Glyphosate-resistant (GR) goosegrass [Eleusine indica(L.) Gaertn.] was recently identified in Brazil, but its resistance mechanism was unknown. This study elucidated the resistance mechanism in this species and developed a molecular marker for rapid detection of this target-site resistance trait. The resistance factor for the resistant biotype was 4.4-fold compared with the glyphosate-susceptible (GS) in greenhouse dose–response experiments. This was accompanied by a similar (4-fold) difference in the levels of in vitro andin plantashikimate accumulation in these biotypes. However, there was no difference in uptake, translocation, or metabolism of glyphosate between the GS and GR biotypes. Moreover, both biotypes showed similar values for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) copy number and transcription. Sequencing of a 330-bp fragment of theEPSPSgene identified a single-nucleotide polymorphism that led to a Pro-106-Ser amino acid substitution in the enzyme from the GR biotype. This mutation imparted a 3.8-fold increase in the amount of glyphosate required to inhibit 50% of EPSPS activity, confirming the role of this amino acid substitution in resistance to glyphosate. A quantitative PCR–based genotyping assay was developed for the rapid detection of resistant plants containing this Pro-106-Ser mutation.

Wild poinsettia (Euphorbia heterophylla L.) is a troublesome broadleaf weed in grain production areas from South America. Herbicide resistance to multiple sites of action has been documented in this species, including protoporphyrinogen oxidase (PPO) inhibitors. We investigated the physiological and molecular bases for PPO resistance in a E. heterophylla population (R-PPO) from Southern Brazil. Whole-plant dose response experiments revealed a cross resistance profile to three different chemical groups of PPO inhibitors. Based on dose response parameters, R-PPO was resistant to lactofen (47.7-fold), saflufenacil (8.6-fold), and pyraflufen-ethyl (3.5-fold). Twenty-four h after lactofen treatment (120 g ha-1) in POST, R-PPO accumulated 27 times less protoporphyrin than the susceptible population (S-PPO). In addition, R-PPO generated 5 and 4.5 times less hydrogen peroxide and superoxide than S-PPO, respectively. The chloroplast PPO (PPO1) sequences were identical between the two populations, whereas 35 single nucleotide polymorphisms were found for the mitochondrial PPO (PPO2). Based on protein homology modeling, the R128L (homologous to R98L in common ragweed (Ambrosia artemisiifolia L.) was the only one located near the catalytic site, also in a conserved region of PPO2. The cytochrome P450 monooxygenase inhibitor malathion did not reverse resistance to lactofen in R-PPO, and both populations showed similar levels of PPO1 and PPO2 expression, suggesting that metabolic resistance and PPO overexpression are unlikely. This is the first report of a R128L mutation in PPO2 conferring cross resistance to PPO inhibitors in E. heterophylla.

Conyza species are important weeds in global agriculture, especially due to their capacity to evolve resistance to multiple herbicide mechanisms of action.We aimed to evaluate the frequency and distribution of resistance to glyphosate and chlorimuron-ethyl in Conyza spp. populations from Brazil. Seed samples were collected from grain production areas across nine Brazilian states over five consecutive years ( 2014to 2018). Prior to resistance monitoring trials, dose-response assays were conducted to determine a single dose of glyphosate or chlorimuron-ethyl to discriminate resistant and susceptible populations. Resistance monitoring based on plant responses to the application of discriminatory doses of glyphosate (960 g ha -1 ) or chlorimuron-ethyl (20 g ha -1 ). Populations were classified as resistant, moderately resistant, or susceptible to either herbicide. While glyphosate resistance was highly frequent (71.2%) in all the five years, chlorimuron-ethyl resistant populations occurred at 39.8% of the total. The frequency of multiple resistance to both herbicides (35.3%) was proportional to the occurrence of chlorimuron-ethyl resistance (39.6%). Resistance to glyphosate and to chlorimuron-ethyl were found across all states evaluated.

-The use of mixtures and rotation of herbicide modes of action are essential for herbicide resistance management. The purpose of this research was to evaluate different pre-and post-emergence herbicides to control goosegrass in soybean and corn. Four greenhouse experiments were conducted, one in preemergence and the three others in post-emergence. In pre-emergence, the number of emerged plants and the control percentage at 20, 35 and 50 days after application were evaluated. In post-emergence, the control percentage was evaluated at 14 and 28 days after application on plants with one tiller and four tillers. The use of residual herbicides to control glyphosate-resistant goosegrass is a very important tool for its effective management. The application stage is also crucial for post-emergence efficacy. Paraquat and [paraquat + diuron] are effective in controlling this species. The application of ACCase inhibiting herbicides alone seems to be more effective than their associations with glyphosate, especially in plants with four tillers. HPPD inhibiting herbicides have high synergism with atrazine and not with glyphosate. Keywords

Wild poinsettia (Euphorbia heterophylla L.) is an important weed species in southern Brazil, especially due to the evolution of multiple herbicide resistance (e.g., acetolactate synthase (ALS)- inhibitors, protoporphyrinogen oxidase inhibitors, and glyphosate). The mechanism of resistance to imazamox was investigated in two wild poinsettia populations (R1 and R2) from southern Brazil and compared to a known susceptible (S) population. Imazamox dose-response experiments revealed high levels of resistance: 45-fold and 224.5-fold based on dry biomass reduction, for R1 and R2, respectively. Extremely high concentrations of imazamox (20,000 µM) were not sufficient to provide 50% inhibition of ALS enzyme activity (I50) for R1 or R2. Hence, resistance levels were estimated to be greater than 123-fold for both populations based on in vitro ALS assays. The ALS gene from all R1 and R2 plants had a Trp574Leu mutation. A genotyping assay was developed to discriminate resistant and susceptible alleles based on the Trp574Leu mutation.

