Age-related mechanisms of propanil tolerance in Jungle-rice,Echinochloa colona

Uptake and metabolism of propanil were measured in both susceptible (S) and resistant (R) biotypes of Jungle-rice, Echinochloa colona (L.) link at different growth stages. Results showed that there was no significant difference in uptake between S and R biotypes of E. colona at any given growth stage, but that uptake was significantly reduced at older plant growth stages in all biotypes studied. Metabolism of propanil was more rapid in R biotypes than in S biotypes at all growth stages studied. Specific and total aryl acylamidase activity, responsible for the first stage of propanil metabolism, was higher in R biotypes than in S at all growth stages, but declined to about 50% of the maximum at older growth stages, confirming the importance of this enzyme in conferring resistance to this herbicide. The area of necrosis that developed around a single drop of propanil deposited on the adaxial leaf surface was used to assess the degree of propanil resistance; it was found that resistance increased at older E. colona growth stages in contrast to the rate of propanil metabolism and amidase activity. Treatment of leaves with the amidase inhibitors, carbaryl or piperophos, simultaneously with propanil, caused a decrease in resistance at growth stages where amidase activity was greatest. This treatment was less effective at older growth stages. These results show that, in E. colona, propanil metabolism is important for conferring resistance in younger plants (four-six-leaf stage). It is suggested that restricted uptake confers resistance in older plants.     

Association between elevated activity of aryl acylamidase and propanil resistance in Jungle-rice,Echinochloa colona

Aryl acylamidase (aryl-acylamine amidohydrolase, EC 3.5.1.13) activity has been measured in crude extracts from leaves of propanil-susceptible (S) and propanil-resistant (R) biotypes of the grass weed. Echinochloa colona (L.) Link from Columbia. Both specific and total amidase activity increased with plant age up to 15 days (four-leaf stage), then decreased beyond 20 days to about 50% of the maximum at 36 days in both R and S E. colona biotypes. Specific activity with propanil in the R biotype was about 80% of that obtained for rice (Oryza sativa L.), compared to 25% in the susceptible biotype. The specific activity of the propanil amidase was three-fold higher in the R biotype than in the S. Partially purified amidase extracts from rice and both S and R biotypes of E. colona were compared biochemically. Both rice and E. colona amidases had a pH optimum of 7.5 and native relative molecular masses, estimated by gel filtration, of 179 000 and 181 000, respectively. Out of six substrates tested, three produced appreciable activity (propanil, 4-chloroacetanilide and acetanilide) in both rice and E. colona. Michaelis constants showed that the rice amidase had a higher affinity for propanil (0.36 mM) than had the E. colona enzyme (1.1 mM). Carbamates and organo-phosphorus pesticides were shown to inhibit amidase activity in partially purified rice and E. colona extracts. Additional preliminary data have implicated peroxidase in the next step of propanil metabolism in vitro. These data demonstrate that increased aryl acylamidase activity contributes to resistance to the herbicide propanil in E. colona weeds. Also, a biochemical comparison of purified aryl acylamidases from S and R biotypes of E. colona is presented for the first time.     

Peroxidase activity and propanil degradation in soil*

The herbicide N-(3,4-dichloropxhenyl)-propionamide (propanil) and a metabolite of propanil, 3,4-dichloroaniline (DCA), were mixed with Nixon loam soil which was subjected to moisture and air-drying treatments. Degradation of propanil was altered by subjecting the treated soil samples to storage conditions of moisture, drying and chloroform. The peroxidase activity in fresh soil was very low when soil samples were collected during the cold season. The amount of 3,3′,4,4′- tetrachloroazobenzene (TCAB) produced from DCA increased with a simultaneous increase in the peroxidase activity in preincubated soil where carbon and nitrogen sources were added.     

Transformation of the herbicides propanil and chlorpropham by micro-algae

Two species of green algae and four of blue-green algae hydrolysed the acylanilide herbicide propanil to the aniline derivative, 3,4-dichloroaniline. Of the cultures tested, only the blue-green alga Anacystis nidulans was shown to be capable of converting the phenylcarbamate herbicides propham and chlorpropham to the corresponding anilines. The green alga Ulothrix fimbriata was apparently unable to hydrolyse propanil or chlorpropham.     

