Chloroacetamide Herbicides Research Articles

Incorporation of Oleic Acid into Sporopollenin and Its Inhibition by the Chloroacetamide Herbicide Metazachlor

Incorporation of exogenous [14C]oleic acid (18:1) into a nonlipid fraction of the green algaScenedesmus acutuswas strongly inhibited by chloroacetamide herbicides. This fraction was solubilized by 12 consecutive steps. Radioactivity from oleic acid was mostly recovered in proteins (soluble and insoluble), in starch, and in a dioxane-soluble subfraction. Incorporation of oleic acid into the protein and starch subfractions was not inhibited but it was strongly reduced in the dioxane subfraction. The nonlipid fraction could not be completely solubilized and a significant proportion of the original radioactivity was recovered in an insoluble subfraction. Inhibition of oleic acid incorporation into that subfraction was more potent than in the total nonlipid fraction. An inhibition of 50% was achieved with 50 nMherbicide. After the nonlipid fraction was solubilized by acetolysis, a residue was obtained in which the incorporation of oleic acid was also completely inhibited by 10 μMmetazachlor. The infrared spectra of the insoluble subfraction and the acetolysis residue were similar to that of sporopollenin isolated with comparable methods. Oleic acid as a precursor of sporopollenin is discussed together with the interference of chloroacetamides with oleic acid metabolism, especially its incorporation into sporopollenin. UsingScenedesmus,the inhibition of oleic acid incorporation into sporopollenin is a sensitive marker of chloroacetamide activity.

Interactions Between SAN 582H and Selected Safeners on Grain Sorghum (Sorghum bicolor) and Corn (Zea mays)

The efficacy of the safeners naphthalic anhydride (NA), CGA-92194, and CGA-133205 as protectants of grain sorghum and of NA, R-29148, CGA-154281, and dichlormid as protectants of corn against injury from the chloroacetamide herbicide, SAN 582H, was evaluated under greenhouse conditions. SAN 582H applied alone reduced the shoot growth of ‘Funk G522DR’ and ‘Funk G623’ sorghum, but had no effect on the growth of the ‘GP-10’ genotype of sorghum. Corn (‘Northrup-King 9283’ hybrid) was considerably more tolerant than grain sorghum to SAN 582H. The rate of SAN 582H causing 50% reduction of corn shoot height (GR50) was 5.1 kg/ha as compared to 1.1 kg/ha for grain sorghum. NA applied as seed dressing at 5 or 10 g/kg seed, provided moderate protection to ‘G522DR’ and ‘G623’ sorghum and no protection to corn against SAN 582H injury. Dressing of sorghum seeds with CGA-133205 provided moderate protection to G522DR sorghum, whereas seed-applied CGA-92194 provided moderate protection to G623 sorghum against SAN 582H. The dichloroacetamide safeners R-29148, dichlormid, and CGA-154281 were all effective as protectants of corn against SAN 582H injury. These results demonstrate that, as with other chloroacetamide herbicides, the tolerance of corn and grain sorghum to SAN 582H can be enhanced with the use of safeners of the dichloroacetamide type and oxime ether type, respectively.

Initial Metabolism of Dimethenamid in Safened and Unsafened Wheat Shoots

The metabolic fate of the chloroacetamide herbicide dimethenamid was examined in excised shoots of unsafened and safened wheat seedlings. Compared to unsafened controls, fluxofenim treatment increased the rate of metabolism of dimethenamid to water-soluble compounds. Thin layer chromatography revealed that similar dimethenamid metabolites were present in extracts from both safened and unsafened wheat shoots. However, three metabolites were more abundant in extracts from fluxofenim-treated wheat relative to unsafened wheat. Reversed-phase high-performance liquid chromatography and mass spectrometry were used to isolate and confirm the identity of dimethenamid metabolites extracted from safened wheat shoots 1 h after treatment with dimethenamid. In addition to the presence of the glutathione conjugate of dimethenamid, gamma-glutamylcysteine and cysteinylglycine dipeptide conjugates, as well as a cysteine conjugate and an oxygenated glutathione conjugate of dimethenamid, were detected. On the basis of time course analysis of dimethenamid metabolites by thin layer chromatography and structural identification by mass spectrometry, it appears that from 5 to 100 min after treatment with dimethenamid metabolism occurs exclusively via the glutathione conjugation pathway in wheat. Thus, the protection conferred to wheat by fluxofenim treatment is most likely due to increased glutathione-mediated detoxification of dimethenamid.

