Selectivity of Benazolin in Wild Mustard and Rape Species

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Abstract
The selectivity of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was studied. On an ED50 basis wild mustard was 19 and 32 times more susceptible to foliar-applied benazolin than was turnip rape and rape, respectively. The addition of surfactant increased the toxicity of benazolin to the Brassica species. Benazolin was less selective when applied via roots. Selectivity was further studied on the bases of differential spray retention and foliar penetration. Rape retained less spray than did wild mustard and turnip rape. The inclusion of surfactants in formulations increased spray retention by rape. Less 14C-benazolin penetrated leaves of the rape species as compared to wild mustard. Surfactant enhanced penetration of 14C-benazolin into leaves of the three species. Leaf surface features which resulted in high spray retention and rapid penetration of benazolin partly explained the susceptibility of wild mustard. The variation in tolerance between the two rape species was attributed to differential spray retention.