Crops, economics, herbicides, India, integrated weed management, non-chemical

Integrated weed management (IWM) is a science-based decision-making process that coordinates the use of macro and micro-environment information, weed biology and ecology, and all available technologies to control weeds by the most economical and ecologically viable methods. The concept of IWM is not new and many advances have been made in recent years in India. The IWM research carried out in India during the last 20 years is reviewed in this paper. Limited ecological studies were carried out on certain problematic weeds. Majority of the research in India on IWM was herbicide-based. Economic analysis revealed that herbicides use in combination with hand weeding was most economical. Weeds are dynamic and it is required to redesign the strategies from time to time for the successful management of ever increasing problem of weeds. IWM research in India must broaden beyond herbicide-centred weed management. Future IWM research in India must focus on decision-making processes, weed biology and ecology, environmentally and economically viable components of IWM practices in cropping systems, herbicide resistance, environmental issues related to transgenic plants, and potential benefits of weeds.

Clodinafop-propargyl, fenoxaprop-P-ethyl, ion efflux, photosynthetic pigments, Phalaris minor,  pinoxaden

Impact of aryloxyphenoxypropionate herbicides used since 1998 to control Phalaris minor in Haryana was evaluated during 2008-09 and 2009-10 under screen house conditions.  Most of the populations evaluated against fenoxaprop-P-ethyl and clodinafop-propargyl exhibited either a high or a medium level of resistance in 2008-09. Similar results were obtained for clodinafop in 2009-10. Some of the populations were also susceptible to fenoxaprop (120 g/ha) indicating segregation of alleles for the resistant and susceptible traits as homozygous as well as heterozygous individuals in the progeny.  Most of the populations were susceptible to phenylpyrazolin derivative- pinoxaden used at 25, 50 and 100 g/ha. However, a fraction of the populations exhibited insensitivity towards pinoxaden without any prior history of exposure. The data are supported by GR50 values, ion efflux tests and pigment retention tests. Selection pressure exerted by the aryloxyphenoxypropionate and/or urea herbicides could possibly be responsible for such an effect. Bioassay methods need to be developed for location specific identification of the resistance to herbicides and their early management.

Growth stages, herbicide efficacy, resistance, management

Pot studies were carried out at Agronomy Research Farm of CCSHAU, Hisar during the rabi seasons of 2005-06, 2006-07 and 2007-08 using isoproturon resistant, susceptible and pristine populations of Phalaris minor. Ten herbicides (isoproturon, chlorotoluron, sulfosulfuron, clodinafop-propargyl, fenoxaprop-P-ethyl, quizalofop-ethyl, premix of mesosulfuron-methyl+iodosulfuron-methyl-sodium, sulfosulfuron+metsulfuron-methyl, pinoxaden and tank mix of pinoxaden+carfentrazone-ethyl) were applied at two growth stages (4 leaf and tillering) of five P. minor populations [J-35 (Jind), F-42 (Fatehabad), K-15 (Karnal), H-2 (Hisar) from Haryana and B-6 (Bihar)] using three application rates by a knapsack sprayer fitted with flat fan multi nozzle boom delivering 500 l water/ha.  The pots were arranged in a CRD design with three replicated earthen pots for each herbicide treatment and populations.  Plant height, weed mortality and fresh/dry weight were recorded to evaluate herbicides effect on P. minor populations. When combined data were analyzed, no significant interaction of weed stage, populations and herbicides was observed for per cent mortality and dry weight, whereas highly significant effect of weed stage, populations and herbicides was recorded.  There was significant interaction of populations and herbicides for mortality data.  Significant interaction for stage, dose and herbicides was recorded when data for each population at two growth stages were subjected to ANOVA, which shows large variations among populations to different herbicides.  P. minor populations, J-35 and K-15 had significantly lower mortality and higher dry weight, data averaged over herbicides, compared to B-6 and H-2, whereas F-42 was intermediate in mortality and accumulated higher dry weight compared to B-6 and H-2. Among the herbicides, lowest mortality was recorded with clodinafop and isoproturon followed by fenoxaprop and quizalofop, whereas highest mortality was recorded with pinoxaden tank mixed with carfentrazone and its alone application followed by chlorotoluron and mesosulfuron+iodosulfuron. Sulfosulfuron alone and premix with metsulfuron had lower mortality compared to pinoxaden±carfentrazone and chlorotoluron.  Similar results were recorded for dry weight also.  Delayed application from 4 leaf to tillering stage lowered the mortality of sulfosulfuron±metsulfuron, mesosulfuron+iodosulfuron, isoproturon and chlorotoluron.  The GR50 (growth reduction by 50%) of herbicides increased with stage of herbicide application; increase was more in isoproturon and clodinafop compared to other herbicides. Populations, K-15 and J-35 had resistance factor (Rf) of 10.85 and 4.91 for isoproturon and 1.70 and 1.25 for clodinafop, respectively, when applied at tillering stage compared to H-2 population. Some variations were also observed in GR50 with other herbicides, but not reflected in dry weight. The study indicated ensuing problems with clodinafop, fenoxaprop and even sulfosulfuron, but there was no loss of efficacy with pinoxaden±carfentrazone or chlorotoluron.

