Weed Science

Parthenium hysterophorus L., commonly known as carrot weed or congress grass in India has been considered as one of the worst weeds responsible for causing health problems in men and animals besides loss to crop productivity and plant biodiversity.  The weed has infested about 35 million hectares of land in India since its first notice in 1955. Now it has become one of the main weeds in almost all types of agricultural lands besides infesting wasteland, community land, road and railway track sides and forests. In an attempt of biological control, search for suitable bioagent began in 1980s in India through systematic surveys. The work on biological control through competitive plants was started with the search of Cassia sericea from south India which lead to more attempts to manage Parthenium by competitive plant species. Casia tora and C. sericea have been recommended most suitable plant species for management of Parthenium in wasteland, on the raod side and community land. Likewise, in spite of hundreds of reports of pathogens causing disease on Parthenium, none of them has qualified as successful bioagent. So far, attempts of developing effective mycoherbicides have not yielded any success. Not even a single indigenous insect species has proved successful in spite of occurrence and infestation by many species. Under classical bilogical control of Parthenium in India, three insect species were imported in 1983 from Mexico, out of which only host-specific leaf-feeding beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) was proved successful. Z. bicolorata has established in many parts of the country and has been found responsible to decrease the Parthenium densities in different parts of India. This paper gives details of current status of biological control of Parthenium and future strategies in India.

A field experiment was conducted at the Crop Research Centre of RAU, Pusa, Bihar during Kharif 2006 and 2007 to evaluate the comparative efficacy of herbicides fenoxaprop-p-ethyl with standard doses of quizalofop and pendimethalin to control grassy weeds in jute grown for seed production.  Losses in seed yield in control plot were observed 63.4% in comparison to hand weeding twice. Weed species count at 40 and 60 days after sowing (DAS) was found lowest in fenoxaprop-p-ethyl at 67.5 g/ha treated plot while seed yield was higher in the  fenoxaprop-p-ethyl at 56.25 g/ha. Morpho-physiological attributes of jute viz., plant height, base diameter, number of capsules per plant, 1000 seed weight and seed yield were  found significantly higher in fenoxaprop-p-ethyl at 56.25 g/ha which showed at par with quizalofop at 62.5 g/ha among the herbicidal treatments. The highest weed control efficiency was observed in fenoxaprop-p-ethyl at 67.5 g/ha but yield attributes and yield were found higher in fenoxaprop-p-ethyl at 56.25 g/ha. The study also revealed post emergence herbicides-fenoxaprop-p-ethyl and quizalofop more effective than pre emergence herbicides pendimethalin in controlling the weeds in jute.

A study on crop-weed competition in field pea comprising of weedy and weed-free conditions upto 30, 60 and 90 days after sowing and at harvest was conducted at the experimental research farm of Pulses Research sub-station, Samba, SKUAST,  Jammu during Rabi seasons of  2003-04 and 2004-05 to find out the critical period of crop-weed competition in field pea. Weed competition index increased with an increase in duration of weedy condition ranging from7.3 to 42.0 during Rabi 2003-04 and 1.19 to 56.3 during rabi 2004-05. On the other hand, increase in weed-free period from sowing to harvest decreased weed competition index from 2.9 to 42.0 during Rabi 2003-04 and 4.3 to 22.0 during 2004-05. Weed free condition beyond 60 days after sowing did not bring significant improvement in field pea seed yield. The highest additional net return (Rs. 2040/ha) and additional net return/rupee invested (0.35) were kept weed free upto 60 days after sowing. The critical period for crop-weed competition was observed to be between 30-60 days after sowing when the crop should be kept free from weeds to prevent the potential yield loss and to economize weeding in field pea.

Microbial activity and population dynamics of bacteria, fungi, actinomycetes, Azotobacter and phosphate solubilizing fungi (PSF) following application of butachlor was studied in a black cotton soil. Microbial population declined significantly due to butachlor treatment. Total population of fungi showed relatively more susceptibility than bacteria to butachlor.  At recommended dose, the toxic effect of butachlor on total bacteria disappeared by 30 days after application (DAA), but the soil could not regain its lost population of Azotobacter, total fungi and PSF during the study period of 45 days. Total microbial activity in terms of CO2 evolution from the soil sharply decreased by butachlor. Addition of glucose at 10 mg/kg soil nullified the adverse effect of butachlor on total microbial activity.

