Weed Science

Rice (Oryza sativa L.) is an important staple crop in India, where it is mainly grown by manual transplanting of seedlings into puddled soil. Recently, however, there is a trend toward dry-seeded rice (DSR) because of labour and water scarcity. In DSR, weeds are the main biological constraint. Herbicides are used to manage weeds in DSR systems, but the use of herbicides alone does not provide effective and sustainable weed control. Therefore, there is a need to integrate herbicide use with cultural weed management approaches, such as the use of a stale seedbed technique, different tillage systems, weed-competitive cultivars, cultivars capable of emerging under anaerobic conditions, crop residue for mulches, high seeding rates, narrow rows, and optimum time and depth of flooding.

Field experiments were conducted to find out the effect of integrated weed management practices on growth and yield of direct seeded rice in Cauvery delta zone. Twelve weed control treatments were tested in randomised block design replicated thrice. The treatments consisted of post-emergence application of metamifop (75, 100, 125 g/ha), pre emergence application of pretilachlor + safener 0.45 kg/ha alone and their combination with one hand weeding at 45 DAS. In addition, post-emergence metamifop 200 g/ha and cyhalofop-butyl 100 g/ha alone was also tested along with two hand weeding at 25 and 45 DAS and unweeded control. The results revealed that two hand weeding was found to be better in terms of weed control and grain yield of rice over other weed management practices. Among the herbicides, the pre- emergence application of pretilachlor + safener 0.45 kg/ha followed by one hand weeding at 45 DAS was effective in controlling all weeds and registered higher yield attributes and yield in wet-seeded rice which was at par with two hand weeding. Greater reduction in grass weed population was observed with post- emergence application of metamifop 100 and 125 g/ha as compared to other herbicides. Pre-emergence application of pretilachlor + safener  0.45 kg/ha followed by one hand weeding at 45 DAS was found to be ideal weed management practice for improving the rice grain yield by eliminating crop-weed competition in wet-seeded rice.

Field experiments were conducted at Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai to evaluate herbicide bispyribac-sodium in transplanted rice varieties ‘ASD 16’ and ‘ADT 37’ during 2010 and 2011. Seven treatments were included in a randomized block design and replicated four times. The treatments consisted of pre–emergence application of butachlor 500 g/ha, post-emergence application of bispyribac-sodium 10 SC at 25, 35 and 50 g/ha , weed free, hand weeding twice and unweeded check. The results revealed that total weed population and dry weight under bispyribac-sodium at 25 g/ha were at par with the higher doses of bispyribac-sodium at 35 and 50 g/ha during both the years of study. The weed control efficiency and weed index under bispyribac-sodium at lower dose were also comparable with that of higher doses indicating the sufficiency of bispyribac-sodium at 25 g/ha for effective weed management in transplanted rice. The effect of bispyribac-sodium at 25 g/ha on producing tillers and panicles was also at par with that of higher doses and twice hand weeding and significantly superior than butachlor application. Post-emergence application of bispyribac-sodium at 25 g/ha recorded a grain yield of 6.84 and 6.51 t/ha during 2010 and 2011, respectively which were at par with higher doses of bispyribac-sodium, twice hand weeding and weed free and significantly higher than butachlor application. Higher net income and benefit-cost ratio were also associated with the application of bispyribac-sodium at 25 g/ha.

A field experiment was conducted to find out the effect of time of sowing and weed control practices on yield and dry weight of weeds during Kharif season of 2010 and 2011 at AICRP on weed management, VNMKV, Parbhani. Sowing of direct-seeded rice (DSR) before onset of monsoon produced higher grain yields as compared to sowing after onset of monsoon. Among the different weed control methods, pre-emergence application of butachlor followed by one hand weeding recorded grain yields at par with weed free treatment.

