Weed Science

Among crop husbandry practices, wheat straw incorporation brought about a significant reduction in Cyperus rotundus population and soil solarization in Cynodon dactylon population at 20 DAS in soybean. The total monocot weed population due to these two treatments was thus significantly lower. Summer cowpea for fodder, on the contrary, recorded the highest population of Cynodon and total monocot weeds, but the population of Commelina benghalensis was zero/nil and Parthenium hysterophorus was greatly reduced. Wheat straw incorporation had significantly higher Trianthema portulacastrum population, which resulted in very high dicot and total weed population. At 40 DAS of soybean, total monocot weed distribution was almost similar to what observed at 20 DAS. However, total weed population was the lowest in soil solarization and differed significantly with others. The monocot, dicot and total weed dry weight followed similar trend as their respective population and soil solarization proved most superior. At harvest of wheat, wheat straw incorporation; however, recorded the lowest total weed dry weight comparable with soil solarization and summer cowpea for fodder. Soil solarization and wheat straw incorporation were at par with each other on soybean grain yield, but solarization recorded significantly higher grain yield than others. Repeated tillage with irrigation and summer cowpea for fodder also recorded soybean grain yield significantly higher than in control/farmers’ practice. Wheat straw incorporation and repeated tillage with irrigation being at par with soil solarization recorded significantly greater number of ear-bearing tillers and grain yield of wheat. However, soil solarization recorded the highest system productivity in the soybean-wheat cropping system closely followed by wheat straw incorporation and repeated tillage with irrigation

Experiments were conducted to evaluate the effects of seed scarification, temperature, light, salt and osmotic stress, and pH on seed germination, and also the effects of seed burial depth on seedling emergence of Sida rhombifolia. Scarification with sulphuric acid released seeds from dormancy and stimulated germination; though germination of scarified seeds was not influenced by light. Seeds treated with sulphuric acid for 120 min resulted in 65% germination compared with 5% for non-scarified seeds. The response to scarification indicates that a hard seed coat is the primary mechanism restricting germination. In two separate experiments, a concentration of 111 mM sodium chloride and an osmotic potential of -0.49 MPa reduced maximum germination (64 to 65%) of S. rhombifolia by 50%. Germination was not influenced by the pH of buffered solutions ranging from 5 to 9, and it varied from 60 to 65% over this range. Seedling emergence was greater than 60% at burial depths of 0.5 to 2 cm, but decreased thereafter, and and no seedlings emerged from the seeds buried at 8 cm. The results of this study identify some of the factors enabling S. rhombifolia to be a widespread and problematic weed in the humid tropics and provide information that may contribute to its control

A field experiment was conducted during kharif 2006 at the Students’ Research Farm, Department of Agronomy, Punjab Agricultural University, Ludhiana on loamy sand soil to study effect of seed rate, spacing and herbicide use on weed management in direct seeded upland rice. Increasing seed rate from 40 to 60 kg/ha and row spacing from 15 to 20 cm, respectively, did not reduce the total weed population and weed dry matter at maturity. Seed rate and row spacing did not influence the grain yield significantly. However, all the weed control treatments i. e. application of pretilachlor 0.75 kg, pendimethalin 0.75 kg and thiobencarb 1.5 kg/ha significantly reduced the total weed population and weed dry matter production resulting in higher weed control efficiency as compared to weedy check. All weed control treatments produced significantly higher yield attributes which ultimately resulted in higher grain yield of paddy as compared to weedy check. Among different herbicidal treatments, thiobencarb 1.5 kg/ha produced highest grain yield of 5.51 t/ha which was at par with other weed control treatments. All weed control treatments reduced nitrogen uptake by weeds making it available to be used by the crop.

Efficacy of azimsulfuron and metsulfuron-methyl alone and in combination was evaluated against complex weed flora in transplanted rice at Karnal, Haryana, India during kharif 2006 and 2007. The experimental field was infested with grassy, broad-leaved weeds and sedges during two years to the extent of 43-54, 32-46 and 11-14%, respectively. Excellent control of broad-leaved weeds and sedges (90-100%) under all the treatments of azimsulfuron alone or admix with metsulfuron was observed. Pretilachlor and pretilachlor fb chlorimuron+metsulfuron provided better control of grassy weeds compared to azimsulfuron alone and in combination with metsulfuron. In this study, there was no significant effect of addition of metsulfuron to azimsulfuron on rice grain yield. Azimsulfuron and metsulfuron being safe for rice crop were found compatible and azimsulfuron 30 g+metsulfuron-methyl 2 g/ha applied at 15-25 DAT could be exploited in situations where weed flora was pre-dominated with broad-leaved weeds and sedges.

