In cropping systems, the persistence of weed seed banks is a major challenge for sustainable weed management. This study aimed to evaluate the efficiency of pre-sowing and post-emergence herbicide management, combined with pre-harvest physical control, in reducing the ryegrass and wild radish seed bank over five seasons in a wheat-soybean succession. The experiment was conducted in a randomized complete block design with a split-plot arrangement. The seed bank evaluation periods (November 2021, July 2022, and November 2022) were allocated to the main plots, and four desiccation management strategies were allocated to the subplots: glyphosate (900 g ha-¹); glyphosate + clethodim (900 + 120 g ha-¹); glyphosate + saflufenacil (900 + 35 g ha-¹); glyphosate + clethodim + saflufenacil (900 + 120 + 35 g ha-¹). For the latter treatment, the remaining plants were manually uprooted prior to harvest. The chemical control alone, regardless of herbicide combinations, was ineffective in reducing the ryegrass and wild radish seed bank after five years of cultivation. In contrast, the integration of herbicide applications and manual weed removal was the most effective strategy, resulting in improved weed control and higher wheat grain yield. Increasing weed infestation over time in areas under exclusive chemical desiccation management compromised the wheat grain production, rendering harvest unfeasible.

Background: Amaranthus spp., known as pigweeds, are aggressive weeds, which are highly competitive with soybean crops. Reports of biotypes resistant to the main mechanisms of action (EPSPs and ALS inhibitors) used for management make it essential to integrate new chemical control strategies. Objective: Assess the efficiency of dicamba and glyphosate and their association with residual herbicides (saflufenacil or flumioxazin), followed by glufosinate alone or combined with metribuzin, in controlling pigweeds resistant to EPSPs and ALS inhibitors, and the effect of phytotoxicity on the final yield of Xtend (TM) soybean. Methods: Two experiments were conducted in the 2021/22 (year 1) and 2022/23 (year 2) growing seasons, using a randomized block design with 15 treatments and four replications. The desiccation treatments were applied 15 days before soybean sowing (DBS) and pre-emergens one (1) day after sowing (DAS), as well as after crop emergence (V3/V4). Phytotoxicity, pigweed control, and final soybean yield were assessed. Results: Initial phytotoxicity, observed mainly via the application of associated pre-emergent herbicides, does not significantly damage the crop. Pigweed control was efficient when dicamba was associated with glyphosate, with sequential application of residual herbicides, especially flumioxazin, as well as glufosinate or glufosinate and metribuzin, in addition to the post-emergent application of fomesafen associated with glyphosate. Conclusions: Pigweeds resistant to EPSPs and ALS-inhibiting herbicides can be effectively controlled under management programs with sequential application of pre-and post-emergent herbicides in soybean, respecting application intervals.

Beardgrass (Schizachyrium microstachyum) is a resilient weed with high dispersal capacity, infesting agricultural areas in Rio Grande do Sul state, Brazil. This study aimed to assess the impact of sowing depth and straw cover on the germination and emergence of beardgrass seeds. The experiments were conducted in a greenhouse at the Federal University of Pelotas (UFPel) in the winter and summer. Different amounts of soybean and oat straw were tested in pots containing 50 seeds, observing seedling emergence and growth. Oat straw was more effective in reducing beardgrass emergence compared to soybean straw, and straw levels of 3.7 Mg ha-1 of oats or 6.5 Mg ha-1 of soybean had a similar effect on reducing beardgrass emergence. Emergence was negatively affected at depths of 4 and 8 cm. Adding of soybean or oat straw to the soil helped reduce emergence. Sowing depths greater than 2 cm significantly reduced emergence regardless of the presence or type of straw used, with no germination observed at 8 cm. Beardgrass emergence decreases with sowing depths over 2 cm, absent at 8 cm. Oat straw is more effective than soybean straw, though higher soybean rates can match its effect. Both straw types reduce emergence.

