Weed Science

Random amplified polymorphic DNA analysis (RAPD) was conducted on isoproturon susceptible and resistant Phalaris minor populations from different wheat growing states in India for assessment of population diversity. Nine isoproturon susceptible populations from different wheat growing locations in India and 10 resistant populations from different locations in Punjab and Haryana states were analysed. Eleven random primers were used for amplification of DNA. Dissimilarity values amongst biotypes ranged from 0.049 to 0.95 indicating high level of heterogeneity among these populations. Cluster tree analysis grouped the biotypes into three major groups. The resistant biotypes were observed in all the three groups indicating the evolution of resistance to isoproturon in the three groups independently. Some of the populations showed resemblance with each other by amplification of common fragments indicating their common origin and spread to other areas possibly by cultivation practices and crop seed.

Field and pot studies were carried out to evaluate the efficacy of tribenuron-methyl 75% PX (paste extruded) formulation used alone and tank mixed with grassy (field conditions) and broadleaf (screen house) herbicides during 2006-07 and 2007-08 at CCS Haryana Agricultural University, Hisar. Tribenuron 15 g/ha was effective against Chenopodium album under field conditions and provided 85-88% control. Increasing the dose from 15 to 30 g/ha or to 45 g/ha further increased control of C. album, but the effect was similar at higher rates. Adding a non-ionic surfactant (0.2%) increased the efficacy of tribenuron compared to no surfactant. 2,4-D ester/ amine 500 g/ha or Sodium salt 1000 g/ha provided 100% control of C. album and the mortality was similar to premix of mesosulfuron+iodosulfuron (Atlantis) 21.6 and 14.4 g/ha, premix of sulfosulfuron+metsulfuron (Total) 16 g/ha, metsulfuron-methyl 4 g/ha or higher rates of tribenuron (26.25, 30 and 45 g/ha with and without surfactant). Tribenuron had no adverse effect on wheat upto 45 g/ha and no residual phytotoxicity was observed on mungbean or sorghum planted after wheat harvest. Effect of carfentrazone 20 g/ha and tribenuron 15 g/ha was similar against C. album but lower than other treatments. All broadleaf herbicides provided significantly higher yield compared to weedy plots, but were inferior to pre- or tank-mix applications of grassy and broadleaf herbicides. Atlantis 21.6 g/ha was phytotoxic to wheat and significantly checked plant growth and produced lower yield than 14.4 g/ha application rate. Tank mix applications of pinoxaden 45 g/ha and clodinafop 60 g/ha with tribenuron 15 g/ha produced highest yield and yield attributes of wheat. Under pot studies, tribenuron 15 g/ha, carfentrazone 20 g/ha, metsulfuron 4 g/ha, 2,4-D ester 250 g/ha and their tank mix combinations were compared with 2,4-D 500 g/ha against Anagallis arvensis, Asphodelus tenuifolius, Chenopodium album, C. murale, Lathyrus aphaca, Melilotus indica. Malva parviflora, Medicago denticulata, Rumex dentatus, R. spinosus, Silene conoidea, Sisymbrium irio and Vicia sativa. Tribenuron 15 g/ha provided 73 to 100% control of A. arvensis, A. tenuifolius, M. denticulata, V. sativa, C. murale, R. spinosus, R. dentatus, C. album, S. irio and S. conoidea, but it was not effective against M. parviflora and L. aphaca. Effect was also lower on M. indica, but tank mix applications with carfentrazone/2,4-D or metsulfuron improved its control by 15 to 25%. The overall weed mortality by tribenuron was similar to that of carfentrazone, but better than 2,4-D 250 g/ha, though the effect was significantly less than metsulfuron or 2,4-D 500 g/ha. Tank mixing of carfentrazone with metsulfuron inflicted maximum weed mortality (data averaged over species), but it was statistically similar to all other mixtures except carfentrazone plus 2,4-D 250 g/ha which has significantly less weed mortality. Similar trend was recorded in fresh weight accumulation by weeds with different treatments. L. aphaca and M. parviflora were most difficult-to-control weeds, whereas S. conoidea and S. irio were most susceptible weeds (data averaged over herbicide treatments). Tribenuron 15 g/ha had no significant edge over metsulfuron 4 g/ha against any of the test species in the screen house, though in tank mix applications with pinoxaden and clodinafop it produced similar yield compared to recommended field herbicides, with the advantage of no residual toxicity on succeeding sensitive crops.

