Critical Period Of Weed Competition Research Articles

Determination Critical Periods of Weed Competition and Weed Control Influence on Yield Productivity of Sweet Pepper (Capsicum annuum L.)

Field experiments were carried out at Sids Research Station, Agricultural Research Center during 2016 and 2017seasons to determine the critical period of weed competition in pepper yield and study the effect of some pre-emergence herbicides on controlling weeds and its reflection on yield and its component of pepper. It could be concluded that some safe alternatives to mechanical weed control hand hoeing (twice), are the use of mulching by black polyethylene or reduced rate of pendimethalin (0.850 L.fed) and butralin (1.25 L.fed.) for weed control during the pepper crop to produce good fruit yield free from herbicidal residues. Mathematical models between weed-free duration periods were quadric 8.3 and 7.0 weeks from transplanting. The application of pendimethalin at 0.850 l.feddan supplemented with one hand hoeing and black polyethylene mulch were the best treatments to reduce weed biomass, followed by hand hoeing twice and butralin at 1.25l.feddan supplemented with one hand hoeing to face weed problem in critical period of weed competition and herbicidal residues in edible pepper fruits were below the maximum residue limit. The relationship between all characters were negatively and significant correlated with weed biomass and positive with pepper fruit yield in both seasons. Practical implications of this research are that planting pepper need weed management in 8 weeks from transplanting from weed competition which can be achieved by either the use of pendimethalin or butralin at a full recommended rates or followed by one hand hoeing or black polyethylene mulching to prevent early weed competition to pepper crop.

Weed management approaches in direct-seeded rice in eastern Indian ecologies - A critical and updated review

Direct-seeded rice (DSR) is significant in modern day agriculture because it requires less water input (20%) and labour (65–80 person-days/ha). Moreover, it enables farmers to establish rice early, which allows the crop stand more power to resist flush flood happening more frequently in the beginning of the monsoon. Direct-seeded rice produces at par or higher yield compared to manual transplanted rice but significantly higher yield (1.07 t/ha) compared to traditional manual broadcasted rice followed by beushening practice. It helps to increase system productivity by 0.25 t/ha, increase income by US$ 150/ha, reduce greenhouse gas emission (20% GWP) besides instrumental in reducing straw burning and environmental footprints. Despite all these advantages, the DSR has not been adopted at large scale at farmers’ field in eastern India particularly in Bihar, Odisha and Uttar Pradesh. One of the most important reasons for this is heavy and diversified weed infestation in DSR which consequently reduces rice yields significantly. In the present review article, the authors have tried to compile relevant information on the weed management approaches in DSR with special reference to eastern Indian states. Detailed discussions on weed species based on their occurrence and infestation, critical period of weed competition and different methods of weed management in DSR in eastern Indian ecologies have been enlightened in this paper. It also includes that weed management options in DSR depend on many factors like land situation, soil condition, water status, planting geometry and resources availability; and therefore, one single method of weed management practices may not be sufficient to control all the flushes of diversified weeds. Integrated approach combining cultural, physical and chemical methods can provide a more robust control of weeds in DSR. Relevant data generated in Odisha representing eastern Indian ecologies have also been included herein to further enrich knowledge and skills regarding DSR productivity, in general and possible weed management options, in particular.

Timing of weed management and yield penalty due to delayed weed management in soybean

Background: Weed interference is a major limiting factor for economically viable soybean production. Appropriate timing of weed management would enable farmers to make more efficient use of resources for weed management. Objective: The objective of this study was to determine the critical period for weed competition and appropriate timing of weed management for optimum yield of soybean. Methods: The treatments consisted of periods of weed infestation and weed removal for the first 14, 28, 42 and 56 days after sowing (DAS), and till harvest in a randomized complete block design with three replications in 2016 and 2017. Results: Soybean yields in both years ranged from 914-945 kg ha-1 with no weed control to 1,984-2,127 kg ha-1 in the weed-free plots; a yield loss of 53-56. Weed infestation for the first 14 DAS had no detrimental effect on growth and yield of soybean provided the weeds were subsequently removed. Increasing period of weed interference from 14 to 42 DAS resulted in a steady decline in growth and yield of soybean. Yield losses equivalent of 32-37 kg ha-1 resulted for each day that weed control was delayed between 14 and 42 DAS. Subsequent weed control after 42 DAS did not improve growth and yield significantly, nor obviate yield depression of the crop compared to crop weed-infested till harvest. Conclusions: Results indicated that the critical period of weed competition in soybean was between 14 and 42 DAS. Hence soybean should be maintained weed-free during this period to avoid high yield loss.