Carfentrazone, sulfosulfuron, surfactant, weed control, wheat

Carfentrazone-ethyl 20%+sulfosulfuron 25% WDG (Premix) was evaluated against mixed weed flora in wheat during rabi seasons of 2008-09 and 2009-10 at the Research Farm of Department of Agronomy, Punjab Agricultural University, Ludhiana. The experimental field was heavily infested with Phalaris minor and broadleaf weeds. Among the herbicidal treatments, post-emergence application (30-35 DAS) of premix herbicide i. e. carfentrazone + sulfosulfuron at 36, 45 and 54 g/ha either with 625 ml or 750 ml/ha of surfactants performed at par with the recommended herbicides i. e. Leader 75 WG (sulfosulfuron) at 25 g/ha and Total 75 WG (sulfosulfuron + metsulfuron) with respect to reduction in dry matter accumulation by P. minor as well as broadleaf weeds and production of grain yield of wheat. The bioefficacy of carfentrazone+sulfosulfuron at 45 g/ha without surfactant was found to be less as compared to its application with surfactants. Higher dose of this formulated herbicide i. e. 54 g/ha was more effective than its lower levels. Also alone application of carfentrazone 20 g/ha as well as unweeded (control) treatment produced significantly higher dry matter of P. minor and less grain yield as compared to all the herbicidal treatments.

Seed production, weed management, wheat, seed quality, cost

A field experiment was carried out at Research Farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, West Bengal during winter (rabi) seasons of 2007-08 and 2008-09 to study the efficacy of different weed management practices on economical, quality wheat (variety PBW 343) seed production. Uncontrolled weeds reduced the wheat seed yield upto 34%. Highest wheat seed yield was observed with two manual weedings followed by hoeing (dutch hoe) + isoguard plus, due to effective weed control.  Despite of additional cost for weed management, all the weed management treatments resulted in additional wheat seed production and additional benefit. Wheat seed produced by weed management in wheat with hoeing at 21 DAS + isoguard plus 1250 g/ha or metribuzin 175 g/ha at 28 DAS showed high vigour in seedling parameters though other treatments were also better than weedy check and seed of local farmers’ field.

Herbicide, Phalaris minor, residue management, weed control, wheat

There is lack of information on the effects of rice residue position and load on the growth and development of Phalaris minor Retz. and the efficacy of different herbicides in wheat under different rice residue management situations. The studies revealed that surface application of rice residues @ 6 and 7 t/ha significantly reduced the growth and development of P. minor and recorded higher weed control efficiency as compared to incorporation and no rice residue treatments. Application of rice residues @ 6 and 7 t/ha also significantly reduced the emergence of wheat seedlings as compared to rice residue incorporation and no rice residue treatments.  Wheat growth parameters, yield attributes, grain and biological yield were statistically at par in all the rice residue management techniques. Application of clodinafop 60 g/ha, sulfosulfuron 25 g/ha and mesosulfuron + iodosulfuron 14.4 g/ha significantly reduced the growth and development of P. minor and registered higher weed control efficiency as compared to unweeded control. Consequently, all the herbicidal treatments recorded significantly higher wheat growth parameters, yield attributes, grain and biological yield as compared to unweeded control treatment.

