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Herbicide promotes physiological and biochemical changes even in tolerant species. The objective of this study was to evaluate the interference of the herbicides clodinafop-propargyl and 2,4-D in the antioxidant system of wheat, and iodosulfuron-methyl in wheat and ryegrass. Two studies, divided into three experiments, were conducted in an entirely randomized design in a greenhouse and phytotron. The first study tested herbicides iodosulfuron-methyl, clodinafop-propargyl, 2,4-D, and a control without application in wheat. The second, divided into two experiments with wheat and ryegrass, tested iodosulfuron-methyl doses (0, 1.75, 3.5, and 7.0 g a.i. ha-1). The variables analyzed were the concentrations of chlorophylls a, b, carotenoids, hydrogen peroxide (H2O2), lipid peroxidation (TBARS), electrolyte leakage, and antioxidant system activity. The herbicide treatments iodosulfuron-methyl, clodinafop-propargyl, and 2,4-D decreased the concentrations of chlorophylls and carotenoids in wheat plants. The herbicides promoted oxidative stress with increased H2O2 and TBARS concentrations. Increasing the dose of iodosulfuron-methyl provided a reduction in the activity of the enzymatic antioxidant system in wheat and ryegrass. [ABSTRACT FROM AUTHOR]

This research aimed to evaluate the phytosociology of weeds in irrigated rice in different soil management systems and crop rotation intensity. Therefore, two field studies were carried out. Study 1 was conducted in an area that has been cultivated since 1994 with three cultivation systems: direct, pre-germinated and conventional ones. Study 2 was carried out in an experimental area in five Integrated Farming Systems, with crop rotation. Phytosociological evaluations were conducted when rice was fully blooming, in the first study, and when grain filling was ending, in the second study. Pre-germinated system of rice cultivation has predominance of aquatic weeds. Conventional system when compared with direct sowing has lower weed densities. Integrated Agricultural Production Systems with higher intensity of crop rotation have been higher infested of perennial species. [ABSTRACT FROM AUTHOR]

The awareness of agronomic practices that affect the resistance selection of weeds to a particular herbicide is of utmost importance in order to advocate management practices that aim to avoid or prolong the resistance. The objectives of this study were to identify and map the occurrence of the wild poinsettia's low-level resistance to glyphosate in Rio Grande do Sul State (RS), Brazil, and to define the main agronomic factors associated with the selection of these biotypes. Seed and / or soil samples in areas with suspected resistance were collected in Roundup Ready® (RR) soybean crops in different counties in the RS region during the 2010/11 and 2011/12 seasons. A questionnaire on the operations history in the area was applied at each site in order to establish relationships between the distribution of wild poinsettia with cases of suspected resistance to glyphosate and the likely agronomic factors involved in this occurrence. The study included the response of wild poinsettia biotypes with suspected resistance to glyphosate and an analysis of the questionnaires carried out with producers. The main agronomic practices used by producers that favor the emergence of resistant biotypes were the continued cultivation of the RR® soybean; an overdependence on the use of glyphosate; a low rate of crop rotation and efficient chemical alternatives for wild poinsettia control and management. [ABSTRACT FROM AUTHOR]

Fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is a polyphagous species capable to develop on several cultivated and non-cultivated host plants, including weeds. On this basis, we evaluated the survival and development of S. frugiperda on leaves of hairy fleabane (Conyza bonariensis L.; Asteraceae) and slender amaranth (Amaranthus viridis L.; Amaranthaceae) in laboratory trials. Spodoptera frugiperda neonates were initially fed on leaves of non-Bt maize and then were transferred to hairy fleabane or slender amaranth leaves at different time points. On hairy fleabane leaves, only 12% of larvae in L5 and L6 stages developed into pupae and adults, with similar duration of immature stage of those developed in maize leaves. In contrast, S. frugiperda larvae from L1 to L6 stages developed into pupae on slender amaranth leaves, but only those from the L2 stage onwards originated adults (9–65%). On maize, > 64% of neonates developed to adulthood. Surviving larvae fed on early instars on slender amaranth leaves had up to 10 d longer developmental time of neonate-to-pupa and neonate-to-adult periods compared to those developed on maize. Pupal weights of surviving insects on slender amaranth leaves were also lower (104.9–67.4 mg/pupa) than on maize (207.4 mg/pupa). In summary, our findings indicate that the hairy fleabane is not a suitable host for S. frugiperda, whereas slender amaranth is a viable food source for the survival end development of this species, mainly for advanced instars. [ABSTRACT FROM AUTHOR]

