Weed Science

Field experiment was conducted during Kharif 2009 and 2010 to study the bio-efficacy of different herbicides in direct-seeded rice. Weed control treatments comprised of pendimethalin 0.75 kg, butachlor 1.50 kg, thiobencarb 1.50 kg, anilofos 0.375 kg, pretilachlor 0.75 kg, oxadiargyl 0.09 kg and pyrazosulfuron ethyl 0.015 kg/ha as pre-emergence and with sequential application of bispyribac 0.025 kg/ha at 30 DAS; two hand weedings and unweeded control. Significantly lower number of grass weeds was observed with application of pendimethalin as compared with other pre-emergence herbicides. Sequential application of pendimethalin and bispyribac recorded the lowest weed biomass and 100% weed control efficiency. Crop dry matter accumulation, number of tillers, and effective tillers were significantly higher in sequential use of pre- and post-emergence herbicides, resulting in more grain yield and net returns. The maximum grain yield was recorded in two hand weedings, which was at par with follow-up application of bispyribac after pendimethalin, butachlor, thiobencarb and oxadiargyl.

A field experiment was conducted during the Kharif season of  2012 to 2014 for three years at Agricultural Research Station, Vadgaon Maval, Pune, Maharashtra to find out the efficacy of different chemical and mechanical weed control methods and its economics in direct-seeded rice. From the pooled data it was observed that the pre-emergence application of oxyfluorfen 0.150 kg/ha and post-emergence application metsulfuron-methyl + chlorimuron-ethyl 0.004 kg/ha as weed control measure in direct-seeded rice gave the highest net returns (` 57,063/ha) with higher B:C ratio (2.3) having lower weed index (2.96) and higher weed control efficiency (91.08 %).

An experiment was conducted during two consecutive rainy seasons at Rajendra Agricultural University, Pusa to study the effect of establishment method, fertility levels and weed management practices on scented hybrid rice. Two crop establishment methods (standard method of transplanting and SRI method of transplanting), three fertilizer levels (80:40:20, 100:60:40, 120:80:60 N, P2O5, K2O kg/ ha) and three weed management practices (weedy check, one hand weeding (HW) at 35 days after transplanting (DAT) and pre-emergence application of pendimethaline at 1 kg/ha were tested in a randomized block design. SRI method of transplanting recorded higher grain yield than the standard method of transplanting. The yield increased with the increase in fertility levels and was maximum with 120:80:60 kg/ha N, P2O5 and K2O/ha. One hand weeding registered higher grain and straw yields. Weed control efficiency was better with one hand weeding at 35 DAT in comparison to pre–emergence application of pendimethalin at 1 kg/ha.

A field experiment was conducted during Rabi season of two consecutive years of 2010-11 and 2011-12 to evaluate the efficacy of different tillage practices in combination with various nutrient levels on productivity and quality along with weed control efficiency in forage oat under plateau region of Jharkhand. Variation in tillage and nutrient level significantly influenced the infestation of crop associated weeds, leaf area index, green forage yield, uptakes of calcium as well as, iron and contents of crude protein as well as crude fiber of forage oat. Population density of narrow, broad-leaved weeds and sedges and its biomass under zero tillage were lesser than conventional and minimal tillage. Application of biofertilizers with 75% recommended dose of fertilizer (RDF) remained at par with 100% RDF. However, maximum forage yield with improved quality was recorded under 125% RDF. Zero tillage practiced in forage oat was equally effective as conventional tillage with regards to productivity and quality of forage oat.

Field efficacy of ready mix formulation of clodinafop-propargyl + metsulfuron-methyl was evaluated against mixed weed flora in wheat during winter seasons of 2010-11 and 2011-12 at Punjab Agricultural University, Ludhiana. The results indicated that ready-mix of clodinafop+ metsulfuron at 75 g/ha + 0.2% surfactant recorded effective control of grass and broadleaf weeds and recorded similar wheat grain yield to sequential application of clodinafop 60 g/ha and metsulfuron 4 g/ha and weed free without any phytotoxicity symptoms on the crop.