Field experiments were carried out at Krishi Nagar Research Farm, J.N. Krishi Vishwa Vidayalya, Jabalpur, (M.P.) during 2007-08 and 2008-09 to study weed composition and weed seed bank as influenced by tillage and crop establishment techniques in rice–wheat system. Sixteen treatments consisted with 4 tillage and planting management for both crop components under rice-wheat system were tested in strip plot design with 3 replications. Tillage and sowing methods were P1- direct drilling in dry field, P2- direct seeding of sprouted seeds through drum seeder in puddled field, P3- manual transplanting and P4- transplanting through self propelled transplanter (SPT) for rice cultivar ‘Kranti’ and T1- conventional tillage sowing, T2- zero till sowing, T3- strip till sowing and T4- bed planting for wheat cultivar ‘GW-273’. The total weed density and weed biomass at 30 DAS and maturity stages were significantly greater under direct drilling in dry field (DSR-P1) than other 3 sowing/planting methods of rice under puddled conditions (P2-direct seeding of sprouted seeds through drum seeder in puddled field, P3-manual transplanting and P4-transplanting through self propelled transplanter). The DSR-P1 had also higher weed seed counts on top layer of soil than other 3 tillage and sowing methods of rice. In wheat, intensity of grasses, sedges and other minor weeds was enhanced at maturity over their intensity at 30 DAS under conventional till sown wheat, while intensity of broad-leaved weeds (BLWs) declined at maturity over their intensity at 30 DAS. The higher weed seed count (40.9/m²) at top layer of soil was obtained extensively under zero-till sowing of wheat than conventional till sowing, strip till sowing and bed planting.

A field experiment was carried out at Instructional Farm, Department of Agronomy, Junagadh Agricultural University, Junagadh (Gujarat) during Rabi of 2008-09 and 2009-10. The weed free treatment recorded significant improvement in yield attributes, viz. number of effective tillers, spikelets per spike and grain weight per plant, followed by pendimethalin 0.9 kg/ha as pre-emergence followed by one hand weeding at 35- 40 DAS. Integration of pendimethalin as pre-emergence with clodinafop, metsulfuron-methyl and 2,4-D amine salt as post-emergence with or without hand weeding proved effective in reducing weed density and dry weight of weeds. All the weed control treatments significantly influenced the grain and straw yield of wheat excluding unweeded control. The pre-emergence application of pendimethalin controlled monocot and dicot weeds, while clodinafop controlled monocot and metsulfuron-methyl controlled dicot weeds. Integrated weed management practices also produced increased nutrient uptake by crop and minimized nutrient due to weeds.

Ten treatments, viz. clodinafop 60 g/ha, sulfosulfuron 25 g/ha, metribuzin 175 g/ha, pinoxaden 50 g/ha, clodinafop 60 + metribuzin 105 and 122.5 g/ha, sulfosulfuron 25 + metribuzin 105 g/ha, sulfosulfuron 25 + pinoxaden + 40 g/ha, weed free and unweeded check were tested during the Rabi season of 2010-11 and 2011-12 at Palampur. Grassy weeds (Phalaris minor,  Avena ludoviciana, Poa annua and Lolium temulentum) constituted 90% of the total weed flora. All the weed control treatments were significantly superior to weedy check in curtailing dry weight of Phalaris, Avena and Vicia sativa. Metribuzin remaining at par with sulfosulfuron effectively reduced the dry weight of Poa annua. Clodinafop alone was least effective against Poa annua. Weed free, clodinafop, pinoxaden, clodinafop + metribuzin resulted in significant reduction in the dry weight of L. temulentum. Clodinafop 60 g/ha + metribuzin  122.5 g/ha, clodinafop 60 g/ha + metribuzin  105 g/ha, pinoxaden 50 g/ha and weed free resulted in significantly higher grain yield of wheat. Weeds reduced grain yield of wheat by 59.3%. Grain yield was negatively associated with weed count and weed biomass and positively associated with plant height, spike length, spikelets/spike and effective tillers. With every 1 g/m2 increase in weed dry weight, the grain yield of wheat was expected to fall by 41.55 kg/ha. The economic threshold levels (number of weeds/unit area) with weed management practices varied between 2.6-45.4/m2. Clodinafop 60 g/ha + metribuzin 122.5 g/ha resulted in highest weed control efficiency, crop resistance index and efficiency index. It gave lowest weed persistence index and weed index. Clodinafop 60 g/ha + metribuzin 122.5 g/ha resulted in highest net return due to weed control. Metribuzin 175 g/ha resulted in the highest marginal benefit: cost ratio.

An experiment was done during Kharif 2008 and 2009 at BCKV, Kalyani to study the weed control efficiency of herbicide as well as its effect on soil microorganisms including urease enzyme in Soybean crop field. Dominent weeds were: Echinochloa colona, Eleusine indica, Dactyloctenium aegyptium, Digitaria sanguinalis, Cyperus rotundus, Euphorbia hirta, Digera arvensis, Physalis minima, Phyllanthus niruri, Alternanthera philoxeroides and Amaranthus viridis. The treatment UPH-203 100 g/ha  + Na-acifluorfen 10% SL 206.2 g/ha was found best for efficient weed control as well as safe use for soil microflora including urease enzyme activity among all the treatments even in comparison to hand weeding treatment.

