This study documents the first case of triazine resistance in wild radish and the resistance mechanism involved. The high survival (57 to 97%) of the resistant (R) biotype progeny plants treated at a rate four times higher than the commonly recommended rate of simazine or atrazine clearly established that the R biotype plants were resistant to triazines. All the plants of the susceptible (S) biotype plants were killed when treated at half the commonly recommended rate of atrazine (0.5 kg/ha) or simazine (0.25 kg/ha). The dry weight of the S biotype was reduced by 89 to 96% at the commonly recommended rate of atrazine or simazine, while the dry weight of the R biotype plants was reduced by only 36 to 54% even when treated at a rate four times higher than the commonly recommended rate of atrazine or simazine. The growth-reduction–ratio values indicated that the R biotype progeny plants were 105 and 159 times more resistant to atrazine and simazine, respectively, than the S biotype plants. Leaf chlorophyll fluorescence yield was reduced by 97% in the S biotype 24 h after application of triazine compared with only 9% reduction in the R biotype, indicating that the resistance mechanism involved is target-site based. The R biotype was effectively controlled by herbicides of different modes of action.

In 1998, field populations of wild radish suspected of being resistant to chlorsulfuron were collected and screened for resistance to this herbicide using the Quick-Test technique. This test successfully identified chlorsulfuron-resistant populations of wild radish. Detailed dose–response experiments with the progeny of these populations confirmed their resistance and validated the use of the Quick-Test for a dicot species. Subsequently in 1999, a random survey was conducted employing this test to establish the current extent of chlorsulfuron resistance in wild radish populations. The survey covered more than 200 fields in the northern, central, and eastern wheatbelt regions of Western Australia. Wild radish plants were collected from wheat crops in 133 of these fields. The Quick-Test method was used to screen these plants with the acetolactate synthase (ALS)-inhibiting herbicide chlorsulfuron. Overall, 21% of randomly collected wild radish populations were found to be resistant to chlorsulfuron.