Critical Period Of Weed Control Research Articles

Sugarcane Growers’ Knowledge Level about Integrated Weed Management Practices in Meerut, UP, India

The study examines the knowledge of Integrated Weed Management (IWM) among sugarcane growers, identifying both positive aspects and areas for improvement. Through survey responses, it was observed that a significant number of respondents were able to identify weeds and common varieties. However, there were noticeable knowledge gaps in specific IWM practices such as intercropping and understanding the critical period for weed control. Furthermore, the study reveals a correlation between certain factors and higher levels of IWM knowledge. Factors like education level, land holding, and access to resources were found to be positively associated with a greater understanding of IWM practices. These findings underscore the importance of targeted extension programs aimed at educating sugarcane growers about best practices for weed control within the framework of Integrated Weed Management. By addressing these knowledge gaps and leveraging key factors that contribute to higher knowledge levels, such programs can significantly enhance weed management strategies in sugarcane production.

Critical Period of Weed Control in Maize as Influenced by Soil Tillage Practices and Glyphosate Application

Increasing evidence on environmental and economic benefits has raised farmers’ interest in adopting alternative, less intensive soil management practices. To evaluate the influence of weed-competitive ability in response to a different tillage regime, a field study was conducted in maize under humid Central European climatic conditions in Slovenia. This study was established as a split-plot arrangement with three tillage practices (TPs) as the main plot: conventional (CN), conservation (CS), and no tillage (NT); this was combined with glyphosate application and the weed removal timing as the subplot. The weed removal timings were at the V3, V6, V9, V15, and R1 maize stages, with weed-free and weed season-long monitoring. The beginning and the end of the critical period of weed control (CPWC), based on a 5% maize yield loss rate, were determined by fitting the four-parameter log-logistic equations to the relative maize dry grain yield. The weed dry biomass from maize germination until the R1 growth stage in the NT TP was consistently lower than that in the CN and CS TP. Moreover, the NT TP resulted in a shorter CPWC (39 days after emergence (DAE)) compared to the CN (57 DAE) and CS (58 DAE). The results of CTWR (critical timing of weed removal) showed that less intensive tillage operations in the CS resulted in an earlier need for weed control (V2 and 23 DAE) compared to the CN (V3 and 39 DAE) and NT (V3 and 40 DAE). Our study suggests that the intensive tillage operations performed in the CN TP and the pre-sowing use of non-selective burndown herbicide in the NT delay the CTWR by more than 2 weeks, thus reducing the need for early post-emergence herbicide application in maize.

Critical Period of Weed Competition in Curcuma Lanna Snow Field

The effects of weeds on crops can cause weed interference, which is the result of their competition with each other. The influence of weed interference periods on growth and inflorescence of Curcuma was investigated under field experiment. The critical period for weed control consists of the increased duration of weed competition period during the weed-infested treatment, and the increased duration of weed free period during the weed-free treatment. Weed-free and weed-infested treatments were used to identify the critical period for weed control with acceptable yield loss of 5 and 10%. The results revealed that weed infested periods at 10, 12, 14 and 16 weeks after planting and weed free periods at 0, 2 and 4 weeks after planting significantly reduced the leaf number, height of inflorescence, width of inflorescence and length of inflorescence of Curcuma, while plant height was slightly affected by weed-free treatment. In addition, the critical period for weed control with 5 and 10% acceptable yield loss was estimated to be between 6 to 10 weeks after planting and 5 to 8 weeks after planting, respectively. The critical period for weed control at 10% acceptable yield loss was shorter than the critical period for weed control at the level of 5%. However, the determination of appropriate critical period for weed control should be concerned to have better crop yield and reduce cost. Weed control estimation and recommendations can enhance more precise weed management, which is helpful in formulating appropriate weed-control strategies in Curcuma fields.

