Among the species of the genus Cyperus occurring in paddy rice, C. esculentus, C. difformis and C. iria are the most important, and the latter two are reported as resistant to herbicides in Rio Grande do Sul (RS). The aim of this work was to characterize and mapping the occurrence of resistant plants of the genus Cyperus in areas of paddy rice in RS State, and to analyze the agronomic factors that interfere in the resistance selection. Seeds from individual plants were harvested in the 2014/15 crop, characterized as control failures by the application of acetolactate synthase inhibitors (ALS), totaling 43 samples. At the time of collection, the grower was inquired on aspects related to the management of weeds in the crop. Seeds were germinated in BOD and when seedlings were in two leaves stage they were transplanted into 0.3 L pots containing substrate. When the plants had 4-6 leaves, imazapyr + imazapic was spray at the registration rate. Thirty days after application, control of the tested biotypes was evaluated, converting the data to binary scale, where zero (0) and one (1) correspond to susceptibility and resistance, respectively. The agronomic factors that denote the high selection pressure of resistant biotypes are the consecutive use of Clearfield® technology, the use of higher doses than the registration and the low crop rotation adoption. Although not mentioned as one of the main weeds, it is observed that almost half of the samples collected from plants of the genus Cyperus are resistant to the ALS inhibitors, distributed in almost all the growing regions.

-Horseweed (Conyza spp.) is considered as one of the major weeds occurring in the agricultural areas of South America, especially in Brazil. This species stands out from the other weeds due to characteristics such as large seed production, continued seed production, dispersion over long distances and resistance to 5-enolpyruvoylshikimate 3-phosphate (EPSP) and acetolactate synthase (ALS) inhibiting herbicides, features that increase their management. Therefore, this study aimed at determining the physiological quality and longevity of horseweed seeds over 12 months. The experiment was established under field conditions, using a randomized block design with four replications. Fifty horseweed seeds were distributed into 50 g of dry soil, placed in permeable nylon mesh bags (10 x 10 cm), which were buried at 1, 2, 4 and 8 cm of depth. Each month, for 12 months, samples were collected and washed with water, and the remaining seeds were submitted to germination test. The percentage (%) of remaining seeds, germination, abnormal seedlings, dead seeds, dormancy and viability were evaluated. It was found that the horseweed seed bank was reduced by 59 % over 12 months. Moreover, horseweed seeds develop a secondary dormancy, regardless of the burial depth. In addition, an increased burial depth increases longevity and physiological seed quality.Keywords: Conyza spp., survival, dormancy, germination, viability. RESUMO -

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use for selective post-emergence control of glyphosate-resistant Conyza spp. in black oats. Adv Weed Sci. 2021:e20210026.