Weed Science

A preliminary survey on weedy rice infestation in rice fields was carried out during 2008 in all the rice producing states of the country including Jabalpur district and adjoining areas in Madhya Pradesh in particular. The study revealed that almost all rice fields were found heavily infested with weedy rice. The extent of infestation was found 5-60% in different states of India, whereas it was observed in the range of 11.32 to 44.28% in cultivators’ field and 0.78 to 2.40% at research farm of DWSR. Ten types of weedy rice (known as Sada or Sadwan) found in the farmers’ field and other two types found in water ponds / tanks (called as Pasai Dhan in Madhya Pradesh) were identified and characterized. Considering mean 10% infestation, the average loss in rice production was assessed to the extent of 9.15 million tones. The damage is likely to increase exponentially in subsequent years, if not managed effectively, challenging the rice production system in the country.

Herbicides are the most effective and economic among the weed management practices. Use of herbicide is rapidly increasing in the world including India. Herbicides have revolutionized the weed management in world agriculture. Along with the advantages there are some inadvertent disadvantages like shift in weed flora, herbicide resistance and environmental concern. Development of resistance against the herbicides in targeted species is the most prominent among them. Herbicide resistance is a worldwide phenomenon and number of resistant biotypes of weeds is increasing at an alarming rate. Recently, almost one dozen species have been reported to be resistant against Monsanto’s very potent broad spectrum herbicide glyphosate which has now become a key issue for all stakeholders. Sometimes the use of the term herbicide resistance is misleading. Before calling it herbicide resistance, the factors for poor efficacy of herbicide should be sincerely evaluated. It is essential to properly understand the herbicide resistance, its development and mechanism to tackle the problem. In this paper an attempt has been made to review of up to date information on current status of herbicide resistance in the world – development of resistance, factors controlling the development of herbicide resistance in weeds, resistance mechanisms, integrated approach of herbicide resistance management and lastly basic research and facilities required for better understanding of herbicide resistance and its management.

A field experiment was conducted during winter months of 2003-04 and 2004-05 on a sandy clay loam black cotton soil to study the feasibility of using water hyacinth mulch for weed control and increasing productivity of potato cv. Kufri Chandramukhi. The weed control treatments consisted of control (no weed control measure), farmers practice (scrubbing the soil of inter rows space and earthing potato rows), water hyacinth mulch (HM), rice straw mulch (SM), metribuzin 250 g/ha as PE + HM, metribuzin 250 g/ha as PE + SM, metribuzin 500 g/ha as PE, and metribuzin 500 g/ha as PE + HM. Sprinkler irrigation was given immediately after planting, and flood irrigation was given during 3rd and 8th week after planting. Both rice straw and water hyacinth mulches controlled weed infestation throughout the growing period of potato, and no additional benefit of herbicide application in terms of weed control or tuber yield was noted in the mulched plots. The lowest tuber yield of 7.2 t/ha was recorded in control, it increased to 13.1, 20.8, 14.8, 21.1, 15.9, 13.0 and 21.4 t/ha respectively in the above mentioned treatments. It was concluded that water hyacinth mulch was superior to rice straw mulch in increasing potato yield in black cotton soil.

Field investigations were carried out for three consecutive rabi seasons (2001-04) on farmers’ field at Bariapur village of Jalaun district in Uttar Pradesh to develop effective weed management technology in field pea involving cultural and chemical measures for managing weed problem especially menace of Carthamus oxyacantha. Results revealed that metribuzin (175 g/ha) as preemergence followed by metribuzin (87.5g /ha) as post-emergence (after first irrigation) demonstrated satisfactory the mortality of C. oxycantha and other associated weeds with an overall weed control efficiency of 72.0% resulting in increased grain yield by 56.8% and greater net monetary returns (Rs 7140 /ha) with higher B:C ratio (5.49) over unweeded. Cross or bidirectional sowing reduced dry weight of weeds to the extent of 1 1% only and failed to incr ease grain yield significantly. Use of five tined hoe caused weed mor tality to the extent of 18-24% resulting in increased grain yield to the extent of 16-17%.

