Abstract Background Amaranthus hybridus, a common agricultural weed in Brazil, has been associated with complications in the management of major crops. Recently, A. hybridus biotypes with suspected resistance to the herbicide glyphosate have been observed in the state of Paraná. Objective To characterize glyphosate-resistant Amaranthus hybridus biotypes. Methods Three independent experiments were conducted to evaluate four biotypes of A. hybridus. Twelve doses of glyphosate were applied, including 64D, 32D, 16D, 8D, 4D, 2D, D, 1/2D, 1/4D, 1/8D, 1/16D, and a control with no herbicide. The dose D of glyphosate applied was 1080 g ha-1 ae. Four replicates for each treatment and a randomized block design were used. At 28 (DAA), the control (%) and residual dry mass of each plot were analyzed. Results The biotypes with suspected resistance (R1, R2, and R3) had a GR50 in the range of 3019.13 to 3316.45 g ha-1 ae and LD50 in the range of 4081.52 to 4310.29 g ha-1 ae whereas the susceptible biotype had a GR50 of 227.63 g ha-1 ae and LD50 of 196.59 g ha-1 ae. Conclusions Biotypes R1, R2, and R3 are resistant to the herbicide glyphosate.

Abstract: Background: Amaranthus hybridus L. (Amaranthaceae) is an annual, dicotyledonous species that is considered one of the main weed infesting agricultural production systems. Some weeds species are considered host plants to insect pests, serving as “green bridges” for subsequent attacks on the main crop during the season, which can cause significant losses. Recording the occurrence of insects that can reach pest status is important for the deployment of mitigation measures against possible damage and economic losses to crops. The presence of Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae) has not been previously registered in association with A. hybridus plants. Objective: Thus, the present study is the first report to describe the occurrence of S. eridania on A. hybridus in the municipality of Piracicaba, São Paulo, Brazil. Methods: Images of the larvae while feeding on A. hybrids were obtained using an Olympus® E-410 digital camera. The pictures were then sent to the Laboratory of Ecotoxicology and IPM (LEMIP) of the Department of Entomology of Lavras Federal University (UFLA) for species identification. Results: We observed S. eridania larvae larger than 7 cm feeding on the inflorescences and leaves of A. hybridus . Conclusions: This note reports the first occurrence of S. eridania larvae feeding on A. hybridus in the city of Piracicaba, SP, Brazil.

Abstract 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 (2014 to 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.

O "banco" de sementes é um reservatório de sementes de plantas viáveis presentes na camada superficial de solo, que determina a composição de plantas daninhas emergidas na área; no entanto, a composição qualitativa e quantitativa do banco de sementes é determinada principalmente pelas práticas culturais empregadas na área. Sendo assim, foi avaliado o "banco" de sementes de plantas daninhas para determinar as possíveis influências dos diferentes sistemas de manejo utilizados na cultura dos citros. Os tratamentos consistiram da aplicação dos herbicidas diuron (2,0 kg ha-1), em pré-emergência, e glyphosate (1,08 kg ha-1), em pós-emergência, na linha de plantio, associados a cinco práticas de manejo na entrelinha da cultura: gradagem, roçada, dose reduzida de glyphosate, guandu (Cajanus cajan) e lab-lab (Dolichus lablab). Retiraram-se amostras de solo das entrelinhas e linhas de citros, nas profundidades de 0-10 cm e 10-20 cm, em épocas chuvosa e seca. As amostras foram colocadas em bandejas e levadas à casa-de-vegetação, para que as sementes presentes germinassem. Avaliou-se a emergência das plântulas aos 15, 30, 60 e 90 dias após implantação, por contagem e identificação de espécies. A utilização de grade e roçadeira proporcionaram maiores percentagens de número de plantas, enquanto que as leguminosas suprimiram a germinação das plantas daninhas.

