Euphorbia heterophylla is a weed species that invades extensive crop areas in subtropical regions of Brazil. This species was previously controlled by imazamox, but the continuous use of this herbicide has selected for resistant biotypes. Two biotypes of E. heterophylla from southern Brazil, one resistant (R) and one susceptible (S) to imazamox, were compared. The resistance of the R biotype was confirmed by dose-response assays since it required 1250.2 g ai ha−1 to reduce the fresh weight by 50% versus 7.4 g ai ha−1 for the S biotype. The acetolactate synthase (ALS) enzyme activity was studied using ALS-inhibiting herbicides from five different chemical families. The R biotype required the highest concentrations to reduce this enzyme activity by 50%. A Ser653Asn mutation was found in the ALS gene of the R biotype. The experiments carried out showed that imazamox absorption and metabolism were not involved in resistance. However, greater 14C-imazamox root exudation was found in the R biotype (~70% of the total absorbed imazamox). Target site mutation in the ALS gene is the principal mechanism that explains the imazamox resistance of the R biotype, but root exudation seems to also contribute to the resistance of this biotype.

RESUMO -A interferência causada pelas plantas daninhas pode reduzir em até 80% a produtividade de grãos do feijão quando não manejadas de forma correta. Portanto, a decisão sobre o momento de controlá-las é um dos principais aspectos do manejo integrado. Nesse sentido, objetivou-se com este trabalho determinar o período anterior à interferência das plantas daninhas (PAI) em cultivares de feijão com diferentes tipos de hábitos de crescimento. Adotou-se o delineamento experimental de blocos casualizados com quatro repetições. Os tratamentos experimentais foram constituídos de dez períodos de convivência da cultura com as plantas daninhas: 0-7, 0-14, 0-21, 0-28, 0-35, 0-42, 0-49, 0-56, 0-97 (colheita) dias após a emergência (DAE) e mais uma testemunha sem convívio com as plantas daninhas. O PAI foi determinado por meio de distintas abordagens: o nível arbitrário de 5% de perda na produtividade, o nível de tolerância (NT) e o de dano no rendimento econômico (PADRE). O PAI obtido foi diferente em todas as abordagens, e os feijoeiros de crescimento indeterminado tipo II apresentaram os menores tempos de convivência. : 0-7; 0-14; 0-21; 0-28; 0-35; 0-42; 0-49;0-56; 0-97 (harvesting) Palavras-chave: Phaseolus vulgaris, cultivares, competição. ABSTRACT -Beans grain productivity may be reduced by up to 80% and, therefore, knowing the proper time to control weeds becomes fundamental, his research was conducted in order to determine the period prior to interference (PPI) on bean cultivars of different types' plant growth through distinct approaches: arbitrary level of 5% productivity loss; tolerance level (TL), and the Weed Period Prior to Economic Loss (WEEPPEL). Experimental treatments were constituted of ten periods of coexistence, periods of the crop with the weeds

The evolution of herbicide resistance in weeds has emerged as one of the most serious threats to sustainable food production systems, which necessitates the evaluation of herbicides to determine their efficacy. The first herbicide resistance case in the Iberian Peninsula was reported about 50 years ago, wherein Panicum dichotomiflorum was found to be resistant (R) to atrazine in Spanish maize fields. Since then, herbicide resistance has evolved in 33 weed species, representing a total of 77 single-herbicide-resistance cases in this geographic area: 66 in Spain and 11 in Portugal. Changes in agricultural practices, namely the adoption of non-tillage systems and the increased use of herbicides, led to the selection of weed biotypes resistant to a wide range of herbicides. Nowadays the most important crops in Spain and Portugal (maize, winter cereals, rice, citrus, fruits, and olive orchards) are affected, with biotypes resistant to several mechanisms of action (MoAs), namely: ALS inhibitors (20 species), ACCase inhibitors (8 species), PS II inhibitors (18 species), and synthetic auxin herbicides (3 species). More recently, the fast increase in cases of resistance to the EPSPS-inhibiting herbicide glyphosate has been remarkable, with 11 species already having evolved resistance in the last 10 years in the Iberian Peninsula. The diversity of resistance mechanisms, both target-site and non-target-site, are responsible for the resistance to different MoAs, involving point mutations in the target site and enhanced rates of herbicide detoxification, respectively. More serious are the 13 cases reported with multiple-herbicide resistance, with three cases of resistance to three–four MoAs, and one case of resistance to five MoAs. Future research perspectives should further study the relationship between management strategies and the occurrence of TSR and NTSR resistance, to improve their design, develop monitoring and diagnostic tools for herbicide resistance, and deepen the study of NTSR resistance.

The levels of resistance to glyphosate of 13 barnyard grass (Echinochloa crus-galli) populations harvested across different agriculture areas in the Southern Iberian Peninsula were determined in greenhouse and laboratory experiments. Shikimate accumulation fast screening separated the populations regarding resistance to glyphosate: susceptible (S) E2, E3, E4, and E6 and resistant (R) E1, E5, E7, E8, E9, E10, E11, E12, and E13. However, resistance factor (GR50 E1–E13/GR50 E6) values separated these populations into three groups: (S) E2, E3, E4, and E6, (R) E1, E5, E7, E8, and E9, and very resistant (VR) E10, E11, E12, and E13. 14C-glyphosate assays performed on two S populations (E2 and E6) showed greater absorption and translocation than those found for R (E7 and E9) and VR (E10 and E12) populations. No previous population metabolized glyphosate to amino methyl phosphonic acid (AMPA) and glyoxylate, except for the E10 population that metabolized 51% to non-toxic products. The VR populations showed two times more 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity without herbicide than the rest, while the inhibition of the EPSPS activity by 50% (I50) required much higher glyphosate in R and VR populations than in S populations. These results indicated that different target-site and non-target-site resistance mechanisms were implicated in the resistance to glyphosate in E. crus-galli. Our results conclude that resistance is independent of climate, type of crop, and geographic region and that the level of glyphosate resistance was mainly due to the selection pressure made by the herbicide on the different populations of E. crus-galli studied.

