Weed Science

Comparative efficacy of penoxsulam against weed control in transplanted rice was studied at Agricultural Research Station, Ummedganj, Kota (Rajasthan). The experiment was laid out in randomized block design with 7 treatments and 4 replications. Results revealed that the major weed flora associated with the transplanted rice were grasses likeEchinochloa colonum and Echinochloa crusgalli; sedges like Cyperus rotundus, Cyperus difformis and Cyperus iria; and broad-leaved weeds like  Eclipta alba and Ammenia baccifera. Penoxsulam at 0.0250 kg/ha applied at 0-5 days after transplanting was most effective to check all types of weed growth. This treatment also gave the maximum grain yield and straw yield,  resulting in the lowest weed index, dry weight of weeds, weed persistence index and highest herbicidal efficiency index

A field study was conducted during 2009 at Raipur in an inceptisol with rainy season rice to evaluate the effect of herbicides application on biochemical characteristics of rhizosphere soil under different tillage systems. Four different types of tillage system were evaluated viz. (i) conventional-conventional (ii) conventional-zero (iii) zero-conventional and (iv) zero-zero. Among weed control measures, comparative effects of hand weeding and recommended herbicides application (butachlor as pre-emergence and fenoxaprop-p-ethyl + ethoxysulfuron as post-emergence herbicide 1.5 kg, 56.25 g and 15 g/ha, respectively) were tested compared with a weedy check (control). The conventional-conventional tillage system was found most effective to improve the biochemical characteristics of soil. Under this system, maximum organic C content was accumulated in rhizosphere soil and also found maximum enzyme activity (dehydrogenase activity, acidic phosphatase activity and alkaline phosphatase activity). Application of pre- and post- emergence herbicide reduced the biochemical activities in soil after its application (3 and 22 days after sowing, respectively) to 35 days of sowing of the crop thereafter it became normalize due to degradation of applied herbicides.

A field experiment was conducted at Varanasi to study the effect of different rates of carfentrazone-ethyl for controlling weeds in rice. Major weed flora were: Echinochloa colona, Echinochloa crussgalli, Dactyloctenium aegyptium, Caesulia axillaris, Ammania baccifera, Eclipta alba and Phyllanthus niruri. Application of carfentrazone-ethyl at 35 g/ha effectively reduced the density, dry matter accumulation and N, P, K depletion by weeds, and recorded the highest weed control efficiency. It also enhanced the growth parameters, grain and straw yield, nutrient uptake by the crop. Herbicides ethoxysulfuron at 15 g/ha, metsulfuron at 4 g/ha and carfentrazone at 15-35 g/ha applied as post-emergence and pendimethalin at 1.0 kg/ha as pre-emergence recorded higher values of yield attributes and yield.

Field and pot studies were conducted to determine the compatibility of dicamba in tank mix combination with sulfosulfuron and clodinafop against weeds of wheat (Triticum aestivum). Dicamba alone was effective against broad-leaf weeds only. No significant difference for broad-leaf weed control was observed between dicamba doses of 240 and 360 g/ha. Dicamba in combination with clodinafop and sulfosulfuron controlled the broad spectrum weed flora. The efficacy of dicamba in combination with clodinafop and sulfosulfuron was not affected for broad-leaf weed control. However, Phalaris minor control with clodinafop was reduced when dicamba applied as tank mix combination. The efficacy of sulfosulfuron was not affected by dicamba when applied as tank mixture and as a result this mixture (sulfosulfuron + dicamba 25 + 120 g/ha) had the highest wheat grain yield (4.99 t/ha). P. minor dry weight reduction with clodinafop 60 g/ha alone and in tank mix combination with dicamba 240 g/ha was 97.3 and 58.3%, respectively. In pot studies also, the tank mixing of dicamba did not affect the sulfosulfuron efficacy but clodinafop efficacy was significantly reduced against P. minor. The P. minor biomass reduction with clodinafop 30 and 60 g/ha was 84.8 and 99.6%, respectively and when dicamba 240 g/ha was added, the fresh weight reduction reduced to 62.6 and 78.6%, respectively, compared to untreated control.

