Abstract Background: Megathyrsus maximus (Jacq.) is a perennial weed that affects many crops. In Argentina, sugarcane is the most affected. Objective: Study effective techniques to break dormancy and the effect of environmental factors on the germination of this weed. Methods: Experiments were carried out in cabinet incubators twice, with five replicates per treatment. The experimental unit was made up for 50 seeds. Results: Seed dormancy was strongly associated with the presence of glumes. Manual extractions of glumes and immersion in sulphuric acid were the most effective techniques for breaking dormancy. Megathyrsus maximus did not depend on light to germinate, and it did so both under a 12 h-light-dark photoperiod and in complete darkness, with maximum mean germination percentages of 73 and 76%, respectively. Mean germination percentage (G) and coefficient of germination (CG: number of germinated seeds per day) showed that this weed responded to a wide range of temperatures, the optimal varied between 25 and 35 °C. Both mean germination percentages and CG decreased as osmotic potential became increasingly negative (0 MPa to -0.6 MPa), and as sodium chloride solution concentrations increased (10 to 130 mmol L-1). No germination was observed at -0.8 MPa and with a 150 mmol L-1 sodium chloride solution. Conclusions: The optimal germination conditions for M. maximus can be found in central sugarcane areas in Argentina, since soils are in ideal conditions and are kept under irrigation. In marginal areas, M. maximus germination would depend on rainfall and certain sodium chloride concentrations in the soil.

Abstract Background: Parthenium weed (Parthenium hysterophorus L.) is an invasive weed that has invaded vast regions of Pakistan in a relatively very short period of a decade or two, threatening the crop fields of the agrarian fed country. Parthenium hysterophorus L. is native of central South America and Gulf of Mexico, has now turned out to be a weed of global significance due to its alarming invasions and profuse spread in approximately all parts of the world. Its invasion is probably due to the contamination of its seeds in the imported grains from other countries of the world. Objective: During comprehensive sampling from Pakistan and Australia, it was observed that parthenium weed accessions exhibited several distinct morphological features present at different geographical regions. Therefore this study focuses on the use of plastid DNA barcodes (psbA-trnH) to evaluate the extent of variations in nucleotide sequences between the parthenium weed sampled accessions. Methods: The variability or genetic diversity was evaluated through sequencing of the amplified products and data was subjected to phylogenetic analysis in Molecular Evolutionary Genetic Analysis (MEGA; version 6.06) software. Results: In Maximum Likelihood tree, mainly two clades with three subdivisions are evident which showed increased heterogenity. The results of sequence based markers showed 12 haplotypes of P.hysterophorus populations (having two parsimony informative sites) with 10 indels and a few SNPs (single nucleotide polymorphisms). Conclusions: The results advocate that there have been multiple introductions of parthenium weed into Pakistan.

Abstract Background: Soybean cultivation has been an option used to diversify the production system and perform herbicide rotation in irrigated rice crops in the lowland soils of the Rio Grande do Sul State, southern Brazil. However, elevated salinity levels have been detected in these soils that can inhibit plant growth due to the reduction of the osmotic potential of the soil solution and can causes toxicity. The combination of stress factors in the plantation areas can intensify deleterious effects, such as changes in salinity associated with herbicides that trigger oxidative stress in crops. Objective: This study aimed to evaluate osmotic potential, cell damage, and enzyme activities of the antioxidant metabolism on soybean after treatment with herbicides and salinity stress conditions. Methods: For this purpose, completely randomized design was used in a factorial scheme with three replicates. The A factor included four herbicide treatments, as follows: control (no herbicide), sulfentrazone, S-metolachlor, and sulfentrazone + S-metolachlor. The B factor was represented by the following three salinity levels: 0 (control), 60, and 120 mM NaCl, which were applied 24 hours after soybean sowing. Results: The results showed a significant alteration in the osmotic potential of soybean plants, mainly at higher salt concentrations. Although an increase in the lipid peroxidation has been detected in some treatments, antioxidant enzyme action combined with osmotic adjustment to reduce oxidative damage were mechanisms found to be employed by plants to reduce hydrogen peroxide levels. Conclusions: We concluded that herbicide treatment, in combination with saline stress, can alter physiological and biochemical processes of soybean plants.