Determination Critical Period of Weed Competition and Their Control Method in Carrot Yield(DaucusCarotaL) With Economic Feasibility

Determination Critical Period of Weed Competition and Their Control Method in Carrot Yield(DaucusCarotaL) With Economic Feasibility

Identification of weed competition and its effect on plant growth and yield in ajwain (Trachyspermum ammi Sprague)

Weeds are one of the major problems for farmers in any crop production, which reduce the availability of nutrients, water, sun light to the crop and provide a tough competition to crop. Hence causing severe loss to the crop quality and produce. Weeds are also considered one of the major problems in seed spices. Ajwain is an important seed spice crop grown in Rajasthan, Madhya Pradesh and Andhrapradesh. The research on Ajwain crop is very meagre, it is severely affected by various. biotic and abiotic factors which affects the yield potential significantly. Plant weed competition is one of the major factors, besides insect pest and diseases causing significant yield and quality losses. Ajwain being a rabi crop faces severe competition with the weeds like Chenopodium album, Coronopus didymus, Melilotus spp., Rumex spp., Cyperus rotundus etc. To enhance the yield potential it is must to have an efficient cost-effective weed management modules.Best growth parameters were observed in weed free condition through out growth period treatment. Maximum (98.91percentage) loss in yield was recorded with the treatment, weedy through out under growth period (T9). Weed count and weed biomass was recorded maximum in T9’whereas minimum in T18. Critical period for weed competition in ajwain was found to be 63 days after sowing. Weedy period up to 75 DAS gave tough competition to the crop for growth which was reflected in yield attributes and seed yield of Ajwain. The maximum yield of 638.15kg/ha was obtained with the treatment weed free throughout growth period, this was also found economically viable which resulted in highest gross return of 99987/ha, net returns 66315/ha and B: C ratio of 1.97. The Benefit: Cost ratio of 0.31 and 1.31 was observed for weed free condition up to 90 DAS (T15) and 120 DAS (T17) respectively.

Mathematical Models for Determination of the Critical Period of Weed Competition in Maize (Zea mays L.)

Two field experiments were conducted on maize during 2014 and 2015 summer seasons at EL-Serw Station, Damietta Governorate, Egypt. Each experiment included ten weed competition and weed removal treatments either at early or late times after sowing which were: - weed competition for the whole season, weed competition for 2, 4, 6 and 8 weeks from sowing, weed free for 2, 4, 6 and 8 weeks from sowing and weed free for the whole season, to determine when a natural infestation of weeds start to reduce maize yield and when to control without yield losses in maize. The most appropriate study of the critical period of weed competition is on the weed community as a whole than single weed specie. Dominant major weeds in experimental fields were Portulaca oleraceae, L.; Corchorus olitorius, L.; Amaranthus caudatus, L.; Echinochloa crus-gali, L. and Echinochloa colonum, L. The obtained results revealed that which weed infestation rate under maize field was 5.834 and 6.043-ton fresh weight / fed.,which reduced drastically grain yield of maize /fed by 56.8 to 57.2 % under weed competition treatment of maize for the whole season in 2014 and 2015 summer seasons, respectively as compared with weed free for whole season treatment. The use of response curves with weed free or weed competition periods showed that grain yield of maize / fed were the highest with the field free from weeds until seven weeks after sowing and the critical period of weed / maize competition was between 3 to 7 weeks after sowing. In regression approach for maize grain yield and weed free or weed competition period the polynomials (linear and quadratic) and logistic functions were tested and quadratic function was fitted to estimate the expected yields which had the high significant with the data recorded and have the highest values of R2 than the other models (linear or logistic model.) for this reason it is used to estimate predict yield losses due to weed competition periods with maize. Also, results showed that the quadratic equations were significant and had the highest R2 (0.990 and 0.985) for weed free period, and (0.994 and 0.993) for weed competition durations in 2014 and 2015 summer seasons, respectively. The important stage of weed competition to maize is the 1-9 weeks period from sowing was required to be weed free showed that to maintain 95% of maximum grain yield of maize and one week of weeds infestation can be allowed after maize sowing without grain yield maize reduction. This information should be taken in consideration for maize growers to plan their strategies of integrated weed management for this important crop. It could be concluded that weeds should be removed within the period of first week and nine weeks in maize crop to pass up 5 and 10% grain yield reduction, respectively.

Effect of plant population dynamics and different weed free regimes on growth, yield and quality of peanut (Arachis hypogaea L.)

