RESISTENCIA DE LA PAJA JOHNSON (Sorghum halepense (L.) Pers.) A LOS HERBICIDAS NICOSULFURON Y FORAMSULFURON+IODOSULFURON EN VENEZUELA

Resistance of Johnsongrass [Sorghum halepense (L.) Pers.] to herbicides nicosulfuron and foramsulfuron+iodosulfuron in Venezuela In order to evaluate the resistance of two accessions of Johnson grass [Sorghum halepense (L.) Pers.] to nicosulfuron and foramsulfuron + iodosulfuron and to determinate their chemical control with other herbicides we established two experiments types: one on dose response and another on chemical control. Two resistant (R) accessions (SH206P and SH209P) and one susceptible (S) (SH194A, as a control) were used. In the dose response experiment, the accessions R were treated with 0, 3.75, 7.5, 15; 30, 60, 120, and 240 g·ha -1 i.a. nicosulfuron; and 0, 4, 8, 16, 32, 64, 128, and 256 g·ha -1 i.a. foramsulfuron+iodosulfuron; and the accessions S with 0, 0.47, 0.94, 1.88, 3.75, 7.50, 15, and 30 g·ha -1 i.a. nicosulfuron; and 0, 0.47, 0.94, 1.88, 3.75, 7.50, 15, and 30 g·ha -1 i.a. foramsulfuron+iodosulfuron. In the chemical control experimet the treatments were nicosulfuron; foramsulfuron + iodosulfuron; piribenxozim, imazapyr+imazethapyr, bispyribac-sodium, penoxsulam, profoxydim, glyphosate, pendimethalin, S-metolachlor and isoxaflutole in doses of 30, 30+2, 50, 115.5+38.5, 40, 60, 160, 2040, 1920, 1440, and 52.25 g·ha -1 i.a., respectively. It was found that SH206P and SH209P have resistance to nicosulfuron and foramsulfuron + iodosulfuron, and their calculated resistance index were of 147 and 1096, and 386.59 and 292.78, respectively. The herbicides profoxydim, glyphosate, pendimethalin, S-metolachlor and isoxaflutole effectively controlled accessions R and S, when these were originated by sexual seeds. R accessions were not controlled with pyribenzoxym and imazapyr + imazethapyr. Bispyribac-sodium controlled SH206P and SH194A, while S. halepense showed to be tolerant to penoxsulam. Additional key words: Chemical control, ALS inhibitors, cross resistance