Resumo em Inglês:

Abstract Background Weed competition is one of the main constraints to rice yield. Objective Determine the period prior to interference (PPI) of barnyardgrass ( Echinochloa spp.) on the irrigated rice crop as a function of the application of the herbicide cyhalofop-butyl alone and associated with penoxsulam. Methods A field experiment was carried out in a randomized block design, with four replications. The treatments were arranged in a 2×7 factorial scheme, with factor A consisting of the herbicides cyhalofop-butyl and the mixture penoxsulam + cyhalofop-butyl, while factor B consisted of seven coexistence periods: 0, 7, 14, 21, 28, 35, and 120 days after rice emergence (DAE). The herbicides were applied in each of these periods. The analyzed variables were crop height and shoot dry mass of the rice and barnyardgrass, number of grains per panicle, thousand-grain weight, and yield. Results The presence of barnyardgrass competing for environmental resources negatively affected the analyzed variables and rice yield for all periods with a coexistence longer than 28 DAE. Barnyardgrass competition during the entire rice cycle (120 DAE) reduced the shoot dry mass of the crop. Conclusions The PPI termination was determined at 14 DAE for the mixture cyhalofop-butyl + penoxsulam and 29 DAE for cyhalofop-butyl alone.

Resumo em Inglês:

Abstract Background The study of corn and palisade grass physiology may assist in determining the best arrangement of the plants and more efficient management of this intercropped system. Objective To evaluate the effects of different palisade grass plant arrangements and their control on physiological characteristics and corn yield. Methods Two trials in randomized complete block design with four replications were conducted in field conditions. In the first, corn was sown with 0.50 m row spacing, whereas the second had 1.00 m row spacing. All the treatments were arranged in the same way in both experiments, in a 2x4 factorial design. The first factor was the nicosulfuron dose applied (0 and 8 g a.i. ha-1), and the second, the forage seeding rates (0, 2, 4, and 6 kg of seeds per hectare). Sowing of both species was performed on the same day. Results The application of nicosulfuron negatively affected stomatal conductance, internal carbon concentration, and increased CO2 consumption and efficiency in water use. The photosynthetic rate was not affected by the herbicide application, however it presented lower values in the 0.50 m spacing. Although the yield was not affected by row spacing, it was higher when nicosulfuron was applied. Conclusions The increase in palisade grass density caused detrimental changes in the water use efficiency with direct consequences to the crop yield. The physiological response and corn yield depend on the arrangement of plants and the palisade grass management adopted.

Resumo em Inglês:

Abstract Background: Studies of sorption and desorption of herbicides in soils are essential in predicting their transport, bioavailability, and transformation in the soil profile. These studies are also vital to predict the agronomic efficiency of the herbicides in controlling weeds. Objective: In this study, atrazine’s sorption and desorption kinetics were evaluated in samples composed of single and a mixture of horizons from the Red-Yellow Latosol profile. Methods: This was performed by the Batch equilibrium method, and the quantification was carried out using a High-performance liquid chromatography (HPLC). Results: Freundlich isotherms were adjusted appropriately to describe the atrazine sorption. The Kf values obtained varied between 0.188 and 2.592, and the Koc values ranged between 37.76 and 143.81, which corresponded to horizons C and A, respectively. The desorption was only possible to determine in horizon A. The other substrates presented low sorption, and the desorption of the remaining atrazine was not significant, therefore not adjusting to the Freundlich model. The organic matter (OM) was the main attribute to the atrazine sorption in the soil, presenting a high correlation with Kf and Koc values. In the horizon A samples, the Kfd value obtained in desorption was higher than the Kf obtained in sorption, which indicated a low desorption capacity and, therefore, low potential mobility of the herbicide in this soil horizon. Conclusions: It was concluded that the organic matter present in greater quantity in horizon A of the Red-Yellow Latosol has a crucial role in the dynamics of atrazine in the horizons of this soil.

