Imidazolinone herbicide

Plan of Study to Determine the Occurrence of Sulfonylurea, Sulfonamide, and Imidazolinone Herbicides in Surface and Ground-Water of the Midwestern United States. US Geological Survey, Washington, DC (1998). Also available on the World Wide Web http //webserver.cr.usgs.gov/midconherh/html/workplan98.html, accessed September 2002. 

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

One application using MAE is a method to determine imidazolinone herbicides and their respective metabolites in plant tissue." Current residue methodologies for determining imazethapyr (imidazolinone herbicide) and its metabolites in crops involve laborious, time-consuming cleanup procedures after an aqueous/organic extraction. 

Electrospray ionization (ESI) and APCI are the two popular API techniques that will be discussed here. The applications to the analysis of pesticides that will be discussed include imidazolinone herbicides, phenoxy acid herbicides, and A-methyl carbamate insecticides. Matrix effects with respect to quantitation also will be discussed. Eor the... 

ESI performs well for the more polar compounds such as imidazolinone herbicides, sulfonylurea herbicides, triazine herbicides, phenoxy acid herbicides, and carbamate pesticides (to name a few). ESI also performs well with proteins and peptides. 

In another example, a multiresidue method using HPLC/ESI-MS was developed to determine six imidazolinone herbicides in five different soil types. Good recoveries (80-120%) and adequate sensitivity at the 2.0 ngg level were obtained for the compounds investigated. In the method, a 50-g soil sample was extracted for 1 h in 0.5N NaOH solution. A portion of the extract was acidified, to precipitate the humic acids, and the supernatant was then loaded on to a preconditioned trifunctional Cig SPE cartridge and eluted with ethyl acetate. Further cleanup was achieved using a tandem strong anion-exchange (SAX)-SCX SPE combination. Analytes were eluted... 

Table 6 List of ions monitored for imidazolinone herbicides using in-source CID (HPLC/ESI-MS)...

Microwave-assisted extraction coupled with gas chromatography-electron capture negative chemical ionization mass spectrometry (i. e., MAE-GC-EC-NCI-MS) was described for the simplified determination of imidazolinone herbicides in soil at the ppb level [715]. 

In Australia, two types of sulfonylurea resistance have been reported (Bumet et al, 1994). Rigid ryegrass exhibited cross-resistance to certain sulfonylurea and imidazolinone herbicides following selection for resistance to other... 

Devine et al. (1991) and O Donovan et al. (1994) reported that chlorsulfuron-resistant chickweed populations were also resistant to other sulfonylurea herbicides. Primiani et al. (1990) reported cross-resistance to several sulfonylurea and imidazolinone herbicides in chlorsulfuron-resistant kochia. Lovell et al. (1996a) also documented that chlorsulfuron-resistant kochia biotypes from Idaho and Montana were cross-resistant to imazethapyr. 

Diebold et al. (2003) concluded that multiple resistance in a Powell amaranth biotype in Ontario was due to the presence of altered target sites for triazine and imidazolinone herbicides. 

Newhouse, K., B. Singh, D. Shaner, and M. Stidham (1991). Mutations in com (Tea mays L) confering resistance to imidazolinone herbicides. Theor. Appl. Genet., 83 65-70. 

Primiani, M.M., J.C. Cotterman, and L.L. Saari (1990). Resistance of kochia (Kochia scoparia) to sulfonylurea and imidazolinone herbicides. Weed Technol., 4 169-172. 

ALS herbicides. Two classes of ALS-inhibiting herbicides are the sulfonylurea herbicides, discussed in Sections 2.1.2.1 and 2.2.3.1, and the imidazolinone herbicides. A third class of ALS-inhibiting herbicides is the 1,2,4-triazolo [1,5-a]pyrimidine-2-sulfonanilides. The triazolopyrimidine sulfonanilides act by disrupting the biosynthesis of branched chain amino acids in plants. Representatives of this class of herbicides include florasulam (Boxer , Nikos ) [151], initially introduced in Belgium in 1999 and used for the postemergence control of broadleaf weeds in cereals and corn, and flumetsulam (Broadstrike ) [152], used alone or in combination with other herbicides for the control of broadleaf weeds in soybean and corn. 

The positive-ion ESI mass spectra of six imidazolinone herbicides, e,g, imazapyr and imazaquin, showed protonated molecules at low cone voltages (40 V),... 

Graphitized carbon black (GCB) materials are frequently used for off-line SPE as well. GCB behaves as a nonspecific sorbent, but because positively-charged adsorption sites are present, it also acts as an anion exchanger, which is useful for the enrichment of acidic compounds [75]. Examples involve the enrichment of chlorinated phenoxy acids [42], aryloxyphenoxypropionic herbicides [45], sulfonylurea herbicides [50], and imidazolinone herbicides [65]. 