The nutrient uptake by red sprangletop (Leptochloa chinensis) and transplanted rice was studied under three off-season land management practices (raising green manure, undisturbed land and frequent cultivations after wheat harvest) in main plots with three crop plant densities (22, 33 and 44 hills/m2) and two weed management practices (pyrazosulfuron 0.015 kg/ha and two hand weedings) alongwith an unweeded control in sub plots. The frequent cultivations were able to significantly reduce the nutrient removal by the weed and increase the nutrient uptake by rice as compared to green manured and undisturbed land after wheat harvest, the latter two being at par. The increase in crop plant density from 22 to 44 hills/m2 reduced the nutrient removal by the weed and increased the nutrient uptake by rice. Two hand weedings and pyrazosulfuron 0.015 kg/ha were equally effective in reducing the nutrient removal by the weed and increased nutrient uptake by rice and were significantly better than the unweeded control.

Field experiments were conducted during summer and kharif seasons of 2001 and 2002 to evaluate the possibility of utilizing the biomass of weeds viz., Ipomoea carnea and Eichhornia crassipes either as fresh or as vermicompost prepared from such weed biomass for substituting fertilizer nitrogen in rice-rice system under puddle soil conditions. Results revealed that vermicompost prepared from either I. carnea or E. crassipes was at par or superior to fresh biomass incorporation and FYM in increasing crop yield, nitrogen uptake and improvement in soil nutrient status. Results also showed the possibility of supplementing 25 to 50% nitrogen through fresh biomass incorporation of I. carnea or vermicompost prepared from either I. carnea or E. crassipes. Significant increase in soil microbial population was also recorded due to incorporation of different sources of organic manure over the recommended nitrogen as fertilizer alone

A field study was conducted at Ladhowal, Ludhiana during 2004-05, 2005-06 and 2006-07 to evaluate alternate herbicides for control of atrazine tolerant Brachiaria reptans in spring sugarcane. Pre-emergence atrazine 1.0 kg (standard), metribuzin 1.4 kg, diuron 1.6 kg and pendimethalin 1.125 kg/ha alone, tank mix of pendimethalin 0.75 kg with atrazine 0.75 and 1.0 kg, metribuzin 0.875 and 1.4 kg and diuron 1.6 kg/ha, three hand hoeings at 30, 60 and 90 days and unweeded control were evaluated in RBD. Atrazine 1.0 kg/ha recorded Brachiaria population and cane yield similar to unweeded control. Metribuzin 1.4 kg and diuron 1.6 kg/ha alone, tank mixing of pendimethalin 0.75 kg with metribuzin 0.875 kg or atrazine 1.0 kg/ha reduced Brachiaria population by 82 to 96% and increased cane yield by 16 to 28% than alone atrazine 1.0 kg/ha. Weed control efficacy under above treatments varied from 67 to 72%, while it was only 12% with atrazine 1.0 kg/ha. Pendimethalin 1.125 kg/ha though reduced Brachiaria density by 89%; however, its lower activity over time resulted in poor weed control efficacy (45%) and similar cane yield to atrazine 1.0 kg/ha. Metribuzin 0.875 kg+pendimethalin 0.75 kg/ha recorded the highest cane yield (76 t/ha), net returns (Rs 48,200/ha) and benefit : cost ratio (0.840). Different weed control treatments did not influence cane quality. Metribuzin 1.4 kg and diuron 1.6 kg/ha alone, and tank mix of pendimethalin 0.75 kg either with metribuzin 0.875 kg or atrazine 0.75 kg/ha were very effective for control of B. reptans and attaining the highest productivity and profitability in spring sugarcane.

Based on two years’ (2004-05 and 2005-06) field experimentation, it was found that chlorsulfuron 30 g/ha, metsulfuron 4 g/ha and triasulfuron 60 g/ha reduced the density of different broadleaf weeds in wheat to the extent of 90-100% and proved better than sulfosulfuron (20 and 25 g/ha) and 2, 4-D Na salt (500 and 750 g/ha). Weed control efficiency (WCE) against total broadleaf weeds based on average dry weight of two years due to chlorsulfuron 30 g/ha, metsulfuron 4 g/ha and triasulfuron 60 g/ha varied between 86-89%; however, triasulfuron 40 and 60 g/ha was at par in this respect. Effective tillers and grain yield of wheat were maximum in the plots kept weed free throughout the crop season; however, statistically it was at par with chlorsulfuron 30 g, triasulfuron 40 and 60 g and metsulfuron 4 g/ha during both the years. Weeds growing throughout the crop season reduced the grain yield to the extent of 46 and 40% during 2004-05 and 2005-06, respectively. Plant height of succeeding crop of sorghum at 45 DAS was significantly reduced by triasulfuron 60 g/ha both under prepared and unprepared field conditions and also by sulfosulfuron 25 g/ha only under unprepared field situation. Similarly, fresh weight of sorghum under prepared field situation at 45 DAS during both the years and fodder yield at harvest during 2004-05 only were significantly reduced due to residual toxicity of triasulfuron 60 g/ha applied in wheat