The weed seed bank is a viable soil seed reservoir present in the top soil profile, which determines the emerged weed species composition in the area, however, the qualitative and quantitative composition of the weed soil seed bank is determined mainly by the cultural practices to which the area is submitted. Therefore the influence of different soil management systems used in a citrus orchard was evaluated in relation to the weed seed bank composition. The treatments consisted of pre-emergence application of diuron (2.0 kg ha-1) and post-emergence of glyphosate (1.08 kg ha-1) on the citrus rows associated with five weed inter-row management practices: disking, mowing, reduced rate of glyphosate, green manure (Cajanus cajan and Dolichus lablab). Soil samples were collected from the row and inter-row at depths of 0-10 cm and 10-20 cm, during the dry and wet seasons of the year. The samples were placed in trays under greenhouse conditions in order to count weed emergence four times. The inter-row mechanical treatments of disking and mowing caused higher weed population, while the legume green manure reduced the weed seed population significantly in the 0-10 cm layer.

Com o objetivo de estudar períodos de interferência entre plantas daninhas e a cultura da cana-de-açúcar, foi instalado um experimento no município paulista de Pradópolis, numa área pertencente à usina São Martinho, onde a cana-deaçúcar foi plantada no mês de abril de 1995 e colhida quinze meses depois. As condições climáticas no estado de São Paulo após o plantio deste experimento (época normal de plantio da cana-de-açúcar no estado de São Paulo) são caracterizadas por deficiência hídrica e temperaturas amenas, sendo que o períodos chuvoso iniciou-se apenas quatro meses após o plantio. O resultados obtidos no experimento permitiram concluir que a cana-de-açúcar suportou um pequeno período de convivência inicial, de zero aos 41 dias após o plantio (DAP), sem sofrer interferência significativa de diminuição da produção. No entanto, o controle da tiririca por um período curto (dos aos 22 dias após o plantio da cana-de-açúcar foi suficiente para assegurar a produção.

The objective of this research was to study interference periods between weeds and sugarcane culture in a experimental area located in Pradópolis, São Paulo State, Brazil. In these experiment, sugarcane was planted in May of 1995, and harvested 15 months later. The climatic conditions in São Paulo State during the months that follow sugarcane planting in the experiment (normal time when growers plant sugarcane), are characterized by negative balance of rain and evapotranspiration and mild temperatures, and the rainy season starting only four months after planting time. According to the results, it was concluded that, in the experiment where purple nutsedge (Cyperus rotundus) was the major infesting weed, sugarcane tolerated only 41 days, after planting, without interference by the weed, due to probably a greater competitive ability and allelopathic effect that have been attributed to this weed during the earlier stages of sugarcane development, interference starts right after initial sugarcane sprouting. On the other hand, purple nutsedge is very sensible to crop canopy shading, and low temperature, so the competition ended at only 22 days after planting (DAP).

Populações de capim-marmelada (Brachiaria plantaginea) infestantes da cultura da soja (Glycine max (L.) Merrill) no município de Mangueirinha, PR, controlada, ano após ano, com herbicidas inibidores da ACCase, apresentaram falhas de controle quando esses produtos foram aplicados na safra 95/96. Experimentos de doseresposta foram conduzidos em condições de casa de vegetação do Departamento de Horticultura da Escola Superior de Agricultura "Luiz de Queiroz", Piracicaba, SP, e da Embrapa Soja, Londrina, PR, com o objetivo de confirmar essa resistência, bem como avaliar o nível de resistência e resistência cruzada a herbicidas pertencentes aos grupos químicos das ciclohexanidionas e ariloxifenoxi-propionato. Plantas de capimmarmelada supostamente resistentes foram tratadas com diversos herbicidas e doses e comparadas com plantas de uma população suscetível dessa infestante. Os tratamentos foram estabelecidos considerando-se as doses recomendadas dos produtos, metade delas e, duas, quatro e oito vezes superiores a recomendada. Os produtos e as doses aplicadas foram haloxyfopmethyl nas doses 0; 60; 120; 240; 480 e 960 g i.a./ha, mais o espalhante adesivo Joint 0,5% v/v, fluazifop-p-butil nas doses 0; 94; 188; 376; 752 e 1504 g i.a./ha, mais o espalhante adesivo Agral 0,2% v/v, sethoxydim nas doses 0; 115; 230; 460; 920 e 1840 g. Os resultados de percentagem de controle foram submetidos à análise de regressão e, através dos modelos ajustados, foram obtidos os valores de GR50 (dose necessária para proporcionar 50% de controle de cada biótipo). As relações médias de GR50 e os diferenciais de controle nas doses recomendadas dos herbicidas (S-R) foram calculados. Os diferenciais de controle nas doses recomendadas (S-R) foram 97 e 11; 96 e 62; 99 e 86; 0,6 e 4; 20 e 17; 88 e 35 para os herbicidas haloxyfop-methyl, fluazifop-p-butil, sethoxydim, clethodim, propaquizafop e fenoxaprop-p-ethyl nos experimentos conduzidos em Piracicaba e Londrina, respectivamente. Conclui-se que o biótipo B-196 é resistente aos herbicidas inibidores da ACCase e apresenta diferentes níveis de resistência cruzada aos herbicidas estudados, exceto clethodim. Os herbicidas sethoxydim, fluazifop-p-butil, haloxyfop-methyl e fenoxaprop-ethyl são os produtos para os quais o biótipo apresentou maior grau de resistência quando comparado com clethodim e propaquizafop.

