|Menendez, J - UNIV. OF CORDOBA, SPAIN|
|DE Prado, J - UNIV. OF CORDOBA, SPAIN|
|DE Prado, R - UNIV. OF CORDOBA, SPAIN|
Submitted to: International Symposium on Weed & Crop Resistance to Herbicides Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 5, 1996
Publication Date: N/A
Technical Abstract: Diclofop-methyl is a major herbicide used to control grass weeds in Spain. High selection pressure due to the continuous use of graminicides has resulted in the appearance of diclofop-methyl-resistant biotypes of Lolium rigidum in Lleida (Northeastern Spain) and Cordoba (Southeastern Spain). One resistant biotype (DCT) was found in a winter wheat field treated with chlorotoluron plus diclofop-methyl and another resistant biotype (DT) was found in a wheat field treated with diclofop-methyl alone. Both biotypes survived diclofop-methyl rates greater than those used by farmers (5 kg a.i. ha-1). A diclofop-susceptible biotype and both diclofop-resistant biotypes metabolized diclofop-methyl to diclofop acid and polar conjugates. However, the level of polar conjugates was approximately 4-fold greater in the DCT biotype compared to the DT or susceptible biotypes. In all Lolium rigidum biotypes, metabolism of diclofop-methyl was inhibited by the mixed- -function oxidase inhibitor 1-aminobenzotriazole. Diclofop acid concentrations that inhibited acetyl-CoA carboxylase activity by 50% (I50 values) were similar in all three biotypes. Although experiments to investigate diclofop absorption and translocation have not yet been conducted, the data suggest that resistance to diclofop-methyl in the DCT biotype is due to enhanced detoxification. The mechanism of resistance in the DT biotype has not been determined.