An experiment was conducted during Rabi season of 2008-09 and 2009-10 at Varanasi (Uttar Pradesh) to evaluate the boiefficacy of carfentrazone-ethyl + sulfosulfuron in wheat. The experimental field was infested with Phalaris minor, Rumex dentatus, Chenopodium album, Anagalis arvensis and Melilotus spp during both the years of study. The result indicated that post-emergence application of carfentrazone + sulfosulfuron with surfactant at 45 g/ha recorded minimum density and dry weight of weeds and it was at par to 54 and 90 g/ha, without any phytotoxicity symptoms on the crop. Significant variation in wheat yield was recorded due to application of different herbicides when compared with control. Carfentrazone-ethyl + sulfosulfuron with surfactant at 45 g/ha recorded significantly the highest grain yield over its rate of 36 g/ha and it was at par to 54 and 90 g/ha. The regration equation indicated that extent of reduction could be 26.5 kg/ha for weed dry weight. The evaluation of weed dry weight and weed control efficiency of the different treatments and the regression of yield on it reveled that reduction in grain yield could be 0.025 t/ha for weed dry weight and 1% increase in the weed control efficiency increased the grain yield by 0.020 t/ha, respectively.

To study the floristic composition of weeds in greengram, 50 fields were surveyed in Hisar, Sirsa, Bhiwani, Mahender Garh and Fatehbad districts of Haryana state during July-August, 2011 and 23 fields were surveyed for blackgram in Shiwalik foot hills region of Panchkula, Ambala and Yamuna Nagar districts of the state during August-September, 2012. Weed flora in greengram was more diverse as compared to blackgram. Twenty-two weed species (5 grassy, 3 sedges and 14 broad-leaved) belonging to12 families were found dominant in greengram, where as in blackgram only 11 weeds of 7 families were found to be very aggressive. Broad-leaved weed Digera arvensis (L.) of family Amarthanceae was the most dominant and aggressive weed of both crops with a relative density and frequency of 511% and 86% in green gram whereas in blackgram it was 38% and 96%, respectively.  Dactyloctenium aegyptium (L.) was the most dominant grassy weed with IVI values of 24.5 and 22.6 in greengram and blackgram, respectively. Important broad-leaved weeds found in greengram were: Trianthema portulacastrum, Mollugo distachya, Cleome viscosa, Cucumis callosus, Corchorus tridens, Corchorus aestuans and Tribulus terristeris, whereas  in blackgram Commelina benghalensis, Physalis minima, Solanum nigrum and Chorchorus olitorious.

A field experiment was conducted at Jabalpur to evaluate the different sowing methods and weed control practices for higher grain yield of soybean. The dominated weed species among monocot weeds were Cyperus iria, Ehinochloa colona and Cynodon dactylon, however among dictot weed species Eclipta alba, Commelina diffusa, Alternenthera sessilis and Phylanthus niruri were observed during the growing season.The results revealed that the weed density of monocot (25.1/m2) and dicot (18.7/m2) weed was lowest in broad bed furrow (BBF) sowing method and application of pendimethalin (0.75 kg/ha) fb imazethapyr (0.75 g/ha. Maximum weed control efficiency (80.0%) was observed with the application of pendimethalin (0.75 kg/ha) fb imazethapyr (0.75 kg/ha). BBF sowing method also recorded highest yield attributes and grain and straw yield (1.47 and 1.51 t/ha). The BBF sowing method of soybean gave maximum net monetary returns and B:C ratio (` 16,584 /ha and 1.87, respectively).

