ABSTRACT
The purpose of this study was to assess the potencies of some newly developed formulations of phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) in relation to Betanal, a commercial phenmedipham product.
Sinapis alba L. and Brassica napus L., grown in a greenhouse, were sprayed at the 2-to 2.5-true-leaf stage and harvested about 3 weeks following spraying.
A four parameter nonlinear regression model of fresh weight on log-dose of phenmedipham formulations was fitted simultaneously to all response curves within an experiment. Since the active ingredient was the same in all formulations, the five and eight response curves in the S. alba and the B. napus experiments, respectively, were assumed to be parallel; i.e., the regression parameters were similar for all response curves except for the parameter determining their horizontal location.
Betanal was about threefold more potent in S. alba (ED50 = 0.37 ℓ ha−1) than in B. napus (ED50 = 1.09 ℓ ha−1).
The potencies of test formulations relative to Betanal were used to rank their phytotoxicity. In the S. alba experiment only one of the four test formulations was as effective as Betanal, and in the B. napus experiment three of the seven tested formulations were as active as Betanal.
The results were discussed in relation to the effect of formulation constituents on phenmedipham phytotoxicity, differences in retention of the spray solution, and the cuticular characteristics of the two test species.