Pinoxaden was evaluated for the control of grass weeds in wheat and barley. It was very effective in controlling Phalaris minor Retz., Avena ludoviciana Dur. and Polypogon monspeliensis (L.) Desf., but was ineffective in controlling broad-leaved weeds. The efficacy of pinoxaden without surfactant was significantly inferior to surfactant application. In various experiments, pinoxaden with surfactant improved the wheat yield >68% over control. The efficacy of pinoxaden (35 g/ha) in controlling grass weeds in wheat was similar to that of clodinafop 60 g/ha, fenoxaprop 100 g/ha and sulfosulfuron 25 g/ha. Wheat yields among these herbicides were similar, where fields were having dominance of grass weeds, but in the presence of both grassy and broad-leaved weeds, sulfosulfuron had an edge over three grass herbicides (pinoxaden, fenoxaprop and clodinafop) tested. Toxicity was not observed on any of the 18 barley genotypes screened for their sensitivity to pinoxaden (30 and 60 g/ha). Pinoxaden @ 30 g/ha effectively controlled isoproturon resistant P. minor in barley and provided 21.6% higher yield compared to isoproturon application.

A field experiment was conducted at Palampur, Himachal Pradesh during kharif seasons of 2002 and 2003, to study the weed competitive ability and productivity of maize as influenced by tillage and weed control methods. Among tillage methods, raised seed bed resulted in significantly lowest density and dry matter of weeds at 60 days after sowing (DAS) and harvest of the crop and was followed by conventional tillage. Raised seed bed and conventional tillage increased grain yield by 13.74 and 16.90% over zero tillage. Among weed control methods, atrazine 1.5 kg/ha being statistically at par with acetachlor 1.25 kg/ha produced significantly lower density and dry matter of weeds and resulted in significant increase in all the yield attributes of maize crop and thereby its grain yield by 75.18 and 71.66%, respectively, over unweeded check.

Field experiments were conducted at the Research Farm, Department of Agronomy, PAU, Ludhiana for three years to find out effective weed management technology in chickpea (gram) on loamy sand soil. Integration of one hand weeding (45 days after sowing) with either pre-plant application of trifluralin (Treflan) at 0.50 kg/ha or pre-emergence application of pendimethalin (Stomp) at 0.50 kg/ha proved very effective for controlling weeds as indicated by 82 and 86% reduction in final dry matter accumulation by weeds, respectively, as compared to the control treatment. Both these integrated treatments increased seed yield of chickpea by 60 and 59% than control and 4.0 and 2% than the standard treatment i. e. pre-emergence application of linuron (Afalon) at 0.94 kg/ha, respectively. Also pre-plant application of trifluralin at 1.25 kg/ha performed comparable to herbicide+hand weeding. Net returns and B : C ratio were also highest in pre-plant application of trifluralin at 1.25 kg/ha and it was followed by integration of hand weeding (45 DAS) with either pre-plant application of trifluralin at 0.50 kg/ha or pre-emergence application of pendimethalin at 0.50 kg/ha

A field experiment was conducted at Palampur during the kharif seasons of 2004, 2005 and 2006 to standardize the doses of new herbicides (acetachlor, trifluralin, haloxyfop and quizalofop) in soybean under mid hill conditions of Himachal Pradesh. Haloxyfop at 0.100 kg/ha (72.0%) and acetachlor 1.50 kg/ha (72.3%) resulted in highest weed control efficiency among post- and pre-emergent herbicides, respectively. Haloxyfop at 0.100 kg/ha and quizalofop at 0.0625 kg/ha were effective against grassy weeds (Panicum, Echinochloa and Digitaria). Acetachlor was most effective against grassy as well as broad-leaved weeds (Ageratum conyzoides, Polygonum alatum and Commelina benghalensis). Haloxyfop at 0.100 and 0.125 kg/ha, quizalofop 0.0625 kg/ha, acetachlor 1.50 kg/ha and trifluralin 1.50 kg/ha resulted in significantly higher plant dry weight, branches/plant, pods/plant, seeds/pod, 1000- seed weight and seed yield of soybean. Haloxyfop 0.100 kg/ha resulted in highest net return and B : C ratio. Weed management index (WMI), agronomic management index (AMI) and integrated weed management index (IWMI) were highest in haloxyfop-methyl 0.100 kg/ha followed by quizalofop 0.0625 kg/ha, haloxyfop-methyl 0.125 kg/ha and trifluralin 1.50 kg/ha.