Inhibition of oleic acid incorporation into a non-lipid fraction by chloroacetamide herbicides

Inhibition of oleic acid incorporation into a non-lipid fraction by chloroacetamide herbicides

Inhibition of oleic acid incorporation into a non‐lipid fraction by chloroacetamide herbicides

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction in Scenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I50= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non‐lipid fraction were investigated. S. acutus cells were cultivated under various conditions with or without inhibitors and [14C]‐oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non‐herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta‐bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non‐lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these herbicides.

Pretilachlor [2-chloro-N-(2,6-diethylphenyl)-N-(2-propoxyethyl)acetamide]- and butachlor [N-(butoxymethyl)-2-chloro-N-(2,6-diethylphenyl)acetamide]-induced accumulation of phytoalexin in rice (Oryza sativa) plants

The chloroacetamide herbicides pretilachlor [2.chloro-N.(2,6-diethylphenyl)-N-(2-propoxyethyl)-acetamide] and butachlor [N-(butoxymethyl).2-chloro-N-(2,6-diethylphenyl)acetamidel trigger accumulation of the phytoalexins momilactone A and sakuranetin in rice leaves. This ability was found to be specific to pretilachlor and butachlor. The accumulation of these phytoalexins was related to the herbicide concentration and period of exposure and was followed by the appearance of necrotic lesions on the rice leaves.

Chloroacetamide Herbicides and Chlorimuron Do Not Predispose Peanut (Arachis hypogaea) to Stem Rot (Sclerotium rolfsii)1

Abstract Field studies were conducted from 1991 through 1993 at Plains, GA to determine the effect of chloroacetamide herbicides and chlorimuron on incidence of stem rot in peanut. The experimental site had a cropping history of more than 25 yr in continuous plantings of peanut and extremely high incidence of stem rot. Incidence of stem rot and peanut yield were not affected (P≤0.05) by chloroacetamide herbicides in 1991, 1992, and 1993. Chlorimuron applied 60 d after emergence had no effect on stem rot incidence or peanut yield. Paired plots treated with thifluzamide had very low stem rot incidence and 27% greater peanut yields. Based on these studies, neither chloroacetamide herbicides nor chlorimuron predisposed peanut to stem rot.

Effect and Metabolism of the Chloroacetamide Herbicide Metazachior

Metazachlor の生物活性およびその消長を, イネとホウレンソウの細胞懸濁培養, およびそれぞれの幼苗で比較した. イネの細胞培養での生長は, metazachlor 200μMで阻害されず, ホウレンソウでは100μMでわずかに阻害された. 対照的に, 幼苗の生長はイネでは metazachlor 0.1μMで50%阻害され, ホウレンソウでは100μMで35%阻害された. イネ幼苗においては, 0.1μMの metazachlor は脂肪酸の不飽和化を著しく減少させたが, 一方100～200μMでも他の3種の試験系ではほとんど何の影響も示さなかった. 細胞懸濁培養はそれぞれの幼苗の試験系に比較して, metazachlor に対する感受性がより低かった. 最も感受性の高かったイネ幼苗において, 薬剤吸収が最も小さかったことから, 吸収で感受性の差異を説明することはできなかった. すべての試験系で metazachlor の代謝が認められたが, ホウレンソウでは200μMの metazachlor 投与72時間後で, 細胞培養では3.3μM, 幼苗では48μMの親化合物がそれぞれ残存していた. また, 0.1μMで培養したイネ幼苗では, 24時間後で18nMの metazachlor が残存していた. Metazachlor はホウレンソウには高濃度で残存するが活性を示さず, 一方イネ幼苗においてはその残存量が少ないにもかかわらず活性を示す. このことはグルタチオン抱合による薬剤代謝が耐性植物における唯一の保護機構ではないことを示唆している.