Herbicide resistance in Amaranthus genus occurs frequently around the word and has become a big problem in cotton producing areas. The objective of this work was to evaluate cross-and multiple-resistance of redroot pigweed (A. retroflexus) to herbicides used in preemergence in cotton fields in Brazil. Seven dose-response experiments were conducted with herbicides atrazine, prometryn, diuron, S-metolachlor, trifluralin, trifloxysulfuron-sodium and pyrithiobac-sodium, and the treatments consisted of application rates of 0, ¼, ½, 1, 2 and 4 times the recommended label rate. Eight A. retroflexus byotipes with suspect of resistance were sampled for experiments in three brazilian states of cotton producing. Resistance to prometryn was confirmed for one biotype in Goiás (GO), and one biotype from Mato Grosso (MT) showed cross-resistance to atrazine and prometryn. One byotipe from GO was identified with cross-resistance to trifloxysulfuron-sodium and pyrithiobac-sodium. One of the GO samples was identified with multiple resistance to prometryn and ALS inhibitors, another one to atrazine and ALS inhibitors, while MT byotipe was confirmed with multiple resistance to triazines and pyrithiobac. The herbicides S-metolachlor, diuron, and trifluralin were efficient for control of this species, therefore, they can be used as managment alternative in those regions.Keywords: redroot pigweed, Gossypium hirsutum L., triazines, sulfonylureas. RESUMO -A resistência a herbicidas em espécies do gêneroAmaranthus ocorre frequentemente no mundo e está se tornando um grande problema em regiões algodoeiras no Brasil. O objetivo deste trabalho foi verificar a resistência cruzada e múltipla de biótipos de caruru-gigante (A. retroflexus) aos herbicidas utilizados em pré-emergência na cultura do algodão no Brasil. Sete experimentos de doseresposta foram realizados em casa de vegetação com os herbicidas atrazine, prometryn, diuron, S-metolachlor, trifuralin, trifloxysulfuron-sodium e pyrithiobacsodium, sendo os tratamentos equivalentes a 0, ¼, ½, 1, 2 e 4 vezes a dose recomendada. Foram avaliados oito biótipos de A. retroflexus coletados em três Estados produtores de algodão do Brasil com suspeita de resistência a esses herbicidas. Confirmou-se a resistência em um biótipo de Goiás (GO) para prometryn, assim como um de Mato Grosso (MT), que apresentou resistência cruzada a atrazine e prometryn. Um biótipo do Estado do Mato Grosso do Sul (MS) e quatro de GO apresentaram resistência cruzada a trifloxysulfuron-sodium e pyrithiobac-sodium. Um biótipo de GO foi identificado com resistência múltipla a prometryn e inibidores Planta Daninha 2019; v37:e019179353 FRANCISCHINI, A. et al. Multiple-and cross-resistance of Amaranthus retroflexus to acetolactate synthase (ALS) and ... 2 da ALS, outro para atrazine e inibidores da ALS, enquanto para o bipótipo do MT foi confirmada resistência múltipla para triazinas e pirimiditio-benzoatos (pyrithiobac). Os herbicidas S-metolachlor, diuron e trifuralin foram eficientes no controle de todas as populações e, portan...

Currently, sourgrass is one of the most important weeds in grain production areas in Brazil. The objective of this work was to evaluate the efficiency of associated systems composed by mowing and chemical control against clumped sourgrass. In the first experiment, different mowing heights (0, 5, 10, 15 and 20 cm), coupled with complementary applications of glyphosate + clethodim, were evaluated on sourgrass control. The second experiment was composed by programs starting with fallow mowing at different times, 50 (early), 35 (intermediate) and 20 (late) days before soybean sowing. After mowing, treatments were followed by herbicide applications according to the need until soybean harvest. The shorter the mowing height associated with herbicide application, the better the control of sourgrass. The weed management programs (anticipated, intermediate and late) were efficient on sourgrass control during fallow and along soybean cycle. Weed management programs starting with mowing provided better or similar control compared to systems that employed chemical control only, indicating that mowing can replace one of the herbicide applications.

Controle de amarelinho (TecomaAbstract -The presence of yellow bells (Tecoma stans) in pastures can compromise the implantation and the development of forage, damaging animal production and hindering mechanized operations with trailing implements. The objective of this paper was to evaluate the yellow bells control after localized herbicides applications and the fitointoxication of pasture composed of Urochloa maxima (syn Panicum maximum). The treatments were triclopyr (4%) and triclopyr (3%) applied to the stump base (SB); picloram (2%) applied on stump after plants (SA); triclopyr + picloram (1% + 1%) and triclopyr + picloram (2% + 2%) SB; plus a check without herbicide application and a check where plants were mowed. All herbicides treatments resulted over 95% control 270 days after application and were more efficient than stump cut treatment, which showed capacity of regrowth. The herbicides promoted injures on pasture, however the symptoms were observed only in the area located around the T. stans plants.