An experiment was conducted to study the production potential of rice under varying population densities of barnyard grass (Echinochloa crusgalli). There was a significant reduction in plant height, dry matter production as well as in yield by rice plant with increasing population density of barnyard grass from 25 plants/m² to 250 plants/m² because weed plants compete for growth factors like light, nutrients and space, etc. The reduction in dry matter was to the tune of 35.76, 32.26 and 35.80% in 250 plants of barnyard grass as compared to pure rice crop in 2005 and 52.11, 45.56 and 44.41% in 2006, respectively. A decreasing trend in panicle length, number of grains per ear, 1000 grain weight, grain and straw yield were observed as plant density of barnyard grass increased from 25 plants/m² to 250 plants/m² during both the years of investigations. At higher densities of barnyard grass, there was a gradual increase in dry matter production. Hence there was more suppression of rice crop at higher weed densities which resulted in significant reduction in grain yield of rice crop.

Field experiments were conducted at wetland farm of TNAU during rabi 2006-07 and kharif  2007, to evaluate the efficiency of mechanical weeders on weeds, productivity and economics of aerobic rice. Minimum weed density, weed dry weight and higher weed control efficiency including grain yield of aerobic rice were obtained in plots receiving pre-emergence application of pendimethalin at 1.0 kg/ha followed by mechanical weeding with single type sweep weeder at 45 DAS followed by single wheel hoe at 45 DAS and both proved more remunerative than hand weeding twice at 25 and 45 days. 

Effect of rice residue management practices (removal, burning and incorporation), weed control measures (weedy check and herbicide) and nitrogen levels (60, 120 and 180 kg/ha) on the weed infestation, wheat yield and fertility status in a swell-shrink black cotton soil was studied during 2003-06.  The herbicide treatment included application of isoproturon 1.0 kg/ha in the 1st year and tank mix of isoproturon 0.75 kg + 2,4-D 0.5 kg per hectare during the subsequent years.  Residue incorporation reduced weed density, especially of Phalaris minor, resulting highest wheat yield during 2nd and 3rd year.  Residue incorporation gave highest net monetary return of Rs. 57781 followed by Rs. 51440 and Rs. 48081 per hectare in the burning and straw removal treatments, respectively.  The highest B:C of 6.79 was also recorded in the residue incorporation treatment followed by 6.19 and 3.86 in the burning and straw removal treatments, respectively.  Herbicide application increased wheat yield and the net monetary return (B : C ratio).  Irrespective of straw management practices, no increase in wheat yield was recorded beyond the N dose of 120 kg/ha. Compared to burning, the incorporation of rice straw significantly increased the organic C, and the bacterial and fungal population in soil.  It was concluded that rice straw incorporation 5 t/ha was best among the given straw management practices in terms of weed density reduction, improved soil health, increased wheat yield, monetary return and B : C ratio.

A field experiment was carried out at Ludhiana during winter 2007-2008 to find out effective and safe herbicides for radish (Raphanus sativus L.). Pre-emergence herbicides viz., pendimethalin (0.37, 56 and 0.75 kg/ha), trifluralin (0.6, 0.9 and 1.2 kg/ha), alachlor (1.25, 1.87 and 2.5 kg/ha), oxyfluorfen (0.117, 0.147 and 0.176 kg/ha), vis-a-vis, two hand hoeing (20 and 40 days after sowing) and unweeded control were evaluated. Uncontrolled weeds reduced the radish root yield by 10.7 to 27.1%. All the herbicidal treatments significantly reduced weed density and dry matter. Trifluralin 1.2 kg/ha recorded the highest radish root yield and was at par with trifluralin 0.9 kg, pendimethalin 0.75 kg, alachlor 1.25 and 2.5 kg, oxyfluorfen 0.147 and 0.176 kg/ha and two hand hoeing. The herbicides did not influence the total soluble solids and isothiocyanate content in radish roots. Herbicide residues in crop roots were below detectable level.

A field experiment was conducted during the rainy (kharif) seasons of 2007,2008 and 2009 to find out the relative efficiency of weed management practices in Okra (Hibicus esculentus L.). The result indicated that the highest weed control efficiency was achieved with the treatments fluchloralin 1.0 kg/ha preplant application + 1 HW followed by alachlor 2.0 kg/ha pre-emergence. application + 1HW. The data on yield attributing charaters viz, number of pods/ plant and plant height were significantly influenced by various weed management treatments. The highest fresh pod yield was recorded with the application of fluchloralin 1.0 kg/ha preplant application supplemented with 1HW. Significantly lowest fresh pod yield of okra was recorded in weedy check plots.