Alexandergrass population in Mangueirinha County, Paraná State, Brazil, was controled by ACCase inhibitor herbicides for more than ten years. However, no control was observed in soybean season 95/96. Dose-response experiments were caried out in greenhouses of Horticulture Department-ESALQ/USP and Embrapa Soja in order to study the level of resistance and cross resistance to aryloxiphenoxypropionic and cyclohexanodione herbicides. The supposedly resistant biotype (B- 196) and susceptible biotype were treated with ACCase inhibitors at rates corresponding to 0, 1/2, 1, 2, 4 and 8 fold the recommended rate. The herbicides and their recommended doses were haloxyfop-methyl (120 g/ha), fluazifop-p-butil (188 g/ha), sethoxydim (230 g/ha), clethodim (108 g/ha), propaquizafop (125 g/ha) and fenoxaprop-p-ethyl (82 g/ha). The adjuvants were added following the recommendation of each herbicide. It was estimated the GR50 values, R/S ratios and S-R (the difference between control percentage of both biotypes at recomendated rates). The results of resistance level among the biotypes and herbicides showed differences, with variable GR50 values for herbicides and biotypes. The S-R values were 97 and 11; 96 and 62; 99 and 86; 0.6 and 4; 20 and 17; 88 and 35 for the herbicides haloxyfop-methyl, fluazifop-p-butil, sethoxydim, clethodim, propaquizafop and fenoxaprop-ethyl in Piracicaba and Londrina, respectively. The Brachiaria plantaginea biotype B-196 is resistant to ACCase inhibitor herbicides and exhibited different levels of cross resistance to the herbicides, except clethodim. Sethoxydim, fluazifop-p-butil, haloxyfop-methyl and fenoxaprop-ethyl were the herbicides which the biotype showed high levels of resistance compared to clethodim and propaquizafop.

A resistência de plantas daninhas aos herbicidas ocorre em função de um processo evolutivo. O desenvolvimento de biótipos de plantas daninhas resistentes é imposto pela agricultura moderna, através da pressão de seleção causada pelo uso intensivo dos herbicidas. O conhecimento dos mecanismos e fatores que favorecem o aparecimento de biótipos de plantas daninhas resistentes é fundamental para que técnicas de manejo sejam utilizadas no sentido de evitar ou retardar o aparecimento de plantas resistentes em uma área. São poucos os relatos ou citações de literatura no Brasil. Sendo assim, este trabalho de revisão procura relatar os principais avanços e descobertas na área de plantas daninhas resistentes aos herbicidas.

Weed herbicide resistance has evolved from weed evolution. The modern agriculture is responsible for this evolution because of the intensive use of herbicides. The knowledge of mechanisms and factors that influence the weed herbicide resistance play an important role in the weed manegement techniques used to avoid or delay herbicide resistance appearence. There are not many report or scientific papers about herbi cide resistance in Brasil. Therefore, this literature review aims to provide information about the main advances and discoveries in the field of weed herbicide resistance.