Resumo em Inglês:

Abstract Background: Weeds reduce water use efficiency in crops due to water used by the weed and to the reduction in crop yield. In addition to the usual presence of weeds in the interrow of different crops, the management of these plants has moved away from the idea of total control. Thus, the amount of water lost through the evapotranspiration of weeds (ETW) must be understood. Objective: Determine the water use and crop coefficient (Kc) of the weed species Commelina diffusa, Cyperus rotundus, and Cynodon dactylon using drainage lysimeters associate with the Normalized Difference Vegetation Index (NDVI). Methods: The experiment was carried out at the Lysimetric Station of the Federal University of Viçosa, in Viçosa-MG, in a randomized block design, with four treatments and four replicates. Reference evapotranspiration (ETo), necessary to calculate Kc, was obtained in situ through lysimeters cultivated with Paspalum notatum. Results: The highest Kc values were found in the final third of the experimental cycle, equal to 1.32, 0.93, and 0.90 for C. diffusa, C. rotundus, and C. dactylon, respectively. The NDVI showed a good correlation with Kc and biomass, with R2 ranging from 30.9 to 54.6% and from 46.1 to 63.1%, respectively. Accumulated ETW values ranged from 336 to 473 mm, with C. diffusa showing the highest water consumption, followed by C. rotundus and C. dactylon. Conclusions: C. diffusa has higher Kc and water consumption than C. rotundus and C. dactylon. NDVI can be used in the estimation of the Kc and biomass of weeds.

Resumo em Inglês:

Abstract Background: Thermal weed control is a viable, cost-effective, and eco-friendly emerging alternative to highly challenged and unsustainable chemical weed control. Objective: To find out the most suitable pre-sowing soil solarization durations for effective weed control and soil fertility enhancement in sesame crop. Methods: A field study was conducted during the summer season of 2016 and 2017. Different soil solarization treatments were applied, including 0, 3, 6, 9, and 12 weeks before sowing (WBS) of sesame by spreading transparent polythene sheets. Results: The temperatures of solarized soil at 10 cm depth were 8-10 oC more than the control. The soil NPK and organic matter contents were gradually increased with increasing solarization durations. The highest soil nitrogen (0.71%), phosphorus (9.63 ppm), K (166.2 ppm), and organic matter content (1.12%) were observed with the longest soil solarization for 12 WBS. Different solarization durations provided 23 to 64% weed control efficiency and up to a 34% rise in sesame yield. Conclusions: Based on the current findings, soil solarization for 12 WBS by polythene sheets is an effective alternative to the chemical weed control method with additional positive effects on soil fertility and sesame yield.

Resumo em Inglês:

Abstract Background: Rice fields in the state of Rio Grande do Sul (RS) are one of the largest areas where the herbicide resistant system is utilized worldwide. Weed management is important to achieve high rice yields, and herbicide resistance is the main limiting factor. Knowledge of practices used by farmers is important to understand the dynamics of weeds in rice fields. Objective: To evaluate the frequency of utilization of weed management practices and the main consequences related to herbicide resistance associated with the utilization of the imidazolinone-herbicide resistant rice in RS. Methods: The study was carried out during the 2017/2018 season based on a survey of 103 consultants about weed management in the Clearfield® flooded rice system. Data were analyzed by non-metric multidimensional scaling (NMDS) and word cloud analysis. Results: The main weeds in Clearfield® rice are weedy rice and barnyardgrass, with Cyperus sp. also mentioned. Currently the main reasons for low weed control efficacy are resistance to herbicides, delay in beginning the flooding and application to plants at advanced developmental stages. The consultants’ perceptions indicate that the number of cases of herbicide resistance and area are increasing to several weed species and herbicide modes of action. The predominant rice establishment system is minimum tillage. Conclusions: Barnyardgrass and weedy rice are still a problem after 15 years of utilization of the imidazolinone-herbicide resistance system, and the adoption of best herbicide practices and integrated weed management is necessary in the rice crop in RS.

Resumo em Inglês:

Abstract Background Goosegrass, one of the problematic weeds in the world. Various herbicides have been widely employed for goosegrass control. However, heavy reliance upon the herbicides has led to the evolution of herbicide-resistant biotypes of goosegrass. Diversified approach is needed for sustainable management of goosegrass. Objective Evaluate the phytotoxicity of selected preemergence herbicide-treated oil palm residue powders on goosegrass emergence and growth. Methods A glasshouse experiment was arranged as complete randomized design with five replications. The oil palm residue powders; leaflet (OPL), rachis (OPR) or frond (OPF, leaflet + rachis) were treated with pre-emergence herbicides, viz S-metolachlor, oxyfluorfen or thiobencarb at their respective ED50 rates (rate that gives 50% inhibition) and applied as mulches. The analyzed variables were emergence and shoot fresh weight of goosegrass seedlings. Results The ED97 value (rate that causes 97% inhibition) of S-metolachlor for growth of goosegrass was reduced by more than 90% when being mixed with the oil palm residue powders. Similarly, the ED97 value of thiobencarb was reduced by 90% when goosegrass was treated with thiobencarb–treated OPF powders. By contrast, the oxyfluorfen-treated oil palm residue powders and thiobencarb-treated OPL or OPR powders provided lower inhibitory effect on the goosegrass. Conclusions Oil palm residues of leaflets, rachis and fronds have potential to reduce rate of preemergence herbicide to inhibit goosegrass seedling emergence and growth depending on herbicide choice and parts of oil palm frond used.

Resumo em Inglês:

Abstract Background The use of desiccant herbicides can allow the anticipation of common bean harvesting by providing a reduction in the humidity of plants and grains. Objective Determine the effect of doses of desiccant herbicides on the moisture content of the plants (stems, leaves and grains), in the 100 grains mass, grain yield and physiological quality of the seeds of two contrasting common bean cultivars. Methods The experimental design for each cultivar (BRS FC 104, super early cycle, 60 days from sowing to harvesting and BRS Estilo, normal cycle, 90 days from sowing to harvesting) as in randomized blocks in the factorial scheme 4 x 3 x 4, with four replications. Treatments consisted of four herbicides (ammonium glufosinate (200 g L-1 of active ingredient, ai), glyphosate (480 g L-1 of acid equivalent), diquat (200 g L-1 of ai) and paraquat (200 g L-1 of ai), with three doses (200 g L-1, 400 g L-1 and 600 g L-1 of ai per ha for ammonium glufosinate, diquat and paraquat, and 480 g L-1, 960 g L-1 and 1,440 g L-1 of ae per ha for glyphosate) with evaluations of the variables at 0, 3, 5 and 7 days after application of the herbicide. Results All desiccants used provided faster drying of the botanical structures allowing faster harvesting in relation to control plants. The dosage of 200 g L-1 of the ai ha1 in the cultivar BRS FC 104 and 1,440 g L-1 of ae per ha for glyphosate and 600 g L-1 of ai per ha for the others dessicants in the cultivar BRS Estilo were those that provided best plant drying. The use of desiccants in plants of common bean did not affect crop grain yield. The dosage of 600 g L-1 of ai per ha of the ammonium glufosinate desiccant provided a reduction in vigor and normal seedlings and an increase in abnormal seedlings in the cultivar BRS FC 104. Conclusion All desiccant herbicides used allowed anticipation of common bean harvesting.

Resumo em Inglês:

Abstract Background Areas simultaneously infested with both glyphosate-resistant sourgrass (Digitaria insularis L.) and fleabane (Conyza spp.) are usual in Brazil. However, there are no effective management strategies to control both species concurrently. Objective The aim was to evaluate the interaction and interval of application of haloxyfop-P-methyl and cloransulam-methyl to effective control sourgrass (from 3- to 4-tillers to flowering stages) and fleabane (12- to 15-cm at the vegetative stage). Methods The experiment was conducted twice in a randomized complete blocks design with four biological replicates. The treatments were composed of sequential applications of haloxyfop-P-methyl (firstly applied) and cloransulam-methyl (secondly applied) and vice-versa. After the first application, the second one was applied in intervals of 3, 6 and 12 days. Haloxyfop-P-methyl and cloransulam-methyl were also applied in sequential (without interval), stand-alone applications of both herbicides and an untreated check. Results All treatments effectively controlled all fleabane plants. Haloxyfop-P-methyl applied ≥ 6 days before cloransulam-methyl controlled 100% of 3- to 4-tillers sourgrass and 60% of flowering sourgrass. Conclusions Therefore, haloxyfop-P-methyl may be applied ≥ 6 days before cloransulam-methyl in a sequential application structure to effectively control fleabane and sourgrass (3- to 4-tillers stage), when present concurrently.