Field investigations were carried out during three consecutive rabi seasons (2000-01 to 2002-03) at Bikaner (Rajasthan) with a view to find out the broad spectrum post emergence herbicide against broad leaf weeds in wheat (Triticum aestivum). Results revealed all cultural and post emergence herbicidal treatments effectively reduced the dry weight of weeds by 33.6-91.3% as compared to weedy check. The highest values of tillers/plant, length of ear, test weight and grain yield of wheat (2530 kg/ha) obtained with B: C 3.1 under post emergence application of metsulfuron-methyl at 0.004 kg/ha. The grain yield recorded with this treatment was at par with that recorded with post emergence 2,4-D EE at 0.5 kg/ha .

Field experiments were conducted to find out the effectiveness of dual cropping of green manure crops, its methods of incorporation and levels of nitrogen on weed management and to study the cost effectiveness of the system of dual cropping of green manure crop in semi-dry rice. Among the two green manure crops, cowpea (Vigna unguiculata (L.) Walp.) was more effective in suppressing weeds and recorded the minimum weed population and weed dry matter compared to horse gram (Macrotyloma uniflorum (Lam) Verdc). Incorporation of green manure crops with 2,4-D significantly reduced weed population and weed dry weight compared to other incorporation methods. Nitrogen application at different levels had no significant influence on weeds. Dual cropping of cowpea and its incorporation at 45 days after sowing using 2,4-D was able to meet 25% N requirement beside reducing the weeds in semi-dry rice with increased productivity and profitability

Field and laboratory experiments were conducted to study the bioefficacy and residues of pre emergence herbicide pretilachlor in transplanted rice with eight treatments involving two doses of pretilachlor viz., 0.75 and 1.5 kg/ha, and with green leaf manure and gypsum as well as the farmer’s practice of two hand weeding and unweeded control. The results had indicated that the application of pretilachlor at 1.5 kg/ha fb HW registered higher weed control efficiency and numerically lower weed dry matter at all the stages. Removal of nutrients by weeds was also significantly differed with different treatments. The analysis of terminal residues of pretilachlor in rice grain, straw and post harvest soil indicated that the residues were below detectable limit.

Mass production of mycoherbicidal agent Sclerotium rolfsii (FGCC#02) under solid substrate fermentation was standardized. Mycoherbicidal potential of inoculum, grown on twenty agro wastes, applied on Parthenium at pre-emergence and post emergence stage was determined. Wheat grains and host leaves colonized inocula incited severe infection and was responsible for significant mortality at pre-emergence application while tea-bagasse-wheat bran-wheat straw (TBWW) was highly effective at post emergence stage. Contrary to these, waste cotton failed to cause appreciable mortality at both the stages.

A field experiment was conducted for two consecutive wheat seasons of 2005-06 and 2006-07 at crop research centre, GBPUA&T, Pantnagar on sandy loam soil to find out the effect of establishment methods and weed management practices on weed dynamics and productivity of wheat grown after harvesting of rice. Wheat was infested with Phalaris minor, Melilotus indica, Medicago denticulate, Chenopodium album and Rumex acetosella in weedy check at 60 days after sowing (DAS). Zero till sown wheat had significantly lesser infestation of all weeds except Rumex acetosella than other wheat establishment methods. Hand weeding twice at 35 and 55 DAS was most effective to minimize the weed density and their dry weight under all the wheat establishment methods. Zero till sown crop led to recorded significantly higher grain yield than other establishment methods, however, hand weeding twice was most effective in increasing the grain yield.

Sixty field demonstrations on herbicidal weed control technology were laid out during kharif of 2003 to 2005 in soybean at randomly selected three villages (Surai, Natwara, Belkharu) of Sahapura block, Jabalpur with an objective to show the performance and profitability of provon herbicides, viz. chlorimuron ethyl (10 g/ha), chlorimuron ethyl (10 g/ha) + fenoxaprop-p-ethyl at (75 g/ha) and imazethapyr at (750 g/ha) on weed growth and productivity of soybean at farmers’ fields. Fields were found infested with mixed weed flora. The herbicides under demonstration were found very effective in increasing grain yield of soybean by 53-98 per cent over farmer’s practice depending upon the intensity and growth of weeds. Benefit over the farmers’ practice were varied from Rs. 11,275/- to Rs. 12,600/- per hectare.

Sixty field demonstrations on herbicidal weed control technology were laid out during kharif of 2003 to 2005 in soybean at randomly selected three villages (Surai, Natwara, Belkharu) of Sahapura block, Jabalpur with an objective to show the performance and profitability of provon herbicides, viz. chlorimuron ethyl (10 g/ha), chlorimuron ethyl (10 g/ha) + fenoxaprop-p-ethyl at (75 g/ha) and imazethapyr at (750 g/ha) on weed growth and productivity of soybean at farmers’ fields. Fields were found infested with mixed weed flora. The herbicides under demonstration were found very effective in increasing grain yield of soybean by 53-98 per cent over farmer’s practice depending upon the intensity and growth of weeds. Benefit over the farmers’ practice were varied from Rs. 11,275/- to Rs. 12,600/- per hectare.

