Herbicidal activity Tween 80 effect

For all regression analyses, herbicidal activity data were taken from the appropriate column in Table VII. Corresponding tt, tt or tt" values were selected from Table VI. Hammett sigma constants (a) were taken from the compilation of Jaffe (13) and correspond to those in Table IV. Since it was assumed throughout that <7 would be relatively unaffected by the presence of surfactant, the <7 values in Table IV were used to correlate data obtained in the presence and absence of Tween 80 for all three weed types. This assumption is reasonable since the surfactant was used at a low 0.1% level in all herbicidal and partitioning tests. Furthermore, surfactant effects would be expected to manifest themselves primarily in the partitioning behavior (tt values) of the TFMS compounds... 

Hansch analyses have shown that the surfactant Tween 80, when used in herbicidal formulations of TFMS derivatives at the 0.1% (w/v) concentration level, can produce one or more of the following effects in pre-emergence herbicidal tests, depending on the weed type and/or TFMS derivative under evaluation (a) no effect, (b) enhancement of herbicidal activity, (c) inhibition of herbicidal activity, or (d) shifting of optimum herbicidal activity from one TFMS derivative to another within each series. Mathematical equations relating structure to activity have been derived for the TFMS compounds both for the surfactant present and surfactant absent cases. 

TFMS Herbicides in the Presence of 0.1% Tween 80. Let us now turn our attention to the effect that the addition of a small amount of Tween 80 to the TFMS herbicidal formulations has on the shape and orientation of the activity plots for Foxtail and Wild Mustard. Considering first the 4-substituted derivatives and comparing Figure 2a with 2c for Foxtail and Figure 3a with 3c for Wild Mustard, we note that the addition of surfactant in both cases has two obvious consequences ... 

In addition to the pronounced effects of surfactant on ir discussed above, addition of Tween 80 to 4-TFMS herbicidal formulations produces smaller changes in the a dependence (cf. Figures 2a and 2c for Foxtail and 3a and 3c for Wild Mustard). In Table XI, this a dependence appears as a slight decrease in the parameter coefficient p for 4-TFMS activity on Wild Mustard and as a large decrease in p for 4-TFMS activity on Foxtail when surfactant is added. Comparing Figures 2a and 2c for Foxtail, this decrease in p manifests itself as a decrease in slope of the activity surface in the positive a direction. For substituents with large positive o- values,... 

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