Productivity of groundnut ( Arachis hypogaea L.) in Bangladesh is very low, due to many limiting factors beset in its cultivation. Plant density and weed competition in crop constitute the main limiting factors. In order to combat the problems, the optimum plant density and most appropriate weeding period for good production in groundnut has been investigated at Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh, Bangladesh. Two plant density viz. 200,000 and 400,000 plants ha -1 , and seven weed competition periods from 0, 25, 40, 55, 70, 85 DAS and up to harvesting time were studied. Nineteen species of weeds representing 10 families were found to grow and population density was 150 plants m -2 . The major infesting species of weeds were Cyperus rotundus L. (Mutha), Chenopodium album L. (Bathua), Physalis heterophylla L. (Foska begun), Gnaphalium luteo-album L. (Shwetomuli) and Paspalum disticum L. (Knot grass) which constituted about 84.66% of the total weed population. Cyperus rotundus alone shared the maximum relative density (57%) having 85.5 plants m -2 area of total weed vegetation and also shared the maximum intensity of infestation (2.85). Intensity of weed infestation was always higher at lower plant density. Weed dry matter production was higher at a density of 200000 plants compared to 400000 plants ha -1 . In contrast, weed dry weight was progressively increased with increasing weed competition period and it was the highest in unweeded plot and critical period of weed competition appeared at 40 DAS. Weed competition period from zero to 40 DAS and thereafter weed free up to crop harvest with a density of 400000 plants ha -1 gave the highest pod yield The pod yield was found to have a significant negative correlation with weed dry matter production i.e. an increase in the dry matter production will lead to a decrease in the yield of pods.

WATER USE EFFICIENCY, GROWTH AND YIELD OF WHEAT CULTIVATED UNDER COMPETITION WITH Setaria

ABSTRACT Understanding the critical period of weed competition is indispensable in the development of an effective weed management program in field crops. Current experiment was planned to evaluate the critical growth period ofSetaria and level of yield losses associated with delay in weeding in rain-fed drip irrigated wheat production system of Saudi Arabia. Field experiment was conducted to evaluate the effect of weeding interval (07-21, 14-28, 21-35, 28-42 and 35-49 days after sowing) and drought stress (75% and 50% of field capacity) on Setaria growth, wheat yield and water use efficiency. Season long weedy check and wellwatered (100% FC) plots were also maintained for comparison. Weeding interval and drought stress significantly (p ≤ 0.05) affected the growth and yield of Setaria and wheat. Drought stress from 75% to 50% FC resulted in reductions of 29-40% in Setaria height, 14-27% in Setaria density and 11-26% in Setaria dry biomass. All weeding intervals except 35-49 DAS significantly suppressedSetaria growth as compared with control. Delay in weeding increased weed-crop competition interval and reduced wheat yield and yield contributors. Therefore, the lowest yield of 1836 kg ha-1 was attained for weeding interval of 35-49 DAS at 50% FC. Water use efficiency and harvest index increased with decreasing FC levels but reduced with delay in weeding. Correlation analysis predicted negative association ofSetariadensity with wheat yield and yield contributors and the highest negative association was for harvest index (-0.913) and water use efficiency (-0.614). Early management of Setaria is imperative for successful wheat production otherwise yield losses are beyond economical limits.

Critical period of weed competition in transplant Aus rice cv. BRRI dhan27 under non-saline agro-ecosystem

A study was conducted to determine the critical period of weed competition in transplant Aus rice for var. BRRI dhan27. Among the treatments, weed free condition, competition of weed for first 10, 20, 30, 40, 50, 60 and 70 days and weed free later on, unweeded condition, one weeding at 20 days after transplanting and one weeding at 40 days after transplanting, the unweeded control plots showed the poor performance result in case of maximum parameters where grain yield was reduced the highest percentage (38.54%). On the basis of cost benefit ratio it was observed that the critical period of crop weed competition extended up to 30 days after transplanting of aus var. BRRI dhan27.Bangladesh Agron. J. 2014, 17(1): 95-102

Mathematical Models for Determination of The Critical Period of Weed Competition In Sunflower (Helianthus annuus L.)