A field experiment was conducted at experimental farm of the Department of Agronomy, Punjab Agricultural University, Ludhiana (Punjab) during rabi seasons of 2004-05 and 2005-06 to study the effect of rice residue management techniques and weed control treatments on the growth and development of Phalaris minor and wheat. The studies revealed that surface placement of rice residues at 6 and 7 t/ha significantly reduced the dry matter accumulation and nutrient uptake by P. minor as compared to incorporation and no rice residue treatments. Grain yield and nutrient uptake by wheat were statistically similar in all rice residue management techniques. Post-emergence application of clodinafop 60 g/ha, sulfosulfuron 25 g/ha and mesosulfuron + iodosulfuron 14.4 g/ha significantly reduced the dry matter accumulation and nutrient uptake by P. minor as compared to control (unweeded). Consequently, all the herbicidal treatments recorded significantly higher grain yield and nutrient uptake by wheat as compared to control treatment.

A field experiment was initiated in 2000-01 at Varanasi Centre of AICRP on Cropping Systems to study the effect of diversification of rice-wheat system on weed dynamics in rice. The results of 2002-03 and 2003-04 i. e. 3rd and 4th year of study revealed that diversification of rice-wheat system through inclusion of greengram in summer, though remained at par to sequences involving summer cowpea for fodder or Sesbania for green manuring, resulted in significantly lowest population of grasses and sedges in 2003-04 and weed dry matter production in both the years. However, the different cropping sequences failed to affect broadleaf weeds population. Similarly, sequences having grain/fodder legume or Sesbania for green manuring produced higher grain and straw yield than rice-wheat sequence. Nevertheless, the differences were significant only in 2003-04 during which rice-wheat-Sesbania though remained at par with rice-wheat-greengram, rice-lentil+mustard (3 : 1)-cowpea, rice-maize+pea (1 : 1)-cowpea and rice-potato-greengram produced significantly higher grain yield than other sequences and registered 14.5% higher grain yield than rice-wheat sequence.

Azimsulfuron was evaluated for its efficacy in controlling mixed weed flora in transplanted rice at HAU Regional Research Station, Karnal, India. Density and dry weight of grassy weeds in the plots treated with azimsulfuron were higher than pretilachlor 1000 g/ha except azimsulfuron 30 g/ha applied at 15 days after transplanting (DAT). Density of broadleaf weeds was significantly lower under all azimsulfuron doses when applied at 15 DAT compared to 25 DAT. All the treatments of azimsulfuron (10-30 g/ha at 15 and 25 DAT) provided excellent control of sedges, which were significantly better than pretilachlor and were as good as weed free check. Yields under azimsulfuron 30 g/ha at 15 DAT during 2006, and 27.5 and 30 g/ha at 15 DAT and 30 g/ha at 25 DAT during 2007 were statistically at par with pretilachlor. There was no phyto-toxicity of azimsulfuron on rice and also there was no residual toxicity on the succeeding crop of wheat during both the years of experimentation.

Field studies were conducted to evaluate the competing ability of weeds with different rice varieties in relation to variable plant populations. Rice variety PR 108 exhibited greater smothering effect on weeds but PR 118 obtained maximum grain yield as compared to PR 108, PR 114 and PR 116 grown under puddled transplanted conditions. The plant population of 50 plants/m2 was found to be significantly superiror to 33 and 25 plants/m2 as it recorded significantly less weed dry matter and highest grain yield compared to other population levels. Application of pretilachlor at 0.75 kg/ha as pre-emergence proved to be very effective in reducing weed dry matter and increasing grain yield upto a significant level as compared to unweeded check

Penoxsulam was evaluated against complex weed flora both as pre-emergence as well as postemergence herbicide in transplanted rice during kharif 2005 and 2006 at Karnal, Haryana, India. Echinochloa crusgalli, E. colona, Ammania baccifera, Euphorbia sp., Fimbristylis miliaceae and Cyperus sp. were the major weeds. Penoxsulam at 25.0 g/ha as pre-emergence (3 DAT) application and 20.0-22.5 g/ha as post-emergence (10-12 DAT) application provided satisfactory control of weeds consequently resulting in grain yield of transplanted rice similar to the weed free plots. There was no residual toxicity of penoxsulam on succeeding crop of wheat

