Weed Science

A field experiment was conducted to study the effect of  irrigation and weed management practices of rice under aerobic culture, laid in split plot design. Among the irrigation schedules, IW/CPE ratio of 1.2 produced significantly higher stature of yield attributes, viz., total number of panicles/m2, total number of grains/panicle and number of filled grains/panicle and grain and straw yield were distinctly superior to other two irrigation schedules.  At all the  stages, with exception at 20 DAS, the lowest of density of weeds and  their corresponding dry weight was recorded with hand weeding at 20 and 40 DAS, which were comparable with oxadiargyl 0.07 kg/ha supplemented with HW at 40 DAS for density of grasses, triasulfuron 0.006 kg/ha supplemented with HW at 40 DAS for density of broad leaved weeds and bensulfuron methyl 0.06 kg/ha supplemented with HW at 40 DAS for density of sedges. The highest density of these entire weed categories was recorded with unweeded check. The study revealed that rice can be successfully grown under aerobic culture in north coastal zone of Andhra Pradesh, with pre-emergence application of oxadiargyl 0.07 kg/ha supplemented with HW at 40 DAS for higher productivity.

Spraying of foliar herbicide to control water hyacinth may lead to mortality of the fish by root exudation of herbicide or accidental drift of herbicide. To overcome herbicide-divalent cations complex formation in hard water at improper pH, increasing herbicide dosage per drop, either by increase of dosage or by reduce the spray volume, was one of the techniques. Using radioactive 14C-glyphosate and 14C-2,4-D, effect of dosage on herbicide retained on the cuticle as dried out residue, distribution with in plant system and moved out as root exudates was assessed. Twice the recommended concentration (2x) of herbicide per drop and drop density per fed spot significantly increased the dried residue on the cuticle 67 to 91 and 68 to 79% over total activity recovered compared to x dose for glyphosate and 2,4-D, respectively.  2,4-D (2x) significantly increased the amount of herbicide cuticle loading and mobility within cuticle but differences in translocation to different  parts was not significant except in root  (2x had lower activity than x). Similarly, significant difference between 2x and x for glyphosate was observed for cuticle loading and root exudates.  At 2x dosage, root exudates of both herbicides was more after 8 days. Half-life in pond water was around 5 days for both herbicides compared to normal water 7 and 11days of glyphosate and 2,4-D respectively. The chances of hherbicide toxicity to fishes were unlikely by foliar applied herbicides.

A field experiment was conducted at Pantnagar during winter season 2005-06 and 2006-07 to study effect of rates of herbicide mixture clodinafop-propargyl 15% + metsulfuron-methyl 1% (UPH-206) for control of mixed weed flora in wheat (Triticum aestivum L.). Grassy weeds such as Phalaris minor, Avena fatua and broad-leaved weeds, viz., Chenopodium album, Melilotus spp., Medicago denticulata, Vicia sativa, Rumex spp., Anagallis arvensis, Coronopus didymus, Lathyrus aphaca and  Polygonum plebejum  were effectively controlled by application of UPH-206  500 g product/ha. The highest grain yield (4.17 t/ha) of wheat was also obtained with the post-emergence application of UPH-206 500 g product/ha being at par with UPH-206 400 g product/ha, and hand weeding at 35 and 55 DAS, but significantly higher than sulfosulfuron, clodinafop and isoproturon at recommended rates. No residual effect of UPH 206 at any of doses tested was obtained on succeeding crops of blackgram and maize.

A field experiment was conducted in an Alfisol to study the degradation of butachlor and its residues in paddy grain during Rabi and Kharif seasons of 2007-08 at College Farm, College of Agriculture, Rajendranagar. Butachlor dissipated with half life varying from 12.5 to 21.5 days when applied at the rate of 1.0 and 2.0 kg/ha under with and without organic manures conditions. The observed half life values were lower for lower dose of applied herbicide as compared to higher dose and the field half life of butachlor was more under without organic manures as compared to organic manures applied plots. Residues of butachlor in field soil were analysed by using gas chromatograph and 100% dissipation of butachlor was observed at the time of harvest of crop.  Very low levels of residues were detected in rice grain below the maximum residue limit of 0.5 mg/kg. Therefore, application of butachlor in paddy for weed management can be considered safe from the point of consumption of grain.