Phosphorus influence on the critical period of weed control in sweet corn

Abstract Understanding the effect of phosphorus (P) fertilization on weed interference with sweet corn is important for deciding appropriate fertilization levels and weed control programs. Field experiments were conducted in 2020 and 2021 in Belle Glade, FL, to determine the influence of P fertilization levels (0 or residual P, 62.5, and 120 kg P2O5 ha−1) on the critical period of weed control (CPWC) in sweet corn on organic soils. Experimental plots were subjected to increased duration of weed interference and weed-free period treatments for each P fertilization level. The beginning and end of the CPWC based on 5% and 10% acceptable yield loss (AYL) levels were determined by fitting log-logistic and Gompertz models to represent the increasing duration of weed interference and duration of the weed-free period, respectively. The log-logistic curves did not estimate the beginning of the CPWC at 5% AYL for 0 and 125 kg P2O5 ha−1 because the estimated upper limits of the curves were lower than the 95% relative yield used for estimation of 5% AYL. Based on a 10% AYL level, the length of the CPWC in sweet corn under optimum P fertilization levels was estimated to be 27 d, from the 6- to 7-leaf stage until the silking stage of growth. Reducing P fertilization by 50% increased the CPWC to 36 d, from the 5-leaf stage until the silking to blister stage of growth. Lack of P fertilization increased the CPWC to 64 d, from sweet corn emergence until the blister to milk stage of growth. These results show that the beginning of the CPWC in sweet corn is delayed and the end is shortened as P fertilization level increases. Therefore reduction in P fertilization will require a more intensive weed management program for sweet corn because of the prolonged duration of the CPWC.

The Critical Period for Weed Control in Safflower Fields of Turkey

Crop-weed competition is among the most significant topics in field crops if the crop is a weak competitor in this rivalry. Safflower is a valuable oil seed crop that is drought tolerant and used as a raw material in the food and biofuel industries. Although it has good drought tolerance, it is a sensitive crop against weed competition, especially wild mustard. The critical period for weed control (CPWC) is a useful tool to decide which time period is more suited for weed control economically. In this study, the beginning and end of the CPWC were determined for the summer safflower fields of Turkey. Weeds caused 50.61, 65.87, and 63.34% safflower yield reductions in 2017, 2018, and 2019, respectively. The beginning of the CPWC was 165, 198, and 225 air growing degree days (air GDD) for these years, while the end of CPWC varied 1348, 1837, and 2268 at 5% acceptable yield loss.

Influence of cover cropping and conservation tillage on weeds during the critical period for weed control in soybean

AbstractLimited research has been directed at evaluating the ability of single cover crop plantings to suppress weeds in crops beyond the initial field season. Thus, this experiment was conducted to investigate the ability of a second-year self-regenerated annual and second-year perennial cover crop planting to suppress weeds during the critical period for weed control (CPWC) in soybean crops. Whole-plot treatments included 1) conventional till, 2) no-till with cover crop residue, 3) living mulch + cover crop residue, and 4) living mulch + winter-killed residue. Subplot treatments involved weed management intensity: a) no weed management (weedy), b) weeds manually removed through the CPWC (third node soybean stage; V3), and c) weeds manually removed until soybean canopy closure (weed-free). Overall, total annual cover crop biomass during the second field season was comparable to biomass obtained from direct seeded stands during the initial field season. All cover crop treatments reduced total weed biomass through the CPWC compared to conventional till. Soybean yield was low across all treatments in this experiment. Still, yield was similar between cover crop and conventional till treatments at one site-year, however, yields were lower in all cover crop treatments at the other site-year.

Cultivation system influenced the critical period for weed control in cotton field

BackgroundThe critical period of weed control (CPWC) refers to the period of time during the crop growth cycle when weeds must be controlled to prevent yield losses. Ultra-narrow row (UNR) is a method of planting of cotton in rows that are 25 cm or less apart. Amongst cultural techniques for weed control, the use of narrow row spacing is considered to be a most promising approach that can effectively suppress weed growth and provide greater yields in cotton. This cultivation system can shorten the length of the critical weed-crop interference duration and results in greater yield. The current research aimed to determination of critical time of weed control in cotton (Gossypium hirsutum L.) under conventional and ultra-narrow row spacing conditions. Field experiments were arranged as factorial experiment in a randomized complete block design with three replications. Factors were cultivation system (conventional (50 cm row spacing) and ultra narrow row (25 cm row spacing and weed treatment including 30, 45, 60, and 75 days weeding after emergence during the growing season (weed free), and 30, 45, 60, and 75 without weeding (weed infested) in the growing season along with weedy and weed-free from sowing to harvesting. A four-parameter log-logistic model was fit to the two sets of relating relative crop yield to data obtained from increasing durations of weed interference and lengths of weed-free period.ResultsIn both years and cultivation systems, the relative yield of cotton decreased with the increasing duration of weed-interference but increased with the increasing duration of weed-free period. Ultra-narrow row cultivation delayed the beginning of the CPWC in cotton. Under ultra-narrow row condition, the CPWC ranged from 21 to 99 days after germination in 2021 and 23 to 91 days in 2022 based on the 5% acceptable yield loss. Under conventional cultivation CPWC ranged from 17 to 102 days after emergence in 2021 and 18 to 95 days after emergence in 2022.ConclusionsUnder both conventional and Ultra-narrow row conditions, weed interference reduces seed yield. Under ultra-narrow row condition, weed interference until 21.1–23.5 days after cotton emergence and under conventional condition, weed interference until 16.9–18.5 days after cotton emergence had not significant reduction on cotton yield.