A field experiment was conducted during the kharif seasons of 2005 and 2006 at the research farm of Uttar Banga Krishi Viswavidyalaya with the objectives to study weed dynamics and yield reduction due to weedcrop competition as well as to determine critical period of crop-weed competition in transplanted and wet seeded rainfed rice. Ten treatments comprising weedy condition for first 20 days after transplanting (DAT)/15 days after sowing (DAS) then weed free, first 40 DAT/30 DAS then weed free, first 60 DAT/45 DAS then weed free, first 80 DAT/60 DAS then weed free, weed free condition for first 20 DAT/15 DAS then weedy, first 40 DAT/30 DAS then weedy, first 60 DAT/45 DAS then weedy, first 80 DAT/60 DAS then weedy, season long weed free and complete weedy conditions were tested in randomized block design with three replications for transplanted/wet seeded rice, respectively. Among the weeds appeared in transplanted rice, the broadleaved weeds Monochoria hastata, Ludwigia parviflora and Nymphoides indicum and grass weed Echinochloa crusgalli were dominant and aggressive because of their long emergence profile. In wet seeded rice field, the broadleaved weeds Monochoria hastata, Ludwigia perennis and the sedges Cyperus flavidus, Cyperus difformis, Fimbristylis miliacea, Scirpus juncoides and grass Cynodon dactylon were aggressive and continuously emerged throughout the crop growth. Critical period of weed-crop competition in transplanted and wet seeded rice was from 20 to 40 DAT and 15 to 60 DAS, respectively. Weedy situation throughout the crop growth caused yield reduction to the tune of 57 to 61% in case of transplanted rice and 64 to 66% in case of wet seeded rice in comparison to season long weed free situation

An experiment was conducted consecutively during kharif 2005, 2006 and 2007 at Regional Agricultural Research Station, Lam Farm, Guntur, Andhra Pradesh to evolve suitable integrated weed management technique for direct-seeded semi dry rice. Results indicated that all the treatments with hand weeding and herbicide integration were found to be superior to alone application of herbicides in reducing weed growth and increasing rice grain yields. Among the integrated treatments, pre-emergence application of pendimethalin at 1.0 kg/ha integrated with one hand weeding at 30 days after sowing (DAS) recorded the lowest weed growth and highest grain yield and was at par with all other treatments with hand weeding and herbicide integration. Pretilachlor 750 g/ha followed by one hand weeding at 30 DAS and pendimethalin 1.0 kg/ha followed by one hand weeding were the cheapest integrated weed management treatments that recorded highest grain yield of semi dryseeded rice

An experiment was conducted at University Seed Farm, Kapurthala during 2006 and 2007 to find out performance of few pre- and post-emergence herbicides in dry seeded rice. During 2006, pre-emergence application of pendimethalin 0.75 kg/ha followed by one hand weeding produced highest seed yield (4049 kg/ha) which was at par with post-emergence application of bispyribac (Nominee gold 10 SC) 30 g/ha (3554 kg/ha). During 2007, significantly higher yield was obtained with the integration of pre-emergence pendimethalin 0.75 kg/ha with postemergence application of bispyribac 25 g/ha (5016 kg/ha).

To tackle the serious problems of weeds in dry direct-seeded rice (DSR), a field experiment was conducted on loamy sand soil at Ludhiana, Punjab during 2006 and 2007 with an objective to identify effective herbicides for the control of complex weed flora of DSR. It is difficult to raise weed free DSR with the application of only one herbicide. Integration of pre-emergence application of pendimethalin 0.75 kg/ha followed by post-emergence (30 DAS) application of bispyribac 25 g/ha or azimsulfuron 20 g/ha or 2,4-D 500 g/ha resulted in effective weed control and higher rice grain yields. Pendimethalin pre-emergence application provided effective control of non-predominant paddy weeds, whereas bispyribac controlled all typical predominant paddy weeds including Echinochloa colona and all Cyperus species. Azimsulfuron or 2, 4-D was effective against all Cyperus spp. and broad-leaved weeds. Integration of pre-emergence application of pendimethalin 0.75 kg/ha with post-emergence application of bispyribac 25 g/ha resulted in 372% increase in rice grain yield as compared to unweeded control

Field experiments were conducted during rabi 2002-03 and 2004-05 at the Regional Agricultural Research Station, Lam, Guntur, Andhra Pradesh to study the optimum time and dose of post-emergence herbicides for Echinochloa spp. control in blackgram grown as relay crop. Results indicated that all the post-emergence herbicides like fenoxaprop-P-ethyl, clodinafop-propargyl and cyhalofop-butyl significantly reduced Echinochloa colona growth and increased blackgram yield by 27 to 42% over weedy check without any crop injury. Among different herbicides and their doses, fenoxaprop 68 g/ha recorded the highest seed yield (1332 kg/ha) and net monetary returns (Rs. 21,993/ha) and B : C ratio of 1.95 and was on par with its lower dose (56 g/ha). Herbicide application at 21 and 28 days after sowing (DAS) resulted in significantly higher reduction in Echinochloa colona density at 20 and 40 days after treatment (DAT) and total weed dry weight compared to its application at 14 DAS. However, blackgram seed yield did not differ significantly due to the time of herbicide application