A field experiment was carried out for two consecutive years during Kharif seasons of 2010 and 2011 to find out practically convenient and economically feasible weed management practice in onion at breeder seed production farm in Mahatma Phule Krishi Vidyapeeth, Rahuri. Different combinations of hand weeding with application of Pendimethalin 1.0 kg/ha (pre-planting) and oxyfluorfen 0.250 kg/ha (post-emergence) were used in onion variety ‘Baswant-780’. Weed free check treatment (three hand weeding at 20, 40 and 60 DAS) recorded significantly lowest weed density, dry weight of weed and higher weed control efficiency. All the growth attributes of onion viz., plant height, neck thickness, bulb weight and bulb diameter were recorded maximum in weed free. This treatment also recorded highest bulb yield and gross monetary return per hectare, however maximum B:C ratio was observed in treatment pendimethalin 1.0 kg/ha (PP)+ Oxyfluorfen 0.250 kg/ha (POE)+ One hand wedding at 40 DAS.

The trial was conducted for two years during November–February 2006 and during December–April 2007. The treatments included fenoxaprop-p-ethyl at 47.44, 51.75, 56.06, 60.38 g/ha, cyhalofop-butyl 62.5 g/ha, Echinochloa spp. were the major weed comprising about 75% of the weed population.  Echinochloa crusgalli and Echinochloa stagnina were present almost in equal proportions. Fenoxaprop-p-ethyl at all the tested doses was effective in  controlling  Echinochloa  spp. Fenoxaprop  sprayed 60.38 g/ha recorded yields on par with hand weeding and standard check cyhalofop. This dose can be recommended in situations where Echinochloa spp. is a major problem.

An experiment was conducted at Oilseeds Research Station, Jalgaon during 2007 to 2009 in order to control groundnut associated weed growing in Kharif season. An experiment was done with seven treatments of pre and post-emergence herbicides comprising weedy cheek and weed free check replicated thrice in randomized block design (RBD) on medium clay loam soils with pH 8.1. The various weeds observed in groundnut field during Kharif season were, Amaranthns viridus, Parthenium hysterophorus, Acalypha indica, Cyperus rotundus , Cynodon dactylon, Phyllanthus niruri, Commelina spp., Eragrostic sp., Celosia argenia and Euphorbia sp. Among the grasses, Cynadon dactylon was predominant and among the sedges Cyperus rotundus was predominant. Among the different herbicides, pre-emergence application of pendimethalin 1.0 kg/ha + post-emergence application of imazethapyr 75 gm/ha at 20 DAS recorded maximum weed control efficiency (74%), minimum weed population (42.67/m2) and weed day matter (185 g/m2). The same treatment combination recorded significantly higher dry pod yield (1997 kg/ha), gross returns (46445/ha) net returns (28705/ha) and B: C ratio 2.44.

A field experiment was conducted at Ranchi, Jharkhand during rainy seasons of 2010 and 2011 to find out the effect of seed rate and weed control methods on wet seeded rice under medium land condition.  Increasing seed rate from 60 to 120 kg/ha did not influence weed density and weed dry matter at 20 and 40 DAS. Application of pyrazosulfuron 0.02 kg/ha early post-emergence reduced density of all categories of weeds. The mean reduction was 61.9 and 35.3% and 66.7 and 41.9% at 20 and 40 DAS compared to butachlor and 2 hand weeding respectively. Pyrazosulfuron being similar to Almix (chlorimuron + metsulfuron) 20 g/ha recorded 70.3 and 87.0% reduced weed dry matter compared to weedy check. Application of 80 kg seed/ha being similar to 100, and 120 kg seed/ha recorded 63.0% higher grain (2.70 t/ha) and 70.9% higher straw (3.81 t/ha) yield compared to 60 kg seed/ha.

Technique enhancing herbicide entry into the plants leads to reduction in dosage and therefore pollution. Higher density of fine droplets along with surfactant increased the herbicide entry points, than coarse droplets for same total spray volume.  But fine droplets evaporate faster resulting in herbicide getting deposited as dried crystals on leaf surface. To overcome this problem, several adjuvants were tried to increase the time required for evaporation. Jaggery (2%) increased the evaporation period (27-162%) on different weed species. Dried out deposition of radioactive glyphosate from fine drops and along with TritonX 200 was more but showed enhanced glyphosate entry into the plant system. Whereas, aqueous extract (2%) of soap nut fruit (Sapindus emarginatus) which acts as bio-surfactant and antioxidant increases the time taken for drying and therefore enhances the translocation of glyphosate to bulb of O. latifolia, which was on par with TritonX 100 surfactant (petroleum product). This approach seems to be more beneficial than increasing the dosage of herbicide per droplet.

