Wild Mustard activity

Wild Mustard activity of the 4-Cl-TFMS derivative in both the presence and absence of Tween 80 is higher than that observed for Foxtail because both r = +0.91 and v = —0.45 for this compound lie closer to their appropriate tr optima (tt0 = +0.36 (no surfactant) tr0 = —0.59 (with surfactant)) than was the case for Foxtail. Hence, the Air2 + Bw contribution for the broadleaf in both the presence and absence of surfactant is more favorable than it is for the grass. The pa contribution is also more favorable for Wild Mustard because of the high value of p for 4-substituted TFMS compounds in the presence and absence of Tween 80 (see Table XI). Thus, for the 4-Cl-TFMS derivative, both enhanced partitioning characteristics and a more favorable electronic situation (more positive pa) combine to give higher Wild Mustard than Foxtail activity. 

Of considerable interest also is the effect that surfactant has on the position of the various tt optima for the Foxtail and Wild Mustard activity surfaces (see Figures 2 and 3). Table XI shows that 7r0 for the para-TFMS derivatives acting on Foxtail in the absence of surfactant is tt0 = +0.16, while in the presence of Tween 80 it is shifted to tt/ = —0.77. Referring now to Figure 6, note that the 7r0 value for the para substituents in the non-surfactant case falls between the tt values for the 4-F- and 4-OCH3—TFMS substituents. In the presence of surfactant, the tt optimum is shifted toward more hydrophilic substituents and is now located between the 7r values of the 4-OCH3- and 4-SOjCH3- substituents. 

Non-crop plants associated with the crop species offer possibilities for allelopathic weed control. In this study Brassica campestris (wild mustard), which is an important weed in Santa Cruz County, and broccoli, a common crop, were intercropped, The allelopathic potential of both species and the changes in this potential throughout their life cycle were demonstrated with experiments in the laboratory. Effects of different planting densities and sowing time of canpestris on the crop yield are analyzed. Preliminary steps to separate the physiologically active compound(s) are described. The possibilities for the use of Brassica campestris in agroecosystem design as a non-crop plant that promotes pest control are described. 

Atrazine plays a central role in ecofallow because of its low cost, effective weed control, and extended soil activity. Atrazine controls volunteer wheat and most of the winter annual weed complex - including cheat, downy brome, wild mustards, and henbit, plus many spring annuals. No alternative herbicide has similar characteristics. Repeated applications of nonresidual, foliar-applied herbicides such as glyphosate or paraquat are not as economical. 

Fay and Duke (23) approached the question of allelopathic expression from oats in a different way. They screened 3,000 accessions of Avena spp. germ plasm for output of scopoletin, a known inhibitor from oats. Some exuded up to three times as much scopoletin as a standard cultivar, and these were the most active in suppressing wild mustard [R taW-tca kabeA (D.C.) L.C. Wheeler] in sand culture. However, in loamy-sand soil this activity was lost. 

Evaluation of TFMS Herbicidal Activity. The herbicidal potency of the 15 substituted TFMS compounds was rated after a 21-day test period on a 0-100% kill scale. Herbicidal test data were collected for two grass species (Foxtail, Cheat Grass) and a broadleaf weed (Wild Mustard) in the presence and absence of 0.1% (w/v) Tween 80. Since the tests... 

Figure 3a. Three-dimensional perspective plot of the Hansch equation describing pre-emergence activity of 4-substituted TFMS herbicides on Wild Mustard (no Tween 80 present)...

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 practical terms, this means that in the presence of surfactant, one has far less latitude in choosing a substituent with a tt value near the tr optimum than one does in the absence of surfactant. For example, in the presence of Tween 80, small deviations in tt from tt0 (relative to those permissible in the absence of surfactant) will lead to a rapid decrease in herbicidal activity. The loss in 4-TFMS activity produced by such deviations should be particularly severe for Wild Mustard, which has such a steep parabolic dependence on tt in the presence of Tween 80 (see Figure 3c). 

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,... 

Finally, Table XII showed that for both 3- and 4-substituted TFMS series, poorer correlations were obtained when herbicidal data obtained in the presence and absence of Tween 80 for a given series acting on a particular weed type were pooled and fitted simultaneously. Comparing the appropriate surface plots in Figures 2-3 for Foxtail and Wild Mustard, it is evident that poor correlations of the pooled data would have been obtained. The very different graphical curve shapes obtained for each TFMS series in the presence and absence of Tween 80 illustrate why correlations of the pooled data produced poor structure-activity correlations. 

As an illustration of the use of the final Hansch relationships in Table XI in explaining biological activity differences between individual TFMS series members, we will examine the activity of 4-S02CH3-TFMS and 4-C1-TFMS against Foxtail, Wild Mustard, and Cheat Grass. Table XIII gives values of the individual terms in the Hansch equations of Table XI which are appropriate to the action of each herbicide on the three weed types. At a later point, we also examine the activity of 2,4-di-Cl- and 2,4-di-F-TFMS derivatives as predicted by the Hansch relationships in Table XI. 

Implications of the TFMS Correlations. Meta-TFMS Activity on Wild Mustard in the Presence of Tween 80. Table XI and Figure 3d showed that the activity of the meta-TFMS herbicides on Wild Mustard in the presence of Tween 80 was anomalous (relative to the other weed types and formulation conditions examined) in the following ways ... 

Item d implies that in terms of the Hansch model of Equation 1, partitioning STEP 1 is the primary rate-controlling process characterizing the herbicidal action of the 3-TFMS compounds on Wild Mustard in the presence of Tween 80. Since all the other Hansch relationships in Table XI include fairly significant pa contributions, partitioning as well as other rate processes (possibly more intimately connected with the receptor site within the plant or seed) must be involved in determining overall herbicidal activity in these latter cases. One may speculate that the anomalous observations (a-c) above are the direct consequence of (d)—the lack of Hammett a dependence. If the pa term in the Hansch equation does indeed reflect rate or equilibrium events occurring at or near the herbicidal site of action within the plant or seed (as is often assumed but not... 

S02CH3-TFMS and 3-S02CH3-TFMS derivatives as they do in the Foxtail surfactant case (see Table XV). Although methylthio-TFMS derivatives might possibly be protected from in vivo oxidation by Tween 80 absorbed by the Wild Mustard seeds (micelle formation), a process of this type would not be observable experimentally since slower ratedetermining partitioning events control the overall herbicidal activity as previously explained. 

Herbicidal Activity Correlations. Tables I and II give pre-emergence herbicidal activity and partition coefficient data gathered in the presence of 0.1% Tween 80 for the 15 TFMS compound evaluated in this study. For reasons discussed previously (6), in the correlations which follow, the Hammett sigma constant was assumed to be relatively unaffected by the presence of the surfactant, so that the o-values listed in Tables I and II could be used to correlate data obtained both in the presence and absence of surfactant. Pertinent herbicidal activity data for the TFMS compounds acting on Foxtail grass are presented in Table I. Similar data for the same compounds acting on the broadleaf Wild Mustard are tabulated in Table II. 

---