Weed Science

Climate change directly affects the geographic range of species, the timing of species life cycle (phenology), the population dynamics of species, the decline and extinction of some species and the invasion of other species. Plants with C3 photosynthetic pathways are expected to benefit more than C4 from CO2 enrichment. However, rising global temperature may give competitive advantage to C4 plants than C3. This differential response of C3 and C4 plants will alter crop weed interaction because of the fact that majority of weeds are C4 and most of the food grain crops are C3. Higher levels of carbon dioxide could stimulate the growth of some weed species and greater production of rhizomes and tubers in perennial weeds making them difficult to control. Warmer temperatures will accelerate the rate at which day degrees accumulate, so the life cycles of some plant species may accelerate. As a result weeds are likely to mature and start to decay earlier.

Several broadleaf herbicides are available for weed control in wheat, but alone they are not effective against all infesting weeds.  Tank mixture often results in antagonism or crop injury, thus reducing crop yield.  Field experiments were conducted at CCS Haryana Agricultural University during 2009-10 and 2010-11 to evaluate the efficacy of premix of carfentrazone-ethyl+metsulfuron-methyl (17.5 to 50 g/ha) with and without surfactant and compared with alone application of carfentrazone (20 g/ha), metsulfuron (4 g/ha) and 2,4-D amine (500 g/ha) along with weedy check treatment. Premix of carfentrazone+metsulfuron at 25 g/ha+0.2% surfactant provided effective control of Malva parviflora, Lathyrus aphaca, Convolvulus arvensis, Rumex dentatus, Melilotus indica, Medicago denticulata, Anagallis arvensis, Coronopus didymus and Chenopodium album which were not effectively controlled by alone application of these herbicides. A non-ionic surfactant (NIS) was essential to increase the efficacy of carfentrazone+metsulfuron mixture. Premix of carfentrazone+metsulfuron 25 g/ha with 0.2% NIS reduced the population of weeds by 97-99% during 2009-10 and 2010-11, respectively, provided 95% control of infested weeds, reducing their dry weight by 98-99%, increasing tiller numbers by 26%, biological yield by 28% and grain yield of wheat by 31% over untreated control.  Crop injury (5-15%) by the application of carfentrazone+metsulfuron with 0.2% NIS or carfentrazone alone was transient and caused no reduction in crop yield. The premix of carfentrazone+metsulfuron 25 g/ha+0.2% NIS had similar level of control to its higher rates of 30 and 50 g/ha, but was significantly better than alone application of 2,4-D, metsulfuron or carfentrazone. In another field study, where Fumaria parviflora and Rumex spinosus were dominant weeds, tank mix of carfentrazone+metsulfuron 20+4 g with 0.2% NIS provided good control than their alone applications in a wheat field during 2009-10. The effect of tank mix application of carfentrazone+metsulfuron at 20+4 g/ha was similar to 600 g/ha of 2,4-D amine and ester, but better than lower rates of 2,4-D formulations. None of the 2,4-D formulations was effective against R. spinosus, whereas metsulfuron, carfentrazone and their tank mix provided 85, 78 and 92% control of R. spinosus, respectively, and produced 41% higher tillers of wheat over untreated check.  Similarly, tank mix of carfentrazone+metsulfuron 20+4 g/ha provided good control of F. parviflora in a fallow field during 2010-11. Alone application of carfentrazone or metsulfuron was not effective though plants treated with carfentrazone+metsulfuron recovered later on, but at later stages crop can smother it and the effect of tank mixture was similar to 600 g/ha of 2,4-D ester, but better than its amine formulation and lower rates of 2, 4-D against this weed.