Shortening critical period of weed control at soybean by residual herbicide mixtures

Shortening critical period of weed control at soybean by residual herbicide mixtures

The Critical Period of Weed Control Influences Sunflower (Helianthus annuus L.) Yield, Yield Components but Not Oil Content

Field studies were conducted in the northeastern part of the Republic of Croatia to determine the influence of the critical period of weed interference on sunflower (Helianthus annuus) yield, yield components, and oil content. For this purpose, different durations of competition were established, allowing weeds to infest the crop for increasing periods of time after planting or maintaining plots weed-free for increasing periods of time after planting. The beginning and the end of the critical period of weed control (CPWC), based on a 5% and 10% loss of sunflower yield, were determined by fitting the four-parameter log-logistic equations to the relative seed yield. The total weed biomass increased progressively in relation to the increase in the competition. The beginning of the CPWC period, based on a 5% acceptable yield loss, ranged from 141 to 234 growing degree days (GDD), which corresponded to the two-to-four true leaf development stage (the V2–V4 growth stages) across both sites and years. The crop had to be kept weed-free until a period when sunflower inflorescence began to open and flower (the R4–R5 growth stage) or from 1365 to 1932 GDD. The sunflower yield and yield components varied between the years and among locations. An increasing duration of weed interference negatively affected crop height, head diameter, and 1000-kernel weight, but not seed oil content.

Determination of Critical Period for Sustainable Weed Management and Yield of Jute (Corchorus olitorius L.) under Sub-Tropical Condition

A field investigation was run to ascertain the critical period of weed control in jute (Corchorus olitorius). The study consisted of two distinct sets of treatments, with one set of weeds being left to invade the crop for a longer period of time, specifically, for 15, 30, 45 and 60 days after sowing (DAS) and up to harvest. In the other set of treatments, the plants remained weed-free for progressively longer periods, i.e., 15, 30, 45 and 60 DAS, and until harvest. The reduction in fibre yield (FY) was recorded as 53.39% when weed interference was permitted from the beginning to harvest, as opposed to the season-long weed-free period. The critical period for weed competition (CPWC) of jute was calculated as being 11 to 68 DAS and 19 to 59 DAS, based on results of 5% and 10% yield loss, respectively. Under the 5% yield loss condition, although yield was higher (3.36 t ha−1), the benefit cost ratio (BCR) was lower (1.65), whereas yield was slightly lower (3.19 t ha−1) but BCR was higher (1.73) with respect to 10% yield loss. Therefore, jute fields should be kept weed free from 19 to 59 days after sowing, and a weed management strategy should be undertaken accordingly.

The critical periods of weed control on the weed species composition, morphological, physiological, and biochemical characteristics responses of black seed (Nigella sativa L.)

A field experiment was conducted to the determine the critical period of weed control and its effect on the weed composition, the yield components, seed yield, oil yield, oil content, and the major secondary metabolites accumulation in the black seed (Nigella sativa L.). Two treatment series: weed-free (WF) and weed-infested (WI) periods, were performed from the seed emergence of the black seed until its maturity. The plots were kept weed-free for 0, 14, 28, 42, 56 and 70 days after emergence of the black seed and vice versa. In the weed community composition, 19 species from 14 families were recorded in the studied experimental field. Among the weeds, the Poaceae family (5) had the highest number of species, followed by the Fabaceae family (2). The major species were Avena sterilis L., Rapistrum rugosum L. (All), and Convolvulus arvensi L. during the harvesting of black seed. Results also revealed that the seed yield, yield components, seed oil content, and oil yield of the black seed significantly decreased due to the longer periods of WI or shorter periods of WF. In this study, weed-black seed competition periods promoted the total alkaloid and total phenolic accumulation, compared to WI periods, which indicated the plant's defensive response against the stress caused by the weeds. However, the decrease in seed yield and oil content indicates the insufficient levels of these compounds to cope with the weed stress. This study also concluded that the highest seed yield was obtained by keeping the plots WF from 42 or 70 days after emergence of the black seed to prevent yield loss higher than 10%. Therefore, this period could be the critical period of WF in the black seed.