ABSTRACT Two field experiments on sunflower were conducted during 2013 and 2014 summer seasons at EL-Serw Station, Damietta Governorate, Egypt. Each experiment included ten weed competition and weed removal treatments either at early or late times after sowing which were: - weed competition for the whole season, weed competition for 2, 4, 6 and 8 weeks from sowing, weed free for 2, 4, 6 and 8 weeks from sowing and weed free for the whole season, to determine when a natural infestation of weeds start to reduce sunflower yield and when to control without yield losses in sunflower. Dominant major weeds in experimental fields were Portulaca oleraceae, L.; Corchorus olitorius, L.; Amaranthus caudatus, L.; Echinochloa colonum, L. and Chenopodium album, L. The obtained results revealed that which weed infestation rate under sunflower field was 5.885 and 6.527 ton fresh weight / fad.,which reduced drastically seed yield of sunflower per faddan by 55.3 to 55.2% under weed competition treatment of sunflower for the whole season in 2013 and 2014 summer season, respectively, as compared with weed free for whole season treatment. The use of response curves with weed free or weed competition period showed that seed yield and oil yield of sunflower were the highest with the field free from weeds until 6 weeks after sowing , and the critical period of weed / sunflower competition was between lie 2– 6 weeks after sowing. In regression approach for sunflower seed yield, oil yield and weed free or weed competition period the polynomials (linear and quadratic) and logistic functions were tested and quadratic function was fitted to estimate the expected yields which had the high significant with the data recorded and have the highest values of R2 than the other models (linear or logistic model.) for this reason it is used to estimate critical periods of weed competition with sunflower. Also, results showed that the quadratic equations were significant and had the highest R2 (0.989, 0.982) and (0.989, 0.984) for weed free period, and (0.899, 0.992) and (0.919, 0.994) for weed competition durations in 2013 and 2014 summer seasons, respectively. According to these results, the critical period of weed competition to sunflower is the first six weeks period from sowing was required to be weed free showed that to maintain 95% of maximum seed and oil yield of sunflower and one week of weeds infestation can be allowed after sunflower sowing without seed and oil yield sunflower reduction. The information should be taken in consideration for sunflower growers to plan their strategies of integrated weed management for this important crop.

The critical period for weed competition in parsley (Petroselinum crispum (Mill.) Nyman ex A.W. Hill) in Mediterranean areas

Weeds are one of the major limiting factors for economically viable parsley production. Field experiments were carried out in central Greece, in 2010 and 2011 to determine the effect of competition from a natural weed flora on growth, photosynthesis and yield of parsley (Petroselinum crispum (Mill.) Nyman ex A.W. Hill). Two treatments were applied; weeds were either allowed to infest the crop or plots were kept weed free for an increasing duration of time (0, 10, 20, 30, 40, 50 days after crop emergence). Total dry biomass of weeds increased as the duration of weed infestation increased. Amaranthus retroflexus L., Datura stramonium L. and Solanum nigrum L. contributed most of the total weed dry weight because of their large size and density. Total weed biomass in both growing seasons decreased with increasing duration of the weed-free period and there were no significant differences between years. Moreover, weed competition reduced parsley dry weight by 93% and 95% in 2010 and 2011, respectively. Late weed competition did not affect parsley dry weight as that at early competition. Dry weight of parsley was reduced by 87–91% when plots kept weed-infested for the first 40 days after crop emergence, while plots kept weed-free for similar period provided 8–10 times higher dry weight. There was significant negative correlation between the dry weight of parsley and weed dry weight. Parsley dry weight was dramatically decreased with weed competition duration longer than 20 days after crop emergence. Results indicated that early weed removal is necessary to prevent yield loss.

Weed Interference Affects Dry Bean Yield and Growth

Dry bean is one of the most important pulse crops in Iran. Field study was conducted in 2011 to evaluate effects of weed competition from a natural flora on growth and yield of dry bean (Phaseolus vulgaris L.). The treatments consisted of weed infestation and weed removal periods (10, 20, 30, 40 and 50 days) after crop emergence. Control plots kept weed-infested and weed-free throughout growing season. To assess the weed competition effect on crop characteristics, Richards, Gompertz and logistic equations were fitted to the data. The most abundant weed species were Chenopodium album and Amaranthus retroflexus. Increase in duration of weed interference decreased the stem height of dry bean. At the end of the growing season, dry bean was 20 cm taller in season-long weed-free treatment compared to the season-long weed-infested treatment. As the number of days of weed interference increased, a declining trend of LAI and number of pods was observed. The minimum number of pods was obtained in season-long weed-infested treatment (5.01 pods/plant). Weed interference during the whole growing season, caused a 60% reduction in yield. Considering 5% and 10% acceptable yield lost, the critical period of weed competition was determined from 20 to 68 and 23 to 55 days after planting (DAE), respectively.