Resumo em Inglês:

Abstract Italian ryegrass ( Lolium multiflorum L.) has become notorious due to glyphosate resistance evolution. To study the demography of susceptible and glyphosate-resistant Italian ryegrass populations, several experiments were conducted in the grower’s field to evaluate seedling emergence, survival and reproductive traits patterns in three cohorts, and the effect of density on seed production. Results showed that seedling emergence is fast, and under suitable environmental conditions, it can happen within 30-days. Lower plant survival was observed in the first two cohorts (2% and 3%, respectively) compared to the last (13%). A larger number of spikes (spk) per plant (pl) was observed in plants of the first two cohorts (50.34 and 47.02 spk pl-1, respectively) in comparison to the last one (26 spk pl-1); however, the third cohort presented a higher potential for flower (flwrs) production per spikelets (spklt) (13.5 flwrs spklt-1) in detriment to the first two (11.9 and 12.12 flwrs spklt-1). Fecundity was 20,300 and 13,830 seeds pl-1 for susceptible and glyphosate-resistant plants, respectively, and presented density-dependent regulation. A knowledge of Italian ryegrass’s demographic parameters provides valuable information for identifying particularly vulnerable life-history processes and developing population dynamics models that can contribute to designing more rational control strategies.

Resumo em Inglês:

Abstract Background In the last two decades, herbicide-resistant biotypes of Conyza bonariensis, Conyza canadensis, and Conyza sumatrensis were identified. Objective: To evaluate herbicide alternatives for the control of C. sumatrensis to replace simplified management at soybean pre-sowing in the no-till system and assess the potential herbicide injury to soybeans. Methods Four experiments were conducted in Palotina, PR, to evaluate alternative managements to the herbicides commonly used in C. sumatrensis , such as synthetic auxins, pre-emergent, and burndown herbicides. All consisted of applications in pre-sowing of soybeans and weed control evaluation. Experiments I and II included evaluations during the crop, such as injury and soybean yield. In all experiments, a randomized block design was used, with four repetitions. Results The treatments with sequential applications were more effective in controlling C. sumatrensis . Triclopyr and dicamba were more effective than 2,4-D. Conclusions Dicamba was the most effective synthetic auxins when applied only with glyphosate, without sequential. With sequential glufosinate, dicamba, and triclopyr application showed the highest efficacy. Glufosinate showed better control when applied sequentially compared to saflufenacil. Pre-emergent herbicides were effective only if combined with dicamba in the first application or with sequential glufosinate. Pre-emergent, synthetic auxins, and burndown herbicides were shown to be potentially selective for soybeans.

Resumo em Inglês:

Abstract Background Palyno-anatomy of wetland species belonging to 10 families was studied in the present research work through light microscopy (LM) and scanning electron microscopy (SEM), to find valuable taxonomic characters. Objective This study aims to provide baseline information of the micro-morphological characters of 24 wetland species which will be helpful for further identification of wetlands weeds flora. Methods 24 weeds were collected from different wetlands of Azad Kashmir. Taxonomic tools like light microscopic and scanning electron microscopic techniques are used for the proper identification of wetland weeds. Results The results show diversity among the qualitative and quantitative characters of epidermal cells, stomata, trichomes, and stomatal pore on both leaf surfaces. In accordance with these variations, a taxonomic key was prepared by using these characters for the identification and differentiation of wetland plant species. In pollen evaluations, variations were observed among exine sculpturing, the number of pores, exine thickness, and diameter of pollens. Conclusions Based on our findings it will be helpful for the taxonomist to identify other wetland species by using these micro-morphological characters. This study also indicates that at different taxonomic levels, LM and SEM of pollen and epidermal morphology is explanatory and significant to identify plants up to the species level.

Resumo em Inglês:

Abstract Background Weeds compete with crops, demanding efficient control to avoid yield losses. Highly competitive cultivars are a cultural method that can increase weed suppression and reduce the effects of crop-weed competition. Objective The present study aimed to assess the competitive abilities of barley cultivars (crop) against black oat (weed) and their interference in crop physiology. Methods A preliminary additive experiment was carried out with increasing densities of barley and black oat to determine the minimal density from where there was no drier mass increasing per area. In the second experiment, a replacement series experiment, five plant proportions (100:0; 75:25; 50:50; 25:75, and 0:100) of the crop were used and the competitor was installed. Fifty days after the emergence, morphophysiological and physiological variables, as well as their respective relative competitiveness indexes, relative clustering coefficient, and species aggressiveness, were all assessed. Results The variables associated with the photosynthesis were dependent on the cultivar. BRS Cauê was the cultivar that performed better against black oat, with an increase in the overall photosynthetic rate, due to a smaller leaf area loss, as the competition increased. BRS Brau reduced the photosynthesis into smaller proportions for the competitor. The water use was not impacted to the same extent as photosynthesis. Conclusions BRS Cauê was the most competitive cultivar, suffering the lowest impact of competition with black oat.