A field experiments was conducted during winter seasons of 2010-12 at Banaras Hindu University, Varanasi to study the effect of herbicides, nitrogen rates and it’s scheduling on associated weeds, crop growth and yield of wheat. Six weed species were common infesting wheat fields were Phalaris minor, Cynodon dactylon, Chenopodium album, Oxalis purpurea, Anagallis arvensis and Cyperus rotundus. Among the herbicidal treatments, post-emergence application (30 DAS) of sulfosulfuron + metsulfuron [32 g/ha] with higher rates 160 kg N/ha and time of application (50% basal + 25% CRI + 25% flowering) performed significantly with respect to reduction in density and biomass of weeds; increased the LAI and SPAD value ultimately enhanced the production of grain yield of wheat. Scheduling of nitrogen (50% basal + 25% CRI + 25% flowering) enhanced the nitrogen uptake efficiency and total nutrient uptake by crop than other scheduling of nitrogen. However, application of herbicide mixtures as a postemergence (30 DAS) with increased dose of nitrogen applied as 1/2 basal and topdressing 1/4 at CRI and 1/4 at flowering is most effective.

Filed experiment was done to evaluate the allelopathic potential of sugarbeet and canola residues on weeds of chickpea field. Five treatments, viz. 1: Chopped residues of canola, 2: Chopped residues of sugarbeet both were separately incorporated to 25 cm depth soil, 20 days before sowing, 3: Shoot aqueous extract of canola, 4: Shoot aqueous extract of sugarbeet which were separately sprayed at post emergence stage and 5: Without any residues and spraying as control. The weed control treatments reduced the total weed cover, weed density and total dry weigh of weed. The reduction in weed density with canola and sugarbeet residues incorporated with soil were up to 42.7 and 57% respectively, at 45 days after sowing and 41% and 52.4%, respectively, at 90 days after sowing, compared to control. However, post emergence spraying of shoot aqueous extract of canola and sugarbeet, suppressed weed density up to 37.2 and 35.6% at 40 days after sowing and 56.7% and 49.2% at 90 days after sowing respectively, compared to control. Weed control treatments reduced weed cover (%), weed biomass and weeds stem length. Incorporation of canola and sugarbeet residues in soil reduced weed cover (%) by 47.9% and 57.6%, respectively, while spraying of shoot water extract of canola and sugarbeet suppressed weed cover (%) by 31.7% and 42%, respectively at 90 days after sowing. Application of canola residues and spraying shoot aqueous extract of canola increased chickpea yield by 25.4% and 39.5% respectively, while application of sugarbeet residues and shoot aqueous extract of sugarbeet decreased chickpea yield by 22% and 29.8% respectively compared to control. All nutrient elements analyzed in the leaves of weed generally were lower than control for all treatments. Incorporation of crop residue of canola and sugarbeet on weeds were more effective than spraying water extract of these plants.

A field experiment was conducted during the Kharif season of 2012 and 2013 to evaluate the effect of weed management practices on weed dry weight, yield attributes, yield and economics of blackgram (Vigna mungo L.). All the weed species were controlled effectively by pre-mix herbicides as compared to alone application of pendimethalin as pre-emergance and imazethapyr as post-emergence. The reduction in total dry weight of weeds (6.13g/m2) and maximum weed control efficiency 95.74% was found significantly higher with weed free treatment over all the weed control treatments except pre-mix herbicide imazethapyr + imazamox at 0.05 kg/ha PoE having 12.20g/m2 weed dry weight and 91.53% weed control efficiency at 60 DAS stage of crop growth. The significantly higher seed (0.89 t/ha) and straw (2.91 t/ha) yield was recorded in weed free plot over all the treatments, which was followed by imazethapyr + imazamox (pre-mix) at 0.05 kg/ha as (0.84 and 2.89 t/ha) and pendimethalin + imazethapyr (pre-mix) at 1.0 kg/ha (0.80 and 2.82 t/ha) treatments. However, the maximum net return of ` 17,135/ha and benefit:cost ratio (2.35) was found with imazethapyr + imazamox (pre-mix) at 0.05 kg/ha followed by pendimethalin + imazethapyr (pre-mix) at 1.0 kg/ha (` 16,410 and 2.30) treatment.

