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.