Resumo em Inglês:

Abstract Background: Purple nutsedge is a weed that has a tough profuse underground tuber system, and is predominantly a perennial species in many crops. Objective: To evaluate the influence of different water regimes to the effectiveness of herbicides used for controlling the purple nutsedge. Methods: Experiment was arranged in a Randomized complete block design (RCBD) with a two-factor factorial design and three replications. The net-house tests were conducted with six treatments and two different water regimes of “watered daily” and “watered weekly”. The tested herbicides were florpyrauxifen-benzyl, halosulfuron-methyl, 2,4-D and glyphosate. Results: Water shortage reduced the weed control efficacy of four tested herbicides. Herbicide efficacy improved when plants were watered daily, the high level of sedge biomass reduction at 60 DAT observed in florpyrauxifen-benzyl (30 g ai ha-1) and halosulfuron-methyl (50 g a.i ha-1) treatment. Glyphosate (480 g ai.ha-1) and 2,4-D (360 g ai.ha-1) exhibited moderate control efficacy on purple nutsedge under daily watered condition. Conclusions: The water regime was a critical component of purple nutsedge herbicide control program. Maintaining soil moisture by watering daily improved the herbicide efficiency and reliability for the management of purple nutsedge.

Resumo em Inglês:

Abstract Background: Weeds are one of the ecological factors that affect the agricultural economy permanently. Thus, understanding the weed emergence and development is essential in decision making for management strategies. Objective: This study aimed to evaluate the effect of different sowing depths and light intensities on the emergence and development of the weed species Euphorbia heterophylla and Desmodium tortuosum under field conditions. Methods: Each species consisted of an experiment carried out in a completely randomized design with four replications. Treatments were arranged in a 6 × 4 factorial scheme, with six sowing depths (0.5, 1.0, 2.0, 4.0, 8.0, and 12.0 cm) associated with four light intensities (100, 70, 50, and 30% of the solar light intensity) obtained with shading screens. Seedling emergence capacity was evaluated daily to obtain the percentage of emergence and the emergence rate index (ERI). Plant height, time to floral induction, plant dry matter during flowering were also evaluated. Results: Seedlings of E. heterophylla emerged under all solar radiation conditions and sowing up to 12.0 cm deep, while seedlings of D. tortuosum showed no emergence only at 12.0 cm deep with light intensities below 70%. The 100% solar radiation condition provided higher total and daily dry matter accumulation in E. heterophylla plants, while D. tortuosum plants showed higher values for both variables under 70 and 50% incidence of solar radiation. Conclusions: The full sunlight condition provided the best development of E. heterophylla plants. Different levels of lightness and sowing depths interfere the emergence and the development of D. tortuosum plants.

Resumo em Inglês:

Abstract Background: The evaluation of selective herbicides for weed control in winter cereals is extremely important. Simple methods to evaluate alterations caused by herbicides in the growth and development of winter cereals can be performed with vegetation indices. Objective: Evaluate the potential of different vegetation indices by optical sensors to detect phytotoxicity caused by herbicides in winter cereals. Methods: The experiment was conducted under field conditions, in a randomized block design with four replications. Herbicides were sprayed when the plants were at Z24. The phytotoxicity was evaluated at 7, 14 and 21 days after treatment (DAT) and the normalized difference vegetation index (NDVI) and the normalized difference red edge index (NDRE) at 16, 22 and 37 DAT. Results: The herbicide 2,4-D was less phytotoxic to winter cereals, while metribuzin and saflufenacil caused higher percentages (up to 50%) of visible injuries. The NDRE discriminated more precisely than NDVI the variations in winter cereals, showing alteration in the chlorophyll content due to the phytotoxicity caused by the herbicides. The canonical correlation analysis found an inverse relationship between phytotoxicity and vegetation indices. Conclusions: The winter cereals studied were tolerant to herbicides, enabling the recovery of growth and development. The NDRE index was the most sensitive and showed greater potential in identifying injuries caused by herbicides. The canonical correlation analysis confirmed the inverse relationship between phytotoxicity and the reduction of vegetation indices.