The field experiment was conducted during Kharif 2010 with finger millet Hebbal, Bengaluru. The finger millet crop was grown followed by groundnut during summer and continued up to 2014. The pooled data of five years of finger millet crop from 2010 to 2014 during Kharif indicated that application of butachlor at 0.75 kg/ha more or less gave similar grain yield (3.12 t/ha) to hand weeding twice (3.52 t/ha) due to good control of weeds. Continuous application of alachlor 1.0 kg /ha in groundnut and 2,4-D sodium salt 0.75 kg/ha in finger millet paved way for dominance of grasses particularly Digitaria marginata, Dactyloctenium aegyptium and Echinochloa colona, whereas pendimethalin treated plots showed higher emergence of Commelina benghalensis. A saving in weeding cost to an extent of ` 6,810 to ` 6,980/ha in finger millet was realized by using herbicides as compared to hand weeding. None of the herbicides affected the establishment, growth and yield of succeeding crops over the past five years, in spite of herbicides being applied continuously on the same piece of land.

Three P2O5 levels, viz. 0, 30 and 60 kg/ha were evaluated under six weed management practices, viz. weedy check, pendimethalin followed by (fb) hand weeding (HW), stale seedbed (SSB), SSB + pendimethalin fb HW, raised stale seedbed (RSSB) and RSSB + pendimethalin fb HW in pea during Rabi 2006-07 and 2007-08 on a silty clay loam soil at Palampur. Phalaris minor, Vicia sp. and Polygonum alatum were the major weeds found growing in association with peas. Stale seedbed and raised stale seedbed were significantly superior to weedy check in reducing total weed dry weight, weed growth rate, NPK depletion by weeds and increasing crop dry matter, crop growth rate (CGR), relative growth rate (RGR), NPK uptake by crop and subsequent radish yield. Superimposition of pendimethalin + hand weeding further improved the effectiveness of stale seedbed and raised stale seedbed in reducing total growth rate of weeds and NPK depletion by weeds and increasing crop dry matter, CGR, RGR, NPK uptake by crop and subsequent radish yield. Weeds in weedy check removed 39.3 and 53.6 kg N/ha, 16.5 and 16.6 kg P/ha and 24.1 and 27.4 kg K/ha during the first and second year, respectively. All weed control methods being at par resulted in significantly higher available P content after pea harvest. Weed dry weight and growth rate of weeds, NPK uptake by green pods and straw of pea, nodules/plant, available soil N and P after harvest of pea and subsequent radish yield increased with increase in the rate of P. NPK depletion by weeds, crop dry weight, CGR and RGR increased upto 30 kg P2O5/ha.

A field experiment was conducted during 2010 to 2012 at Junagadh (Gujarat) to study the integrated weed management in sesame. Pendimethalin as pre-emergence, while imazethapyr and quizalofop-ethyl as postemergence were tested alone and in integration with hand weeding and interculturing. The quizalofopethyl 40 g/ha as post-emergence (20-25 DAS) + HW and IC (45 DAS) and pendimethalin 450 g/ha as preemergence + HW and IC (30 DAS) were found equally effective to the weed free check in controlling weeds and improving growth and yield attributes and ultimately seed yield (1.21 and 1.16 t/ha) and stalk yield (2.01 and 1.85 t/ha) of sesame. These treatments also recorded higher net returns (` 44,066 and 42,242/ha) and B:C ratio (3.58 and 3.54), therefore, these integrated weed management practices could become effective and economical under south Saurashtra agro-climatic conditions of Gujarat.