A field experiment was conducted during summer season of 2006 and 2007 under irrigated condition in a sandy loam soil at Sriniketan, West Bengal to determine the critical period of crop-weed competition in sesame. Results revealed that weed-free condition between 15 and 45 days after sowing (DAS) significantly increased the yield of sesame, whereas the lower yield of was recorded when weeds were allowed to grow during this period. The maximum competition between crop and weed was between 15 and 45 DAS, which can be considered as critical period of crop-weed competition. However, the extrapolated critical period was determined from 19-42 DAS. To avoid the yield loss, weed management should be done in such a time so that minimum weed infestation is achieved in summer sesame. 

A field experiment was conducted at  GB Pant University of Agriculture & Technology, Pantnagar (Uttarakhand) to study the effect of different weed management practices on sugarcane ratoon.  The soil of the experimental field was clay loam in texture, medium in organic carbon (0.64 %), available phosphorus (26.5 kg P/ha) and potassium (240.3 kg K/ha) with PH 7.3. Experiment consisted of eight treatments was laid out in randomized block design with three replications. In the experimental field, Digitaria sanguinalis, Echinochloa spp., Ipomoea spp.,Cyperus rotundu and Parthenium hysterophorus were major weeds in both the years. Other weeds were Brachiaria mutica, Euphorbia hirta, Cleome viscosa, Phyllanthus niruri, Cannabis sativa, Lippia graveolens, Trichosanthes cucumerina and Physalis minima. Lowest density as well as dry weight of total weeds were recorded with hand weeding thrice at 30, 60 and 90 days after ratoon (DAR) of main crop which was at par with metribuzin 0.88 kg/ha at 3 DAR followed by (fb) one hoeing at 45 DAR followed by (fb) 2,4-D (Na Salt) 0.75 kg/ha at 2-4 leaf stage of broad-leaved weeds fb pre-emergence application of atrazine 1.5 kg/ha at 3 days after ratooning (DAR) fb 2,4-D (Na salt) 0.75 kg/ha at 2-4 leaf stage of broad-leaved weeds. The highest cane yield was recorded with the execution of three hand weedings at 30, 60 and 90 DAR treatment which was closely fb metribuzin at 0.88 kg/ha at 3 DAR fb one hoeing at 45 DAR fb 2,4-D (Na salt) 0.75kg / ha at 2-4 leaf stage of weeds.

A field experiment was carried out at Ludhiana, Punjab during 2009 and 2010 to study the effect of different weed control treatments on growth and yield of rapeseed. Eight herbicide treatments, viz. trifluralin at 0.48 kg and 0.60 kg/ha (pre-plant and pre-emergence), pendimethalin at 0.56 kg and 0.75 kg/ha (pre-emergence), pendimethalin at 0.75 kg/ha (pre-plant) and oxyfluorfen at 0.25 kg/ha (pre-emergence), two hand weeding (25 and 45 days after sowing) and unweeded control were kept. Two hand weedings, pre-plant application of trifluralin at 0.60 kg/ha, and pre-plant and pre-emergence application of pendimethalin at 0.70 kg/ha significantly decreased dry weight of associated weeds as compared to unweeded control. Weed control efficiency recorded similar trend as of dry matter of weeds.  Accordingly, the increased with application of these weed control treatments.

Parthenium  hysterophorus, is an annual herb that aggressively colonizes disturbed sites. In Pakistan, this weed is spreading very fast especially in north eastern parts of the province, Punjab. Due to lack of information on its spread, a survey was carried out in the district Rawalpindi where 8 sites were selected for sampling. The survey revealed very high density of P. hysterophorus at all sites and a total of 33 plant species were associated with P. hysterophorus. The relative density of weed in different sites of the district ranged from 8.2-64.5% while the relative frequency ranged from 14.2-29.6%. The extent of infestation was highest in denuded and fallow lands, especially in areas where soil has been disturbed. It was concluded that Parthenium is an extremely aggressive and prolific invasive weed in distract Rawalpindi and coordinated efforts are needed to manage this weed to stop its further spread.