A field experiment was conducted at Agricultural Research Station, Karad, Satara, Maharashtra to find out the suitable integrated weed management method to enhance the yield in soybean. Higher yield component and yield were recorded under weed free treatment. Weed biomass was reduced significantly by the integrated weed management methods comprising quizalofop ethyl 0.05 kg/ha + chloromuron-ethyl  0.009 kg/ha as post-emergence application at 15 DAS + hand weeding at 30 DAS.

Experiment was conducted to evaluate the efficacy of pre- and post-emergence herbicides and organic and plastic mulches to control weeds in jujube (Zizyphus mauritiana ) nursery. Nutsedge (Cyperus rotundus) was the major monocot weed (67.9%), followed by wiregrass Eleusine indica (18.2%), love grass, Eragrostis tenella (8.2%) and bermuda grass, Cynadon dactylon (5.8%).  Among the dicot weeds, puncture vine (Tribulus terrestris) was the major weed (88.1%), followed by 10.3% in case of pigweed (Amaranthus viridis).  All the herbicidal treatments hampered jujube seed germination. Pendimethalin resulted in highest inhibition of jujube seed germination. Paraquat resulted in poor seed germination as compared to glyphosate treatments. Pyrazosulfuron-ethyl delayed germination, led to plants with lesser plant girth and reduced proportion of buddable plants. The highest proportion of buddable plants (85.9%) was obtained with straw mulch which did not differ significantly from proportion of buddable plants recorded with weed mulch, black polythene mulch and weed free check. Paraquat treatments resulted in lesser number of buddable plants as compared to glyphosate. At all the intervals, highest weed control efficiency was obtained with straw mulch which did not differ significantly from the weed control efficiency obtained with weed mulch. Among the herbicidal treatments, double application (10 and 60 DAS) of glyphosate resulted in the best control of monocot as well as dicot weeds.

Net profit from raw jute (jute and mesta together are called raw jute) cultivation is very poor owing to its high cost involvement (35-40% of the total cost of cultivation) in conventional manual weeding process. So far only post-emergence grass weed killing herbicides have been found to be successful in jute. After controlling grassy weeds, Cyperus rotundus and other broad-leaved weeds have become menace to these fibre crops which were effectively controlled adopting stale seedbed technique (herbicides applied on established weeds 10 days ahead of sowing jute and mesta) in Bararckpore, West Bengal. In stale seedbed method in jute,(cv ‘JRO-524’), glyphosate 2.46 kg SL/ha and 2,4-D 2 kg/ha in combination, and glyphosate 2.46 kg SL/ha and pyrazosulfuron-ethyl 60g/ha in combination followed by one hand weeding were found promising to control mixed weed flora in jute field. After two years’ cycle, these herbicide combinations reduced the Cyperus rotundus population by more than 80% over control and produced a mean of fibre yield of 28 to 3.04 t/ha and a maximum of 4.3 t jute fibre/ha in 2006-08. In mesta (cv. ‘HC-583’), in stale seedbed method, butacholor 0.75 kg/ha and 2, 4-D 2 kg/ha in combination followed by 2-HW produced a mean fibre yield of 2.65 t/ha with a maximum 3.2 t mesta fibre/ha in 2007-08 and kept the mesta field free from weed for a couple of weeks. Pretilachlor (0.5 kg/ha) and paraquat (0.48 kg SL/ha) in combination, when applied 10 days ahead of mesta sowing on established weeds, it controlled mixed weed flora and produced a mean mesta fibre yield of 2.68 t/ha. Quizalofop-ethyl 5% EC 60 g/ha and  Dhanuvit 0.5 to 0.6 l/ha at  21 DAE and  one hand weeding produced a mean mesta fibre yield of 2.76 t/ha with a maximum of 3.45 t fibre/ha in 2007-08. Except chlorimuron-ethyl, other herbicides did not affect the soil microbial flora in post harvest jute soil. All these methods produced mean fibre yields at par with two manual weedings.