A field investigation was carried out during the rainy seasons of 2001 and 2002 to test the bioefficacy of post-emergence herbicides for controlling weeds in direct seeded rice (Oryza sativa L.). All the herbicidal treatments significantly r educed the density and biomass of weeds and increased grain yield of the crop significantly over unweeded check. Uncontrolled growth of weeds caused 68% reduction in the crop yield as compared to weed free in both the years of investigation. Pre-emergence application of butachlor at 1500 g/ha followed by one hand weeding produced maximum grain yields in both the years among all herbicidal weed control treatments, which were comparable to those obtained with post-emergence application of pyrazosulfuron at 25 g/ha, chlorimuon+metsulfuron at 4 g/ha, butanil 4000 ml/ha and bentazone at 1250 g/ha. The same treatments also resulted in maximum reduction in the density and growth of the weeds. Application of fenoxaprop reduced the population of grassy weeds, whereas butanil and pretilachlor reduced the grassy as well as broad leaved weeds. Post-emergence application of chlorimuon+metsulfuron, bentazone and pyrazosulfuron were most promising for controlling broad leaved weeds and sedges in direct seeded drilled rice.

Parthenium contact cause skin allergy, pollen leads to breathing problems in sensitive human and if deposited on stigmatic surface fruits gets aborted in brinjal. Parthenium harbors organisms of virus diseases and infect the crop later. Managing the Parthenium is absolutely essential but costly. Non-availability of timely labour force and the awareness of chemical pollution causes dilemma of herbicide usage. Alternative technique to manage Parthenium weed is a welcome challenge.Aqueous extracts of fresh or dry leaves (1%) of Lantana camara and Hyptis sulvelolensis suppressed germination of Parthenium more than that by Cassia uniflora extracts. Mulching of these botanical agents (10 t/ha) suppressed Parthenium till 60 DAS, but stimulated the growth of sunflower and tomato, respectively. Mulching of fresh or 30 days deposited materials suppressed the germination and growth of Parthenium. Soil sterilization enhanced the allelochemical efficacy of botanical agent indicating the role of soil microbes in degrading the allelochemicals.

An experiment was conducted during kharif 2005 and 2006 in MPKV, Rahuri, Dist. Ahmednagar (MS) to find out the effect of parthenium compost in maize yield and soil health. The results indicated that application of 50% N through parthenium compost + 50% N through RDF (60:30:30 NPK kg/ha) and 50% N through vermicompost + 50% N through RDF were found at par with each other and recorded significantly higher grain and stover yield of maize over rest of the treatments. Organic carbon status of soil was not influenced by addition of different levels of organic compost and inorganic fertilizer. However, available N, P2O5 and K2O in the soil after harvest of crop was found significantly higher with the application of 50% N through parthenium compost + 50% N through RDF and 50% N through vermicompost + 50% N through RDF.

A field experiment was conducted during 2002-03 and 2003-04 at Jabalpur to study the effect of three intercropping systems viz., maize (Zea mays L.) sole, maize + cowpea [Vigna unguiculata (L.)] for grain and maize + cowpea for fodder, two treatments of weed control viz., pendimethalin 1.0 kg/ha + 1 hand weeding at 30 DAS and weedy check, and three levels of nitrogen viz. 0, 50 and 100 kg N/ha on weed infestation and crop productivity. The total weed population at 60 DAS was significantly reduced by 36 and 32% under intercropping combinations of maize + cowpea (grain) and maize + cowpea (fodder), respectively as compared to sole crop of maize. The maize grain yield was at par (2969 kg/ha) in sole maize and maize + cowpea (grain). However, it was significantly reduced to 2225 kg/ha under maize + cowpea (fodder). The maize equivalent yield was higher under maize + cowpea (grain) treatment. The maize grain yield was significantly reduced under weedy check (2140 kg/ha). Increasing levels of N significantly increased the maize grain and maize equivalent yields. The uptake of N by weeds was significantly reduced under maize + cowpea intercropping combinations. The highest net monetary returns of Rs14547/ha and B: C ratio of 1.54 were obtained from maize + cowpea (grain) treatment

An experiment was conducted during rabi season of 2006-07 and 2007-08 to evaluate the effect of time of application on the efficacy of Combi (mixture of glyphosate 35% + 2,4-D 35%) and glyphosate alone against weeds particularly Paragrass (Brachiaria mutica) in noncropped area. All the herbicidal treatments had marked influence on the density, dry weight, shoot length and root length of Brachiaria mutica. Application of combinations 2.5 kg/ha during noon hours (12.00-14.00) totally killed Brachiaria mutica within 60 days in comparison of its evening and morning application as well as aplication of glyphosate alone at 2.0 and 2.5 kg/ha at the same time (noon), which took longer time ( 90 days) for total weed kill

