Development as herbicides

This paper describes the initial phase of research directed toward the discovery of compounds produced by soil microorganisms, primarily actinomycetes, having potential for development as herbicides. Our interests include both new compounds, as well as previously known ones having heretofore unrecognized herbicidal properties. 

The first pyridazine for which plant growth regulating activity was patented was maleic hydrazide ( 1). Since the introduction of MH in the late 1940 s, at least four other pyridazines have been developed as herbicides Pyramin by BASF in 1962, Kusakira by Sankyo in 1970, Zorial by Sandoz A. G. in 1971 and pyridate by Chemie Linz in 1976 (2). 

Recently, however, new interest has developed due to their chemotherapeutic and bacteriostatic usefulness in animal husbandry. They also have been patented as herbicides and plant-growth-regulating agents. 

PERFLUOROALKYLPYRIDINES New developments ia trifiuoromethylpyridine technology are associated with the commercialization of numerous crop-protection chemicals as herbicides, fungicides, and iasecticides (Table 15). Physical properties for representative trifiuoromethylpyridines are fisted ia Table 13. 

Sevin. 1-Naphthalenol methylcarbanate [63-25-2] (Sevin) (44) was developed as an insecticide. However, the conception of the molecule, in the mid-1950s, was as a possible herbicide. The compound ultimately was useless as a herbicide, but in routine testing it was discovered to be an excellent insecticide. Sevin was active in the oat mesocotyl assay and demonstrated weak auxin-like activity. During the development of Sevin, it caused massive apple drop in the western United States in an orchard being treated for insects. It is used (ca 1993) as an abscising agent to thin apples. 

Many organophosphorus compounds are highly toxic and frequently lethal. They have been actively developed for herbicides, pesticides and more sinister purposes such as nerve gases which disorient, harass, paralyse or kill. ... 

This is a large subject that can only be dealt with in the barest outline in the present text. Many antibacterial and antifungal compounds have been discovered in microorganisms, and some of them have been successfully developed as antibiotics for use in human and veterinary medicine. They lie outside the scope of this book. A considerable number of other microbial compounds act as insecticides, acaricides, or herbicides, although few of them have been developed commercially (Copping and Menu 2000, Copping and Duke 2007). 

Pyraflufen-ethyl was primarily developed as a cereal herbicide to control a broad spectrum of broadleaf weeds. Pyraflufen-ethyl applied in early postemergence at 12 g a.i. ha provides excellent control of some important weeds such as Anthemis arvensis, Lamium purpureum and Sinapis arvensis and good suppression of Matricaria chamomilla, Stel-iaria media, Veronica persica and Viola spp. 

Although penicillic acid (59) is produced in high quantities in cultures of Penicillum cyclopium and Penicillum canescens isolated from corn seeds, its toxicity to animals have precluded further development as a herbicidal agent. 

Qulzalofop-ethyl Q) (4) which has been developed as an effective herbicide by Nissan Chemical Industries Ltd. Is needed as Its crystalline state In commercial production. But no physical properties solubilities and/or any other Information useful for the crystallization of the compound have not appeared to be available. 

Our discussion of pesticides has focused primarily on insecticides. In the United States the primary use of pesticides is in the form of herbicides, those pesticides used to control weeds. Approximately 70% of the pesticides used in the United States are herbicides and 20% are insecticides. The use and development of herbicides parallels that of insecticides. The first herbicides were inorganic metal compounds and salts. During World War II organic herbicides were synthesized and their use increased dramatically. One of the first major classes of herbicides synthesized in the mid-1940s was phenoxyaliphatic acids. As this name implies, the phenoxyaliphatic acids contain the benzene ring, oxygen, and an aliphatic acid. The two most common phenoxyaliphatic acids are 2,4 dichlorophenoxyacetic acid, called 2,4-D and 2,4,5 trichlorophenoxyacetic acid, known as 2,4,5-T (Figure 18.10). The numbers in these... 

The notion of using exogenous chemicals to control plant growth, and hence productivity, is not new. Many of the first commercial herbicides (auxin herbicides) were developed as a direct consequence of plant growth regulator research (see Chapter 1, Section 3.3). 

A more recent factor affecting weed management has been the introduction of crops genetically altered for tolerance or resistance to herbicides. The first herbicide-tolerant field com (IMI hybrid corn) was developed as a way to reduce the effects of carryover from imidazolinone and sulfonylurea herbicides applied to soybean in a corn-soybean rotation. These hybrids also soon found use in areas where triazine use was restricted. 

The science and technology of analytical chemistry have made steady and remarkable advances over the last 50 years. Nowhere has this been more evident than for progress on methods to analyze organic chemicals developed as pesticides and, in particular, the triazine herbicides. Methods of triazine analysis traditionally involve an extraction step in which the analyte is removed from the matrix - such as soil, water, or crop. This extract is then subjected to a clean up in various ways to isolate the analyte further from the other chemical components that are extracted. The next step is to concentrate the purified fraction to a smaller volume to allow the analyte to be detected. A small portion of this final fraction is then injected into an instrument capable of selectively detecting and quantifying the triazine in the sample. 

Analytical methodologies for the triazine herbicides have improved significantly since their original development. During the 50-year period in which the triazines have been used as herbicides, analytical equipment and extraction systems have evolved to be able to detect very small amounts of triazines in samples. More recently, methods have also been developed for extracting and isolating a wide array of metabolites. 

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