To standardize dose and time of application of post-emergence herbicides in garden pea (Pisum sativum var. hortense) under mid-hills of Himalaya, eleven treatments, viz. imazethapyr 100 and 150 g/ha at 20 and 40 DAS, quizalofop 25 and 37.5 g/ha at 20 DAS, isoproturon 1.0 and 1.25 kg/ha at 40 DAS, pendimethalin 1.5 kg/ha (pre-emergence), hand weeding twice (30 and 60 DAS) and unweeded check were tested during the winter (Rabi) season of 2005-06 and 2006-07 at Palampur. The major weed flora was constituted of Phalaris minor, Avena fatua and Vicia sativa in both the year. Post-emergence application of all the herbicides except quizalofop 25 g/ha at 20 DAS and hand weeding twice resulted in significantly lower dry weight of weeds over pre-emergence pendimethalin 1.5 kg/ha. Higher doses of all the post-emergent herbicides were superior to their lower doses. Significantly lower dry matter accumulation of all the weed species and highest weed control efficiency was obtained with imazethapyr 150 g/ha (40 DAS). Imazethapyr 150 g/ha at 40 DAS resulted in maximum plant height, dry matter accumulation, crop growth rate, relative growth rate nodule count and weight and green pod and haulm yields. Weeds in untreated check reduced pea pod yield by 56.8% over the best post-emergent herbicidal treatment (imazethapyr 150 g/ha at 40 DAS) in 2005-06 and 60.1% in 2006-07.

Intensive use of agro-chemicals coupled with congenial edaphic and weather conditions during Kharif season aggravate the weed menace, resulting into low yields of soybean. The experiment was conducted on the agricultural farm at Jawaharlal Nehru Krishi Vishwa Vidyalaya at Jabalpur in 2011-12. The rampant weed species identified in the experimental field was monocot weeds Cyperus rotundus (25.8 and 23.6%) followed by Echinochloa colona (23.1 and 23.3%) and Commelina benghalensis (15.6 and 17.8%). Beside these dicot weeds Eclipta alba (19.1 and 20.3%), and Alternanthera philoxeroides (16.4 and 14.9%) were also found in soybean ecosystem at 45 DAS and harvest stage, respectively. The weed menace was minimum under weed free treatment. Among the propaquizafop treatments, activity of propaquizafop at lowest dose 62.5 g/ha and highest dose 75 g/ha as post emergence was not well marked against most of weeds (broad-leaved) but imazethapyr applied at 50, 75, 100 g/ha controlled broadleaved and grassy leaved weeds. Among herbicidal treatments, combined application of propaquizafop + imazethapyr as post-emergence 75 + 100 g/ha was most effective to reduced most of weed flora.

A field experiment was conducted to study the efficacy of different pre- and post-emergence herbicides and their combinations to control the weeds in soybean during Kharif season of the year- 2012. Application of imazethapyr 0.100 kg/ha + quizalofop-ethyl 0.075 kg/ha as post-emergence was found to be more efficient to control monocot and dicot weeds in soybean which recorded lowest weed density, dry matter and weed index. It also found superior in respect of various growth and yield attributes. Highest seed yield (2.45 t/ha) and straw yield of soybean and maximum gross return (` 81,500/-) and net return (` 56,269/-) were also recorded in imazethapyr 0.100 kg/ha + quizalofop-ethyl 0.075 kg/ha as postemergencewith highest B:C ratio of 3.23. It was also found responsible for highest uptake of N, P and K by soybean crop and lowest uptake of these plant nutrients by weed plants.

Imazethapyr is widely used in pulses and leguminous crops including soybean for control of a broad spectrum of weed species. This has often resulted in carryover effects on several sensitive rotational crops. Therefore field studies were conducted for two consecutive years to evaluate residues of imazethapyr in the soil and the soybean crop produce. Imazethapyr was applied at 100 and 200 g/ha as post-emergence herbicide in soybean field. Residues of imazethapyr were found in the range of 0.011 to 0.063 μg/g in the straw following an application in soybean field at 100 to 200 g/ha in both the years. However in the soil and soybean oil, residues were found below 0.01 μg/g in both the years at two levels of application of imazethapyr. The overall residues were less in the soil as compared to the plant samples. Terminal residues of imazethapyr in soybean plant and soil were found below maximum residue level (MRL) limits. This study demonstrated enrichment of imazethapyr residues in soybean plants after repeated application. Based on this study a pre-harvest interval of 80-90 days for soybean crop after imazethapyr application is suggested.