Critical Period of Weed Control in Cotton (Gossypium hirsutum L.) at Three Nitrogen Levels*

The critical period for weed control is that part of the cropgrowth cycle during which the crop must be kept weed-free to preventunacceptable yield losses. Field studies were conducted for twoconsecutive years, 2004 and 2005, in the Thessaly plain in central Greeceto determine the critical period for weed control in cotton at three nitrogenlevels (50,100, and 150 kg N ha-1 ).Treatments of increasing duration ofweed interference and weed-free period were imposed at biweeklyintervals from 0 to 10 weeks after crop emergence (WAE). Based on anarbitrarily acceptable yield loss level of 5% and 10%, the beginning andend of the critical period were determined by fitting the polynomialregression to relative yield data representing increasing duration of weedinterference and weed-free period. Plant height, shoot and root dryweights and yield of cotton were reduced by prolonged delays in weedremoval at all nitrogen levels in 2004 and 2005. The results showed thatweeds reduced cotton shoot and root dry weights, respectively, by 55%and 38 % at 50 kg N ha-1 , 50% and 42 % at 100 kg N ha-1 and 40% and 46% at 150 kg N ha -1 , when allowed to compete for two weeks. At 10%acceptable yield loss level, the critical period was 8.2 weeks, starting 0.4WAE and ending 8.6 WAE at 50 kg N ha -1 , and was decreased to 7weeks, starting 1 WAE and ending 8 WAE at 100 kg N ha-1 . The criticalperiod decreased to 6.1 weeks, at 150 kg N ha -1 , starting 1.3 WAE andending 7.4 WAE. These findings showed that the supply of nitrogen to thecrop and weeds significantly influenced the crop-weed interferenceduration. This information will be useful for providing weed controlrecommendation to cotton producers.

The Critical Period of Weed Control in Maize (Zea mays L.) in Sudan

Competition between maize (Zea mays L.) and weeds is aserious challenge to crop production. A field study was conducted at theDemonstration Farm, Faculty of Agriculture, University of Khartoum,Sudan, during 2008/09 and 2009/10 winter seasons, to determine themagnitude of yield losses due to weed competition and identify thecritical period of weed interference in maize. The experiment consisted oftwo sets. In the first set the crop was kept weed-free for 0, 2, 4, 6, and 8weeks after sowing. In the second set weeds were allowed to competewith the crop for 0, 2, 4, 6, and 8 weeks after sowing. Unrestricted weedgrowth reduced maize cob length, cob weight, grain number/ plant, 100seeds weight and grain weight/ plant by 62%, 82%, 75%, 49% and 87%,respectively in the 2008/2009 season and by 62%, 89%, 75%, 41% and85%, respectively in the 2009/2010 season. The presence of weedsthroughout the crop growth duration resulted in 82% and 84% loss ingrain yield in seasons 2008/09 and 2009/10, respectively. The criticalperiod of weed control in maize was found to be between 2 and 6 weeksafter sowing

Períodos de interferência de plantas daninhas na cultura do feijão-caupi

ABSTRACT Cowpea is one of the pulse crops that present the highest potential for growing in the Semiarid region of Brazil. Lowcost vegetable protein source, it has resilience to adverse conditions, however, in competition with weeds, its productivity can be strongly compromised. To overcoming this situation, it is essential for integrated management programs to determine the critical period for preventing interference. Thus, the objective of this work was to determine weed interference periods and the effect of coexistence periods on cowpea grain yield in the Semiarid region of the state of Minas Gerais, Brazil. The treatments were arranged in a 2×9 factorial scheme, as follows: cultivation in coexistence with weeds and cultivation under weed control, for nine crescent periods (0-7, 0-14, 0-21, 0-28, 0-35, 0-42, 0-49, 0-56 and 0-63 days after crop emergence), in a randomized experimental block design with four replications. The weed community was studied through phytosociological survey and evaluation of dry matter production and cowpea was evaluated for dry matter production, 100-grain mass and grain yield. The interference periods were determined using a non-linear logistic regression model. The weed community found was composed of 70% dicotyledonous and 30% monocotyledon plants, distributed in seven families and ten species. The coexistence with weeds results in losses of up to 90% in cowpea grain yield. The critical period of weed control in cowpea crop in the Semiarid region of the state of Minas Gerais, Brazil, is 11 to 36 days after crop emergence.