Background: Hairy beggarticks (Bidens pilosa L.) is a highly adaptable weed species that thrives in diverse environmental conditions. Understanding the environmental factors that influence its germination is essential for developing predictive emergence models and supporting integrated management strategies. Objective: The present study aimed to estimate the cardinal temperatures and water potentials for B. pilosa germination, assess seed bank longevity, and develop a field-based emergence model. Methods: Laboratory experiments were conducted to determine base temperature and water potential thresholds for seed germination. Eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 degrees C) and 10 water potentials (0,-0.05,-0.1,-0.2,-0.4,-0.6,-0.9,-1.2,-1.5, and-2.0 MPa) were tested. Field experiments were conducted from 2014 to 2018, with seedling emergence monitored under three sowing conditions. To assess seed bank longevity and persistence, a factorial experiment was set up using three burial depths (0, 3, and 6 cm) and five seed retrieval times (0, 1, 4, 10, and 16 months). Results: The base, optimal, and maximum temperatures for seedling emergence were 10.4, 24.7, and 41.9 degrees C, respectively. The base water potential was-0.85 MPa. Thermal and hydrothermal models were adequate to predict the emergence of hairy beggarticks at different soybean sowing dates. The species forms transient seed bank; however, the greater burial depth was associated with increased seed longevity (16 months) in the soil. Conclusions: The models are able to predict emergence under the evaluated conditions, and deeper seed burial was associated with longer seed bank longevity.

ABSTRACT: We evaluated the host suitability of the weeds associated with rice crops regarding Meloidogyne ottersoni and M. graminicola. Both plant-parasitic nematodes can develop in Oryza sativa, but Cyperus ferax plants were resistant to M. ottersoni. Plants of Cyperus iria, Cyperus difformis, Echinochloa crus-galli and Echinochloa colonum were susceptible to M. ottersoni, but resistant to M. graminicola. Besides this, Aeschynomene denticulata and Leersia hexandra were immune to M. graminicola and susceptible (1st assessment) and resistant (2nd assessment) regarding M. ottersoni. The results shed light on the role of hosts of M. ottersoni and M. graminicola, demonstrating that weed management should be included in strategies to control root-knot nematode diseases.

Abstract To develop models capable of predicting the emergence of hairy beggarticks and assist integrated management, it is fundamental to have knowledge of the environmental factors that influence the germination of the species. The objective of this study was to estimate temperature and water potential cardinals for hairy beggarticks germination, the longevity of its seed bank, and to develop a model of its emergence in the field. Experiments were carried out in the laboratory to determine the temperature and water potential base for seed germination. Eight different temperatures (10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, and 45.0°C), and 10 different water potentials (0, -0.05, -0.1, -0.2, -0.4, -0.6, -0.9, -1.2, -1.5, and − 2.0 MPa) were tested. The field experiments were conducted between 2014 and 2019 using three monitoring seedling emergences. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted with three burial depths (0, 3, and 6 cm) and five seed retrieval moments (0, 1, 4, 10, and 16 months). Base, optimal, and maximum temperatures for hairy beggarticks germination are 10.4°C, 24.7°C, and 41.8°C, respectively. The base water potential for the emergence of hairy beggarticks is -0.85 MPa. The thermal and hydrothermal time models are adequate to predict the emergence of hairy beggarticks in different soybean sowing dates. The species has a transient seed bank, however, the greater the seed burial depth, the greater the longevity of the soil seed bank.

Theoretical Reference: Identifying, tracking, and analyzing weed infestation levels in rice crops are essential for developing more effective control strategies, ultimately enhancing efficiency, reducing costs, and minimizing environmental impact. This study focuses on the geographic distribution and abundance of species within the Pycreus genus (family Cyperaceae) in rice fields in Rio Grande do Sul (RS), Brazil. Method: During the 2005/06 growing season, collections and abundance assessments of Pycreus species were conducted across three irrigated rice fields located in three municipalities within five major rice production regions of RS. Plants were collected during vegetative or reproductive stages, dried, and identified using specialized literature. Specimens were then deposited as vouchers in the PEL Herbarium at the Department of Botany, Federal University of Pelotas. Results and Conclusion: The study revealed the presence of Pycreus species in rice fields across RS, with P. polystachyos (Rottb.) P. Beauv. being the most abundant and frequently observed species. P. macrostachyos (Lam.) J. Raynal and P. lanceolatus (Poir.) C.B. Clarke were also identified, though less commonly. The highest abundance of Pycreus species was recorded in the coastal physiographic region, particularly within the Internal Coastal Plain of Lagoa dos Patos and southern rice production areas. Implications of Research: These findings emphasize the need for targeted weed management strategies in rice cultivation, particularly in regions where Pycreus species are most prevalent, to enhance crop productivity and sustainability. Originality/Value: This study provides valuable insights into the distribution and abundance of Pycreus species in RS rice fields, contributing to the understanding of weed dynamics in rice production and offering a basis for the development of more effective control measures.