To study the efficacy of pendimethalin alone or in combination with neem cake and castor cake, seed treatment with various herbicides and post-emergence application of glyphosate at very low concentrations, field experiments were conducted during Rabi season of 2008-09 and 2009-10, at village Obera, Distt. Bhiwani and Dry land Research Area of CCS HAU Hisar (Haryana). Feasibility of adoption of results of study was tested by multi location field trials conducted through farmers’ participatory approach in different parts of state during 2010-2013. Pre-emergence, pre-plant incorporation or herbigation of pendimethalin along with hoeing as well as use of organic manures, viz. castor cake and neem cake proved ineffective in minimizing density of this weed. Seed coating of mustard seeds with 1.0 ppm of chlorsulfuron or triasulfuron gave 70-98% control of Orobanche aegyptiaca but efficacy of seed treatment with sulfosulfuron was poor. Post emergence application of glyphosate at 25 and 50 g/ha with 1% solution of (NH4)2SO4 at 25 and 55 DAS showed promise with 63-100% control of this weed not only in experimental fields but in large scale farmers’ fields. Glyphosate dose range is very limited. Over dosing of glyphosate, resulted in 15-35% toxicity to mustard in terms of marginal leaf chlorosis, slow leaf growth and bending of apical stems and stunting with yield penalty. Bleaching of few leaves of mustard occurred with 50 g/ha dose at 55 DAS, which also recovered within 20 days resulting with no loss in yield.

Field experiment was conducted to study the influence of integrated weed management practices on seed pod yield in groundnut at Agricultural Research station, Vaigaidam during Rabi 2011-12. Weed control efficiency was higher with pre-emergence application of oxyfluorfen at 0.25 kg/ha followed by hand weeding on 20 DAS and pendimethalin at 0.75 kg/ha followed by a hand weeding on 20 DAS at different intervals of 10, 25, 40 and 60 DAS. Weed density of sedge was significantly lowered with preemergence application of oxyfluorfen at 0.25 kg/ha on 3 DAS. Number of pods per plant and seed pod yield was significantly higher with pre-emergence application of pendimethalin at 0.75 kg/ha, alachlor 1.0 kg/ha) and oxyfluorfen at 0.25 kg/ha followed by hand weeding at 20 DAS. Layby application of pendimethalin at 0.75 kg/ha at 3 and 45 DAS after earthing up was also at par with pre-mergence herbicide followed by hand weeding. Phytotoxicity symptoms has been observed with layby application of oxyflourfen 0.25 kg/ha on 45 DAS after earthing up and this resulted lower yield even if this treatment has recorded lesser weed density.

Application of herbicides and other agro-chemicals used in agriculture affects the vital functions and population dynamics of soil microorganisms. Soil microbial population was assessed in 30 days interval up to 90 days in mango and citrus orchards. Among the treatments, intercropping of greengram-peagreengram recorded higher bacterial population (21.7 x 106cfu/g), was followed by intercropping of cowpea-pea-cowpea (19.5x106 cfu/g) at 90 days after spraying. It was found that the highest fungi population was recorded in intercropping of greengram-pea-greengram combined with herbicide application treatment (14.4 x 103 cfu/g). Similarly, higher actinomycetes population was observed in intercropping of greengram-pea-greengram treatment (8.2 x 103cfu/g) followed by intercropping of cowpea-pea-cowpea (7.3 x 103cfu/g) in mango orchard. In citrus field, highest bacterial population was observed in intercropping of greengram-pea-greengram treatment (21.3 x 106cfu/g).This was followed by intercropping of cowpea-pea-cowpea (18.4 x 106 cfu/g). The maximum fungi population (14.8 x 103cfu/g) was observed in cowpea-pea-cowpea treatment and maximum actinomycetes (8.4 x 103 cfu/g) population was recorded in intercropping of greengram-pea-greengram treatment. Basal respiration was significantly more in treatments of intercropping systems. Among the treatments, intercropping of greengram-pea-greengram treatment (193 mg/kg of CO2-C) had more basal respiration rate during Kharif season in mango orchard. Similar trends were observed in citrus orchard.