Flora and fauna of Western Ghats, a biodiversity hot spot are under major threat due to various factors. Invasion of exotic species has been considered as one of the major threat in the area. In the present study, potential distribution of three obnoxious weeds, viz. Chromolaena odorata, Lantana camara and Parthenium hysterophorus was modeled using 32 environmental variables and MAXENT modeller. These three species showed distinct potential distribution patterns with only slight overlap between C. odorata and L. camara, and between L. camara and P. hysterophorus. Overlap of the former pair was seen mostly along the wet western slopes of Western Ghats, and latter along the eastern, rain shade dry areas. The environmental variables that contributed to the model showed that it was basically precipitation and temperature seasonality that defined their distribution. It was interpreted that the weeds might have adapted to different sets of environmental conditions throughout their distributional range; and hence, the variables operating in the study area contributing to the model may not be useful in predicting their presence elsewhere. It is concluded that to understand the full adaptability of these weeds, environmental variables can be studied at local levels and the results compiled for larger areas to get the full spectrum.

Adsorption–desorption of atrazine was measured in four soils of Hyderabad using batch equilibrium method at 27+1oC. The Freundlich equation was used to describe batch results. Both adsorption and desorption isotherms were well described by the Freundlich model. Fitted Kf value for desorption isotherms were consistently higher than those associated with adsorption. The opposite trend was observed for the exponential parameter n. The results revealed that the desorption data deviated significantly from adsorption data. The deviation, which is commonly referred to as hysteresis, was more prominent with higher adsorbed concentration of atrazine and incubation time. Desorption was significantly higher at the lowest adsorbed level of atrazine. The Freundlich Kf  and n values were higher than that for adsorption and increased with increase in initially adsorbed concentration of atrazine.

Weeds can be controlled effectively only when the management practices are employed at and early growth stage. Therefore, identifying weeds at seedlings stage is very essential for designing an efficient strategy for their management. However, it is a difficult task unless one has enough knowledge and experience. To help identifying weeds at seedling stage, an expert system has been developed at the Directorate. The expert system uses scientific name-based classification and a mix of the text description and images. The system is supported by a database containing information on 138 weed species with colour images of weed seedling at five growth stages. The expert system was evaluated following the conventional expert system evaluation methodologies. Results indicated that non-expert users were able to make weed seedling identification using the expert system more efficiently.

An experiment was conducted in randomized block design with 7 treatments comprising butachlor 1.5 kg/ha at 5-7 DAT, bispyribac-sodium 25 g ha at 15-20 DAT, bispyribac-sodium 35 g/ha at 15-20 DAT, bispyribac-sodium 50 g/ha at 15-20  DAT, weed-free, until harvest, two hand weedings at 20 and 40 days after transplanting and unweeded control. Results revealed that application of bispyribac-sodium 50 g/ha at 15-20 DAT resulted in significantly higher grain yield (5.70 t/ha), which was at par with bispyribac-sodium  35 g/ha at 15-20 DAT. Number and dry weight of weeds was also minimum in these treatments. However, the highest grain yield (6.05 and 6.55 t/ha) was obtained from weed-free treatment. Significantly lower weed density (9-10/m2), weed dry weight (12.5-13.7 g/m2), weed persistence index (0.03) and weed competition index (8.05-12.55) were recorded in the plots where bispyribac-sodium 35 g/ha at 15-20 DAT was applied. Significantly higher weed control efficiency and herbicidal efficiency index were recorded with bispyribac-sodium 35 g/ha at 15-20 DAT.