In groundnut, glyphosate resistant plants (cul. TMV-2) were developed by over expressing pEGADEPSPS with altered kinetics of enzyme, which do not bind to glyphosate. Agrobacterium mediated in planta transformation adopted to develop transgenic groundnut lines expressing EPSPS. Single leaflet glyphosate induced chlorosis bioassay was standardized and used to assess the glyphosate resistance in groundnut transgenic lines of T1 and T2 generations. The T1 generation plants grown under transgenic housing facilities along with wild type and their relative tolerance analyzed by the leaf swabbing technique indicated the integration of the transgene in tolerant plants by PCR. The T2 generation plants screened for glyphosate resistance by swabbing 3000 ppm of glyphosate at 45 DAS observed that 30% of transgenic plants showed some degree of yellowing and leaf mortality and resistance confirmed by PCR. The chlorophyll degradation was less in transgenic and also maintained higher membrane integrity compared to wild type plant

Chlorophyll fluorescence has been used widely to detect the effect of herbicides in crops and weeds as it is a simple, sensitive and non-destructive method. Among the chlorophyll fluorescence parameters, maximum quantum efficiency, Fv/Fm, can be used to study the effects of herbicides as well as to monitor the development of herbicide resistance in weeds. In the present study, an attempt was made to assess the effectivity of sulfosulfuron, a sulfonylurea herbicide, in controlling Phalaris minor, a notorious weed of wheat crop in the Indo-Gangetic plains. Sulfosulfuron is very effective in controlling the isoproturon resistant population of P. minor. Differences in Fv/Fm values were observed among the control and treated plants within a week after treatment.

Soil microbial population in soil was suppressed due to application of metribuzin 0.35 kg/ha and fluchloralin 1.0 kg/ha, but simultaneous application of FYM (10 t/ha) supported the proliferation of microbial population. Bacterial population was significantly declined due to application of herbicides at 1st and 7th day of spraying, while fungal and actinomycetes population were significantly declined at 1st, 7th and 15th day of spraying. No significant change was observed in soil pH, electrical conductivity, available phosphorus and available potassium due to application of fluchloralin or metribuzin alone or with 10 t FYM/ha at harvest while nitrogen content was significantly changed. Total nitrogen content of the soil was significantly the highest in application of fluchloralin with FYM. Fluchloralin residues were gradually reduced with time. FYM application supported the fluchloralin decomposition.

Field experiment was conducted to study the effect of post emergence herbicide imazethapyr on weed infestation and yield of black gram variety (ADT 3) under rice fallow situation (relay cropping). The treatments consisted of three times (14, 21 and 28 days after sowing) of application in main plot and post emergence herbicide imazethpyr at 60, 75 and 90 g/ha and an absolute control formed the subplot treatments. The effect of imazethapyr on weed density, weed dry weight and weed control efficiency was at par when applied on either 21 or 28 DAS. Imazethapyr of 90 g/ha recorded lowest weed density and weed dry weight and was at par with that of 75 g/ha. Higher growth and yield attributes of black gram were associated with imazethpyr application on 21 DAS at 90 g/ha. The highest grain yield of 759 kg/ha was recorded under 21 DAS than other times of application of herbicide. Among the doses, application of imazethapyr at 90 g/ha registered significantly high grain yield (751 kg/ha) in comparison of other doses and control. The favorable economic benefits in terms of higher gross income, net income and benefit cost ratio was high by the application of imazethpayr at 90 g/ha on 21 DAS

Two field experiments were conducted at Chaudhary Charan Singh Haryana Agricultural University, Hisar during winter season of 2005-06 and 2006-07 to study the bioefficacy and phytotoxicity of herbicide UPH-206 (Clodinafop propargyl 15% + Metsulfuron 1%) for the control of complex weed flora in wheat (Triticum aestivum L.). Dominant grassy weeds, viz., little seed canary grass (Phalaris minor Retz.), wild oat (Avena ludoviciana and broadleaf weeds like common lambsquartres (Chenopodium album L.), yellow sweet clover (Melilotus indica All), golden dock (Rumex dentatus L.) and swine grass (Coronopus didymus L.) were effectively controlled by post emergence (35 DAS) application of UPH-206, a ready-mix formulation of clodinafop 15% + metsulfuron 1%) at 60 + 4 g /ha. Maximum grain yield (4890 and 4894 kg/ha) was obtained with the use of UPH-206 + S at 75+5 g/ha which were at par with weed free check and ready mixture of sulfosulfuron + metsulfuron and UPH 206 + S at 60 + 4 g/ha but significantly higher than clodinafop and sulfosulfuron. No carry over effect of this herbicide at any of doses tested was observed on succeeding sorghum crop