Lethal soil temperature impedes tuber formation, enhances respiration and depletes the tuber’s reserves and reduced size and viability. Attempts were made to increase soil temperature to lethal level by clear plastic mulch (PM), with hot water irrigation (HW), and its effect was assessed on growth of C. rotundus. During June 2010, quantity and frequency of hot water irrigation required to maximize the soil temperature was standardized using rain out shelter, load cell–digital weighing device by gravimetric method (40 liter/m2 and once in 4 days). During September 2011, effect of randomly stitched varied thickness 50, 75, 125 and 175 micron plastic mulch of size 1.25 x 1.25 m2 was spread over C. rotundus infected micro-plot and HW irrigated on soil temperature was assessed. Increased soil temperature under different thickness PM was at par with 175 micron. Further, the mean soil temperature and day/night fluctuation in plastic mulch with hot water (PM + HW) plot was congenial for C. rotundus growth, enhanced spouting and development of new tubers during September. During April 2012, hot water irrigated during 2.00-3.00 PM, soil temperature reached lethal level. Further, woolen blanket cover (WBC) between 4.0 PM to next day 9.0AM, retained warm temperature during night and maintained higher initial soil temperature next day. Thus during April, led soil temperature (58º C) to lethal level during 30 days of integrating PM + HW + WBC and caused drastically reduction of biomass (87%), number of tubers (62%) per 0.025m2 with loss of tuber viability.

Population dynamics and sex ratio of two co-existing species of Water hyacinth weevils, Neochetina bruchi Hustache, 1826 and N. eichhorniae Warner, 1970 (Coleoptera: Curculionidae) were studied. The weevil attack on Water hyacinth was investigated monthly for four years in different water bodies. The weevil’s abundance was affected by temperature, humidity and rainfall. The population of the weevils in general was highest (14.97 weevils/plant) in September when the humidity level was very high (88%) with the average of temperature almost 26o C. The lowest abundance (2.49 weevils/plant) was in January when the temperature was the lowest (15.7o C). The abundance of N. bruchi was significantly higher than the population of N. eichhorinae (1:0.04) in Jabalpur, India. Statistical studies revealed that the sex ratio was in favour of female in both the species (1:0.52 and 1:0.70 for N. bruchi and N. eichhorniae, respectively).

The present study was conducted to find out the extent of leaching of butachlor, pretilachlor, 2,4-D and oxyfluorfen in two soil types, viz. Type I [coarse textured low organic matter soil (Mannuthy–Ultisol] and Type II [fine textured high organic matter soil (Alappad-Inceptisol]. Intact soil columns were collected from the paddy fields after the harvest of second crop. Butachlor, pretilachlor, 2,4-D and oxyfluorfen were applied in moist soil columns at the recommended rate of application. Soil samples from different depths up to 10 cm (top 5 segments of 2 cm each) and the leachate at 30 and 60 cm depths were analyzed for herbicide residues using gas chromatography. Among the four herbicides tested, 2,4-D registered highest level of residue in the leachate (0.20 ppm at 60 cm depth). Pretilachlor and butachlor followed the same trend in the pattern of movement of residue through the soil columns. However, the leachate of pretilachlor registered much lower quantity of residue (0.006 ppm). Fine textured organic matter rich soil recorded lower residue levels compared to the soil with coarse texture and poor organic matter. It could be attributed to the high adsorptive power of the soil, especially at the top layers with high organic matter content. Oxyfluorfen residues could not be detected in the leachate, because of its poor water solubility.

The term ‘weed’ always has a negative connotation not only by its presence as a plant but as a seed also. The movement of most of the weeds from one location to the other is mainly through their seeds. Correct identification of weed seeds is therefore necessary for strict quarantine to check the spread of weed seeds from one place to another. Accurate identification of weed seeds requires skill and good judgment on the part of the examiner and it is a difficult task for a layman. Therefore, availability of a state of art technology for identification of weed seeds is very much needed. For identification of weed seeds, a Knowledge Based System (KBS) contains information about 120 weed seeds with 11 parameters each has been developed at the Directorate of Weed Research, Jabalpur (India) using Visual Basic. Net as front-end application and MS Access as back-end application with user-friendly menus. In this study, a rule based system for identification of weed seeds was developed that helps the stakeholder in identifying the weed seeds.

-

-

-

-

-