Direct seeded rice, weed management, azimsulfuron, broadleaf weeds, sedges

Field experiments were conducted at Karnal (Haryana) and Pusa (Bihar) during kharif 2006 to assess efficacy of azimsulfuron alone and in combination with ready mix of metsulfuron+chlorimuron (almix)  applied to the dry direct seeded rice (DSR) crop. Azimsulfuron at 25-30 g/ha applied 25 days after sowing controlled effectively broadleaf weeds and sedges especially Cyperus rotundus in DSR but failed to control grasses.Tank mixing of almix did not improve efficacy of azimsulfuron for the control of grasses, sedges or broadleaf weeds across the locations. Azimsulfuron alone or tank mixed with almix was not effective against grasses. On an average, uncontrolled weeds reduced the grain and straw yield of rice by 42 and 46%, respectively. Azimsulfuron applied alone or in tank mixed with almix and pre-emergence application of pendimethalin followed by almix had no toxicity in rice cultivar HBC-119 but phytotoxicity was observed in rice cultivar Rajshree at Pusa with higher doses of azimsulfuron.

Green manuring, non-chemical methods, stale seedbed, weed management, wet seeded rice

Experiments to compare different seedbed techniques and non-chemical methods in wet seeded rice were conducted during 2005-06 and 2006-07.  The trials were laid out in a split plot design with three main plots, five sub-plots and three replications.  Adopting stale seedbed technique either for 7 or 14 days significantly reduced the population of grass weeds. It gave successful control of broadleaf weeds too. Among the weed management treatments, pre-emergence spraying of (Sofit) pretilachlor+safener and concurrent growing of sesbania gave significant reduction in the population and dry weight of weeds.  Pretilachlor spray exhibited the greatest influence on broadleaf weeds.  Stale seedbed preparation significantly improved grain and straw yields of wet seeded rice compared to normal seedbed.  An increase in stale seedbed period contributed to corresponding increase in yields as evident by higher grain and straw yields in plots with stale seedbed for 14 days.  Among the weed control treatments tried, pretilachlor+safener sprayed and hand weeded plots gave higher yields.

Aerobic rice, integrated weed management, economics

A field experiment was conducted during kharif 2009 at Zonal Agricultural Research Station, V. C. Farm, Mandya, Karnataka. The  experiment consisted of  12 treatments laid out in randomized complete block design with three replications consisting of four pre-emergence herbicides integrated with one intercultivation at 40 days after sowing, hand weeding twice at 20 and 40 days after sowing, intercultivation thrice at 20, 40 and 60 days after sowing compared with weed free and unweeded check. The predominant weed flora observed in the experimental field were Echinochloa colonum, Digitaria marginata, Ageratum conyzoides, Spilanthus acmella, Commelina benghalensis, Celosia argentia, Cyperus iria and Cyperus rotundus. The results revealed that pre-emergence application of bensulfuron methyl+pretilachlor (6.6 GR) @ 0.06+0.60 kg/ha+one intercultivation at 40 days after sowing recorded significantly higher grain and straw yield (4425 and 5020 kg/ha, respectively), lower weed population and their dry weight (17.0 g and 2.32 g 0.25/m2, respectively). Further the net returns and B : C ratio were also high with the pre-emergence application of bensulfuron methyl + pretilachlor (6.6 GR) @ 0.06 + 0.60 kg/ha+one intercultivation at 40 days after sowing.

Green cob yield, planting pattern, plant population, sweet corn, weed control practices

