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 Background Species of Amaranthus genus are common in agricultural areas of Brazil. Such weeds are problematic, and they bring complexity to the management mainly due to herbicide resistance. Thus, the monitoring and mapping of chlorimuron-resistant Amaranthus spp. is necessary to detect resistance in different locations of Brazil. Objective Elaborate discriminating dose of distinction between Amaranthus spp. populations that are susceptible and resistant to chlorimuron and monitor the resistance dispersal throughout five crops. Methods 33 pigweed populations from the main grain producing properties in Brazil by means of dose-response curves were evaluated. For the D dose, chlorimuron dose of 20 g ha-1 ai was considered. Once the discriminating dose was identified, a monitoring screening of the dispersal of resistance of Amaranthus spp. to chlorimuron was conducted with 226 samples between the 2016 and 2020 crops. Results The discriminating dose (“base line”) considered ideal to control susceptible plants was 20 g ha-1 of chlorimuron. Among 226 pigweed samples evaluated in the five years of monitoring, 74% of populations were considered susceptible (S), while those classified as resistant (R) and segregating (r) did not exceed 26.0%. Conclusions By comparing susceptible biotypes of Amaranthus spp. with international scientific literature standards and leaflet averages, it could be safely concluded that the discriminating dose of chlorimuron is 20 g ha-1. Resistance of Amaranthus spp. to chlorimuron in Brazil is present in the main soybean producing regions evaluated, with a frequency of 26% of the total samples evaluated.

Abstract Background Phytosociological surveys of weeds in agricultural regions, such as the coffee growing Cerrado Mineiro Denomination, are essential for understanding the predominant species in a cultivation area. Objective This study aimed to determine the predominant weed species in coffee crops in Cerrado Mineiro through phytosociological surveys during two periods of the year. Methods 26 coffee farms in 12 municipalities within the Cerrado Mineiro Denomination of Origin of were visited. The inventory square method was used for the phytosociological surveys. In each area, 40 m2 was evaluated and divided into two study periods (summer and winter). Calculations of the variables were performed using the following data: frequency, density, abundance, importance value index, similarity coefficient, rarefaction curve, Shannon index, and hierarchical grouping analysis using Jaccard’s similarity. Results In the summer (rainy period), 54 species from 16 families were found, with Poaceae, Asteraceae, and Amaranthaceae predominating. In winter (dry season), 56 species from 16 families were found, predominantly Asteraceae, Poaceae, and Brassicaceae. There was a predominance of 17 and 16 species, with similarity levels (Jaccard) of 45.58% and 40.78% for summer and winter, respectively. Conclusions The weed community in the Cerrado Mineiro coffee plantation is dominated by two main families, Poacaeae and Asteraceae, with Eleusine indica (summer) and Conyza spp. (winter) being the species with the highest importance values.