Propanil activity, uptake and metabolism in resistant Echinochloa spp. biotypes

Field resistance of Echinochloa spp. to propanil has been previously reported in Costa Rica, Colombia and Arkansas (USA). In this study, the mechanism of resistance was investigated in three resistant (R) and three susceptible (S) biotypes. The shoot fresh weight reduction in pot-grown plants from a post-emergence spray of propanil at 2.44 kg a.i. ha⁻¹ on biotypes R/S from Costa Rica, Colombia and Arkansas was 35/98%, 25/79% and 20/82% respectively. In vitro chlorophyll fluorescence data from leaf tissue incubated in propanil showed that photosynthesis was inhibited in all biotypes, indicating that the propanil-binding site and enzyme were not altered. After transfer to herbicide-free solution, photosynthesis recovered only in resistant biotypes, indicating that the mechanism of resistance was caused by enhanced metabolism of the herbicide. Simultaneous treatment with fenitrothion, an aryl acylamidase inhibitor, prevented the recovery of photosynthesis in leaf tissue in two resistant biotypes. In contrast, the cytochrome P450 mono-oxygenase inhibitor, 1-aminobenzotriazole, did not prevent recovery from propanil in leaf tissue. Application of ¹⁴C-propanil to the second leaf of intact Echinochloa plants showed that c . 90% of the radioactivity remained in the treated leaf for up to 72 h after application. No major differences in translocation between R and S biotype plants were found. TLC analysis of tissue extracts from the treated leaves showed substantially less radioactivity associated with propanil, present after 72 h in rice or in the three R biotypes, compared with S biotypes.     

Microbial metabolism of propanil and 3,4-dichloroaniline

A Pseudomonas sp. which grew on 4-chloroaniline as a sole source of carbon and nitrogen was able to degrade 15% of 0.05 mM [¹⁴C]3,4-dichloroaniline to ¹⁴CO₂ within 10 days in presence of 1.5 mM 4-chloroaniline. The catabolic enzymes which degraded 3,4-dichloroaniline to CO₂ were inducible by 4-chloroaniline and by 3,4-dichloroaniline. However, their activity was much lower on 3,4-dichloroaniline than on 4-chloroaniline. The strain showed no significant growth on 3,4-dichloroaniline as a sole source of carbon and nitrogen. Soils supplemented with [ring-¹⁴C]propanil and the Pseudomonas sp. evolved 25–50% ¹⁴CO₂ within 5 days. The ¹⁴CO₂ evolution remained below 1% in absence of the Pseudomonas sp.     

Resistance Mechanism of Propanil-Resistant Barnyardgrass: II. In-vivo Metabolism of the Propanil Molecule

Propanil-resistant barnyardgrass populations, previously verified in Arkansas rice fields and in greenhouse tests, were examined in the laboratory to ascertain if the resistance mechanism in this weed biotype was herbicide metabolism. Propanil-resistant barnyardgrass was controlled >95% in the greenhouse when carbaryl (an aryl acylamidase inhibitor) was applied two days prior to propanil. Laboratory studies with ¹⁴C-radiolabelled propanil indicated that the herbicide was hydrolysed in propanil-resistant barnyardgrass and rice to form 3,4-dichloroaniline, but no detectable hydrolysis occurred in susceptible barnyardgrass. Two additional polar metabolites were detected in propanil-resistant barnyardgrass and rice and tentatively identified by thin layer chromatography. Overall, metabolites in the resistant barnyardgrass had R_f values similar to those in rice, indicating similar metabolism for both species. These data, coupled with data from a previous report on the resistant biotype showing no differential absorption/translocation or molecular modification of the herbicide binding site in the resistant biotype, indicate that the resistance mechanism is metabolic degradation of propanil. © of SCI.     