The use of dual-SPE approaches has also been described, e.g., extraction of A-methylcarbamates insecticides and their metabolites from urine by means of GCB and further clean-up using NHj-modified silica [18], or the use of RP-102 extraction cartridges with further clean-up of extracts on a strong anion-exchange column in the determination of selected sulfonylurea and imidazolinone herbicides [51]. 

Examples of the application of the three-ion-criteria in SIM mode can be found in reports on the analysis of acidic pesticides [42], sulfonylureas [49-51], and imidazolinone herbicides [51]. Rodriguez and Orescan [51] actually apply... 

A. Lagana, G. Fago, A. Marino, Simultaneous determination of imidazolinone herbicides from soil and natural waters using soil column extraction and off-line SPE followed by LC with UVdetection orLC-ESI-MS, Anal. Chem., 70 (1998) 121. 

G. D Ascenzo, A. Gentili, S. Marchese, A. Marino, D. Ferret, Optimization of LC-MS apparatus for determination of imidazolinone herbicides in soil at levels of a few ppb. Rapid Commun. Mass Spectrom., 12 (1998) 1359. 

Figure 3. Relative potencies of N-phthalyl-L-valine anilide, L-valine, the imidazolinone herbicide, Scepter, and the sulfonylurea herbicide, chlorsulfuron, as inhibitors of acetohydroxyacid synthase from Zea mays. (Reproduced with permission from Ref. 53. Copyright 1985 Verlag der Zeitschrift fur Naturforschung.)...

Lolium biotypes exist which have resistance to the sulfonylurea herbicides chlorsulfuron and metsulfuron methyl (4). The biotype used in the studies presented here is resistant to both these sulfonylurea herbicides. Sulfonylurea herbicides inhibit the chloroplastic enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS) (16). Inhibition of this enzyme results in disruption of the synthesis of the branched-chain amino acids valine and isoleucine (161. The imidazolinone herbicides also inhibit ALS Q2). In some species auxins can protect against chlorsulfuron inhibition (S. Frear, USDA North Dakota, personal communication) the mechanistic basis for this protection is not known. We have measured the ALS activity in the resistant and susceptible Lolium and have also checked for any induction of ALS activity following treatment with the sulfonylurea herbicide chlorsulfuron. 

In the second approach, herbicide-resistance mutations in the Arabidopsis ALS gene were studied in E. coli. To do this, wild type and mutant Arabidopsis genes were functionally expressed in E. coli, such that the plant genes complemented a branched chain amino acid auxotrophy in the bacteria (Smith et al. 1989, PNAS in press). ALS enzyme assays on extracts prepared from E. coli expressing the mutant Arabidopsis gene indicated that the mutant enzyme is resistant to sulfonylurea herbicides but is sensitive to the imidazolinone herbicide imazaquin. This selective... 

Genetic Modification of Crop Responses to Imidazolinone Herbicides... 

In 1982, American Cyanamid began commercial development of the imidazolinone class of herbicides. These herbicides control a broad spectrum of economically important weeds in corn and soybeans. Although differences in tolerance of corn hybrids for imidazolinone herbicides exist (5), no hybrids with sufficient tolerance to allow application of current imidazolinone herbicides to corn fields have yet been identified. Other methods to supplement the inadequate levels of natural tolerance have likewise been ineffective. 

Identification of the mode of action of the imidazolinones occurred while resistant cell lines were being isolated. Imidazolinones inhibit acetohydroxyacid synthase (AHAS EC 4.1.3.18), the first enzyme in the pathway of branched chain amino acid synthesis (8). Imidazolinone-resistant cell lines provide proof that inhibition of AHAS is the site of action of the imidazolinones AHAS activities in extracts from resistant corn cell lines are highly resistant to inhibition by imidazolinone herbicides (7). 

The imidazolinone-resistant corn project successfully identified mutant alleles that confer greater than 1000-fold increased resistance to imidazolinone herbicides. Still, key questions must be answered before the resistant corn can be marketed. 

Close coordination between the seed company and the chemical company is essential to assure that yield trials, efficacy trials, hybrid seed production, and the required herbicide label extensions proceed in a concerted fashion. The imidazolinone herbicide must be ready to be used when imidazolinone-resistant corn is ready for sale. Joint launch of the resistant hybrids and the herbicide label extension that includes resistant com will be coordinated by American Cyanamid and Pioneer Hi-Bred. 

The project to develop corn hybrids resistant to imidazolinone herbicides has been very successful. Corn with excellent resistance characteristics was selected, and semidominant resistance alleles are being introduced into proprietary inbred lines of Pioneer Hi-Bred International, Inc. Commercial corn hybrids resistant to imidazolinone herbicides will be the first major biotechnology product in cereals to enter the marketplace. 

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