Terrestrial form of alligatorweed has been reported as a difficult weed to control by the herbicides due to heavy regrowth. No quantitative data is available on regrowth of alligatorweed after herbicides application except visual observations. Hence a comprehensive study was conducted in pot, plot and field conditions to evaluate the effect of three most recommended herbicides in context to superficial control and regrowth. After herbicide application, superficial control of alligator weed was achieved in pot, plot and field conditions but regrowth appeared from the no killed rhizomes. In pot experiment, hundred percent superficial control of alligatorweed at 15 DAA (days after application) was noticed with 2,4-D (2.5 and 3.5 kg/ha) and glyphosate (3.5 and 4.5 kg/ha) and by 20 DAA with metsulfuron-methyl (MSM) at 0.016 and 0.020 kg/ha. In plot experiment, 2,4-D (1.5 kg/ha) and glyphosate (2.0 kg/ha) caused almost 100 percent superficial killing at 10 and 15 DAA, respectively. MSM was most effective at 0.024 kg/ha, however, 0.020 kg/ha was at par with glyphosate (3.0 kg/ha) and 2,4-D (2.0 kg/ha). In plot experiment, little regrowth was noticed in higher doses of glyphosate, 2,4-D and MSM. Repeat application of same herbicides after 90 days of first application revealed no significant difference in regrowth at 30 DAA, however significant difference appeared at 60 and 90 DAA. Effect of MSM (0.020 kg/ha) was at par with higher dose of glyphosate (3.0 kg/ha) on regrowth after repeat application. In naturally infested area, no regrowth appeared in higher doses of glyphosate (3.5 and 4.0 kg/ha) up to 180 DAA, while glyphosate (3.0 kg/ha) and 2,4-D (2.5 kg/ha) were at par with MSM (0.020 kg/ha) at 360 DAA. This information may aid in the development of more effective management of alligatorweed by herbicide application.

Parthenium hysterophorus, a weed commonly known in India as congress grass was evaluated for its pulp and paper making properties. Studies on chemical constituents, fibre dimensions, unbleached, bleached yield and physical strength properties of pulp sheets were carried out. The proximate analysis of Parthenium hysterophorus showed that its plant material contained 78.0% holocellulose and 17.2% lignin. The pentosan was 15.8% and solubility in hot water and alcohol benzene was 11.25% and 5.89%. The unbleached pulp yield was 41.8% to 43.8% with varying alkali charge from 14-16% in soda cook. Kappa number was 27.2 to 30.2. Pulping pulp yield and kappa number decreased with the increase in alkali charge under the identical conditions. The pulp produced using 14% alkali charge had better strength properties as compare to pulp produced using 15% and 16% alkali charge. Laboratory handmade pulp sheets with adequate strength properties were obtained from soda pulp prepared from this plant material

Persistence of sulfosulfuron applied at 25 g/ha in rabi 2006-07 in wheat crop was determined in soil, wheat grains and straw. Soil samples treated with sulfosulfuron were collected at 1, 15, 30, 60, 90 and 120 days after herbicide application and were analyzed for herbicide residues. Wheat grains and straw were sampled at the time of harvest. HPLC coupled with PDA detector was used to detect sulfosulfuron residues. Sulfosulfuron degraded rapidly in soil and was not detected in soil, wheat grains and straw at harvest. Half-life of sulfosulfuron was found 14.40 days.

A field study was conducted in an inceptisol with rainy season rice to evaluate the effect of different tillage systems vis-à-vis different weed control measures on the survival and growth of total bacteria, actinomycetes, fungi, Rhizobium and Azotobacter in rhizosphere soil. Four types of tillage system were evaluated viz. (i) conventional-conventional (ii) conventional-zero (iii) zero-conventional and (iv) zero-zero tillage systems. Among weed control measures comparative effect of hand weeding and recommended herbicidal application (butachlor as pre emergence and fenoxaprop ethyl + ethoxysulfuron as post emergence) were tested along with a weedy check. The results of the investigation revealed that maximum growth of different microorganisms was observed in conventional-conventional tillage system, whereas minimum was in zero-zero tillage system. Pre emergence herbicide suppressed the microbial population between 0 to 10 days after emergence of plant (DAE), whereas post emergence herbicide inhibited the microbial population for a period of 10 days between 20 to 30 DAE. In weedy check, the microbial population was found significantly higher over other weed management practices in most of the cases.