Abstract Background: Information on the carryover of herbicides applied to the destruction of cotton stalks, as well as the withdrawal period necessary to prevent the development and productivity of the crop in succession from being affected are limited in the literature. Objective: The objective was to identify the carryover effect promoted by herbicides used in the management of the destruction of cotton stalks and to estimate the host free period for sowing soybean in succession. Methods: Two individual experiments were conducted simultaneously, one for single application and the other for sequential application of herbicide treatments. The experiments were installed in a factorial scheme (15x5), in a randomized block design with four replications. The first factor evaluated was herbicide treatments and the second factor was five soybean sowing times after application (0, 30, 60, 90 and 120 days). The herbicides used in the treatments were 2,4-D, glyphosate, saflufenacil, [imazapic + imazapyr], dicamba, fluroxypyr and sulfentrazone. Results: As this work was conducted, the results provide a carryover indicator. It is concluded that the single application and the sequential application of the glyphosate + dicamba + saflufenacil treatment has great carryover potential for soybean crops, with the host free period for sowing the crop exceeding 120 days after application. Conclusions: The treatments 2,4-D, 2,4-D + glyphosate, glyphosate + saflufenacil + fluroxypyr had the lowest host free period intervals, even when in sequential application. The treatment with application of 2,4-D alone showed the lowest carryover potential for soybean.

Abstract Background: Inconsistent control of Barnyardgrass has been reported repeatedly by farmers in major rice growing areas of Iran and Turkey. Objective: Thus, a greenhouse study was conducted to investigate the resistance of Barnyardgrass to acetyl CoA carboxylase (cyhalofop-butyl) and acetolactate synthase (penoxsulam, bispyribac-sodium) inhibiting herbicides. Methods: The seeds were sown in pots in a greenhouse and after screening, were sprayed with various rates of cyhalofop-butyl, penoxsulam and bispyribac-sodium herbicides at 3-4 leaf stage. Four weeks later, the above ground biomass was cut, dried in an oven and weighted. The results were then analyzed in the R software (drc package) using a four or three parameter log-logistic function. All experiments were repeated twice. Results: While 30% of biotypes collected from Turkey were not controlled by ACCase inhibitors at twice the recommended rates, no resistance was observed in Iran’s samples. Only one biotype exhibited cross-resistant to penoxsulam and bispyribac-sodium in Iran, which was due to consecutive application of herbicides with modes of action similar to these herbicides. In contrast, several Turkish biotypes showed cross-resistance as well as multiple resistance to ACCase and ALS inhibitors. Conclusions: The rapid expansion of herbicide resistance in both countries indicate the necessity of adopting integrated weed management practices to hinder the further evolution of resistance in future.

Abstract Background: Lettuce-production areas in Brazil are frequently infested by pigweed plants, which can interfere with production by competing for resources or releasing allelopathic compounds in the environment. Objective: The present study evaluated the effect of redroot pigweed (Amaranthus retroflexus) density and distribution on lettuce crop (Lactuca sativa L.). Methods: The cultivars Lídia, Verônica, Lucy Brown and Salad Bowl were used. After transplanting, these plants coexisted until harvest with four pigweed plants (equivalent to 16 plants m-2) located within or outside planting rows, or with one pigweed plant located at the center of the plot (4 plants m-2), as well as a control without weed. The experiment was conducted in an open and semi-controlled area, with treatments arranged in a 4x4 factorial scheme, in a completely randomized experimental design with three replicates. Evaluations included: the number of leaves, fresh matter (lettuce only), height, leaf area and dry matter of lettuce and redroot pigweed plants. Results: The coexistence with redroot pigweed caused yield losses of up to 45% for cultivar Lídia; 41% for Salad Bowl; 33% for Verônica; and 28% for Lucy Brown. Conclusions: The density of 16 plants m-2 of redroot pigweed was the one that most negatively affected the growth of the cultivars, in which the positioning in the planting lines resulted in greater interference to the crop growth. Among the cultivars tested, Lucy Brown showed greater tolerance to coexistence with redroot pigweed plants, while the cultivar Lídia was the most sensitive to the imposed interference.