Survey and Assessment of the Natural Enemies of Water Hyacinth,Eichhornia crassipes

Abstract

In northern Queensland, the addition of 2,4,5‐T butyl ester was found to be unnecessary to maintain the control of Echinochloa colona (L.) Link and Cyperus Iria L. In dry seeded rice when propanil rates were reduced below the registered rate of 4 kg a.i. ha^?1. Adequate weed control was obtained with 1.3 kg a.i. ha^?1 propanil alone. No adverse effects on rice yield were found with any of the propanil × 2,4,5‐T treatments. Low rates of propanil, 1.3 and 0.72 kg a.i. ha^?1, compared favourably with pre‐emergence treatments of thiobencarb, butachlor, oxyfluorfen and pretilachlor (plus a safener) when weed yields were low. Where water management was poor and Ischaemum rugosum Salisb. was the dominant weed, oxyfluorfen applied pre‐emergence at 0.96 kg a.i. ha^?1 produced a higher rice and a lower weed yield than the low rates of propanil. In three of the five experiments, weed growth was insufficient to depress rice yields significantly.     

Metabolism of the pesticide metabolites 4-nitrophenol and 3,4-dichloroaniline in carrot (Daucus carota) cell suspension cultures

The metabolism of [ 14 C]-4-nitrophenol and [ 14 C]-3,4-dichloroaniline (the xenobiotics are degradation products of parathion and propanil, respectively) was studied in cell suspension cultures of carrot (Daucus carota L.). 4-Nitrophenol was transformed almost quantitatively to water-soluble conjugates with minor amounts of non-extractable residues. The conjugates identified were 1-(O-β-D-glucopyranosyl)-4-nitrobenzene and 1-(6′-O-malonyl-O-β-D-glucopyranosyl)-4-nitrobenzene. In addition, two unidentified metabolites were observed, possibly a disaccharide and another malonylated glycoside of 4-nitrophenol. Time-course studies demonstrated that 4-nitrophenol was rapidly taken up and conjugated; all metabolites remained associated with the cells rather than nutrient medium. 3,4-Dichloroaniline was transformed quantitatively to water-soluble conjugates and bound residues (3.6%). The water-soluble metabolites were identified as 6′-O-malonyl-N-(β-D-glucopyranosyl)-3,4-dichloroaniline, N-(β-D-glucopyranosyl)-3,4-dichloroaniline and N-malonyl-3,4-dichloroaniline. A time-course study showed that the glucosides were formed initially, then decreased, possibly due to hydrolysis. This decrease was paralleled by an increase of the main metabolite, N-malonyl-3,4-dichloroaniline, which was predominantly recovered from the medium.     

The role of pendimethalin in the integrated management of propanil-resistant Echinochloa colona in Central America

Pre-emergence activity of pendimethalin on propanil-resistant jungle rice (Echinochloa colona) was demonstrated in glasshouse trials. Both susceptible and resistant populations, collected from Costa Rica, were controlled by 1·25 kg ha^-1, the usual application rate used in the field where Rottboellia cochinchinensis is also a problem. When applied post-emergence, propanil performance was improved by the addition of low doses of pendimethalin to the herbicide mixture. A propanil-resistant selection was controlled by 0·23 kg ha^-1 pendi-methalin+0·54 kg ha^-1 propanil at the one-to-two leaf stage, and 0·23 kg ha^-1 pendimethalin+1·08 kg propanil at the three-to-four leaf stage compared to 1·08 kg and 2·16 kg ha^-1 respectively when propanil was applied alone. This suggests that pendimethalin improves post-emergence control in the field compared to the standard propanil treatment and can provide residual pre-emergence control of late-germinating individuals, so reducing the propanil selection pressure. For effective jungle rice control, growers apply propanil (3·84 kg ha^-1) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop-P-ethyl (0·045 kg ha^-1) at 35 DAP. Field experiments, conducted in dry-seeded upland rice in southern Costa Rica, demonstrated that under high jungle-rice population pressure, one application of pendimethalin at 1·5 kg ha^-1 provided an effective replacement for propanil, resulting in reduced weed-control costs. ©1997 SCI     