Irrigation Methods affect critical period of weed competition in potato production

Irrigation Methods affect critical period of weed competition in potato production

Screening Tactics for Identifying Competitive Soybean Genotypes

Weed control is the biggest obstacle for farmers transitioning to organic soybean production. The breeding of competitive cultivars may provide organic soybean producers with another weed-management tactic. Soybean breeders need screening protocols to identify competitive genotypes. In 2007 and 2008, we tested two screening tactics to nondestructively estimate canopy coverage during the critical period for weed competition. Overhead photography at 3 and 5 weeks after emergence and light interception measurements at 4 and 6 weeks after emergence were compared in their ability to predict soybean and weed biomass at the end of the critical period for weed competition. Photographic digital image processing techniques were compared. Overhead photography at 5 weeks after emergence was most effective at predicting weed-free soybean biomass but overhead photography at 3 weeks after emergence was best able to predict weed biomass associated with soybean genotypes at the end of the critical period for weed competition.

The critical period for weed competition in French bean ( Phaseolus vulgaris L.) in Mediterranean areas

Field experiments were carried out in 2004 and repeated in 2005 and 2006 in central Italy to determine the effect of competition from a natural weed flora on growth and yield of French bean ( Phaseolus vulgaris L.). Two treatments were applied; weeds were either allowed to infest the crop or plots were kept weed free for an increasing duration of time (0, 7, 21, 28, 35, 45 days) after crop emergence. To assess the critical period of weed competition (CPWC) and the influence of weed infestation on yield, the Gompertz and logistic equations were fitted to data which represented the increasing duration of weed-free and weed-infested periods, respectively. During the three years of the experiment weeds, allowed to interfere for the whole growing season, reduced fresh pods yields up to 60%, 65% and 59% of the weed-free bean plots. Based upon an arbitrary yield loss (AYL) of 5%, the CPWC was from 50 Growing Degree Days (GDD) to 284 GDD, i.e. from 11 days after emergence (DAE) to 28 DAE. These values correspond to the lowest and highest values observed in the three experiments respectively for the weed-infested and weed-free period.

THE CRITICAL PERIOD OF WEED COMPETITION OF DIRECT SEEDED RICE IN SALINTY LAND

Two Field experiments were conducted during the two summer seasons of 2007 and 2008 at EL-Serw Agricultural Research Station, Damietta Governorate, Egypt to study the effect of the time removal of weeds on associated weeds, growth, yield and its components in direct seeded rice in salinity land. Echinochilon crus – galli, Echinochilon colunum, Cyperus difformis, Cyperus longus and Dicanthium annulatum were the major weed species. Competition beyond 8 and 10 weeks from sowing and weed competition for the whole season caused drastic reduction in the panicle length, number of panicles / m2 weight of 1000grain and grain yield. Grain yield of rice increased significantly with the increase of the duration of weed-free period. Weed free for the whole season and weed free for 10,8,6 and 4 weeks from sowing and weed removal at 4 and 6 weeks from sowing gave good results in this respect in both seasons. The period during 4 and 6 weeks after sowing was found to be an important factor in crop/weed competition. Weed cause 20 to 95% yield loss. Direct seeded rice ecosystems are most vulnerable to weed competition. Weed free is the most common and predominant method of control and is cost-effective. In direct seeded rice emergence of weeds begins with the germinating rice seedlings. This leads to competition between weeds and crop right from the very early stages. The degree of yield losses would depend on the type of weeds and the stage and duration of their competition with the crop. It could be concluded that the critical period of weed competition in direct seeded rice among 4- 6 weeks from rice sowing, thus it's important to remove the weeds at this time.

TOLERÂNCIA DO FEIJÃO-CAUPI AO HERBICIDA OXADIAZON

The use of herbicides for weed control in cowpea [ Vigna unguiculata (L.) Walp.] can result in highly effective control and lower production costs, if compared to mechanical control, especially weeding. However, not many studies were conducted in order to evaluate crop tolerance to herbicides. The objectives of this study were to evaluate cowpea tolerance, BRS Guariba cultivar, to the oxadiazon herbicide, applied in pre-emergence, at 200 g, 400 g, 600 g, 800 g, and 1,000 g of active ingredient (a.i.) ha -1 , and weed control effectiveness. The weeds identified were Cleome affinis , Commenlina benghalensis , Cyperus rotundus , and Euphorbia heterophylla . The cultivar BRS Guariba was very tolerant to all doses tested, and the weed control level was good. Grain yields obtained with doses above 600 g a.i. ha -1 were excellent, comparable to weeding performance during the critical period of weed competition, between 20 and 40 days after seedling emergence (1,561 kg ha -1 ). The negative interference of weeds, throughout the cowpea life cycle, decreased yield by 59%. KEY-WORDS: Vigna unguiculata ; chemical weed control; floristic inventory.