Abstract Background: Plants synthesize compounds of specialized metabolism to defend themselves against biotic and abiotic stresses. These compounds could be used as models for pesticide development. Among the species that have not yet been studied for the potential to produce active compounds is the kidney leaf mud plantain (Heteranthera reniformis). Objective: The goal was to evaluate the effect of hexanic, ethyl acetate and methanolic extracts of H. reniformis leaves on cress (Lepidium sativum) seed germination to determine which one have the highest biological activity; and to evaluate different concentrations of extract with the highest biological activity on lettuce (Lactuca sativa), barnyard grass (Echinochloasp.) and giant arrowhead (Sagittaria montevidensis) germination. Methods: The seeds were placed on petri dishes containing two sheets of germitest paper, and after the application of the extract, they were sealed and placed in growth chambers with controlled temperature and photoperiod. The variables analyzed were 1st and 2nd germination count, germination speed index and length of the aerial part and roots. Results: The ethyl acetate extract provided greater phytotoxicity on cress than the other extracts. In general, the highest concentration of ethyl acetate extract was the most efficient in reducing variables for all species. Conclusions: The ethyl acetate extract of H. reniformis presents inhibitory activity on the seeds of cress, lettuce, giant arrowhead and barnyard grass, but this activity was dependent on the concentration of the extract and the species studied. H. reniformis synthesizes compounds with phytotoxic activity and purification of extracts is required to isolate, identify and characterize the action mechanism of the compounds with herbicide activity, so that in the future these can be used as models for the development of herbicides.

Abstract Background: The application of Acetyl CoA carboxylase (ACCase) inhibitors prior to sowing of grass crops may result in crop damage due to residual effect of these herbicides in soil. The hypotheses was that different corn hybrids and ACCase herbicides can result in different plant-back intervals after burndown treatments. Objective: This work was planned to determine safe plant-back periods for three corn hybrids where ACCase herbicides clethodim and haloxyfop-methyl are applied. Methods: Herbicides were sprayed at 21, 14, 7, 2 and 0 days before sowing (DBS) at 192 g a.i. ha-1 (clethodim) and 120 g a.i. ha-1 (haloxyfop-methyl). Individual experiments were carried out with three hybrids: KWS9110 and 2B587 with glyphosate and glufosinate tolerance and Enlist with aryloxyphenoxypropionate tolerance. Results: Haloxyfop-methyl resulted in higher damage potential compared to clethodim for the hybrids KWS9110 and 2B587. For these hybrids, significant crop stand and grain yield reductions were observed mainly when haloxyfop was applied closer to sowing date (7, 2 and 0 DBS). Conclusions: Based on the effects on corn grain yield, a safe plant-back period for haloxyfop was estimated to be 8 and 11 days for the hybrids KWS9110 and 2B587, respectively. For the Enlist corn hybrid, there were no yield decreases, even when haloxyfop was applied at 0 DBS. Clethodim did not affect corn yield of any hybrid in any application time.

Abstract Background: The application of appropriately timed herbicide is an affordable approach to optimize the activity of herbicides. Objective: The study aims to determine the best night-time to apply glufosinate, oxyfluorfen, and paraquat with emphasis on the role of the period of dark exposure after herbicide application. Methods: The study was conducted at two fields in Iran, the fresh weight: dry weight (FW/DW) ratio of five weed species treated with glufosinate, oxyfluorfen, and paraquat at 0.5x and 1x of labeled doses after sunset or before sunrise was assessed. Results: The application time-of-day effect for tested herbicides was affected by application dose of herbicide and was more pronounced when the herbicides were applied at the 0.5x as compared to at the 1x. In 14 out of 18 cases, foliage tissues were more desiccated with the sunset applications of herbicides at the 0.5x than with the sunrise applications. When applications were made after sunset, an increased foliage tissues desiccation of Chenopodium album L. treated with paraquat (29.6%) in field 1 and C. album treated with glufosinate (27.2%) or paraquat (23.7%), and Malva neglecta Wallr. treated with glufosinate (21.6%) or oxyfluorfen (31.6%) in field 2 was detected by increasing the dose from 0.5x to 1x. Except 4 out of 18 cases, the herbicides applied either at the 0.5x after sunset or at the 1x before sunrise resulted in similar FW/DW ratio in all weed species. Conclusions: If contact herbicides are used at night-time after sunset, it is possible to take advantage of their reduced doses.

