Weed-free Conditions Research Articles

Effect of weed management practices on the performance of transplanted aman rice varieties

A field experiment was carried out to study the effect of weed management practices on the performance of transplanted aman rice varieties. The experimental treatments comprised three varieties viz. BR11, BRRI dhan39 and Binadhan7 and seven weeding treatments viz., weedy check, hand weeding at 15 and 35 DATs, application of early post-emergence herbicide Manage (Pyrazosulfuron ethyl), application of pre-emergence herbicide Rifit (Pretilachlor), Manage + one hand weeding at 35 DAT, application of Rifit + one hand weeding at 35 DAT and weed free. The experiment was laid out in a randomized complete block design with three replications. The results reveal that varieties should significant variation on plant height, number of total tillers hill-1, number of effective tillers hill-1, number of non-effective tillers hill-1, panicle length, number of grains panicle-1, number of sterile spikelets penicle-1, 1000-grain weight, grain yield, straw yield and harvest index. Grain yield was the highest in BRRI dhan39. Weeding regime had also significant effect on all the studied crop parameters except 1000-grain weight. The highest grain yield was obtained from weed free condition followed by hand weeding at 15 and 35 DATs. Interaction between variety and weeding regime had significant influence on all the studied crop parameters except 1000-grain weight. The highest grain yield was obtained from the interaction of BRRI dhan39 × weed free condition which was statistically identical (5.50 t ha-1) with interaction of variety BR11 × two hand weedings at 15 and 35 DATs. Therefore it may be concluded that BR11 rice could be cultivated using two hand weedings at 15 and 35 DATs for obtaining higher yield.J. Bangladesh Agril. Univ. 14(1): 17-22, June 2016

Evaluation of the Impact of Weed Control Methods on Quantitative and Qualitative Characteristics of Moldavian Balm; A Medicinal Plant

Abstract Moldavian balm is an annual herbaceous plant and its lemon-scented leaves contain essential oil. However, weeds adversely affect its growth by release of allelochemicals, and/or direct competition for nutrient, moisture, light and space. Current experiment was conducted to evaluate the different weed control methods including preventive approach (soil pasteurization), mechanical methods (one hand weeding, two hand weeding, and successive hand weeding for weed free condition), and chemical control by synthetic herbicides (haloxyfop-R-methyl and trifluralin). Results revealed that stem diameter, quantity of secondary branches, flower-bearing branches and leaves were significantly affected by weed control treatments; the highest lateral growth was obtained by successive mechanical weed control and two hand weeding method, respectively. This trend was also observed in canopy spread and chlorophyll content. Pre-emergence control by trifluralin considerably accelerated the initiation of flowering in Moldavian balm. However, observation of qualitative traits showed that the highest essential oil content and oil yield was obtained when the plants grew in weed free soil which was pasteurized. Considering the recognized essential oils, the most responsive composition was including Geranial, Geranyl acetate, Neral and Geraniol. The lowest amount of Neral was recorded in postemergence control performed by means of haloxyfop-R-methyl herbicide.

Implications of narrow crop row spacing in managing weeds in mungbean (Vigna radiata)

The mungbean production area is increasing in Australia due to increasing demand for the grain in Asian countries. However, the mungbean crop is generally grown with wide row spacing, and therefore, it is prone to heavy weed infestation which has a significant impact on the mungbean grain yield. Experiments were conducted in 2015 and 2016 to determine the row-spacing impact on crop yield and weed growth for mungbean grown in 25, 50, and 75 cm space rows. Row spacing did not affect weed biomass and mungbean grain yield when weeds were allowed to grow from crop sowing to maturity. However, narrower row spacing (25 and 50 cm) had lower weed biomass and higher grain yield when weeds were allowed to grow beyond 3 and 6 weeks after planting (WAP). Mungbean grown at 25 and 50 cm rows had 60–70% and 70–92% less weed biomass than the mungbean grown at 75 cm rows for the weeds grown beyond 3 and 6 WAP, respectively. In weed-free conditions, too, mungbean grain yields were greater in narrow rows than in wider rows. Weeds grown beyond 6 WAP did not affect grain yield of 25 and 50 cm rows but reduced mungbean yield with 75 cm rows. The practical implication of this study is that narrowing row spacing in mungbean could lead to reduced weed growth and seed production and increased crop yield.