A field experiment was conducted during the Rabi 2004-05 and 2005-06 to study the effect of planting pattern and weed conrol practices on weed dynamics and productivity of sweet corn. Planting pattern of 60 x 20 cm with 83,333 plants/ha proved to be very effective in suppressing weeds, recording the lowest density of grasses, sedges and broad-leaved weeds at 30 and 45 days after sowing (DAS). At harvest also, it resulted in the lowest total weed density, weed dry weight with the highest weed control efficiency (WCE) and was at par with 75 x 16 cm. These two planting patterns were found to be significantly superior to 60 x 25 cm and 75 x 20 cm with 66,666 plants/ha. Though the highest cob length and green cob weight of sweet corn were realized with 60 x 25 cm, the green cob (13.9 and 13.2 t/ha) and green fodder yield (17.6 and 16.6 t/ha) were found to be the highest with 60 x 20 cm and resulted in higher net returns (Rs. 24, 987 and 23,024/ha). Pre-emergence application of atrazine @ 1 kg/ha followed by (fb) hand weeding at 30 DAS provided significant weed control during the citical crop-weed competition period in sweet corn upto 45 DAS. It also recorded the lowest total weed density and dry weight with the highest weed control efficiency at harvest, which resulted in the highest green cob yield (14.2 and 13.4 t/ha) and green fodder yield (18.0 and 17.1 t/ha) of sweet corn with enhanced net returns (Rs. 25,251 and 23,221/ha) and B : C ratio, though at par with two hand weedings at 15 and 30 DAS and pre-emergence application of atrazine @ 1 kg/ha fb post-emergence application of paraquat @ 0.5 kg/ha at 30 DAS. Uncontrolled weed growth throughout the crop growth period reduced the green cob yield to an extent to 40-42% during both the years of experiment.

Cyperus rotundus, herbicide, maize, 2, 4-D

Cyperus rotundus is a troublesome perennial weed of kharif season. In maize, it is not controlled with the already recommended herbicide i. e. atrazine 50 WP. All the three formulations of 2,4-D i. e. sodium, di-methyl amine and ethyl ester were applied as post-emergence on C. rotundus infested crop of maize from 2007 to 2009 as blanket spray after the pre-emergence application (20-25 DAS) of atrazine 1.0 kg/ha. Out of the three formulations, post-emergence application of 2,4-D di-methyl amine at 0.44, 0.58 and 0.73 kg/ha was found more effective for controlling C. rotundus as compared to other formulations i. e. sodium and ethyl ester. All the three formulations showed no adverse effect on plant growth and produced grain yield of maize statistically similar to each other. On an average of three years, post-emergence application of 2,4-D di-methyl amine at 0.44, 0.58 and 0.73 kg/ha increased maize grain yield significantly over unweeded control and all these treatments produced 23.8, 31.1 and 26.7% higher yield than unweeded control treatment, respectively.

Herbicides, Phalaris minor, tank-mix combinations, weed control, wheat 

A field experiment was conducted at CCS Haryana Agricultural University Regional Research Station, Karnal during rabi 2006-07 and 2007-08 to evaluate the efficacy of tank-mix combinations of different herbicides against Phalaris minor in wheat. The experimental field was dominated mainly by grassy weed P. minor Retz. The major weeds among broad-leaved weeds (BLW) were Coronopus didymus L., Anagallis arvensis L., Melilotus indica All. Fl. Ped., Medicago denticulata L., Rumex dentatus L., Vicia sativa L. and Lathyrus aphaca L. Intra-group combinations of herbicides viz., ACCase inhibitor (clodinafop/fenoxaprop/pinoxaden) with ACCase inhibitor and ALS inhibitor (sulfosulfuron/ mesosulfuron+iodosulfuron) with ALS inhibitor were compatible and resulted in very effective control of P. minor and consequently yields of wheat (5552-5861 kg/ha in 2006-07 and 5510-5897 kg/ha in 2007-08) were comparable to weed free checks (5909 kg/ha in 2006-07 and 5850 kg/ha in 2007-08). While inter-group combinations (clodinafop/fenoxaprop/pinoxaden with sulfosulfuron/mesosulfuron+iodosulfuron) were not found compatible and resulted in lower control of P. minor with lower yields (5054-5239 kg/ha in 2006-07 and 4285-4976 kg/ha in 2007-08). Alone application and all combinations having sulfosulfuron or mesosulfuron + iodosulfuron provided good control of BLW even under inter-group combinations. There was no phyto-toxicity of any of the herbicidal treatments on wheat, except some recoverable symptoms under treatments having mesosulfuron+iodosulfuron during 2007-08

