A field assay was carried out at the "Embrapa Soja", an experimental station in Londrina, Paraná, Brazil, to evaluate the adequate timing for sunflower sowing combined with 2.4-D, during the growing season of 1995/96. The treatments consisted of three rates of 2.4-D herbicide (0.0, 536 and 1,005 g a.e. ha-1) and seven periods of sunflower sowing: -1 day (sunflower sowing was conducted one day before herbicide application); 0 day (sunflower sowing and herbicide application were conducted at the same day) and sunflower sowing at one, four, seven, 10 and 13 days after herbicide application. The results showed that sunflower growth was reduced mainly when sowing occurred at a time close to the 2.4-D application. Reduced herbicide damage on sunflower plants was observed when a longer period was kept between sowing time and herbicide application. It was concluded that areas treated with 2.4-D at rates 536 and 1,005 g a.e. ha-1 can be used for sunflower cultivation provided at least a four day - period is kept between herbicide application and sunflower sowing.
soil persistence; residual herbicides