Screen house and field studies were carried out at CCS Haryana Agricultural University, Hisar during 2009-10 and 2010-11 to evaluate the efficacy of ready-mix formulation of fenoxaprop and metribuzin (Accord Plus) applied at two growth stages of Phalaris minor.  Metribuzin 150, 180 and 210 g/ha and Accord Plus 275 g a.i. /ha were compared with tank mix of pinoxaden+carfentrazone 50+20 g/ha each applied at 38 and 60 days after sowing (DAS) of wheat under field conditions during 2010-11. Delayed application resulted in 33 and 28% reduced efficiency of herbicides against P. minor, respectively, at 3 and 5 weeks after treatment (WAT) (data averaged over treatments). Metribuzin 150 and 180 g/ha was least effective against P. minor when applied 60 DAS, whereas its application at 210 g/ha and Accord Plus resulted in 44 and 16% lower mortality of P. minor, respectively, over their application 38 DAS.  Delayed application also lowered wheat tillers resulting in lower grain yield.  Wheat yield was reduced by 23 and 18% by metribuzin 210 g/ha and Accord Plus 275 g a.i./ha compared to 14% in tank mix of pinoxaden+carfentrazone when applied 60 over 38 DAS.  Under screen house conditions, 19 populations of P. minor were evaluated at two growth stages (2-4 leaf and 4-6 leaf) with three rates of Accord Plus (137.5, 275 and 550 g a.i./ha) during 2009-10 and 2010-11.  Mortality of P. minor populations was 44, 65 and 97% at the 4-6 leaf stage of application compared to 83, 98.5 and 100% when applied at the 2-4 leaf stage, respectively, with three rates of Accord Plus (data averaged over populations).  Accord Plus 275 g a.i./ha applied at the 2-4 leaf stage provided 90-100 % control of all the populations of P. minor, whereas delayed application at 4-6 leaf stage provided 45 to 85% control. P. minor populations, Rasidan, Nangla, Barhi, Suchan Kotli and Uchana were controlled by <50% by 275 g a.i./ha of Accord Plus application at 4-6 leaf stage. P. minor populations, Barhi, Suchan Kotli, Koyal, Jakholi and Chanarthal were not completely knocked down by even 550 g a.i./ha of Accord Plus with delayed application at the 4-6 leaf stage. Some of these populations have already exhibited loss of efficacy against fenoxaprop and clodinafop under field conditions.  Care need to be taken in timely application of Accord Plus where efficacy of one of the mixture partners (fenoxaprop) is questionable.

Wheat (Triticum aestivum L.) is the major staple food of India and its increased production is essential for food security. Weeds constitute one of the biggest problems in agriculture that not only reduce the yield and quality of wheat crop but also utilize essential nutrients. Hence, weed control is essential for increasing wheat production. Despite of its control on weeds, herbicides also affect beneficial non-targeted soil microbes including VAM fungi. Fenoxaprop-P-ethyl and 2,4-D ethyl-ester are two most widely used herbicides in northern India to control monocot and dicot weeds, respectively. However, their effects on mycorrhizal fungi are seldom highlighted. Therefore, the present investigation was focused on the effect of these herbicides on soil fungi of wheat crop alongwith special emphasis on mycorrhizal fungi. Three doses of each herbicide i. e. fenoxaprop and 2,4-D (recommended dose 0.1 kg/ha; 0.5 kg/ha, half of the recommended dose 0.05 kg/ha; 0.25 kg/ha  and double of the recommended dose 0.2 kg/ha; 1.0 kg/ha), respectively, were applied and their effect on soil fungi was studied at 30th, 60th, 90th and 120th day of treatment. Warcup’s soil plate method, wet sieving and decanting technique and rapid clearing and staining techniques were used for qualitative study, isolation of mycorrhizal spores and root colonization, respectively. Our results indicate that both herbicides had significant deleterious effects on soil fungi, mycorrhizal spore numbers and percentage root colonization and this effect increased with herbicide concentration. In our chemical warfare against weeds, it is necessary to avoid serious injuries to the beneficial soil microbes. Therefore, use of herbicides in high doses should be resorted to carefully and judiciously.

An experiment was conducted for three years at the Research Farm of Department of Agronomy, Punjab Agricultural University, Ludhiana during rabi seasons of 2007-08 to 2009-10. The experimental field was heavily infested with Phalaris minor and broadleaf weeds. A new herbicide i. e. AEF 04 6360-8%+DIC 1468-14%-22% EC (fenoxaprop-P-ethyl+metribuzin) was applied at 165, 220, 275, 330 and 550 g/ha as post-emergence (30-35 DAS). The results of three years revealed that application of this herbicide at 275 and 330 g/ha provided effective control of P. minor and broadleaf weeds in wheat crop and were found statistically at par with Atlantis 3.6 WDG (mesosulfuron 3.0%+iodosulfuron 0.6% at 12+2.24 g) on dry matter accumulation by P. minor and broadleaf weeds. On an average of three years, post-emergence application of AEF 046360-8%+DIC 1468-14%-22% EC at 275 and 330 g/ha as well as Atlantis 3.6 WDG at 14.4 g/ha increased wheat grain yield by 58.8, 64.2 and 67.3% as compared to unweeded (control) treatment, respectively.