A field experiment was conducted at S.V. Agricultural College Farm, Tirupati to identify the effective and economic weed management practices for the control of weeds in drum seeded rice. The major weed flora in experiment field were Cyperus difformis (40.0%), Cyperus iria (21.40%), Cyperus rotundus (12.22 %), Echinochloa colonum (10.1%), Eclipta alba (6.5%) and Ammania baccifera (4%). Among the weed management practices, pre-emergence application of oxadiargyl 75 g/ha fb azimsulfuron 30 g/ha was found to be the most effective weed management practice in reducing the density and dry weight of weeds with higher weed control efficiency, higher yield attributes and yield (5.75 t/ha) including benfit : cost ratio (3.30) but it was being at par with two hand weedings. The reduction in grain yield due to heavy weed infestation in unweeded check was 51% compared to best weed management practice. Post-emergence application of azimsulfuron 30 g/ha was found effective in controlling sedges and bispyribac-sodium 30 g/ha was very effective in suppressing the grasses and broad-leaved weeds in drum seeded rice.

An investigation to study the sensitivity of nine wheat varieties, viz. ‘WH 1022’, ‘HD-2687’, ‘C-306’, ‘UP-2338’, ‘PBW-343’, ‘WH-542’, ‘WH-711’, ‘WH-283’ and ‘WH-147’ to  most popular used herbicide combination, i.e. sulfosulfuron + metsulfuron (R.M.) was undertaken at Hisar during Rabi seasons of 2005-06 and 2006-07.  At 15 DAT with recommended dose of herbicide 32 g/ha, the leaves of all wheat varieties except ‘C-306’ showed slight yellowing of leaves which disappeared with passage of time as at 30 days after treatment no yellowing was visible on leaves even at  double to recommended dose (64 g/ha).  In all wheat varieties, the grain yield  with x and 2x  doses was at par with weed-free check but higher than weedy check, indicating no detrimental effect of the herbicide on any variety tested.

An average decrease in grain yield by 15.42 % was observed due to season-long weed-crop competition. Lowest monocot and dicot weeds were observed with weed free treatment. The best weed control efficiency in case of monocot (90.8%) and dicot (82.8%) was achieved with metsulfuron-methyl and metribuzin, respectively compared to other herbicides namely pendimethalin, carfentrazone, fenoxaprop and 2,4-D. All the treatments except fenoxaprop, carfentrazone, 2,4-D and mixture of metribuzin and fenoxaprop application gave significantly higher grain yield compared to weedy check. However , higher additional net return (Rs. 31,359) was obtained with metsulfuron-methyl followed by metribuzin (Rs. 30,907).

A field experiment was conducted during Rabi     season of 2008-09 at Faizabad to study the effect of sowing methods and weed management practices on growth and productivity of wheat. Cross sowing recorded significantly higher growth, yield attributes in terms of plant height, number of shoots/m2, dry matter accumulation, number of spike/m2, spike length, number of grains/spike and grain (3.8 t/ha) and straw (5.5 t/ha) yields. The values of growth, yield attributes and grain (4.1 t/ha) and straw (6.1 t/ha) yields were higher in weed-free check. Application of isoproturon at 1.0 kg/ha + 2,4-D  500 g/ha was found best as compared to other herbicide treatments.

Pollen germination was tested in six Phalaris minor populations in a germination medium consisting of raffinose (7.5%) + boric acid (20 ppm) + calcium chloride (300ppm) supplemented with 0.1–2000 µM of fenoxaprop-p-ethyl, clodinafop-propargyl  and pinoxaden. The populations were also tested in a pot culture assay. A parallel response was observed with regard to the level of resistance in the two systems. The method showed the possibility of a rapid screening test for resistant populations.

In a study on chickpea at Parbhani, two hand weedings resulted in  the highest plant height, plant spread, branches, root nodules and dry matter followed by one hoeing  + 2 hand weedings, pendimethalin 0.75 kg/ha as pre-emergence, and quizalofop-p-ethyl 40 g/ha as post-emergence. Among the herbicidal treatments, the pre-emergence application of pendimethalin 0.75 kg/ha was effective in recording higher growth parameters followed by quizalofop-p-ethyl 40 g/ha as post-emergence. The highest grain and straw yields were recorded with one hoeing + two hand weedings, followed by 2 hand weedings.