Resumo em Inglês:

Abstract Background Sweet corn is susceptible to weed competition for nutrients, moisture, and light interception. Herbicides labeled for use on sweet corn are limited. Hence, it is necessary to provide information about the POST sulfonylurea herbicides and mixtures and their different degrees of sensitivity in sweet corn varieties. Objective The objectives of this experiment were to evaluate the efficacy of sulfonylureas and nicosulfuron+bromoxynil/MCPA and mesotrione/s-metolachlor/terbuthylazine as post herbicide mixtures on broadleaves and grasses weed species, sweet corn grain yield and crop injury. Methods Field experiments were conducted in 2017-19 to investigate the efficacy of the acetolactate synthase (ALS)-inhibiting herbicides nicosulfuron at 80 g a.i. (active ingredient) ha-1, nicosulfuron/rimsulfuron (37.5+37.5)% at 131.25 g a.i. ha-1, foramsulfuron at 45 g a.i. ha-1, and mixture of herbicides nicosulfuron at 80 g a.i. ha-1+bromoxynil/MCPA (20+20)% at 600 g a.i. ha-1, mesotrione/s-metolachlor/terbuthylazine (3.75+37.5+12.5)% at 1343.75 g a.i. ha-1 on the grain yield of three sweet corn varieties . Results: The results indicated that nicosulfuron, nicosulfuron+bromoxynil/MCPA and nicosulfuron/rimsulfuron, respectively, controlled ≥ 90% of Amaranthus retroflexus L. and Solanum nigrum L. at Mashhad. A reduction in biomass nearly ≥ 80% was observed in A. retroflexus , Cyperus rotundus L., Heliotropium europaeum L., Echinochloa crus-galli (L.) Beauv., Abutilon theophrasti Medik. by these herbicides in Sari, Iran. The applications of nicosulfuron, foramsulfuron and mesotrione/s-metolachlor/terbuthylazine at 80, 45 and 1343.75 g a.i. ha-1 respectively, to ‘Golden KSC403su’, mesotrione/s-metolacholor/terbuthlazine at 1343.75 g a.i. ha-1 to ‘Merit’ and nicosulfuron and mesotrione/s-metolachlor/terbuthylazine at 80 and 1343.75 g a.i. ha-1 respectively, to ‘Chase’ were associated with the maximum sweet corn yield. Conclusion The experiment showed that weed control improved grain yield on sweet corn varieties through sulfonylurea herbicide applications.

Resumo em Inglês:

Abstract Background Recent studies have demonstrated an increase in plant growth due to the application of low doses of glyphosate, which is part of the phenomenon known as hormesis . Objective The present study aimed to evaluate the effects of glyphosate doses on the physiological and morphological parameters of Panicum maximum cv. Mombaça. Methods The experiment was carried out in a greenhouse for 49 days after the application of glyphosate, in pots arranged in a completely randomized design, with four replications. The treatments consisted of ten doses of glyphosate (0; 3.78; 8.10; 16.64; 33.48; 67.7; 135; 270; 540 and 1,080 g a.e. ha-1). Evaluations of growth, gas exchange, leaf temperature and plants’ intoxication were carried out. The data were subjected to ANOVA and when significant, regression analysis was performed using the models for dose-response curves. Results The physiological parameters, as well as the growth, were positively affected by the subdoses of glyphosate, with higher values than the control. The leaf temperature increased progressively according to the increase in doses. Conclusion Subdoses of 3.78 to 270 g a.e. ha-1 of glyphosate promoted an increase in plant’s growth and physiological parameters.

Resumo em Inglês:

Abstract Background Redbean (Phaseolus calcaratus L.) is cultivated as an economic crop in the Mazandaran Province, Iran. Velvetleaf (Abutilon theophrasti Medik.) competes severely with red bean growth and reduces yield. Imazethapyr is a selective herbicide recommended for management of grasses and dicotyledonous weeds in different crops including beans. Objectives This research was conducted to develop an empirical model of red bean yield that incorporates the dose-responses of imazethapyr and velvetleaf densities. Methods Modeling of imazethapyr herbicide dose on red bean and velvetleaf competition was conducted using four levels of velvetleaf densities and five dosages of imazethapyr arranged in a factorial design. Results Velvetleaf competitiveness decreased with the increasing imazethapyr dose represented by the standard dose-response curve. A model was improved to composing the dose-response standard curve with the rectangular hyperbola equation. This model estimated red bean economic yield under velvetleaf-free conditions, weed competitivity with no-herbicide application, and the imazethapyr dosage needed to decrease velvetleaf competitiveness about 50%. Imazethapyr at the 0.66 L ha-1 dose was sufficient to control the highest density (12 plants m-2) of velvetleaf. Conclusions Information gained from this study will be important in evaluating economic and environmental terms.