ABSTRACT: 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.

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(degrees)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.

Arrowleaf sida (Sida rhombifolia L.) is a weed that has a fibrous stem, aggressive root system and waxy leaves that can hinder herbicide absorption. Based on knowledge of the environmental requirements for germination of this species, it is possible to predict emergence to assist in integrated management. The aim of this investigation was to characterize the air temperature and soil water potential requirements for arrowleaf sida germination, to model the emergence in the field using thermal and hydrothermal time models and to evaluate the longevity of the arrowleaf sida seed bank. Laboratory experiments were conducted to determine the temperature and water potential for seed germination by testing eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 degrees C) and 10 water potentials (0, -0.05, -0.1, -0.2, -0.4, -0.6, -0.9, -1.2, -1.5, and -2.0 MPa). Field experiments were conducted between 2014 and 2018 to model the emergence using three sampling times (starting on 10/20, 11/10, and 12/01), during which soybean seeds were sown. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted, in which the first factor included three burial depths (0, 3, and 6 cm) and the second factor included five collection times (0, 1, 4, 10, and 16 months) after seed burial. The base, optimal and maximum temperatures for arrowleaf sida germination were 10.0, 24.8, and 42.5 degrees C, respectively, and the base water potential was -1.20 MPa. It is possible to predict the emergence of arrowleaf sida in the field by hydrothermal and thermal time models under different environmental conditions. In addition, this species has a persistent seed bank, with 30% of seeds being viable after 16 months of burial.

ABSTRACT: 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.

Resistance to acetolactate synthase (ALS) inhibitors have increased recently in South Brazil where the major weeds of flooded rice (barnyardgrass and weedy rice) have evolved resistance to imazapyr+imazapic. The aim of this research was to evaluate a growth medium for tissue regeneration of tillers in barnyardgrass, as well as an agar-based bioassays test (also from tillers) to detect susceptible and resistant biotypes of weedy rice and barnyardgrass to imazapyr+imazapic in vitro. Greenhouse experiments were conducted to detect ALS-resistant (R) and susceptible (S) weedy rice and barnyardgrass biotypes, and bioassays were carried out to evaluate an adequate growth medium for barnyardgrass tiller regeneration and determine the concentration of herbicide to distinguish R and S plants. The culture medium that provided a suitable barnyardgrass growth was MS 50% with the addition of benzylamino-purine. The tissue regeneration in vitro with the growth medium containing imazapyr+imazapic allowed to discriminate between R and S barnyardgrass and weedy rice plants. The concentration required for satisfactory control of susceptible barnyardgrass and weedy rice explants grown in vitro was 0.9 μM and 1.3 μM of imazapyr+imazapic herbicide, respectively. The bioassay in vitro using tiller regeneration provides an opportunity to predict effectively imazapyr+imazapic resistance in barnyardgrass and weedy rice.