A field experiment was conducted to evaluate the bio-efficacy of new herbicides AEF 046360-8% EC and DIC 1468-14-22% EC alone and in combination at different doses against the complex weed complex in wheat crop. Wheat crop was mainly infested with grassy weeds like Avena ludoviciana, Phalaris minor and broad leaf weeds viz., Coronopus didymus, Anagallis arvensis, Melilotus spp. And Chenopodium album. Combined application of AEF 046360-8% EC and DIC 1468-14-22% EC (100+175 g/ha) was found effective against all the weeds as shown by the the lowest weed density of grassy as well as broad leaf weeds. AEF 046360-80% had better control over grassy weeds, whereas, DIC 1468-14-22% EC was found effective against broad leaf weeds. The highest grain yield was obtained with the application of AEF 4630-8% EC+ DIC 1468–14-22% at (100 + 175 g/ha) and was found at par with application of sulfosulfuron and AEF 4630-8% EC + DIC 1468-14-22% EC with their lower doses (80 + 140 g/ha).

A field experiment was conducted to study the efficiency of different weed management interventions in improving the carrying capacity of tiger grass (Saccharum spontaneum L.) infested pastures existing on riverbed deposits during 2002-03 to 2004-05 with nine treatment combinations comprising of manual eradication, glyphosate application 0.75 and 1.0% and agrostological interventions with 3 grass species in a randomized complete block design with three replications. After three years of treatment imposition, it was found that the application of either 0.75 or 1.0% glyphosate followed by planting either of napier hybrid (NB-21) or Cenchrus ciliaris was found equally effective in establishing a good grass cover as compared to Setaria as well as in smothering the regenerated growth of Saccharum plants resulting in reduction of its fresh biomass to 9.02-13.0 q/ha i.e. less by 90-94% as compared to its initial biomass of 116 q/ha which in turn was statistically similar to manual eradication of this weed. However, the application of glyphosate 0.75% on the regenerated growth of spring shaven Saccharum just before rainy season followed by planting of napier cuttings or Cenchrus ciliaris Rooted slips was found to be economically better with a net saving of Rs 500 and Rs 13970 over all the other similar treatment combinations of 1% glyphosate as well as manual eradication, respectively, besides a sizeable enhancement in forage yield.

Pretilachlor (2-chloro-2',6'-diethyl-N-(2-propoxyethyl)acetanilide) is a soil-applied post-emergent herbicide selectively used in rice. Photolysis of pretilachlor was studied on soil surfaces under UV light and sunlight. The rates of photodegradation of pretilachlor on different solid surfaces followed first-order rate kinetics, with half-lives of 7.2 min, 31.0 min, 30.1 min and 10 h, 30.1 h, 30.0 h for glass surface, black cotton soil and alluvial soil under UV and sunlight, respectively. Pretilachlor was stabilized on soil surface by organic and inorganic constituents

Experiment was conducted to see the effect of balance and imbalance level of nutrients on residue of imazethapyr. Imazethapyr was applied at 100 g/ha 25 days after sowing of soybean crop for managing annual and perennial broad-leaf weeds and sedges. Soil and crop samples were collected at harvest and analyzed by HPLC using photo diode array detector. Retention time of imazethapyr was found to be approximately 3.5 minutes. Residues of imazethapyr in soil at various treatments were found 0.0124 to 0.0121 mg/g. Concentration of imazethapyr in soil was maximum in 100% N + imazethapyr (T ) and minimum in (100% NPK + imazethapyr (T ) treatments respectively. At 7 8 harvest residue of imazethapyr was not found in soybean grains and straw in any set of treatments except T (100% N).

A field experiment was conducted at Agricultural Research Station, Ummedganj, Kota during kharif 2005 to evaluate suitable integrated weed management practices for increasing productivity and profitability of soybean and comprised eight treatments laid out in randomized block design with three replications. Hand weeding twice gave significantly higher branches/plant, seeds/pod, seed yield, straw yield and highest weed control efficiency (88.2%) at 60 DAS and least weed density and its dry weight at 30 and 60 DAS compared to rest of the treatments. Next best treatments were in situ mulching with weeds at 30 DAS and quizalofop ethyl 50 g/ha + chlorimuron ethyl 9 g/ha significantly reduced weed density, its dry weight and recorded higher seed, straw yield and weed control efficiency as compared to rest of the herbicidal treatments.

