Crop safety

Premixes of Atrazine and Other Herbicides The first prepackaged mixture of a grass herbicide with atrazine was Primaze , a combination of two products prometryn (Caparol) and atrazine. The prepack was first sold in 1968. However the margin of crop safety for prometryn was narrow, and it was marketed for only 2 years. 

Crop safety, drift injury to nontarget plants, and hazards to the environment and the operator contributed to the complexity of weed management decisions. Products with difficult handling characteristics or narrow tolerances for crop injury were put aside as improved herbicides became available. Weed scientists were struggling to learn when and how to best control weeds and how to best convey information to growers about this important emerging agricultural discipline. 

In corn, the catalyst for adoption of preplant incorporated applications was not the introduction of an herbicide, but the introduction of safeners. The thiocarbamate herbicide S-ethyl dipropylthiocarbamate (EPTC) for corn weed control was first used in Illinois as early as 1961 however, the propensity for EPTC to injure com limited its use to 1% or less of the Illinois crop up to 1970 (Table 4.1). Dichlormid, a safener later packaged with EPTC, greatly improved crop safety and resulted in nearly one-quarter of the com acreage being treated with EPTC throughout the Corn Belt by 1976. 

Triazine herbicides have been important tools in the development and implementation of conservation tillage systems. Postemergence and residual activity, low vapor pressure, weak adsorption to surface crop residue, root uptake, broad weed control spectrum, and crop safety make these herbicides compatible with the high crop residue conditions of conservation tillage. 

Atrazine is widely used in corn production due to its efficacy, application flexibility, low cost, and crop safety. Its efficacy ratings for some common weed species are listed in Table 34.1a. Table 34.1b presents estimates of the infestation of these important weeds in Illinois and of the potential yield loss that would occur if these weed species were uncontrolled. These data indicate that atrazine provides significant levels of control for most of the important weed species that are widely distributed and those that would cause significant com yield loss if left uncontrolled. 

The first PC compound was prepared using the 2-methanesulfonylpyrimidine (OMSP) 6 and the salicylic acid ester in DMF. The sulfonyl compound 6 was a very efficient intermediate to synthesize 2-substituted pyrimidines [8]. The meth-anesulfonyl group in 6 is easily replaced by nucleophilic reagents like 7 and 8 (Fig. 2.5.5) [7, 9, 10]. This method was generally employed to synthesize numerous analogues aiming at new herbicides, not only with a high potency but also with an enhanced crop safety. Structural modifications were first made with the skeletal structure 9 (Fig. 2.5.6) [3]. 

To ensure maximum crop safety, safeners that are applied in mixture with the herbicides need to act quicker than the herbicide injury develops. The mechanism of action of safeners has received much scientific attention and will be dealt with in some detail in this chapter (Section 5.3). 

Products such as Dual-II-magnum and Cinch are also labeled for use on sorghum seed treated with fluxofenim or flurazole. This is a notable example of safe-ners used in sequence so as to obtain optimal crop safety. Table 5.4 indicates that benoxacor has a favorable toxicological profile. 

Pinoxaden is applied post-emergence at use rates of 30-60 g-a.i. ha [7]. Interplay of the active compound with a safener proves essential to maximize the tolerance [7]. Methyl oleate as adjuvant enhances the level of activity without impairing the crop safety [86]. 

Very distinct are its rapid leaf uptake and translaminar movement, its extremdy broad activity spectrum, and its outstanding crop safety and yield enhancements [46b, 48]. This bundle of positive properties may - or may not - have its origin in the fact that pyradostrobin possesses the lowest melting point of all the presently commercialized strobilurins, which should favor rapid bioavailability in molecu-larly dispersed form (see Section 13.2.3.3). 

Kasugamycin has been developed as a specific and effective antibiotic to control rice blast since 1965. The antibiotic controls the disease when applied at 20 ppm in aqueous solution and shows both protective and curative activity [20]. Kasugamycin has been used to control rice blast on a large scale. In practice, the antibiotic is predominantly used as a dust at 0.3% of the active ingredient. In addition, seed treatment with 2% wettable powder of kasugamycin protects rice plants against blast for one month. The antibiotic exhibits a high crop safety no phytotoxicity has been observed. 

Primisulfuron-methyl (99) [191] is a maize-selective herbicide. Comparison with the unfluorinated triazine counterpart metsulfuron-methyl (94) indicates that crop safety for maize is achieved by replacement of the triazine methoxy (R ) and methyl (R" ) group in ring B with two difluoromethoxy groups (R, R" ). 

Numerous substituted p pmidine and tiiazine amines have found utility as precursors to highly active and crop selective sulfonylurea herbicides. In the process of optimizing herbicidal efficacy and crop safety within this class, a variety of structurally diverse heterocyclic amines have been synthesized and evaluated. This paper reviews the methods of preparation that have been developed for some of the different structural types used as intermediates to active sulfonylurea herbicides. These methods include cyclizations, rearrangements, and side-chain metalations that have led to furo[2,3-d]pyriiindines, pyrazinones, and selectively functionalized pyrimitoes, triazines, triazoles, and pyridines. 

In comparision to other members of the imidazolinone series, the pj lopyridines are quite active. In Table 3, two of the more active compounds in this series, 32a and 32b, are compared to AC 252,214. The broad spectrum weed control demonstrate by these compounds is comparable to this commercial standard. All three compounds display crop safety in soybeans. 

The heterocyclic analogs of EL-107 showed interesting herbicidal activity as preplant incorporated (PPI) and surface applied (SA) materials (Table). At high rates (8 Ib/acre) they showed postemergence activity. When preplant incorporated and surface applied, these compounds were best described as broadleaf herbicides most effective on redroot pigweed, jimsonweed, nightshade, and mustard. Some degree of foxtail millet control was seen at 0.5 to 1.0 Ib/acre. Crop safety was seen on the cereals and corn. 

Primisulfuron-methyl is a selective herbicide for the control of grasses in maize. Comparison [81] with its unfluorinated triazine counterpart methsulfuron-methyl indicates that crop safety for maize is achieved by the replacanent of the triazine methoxy and methyl substituents with two difluoromethoxy groups. It has been shown that primisulfuron-methyl is deactivated in maize by hydroxylation of the phenyl and pyrimidyl moieties followed by hydrolysis or conjugation [82]. 

The development of a new class of synthetic agricultural fungicides based on the naturally occurring P-methoxyacrylates is described. A consideration of structure-activity relationships and key physical properties has led to a series of tricyclic compounds which still incorporate the P-methoxyacrylate toxophore. The best examples of these compounds combine high levels and a broad spectrum of stemic fungicidal activity with good crop safety. 

Crop safety of aminium salts IU-11 and nj-24 for rice (Oryza sativa), maize (Zea mays), cotton (Gossypium hirsutum), soybean (Glycine max), wheat (Triticun aestivum), and rape (Brassica campestris) was examined (Table 3.38). Both IU-11 and lU-24 were unsafe to rice, cotton and rape, but they showed good selectivity... 

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