Comparative Response of Three Peanut Cultivars To Multiple Herbicide Applications1

Abstract Field studies in 1990 and 1991 at Tifton, GA and Gainesville, FL evaluated the response of Florunner, Southern Runner, and NC 7 peanut to multiple herbicide applications. A split-split plot experimental design was used with peanut cultivars as main plots. Sub-plots were four levels of chloroacetamide herbicides applied sequentially preplant incorporated and at vegetative emergence. Sub-subplots were five postemergence herbicide treatments. All herbicides were applied at registered rates and times of application. There were no interactions between cultivars, choloracetamide, and/or postemergence herbicides for canopy width, yield, and grade of peanut. There were no interactions between chloroacetamide and postemergence herbicides for the same parameters. Main effects were the only sources of significant (P = 0.05) differences in the data. Based on these results, unusual precautions in using these herbicide combinations on these cultivars are not needed.

Addressing Real Weed Science Needs with Innovations

Weed science is responsible for reducing weed competition with crops, within constraints, allowing food production for a growing world population. We have been successful, but with an increasing reliance on the fantastic arsenal of herbicides. Heavy herbicide usage and the concomitant loss of control due to changing weed species spectra, as well as evolved herbicide resistance, along with cancellations of registrations, limit chemical options. Old “innovations” such as well-conceived rotations and various mechanical procedures partly alleviate chemical dependency. We must try innovative, meaningful herbicide mixtures, whether synergistic or additive, mixtures of crop varieties, more competitive varieties, including allelopathic varieties, which could all help to lower chemical dependency. Three cases where innovative genetic-engineering coupled with chemistry seem to be needed are: (a) for the control of parasitic higher plant weeds such as broomrapes (Orobanchespp.), dodders (Cuscutaspp.), witchweeds (Strigaspp.) that cannot be controlled by mechanical or selective chemical means with a sufficient margin of user error; (b) for the control of weeds in wheat (Triticumspp.) that are evolving multiple and cross resistances toallwheat-selective herbicides; and (c) to replace the majors-triazine and chloroacetamide herbicides in corn (Zea maysL.) that are under attack and where many local restrictions and cancellations have been imposed. We need better replacements than the resistance-prone inhibitors of acetolactate-synthase and acetyl-CoA-carboxylase. Much of the long-term innovative planning and research must come from the public sector as no one else seems willing to fill the needs.

Chloroacetamide herbicides reduce incidence of Fusarium wilt in melons

Pretreatment of muskmelon seedlings with four chloroacetamide herbicides at 0.1 μg g −1 reduced the incidence of Fusarium wilt by 22–79%. Acetochlor also induced resistance to Fusarium wilt in watermelon and tomato seedlings inoculated with the appropriate formae speciales. Acetochlor reduced Fusarium wilt in muskmelon seedlings also when applied as a seed treatment [soaking for 5 h in solution (50 μg ml −1)] and, to a lesser extent, when applied as a foliar spray. In a field trial carried out in a naturally infested soil, acetochlor significantly reduced the incidence of Fusarium wilt in muskmelons cv. En Dor during the first 43 days postemergence. Acetochlor, and possibly other chloroacetamide herbicides, is potentially valuable in disease control.

Synthesis and Herbicidal Activity ofN(1-Arylethenyl)-2-chloroacetamides

N-(1-Alkenyl)-2-chIoroacetamides, which bear an aryl substituent at the 1-position of the alkenyl moiety, were synthesized and their herbicidal activities were tested. Some of them were active against paddy field weeds. In particular, a new type of chloroacetamide herbicide, 2-chloro-N-methyl-N-(2-methyl-1-phenylpropen-1-yl)acetamide, having no 2,6-dialkyl substituted phenyl moiety, which has been considered essential for activity, was found to be active against barnyardgrass.