Effect of crimson clover on the critical period of weed control in conservation tillage corn

An increasing number of herbicide-resistant weeds, in addition to troublesome weeds, pose a significant challenge for chemical weed control in corn. Simultaneously, high-biomass cover crop adoption has gained popularity among farmers as an efficient weed control strategy. While the critical period of weed control (CPWC) following conventional tillage has been well documented, there is little knowledge of CPWC following high residue cover crops in corn. A two-year field experiment was conducted to estimate the influence of a high biomass crimson clover cover crop and conservation tillage on the critical period of weed control (CPWC) in corn. The experiment was implemented in a split-plot design in which the main plots were conventional tillage (CVT), conservation tillage following winter fallow (CT + WF), and conservation tillage following crimson clover (CT + CC), and the subplot included multiple durations of weedy plots (estimation of critical timing of weed removal (CTWR), i.e., beginning of weed control) and weed-free plots (estimation of critical weed-free period (CWFP), i.e., end of weed control). The results described that the estimated duration of CPWC in three systems, included CT + CC, CT + WF and CVT equals 2.8 weeks, 3.5 weeks, and 4.9 weeks respectively in 2019. In 2020, the predicted value of CTWR under CT + CC equals 3.8 weeks after planting and the predicted values of CWFP were 5.1 and 5.7 weeks after planting under CT + WF and CVT systems, however, the model did not predict some values within the fitted 8 weeks of time. In conclusion, the presence of a crimson clover cover crop delayed the CTWR and caused the early beginning of CWFP and hence shortened CPWC in 2019. During most of the growing season, weed biomass production was less under CT + CC plots than CVT and CT + WF systems of weedy treatment in both years. While weed biomass production fluctuated in CT + CC, CVT and CT + WF systems in weed-free treatment.

Influence of a cereal rye cover crop on the critical period for weed control in soybean

AbstractSoybean is the world’s most widely grown leguminous crop and is an important source of oil and protein for food and feed in addition to other industrial uses. However, herbicide-resistant and troublesome weed control challenges limit yield potential and threaten conservation tillage (CT) systems. Cover crops have been widely adopted as an integrated pest management component in CT systems to suppress weeds and maintain soybean yield potential. A 3-yr field experiment was conducted to estimate the influence of a cereal rye cover crop following CT on the critical period for weed control (CPWC) in soybean. The experiment was implemented in a split-plot design in which main plots as CT following cover crop (CT + CC), CT following winter fallow (CT + WF), and conventional tillage (CVT), and subplots were multiple durations of weed-free and weed interference. Results showed that the estimated CPWC of CT + CC and CT + WF treatments was 0 wk and >7 wk, respectively, in 2018. In 2019, the estimated CPWC was 0 wk, 5.0 wk, and 1.3 wk under CT + CC, CT + WF, and CVT treatments, respectively. In 2020, the estimated CPWC was 3.5 wk, >6.2 wk, and 0 wk under CT + CC, CT + WF, and CVT treatments, respectively. The presence of a cover crop delayed the CTWR and caused an early beginning of the CWFP compared with CT + WF treatment, and hence shortened the CPWC in 2018 and 2019. In conclusion, the CT + WF system did not reduce the weed competition and subsequent yield loss in soybean compared to the CT + CC system.

Períodos de interferência de plantas daninhas na cultura da alface

ABSTRACT The knowledge of the adequate period for the beginning of weed management in lettuce crop can increase the efficiency of production, reducing the costs with management. The aim of this study was to determine the pre-interference period (PIP), the critical time for weed removal (CTWR) and the critical period of weed control (CPWC) in three lettuce cultivars, Elisa, Lucy Brown and Solaris. Coexistence and the absence of weeds were evaluated for each cultivar. The design was in randomized blocks with seven treatments (0, 7, 14, 21, 28, 35 and 42 days after transplanting - DAT) of coexistence and the same seven periods of weed absence with four replicates in each experiment. The highest infestation densities were with the species Oxalis latifolia, Coronopus didymus and Amaranthus hybridus. The leaf area and number of leaves per plant were reduced by up to 50% and 66%, respectively, in relation to the longest period of coexistence with weeds and yield reduced by 48% (Elisa), 40% (Lucy Brown) and 33% (Solaris). The cultivar Solaris showed greater tolerance to weed interference. Based on yield, PIP was 1, 3 and 3 DAT and CTWR was 37, 37 and 35 DAT, and CPWC was 2 to 37, 3 to 37 and 3 to 35 for the cultivars Elisa, Lucy Brown and Solaris, respectively.