Background: Ryegrass is considered an important weed in crops in the state of Rio Grande do Sul, Brazil, for being resistant to the herbicide glyphosate. Objective: This study evaluates ryegrass control by applying different spray volumes and doses of clethodim alone or in combination with glyphosate and/or 2,4-D. Methods: Two field experiments were conducted in a 5 x 3 factorial design. In experiment I, factor A consisted of clethodim (96 g a.i. ha(-1)); clethodim (96 g a.i. ha(-1)) + glyphosate (1,080 g a.e. ha(-1)); clethodim (96 g a.i. ha(-1)) + 2,4-D ( 1,047 g a.e. ha(-1)); clethodim (96 g a.i. ha(-1)) + glyphosate (1,080 g a.e. ha(-1)) + 2,4-D (1,047 g a.e. ha(-1)); and control without treatment. Factor B consisted of three spray volumes (40, 80, and 120 L ha(-1)). In the second experiment, factor A consisted of the same herbicides and their associations aforementioned and factor B consisted of three increasing doses of the herbicide clethodim (96, 192 and 288 g a.i. ha(-1)). The herbicides were applied at the milky stage of ryegrass grains. Ryegrass control at 10, 20, and 30 days after application (DAA) of herbicides and dry matter were evaluated. Results: Spray volume reduction did not interfere with ryegrass control by clethodim and glyphosate or clethodim, glyphosate, and 2,4-D at 30 DAA, but it did interfere with the application of clethodim alone or associated only with 2,4-D. Doses above 192 g a.i. ha(-1) of clethodim alone or in mixture were efficient for ryegrass control. Conclusions: Greater clethodim doses and spray volume increased control of ryegrass at the milky grain stage and decreased the antagonism in the associations with 2,4-D.

ABSTRACT The drought stress tolerance may differ among species and cultivars. The drought effect on plants depends on the impact on the plant’s physiological, biochemical and molecular processes, as well as on its ability to adapt under these conditions. This study aimed to evaluate the physiological and biochemical responses, and determine the expression of the genes OsAPX2, OsHSP24.15, OsHSP71.10 and OsHSP85.88 under drought conditions in rice, weedy rice and barnyardgrass. A greenhouse experiment was performed in a complete randomized design, with four replications and two factors: water conditions (well-watered and water deficit) and plant species [rice (Oryza sativa cv. Puitá), weedy rice (Oryza spp.) and barnyardgrass (Echinochloa spp.)]. Under drought conditions, the rice and weedy rice plants showed more cellular damage than the barnyardgrass, and the three species showed a reduced photosynthetic rate. C3 plants (rice and weedy rice) increased the damage to lipids and proteins at 5 days of drought. However, for C4 plants (barnyardgrass), the drought conditions did not affect the biochemical parameters. The expression of the OsHSP85.88 gene increased in the three plants exposed to water deficit.

Italian ryegrass (Lolium perenne spp. multiflorum Lam.) is a troublesome weed commonly found in winter cereals. Winter cover crops represent an alternative for weed suppression, reducing weed soil seed banks, and future infestations. The aim of this study was to evaluate the suppression of winter cover crops on reducing the soil seed bank and infestations of Italian ryegrass in fields managed under no-tillage system. Field experiment was carried out during three consecutive years, in a strip-plot design with four blocks, containing the winter cover crops. Wheat (Triticum aestivum), canola (Brassica napus), barley (Hordeum vulgare), common vetch (Vicia sativa), cereal rye (Secale cereale), feral radish (Raphanus sativus), and black oat (Avena strigosa) were sown in each strip (block) under no-tillage system and compared with weedy fallow. Seed bank was quantified at 0.0- to 0.05- and 0.05- to 0.10-m depths, whereas Italian ryegrass infestations were measured with a sample frame of 0.0625 m(2). Greater suppression and lower soil seed bank were reported in plots managed with cereal rye, common vetch, black oat, and feral radish, reducing up to 80% in the first year, and up to 96% after 3 yr of continuous management in comparison to weedy fallow. Italian ryegrass infestations increased four- to six-fold when managed with canola. High suppressor potential of Italian ryegrass occurred for cover crops with biomass dry accumulation greater than 8.7 tons ha(-1), especially to plants with a height upper to 1 m, plant characteristics essential to reduce strongly Italian ryegrass infestations and ensure weed-free fields throughout the time.

Weedy rice ( Oryza sp.) is one of the most troublesome global weeds in cultivated rice. Its troublesome status is associated with characteristics such as seed shattering and dormancy, allowing for long‐term reinfestation and persistence in rice fields. However, the role of rising carbon dioxide levels (CO 2 ) and other climate variables on these characteristics has not, to date, been assessed. The current research objectives were to evaluate two aspects related to climatic change, increased CO 2 concentration (400 ± 50 μmol mol −1 and 700 ± 50 μmol mol −1 ) and water management (continuous and alternate‐wetting drying), to assess plant development, seed shattering and seedbank longevity of weedy rice. Our results indicated that elevated CO 2 (700 ± 50 μmol mol −1 ) increased weedy rice growth and biomass, seed shattering and lengthened viability within the seedbank. Water management did not affect weedy rice growth, seed shattering and seed dormancy. These results suggest that in areas where weedy rice is dominant, its seed bank persistence and potential competition may be exacerbated with rising CO 2 levels, with negative consequences for rice production.

