RESISTANCE TO CHLOROTOLURON OF A SLENDER FOXTAIL (ALOPECURUS-MYOSUROIDES) BIOTYPE

The effect of chlorotoluron on different slender foxtail populations t hat survived normal agricultural rates of this herbicide (2.5 to 3.5 k g ai ha-1) was investigated under controlled laboratory conditions. Am ong five populations tested, two had tolerance for the herbicide. The ED50 values for these biotypes ranged from 0.33 to 2.43 kg ha-1. Assay s with radiolabeled C-14-chlorotoluron indicated similar absorption an d translocation of the herbicide between susceptible and resistant bio types. Chlorophyll fluorescence and Hill reaction analysis seem to sup port the view that the mechanism of resistance of one biotype to the h erbicide is due to degradation/detoxification rather than to modificat ion of the target site, although compartmentation processes cannot be ruled out. This resistant biotype had high tolerance to other photosyn thetic inhibiting phenylureas, including linuron, chlorbromuron, diuro n, monolinuron, and neburon.