Effect of a diquat-paraquat herbicide mixture and straw cover on wild oat (Avena fatua) seedling emergence

Abstract

Paraquat is an herbicide that inhibits germination and seedling growth of grasses, including wild oat (Avena fatua L.), a problematic weed in winter cereals. Outdoor pot experiments were conducted to determine the influence of paraquat on wild oat seedling emergence to evaluate the efficacy of this herbicide as a tool for an integrated management system. A diquat+paraquat liquid formulation (7.0% diquat dibromide and 5.0% paraquat dichloride) was sprayed at a rate of 1,000ml/10 a directly onto wild oat seeds placed on the soil surface, and the soil was not disturbed during the following year. Fewer viable wild oat seeds were recovered from the diquat+paraquat treatment relative to a glyphosate ammonium salt (41.0%, 500ml/10 a) treatment. A treatment of diquat+paraquat greater than 3,000ml/10 a markedly reduced wild oat seedling emergence if the seeds were incorporated into the soil soon after the application. However, when the wild oat seeds were covered with chopped straw, no suppression of emergence could be detected with diquat+paraquat application even at a rate of 4.6 times the recommended dose. Increasing the dilution water volume also decreased the effectiveness of emergence suppression. Our results suggest that diquat+paraquat spray following wheat harvest would not be effective for reducing wild oat germination and seedling emergence in the summer.