One of the most efficient methods of weed control in agriculture is the use of selective herbicides. However, repetitive use of the same herbicide or herbicides having the same mechanism of action, has led to the appearance of weed biotypes which have developed resistance. Thus, an experiment was carried out at Embrapa Soja, in Londrina, Paraná State, Brazil, in order to confirm whether or not there has been resistance of the weed E. heterophylla to the ALS inhibitor herbicides which had been sprayed for several years in a soybean field where the grower has observed failure of the weed control by the ALS inhibitor herbicides. The suspected resistant plants (E-298) from Cafelândia county, Paraná, Brazil, were treated with various doses of several herbicides, compared to a known susceptible biotype. The herbicides and its doses were cloransulan 0,0; 0,015; 0,03; 0,06; 0,12; 0,24 kg a.i./ha, plus Agral 0,2% v/v, imazetaphapyr 0,0; 0,05; 0,1; 0,2; 0,4 e 0,8 kg a.i./ha, imazaquin 0,0; 0,075; 0,15; 0,3; 0,6; 1,2 kg a.i./ha, plus Assist 0,3% v/v, sulfentrazone 0,0; 0,3; 0,6; 1,2; 2,4; 4,8 kg a.i./ha, plus Assist 0,3% v/v and lactofen 0,0; 0,082; 0,165; 0,33; 0,664; 1,329 kg a.i./ha.The results indicated different patterns of cross resistance to cloransulan, imazethapyr and imazaquin; and the GR50 ratios were 97.74; 11.90 and 10.86, respectively. The dose response curves of the resistant biotype presented lower values than the susceptible biotype in all the studied rates for the herbicides cloransulan, imazethapyr and imazaquin. On the other hand, there was no difference in the control between the resistant and susceptible biotypes when sulfentrazone and lactofen were sprayed. It was observed efficient control, mainly with the highest rates of both herbicides, proving that there is no multiple herbicide resistance of the wild poinsettia studied.
cross resistance; multiple resistance; weed; Euphorbia heterophylla