Field experiment was conducted during kharif seasons of 2003 and 2004 to evaluate the economic feasibility of weed management practices in soybean crop in south-eastern Rajasthan. Post- emergence application of imazethapyr reduced the density and dry biomass of broad as well as narrow leaved weeds significantly as compared to pre-plant and pre-emergence and rest of post-emergence herbicides under study. The lowest weed density and biomass were recorded with two hand weedings at 30 and 45 days after sowing (DAS) followed by imazethapyr at 100 and 75 g/ha. Imazethapyr at 75 g/ha was found most agro-economic feasible by giving highest net returns (Rs.10235/ha) and incremental cost : benefit ratio (9.89).

Field studies were carried out to determine the critical period of crop-weed competition in blackgram (Phaseolus mungo). Trianthema portulacastrum, Digera arvensis, Echinochloa crusgalli, Parthenium hysterophorus, Phyllanthus niruri and Cynodon dactylon were the most predominating weeds. Grain yield loss increased with the increase in the duration of competition and maximum loss (67%) occurred due to full season competition. Significantly higher grain yield (12.42 q/ha) and yield attributing characters were obtained in plots remaining weed free upto harvest. The critical period of weed competition was between 30 to 45 DAS during which the crop should be kept free of weeds to prevent the potential loss in blackgram grain yield.

Field experiment was carried out in Mogra Block Farm, Hooghly, West Bengal in pre-kharif 2005 and 2006 to evaluate the relative efficacy of different herbicides alone and in combination with hand weeding. Results revealed that pre-emergence application of herbicides integrated with one hand weeding were superior to their sole application in controlling Trianthema portulacastrum and increasing seed yield of sesame. Butachlor with one hand weeding proved its superiority over rest of the treatments in respect of weed control efficiency, seed yield and net return. Farmers' practice recorded at par result with butachlor integrated with one hand weeding in seed yield of sesame

Glyphosate applied at 0.6 kg/ha at active vegetative stage caused yellowing and drying up of Mimosa invisa. 2, 4-D at very high dose (5 kg/ha) even though caused epinasty was ineffective. Paraquat applied at 1 to 1.2 kg/ha at active vegetative stage was effective, but the labour and time requirement for efficient spraying of the contact herbicide was very high. All the herbicides applied at seedling stage were ineffective because of fresh germination from seed bank. The best chemical for controlling M. invisa was glyphosate @ 0.6 kg/ha and best time of application was active vegetative stage (100 days after germination).

Phytosociological studies of the weed flora of tea plantations in south India were carried out to generate information that could assist in identifying important and recalcitrant weeds during different seasons and in various situations which in turn should help in formulating effective measures for their control. One hundred and twelve weed species were found to occur in the tea fields of south India during the rainy seasons (June to December). The weed flora during the rainy season was dominated by Drymaria cordata, Bidens pilosa, Ageratum conyzoides, Crassocephalum crepidioides and Spermacoce ocymoides. During the dry season (January to March) only 34 weed species were recorded and the dominant weed species were Conyza leucantha, Conyza bonariensis, Ageratum conyzoides, Panicum repens and Paspalum conjugatum. Tea fields adjacent to human habitats favoured the growth of Drymaria cordata, Amaranthus viridis, A. spinosus, Rorippa dubia and Persicaria barbata. Panicum repens, Paspalum conjugatum, Axonopus compressus and Cyperus rotundus were the dominant weeds in tea fields adjoining water sources. Tea fields bordering forest boundaries had Persicaria chinensis, Chromolaena odorata, Pteridium aquilinum, Mikania cordata and Urena lobata

Survey and field experiments were conducted in the Department of Agronomy, Annamalai University during 2000 and 2001 to study some of the ecological traits of Congress grass (Parthenium hysterophorus L.) in Veeranum Ayacut region of Tamil Nadu state and to compare the bio-efficacy of some herbicides for controlling this weed. Results showed that the weed had two generations in a calendar year. Congress grass germinated with maximum temperatures between 30° and 34° C coupled with available soil moisture between 40 and 60% coincided with February and September months. The weed occurred only in the wastelands and did not expand into cultivated fields. Associated flora included predominantly grasses. Glufosinate ammonium @ 2.5, 3.0 l/ha and glyphosate @ 2.5 l/ha were effective in imparting a complete control of Congress grass