A field experiment was conducted at Chatha, Jammu during winter season of 2004-05 and 2005-06 to study the effect of different herbicides and its mixtures on weeds and yield of wheat (Triticum aestivum). Unchecked weeds growth caused 40.3% reduction in grain yield of wheat. Application of sulfosulfuron (25 g) + 2,4-D (500 g/ha) reduced weed population and  biomass significantly and thereby caused increase in crop growth and grain yield of wheat. This was at par with tank-mix application of clodinafop (60 g) + metsulfuron-methyl (2 g/ha), isoproturon (750 g) +2,4-D (500 g/ha) and fenoxaprop (120 g) + metribuzin (100 g/ha). Maximum grain yield was recorded in weed-free (5.05 t/ha), but the highest B:C ratio was observed with isoproturon+2,4-D (1.79). There was a significant positive correlation between N uptake by crop and grain yield of wheat (0.99), but a negative correlation was observed between grain yield and density and N removal by weeds.

A field experiment was conducted during Rabi seasons of 2006-07 and 2007-08 at Research Farm of GBPUA&T, Krishi Vigyan Kendra Dhakrani, Dehradun to study the effect of weed control practices on weed dyanamics, nutrient uptake and yield of wheat (Triticum aestivum (L.) emend. Fiori and Paol). Results revealed that application of clodinafop-propargyl + metsulfuron-methyl (60+4 g/ha) being on at par with clodinafop propargyl + 2,4-D (60+500 g/ha) reduced the weed population significantly over weedy check (97.2%) and other weed control treatments. Clodinafop-propargyl+ metsulfuron-methyl (60+4 g/ha) applied as post-emergence (35 DAS) recorded 14.3, 15.5, 23.7, 29.5, 45.9, 47.4 and 69.7 per cent more grain yield over pendimethalin, isoproturon + metsulfosulfuron-methyl, fenoxaprop-p-ethyl + metsulfuron-methyl, fenoxaprop-p-ethyl, isoproturon, clodinafop-propargyl and weedy check, respectively. The weeds removed the 28.7 kg of N, 13.4 kg P2O5 and 21.5 kg of K2O/ha, and reduced the wheat grain yield by 78.8% as compare to weed free conditions. Application of clodinafop-propargyl + metsulfuron-methyl reduced the nutrients removal by weeds and increased its removal by wheat.

A field experiment with 11 weed management practices including herbicide and hand weedings was conducted at Jagdalpur during 2006 and 2007. Digitaria sangunalis, Eleusine indica and Echinochloa colona among monocots, and Celosia argentia and Spilanthes acmella among dicots were the major weeds. Dry weight of weeds and weed control efficiency were the lowest under weed-free condition throughout crop growth period fb weed-free up to 40 and 50 DAS, and hand weedings at 20 and 40 DAS. These treatments also led to higher yield attributes and yields of finger millet. The highest B:C ratio (3.79) was obtained when isoproturon 0.5 kg/ha was applied as pre-emergence followed by its lower dose (0.05 kg/ha).

Field experiment was conducted at Agricultural College and Research Institute, Madurai during Rabi 2010-2011 to study the efficacy of new  herbicides for controlling weeds in aerobic rice.  Minimum grass, sedge, broad leaved weed and total weed density and their dry matter production and higher weed control efficiency were obtained in plots receiving post-emergence mixture of fenoxaprop + (chlorimuron + metsulfuron) on 30 DAS followed by sequential application of pre-emergence oxyfluorfen and post-emergence 2,4-D on 30 DAS and post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS.  The result on phyto-toxicity rating revealed that pre-emergence oxyfluorfen and post-emergence 2,4-D on 30 DAS  showed phyto-toxicity rating of 5 on 10 DAS and 4 on 20 DAS and no toxicity before harvest.  Post-emergence mixture of fenoxaprop + ethoxysulfuron on 30 DAS  recorded significantly higher grain yield of 6278 kg/ha.     