Ayçiçeğinde Yabancı Ot Kontrolünde Kritik Periyot ve Uygulamaların Yabancı Ot Türleri ve Çeşitliliğine Etkileri

This study was carried out under field conditions in Adana, Turkey in 2018 and 2019 to determine the critical period for weed control in sunflower depending on the daily growth temperature (GDD) and weed species. A log-logistic model with four parameters was used to determine the relationship between relative crop yield and both increased weed intervention time and length of weed-free periods. In addition, dominant weeds and weed densities were determined in the experimental area. Data obtained from different periods of weed intervention were compared with data obtained from seasonal weed-free plots. During the sunflower growing season, 37.4% – 41.04% yield loss was determined in sunflower due to weed competition. For 5% acceptable yield loss in the first year, the critical period in weed control was determined as 243-1181 GDD; this is 24-86 days after the crop emergence (DAE) . It was found between 269 and 1409 GDD (16-72 DAE) in the second year. In sunflower, it was determined that the removal of weeds from the plot in the weed-free period started within 2-3 weeks from the emergence and continued for 10-12 weeks. These findings may help sunflower growers to plan and implement cost-effective and appropriate weed control programs.

Critical period of weed control in an interseeded system of corn and alfalfa

AbstractAlfalfa (Medicago sativa L.) hectares in Michigan are declining partly due to reliance on corn (Zea mays L.) silage as a continuous feed source. By interseeding corn and alfalfa, farmers can replace the low alfalfa yield in the establishment year with corn silage while simultaneously establishing alfalfa. A randomized split-block field study was conducted in East Lansing, MI, over 3 yr (2019 to 2021) to determine the critical period of weed control (CPWC) in the interseeded corn and alfalfa system using two corn hybrids with differing leaf architecture (pendulum vs. upright). Whole plots were assigned to corn hybrids interseeded with alfalfa, and subplots were assigned to a surrogate weed, Japanese millet [Echinochloa esculenta (A. Braun) H. Scholz], for the duration of competition treatments. Weed-free and weedy plots were included as controls. At the end of the interseeding year, corn was harvested, while alfalfa was harvested the following year. The CPWC is made up of two components: the critical timing of weed removal (CTWR) and the critical weed-free period (CWFP). Corn hybrid had no impact on the CTWR or CWFP for interseeded corn or alfalfa. Averaged across hybrids, the CTWR was 303 growing degree days (GDD), and CWFP was estimated to be greater than the study duration. The CTWR in the first cutting of alfalfa was estimated to be 369 GDD. The CWFP was estimated to be 394 GDD for a 5% acceptable yield loss for the first alfalfa cutting. Identification of the CPWC in the interseeded system will increase adoption and interest in other interseeded systems that can mitigate potential negative environmental and economic impacts of monoculture agriculture.

Critical period of grass weed control in ALS-tolerant grain sorghum (Sorghum bicolor) is affected by planting date and environment

Field experiments were conducted at two locations in North Carolina (Clayton and Rocky Mount) to determine the influence of row spacing and planting date on the critical period of weed control (CPWC) of grass weeds in ALS-tolerant grain. Grain sorghum was planted in May and June 2019, with either a 38 or 91 cm row spacing using an ALS-tolerant sorghum variety. Treatments consisted of “weedy” or “weed-free” plots up to 2, 3, 5, and 7 weeks after crop planting (WAP) and two control treatments of weedy and weed-free all season. Selection of grass weed species was achieved by controlling broadleaf weeds with a premix of bromoxynil plus pyrasulfutole at a rate of 264 g a.i. ha-1.Grass weeds were controlled using nicosulfuron at a rate of 69 g of a.i. ha-1. The CPWC was significantly different across locations. Row spacing and planting date factors did not influence the CPWC at Clayton. Planting date was a significant factor for the CPWC at Rocky Mount, however row spacing did not have any effect on the CPWC. Results for the CPWC are presented in terms growing degree days (GDD) from the date of crop sowing. The CPWC for grass weeds in grain sorghum at Clayton was from 368 to 849 GDD. The CPWC at Rocky Mount for May-planted grain sorghum was from 405 to 876 GDD, while the CPWC for June-planted grain sorghum ranged from 228 to 1042 GDD. These results demonstrate that cultural and environmental factors may influence the beginning, duration and end of the CPWC.