-Determining the periods of weed competition with crops helps the producer to choose the most appropriate time to use weed control practices. This strategy allows for the reduction of the number of herbicide applications, reducing costs and the environmental impact of pesticides. The objectives were to determine the period before the interference (PBI) of crabgrass (Digitaria ciliaris) competing with flooded rice, the critical period of interference prevention (CPIP) of crabgrass with soybean and the effects of competition on the grains yield and their components. Experiments were conducted with the coexistence of BRS Querência rice cultivar with crabgrass, for periods of 0, 7, 14, 21, 28, 35, and 110 days after emergency (DAE) and Fundacep 53RR soybean cultivar, whose periods of coexistence and control of crabgrass were 0, 7, 14, 21, 28, 35, and 156 DAE. Rice can grow with crabgrass infestation until 18 DAE, while soybean should remain free from the presence of crabgrass in the period between 23 and 50 DAE. The grain yield and its components, in the crops studied, are affected when grown with crabgrass. BRS Querência, com milhã, por períodos iniciais crescentes de 0, 7, 14, 21, 28, 35
Keywords: Digitaria ciliaris, Oryza sativa, Glycine max, interference
RESUMO -A determinação dos períodos de competição das plantas daninhas com as culturas auxilia o produtor na escolha do momento mais adequado para utilizar medidas de manejo. Essa estratégia possibilita reduzir o número de aplicações de herbicidas, com consequente redução de custo e menor impacto dos agrotóxicos ao ambiente. Assim, os objetivos deste trabalho foram determinar o período anterior à interferência (PAI) de milhã (Digitaria ciliaris) na cultura do arroz irrigado, o período crítico de prevenção à interferência (PCPI) de milhã na cultura da soja e os efeitos da competição na produtividade de grãos e seus componentes. Para isso, foram conduzidos experimentos de convivência de arroz irrigado, cultivar