Resistance mechanism of Leptochloa chinensis Nees to propanil

The resistance mechanism of Leptochloa chinensis Nees to propanil was investigated, based on propanil metabolism, aryl acylamidase activity, and chlorophyll fluorescence at the 8 week growth stage of L. chinensis. The concentration of propanil in the leaf and culm extracts of the resistant (R) and susceptible (S) biotypes, as measured by gas chromatography (GC), was found to increase after propanil treatment. The concentration of propanil in the leaf and culm extracts of the S biotype at 72 h was 1.55 and 0.49 µg mL^?1, respectively. However, a lower concentration of propanil was observed in the R biotype, as compared to that in the S biotype. The residue of 3,4‐dichloroaniline, as measured by GC, was detected only in the leaf extracts of the R biotype. In contrast, no residue of 3,4‐dichloroaniline was observed in the S biotype. The level of aryl acylamidase in the leaf tissue extracts of the R biotype was ～140% higher than that in the S biotype. The fluorescence studies showed that propanil inhibited the quantum efficiency of the photosystem II in both the R and S biotypes after 2 h of incubation time. However, when the leaf disks were transferred and incubated in deionized water for 48 h, the quantum efficiency increased in the R biotype but decreased in the S biotype. These results suggest that propanil metabolism, enhanced by aryl acylamidase activity, is the most likely factor contributing towards the mechanism of propanil resistance in L. chinensis plants at the 8 week growth stage.     

Mechanism of resistance to bensulfuron-methyl in Alisma plantago-aquatica biotypes from Portuguese rice paddy fields

Two Alisma plantago‐aquatica biotypes resistant to bensulfuron‐methyl were detected in rice paddy fields in Portugal’s Mondego (biotype T) and Tagus and Sorraia (biotype Q) River valleys. The fields had been treated with bensulfuron‐methyl‐based herbicide mixtures for 4–6 years. In order to characterize the resistant (R) biotypes, dose–response experiments, absorption and translocation assays, metabolism studies and acetolactate synthase (ALS) activity assays were performed. There were marked differences between R and susceptible (S) biotypes, with a resistance index (ED₅₀R/S) of 500 and 6.25 for biotypes Q and T respectively. Cross‐resistance to azimsulfuron, cinosulfuron and ethoxysulfuron, but not to metsulfuron‐methyl, imazethapyr, bentazone, propanil and MCPA was demonstrated. No differences in the absorption and translocation of ¹⁴C‐bensulfuron‐methyl were found between the biotypes studied. Maximum absorption attained 1.12, 2.02 and 2.56 nmol g⁻¹ dry weight after 96 h incubation with herbicide, for S, Q and T biotypes respectively. Most of the radioactivity taken up by the roots was translocated to shoots. Bensulfuron‐methyl metabolism in shoots was similar in all biotypes. The R biotypes displayed a higher level of ALS activity than the S biotype, both in the presence and absence of herbicide and the resistance indices (IC₅₀R/S) were 20 197 and 10 for biotypes Q and T respectively. These data confirm for the first time that resistance to bensulfuron‐methyl in A. plantago‐aquatica is target‐site‐based. In practice, to control target site R biotypes, it would be preferable to use mixtures of ALS inhibitors with herbicides with other modes of action.     

Synergism of diazinon toxicity and inhibition of diazinon metabolism in the house fly by tridiphane: Inhibition of glutathione S-transferase activity