Introduction: A. hybridus interference in soybeans varies with population size and may be quantified by mathematical models that allow establishing the threshold levels. Objective: Determine the interference of A. hybridus escaped from an herbicide program and with multiple resistance to EPSPs and ALS-inhibiting herbicides on soybean yield and its economic threshold (ET). Methods: Two experiments were conducted in a randomized block design. The treatments consisted of populations of A. hybridus ranging from 0 to 41 plants m(-2) (2018/19) and 0 to 32 plants m(-2) (2019/20). The yield components and yield plant(-1) of soybean were evaluated. The rectangular hyperbola model was fitted to the soybean yield loss. ET was calculated according to yield potential, price paid for grains, control cost and weed control efficiency Results: The increase in populations of A. hybridus has decreased in the number of pods and grains(-1) of soybean in both periods. The parameter i was 4.47 and 8.32%, and the ET ranged from 0.16 to 1.21 plants m(-2) in 2018/19 and from 0.09 to 0.65 plants m(-2) in 2019/20. Conclusions: One A. hybridus m(-2) may reduce 6.4% in the grain yield of soybean. ET occurs within the range of 0.09 to 1.21 plants m(-2).

Conyza spp. é uma espécie de difícil controle, principalmente quando se encontram com maior estatura e em estádios mais avançados de desenvolvimento. O estudo objetivou avaliar a eficiência de controle de 2,4-D colina e da mistura formulada de 2,4-D colina e glifosato em Conyza spp. com diferentes estaturas e estádios de desenvolvimento. Os fatores avaliados foram três estaturas de Conyza spp. (1-2; 10-12 e 25-30 cm); dois herbicidas [2,4-D colina (EC) e 2,4-D colina + glifosato (ED)]; e doses destes herbicidas correspondentes a 0x, 1/2x, 1x, 2x e 4x a dose recomendada. O herbicida ED proporcionou melhor controle comparativamente ao EC em todas as doses e estaturas avaliadas. O controle de Conyza spp. deve ser realizado em estágios iniciais de desenvolvimento, pois ambos os herbicidas nas doses iguais ou superiores as doses de registro são eficazes para o controle, o que não ocorre em estatura maiores que 10 cm ou estágio de 19 folhas.

(1) Background: Eragrostis plana Ness is a invasive C4 perennial grass in South America and very adaptable to environmental stresses. Our hypothesis is that there is a transgenerational cross-talk between environmental stresses and weed response to herbicides. This study’s objectives were to: (1) evaluate if E. plana primed by drought stress (DRY), a sub-lethal dose of quizalofop-p-ethyl (QPE), or a combination of both drought and herbicide stresses (DRY × QPE), produce a progeny with decreased sensitivity to quizalofop and (2) investigate the potential mechanisms involved in this adaptation; (2) Methods: A population of E. plana was isolatedly submitted to treatments for drought, quizalofop or drought plus quizalofop for two generations. The progenies were analyzed for sensitivity to the herbicide quizalofop and performed biochemical, chromatographic and molecular analyses.; (3) Results: In the G2 generation, the quizalofop-treated CHK population had reduced stomatal conductance and increased hydrogen peroxide and lipid peroxidation. On the other hand, there was no change in stomatal conductance, hydrogen peroxide level, and lipid peroxidation in the quizalofop-treated DRY population. In addition, this population had increased antioxidant enzyme activity and upregulated CYP72A31 and CYP81A12 expression, which was accompanied by reduced quizalofop-p-ethyl concentrations; (4) Conclusions: E. plana demonstrated a capacity for transgenerational adaptation to abiotic stresses, with the population exposed to drought stress (DRY) becoming less sensitive to quizalofop-p-ethyl treatment.