Three‐lobe morning glory (Ipomoea triloba L.) is an annual weed, which presents vigorous growth, long cycle, and tolerance to glyphosate. Thus, knowledge of aspects related to germination and behavior in the seed bank of this species are essential for the adoption of appropriate management practices to reduce the population in agricultural fields. Therefore, the objective of this work was to characterize the requirements for three‐lobe morning glory germination, perform field emergence modeling using thermal and hydrothermal time models, and determine the longevity of the seed bank. Eight temperatures and 10 water potentials were tested in the laboratory to determine the base temperature and water potential for seed germination. For the modeling of the emergence, field experiments were conducted between the years 2014 and 2018 considering three sampling times (10/20, 11/10, and 12/01), which coincide with the sowing times of summer annual crops. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted in which factor A consisted of three burial depths and factor B consisted of five harvesting times. Base values for three‐lobe morning glory emergence are base, optimum, and maximum temperatures of 12.32, 29.82, and 43.31°C, respectively, and base water potential of −0.80 MPa. Both models are adequate to predict the emergence of three‐lobe morning glory in the three sampling times. The species has a persistent seed bank, in which the greater the depth of seed burial, the greater the longevity of the seed bank, and can remain viable for up to 16 months. [ABSTRACT FROM AUTHOR]

Weedy rice (Oryza sativa L.) is the most problematic weed in rice fields due to the few control management alternatives to control it, because of the genetic similarity with the crop. Different cropping systems (regarding soil preparation before sowing) have been used as options to control the persistence and emergence of the weed seedbank. Therefore, the objective of this study was to evaluate the longevity and vertical distribution of weedy rice seeds in the soil seedbank after 22 years of different rice cropping systems. Data was analyzed as a two-way factorial, with cropping systems carried out for 22 years [no-tillage (NT), conventional tillage (CT), wet direct-seeded (WDS)] as one factor and sampling depth (0-2, 2-5, 5-10 and 10-20 cm) as the other factor. The number of whole and deteriorated seeds per m-2 were assessed, as well as the viability (%). No effect between the systems were detected up to 5 cm, however at 5-10 cm CT and WDS showed higher amount of seeds, and WDS at 10-20 cm. As the sampling depth increased, NT showed fewer amount of seeds, while less reduction of the soil seedbank was observed in WDS. CT and WDS spread viable seeds in the soil profile from 0 to 20 cm depth. After 22 years there are viable weedy rice seeds up to 10 cm of depth in the three cropping systems and there is no difference among them up to 5 cm of depth, demonstrating the serious problem of the seedbank for this species. [ABSTRACT FROM AUTHOR]

The objectives of this study were to evaluate the response to fertilization and different weed control periods in the accumulation of dry matter of cassava leaves, stems, roots, and fresh mass roots yield. Two experiments were carried out on commercial fields in Ibarama, and Santa Maria municipalities located at the Rio Grande do Sul State, South Brazil, during the 2018/2019 growing season. Five treatments, varying chemical fertilizer applications and herbicides were used to represent management practices commonly used by farmers in Southern Brazil. The Simanihot process-based model simulated cassava growth, development, and productivity under potential conditions. Results show that the recommended dose of fertilizers and liming combined with pre-emergent herbicide and three mechanical weed clear management showed a 72% increase in root productivity compared to the management used by the average yield of smallholder farmers. Therefore, it is possible to reach 80% of the potential productivity by keeping the cassava crop free from weed interference and applying fertilizers. The presence of weeds during the first 100 days after planting reduced about 50% of the plant dry matter production in Ibarama and Santa Maria. Interestingly, it also affects 79.2% of fresh roots productivity in Ibarama. [ABSTRACT FROM AUTHOR]