Water hycienth is one of the worst weeds of water bodies in India. It is responsible for causing great loss to water by evapotranspiration besides blockage of water, loss to fish production and responsible for creating breeding sites for mosquitoes and other disease causing organisms. The host specific waterhyacinth weevils, Neochetina bruchi Hustache and N. eichhorniae Warner (Coleoptera: Curculionidae) are the most important biocontrol agents used against waterhyacinth with notable success in India. Bioagent if used alone takes longer time, hence integration of herbicide in the area of 15 to 25% of the weed mats at suitable interval is recommended. These herbicides may cause harmful effects on bioagent. Significant impact of herbicides was observed on the mortality of the weevils. When herbicide was sprayed on both the leaves and weevils, 3.3 % mortality was seen on all doses of glyphosate, paraquat and the lower (0.5x) dose of 2,4-D while higher dose (x) caused significantly high mortality of 20% by 24 hours. 2,4-D at a higher concentration caused 53% mortality followed by paraquat (50%) when herbicide was sprayed directly on weevils. Glyphosate caused the lowest mortality among the three herbicides tested

Lantana is an obnoxious weed in the pastures and forest land. The prospect of utilizing its huge biomass as an organic source of nutrient compared to Sesbania, wheat straw, mustard straw and chickpea straw was studied under submerged field conditions. These were chopped, taken in nylon mesh bags and then placed (0-10 cm) in a puddled field. One set of bags was dipped in butachlor solution (3000 ug/ml) prior to its placement in field. Three replicates of each treatment were taken out periodically and analysed for NPK and S content. The butachlor showed no effect on dry matter decomposition rate. The decomposition half-life of Lantana (26 d) was lower than that of wheat (45 d), mustard (41 d) and chickpea (34 d) straws and similar to Sesbania (26 d). Lantana was also superior to wheat, mustard and chickpea straws, and comparable to Sesbania in terms of NPS mineralization

25 field demonstrations were laid out during the rabi seasons of 2002-03 to 2004-05 in randomly selected two villages (Kushner and Chheri Boroda) adjoining to the National Reserach Centre for Weed Scienc, Jabalpur (Madhya Pradesh) with an objective to demonstrate the performance and profitability of zero tillage and herbicides on weed and productivity of wheat crop under rice-wheat system at farmers’ fields. Higher weed density and population of Phalaris minor were recorded in conventional tillage than zero tillage. Maximum reduction in weed density was obtained with the application of 2,4-D and isoproturon (500g + 750 g/ha) as tank mix under ZT and CT system. Higher average grain yield and monetary returns due to treatment were also achieved under zero tillage wheat with tank mixed application of 2,4-D and isoproturon as post emergence. Yield achieved in zero tillage was comparable to conventional tillage with clodinafop application.

Effect of different manually operated weeders on weeds and grain yield of maize was studied. Among the manually operated weeders evaluated, wheel hoe registered an yield increase of 154% over control, took lowest weeding time (71.43 hr/ha), covered maximum area with minimum cost of operation (Rs. 714/ha) on weeding twice on 25 and 45 DAS which was on par with pre-emergence application of atrazine 0.5 kg/ha on 3 DAS followed by hand weeding on 45 DAS.

Field studies conducted during kharif season 2003 at UAS, Dharwad revealed that post emergence application of imazethapyr 75 g/ha alone and with hand weeding was most effective in minimizing weed growth and enhancing the grain yield of soybean (Glycine max (L)). Although recommended soybean herbicides, viz., chlorimuron ethyl and pendimethalin reduced the dry weed bio-mass markedly compared with weedy plot both were found inferior to weed free check. Soybean grain yield due to weed free check was similar to that of imazethapyr 75 g/ha alone and with hand weeding and imazethapyr 100 g/ha fb HW. Crop phytotoxicity symptoms were not observed in soybean due to application of imazethapyr. Imazethapyr 75 g/ha was found also effective provided profitable and comparable with other treatments