Garlic, weed, bulb yield, bioassay

A field experiment was carried out during the Rabi seasons of the years 2007-08 and 2008-09 at Junagadh (Gujarat) to study the effect of some herbicides for weed management in garlic and their persistence. The results indicated that all the treatments reduced the density and dry weight of weeds and increased yield and yield attributes significantly over unweeded check. A pre-emergence application of oxyfluorfen 240 g/ha showed its effect on indicator plants like sorghum and cucumber. Effect of oxadiargyl 90 g/ha was observed on cucumber at 30 DAS which disappeared at 60 DAS. Post-emergence application of oxadiargyl 90 g/ha, quizalofop-ethyl 40 g/ha and fenoxaprop-p-ethyl 75 g/ha made at 60 DAS did no show persistence effect on sorghum and cucumber at 90 DAS. Similarly, post-harvest study on succeeding crops of groundnut, greengram and pearl millet indicated that there was no residual phytotoxic effect of either pre- or post-emergence herbicides tested in the experiment.

Temperature, salinity, osmotic potential, light, seeding depth, flooding, management

Laboratory and screen house experiments were conducted to evaluate the effect of temperature, salinity, osmotic potential, light/dark periods, seeding depth and flooding on germination of Convolvulus arvensis and Lathyrus aphaca. Maximum germination of C. arvensis (41%) and L. aphaca (91%) was recorded at 20°C which decreased with any increase or decrease from optimum temperature. C. arvensis and L. aphaca had maximum germination with distilled water compared with salt solution. C. arvensis and L. aphaca germination was 20 and 55%, respectively, at 200 mM NaCl conc. Osmotic potential of -0.8 MPa reduced the germination of C. arvensis to zero, whereas 3% L. aphaca germinated at this stress. Light was not pre-requisite for the germination of these weed species. Optimum depth for the germination of C. arvensis and L. aphaca was 1.0 cm where corresponding germination was 40 and 79%, respectively. Reduction in germination and growth was recorded with increase and decrease from the optimum depth. L. aphaca was able to germinate and emerge from higher depths of 8.0 cm. Tolerance towards flooding was significant for both species as C. arvensis tolerated 20 days of flooding, whereas L. aphaca germinated (17%) after 40 days of flooding and 2% after 80 days of flooding. These factors can be exploited for their management.

Sunflower, planting pattern, weed management, weed flora, yield

A field study was undertaken, at S.V. Agricultural College, Tirupati during the Rabi seasons of 2002 and 2003 to identify effective and economical weed management options for sunflower by studying the effect of planting pattern and weed management practices on weed flora and seed yield of Rabi sunflower. Planting pattern of 45 x 30 cm recorded significantly lower weed density and biomass thus resulting in higher seed yield over 60 x 22.5 cm. Among the weed management practices, the lowest density and biomass of weeds at harvest were recorded with hand weeding (HW) twice closely followed by fluchloralin at 0.5 kg/ha+ pendimethalin at 0.5 kg/ha supplemented with one HW at 40 DAS. However, sunflower seed yield was the highest with HW twice followed by application of pendimethalin at 1.0 kg/ha.  The use of planting pattern of 45 x 30 cm and managing associated weeds with HW twice at 20 and 40 DAS or pre-emergence application of pendimethalin at 1.0 kg/ha resulted in higher net returns and seed yield of irrigated Rabi sunflower.

Bacteria, fungi, actinomycetes, 2, 4-DEE, butachlor, pretilachlor, pyrazosulfuron ethyl

Herbicides being biologically active compounds, an unintended consequence of the application of herbicides is that it may lead to significant changes in the populations of microorganisms and their activities thereby influencing the microbial ecological balance in the soil and affecting the productivity of soils. The increasing reliance of rice cultivation on herbicides has led to concern about their ecotoxicological behaviour in the rice field environment. Hence, in this study, the herbicides viz., 2,4-DEE, butachlor, pretilachlor and pyrazosulfuron ethyl were evaluated at different concentrations of 1 FR (Field rate), 2 FR (two times field rate), 5 FR, 10 FR and 100 FR for their effect on total heterotrophic bacteria, fungi and  actinomycetes in laboratory microcosms. The results of this experiment revealed that the application of herbicides reduced the population of all the bacteria counted during the study with butachlor showing highest reduction in the populations. This effect was stronger with increasing concentration of the herbicides employed. However, the populations at 1 FR (and also 2 FR for pyrazosulfuron ethyl) concentrations recovered within 30 days to reach populations not significantly different from the control treatments.