Comparative Effectiveness and Mode of Action of Safeners for Chloroacetamide Herbicides in Maize Seedlings

Abstract In growth room bioassays, four herbicide safeners {BAS-145138: 1-dichloroacetyl-hexa-hydro-3,3,8a-trimethyl-pyrrolo(1,2a)pyrimidin-6(2H)-one, dichlormid: N,N-diallyl-2,2-dichloroacetamide, flurazole: phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazole-carboxylate and MG-191: 2-dichloromethyl-2-methyl-1,3-dioxolane} were compared for their effective­ ness in reducing metazachlor {N-(2,6-dimethylphenyl)-N-(1-pyrazolylmethyl)-chloroacet-amide} injury to maize seedlings. Three of these compounds (BAS-145138, dichlormid and MG-191) and two different compounds (AD-67: N-dichloroacetyl-1-oxa-4-azaspiro-4,5-de-cane and DKA-24: N ,N2-diallyl-N2-dichloroacetylglycineamide) were also evaluated as safe­ners for acetochlor {N-(2-ethyl-6-methylphenyl)-N-(ethoxymethyl)chloroacetamide} in maize seedlings. Both BAS-145138 and dichlormid were highly effective as safeners for metazachlor and BAS-145138 and DKA-24 were equally good safeners for acetochlor. Metazachlor and acetochlor uptake and metabolism by maize seedlings were enhanced sig­nificantly in response to treatment with every safener examined. Rates of metazachlor and acetochlor uptake and metabolism were greatest in seedlings treated with BAS-145138 -the most effective safener. In the absence of any safener treatment, the non-enzymatic conjugation of the herbicides with glutathione either exceeded (metazachlor) or was similar (acetochlor) to enzymatic conjugation. However, the rate of enzymatic conjugation was generally increased by safener treat­ ment. This was particularly true when the herbicide (14C-labeled) was employed as a conjuga­tion substrate instead of the less specific substrate, CDNB (1-chloro-2,4-dinitrobenzene). A significant linear correlation was observed between safener effectiveness and rates of metazachlor metabolism or glutathione S-transferase activity in maize seedlings. However, a similar correlation could not be established for the five compounds evaluated as safeners for acetochlor.

Lipid Biosynthesis Inhibitors

Five classes of herbicides (carbamothioates, chloroacetamides, substituted pyridazinones, cyclohexanediones, and aryloxyphenoxypropionic acids) have been reported to inhibit lipid biosynthesis in higher plants. Carbamothioates impair the synthesis of surface lipids (waxes, cutin, suberin). These effects have been attributed to the ability of this herbicide class to inhibit one or more acyl-CoA elongases. Though as yet poorly characterized, these enzymes are associated with the endoplasmic reticulum and catalyze the condensation of malonyl-CoA with fatty acid acyl-CoA substrates to form very long-chain fatty acids used in the synthesis of surface lipids. There is contradictory evidence regarding the effects of chloroacetamide herbicides on de novo fatty acid biosynthesis. Selected substituted pyridazinones decrease the degree of unsaturation of plastidic galactolipids. This effect is attributed to the ability of selected members of this herbicide class to inhibit fatty acid desaturases which are thought to be located in the chloroplast envelope. Aryloxyphenoxypropionic acid and cyclohexanedione herbicides inhibit de novo fatty acid biosynthesis in grasses. The target site for these herbicide classes is the enzyme acetyl-CoA carboxylase which is found in the stroma of plastids. In most cases, selectivity between grasses and dicots is expressed at this site. Aryloxyphenoxypropionic acids and cyclohexanediones are reversible, linear, noncompetitive inhibitors of acetyl-CoA carboxylase from grasses. Both classes are also mutually exclusive inhibitors of grass acetyl-CoA carboxylase which suggests that they bind at a common domain on the enzyme.

One-Step Hydroamidation of a Schiff Base with Trichlorosilane

Abstract We have found that the treatment of a Schiff base (2) with trichlorosilane and chloroacetyl chloride results in a highly active chloroacetamide herbicide (1) in an excellent yield. This one-step hydroamidation reaction of a Schiff base is a useful synthetic method.