Effect of crop plant density on critical period of weed competition in potato

A field study was conducted in Hamedan western Iran in 2006 to establish the critical period of weed competition (CPWC) in potato ( Solanum tuberosum L.) for commercial and seed production plant densities. A quantitative series of treatments concerned with both increasing duration of interference and length of weed-free period were imposed within each commercial and seed potato production plant density. The beginning and end of the CPWC based on a 10% loss of tuber yield was determined by fitting logistic and Gompertz equations to the relative tuber yield data representing increasing duration of weed interference and weed-free period, respectively. At a 10% tuber yield loss level, the duration of weed interference for 571 and 676 growing degree days (GDDs) from crop emergence, corresponding to 40% and 50% canopy closure, marked out the beginning of the CPWC for commercial and seed production plant densities, respectively. When maintained weed-free for 1163 and 1014 (GDD), corresponding to 100% and 80% canopy closure, weed emerging later caused tuber yield losses of less than 10% for commercial and seed production plant densities, respectively. Practical implications of this study are that post-emergence herbicides or other weed control methods should be used in western Iran to eliminate weeds from 19–24 days post-crop emergence up to 43–51 days. Such an approach would keep yield loss levels below 10%. Interactions between plant density and weed competition durations indicated that weed management in commercial plant density of potato could be less intensive than that of seed production plant density, reducing herbicide use and risk of herbicide carryover to sensitive rotation crops.

Weed competition in cauliflower ( Brassica oleracea L. var. botrytis) in the Jordan Valley

A field experiment was carried out in 1996/1997 and repeated in 1997/1998 at the Jordan University Research Station located in the central Jordan Valley to determine the effect of weed competition on growth and yield of cauliflower Brassica oleracea var. botrytis cv. “White Cloud”. The treatments consisted of either allowing weeds to infest the crop or maintaining plots weed-free for increasing durations after transplanting. Results showed that longer periods of weed/cauliflower competition greatly reduced crop growth and head yield. Average reductions in shoot dry weight and head yield were 81% and 89%, respectively. Maintaining a weed-free crop for any period after transplanting increased cauliflower growth and head yield compared with the weed-infested control. Weed competition for 14 days after transplanting reduced cauliflower average head yield by 41%. To determine the critical period of weed competition and the influence of weed infestation on cauliflower head yield the Gompertz and logistic equations were fitted to data representing increasing duration of weed-free and weed-infested periods, respectively. Based upon an arbitrary 5% level of head yield loss, the critical period of weed competition occurred at 0–38 days after cauliflower transplanting which corresponded with the rapid increase in weed biomass. Results indicated that early weed removal is necessary to prevent yield loss.

Studies on competition between wheat and <i>Chenopodium album</i> L.

A field experiment was conducted at the Agronomy Field of Bangladesh Agricultural University (BAU), Mymensingh during the period from November 2001 to March 2002 to investigate the effect of Chenopodium album competition on growth and yield of wheat and to determine the critical period of weed ( C. album ) competition in wheat. The experiment was consisted of 7 treatments viz., weed free for whole crop life, weed competition (WC) for 20, 40, 60, and 80 days after emergence (DAE), WC for 110 DAE (no weed control) and weed monoculture. The highest grain yield (3.95 t/ha) was obtained from weed free and that of the lowest from weedy (2.65 t/ha) condition. Grain yield decreased gradually with the increase in weed competition duration. Wheat yield reductions due to C. album competition for 20, 40, 60, 80, and 110 DAE were 12.65, 28.10, 29.11, 31.64, and 32.9 %, respectively. The highest rate of yield decrease was in between 20 and 40 DAE. The highest reduction of wheat yields under weedy check treatment (32.91% grain and 33.75% straw) were the results of 31.0 % reduction of total tillers/plant, 43.34% reduction of effective tillers/plant, 14.57% reduction of grains/spike, 34.5% reduction of total dry weight of wheat. The plant height of C. album was reduced due to wheat competition by 32.3% and that of total dry matter by 34.2 %. The critical period of weed competition lies between 20 and 40 DAE. Bangladesh J. Agril. Res. 32(2) 2007: 191-203.