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Abstract

14C-Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid), labelled in the carboxyl carbon, was applied to barley and other cereals, ryegrass, clover, and chickweed, and the loss of radioactivity was studied. Radioactivity was readily removed from the leaves by washing with water soon after application, but, generally, only 40 % or less of the applied dose was recoverable in this way after 3 days. the total level of radioactivity was reduced to approximately 5% of that applied to the plants 4 weeks after application in the case of clover and ryegrass, and 8 weeks after application to barley. Analysis of all field-grown cereals showed no detectable residue in grain or straw at the time of harvest, using a method capable of detecting 0.04 ppm.

Autoradiography of thin-layer co-chromatograms of the extracts showed that most of the radioactivity was present as unchanged benazolin.

There appears to be no simple relationship between the concentration of benazolin accumulating in the plant and herbicidal activity, as judged by parallel experiments on barley and ryegrass (resistant) and chickweed (susceptible species). It is concluded that the resistance cannot be related simply to an ability to exclude or metabolise 14C-benazolin.

Column percolation experiments showed that benazolin was readily removed from the soil by water.