Early‐Season Lactofen Application Fails to Increase Soybean Yield under Weed‐Free Conditions

In an effort to increase soybean [Glycine max (L.) Merr.] yield, growers may consider non‐traditional use of crop inputs. One non‐traditional input use is the application of lactofen {2‐ethoxy‐1‐methyl‐2‐oxoethyl 5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoate} herbicide to early‐vegetative soybean to promote increased branch development and ultimately increase seed yield. The purpose of this study was to evaluate the effect of early‐season lactofen application and simulated herbicide injury on stands, plant height, light interception, and seed yield. The experiments were conducted at two locations in Kentucky during the 2013 and 2014 growing seasons. Treatments included lactofen herbicide applied at 240 g a.i. ha−1 and fomesafen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐N‐methylsulfonyl‐2‐nitrobenzamide} herbicide applied at 600 g a.i. ha−1. A meristem removal treatment was included, where the apical meristem of each soybean was physically removed, and a leaf removal treatment was also performed. All treatments were applied to soybean at V1, V2, V3, and V4 growth stages. The herbicide application timing had no effect on any of the above mentioned agronomic measurements. The apical meristem removal reduced plant stands and plant height in 2 site‐years while lactofen and leaf removal decreased early‐light interception in all site‐years. Meristem removal and leaf removal reduced seed yield in 1 site‐year, while lactofen, leaf removal, and meristem removal reduced seed yield in another site‐year. None of the treatments increased seed yield compared with the untreated control. Despite a limited number of trials, this study suggests that application of lactofen to soybean for non‐weed control purposes is not a viable strategy to increase soybean yield.Core Ideas Leaf removal and lactofen application decrease early‐season light interception in soybean. Destroying the soybean apical meristem either decreases or does not affect soybean yield. Lactofen application to early vegetative soybean does not increase yield under weed free conditions.

Weed Competition Periods Affect Grain Yield and Nutrient Uptake of Black Seed (Nigella Sativa L.)

The combination of the relatively open plant canopy and slow growth, especially at early growth stages, results in lower competitiveness of black seed (Nigella sativa L.) than weeds. Thus, weed interference is known as an important factor affecting black seed yield. Therefore, to determine the critical period of weed control and its effects on nutrients uptake of black seed field experiments were conducted in 2011 and 2012. Two quantitative series of weed removal treatments including weed-infested and weed-free treatments were implemented from black seed emergence to maturity harvest. To determine critical period of weed control, plots were weed-infested or weed-free for 0, 14, 28, 42, 56, 70 days after emergence, in weed-infested and weed-free treatments, respectively. The results revealed that N, P and K contents in weed tissues significantly increased with increasing weed-infested periods during both years of the experiment. The reduction in grain and oil yield due to longer periods of weed-infested conditions or shorter periods of weed-free conditions were accompanied by simultaneous reduction of N, P and K uptake in black seed grains and tissues. Overall, N, P and K contents in weed tissue were found to be 1.8 to 2 times higher than that of black seed. It was concluded that 58 or 49 days weed-free periods are required to avoid yield loss (above 5% or 10%) in black seed.

Mechanical weed control on small-size dry bean and its response to cross-flaming

Dry bean (Phaseolus vulgaris L.) can be a profitable crop for farmers; however controlling weeds effectively without a decrease in yield remains a problem. An example where mechanical weed control is difficult to conduct is dry bean ‘Toscanello’, which is a small sized high-income niche product growing low to the ground. Concerning intra-row weed control, also flame weeding could be an opportunity but the dry bean heat tolerance needs to be studied. The aims of this research were to study the weed control efficacy of a spring-tine harrow and an inter-row cultivator in this bean variety, and to test the tolerance of dry bean cultivated under weed-free conditions to cross-flaming applied with different liquefied petroleum gas (LPG) doses. Flame weeding was applied at BBCH 13 and BBCH 14 bean growth stages by pairs of burners producing direct double flame acting into the intra-row space, with bean plants placed in the middle. The results suggest that the spring-tine harrow used two times at BBCH 13 and 14, respectively, lead to a yield similar to that of the weedy control. The inter-row cultivator could be an opportunity for small-sized dry bean crops producers, enabling them to obtain a similar yield compared to the hand-weeded control. Concerning the bean tolerance to cross-flaming the results showed that bean flamed at BBCH 13 stage had little tolerance to cross-flaming. Bean flamed at BBCH 14 stage was tolerant until an LPG dose of 39 kg/ha, giving yield responses similar to those observed in the non-flamed control.