Field experiments were conducted to study the effect of integrated weed management practices on growth, regeneration and tuber viability of purple nutsedge in okra for two years during summer seasons at College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, India. Eleven treatments tested in RBD with three replications were combinations of stale seedbed with glyphosate application and black polythene mulching, eucalyptus leaf mulching and cowpea smother cropping in relation to weed free and weedy check. Among the treatments, stale seedbed combined with pre-plant application of glyphosate 1.5 kg/ha (before sowing okra) followed either by polythene mulching or directed application of glyphosate 1.5 kg/ha between rows of okra was the most effective treatment in controlling nutsedge tuber production. Tuber viability and regeneration were lowest under stale seedbed in combination with pre-plant followed by post-emergence directed application of glyphosate or black polythene mulching. A combination of stale seedbed with glyphosate application followed by black polythene mulching was the best treatment for nutsedge management in okra.  

A study was conducted at Vermiculture and Vermicomposting Centre of the University in 2009-10 on Saccharum munja as a feed material for the compost worm, Eisenia foetida, using three combinations with cattle dung. Impact of weed-dung combinations on the biomass of worms and their rate of reproduction was evaluated. Physico-chemical parameters of weed-dung combinations and vermicompost produced from these combinations were tested on the growth parameters of Vigna radiata. Fresh weed was chopped into 2 cm size, mixed with fresh cattle dung in 1:3, 1:1 and 3:1 combinations separately in rectangular plastic tub sized 43 x 32 x 14 cm in replicates of five. After pre-decomposition period of 15 days, 10 g matured E. foetida were introduced in each tub. It was found that worms fed upon 1: 3 (weed : dung) combination faster than other two combinations and transformed it earlier into vermicompost. Rate of reproduction of worms was recorded 2.47 times faster and total biomass of worms was 2.15 times more in 1 : 3 combinations than that of 3: 1.  Application of vermicompost, transformed from 1:3 combination of weed: dung medium, with soil of known parameters in 1:1 combination showed an increase in the shoot length of V. radiata by 1.68 times compared to 3:1 combination.

Though herbicides are designed as biologically active but often their residues are found in crop produce and water. Herbicides may reach to ground water through runoff, drift, untargeted spray and heavy rain. Therefore, leaching beahiviour of imazethapyr, was evaluated in soil columns under natural rainfall conditions. Imazethapyr was applied at 100 and 200  g/ha on the soil columns. Columns were arranged randomly and allowed to receive approximately 850 mm rain for three months. Soil and leachates were analyzed for imazethapyr residues. Maximum concentration of imazethapyr was recovered from 0-10 cm depth. Results indicated that imazethapyr could leach in clay loam soil up to the depth of 70 cm.

Systematic surveys of Parthenium hysterophorus L. infested regions on 12  selected national highways of North-Eastern India were conducted during 2009-2011.  In all the surveyed sites, Parthenium hysterophorus was present but its abundance was more during the month of June to August. Complete inhibition of Parthenium seed germination was recorded at 20% of leaf and stem extracts of Cassia sericea, Mimosa pudica and Cassia tora.  Different stages of Zygograma bicolorata (grubs to adult) showed reduction in plant height, shoot length, root length and biomass of Parthenium when exposed in mosquito net cages.

Application 2,4-D at three levels in 0.5, 1.0 and 2.0 kg/ha in wheat crop at 35 days after sowing persisted in soil up to 15, 45 and 75 days, respectively. The logarithmic plots of herbicide residues versus time obtained by fitting the regression equation indicated that disappearance of 2,4-D in soil followed a first order kinetics decay curve at all the levels of application with the half life period varying from 4.21-17.70 days. Residues of 2,4-D were found below detectable level (0.02 ppm) in wheat grain and wheat straw.

Among different parts of Coleus spp., dried leaf powder (25 g/l of water) was found most effective in reducing the fresh weight and chlorophyll content of E. crassipes and showed 100 reduction on 9 and 6 days after treatment, respectively. Combination of 3/4th of dried leaf powder (18.75 g/l) + 1/4th of dried whole plant powder (6.25 g/l) was also found effective next to 25 g/l dried leaf power. Dried stem powder (25 g/l) showed minimum reduction in fresh weight and chlorophyll content.

A field experiment was conducted during Kharif season of 2009-10 at Research Farm, Adhartal, JNKVV, Jabalpur to study the effect of early post-emergence herbicides against weeds in soybean (Glycine max L.). The density and dry weight of weeds were higher under weedy check treatment. However, identical reduction in density and dry weight of weeds were observed when weeds were controlled chemically. Significantly higher weed control efficiency (81.82%) and seed yield (2.9 t/ha) was observed under Odyssey (mixture of imazethapyr + imazamox)  + adjuvant (87.5 g + 1000 ml/ha). The maximum net profit ( 43233/ha) and B: C ratio (3.67) were also recorded under the same treatment.