This study aimed to assess the phytosociology of weeds as a function of different crop management technology levels in cassava production. Field experiments were conducted in Santa Maria (29°41'03" S; 53°48'25" W) and Itaqui (lat. 29°07'31" S; long. 56°33'11" W), Rio Grande do Sul, Brazil. Treatments consisted of three technology levels: low (postemergence weeding without basal dressing); medium (weeding performed at 7 and 40 days after planting and fertilization with 6.25, 25, and 25 kgha21 of N, P, and K, respectively); and high (postemergence application of s-metolachlor; 1250 kg.ha-1 of lime and 12.5, 50, and 50 kg.ha-1 of N, P, and K, respectively). Weed frequency, density, relative abundance, and importance values were calculated for each location. Then, locations were compared using a dissimilarity matrix. Weed density and diversity decreased linearly as technology levels increased. The predominant weed species found in Itaqui and Santa Maria belong to the Poaceae family. Itaqui presented highest weed diversity among the locations. The genus Cyperus had the highest importance value index in Santa Maria. The use of S-metolachlor at the high technology level provided a lower frequency and lower diversity of weed species than did levels without chemical control in Itaqui and Santa Maria. [ABSTRACT FROM AUTHOR]

Efficient herbicide absorption and translocation, and satisfactory weed control can be affected by the site of herbicide application. However, during harvesting of crops of previous soybean sowing, the cutting process made by harvesters on the fleabane may generate a difficult management in pre-sowing of the crop by limiting the leaf area of the absorption of the herbicide. Experiments were conducted to evaluate the control efficiency and translocation potential of saflufenacil in fleabane plants with different leaf and stem conditions. Experiment I was arranged in a 2x10 factorial scheme, with factor A corresponding to leaf integrity, and factor B corresponding to different levels of injury and saflufenacil application. Weed control was evaluated at 7, 14, and 21 days after herbicide treatment (DAT), and dry matter was evaluated at 21 DAT. Experiment II consisted of applying saflufenacil to different fleabane structures, where the percentage of necrotic area was evaluated at 1, 3, 5, and 7 DAT. Fleabane control was higher than 75% in all treatments with saflufenacil application, with greater control in plants previously defoliated. Saflufenacil application on 10 and 20 cm hairy fleabane plants was also efficient in all treatments. Saflufenacil application in old stem showed a larger necrotic area, while application in the site of the cutting resulted in a lower necrotic area. The main pathway for translocation of saflufenacil is via xylem and the stem proved to be the absorption element of the herbicide when leaf area is limited. [ABSTRACT FROM AUTHOR]

The objectives of this research were to evaluate the interaction between herbicides mixed with saflufenacil for the control of barnyardgrass and to determine the effect on photosynthetic and chlorophyll fluorescence parameters. The experiment was conducted in a greenhouse in a 2x8 factorial scheme, whose factor A tested resistant and susceptible biotypes; and factor B the herbicides: saflufenacil (70 g a.i. ha-1), clomazone (180 g a.i. ha-1), imazapyr + imazapic (73.5 + 24.5 g a.i. ha-1), and cyhalofop (360 g a.i. ha-1), the mixtures of these herbicides with saflufenacil, and control without treatment. Weed control was assessed 7, 14, 21 and 28 days after herbicide application (DAA), as well as shoot dry matter at 28 DAA, photosynthetic parameters using infrared gas analyzer (IRGA), and emission of chlorophyll a fluorescence after 24 and 28 hours ofapplication of treatments, respectively, and interaction of herbicides. Combination of saflufenacil with the herbicides tested in general did not change the response of both barnyardgrass biotypes to the herbicides used. The resistant biotype showed a lower negative effect on chlorophyll fluorescence and photosynthesis parameters in the combination of herbicides with saflufenacil. The herbicide cyhalofop was effective for the control of ALS-susceptible and resistant barnyardgrass. [ABSTRACT FROM AUTHOR]

The plant safener dietholate can be used for seed treatments (ST) to improve the selectivity of clomazone in rice cultures, thus allowing the application of higher dosages of this herbicide. The objective of this research was to evaluate the interaction between seed fungicide-insecticide treatments with and the plant safener dietholate in irrigated rice. Three experiments were carried out, and the first of them was conducted in a laboratory, following a completely randomized experimental design with four replications. Different ST and treatment-to-sowing intervals were evaluated. The second and third experiments were performed in field conditions, in a completely randomized block design with four replications. In experiment two, seeds were treated with different fungicides, in association or not with dietholate; while in experiment three, the effect of the ST with fungicides and dietholate with clomazone application were assessed. The results evidenced that the association between carboxin + thiram + dietholate reduced seed germination, vigor, and the dry mass of shoot of rice plants. The longer it takes between ST and sowing, the more rice seed germination is negatively affected. The association between fungicides and dietholate may have been antagonistic, and thus interfered with the culture growth potential. [ABSTRACT FROM AUTHOR]