Differential competitive and allelopathic ability of Cyperus rotundus on Solanum lycopersicum, Solanum melongena and Capsicum annuum

ABSTRACTA 2-year greenhouse and laboratory study was conducted to investigate the competition and allelopathy between Cyperus rotundus L. and Solanum lycopersicum L., S. melongena L. and Capsicum annuum L. All crops showed low ability to withstand competition of C. rotundus and this was the reason for the reduction of their total fruit number and fruit yield by 81%–94% and 86%–96%, respectively. The aqueous extracts from C. rotundus plant parts decreased the seed germination and root length of all vegetable cultivars, indicating supplementary allelopathic activity of C. rotundus on all vegetables. The low correlation coefficient between the total fruit yield of the cultivars grown under weed-free conditions and total fruit-yield reduction due to C. rotundus interference indicates clearly that the yielding ability of the cultivars is not related with their tolerance to C. rotundus interference.

Effect of weed control treatment on weed dynamics and yield of mustard [Brassica juncea (L.) Czern and Coss.

Field experiment was carried out at Agronomy Instructional Farm, Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, Gujarat during the rabi season of 2013 to study the effect of weed control treatment on weed dynamics and yield of mustard [Brassica juncea (L.) Czern and Coss.]. Besides weed free condition, pendimethalin 1.0 kg/ha and oxyfluorfen 0.15 kg/ha as PE were found equally effective in reducing the weed population (viz., grassy, broad-leaved and sedges), while oxyfluorfen 0.15 kg/ha as PE resulted in higher weed control efficiency, lower weed index and weed biomass. Among the herbicidal treatments, oxyfluorfen 0.15 kg/ha as PE gave significantly higher seed yield (2417 kg/ha) and stover yield (4886 kg/ha) over rest of herbicide treatments and weedy check.

Integrated weed management in aerobic rice

Field experiment was carried out to study the effect of integrated weed management in aerobic rice (Oryza sativa L.) for consecutive two Kharif seasons in 2011 and 2012 at Karaikal, Puducherry Union Territory with seven treatments in three replications. Grassy weeds dominated the weed flora, with Echinochloa colona as the major weed. Weed free condition maintained throughout the crop growth recorded significantly lower weed density, dry weight and higher weed control efficiency. Though the highest gross monetary returns ( 56, 000/ha) and net returns ( 25, 360/ha) was recorded in weed free condition, maximum B: C ratio (1.94) was recorded in pre-emergence application of pendimethalin 1.0 kg/ha along with a hand weeding at 30 days after sowing (DAS). Uncontrolled weeds accounted for 86.3% yield loss in aerobic rice under coastal ecosystem of Puducherry UT, India.

Genotypic stability of weed competitive ability for bread wheat (Triticum aestivum) genotypes in multiple environments

Weed control in broadacre cropping systems is becoming increasingly difficult owing to widespread evolution of herbicide resistance in major weed species. The importance of crop competition in weed management is often overlooked but it can play an important role in cropping systems. Competitive ability of 86 wheat (Triticum aestivum L.) genotypes varying for early vigour was investigated at two sites over two growing seasons against cultivated oats (Avena sativa L.) as a weed mimic. There were significant (P < 0.001) treatment effects of weed, wheat genotype and weed × genotype interaction at the different sites. Mature crop height and early crop vigour were strongly correlated with improved weed suppression and tolerance. Negative correlation between early vigour (normalised difference vegetation index and visual score) and weed-free yield indicates the presence of some yield penalty in high-vigour (HV) lines. Wheat genotypes with high grain yield under weed-free conditions tended to suffer high yield loss from weeds (low tolerance) and allowed greater production of weed seed (low weed suppression). However, many of the HV lines produced significantly higher grain yield than the tested commercial cultivars under weedy conditions. The use of the Finlay–Wilkinson regression approach for assessing cultivar stability revealed a strong association between genotype mean weed suppression and stability across the four environments. Several HV lines showed consistently greater weed suppression than the wheat cultivars investigated. Genotypic variation was much greater for weed suppression than weed tolerance, suggesting greater opportunity for the selection of improved weed suppression in wheat. However, strong positive correlation between weed suppression and tolerance (r = 0.79, P < 0.001) suggests that wheat lines selected on the basis of high weed suppression may also exhibit improved weed tolerance.

