Fleck, Nilson Gilberto, and Paulo Regis Ferreira da Silva. “Kinds of Weed Control in Sunflower Culture through Different Hoeings”. Pesquisa Agropecuaria Brasileira, vol. 26, no. 9, Sept. 1991, pp. 1523-9, doi:10.1590/S1678-3921.pab1991.v26.3494.