Resumo em Inglês:

Abstract Background Achieving satisfactory weed control levels in black oat (Avena strigosa) fields is often difficult, owing to the limited number of registered herbicide molecules. Objective To determine novel options for selective, post-emergence chemical weed control in this crop. Methods Eight herbicide treatments were sprayed in the field onto black oat plants at the tillering stage to evaluate crop safety and control of Conyza spp. and Gamochaeta americana, two major weeds of Brazilian black oats. A separate trial was conducted to further assess herbicide safety in a controlled-environment setting, and mesotrione selectivity was then re-evaluated separately in the greenhouse during the following growing season. Crop phytotoxicity was determined using biomass production both in the field and in greenhouse trials. Results Mesotrione, bentazon, 2,4-D, and a 2,4-D+bentazon tank-mix produced light symptoms of crop phytotoxicity, from which plants quickly recovered. Conyza spp. control was achieved via applications of mesotrione (192 g a.i. ha-1), metsulfuron-methyl (3.9 g a.i. ha-1), and a 2,4-D + bentazon tank-mix (502.5 g a.e. ha-1 + 720 g a.i. ha-1, respectively), whereas proper G. americana control was only achieved via applications of either mesotrione or metsulfuron-methyl. Biomass accumulation by black oat plants in the greenhouse was similar across mesotrione-treated and untreated plants. Conclusions Mesotrione could become an option for selective, post-emergence weed control in black oat fields, aiding in the fight against multiple herbicide-resistant Conyza spp. populations which are widespread across major black oat-growing areas in Brazil.

Resumo em Inglês:

Abstract Background Invasive weeds pose a serious threat to agricultural systems worldwide and the management of such species requires information on their distribution. Objective This research work aimed at assessing the evolution in the distribution of Siaw weed across biogeographical zones in Benin as first step toward the development of management policy and to give insight into the threat it poses to agriculture and biodiversity. Methods Field and roadside surveys were carried out to record the presence of the species. Geographical coordinates were collected and incorporated in GIS software to map the distribution of the plant. Abundance data were submitted to analysis of variance to compare infestation level across biogeographical zones, and correlation of the species distribution with environmental factors was examined. Results The extent of occurrence of the species has increased and fell within latitudes 6°30’ and just beyond 10° North and range from about 0 m to 438 m in elevation, covering the entire area from south to center, and in part the north of the country. This weed is significantly more abundant in sudano-guinean zone (7.28 ± 0.18) than guinean zone (4.72 ± 0.20) and sudanian zone (3.5 ± 0.5). The species distribution is significantly correlated to the major climate variables and soil pH. Conclusion The distribution of Siam weed mapped here shows progress in its occurrence points. Further studies are needed to better investigate the importance of soil and climate variables in its distribution and the vulnerability of the center zone ecosystems.

Resumo em Inglês:

Abstract The use of herbicides is essential to preserve the productivity and efficiency of crops in land use and growth factors. The general public has questioned the use of herbicides and pesticides, even when used rationally and following the procedures approved by regulatory agencies. It is essential to present accurate information about these products’ use and the risk associated with this use in this context. The mean dose and the Environmental Impact Quotient (EIQ) continuously decreased as a function of the year of release of new active ingredients with herbicidal action in Brazil, which indicates that the new products are more efficient and present lower risks to the environment, farmworkers and consumers. The mean EIQ for each herbicide application in soybean, maize, sugarcane, and cotton has decreased in Brazil. The proportion of herbicides in the number of applications has decreased compared to other classes of pesticides, except for cotton. The risk of products decreased over time, with continuous reductions in EIQ values per unit of the treated area; the EIQ values determined per production remained stable despite the increased complexity of pest management, which caused an increase in the number of applications.