Abstract 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.

Abstract Background: Plant-derived compounds are alternatives of synthetic insecticides in sustainable agriculture. Objective: This study investigated the phytotoxic effect of higher concentrations (2, 4, 8 and 16%) of four plants extracts (Azadirachta indica, Mentha arvensis, D. stramonium and Citrus limonium) on cotton plants. Methods: Each concentration was replicated four times to check the phytotoxic effect (CO2-in, CO2-out, H2O-in, H2O-out and photosynthesis absorption rate (PAR) in randomized complete block design. Data was recorded after 12, 24, 48 and 72 hours of spray with the help of Photosynthetic CL 340 meter. Results: The results showed that CO2-in was more affected by the D. stramonium (131.65±0.38) at 8% concentration. The overall progress showed that C. limonium was more affected the CO2-in of cotton crop. CO2-out was less affected by the C. limonium (117.83±1.46) at 4% concentration than M. arvensis (116.99±1.25) at 8% concentration and D. stramonium (115.77±0.74) at 16% concentration, but was more affected by the A. indica (118.15±0.71) at 4%. H2O-in was more affected by the C. limonium (0.39±0.05) than D. stramonium, A. indica and M. arvensis at 16% concentration. H2O-out of cotton was least affected by the D. stramonium (7.63±0.01) at 2% and more affected by the C. limonium (1.56±0.15) at 16% concentration. PAR was more affected by the A. indica (931.47±8.39) at 4% concentration and least affected by the M. arvensis (1499.7±9.94) at 8% concentration. Conclusions: Different dosages of various botanicals influenced the opening and closing of stomata and photosynthesis of cotton plants.

Abstract Background: Weeds are unwanted and undesirable plants which deteriorate the quality of agricultural products and interfere with farming activities. Most of the weeds (indigenous and invasive) seeds get preserved in soil horizons as weed seed bank which ensure their survival leading to the spoilage of quantitative and qualitative functioning of agricultural farms. Objective: To keep weeds below threshold level, elimination of weeds seed before germination can be a viable and pro-ecological approach. To achieve this objective, weed seeds reserved in the soil which serve as an effective pool to ensure their survival necessitate weed-seed bank management. Thus the ultimate goal was to synthesize and analyze research findings on weed seed bank management leading to formulating the most effective strategy encompassing viable control of weeds in maize. Methods: This study reviewed and analyzed the characteristics which impart botanical superiority to weeds and impact of all prevalent weed control strategies on weed seed bank, weeds density and maize yield. The research findings pertaining to different agronomic practices and technological packages were critically analyzed to sort out the most effective and eco-friendly approach to control weed-seed bank and weeds density in maize crop. Results: The synthesis and critical evaluation of research findings pertaining to weed control methods revealed that manual and mechanical methods were eco-friendly but involved expensive labor, while the chemical approach involving the use of herbicides led to serious deterioration of agro-environmental resources. Two or more techniques used in coherence which encompassed deep tillage to burry weeds seed and prevented their germination through mulches of biotic and synthetic materials along with optimizing sowing method especially raised bed technique reduced weed seed bank and weeds density in maize. Conclusions: It is inferred that integrated approach entailing cultural, manual, mechanical and chemical control can be developed as a pro-environmental and farmer friendly approach for weed control by reducing weed seed reserves which can potentially lead to higher economic returns through higher maize yield.

