-Species of the orchidaceae family are grown for marketing flowers and among them the genus Cattleya stands out. However, due to its slow growth, the substrate is subjected to weed infestation. Therefore, this study aims to evaluate the selectivity and efficiency of herbicides in controlling Pilea microphylla in Cattleya orchid seedlings (Cattleya tenebrosa x Cattleya leopoldy). We used a completely randomized design with four replications. The evaluated herbicides were oxyfluorfen (0, 120, 240 and 480 g ha ) and metsulfuron-methyl (0, 1.2, 1.8 and 2.4 g ha -1). At post-emergence applying time, the Cattleya plants had three bulb sand were 10 cm tall, while P. microphylla, where 5 cm tall. Nicosulfuron, mesotrione and clethodim herbicides did not control P. microphylla, while oxyfluorfen and flumioxazin showed over 90% efficiency level sin controlling P. microphyllafrom 14 days after application (DAA). As to metsulfuron-methyl, it showed efficiency superior to 90% from the control dose of 1.8 g ha -1at 28 DAA. All herbicides were selective plants of Cattleya, however, only oxyfluorfen, flumioxazin and metsulfuronmethyl were effective in controlling P. microphylla.Keywords: weed, herbicide, floriculture, selectivity. ), flumioxazin (0, 12,5, 25 e 40 g ha -1 ), nicosulfuron (0, 20, 40 e 80 g ha -1 ), mesotrione (0, 96, 144 e 192 g ha -1 ), clethodim (0, 60, 84 e 108 g ha -1 ) e metsulfuron-methyl (0, 1,2, 1,8 RESUMO -Espécies da família

-Orchidaceae species are produced on a large scale for commercialization of its flowers. However, because of its slow development, the substrate is subject to weed infestation, such as brilhantina (Pilea microphylla). Thus, we aimed to evaluate the selectivity of herbicides to the orchid seedlings of genre Rhynchostylis ([Rhynchostylis gigantea Alba x Rhynchostylis gigantea] X Rhynchostylis gigantea Semi-Alba) and control of P. microphylla. A completely randomized design with four replicates per treatment was adopted. The herbicides studied were oxyfluorfen (0, 120, 240, and 480 g ha -1 a.i.), flumioxazin (0, 12.5, 25 and, 40 g ha -1 a.i.), nicosulfuron (0, 20, 40, and 80 g ha -1 a.i.), and mesotrione (0, 96, 144, and 192 g ha -1 a.i.), with a control without application for each molecule. At the time of spraying, the plants of orchid presented four leaves and were 5 cm high, while P. microphylla was 10 cm high. Nicosulfuron did not control P. microphylla, while oxyfluorfen and flumioxazin showed control levels exceeding 90% on 14 days after application (DAA). The mesotrione showed low ability to control the weed, reaching around 35% efficiency at 49 DAA. All herbicides were selective to the hybrid seedlings Rhynchostylis. The oxyfluorfen and flumioxazin molecules were efficient in controlling P. microphylla in the tested dose ranges. Keywords: Rhynchostylis spp.; brilhantina; herbicide; floriculture; selectivity Resumo -Espécies da família Orchidaceae são produzidas em larga escala para comercialização de suas flores. Entretanto, devido ao seu lento desenvolvimento, o substrato fica sujeito à infestação de plantas daninhas, como a brilhantina (Pilea microphylla). Assim, objetivou-se avaliar a seletividade de herbicidas à mudas de orquídeas do gênero Rhynchostylis ([Rhynchostylis gigantea Alba x Rhynchostylis gigantea] X Rhynchostylis gigantea Semi-Alba) e controle de P. microphylla. Adotou-se delineamento inteiramente casualizado, com quatro repetições por tratamento. Os herbicidas estudados foram: oxyfluorfen (0, 120, 240 e 480 g ha -1 i.a.), flumioxazin (0, 12,5, 25 e 40 g ha -1 i.a.), nicosulfuron (0, 20, 40 e 80 g ha -1 i.a.) e mesotrione (0, 96, 144 e 192 g ha -1 i.a.), com uma testemunha sem aplicação para cada molécula. Na ocasião da pulverização as plantas de orquídea apresentavam quatro folhas e 5 cm de altura, enquanto que a P. microphylla possuía 10 cm de altura. O nicosulfuron não controlou P. microphylla, enquanto o oxyfluorfen e o flumioxazin apresentaram eficiência de controle superior a 90% a partir dos 14 dias após a aplicação (DAA). A mesotrione demonstrou baixa capacidade de controle da infestante, atingindo em torno de 35% de eficiência aos 49 DAA. Todos os herbicidas foram seletivos às mudas do híbrido de Rhynchostylis.