Response of chemical weed management in maize and cowpea intercropping system grown for quality fodder in Eastern Uttar Pradesh

Field experiment was carried out during Kharif 2005 and 2006 using different herbicides to study the response of weed control treatments in maize and cowpea intercropping system for quality fodder. Pre-emergence application of alachlor, metolachlor and pendimethalin @ 1.00 and 1.50 kg a.i./ha each and post emergence application of imazethapyr @ 0.10 and 0.15 kg a.i./ha at 20 days of crop sown combined with weedy and weed-free conditions. All the herbicides at each dose effectively controlled the weeds and reduced its dry weight as compared to weedy condition. Alachlor, metolachlor and pendimethalin at 1.5 kg a.i./ha and pendimenthalin at 1.0 kg a.i./ha significantly reduced the population and dry weight of total weeds over the other rates of herbicides. Pendimethalin @ 1.5 kg/ha gave maximum green forage and dry matter yield (448 and 102 q/ha) among herbicide treated plots which were at par with that of weed free condition (466 and 109 q/ha). All the herbicides at higher doses followed the same trend in reduction of dry matter accumulation of weeds and increased in green forage and dry matter yield of maize and cowpea mixed fodder over control. Similarly, with increase in the dose of herbicide the crude protein, nitrogen uptake and DM (dry matter) per cent increased significantly.

Growth and yield attributes as influenced by integrated weed management in soybean [Glycine max (L.) Merrill

A field experiment was conducted in alluvial loamy soil at Experimental Farm of Division of Agronomy, IARI, New Delhi during Kharif season of 2010. The experiment was laid out in Randomized Block Design and replicated thrice. The experiment consisted of twelve treatments of weed control measures (T 1 - pendimethalin @ 1000 g/ha PE; T 2 - pendimethalin @ 750 g/ha PE + 1 cono weeding at 30 DAS; T 3 - diclosulam @ 18 g/ha PE; T 4 - diclosulam @ 16 g/ ha PE + 1 cono weeding at 30 DAS; T 5 - diclosulam @ 22 g/ha PE; T 6 - diclosulam @ 20 g/ha PE + 1 cono weeding at 30 DAS; T 7 - diclosulam @ 26 g/ha; T 8 - diclosulam @ 24 g/ha PE + 1 cono weeding at 30 DAS; T 9 - imazethapyr @ 75 g/ha at 20 DAS; T 10 - two cono weedings at 20 and 40 DAS; T 11 - weedy-check; T 12 - weed-free check). The result in treatment weed-free check significantly higher of CGR and plant population/m 2 were at harvest and remained at par with two cono weedings at 20 and 40 DAS (30-90 DAS). However, application of pendimethalin @ 1000 g/ha PE being significantly was higher and it remained at par with application of diclosulam @ 24 g/ha PE + 1 cono weeding 30 DAS (60-at harvest). The application of pendimethalin @ 1000 g/ha PE being significantly higher it remained at par with application of weedy check over the rest of treatments at 60-at harvest of RGR. The result in treatment weed-free check significantly higher harvest and remained at par with diclosulam @ 20 g/ha PE +1 cono weeding at 30 DAS and two cono weedings at 20 and 40 DAS (30-90 DAS) over other treatments. The application of pendimethalin @ 1000 g/ha PE in case of HI and remained at par with the application diclosulam @ 18 g/ha PE, diclosulam @ 22 g/ha PE, diclosulam @ 24 g/ha PE + 1 cono weeding at 30 DAS, imazethapyr @ 75 g/ha 20 DAS and weedy-check over rest of treatments. The treatment weed-free check was significantly higher in case of 1000-seed weight over the rest of treatments. They did not significantly affect the integrated weed management on RGR (30-60 DAS) and seed per pods. Season long weed free condition brought the higher increase in the yield attributes, seed yield and stover yield of soybean which was statistically similar with two cono weedings at 20 and 40 DAS and pre-emergence application of diclosulam @ 20 g/ha + 1 cono weeding at 30 DAS. Season long weed free situation recorded 76.96 per cent increase in grain yield as compared to season long weed competition. Herbicidal treatments provided a yield advantage of 54.44 to 74.53 per cent over weedy-check.

The Critical Period for Weed Control (CPWC) in Potato (<i>Solanum tuberosum</i> L.)