An experiment on evaluation of soil solarization on weed seed bank of soil was conducted in 2004 at College of Agriculture, Gwalior, in randomized block design with six non chemical agronomical weed management practices viz., solarized (45 days) non-solarized, stale seed bed, deep ploughing, green manuring and mulching by green biomass. The soil temperature recorded under solarized conditions were 43.90C and 43.80C at 10 and 15 cm depth and it was 4.60C and 4.50C higher than non-solarized soil respectively.  In solarized soil total number of grassy, broad leaved and sedges weeds waslowest, while highest grasses were reported in non-solarised soil. Total number of weeds was highest in non solarized soil followed by green manuring, stale seed bed, mulching, deep ploughing and non-solarised soil. Thus soil solarization was found to be the best non chemical agronomical practice for weed management methods used resulting to lowest weed seed bank.

A field experiment was conducted to evaluate relative performance of weed management practices in sugarcane ratoon during 2006-09 at Padegaon, Maharashtra. Trash mulching between all rows with recommended practice recorded significantly higher cane yield (98 t/ha), which was at par with trash mulching in alternate rows + hoeings at 1st and 6th week after ratoon initiation (95.3 t/ha) and three hoeings at 1, 4 and 7 weeks after ratoon initiation (94.0 t/ha). Highest net returns (69,719/ha) and B:C ratio (2.83) were observed due to trash mulching between all rows for sugarcane ratoon with recommended practice.

A field experiment was conducted during Rabi season of 2009-10 at College of Agriculture, Pune to study the eficacy of different herbicides on growth and productivity of wheat. The growth  attributes of wheat crop in terms of plant height, number of tillers/plant, leaf area index, and dry matter accumulation/plant were maximum with weed free check. Among the herbicide treatments, post-emergence application of sulfosulfuron 25 g/ha recorded higher values of all these growth attributes characters and were on par with hand weeding at 30 DAS and application of metribuzin 175 g/ha. However, substantial reduction in growth characters was observed in weedy check. The values of yield attributes were higher in magnitude in weed free check treatment. The next best treatment was application of sulfosulfuron 25 g/ha. Amongst the weed control treatments, application of sulfosulfuron 25 g/ha, recorded maximum grain and straw yield of 3.71 and 4.78 t/ha, respectively, as compared to other treatments. However, substantial reduction in growth and yield attributes and yield were observed in weedy check.

A field experiment was carried out at Gwalior during Kharif season of 2010 to access the effect of weed management practices to sesame on seed yield and nutrient uptake by crop and weeds and net returns. Two hand weeding at 15 and 30 DAS registered highest yield (1190.22 kg/ha) and net return ( 42391/ha) in addition to higher NPK uptake by crop and lower NPK uptake by weed. Among herbicidal treatments application of trifluralin 0.75 kg/ha followed by one hand weeding at 30 DAS was found superior for yield, NPK uptake by plant and net return. Integration of herbicides viz., trifluralin, pendimethalin, quizalofop ethyl and clodinafop with one hand weeding at 30 DAS was found more effective as compared to their alone use. NPK removed by weeds was heighest in weedy check and lowest in two hand weeding followed by trifluralin 0.75 kg/ha integrated with one hand weeding at 30 DAS.

The study was conducted in Sinduri village of Shahdol district in Madhya Pradesh to evaluate rotary weeder’s ergonomic effectiveness in terms of energy requirement, subjective judgement of Work Related Body Discomfort (WRBD) and work performance in comparison with hand weeding.  Ergonomic results showed that the energy requirements for farm women were 16.0 and 11.04 kj/min for rotary weeder and hand weeding, respectively. The area covered by rotary weeder was 110 m2/hr as compare to 30m2/hr by hand weeding (nearly 4 times). The Overall Rated Perceived Exertion (ORPE) was used to express WRBD.  It was more in hand weeding due to continuous bending posture as against standing posture.

Field experiment was conducted to evaluate the efficacy of imazethapyr on weed control in soybean and its residual effect on succeeding crops. Early post-emergence application of imazethapyr reduced broad-leaved weeds and grass density as well as dry weight when compared with pre-emergence application of pendimethalin and oxyfluorfen. Imazethapyr at 200 g/ha decreased the dry weight accumulation of all weeds significantly followed by imazethapyr 100 g/ha. Due to phytotoxic effect at 200 g/ha during initial stages yield and yield attributes were get reduced. Imazethapyr at 100 g/ha was found best treatment by giving more seed yield. To study the residual effect of imazethapyr on succeeding crops, sunflower and pearl millet were grown without disturbing the soil. The residues of imazethapyr at different doses did not influence germination, growth, yield of sunflower and pearl millet and was statistically at par with checks.