Persistence of Selected Pesticides in Ground‐Water Samples

AbstractThis study was conducted to determine the stability of five commonly used herbicides fortified into freshly collected ground water. No aquifer materials were present. Ground‐water samples obtained from three sites in eastern Arkansas were fortified with an aqueous mixture containing either the chloroacetamide herbicides, alachlor, metolachlor, and propanil, or the phenoxy herbicides, 2,4‐D and dichlorprop. Experiments were conducted at tempersitures comparable to Arkansas' extreme ground‐water temperatures, 15 and 22° C, and at initial concentrations of 1 and 5 μg/1. Degradation occurring for each herbicide was determined at two‐month intervals, for a period of 18 months.Results indicated that degradation did not begin immediately, but generally required a lag period of several months. Of the five herbicides studied, propanil degraded the fastest and to the greatest extent. After eight months, 44% to 69% of propanil at the lower fortification level and 85% to 99% at the higher level had degraded, The remaining four herbicides exhibited little or no degradation at the lower concentration during the first 12 months. By 18 months, however, significant degradation of each herbicide had occurred. Degradation generally occurred earlier for each herbicide at the higher fortification level. With the exception of 2,4‐D, a higher percentage of herbicide was broken down at the greater fortification level. Degradation was more extensive at the elevated storage temperature. In general, the degradation rate was faster in ground water taken from shallower depths. Zero‐order rate constants and half‐lives are presented. Half‐lives, including lag periods, ranged from 196 to 1907 days.

Development of an Enzyme Immunoassay for the Determination of Metazachlor

Abstract A sensitive, solid phase microtitre plate enzyme immunoassay (ELISA) was developed for the determination of the herbicide metazachlor, which belongs to the class of α-chloroacetamides. The antisera were raised in rabbits by immunization with a metazachlor-BSA conjugate containing 27 metazachlor residues per molecule. A competitive ELISA with a peroxidase-metazachlor tracer was performed. Metazachlor could be detected within the range of 0.01 and 1 μg/I. The test showed no cross-reactivity with other structurally similar chloroacetamide herbicides and little cross-reactivity with derivatives of metazachlor.

Further effects of chloroacetamides and evidence for inhibition of acetylation of DNA-associated protein

By short-term experiments the incorporation of [ 14C]acetate was followed into fatty acids and into a nucleic-acid fraction using Scenedesmus acutus. The content of labeled fatty-acid species was strongly influenced by alachlor or metazachlor. Linolenic acid decreased while oleic acid increased, which could not be shown with the substituted pyridazinone BAS 13–338. Acetate uptake was inhibited by the chloroacetamides but not by the pyridazinone, while labeling of the fatty acids formed was reduced with the pyridazinone and not with the chloroacetamides present. Chloroacetamides, however, inhibited acetate labeling of a nucleic-acid fraction. Using agarose-gel separation of this nucleic-acid fraction the radioactivity was found in a band containing DNA and protein, and no label was detected in either the DNA or the RNA bands. Presumably, the site of inhibition of acetate incorporation into the nucleic-acid fraction is at the level of a DNA-associated protein (histones). Chloroacetamides influenced neither the uptake of labeled lysine into the cells nor its incorporation into the DNA-associated protein fraction. Apparently, the chloroacetamide herbicides as exemplified here with metazachlor and alachlor have at least three modes of action: (1) decreasing the uptake of acetate; (2) modification of the fatty acid profile; (3) inhibition of acetate labeling of chromatin.

Synthesis and Herbicidal Activity of N-(1-Arylethenyl)-2-chloroacetamides.

N-(1-Alkenyl)-2-chIoroacetamides, which bear an aryl substituent at the 1-position of the alkenyl moiety, were synthesized and their herbicidal activities were tested. Some of them were active against paddy field weeds. In particular, a new type of chloroacetamide herbicide, 2-chloro-N-methyl-N-(2-methyl-1-phenylpropen-1-yl)acetamide, having no 2,6-dialkyl substituted phenyl moiety, which has been considered essential for activity, was found to be active against barnyardgrass.

Lactofen Systems for Broadleaf Weed Control in Peanuts (Arachis hypogaea)

Weed management systems using a chloroacetamide herbicide applied preplant incorporated (PPI) and at cracking (AC) plus lactofen applied AC and early postemergence (POST) controlled at least 98% of common lambsquarters. Similar systems using a chloroacetamide herbicide applied PPI and early POST plus lactofen applied early POST and postemergence (POST) controlled less than 70% of common lambsquarters. All sequential lactofen systems controlled common ragweed completely and at least 86% of morningglory species. Highest peanut yields and net returns were obtained with weed management systems consisting of sequential applications of lactofen applied AC and early POST, or systems that used acifluorfen plus bentazon POST, or lactofen plus bentazon applied early POST or POST.