Accurate assessment of crop-weed control period is an essential part for planning an effective weed management for cropping systems. Field experiments were conducted during the seasonal growing periods of potato in 2012 and 2013 in Kayseri, Turkey to assess critical period for weed control (CPWC) in potato. A four parameter log-logistic model was used to assist in monitoring and analysing two sets of related, relative crop yield. Data was obtained during the periods of increased weed interference and as a comparison, during weed-free periods. In both years, the relative yield of potato decreased with a longer period of weed-interference whereas increased with increasing length of weed free period. In 2012, the CPWC ranged from 112 to 1014 GDD (Growing Degree Days) which corresponded to 8 to 66 days after crop emergence (DAE) and between 135-958 GDD (10 to 63 DAE) in the following year based on a 5% acceptable yield loss. Weed-free conditions needed to be established as early as the first week after crop emergence and maintained as late as ten weeks after crop emergence to avoid more than 5% yield loss in the potato. The results suggest that CPWC could well assist potato producers to significantly reduce the expense of their weed management programs as well as improving its efficacy.

Response of leaf area and dry matter of crop, weeds and cover crops to competition and fertilizer resources

Plasticity of plants to allocate leaf area and dry matter to upper layer of canopy play important role in canopy architecture and competition. In order to study the vertical distribution of leaf area and dry matter of corn (Zea mays L.), cover crops and weeds canopy in different fertilizer condition and competition, a randomized complete block design experiment with 8 treatments and 3 replicates was conducted at Sari Agricultural Sciences and Natural Resources University in 2012. Treatments were included corn with soybean (Glycine max (L.) Merr.) as cover crop without fertilizer application, corn with soybean as cover crop with chemical fertilizer application, corn with soybean as cover crop with compost fertilizer application, corn with wheat (Triticum aesitivum L.) as cover crop without fertilizer application, corn with wheat as cover crop with chemical fertilizer application, corn with wheat as cover crop with compost fertilizer application and corn monoculture both in weedy and weed free conditions. The results showed that weed infestation reduced total leaf area and dry matter of corn. Corn distributed more leaf area and dry mater of canopy to the upper layer in weedy conditions. Between cover crops, soybeans allocated corn leaf area and dry mater to the higher layers of canopy than wheat. Also, soybean reduced leaf area and dry mater production of weeds more than wheat. Soybean as cover crop with the use of compost treatment was more efficient in reducing of weed biomass and corn yield production.

Goss’s Wilt Incidence in Sweet Corn Is Independent of Transgenic Traits and Glyphosate

Recently, claims have been made that the use of glyphosate and transgenic crop traits increases plant susceptibility to pathogens. Transgenic traits used widely for years in dent corn are now available in commercial sweet corn cultivars, specifically, the combination of glyphosate resistance (GR) and Lepidoptera control (Bt). The objective was to assess the interactions of the GR+Bt trait, glyphosate, and Goss’s wilt on sweet corn. Nine treatments were tested under weed-free conditions at two sites in 2013 and 2014. Treatments included two isogenic cultivars differing only in the presence or absence of GR+Bt, with and without postemergence application of glyphosate, and inoculation with the causal agent of Goss’s wilt (Clavibacter michiganensis ssp. nebraskensis) before glyphosate application, after glyphosate application, or no inoculation. Results failed to show glyphosate or the GR+Bt trait influenced sweet corn susceptibility to Goss’s wilt. The only factor affecting Goss’s wilt incidence was whether plants were inoculated with C. michiganensis ssp. nebraskensis. In the absence of glyphosate application, yet under weed-free conditions, several yield traits were higher in sweet corn with the GR+Bt trait. Results showed that the GR transgene confers the same level of tolerance to glyphosate in sweet corn as observed previously in dent corn. If true, recent claims about glyphosate and transgenic traits increasing plant disease would be of major concern in sweet corn; however, no relationships were found between the GR+Bt trait and/or glyphosate to Goss’s wilt incidence in sweet corn.

The effects of planting arrangement and phosphate biofertilizer on soybean under different weed interference periods