Abstract Background: Continuous use of commercial herbicides is posing a severe threat to environment and creating herbicide resistant weeds. Allelopathy offers a promising alternative to commercial herbicides for sustainable weed management. The farmers are highly concerned with maximum yield as well as cost of the weed control techniques. Objective: To investigate economic and weed control efficiency of allelopathic crop water leachates mixed with lower rates of herbicide. Methods: Rapeseed (Brassica napus L.), sunflower (Helianthus annuus L.) and sorghum (Sorghum bicolor L.) crop leachates (18 L ha-1 each) tank mixed with lower doses (25, 33 and 50% of recommended dose) of S-metolachlor+atrazine were sprayed as pre-emergence for horse purslane (Trianthema portulacastrum L.) management in maize (Zea mays L.). Label dose (1,080 g a.i. ha-1) of herbicide (S-metolachlor+atrazine) and a weedy check treatment were also maintained. Results: The results showed that rapeseed+sunflower+sorghum allelopathic leachates mixed with half dose (540 g a.i. ha-1) of S-metolachlor+atrazine was effective against horse purslane and increased maize yield (grain) by 45% and 5% as compared with control and label dose of herbicide, respectively. Likewise, economic analysis showed that the same treatment was most economical with 40% and 9% higher net benefits than control and label dose of herbicide, respectively and 2407% marginal rate of return. It also gave an additional benefit of US$ 24.07 for investment of every US$1. Conclusions: By using this technique, herbicides use can be minimized by 50% for sustainable weed management without compromising maize yield and net benefits.

Abstract Background: Allelopathic plants like safflower (Carthamus tinctorius) can be considered as natural herbicides for weeds management in field. But there is not enough research on safflower genotypes allelopathy potential. Objective: So in this study, allelopathic effect of the four safflower genotypes on weeds (Amaranthussp., Hordeum spontaneum), crops (Sesamum indicum, Triticum aestivum) and on autotoxicity of Carthamus tinctorius was evaluated in bioassay using sandwich method. The results can be used in the management of weeds in safflower fields and also in the rotation with other crops. Methods: Two genotypes with high allelopathic potential and two genotypes with low allelopathic potential were selected from forty genotypes of safflower. Growth traits including radicle length, hypocotyl length, shoot length, fresh biomass weight and germination percentages were measured. Results: Results showed that Amaranthussp. and C. tinctorius displayed the most and least susceptibility to safflower residues, respectively. Khorasan (Khorasan330) and Egypt (PI657800) had the greatest with Kerman (CTNIR9) and Australia (PI 262424) had the least inhibitory effects on target plants. PI 262424 stimulated hypocotyl growth by 51%, 18% and 7% in H. spontaneum, T. aestivum and C. tinctorius, respectively. CTNIR9 enhanced this trait by 16% in T. aestivum and 10% in C. tinctorius. In large-seeded species (H. spontaneum, T. aestivum and C. tinctorius, Kerman (CTNIR9) and Australia (PI 262424) stimulated seedling growth. Conclusion: It can be concluded that effectiveness of allelopathic residues of safflower on target plants depended on the seed size of target plant with smaller seed size (Amaranthussp.) were more susceptible to allelopathic residues than those with larger ones. In addition radicle length was affected more than other growth traits by safflower residues.

Abstract Background: The use of commercial mix and tank mix with two or more herbicides is a widespread practice. However, despite its several possible benefits, little is known about its effect on the behavior of the molecules in the soil, which can increase or reduce the leaching potential of these molecules. Objective: This study evaluated the leaching potential of the herbicides diuron and sulfentrazone applied, using commercial mix and tank mix, in soils with different textures. Methods: The herbicides diuron (1,750 g ha-1) and sulfentrazone (875 g ha-1) were applied in three soils with different textures (clayey, medium, and sandy), using a commercial mix (Stone®) and a tank mix (Herburon 500 BR + Boral®). Subsequently, the treated soils were reconstituted in soil columns subjected to rainfall simulations with accumulated rainfall volumes of 40, 80, and 120 mm; the leached solutions were collected and analyzed by LC-MS/MS. Results: The results indicated a low descending movement of diuron in the three soils evaluated, when applied using commercial and tank mixes with sulfentrazone. Higher rainfall volumes (80 and 120 mm) were required to increase the diuron movement (≈20% of diuron applied). Sulfentrazone showed a high leaching potential in the soils, whereas the tank mix increased the leaching potential in sandy soil with the rainfall depths of 80 and 120 mm. Conclusions: The formulations did not affect the leaching potential of the herbicides in clayey and medium soil. However, the tank mix promoted greater leaching of the herbicides in the sandy soil when compared to the commercial mix.