Field investigations conducted at CCS Haryana Agricultural University, Hisar, India during  2007-08 and 2008-09 revealed that both the doses and sources of nutrients increased weed emergence in pearl millet-wheat cropping system. The increase in fertilizer dose decreased weed emergence and manures as source of nutrients increased weed emergence during both the crops. The increase in fertilizer dose increased pearl millet, wheat and wheat equivalent yield and highest yield was recorded with the application of 50% recommended NPK dose through fertilizers+50% N through farm yard manure in kharif and 100% recommended NPK dose through fertilizers in rabi season during both the years and it was closely followed by the treatment where recommended dose during both the years was applied through chemical fertilizers. Among the organic sources, the increase in yield was highest with farm yard manure (FYM) and it was followed by green manure and wheat straw in descending order of magnitude.

Bioefficacy and phytotoxicity of imazethapyr and chlorimuron in clusterbean and its carryover effect on succeeding rabi crops was studied in field experiments at CCSHAU, Hisar during kharif 2006-07 and 2007-08. Weed flora of the experimental field was dominated by Digera arvensis, Trianthema portulacastrum, Physallis minima, Corchorus olitorius, Solanum nigrum and Cyperus rotundus. Post-emergence application of chlorimuron at 6 and 8 g/ha although provided good (90-92%) control of weeds but caused 20-30% injury to clusterbean resulting in severe yield reductions. PPI (pre-plant incorporation), PRE (pre-emergence) and POE (post- emergence) application at 21-28 DAS at 80-100 g/ha of imazethapyr provided season long control (85-95%) of clusterbean weeds. POE application of imazethapyr at 80 and 100 g/ha although caused mild injury to clusterbean in terms of yellowing of leaves and stunted crop growth upto 7 DAT, but it diminished within three weeks without any yield reduction. Maximum seed yield (1424 kg/ha) of clusterbean was obtained with imazethapyr at 100 g/ha PRE which was at par with weed free check, but during 2007, PRE application of imazethapyr at 80 g/ha gave maximum seed yield (1720 kg/ha) which was at par with its application at 80 and 100 g/ha as PRE, PPI or post-emergence 21 DAS. Chlorimuron and imazethapyr, irrespective of their dose and time of application, did not cause any injury to wheat, barely and chickpea planted as succeeding crop after harvest of clusterbean, but both these herbicides caused severe injury to mustard.

A field study was conducted at Agricultural Research Station, Kampasagar, Nalgonda district of Andhra Pradesh during the kharif seasons of 2008 and 2009 to find out the effect of irrigation schedules, weed management practices and nitrogen levels on weed growth, nutrient depletion and yield of aerobic rice. The major weed flora observed in the experimental plot was Echinochloa colona L., Cynodon dactylon Pers., Dactyloctenium aegyptium Beauv., Cyperus rotundus L. (Monocots), Eclipta alba Hassk., Trianthema portulacastrum L. and Amaranthus viridis L. (Dicots) during both the years. Irrigation scheduled at seven days interval during vegetative stage and four days interval during reproductive stage resulted in significantly higher weed density, weed dry matter production and NPK removal by weeds and higher panicle number and weight, filled spikelets per panicle grain yield and NPK uptake at harvest than that of irrigation scheduled once in two days. Pre-emergence application of pendimethalin @ 1 kg/ha fb cono weeding at 30 DAS and one HW at 45 DAS recorded significantly lower weed density, weed dry matter production and NPK uptake by weeds and significantly higher panicle number and weight, filled spikelets per panicle, NPK uptake at harvest and grain yield than that of pre-emergence application of pendimethalin @ 1 kg/ha fb 2, 4-D Na salt @ 1 kg/ha at 40 DAS and HW at 20 and 45 DAS. Among latter treatments, significantly lower values of above said weed parameters and significantly higher crop parameters were observed with pre-emergence application of pendimethalin @ 1 kg/ha fb 2, 4-D Na salt @ 1 kg/ha at 40 DAS as compared to HW at 20 and 45 DAS. Weed density, weed dry matter production and NPK removal by weeds and panicle number, length and weight, filled spikelets per panicle, grain yield and NPK uptake at harvest were significantly higher at 180 kg N/ha during both the years.