RESUMO -Uma das áreas da matologia (herbologia em Portugal) que tem avançado nas pesquisas científicas em Portugal e no Brasil nas últimas três décadas é a de nível de prejuízo das infestantes às culturas agrícolas. Contudo, durante esse período ocorreu uma multiplicidade de traduções de termos técnicos para a língua portuguesa, que atualmente dificultam o intercâmbio de informações técnico-científicas. Os objetivos desta revisão de literatura foram: definir os cinco diferentes termos referentes aos níveis de prejuízos das infestantes utilizados em herbologia; consolidar no idioma português os acrônimos utilizados para esses termos; apresentar as designações que têm correspondência nas línguas francesa e inglesa; indicar as perguntas científicas a que o termo responde; e apresentar as formas de cálculo que podem ser utilizadas para cada nível de prejuízo definido. Os termos estudados nesta revisão foram: densidade crítica, nível prejudicial de ataque (NPA ou nível de dano econômico = NDE), nível econômico de ataque, nível de tolerância e nível de segurança de ataque. Os modelos de cálculo do NPA = NDE no caso de infestações contendo uma única espécie vegetal são deduzidos a partir dos modelos linear, hiperbólico, múltiplo linear e múltiplo não linear; e para as situações de infestações com mais de uma espécie vegetal, a partir da equação linear múltipla entre a densidade de plantas e o rendimento da cultura.Palavras-chave: equações, densidade crítica, nível prejudicial, nível de dano econômico, nível de tolerância, nível de segurança.ABSTRACT -Weed threshold levels of injury to agricultural crops is a branch of weed science that has presented advanced scientific research in Portugal and Brazil in the last three decades. However, during this period there has been a multitude of translations of technical terms from the English or French into Portuguese that have currently hindered the exchange of technical scientific information. The objectives of this literature review were to define the terms relating to five different levels of weed injury used in weed science; to consolidate the acronyms used for these terms in the Portuguese language, to provide the names that have correspondence in French and English, to indicate the scientific questions that the terms imply, and to present the forms of calculation that can be used for each level defined. The terms studied in this review were: critical density, economic injury level, economic threshold, level of tolerance, and level of security attack. The forms of calculation of economic threshold in the case of infestation with a single plant species are derived from linear, hyperbolic, multiple linear and multiple non-linear models; for cases of infestation involving more than one plant species, these forms are derived from multiple linear equation between weed density and crop yield.

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The aim of this study was to assess the composition of weed communities starting from a rainfed farming system (1997), to the early period of transformation in agricultural systems with the adoption of irrigation (2007). The assessments were made within a 10-year interval and the floristic surveys were conducted in the same georeferenced plots. In 1997, the surveys were mostly performed in winter cereals (wheat, oat, barley), while in 2007, considering the same georeferenced plots, there were winter cereals and also irrigated olive groves, parcels of fallow, pasture and pine forest. Weed flora was determined by means of relative frequency, abundance and weed infestation degree. The effect of time was also evaluated by applying the methodology of variance analysis on the values of Shannon-Wiener Index. Canonical Correspondence Analysis was used to complement this information only for 2007 to know how the flora was distributed by the different cultures. Our results revealed that in both cases weed flora was of high diversity (229 and 264 species in 1997 and 2007, respectively), with the most representative families being always the same, namely Asteraceae, Poaceae and Fabaceae. The number of weeds that could be of concern for the farmers revealed to be relatively low. Our study confirmed that despite of the intensification of the agricultural production system, biodiversity increased over time. In both years, Lolium rigidum was present at high densities.

Conyza spp. are broadleaf weeds that occur in many crops but are also common in non-crop systems such as roadsides and railways. Conyza have selected for glyphosate resistance along railway tracks in southern Spain due to the misuse of this herbicide and the high seed dispersal rate of these species. Twenty-three samples of the genus Conyza (11 Conyza canadensis and 12 Conyza bonariensis) were collected from the margins of railways in different routes of the Andalusia railway network running adjacent to nearby crop fields. The glyphosate resistance level of Conyza populations was evaluated through GR50 (herbicide rate causing 50% growth reduction) and resistance factor (RF) values in every population collected. The highest GR50 were 1851.2 g a.e. ha−1 (RF = 52.53) in C. canadensis (Malaga–Cordoba route) and 1972.4 g a.e. ha−1 (RF = 35.20) in C. bonariensis (Seville–Cordoba route), and the lowest were 46.9 g a.e. ha−1 (RF = 1.33) in C. canadensis (Seville–Cordoba route) and 23.2 g a.e. ha−1 (RF = 0.41) in C. bonariensis (Seville–Cordoba route). The results showed that, among all the C. canadensis populations collected, 18.2% were glyphosate-resistant (RF > 10), 45.5% showed a tendency to develop resistance (RF = 2.5–5), and 36.4% were susceptible (RF < 2.5). Of the 25% of C. bonariensis populations that had resistance to glyphosate, 16.7% had moderate resistance (RF = 5–10) and 58.3% were susceptible. This study found that there are already glyphosate-resistant Conyza spp. along the railway network in southern Spain. This could lead to possible seed exchange between the railway and adjacent places. Therefore, it is vital to consider the railway network when planning control measures against resistance.