A field experiment was conducted to evaluate the bio-efficacy of azimsulfuron 50 DF against sedges especially Cyperus rotundus. As dose of azimsulfuron was increased from 25 to 30 g/ha, weed density and dry weight of weeds reduced at all the crop growth stages. Azimsulfuron was found comparable to pendimethalin and metsulfuron-methyl (MSM) alone but recorded significantly higher weed dry matter as compared to pendimethalin fb MSM at 45 DAS. Pendimethalin alone and azimsulfuron (30g) combined with MSM were comparable to standard check i.e. pendimethalin 1 kg/ha fb MSM 4 g/ha in terms of weed dry weight at 70 DAS. Azimsulfuron 30 g/ha along with MSM 2 g/ha recorded significantly higher yield (554 kg/ha) as compared to 25 g/ha along with MSM. There is no advantage of tank mixed application of azimsulfuron with MSM over azimsulfuron alone for the control of sedges and broad leaved weeds.

To find out the effect of different methods of herbicide application in garlic, a study was carried out during rabi season of 2006 at CCS Haryana Agricultural University, Hisar. Percent control of weeds was not affected due to method of application of herbicides. Pre-emergence application of pendimethalin at 1.0 kg/ha, oxyfluorfen at 200 and 250 g/ha, pre-emergence spray of trifluralin at 1.0 kg/ha either through sand mixing or spray and oxadiargyl at 100 g/ha applied as pre emergence or 10 and 25 days after transplanting (DAT) as post emergence spray supplemented with one hoeing proved very effective in minimizing population of C. album, Melilotus indica and Coronopus didymus. Efficacy of early post emergence application of oxadiargyl was more as compared to its pre emergence application.

An experiment was conducted during kharif 2003 at Post Graduate Institute Farm, Mahatma phule Krishi Vidyapeeth, Rahuri in randomized block design with three replications and nine treatments. Weed intensity and weed dry matter at harvest was significantly less in weed free treatment followed by fluchloralin as pre-planting incorporation (PPl) 1.0 kg/ha plus glyphosate at 45 days after sowing (DAS) were in second order. Whereas, weed intensity and weed dry matter was maximum in weedy check treatment (206.57 m2 and 12.22 q/ha respectively). Dicot weeds were found higher in proportion than monocot weed. The weed control efficiency and weed index were influenced by various treatment. It was higher (75.64%) weed control efficiency and lower (14.06%) weed index in pendimethalin PE 1.0 kg/ha plus glyphosate 1.0 kg/ha at 45 DAS as compared to other treatments except weed free treatment. Beneficial effect due to above treatments on growth characters resulted in enhanced yield. Maximum values of yield attributes were observed in weed free treatment followed by IWM treatments viz., pendimethalin PE 1.0 kg/ha plus hand weeding at 45 DAS, two hand weeding at 20 and 45 DAS and pendimethalin PE 1.0 kg/ha plus glyphosate 1.0 kg/ha at 45 DAS. The seed yield of pigeonpea (22.98 q/ha) and stick (65.03 q/ha) was maximum in weed free treatment followed by IWM treatment viz., pendimethalin 1.0 kg/ha plus hand weeding at 45DAS

Field experiments conducted consecutively for four years (2002-2005) during kharif at OUAT Research Farm in upland condition revealed that recommended practice (butachlor 1.0 kg/ha + HW at 25 DAS) produced significantly higher grain and straw yield of 3767 and 4980 kg/ha, respectively. The same treatment also registered higher net return of Rs. 8070/ha with B:C ratio of 1.55. Population of grasses, broad leaf and sedges were lowest at 60 DAS where recommended practice (butachlor 1.0 kg/ha along with one hand weeding at 25 DAS) was followed. Weed control efficiency was found to be maximum (86.2%) in farmer’s practice (HW at 25 and 45 DAS) at 60 DAS.

Experimental site constituted by monocot weeds viz., Brachiaria spp. Echinochloa colonam L. Cav. dicot weeds viz., Amaranthus viridis, Digeria arvensis, Chenopodium album and Euphorbia hirta L. and sedges viz., Cyperus rotundus L. Integration of pendimethalin as pre-emergence (PE) with clodinafop, metsulfuron-methyl and 2,4-D amine salt post emergence with or without hand weeding proved effective in reducing weed density and dry weight of weeds. Significantly the higher yield attributing characters were recorded under weed free, closely followed by pendimethalin 0.9 kg/ha as pre emergence followed by one hand weeding at 35-40 DAS. The maximum net return was obtained under pendimethalin 0.9 kg/ha as pre-emergence + 1 HW at 35-40 DAS and which was closely followed by pendimethalin 0.9 kg/ha PE + clodinafop 60 g/ha as post emergence at 35-40 DAS.