aesthetic value already lost due to Parthenium

A field experiment was conducted on sandy loam soil at Research Farm of SKUAST-J, Chatta, Jammu during the years 2006 and 2007 to study the effect of weed management and crop establishment methods on weeds and grain yield of rice as well as residual effect of treatments (applied to rice) on weeds and yield of wheat. There was severe competition between Echinochloa crusgalli and Echinochloa colona with rice and between broad leaf weeds and wheat. Phalaris minor infestation was lower during the experiment. Among weed management methods, maximum yield of rice ( 4256 kg/ha and 4393 kg/ha) during 2006 and 2007, respectively was recorded in the treatment where mechanical hoeing using conoweeder (at 15 and 30 DAT) was done during the first and second years of study. Fenoxaprop-p-ethyl (0.06 kg/ha, 20 DAT) + 1 HW at 30 DAT, metasulfuron methyl + chlorimuron ethyl (0.004 kg/ha, 20 DAT) + 1 HW at 30 DAT and fenoxaprop-p-ethyl (0.06 kg/ha, 20 DAT) and metasulfuron methyl + chlorimuron ethyl (Almix 0.004 kg/ha, 20 DAT) were the next best treatments. However, metasulfuron methyl + chlorimuron ethyl (0.004 kg/ha) was found to be more effective against broad leaf weeds and very little to sedges, hence failed to control major grassy weeds during the experiment. Among the establishment methods of rice, conventional and system of rice intensification (SRI) methods were at par with respect to grain and straw yield. The residual effect of treatments (applied to rice) was not well pronounced on weed population, weed dry matter accumulation by weeds and yield of wheat during both the years. Under wheat establishment methods, the two tillage systems did not produce significant variation with respect to total weed population, weed dry matter accumulation and grain yield. However, conventional tillage exhibited a marginal edge over zero tillage during both the years.

A field experiment was conducted at G.B. Pant University of Agriculture & Technology, Pantnagar, Uttrakhand to evaluate the bio-efficacy of haloxyfop (10 EC), a post-emergence herbicide for weed control in soybean during kharif of 2007 and 2008. The experiment was conducted in randomized block design by taking eight treatments comprising, haloxyfop (10 EC) at 75, 100 and 125 g/ha, quizalofop 50 g/ha, fenoxaprop 100 g/ha, hand weeding (twice at 30 and 45 DAS), weed free and weedy. To evaluate the bio-efficacy of herbicides against grassy weeds, the broad leaf weeds were removed at 20 days after sowing of crop. The experimental field was mainly infested with Eleusine indica, Digitaria sanguinalis, Eragrostis japonica and Brachiaria species. Haloxyfop 100 g/ha was found effective when applied as post emergence to grassy weeds as compared to other treatments. This dose was found at par with haloxyfop 125 g/ha and better than Haloxyfop 75 g/ha. There was no phytotoxic effect on the crop due to haloxyfop. Untreated plot recorded 43 and 47% lower grain yield respectively in 2007 and 2008, as compared to weed free treatment. Application of fenoxaprop and quizalofop recorded comparable weed density with haloxyfop at 100 and 125 g/ha during the years.

Application of isoproturon was most effective for the control of all weeds, which resulted 99.32% weed control efficiency and 49.0% higher mean seed yield over unweeded control. The higher water use efficiency (WUE) (3.61 kg/ha mm) was observed under 0.4 IW:CPE ratio and higher net return (Rs/ha 28904) were obtained under the treatment combination (0.4 IW:CPE ratio and application of isoproturon 0.5 kg/ha as pre-emergence). The interaction effect of irrigation schedule and herbicidal weed control practices was found non-significant in some cases

A field experiment was conducted during kharif 2007 at Tamil Nadu Agricultural University, Coimbatore to study the effect of different densities of Trianthema portulacastrum on growth and yield of cow pea. Plant height, leaf area and dry matter production of cow pea was reduced with increase in weed density from 0 to 64 weeds/m2 in all growth stages. The infestation of 16 weeds/m2 of Trianthema portulacastrum significantly decreased the dry matter production of cow pea (36.3 g/plant) compared to zero weeds/m2 (64.5 g/plant). The maximum yield reduction (34.8%) was observed with 64 weeds/m2. It was concluded that the population of 8 weeds/m2 of T. portulacastrum is the threshold value for cow pea

An experiment was conducted to evaluate the field performance of power weeder for interculturing operation in maize crop (Zea mays L.) to compare the cost of operation of power weeder in maize vis-a-vis grubber, wheel hoe and 'Khurpi' as control treatment. Power weeder having the higher field capacity (0.067 ha/hr) was found most efficient tool for weeding, particularly in view of time taken in operation followed by the wheel hoe (0.009 ha/hr), grubber (0.008 ha/hr) and 'Khurpi' (0.002 ha/hr). The highest field efficiency was attained in case of 'Khurpi' (94.73%) followed by wheel hoe (90.54%), grubber (84.40%) and power weeder (76.39%). The highest weeding efficiency (99.44%) was recorded in treatment 'Khurpi' followed by grubber (96.8%), wheel hoe (94.64%) and power weeder (89.8%). The plant injury was highest under power weeder (1.94%) followed by wheel hoe (1.01%), grubber (0.76%) and 'Khurpi' (0.46%). The cost of operation of 'Khurpi' was maximum (Rs. 4051/ha) followed by power weeder (Rs. 1350/ha), grubber (Rs. 1158/ha) and wheel hoe (Rs. 1152/ha). In spite of the marginal higher cost of operation of power weeder over other tools, power weeder ensures timeliness weeding in operation than other weeding tools.