This study was conducted to evaluate the effects of planting arrangement and phosphate biofertilizer on soybean yield and yield components under different weed interference periods at the Agricultural Research Farm of Razi University, Kermanshah, west Iran. The experiment was a factorial with three factors arranged in a randomized complete block design with four replications. The first factor wa s planting arrangement (50 and 5 cm (P1) or 25 and 10 cm (P2) for inter-row and inter-plant spacings, respectively), the second factor was phosphate biofertilizer (no-inoculation (I0 ) and inoculation (I1)) and the third factor was weed treatment (full season weed-free condition (W0), weedy condition until soybean 4-trifoliate stage (W1), weedy condition until soybean flowering stage (W2) and full season weedy condition (W3)). Resu lts revealed that the highest soybean yield occurred when weeds were controlled throughout the growing season and soybean was planted at the inter-row and inter-plant spacings of 25 and 10 cm, respectively (P2) whether phosphate biofertilizer was used or not. For both planting arrangements, full season weedy condition at the lack of the biofertilizer led to the lowest soybean yield produced. Weed biomass was not significantly affected by use of biofertilizer. The highest weed biomass was established in plots without weed control throughout the whole growing season and soybean was planted in a wider row spacing and a less uniform spatial arrangement (P1). Moreover, For W2 and W3 treatments, soybean planted in a narrower row spacing and a more uniform spatial arrangement (P2) produced a notable lower weed biomass, so that, this planting arrangement reduced weed biomass by 31.8 and 31.7 % in W2 and W3, respectively as compared to the P1 planting arrangement. It can be co ncluded that soybean planting in a more uniform spatial arrangement via a narrower row spacing can significantly improve soybean yield and suppress weeds. Phosphate biofertilizer had no sign ificant effect on soybean yield when soybean was planted as the P2 and weeds were controlled throughout the growing season

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

Organic amendments application downweight the negative effects of weed competition on the soybean yield

Applying organic nitrogen (N) sources have been recommended to increase soil fertility and crop growth in organic production systems; however, less information is available on the effects of organic inputs on crop growth in the presence of competing weeds. Field experiments were conducted across two locations during 2012 to investigate the impact of organic and chemical N sources on weed growth and grain and oil yield of soybean. We hypothesized that competition from redroot pigweed against soybean would be weaker when N was supplied by organic sources than when chemical N sources was applied in weed-infested systems. This hypothesis was tested under field conditions with different weed pressures in a randomized complete block design with a split-plot treatment arrangement. Across all fertilization treatments, seed yield losses were 37% for the low weed density and 67% for the high weed density compared with weed-free conditions, the lowest weed biomass obtained for the application of organic amendments. For the high weed density, seed yield loss due to redroot pigweed competition was 9% more for the application of inorganic fertilizer alone than for the application of organic amendments in the combined and alone forms. Soybean grown under the combination of organic and inorganic inputs produced the greatest or equivalent to the greatest LAI, leaf chlorophyll, seed and oil yield for all weed densities. We conclude that weed interference in the soybean cropping system can be reduced by using organic amendments as nutrient sources.

Nitrogen application influenced the critical period for weed control in cotton

The critical knowledge of crop-weed competition period is important for designing weed management strategies in cropping systems. Field experiments were conducted in 2012 and 2013 growing seasons at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effect of three nitrogen (N) rates (0, 150 and 300 kg N ha−1) on the critical period for weed control (CPWC) in cotton. 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. In both the years and regardless of the N application rate, the relative yield of cotton decreased with increasing duration of weed-interference and increased with increasing duration of weed-free period. The application of N fertilizer delayed the beginning of the CPWC in cotton. At the 0 kg N ha−1, the CPWC ranged from 44 to 537 GDD (growing degree days) (7–51 days after crop emergence [DAE]) in 2012 and 87–605 GDD (14–57 DAE) in 2013 based on the 5% acceptable yield loss. At the 150 kg N ha−1, the CPWC ranged from 124 to 597 GDD (18–56 DAE) in 2012 and 183–551 GDD (22–49 DAE) in 2013. Depending on the N application rate, weed-free conditions need to be established as early as one week after crop emergence and maintained as late as eight weeks after crop emergence to avoid more than 5% loss in cotton yield. These findings could help cotton producers improve the cost effectiveness and efficacy of their weed management programme under different N application rates.

Wild poinsettia (Euphorbia heterophylla): an emerging weed in cotton and processing tomato in Greece

Summary Euphorbia heterophylla (wild poinsettia) is reported as an emerging weed in cotton and processing tomato in Kopaida plain, region of Viotia, in central Greece. This is the first record of E. heterophylla in tomato crop in Greece. In a field experiment, mature plants grown under weed-free conditions produced on average 19 heads, 64 capsules, and 192 seeds per individual plant. Mature seeds exhibited no dormancy and the maximum germination (82 to 90%) occurred at temperatures from 25 to 35°C, with a drastic decline (<38%) at 15 and 40°C. Light had no significant effect on seed germination in the whole range of temperatures tested. Fully mature plants were taller than cotton, exerting strong competition. Having no light dependence for germination, seeds might have the potential to germinate and emerge from greater soil depths. This short communication summarizes information for the identification, seed germination and growth of this weed species that would support a proper weed management