A field study was carried out during kharif seasons of 2006 and 2007 at university research farm for generating information on weed flora and to work out integrated weed management practices with its economics in dry direct seeded kharif rice. Among the weed flora, emergence of grasses like Cynodon dactylon and Echinochloa colona, sedges like Cyperus rotundus, Cyperus iria and Fimbristylis miliacea and broad-leaved weeds like Ludwigia parviflora, Ageratum conyzoides, Spilanthes paniculata, Eclipta alba and Enhydra fluctuans were recorded during experimentation. Among the integrated weed management practices, butachlor 1.5 kg/ha as pre-plant surface application followed by practices of brown manuring and post-emergence application of 2,4-D 0.50 kg/ha at 40 days after sowing recorded highest grain yield (3.0 and 3.88 t/ha), highest net returns (Rs.11889 and 19029/ha) and benefit : cost ratio (0.74 and 1.19) during both the years of investigation. The grain yield was statistically at par with the grain yield (3.14 and 3.98 t/ha) obtained from season long weed free condition. There has been considerable improvement in nutrient use efficiency due to adoption of weed control practices coupled with nitrogen management and among the integrated weed management practices highest nutrient use efficiency of N (50.00 and 64.67 kg grain yield/kg nutrient applied), P (229.36 and 296.64 kg grain yield/kg nutrient applied) and K (90.36 and 116.87 kg grain yield/kg nutrient applied) were highest with butachlor 1.5 kg/ha + brown manuring + 2,4-D 0.5 kg/ha in both the years.

An investigation was conducted at Chatha Farm of Sher-e-Kashmir University of Agricultural Sciences and Technology of Jammu during kharif seasons of 2006 and 2007 on the efficacy of different herbicides on growth and yield of direct wet seeded rice (DWSR) sown through drum seeder. Fourteen weed control treatments were tested in randomized block design replicated thrice. All the weed control treatments significantly reduced the population and dry weight of weeds which resulted in significantly higher growth and yield of rice over weedy check.  Though the weed free treatment yielded significantly higher than other treatments, but it was not economical (1.55 B : C ratio).  Among the herbicides pretilachlor @ 0.5 kg/ha at  6 DAS fb rotary hoe at 20 DAS not only significantly reduced population and dry weight of weeds but also increased the grain yield of rice with the concomitant increase in the yield attributes and also resulted in highest net returns (Rs. 25918/ha) and benefit : cost ratio (2.25).

A field experiment was conducted during rabi 2006-07 to 2008-09 at RARS, Lam Farm, Guntur to find out most suitable integrated weed management practice for control of weeds in chickpea. Results indicated that weed control treatments significantly reduced the density and dry weight of weeds in chickpea. Post-emergence application of imazethapyr 63 g/ha caused 20% crop injury among the herbicides under study. Integrated treatments were found to be superior (83-89% WCE) to alone application of herbicides. Among the treatments, pre-emergence application of oxyfluorfen 100 g/ha fb hand weeding at 30 DAS recorded maximum (2272 kg/ha) and was on par with all other integrated treatments and also with hand weeding at 15 and 30 DAS. Among the individual herbicides, pre-emergence application of pendimethalin 1.5 kg /ha recorded maximum grain yield and was on par with other individual herbicides.

A field experiment was conducted at the Agronomy Farm, ARS, Durgapura, Jaipur during 2003-05 on loamy sand soils analyzing low in available N and S and medium in available P and K. The increasing rates of S did not influence the weed density by markedly increasing the dry matter of weeds. Hand weeding twice showed the maximum control of weeds, which was significantly superior to other treatments. The successive rates of S nutrition upto 60 kg S/ha markedly enhanced the dry matter, siliquae, seeds/siliqua and seed yield plant in both the years. However, plant height and 1000-seed weight showed significant response only upto 40 kg S/ha and remained at par with higher levels of S nutrition. The yield of succeeding fodder pearl millet was highest (370.0 q/ha) weed control measures  brought about measurable improvement in growth and yield attributes, and yield of mustard compared with the weedy check. The two HW being at par with the herbicides coupled with HW increased the pooled mean seed yield of mustard significantly by 46.3% over weedy check. The application of 60 kg S/ha recorded significantly highest (Rs. 21077/ha) pooled mean, net return and B : C ratio (2.51) of mustard over lower levels. Two HW being at par with both the herbicides coupled with HW gave highest net return (Rs. 20050/ha), whereas B : C ratio was significantly higher under isoproturon @ 0.50 kg/ha with 60 kg S/ha.

