Herbicidal activity requirements

The above SAR analyses indicated that improvement of herbicidal activity required a reasonable combination of both phosphorus-containing moiety and phenoxyacetate moiety. Herbicidal activity was remarkably variable by chemical modification of R R, R, R", and Y . As shown in Scheme 2.17, when 2,4-Cl2 were kept unchanged as Y , inhibitory potency against the growth of the root of cucumber was greatly enhanced by the chemical modification of substituents in the phosphorus-containing moiety. 

The above results indicate that the improvement of both inhibitory potency against plant PDHc and herbicidal activity requires a reasonable combination of R, R, R and Y . 

SAR analyses indicated that R R, and Y in the alkylphosphonates lo were the most essential sites for both enzyme inhibition and herbicidal activity. Me or Na as R and R, and 2,4-Cl2 as were most beneficial to activity. When 2,4-Cl2 were kept constant as Y , enzyme inhibition could be greatly enhanced by the chemical modification of R and R. Sodium salts IIB-2 and IID-10 exhibited more powerful enzyme inhibition than the corresponding alkyl phosphonates IC-22 and IG-21. However, good enzyme inhibition and herbicidal activity required an optimal combination of R, R, R, R", and Y in... 

Table I shows the herbicidal activity of a number of structures already discussed. These are greenhouse data and, although not obtained in a side-by-side test, they do give some indication of their relative activity. The term "control rate" as used in Tables I-III is defined as the amount of chemical required to produce a 91-100% reduction of growth of the weed when compared to the control plant.

It is a broad-spectrum herbicide active both pre- and post-emergent. Studies with radiolabelled compounds ( ) show it to be rapidly translocated particularly to the meristematic regions. Translocation to the underground storage organs of perennial weeds prevents regrowth of these weeds. Most herbaceous and woody plants are controlled in the field at 0.4-1.0 kg a.e./ha whereas most woody plants require 0.7-3.0 kg a.e./ha (10). 

Hydrophobicity is often an important, or even a dominant, parameter in herbicidal activity. At the present state of the art, it might be fair to state that de novo calculation of log P may not be sufficiently accurate for regression analysis, but coupled with measurements of one or two key analogs, it may eliminate the need to measure each and every chemical in the set. Certainly de novo calculation can be used as a predictive tool prior to synthesis, and it can serve quite adequately for the less demanding require-... 

Surfactant. Polyoxyethylene (20) sorbitan monooleate (also known as Tween 80, At-Plus 109, or Polysorbate 80) was obtained from Atlas Chemical Industries and used as received. It was used at the 0.1% (w/v) concentration level in all herbicidal activity evaluations and partitioning studies requiring the use of surfactant. 

A novel class of N.N -diphenyl vinylogous urea herbicides was shown to have several strict structural requirements. All of the following are important for optimum herbicide activity an alpha-cyano... 

In view of the structural novelty of this series of chiral herbicides, it was imperative to determine to what extent herbicidal activity is specifically linked to its molecular structure, and to define its structure-activity relationship requirements as a preliminary step toward designing even more potent representatives for this new series of herbicides. The... 

Another question that needed to be raised was whether the configuration at the C-3 carbon position where the benzyloxy group is attached to plays an important role in activity. The 3-epimer was synthesized and tested in our screens and was found to be essentially devoid of herbicidal activity. This result clearly demonstrated that a cis relationship between the ethyl group and the benzyloxy group is required for activity. 

The criteria required for optimum herbicidal activity for these sugar compounds can now be summarized as follows ... 

Direct-seeded rice does not tolerate pretilachlor in doses required for adequate weed control. The Ciba Geigy AG has discovered and developed a new safening agent, 4,6-dichloro-2-phenyl-pyrimidine (CGA123 407,23), which protects the rice seedling from damage and does not interfere with the herbicidal activity of pretilachlor. 

The present paper is a discussion of the photosystem II herbicides and their mechanisms of action. Among the topics covered are the green plant photosystems, photochemistry and electron transfers within photosystem II, requirements for herbicidal activity, mechanisms of action, herbicide selectivity and resistance, herbicide-binding proteins, and theoretical studies of herbicidebinding site interactions. 

By measuring the rate of Rb efflux from excised and preloaded cucumber cotyledons, AFM injury was detected at concentrations as low as 10 nM ( ). Also, because AFM has an absolute requirement of light for expression of herbicidal activity, plant tissues can be pretreated in darkness without injury. Then, following light-activation, damage can be detected in relatively short time periods (10 to 15 min) (1 ). We believe these observations are indicative of its primary biochemical mechanism of action. 

To date, none of these experiments have been successful. Protein-carotenoid complexes destroyed by the organic extraction procedures used might be required for herbicidal activation. 

Another vitro system for studying details of the mechanism of action of DPE s involves the binding of commercially available PUFA (e.g., linolenic acid) to silica plates (48) and adding the various subcellular components thought to be required for herbicidal activity. The DPE-initiated radical reactions in the PUFA monolayers could be followed by detection of TBARM or by measurement of oxygen consumption (59). 

Fig. 2 Examples of insecticides, fimgicides and herbicides that require transformation to produce the biologically active molecule...

Six imidazolinones are commercially available. These herbicides have extremely low toxicity or are non-toxic to mammals, birds, invertebrates and fish [36]. The crops on which these herbicides are registered and whether or not they are applied to foliage or to the soil is determined by the structure of the chemical (Table 2.3.2). When applied to the foliage of plants, a non-ionic surfactant or oil adjuvant is required for maximum activity. The addition of either urea or another form of nitrogen can also increase herbicidal activity. 

The triketones can be separated into two parts for analysis of the structure-activity relationships, namely the benzoyl and the dione moieties. Each part can be examined independently, as they appear to play distinct and different roles in the overall expression of herbicidal activity [1]. Apart from the necessity of an ortho-substituent on the phenyl ring, it was established that 2,4,- or 2,3,4-benzoic acid substitution patterns were required for optimal activity, with the 2,5-... 

In the original system of Rebeiz et a/. (5), a rather long post-spray dark period was required for sufficient accumulation of porphyrins for herbicidal activity occur. The herbicidal effect of ALA plus DP was age and species dependent however, there was not always a strong correlation between the effect on porphyrin... 

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