A field experiment was conducted during the winter (rabi) seasons of 2003-04, 2004-05 and 2005-06 to assess the efficacy of pendimethalin, trifluralin and linuron in chickpea (Cicer arietinum) at Punjab Agricultural University Regional Station, Bathinda under irrigated conditions. All the herbicidal treatments reduced the dry matter of weeds significantly than weedy check. Pre-emergence application of pendimethalin at 0.75 kg/ha had minimum dry weight of weeds than other herbicidal treatments. Pendimethalin at 0.75 kg/ha was most effective in enhancing the yield attributes and resulted in maximum grain yield (1507 kg/ha). Amongst different weed control treatments, an application of pendimethalin at 0.75 kg/ha recorded the maximum net return (Rs. 11,149/ha) and benefit : cost ratio (1.43) followed by pendimethalin at 1.0 kg/ha.

Malva neglecta is a winter season weed and its seeds can germinate in Petri dish at a temperature range of 10-30°C but maximum seed germination was observed at 20°C in case of fresh, one season old and two seasons old seeds under scarified and unscarified seed conditions. Two seasons old weed seeds showed higher germination percentage as compared to one season old seeds followed by fresh seeds. Unscarified seeds showed significantly lower germination in comparison to scarified seeds at all temperatures in fresh, one season and two seasons old weed seeds. In pot experiment, weed seedlings emergence, height of weed plants, number of branches produced per plant and dry matter accumulation by weed showed an increasing trend with increase in ponding duration during preceding summer season. Least weed emergence and growth of weed was recorded in pots kept dry throughout the summer season and maximum weed emergence and growth was observed where ponding of water during summer months remained for four weeks followed by continuous moist throughout the season

Pot studies were carried out in the screen house for three years (2006-07 to 2008-09) to assess the role of seeding depth and flooding durations on the emergence of Malva parviflora, Rumex dentatus and R. spinosus. Seeding depths of 0, 0.5, 1, 2, 4, 8 and 16 cm and flooding durations of 0, 5, 10, 20, 40 and 80 days were maintained with three replications. Maximum emergence was recorded from 1 cm depth which significantly decreased with increasing depths of 4 cm and higher, data averaged over species. Emergence of R. spinosus was significantly more compared to M. parviflora and R. dentatus from deeper depths. R. dentatus emergence was significantly reduced at 2 cm depth and there was no emergence beyond 4 cm unlike R. spinosus which was able to emerge even from 16 cm, though in reduced numbers. M. parviflora emergence was significantly reduced at 0, 4 and 8 cm, and had no emergence from 16 cm depth. Both species of Rumex showed good emergence when the seed was placed on soil surface (0 cm depth), though emergence was significantly less for M. parviflora compared to 0.5 to 2 cm depths. Flooding encouraged M. parviflora emergence, but inhibited R. spinosus and had no significant reduction in the emergence of R. dentatus except 40 days flooding. Increasing the flooding duration from 0 to 80 days increased the emergence of M. parviflora from 37 to 67%, whereas five days flooding period decreased emergence of R. spinosus by 54% compared to no flooding and no emergence was recorded after 40 days flooding. On the other hand, a flooding duration of 80 days resulted in lowering the emergence of R. dentatus by 46% only. The emergence and growth of R. dentatus was not suppressed by flooding duration except 80 days period. All the three species behaved uniquely to seeding depths and flooding durations and need characteristically different strategies for their management under field infestations. The greater propensity of R. dentatus to emerge from shallow depths can be exploited by tillage manipulations. Allowing the seed on the surface after crop harvest for its predation, greater emergence in the next growing season from surface and its killing by pre-seeding herbicide application or tillage can lower the soil seed bank. Placing seed deeper than 4 cm by tillage operations will also render the seed to lower and delayed emergence posing no competition to crops. Similarly, lower emergence of M. parviflora from surface and susceptibility of R. spinosus to flooding can be exploited to lower their menace.

A field experiment was conducted during rabi seasons of 2002-03 and 2003-04 at College Farm, Gwalior to evaluate the performance of some weed management practices in potato. Results showed that herbicide prometryne 1.0 kg/ha PE was more effective to control the weeds. The next best treatments were pendimethalin 1.0 kg/ha PE and two hand weedings