Panicum colonum, Celosia argentea, Commelina benghalensis, Eragrostis major, Cyperus rotundus and Digera arvensis were the dominant weeds in pigeonpea. Integration of pendimethalin as preemergence, quizalofop ethyl as post-emergence and oxadiargyl as pre-emergence with one hand weeding and one interculture operation at 40 days after sowing (DAS) proved effective in reducing total weed density and dry weight of weeds. The maximum growth parameters, yield attributes and yield were significantly recorded under weed free condition which was closely followed by pendimethalin 900 g/ha as pre-emergence with one hand weeding and one inter-culturing at 40 DAS, quizalofop ethyl 40 g/ha as post-emergence with one hand weeding and one interculturing at 40 DAS and oxadiargyl 90 g/ha as pre-emergence with one hand weeding and one interculturing at 40 DAS. Chemical analysis of plant indicated that weed free treatment gave maximum N, P and K uptake in grain as well as in stover. Integration of pendimethalin, quizalofop ethyl and oxadiargyl with one hand weeding and one interculturing were found at par with weed free. The maximum net return was acquired under pendimethalin 900 g/ha as pre emergence with one hand weeding and one interculturing at 40 DAS closely followed by, weed free, quizalofop ethyl 40 g/ha as post emergence with one hand weeding and one interculturing at 40 day after sowing and oxadiargyl 90 g/ha as pre emergence with one hand weeding and one interculturing at 40 DAS.

Weeds infestation is very common in soybean which can reduce the yield potential drastically under kharif crop. It is two dimensional crop containing protein and oil. The weeds were rampant if they would not be controlled at proper time. To overcome the weeds problem of soybean, the study was carried out comprising different herbicides alone and in combination. The post-emergence application of lactofen 120g/ha + propaquizafop 60 g/ha was found having higher weed control efficiency with higher grain yield. All the recorded weed flora were found with reduce dry matter accumulation by combined application of herbicides rather than alone application

A field experiment was conducted during rabi 2007-08 at NRC-Weed Science, Jabalpur (M.P.) to assess the effect of tillage and weed control practices on weed flora and yield of wheat in direct seeded rice-wheat cropping system. Yields were not influenced by any of the tillage packages adopted in wheat. But chemical weed control (clodinafop 0.060 fb 2,4-D 0.50 kg/ha) or integrated weed management practice (IWM) (clodinafop 0.060 fb 2,4-D 0.50 kg/ha + 1 HW at 40 DAS) after all the tillage packages increased grain and straw yields of wheat compared to weedy check plots. IWM practice (clodinafop 0.060 fb 2,4-D 0.50 kg/ha + 1 HW at 40 DAS) produced significantly higher grain yield of wheat than chemical control alone (clodinafop 0.060 fb 2,4-D 0.50 kg/ha). benefit per rupee of investment was higher in plots receiving clodinafop fb 2, 4-D in zero tilled wheat after conventional tillage in rice as well as IWM in wheat under zero tilled wheat after zero tillage in rice. Zero tilled wheat after zero tillage in rice had lower weed density and dry weight of weeds than other tillage (clodinafop 0.060 fb 2,4-D 0.50 kg/ha + 1 HW at 40 DAS) packages adopted in wheat after rice. Similarly post-emergence application of clodinafop 0.060 fb 2,4-D 0.50 kg/ha or integrated weed management in wheat, was found effective in curtailing the population including dry weight of dominant grassy and dicot weeds.

The impact of waste water irrigation on weeds in wheat was studied during rabi season of 2008. It was observed that higher weed density was recorded in waste water irrigated sites as compared with tubewell water. The effect of untreated drain water was subsequently tested on major weed such as Avena ludoviciana in lab. The results revealed that the drain water increased the weed germination and promoted the shoot and root length of A. ludoviciana in wheat.

A field investigation was carried out during rabi 2007 at Tamil Nadu agricultural University, Coimbatore to evaluate the threshold values of horse purslane (Trianthema portulacastrum) in onion. Increase in densities of T. portulacastrum increased the yield reduction linearly in onion crop. The maximum percentage of yield reduction was recorded with 64 weeds/m2 (54.8%) over the zero weeds/m2. The lowest yield reduction was with 4 weeds/m2 (8.8%) followed by 8, 16, 32 weeds/m2 ( 27.1, 38.61, 46.38% respectively). It is evident that a density of 4 weeds/m2 was the threshold value of Trianthema portulacastrum for onion crop to avoid significant yield reduction.