Field experiments conducted during summer seasons for four years (2002, 2003, 2004 and 2005) and during kharif seasons for three years (2002, 2003 and 2005) showed that unchecked weeds caused a reduction of 41.2 and 41.6% in blackgram yield during the two respective seasons. In summer season, pendimethalin 0.75 kg/ha, pendimethalin 0.45 kg/ha+hand weeding (HW) 25 days after sowing (DAS), fluchloralin 0.675 kg/ha, two HW 25 & 40 DAS and weedy check recorded weed dry matter of 4.87, 3.45, 5.87, 3.40 and 23.6 q/ha and grain yield of 11.47, 11.75, 10.72, 11.95 and 7.02 q/ha with net returns of Rs. 10033, 10035, 9401, 9330 and 4828/ha, respectively. In kharif season, the respective treatments had weed dry matter of 4.16, 4.26, 4.93, 2.90 and 20.9 q/ha and grain yield of 10.43, 10.76, 10.60, 11.76 and 6.86 q/ha with net returns of Rs. 8577, 8649, 9233, 9064 and 4604/ha.

Imazethapyr, quizalofop-P-ethyl, pendimethalin and alachlor at 0.1, 0.06, 1.0 and 2.0 kg/ha, respectively, alone and with hand weeding 40 DAS were compared with one and two hand weedings against mixed weed flora in clusterbean. All the weed control treatments significantly reduced the dry weight of complex weed flora, although they differed in their effect on monocot and dicot weeds. Imazethapyr alone and with hand weeding 40 DAS effectively controlled both monocot and dicot weeds, while quizalofop-ethyl controlled only monocot weeds. Uninterrupted weed growth depleted 108.5 kg N, 15.8 kg P and 151.6 kg K/ha, while such losses were lowest with two hand weedings 20 and 40 DAS. Highest grain yield was obtained with weed free check (1840 kg/ha) followed by two hand weedings (1720 kg/ha) and imazethapyr 100 g/ha+hand weeding 40 DAS (1711 kg/ha) and it was significantly higher than all other treatments. Maximum uptake of N (133.8 kg/ha), P (32.5 kg/ha) and K (135.1 kg/ha) by clusterbean was recorded in two hand weedings (20 and 40 DAS), while in weedy check plots N, P and K uptake by crop was 40.6, 9.8 and 41.1 kg/ha, respectively.

A study was conducted to examine the effect of ammonium sulfate (AMS) applied with and without surfactants (Induce, Silwet L-77 and Methylated seed oil) on the efficacy of glyphosate. Herbicide treatments were applied to broadleaf weeds–Brazil pusley (Richardia brasiliensis), Spanish needles (Bidens pilosa), Florida beggarweed (Desmodium tortuosum) and Pigweed (Amaranthus retroflexus) and grassy weeds–Guineagrass (Panicum maximum), Johnsongrass (Sorghum halepense) and Crowfoot grass (Dactyloctenium aegyptium). The per cent control of both weed types was significantly higher with the application of AMS or the surfactant individually, or the surfactant plus AMS to glyphosate at 370 g/ha over no surfactant or AMS. Per cent control of grass weeds was 100 with the addition of any one of the surfactant except with glyphosate+L-77, where per cent control of Guinea grass and Johnson grass was only 82 and 85, respectively, two weeks after treatment (WAT). Per cent control of Brazil pusley and Spanish needles with glyphosate at 370 g/ha was low (20-38) 1 WAT. Addition of AMS improved efficacy of glyphosate in Brazil pusley 1 and 2 WAT. This effect, however, could not be observed 3 WAT. Effect of addition of AMS was apparent in Spanish needles and Florida beggarweed 2 WAT. Glyphosate alone, however, provided 93-100% control of Spanish needles, Florida beggarweed and pigweed 3 WAT. Per cent control of grassy weeds was complete 2 WAT with glyphosate at 370 g/ha with or without surfactants except with L-77 where it showed antagonistic effect.

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