Diazinon toxicity to a susceptible strain of house fly (Musca domestica L.) was synergized by tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane], a herbicide synergist. Both diazinon and tridiphane were partially metabolized in the house fly by glutathione (GSH) conjugation. Synergism appeared to be due to inhibition of diazinon metabolism/detoxification. Crude glutathione S-transferase (GST) preparations from the house fly catalyzed GSH conjugation of diazinon, tridiphane, 3,4-dichloronitrobenzene (DCNB), and chloro-2,4-dinitrobenzene (CDNB). Tridiphane and the GSH conjugate of tridiphane appeared to inhibit diazinon GSH conjugation, but diazinon did not inhibit tridiphane GSH conjugation. The enzymatic rate of tridiphane GSH conjugation was 22 times the rate of diazinon GSH conjugation; therefore, attempts to assay tridiphane as an inhibitor of diazinon GSH conjugation were inconclusive because of the high concentration of tridiphane GSH conjugate produced during the assay. CDNB underwent enzymatic GSH conjugation at a rate 240 times faster than that of tridiphane and 5000 times faster than that of diazinon. GSH conjugation of CDNB was not inhibited by tridiphane, but was inhibited by the GSH conjugate of tridiphane. In vivo, the GSH conjugate of tridiphane was produced in sufficient concentration to cause the observed inhibition of diazinon metabolism and synergism of diazinon toxicity. However, the possibility that parent tridiphane caused or contributed to the inhibition of diazinon metabolism and synergism of diazinon toxicity could not be excluded. Inhibition of diazinon metabolism did not appear to be due to depletion of either GSH or GST.     

Herbicide‐resistant weeds in the Philippines: Status and resistance mechanisms

Two major weeds in rice in the Philippines, Sphenochlea zeylanica Gaertn. and Echinochloa crus‐galli (L.) Beauv., are controlled with chemical and cultural methods. In the 1980s, after >10 years of continuous use of 2,4‐D, S. zeylanica evolved resistance to the chemical in those rice fields that had been treated with 2,4‐D once or twice every cropping season. In the 1990s, E. crus‐galli evolved resistance to butachlor and propanil in rice monocrop areas where both herbicides were used continuously for 7–9 years. Rice farmers continue to use 2,4‐D, butachlor and propanil extensively and are often unaware of herbicide resistance or the potential for cross‐resistance, its causes or its implications. In order to control herbicide‐resistant E. crus‐galli, farmers are shifting to locally available herbicides with different modes of action, such as bispyribac, an acetolactate synthase inhibitor, and cyhalofop, an acetyl coenzyme A carboxylase inhibitor. Follow‐up manual weeding or rotary weeding after herbicide spraying, a common farmers’ practice, removes the susceptible and resistant biotypes and could help to delay or prevent the evolution of resistance. Although the resistance mechanisms of both weeds are not determined yet, they could be related to enhanced degradation that is similar to the mechanisms that are shown by the resistant biotypes in other countries.     

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] an atrazine synergist: Enzymatic conversion to a potent glutathione S-transferase inhibitor

Glutathione S-transferases (GST) from corn, giant foxtail, onion, pea, house fly, and equine liver catalyzed conjugation of tridiphane with glutathione (GSH). The conjugate was characterized by soft ionization mass spectral methods. Tridiphane and the GSH conjugate of tridiphane both inhibited GSH conjugation of atrazine in vitro (corn and giant foxtail). Tridiphane did not inhibit GSH conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) in corn or giant foxtail; however, the GSH conjugate of tridiphane was a competitive inhibitor with respect to GSH and was four times more effective with extracts from giant foxtail (K_i = 2 μM) than from corn (K_i = 8 μM). The GSH conjugate of tridiphane inhibited a variety of GST enzymes with several different substrates. When compared to other inhibitors of GST, only triphenyl tin chloride was more effective than the GSH conjugate of tridiphane in inhibition of GST from giant foxtail. Both GST and GSH decreased in corn and increased in giant foxtail as tissues matured. The catabolism of the GSH conjugate of tridiphane was compared in crude enzyme systems from corn, giant foxtail, and onion. The rate of catabolism was much greater in extracts from corn leaves than from giant foxtail leaves. Inhibition of GSH conjugation of CDNB was reversed as the GSH conjugate of tridiphane was catabolized. The possibility that synergism of atrazine toxicity by tridiphane is mediated by conversion of tridiphane to a GSH conjugate is discussed in relationship to the relative rates of GSH conjugation of tridiphane and atrazine, concentrations of GSH, K_i values, tissue age, and stability of the conjugate in different tissues.     

Properties of an Aspergillus nidulans propanil hydrolase

Aspergillus nidulans is able to hydrolyze the herbicide propanil (3′,4′-dichloropropionanilide) with liberation of 3′,4′-dichloroaniline. When the fungus is grown with or without propanil, the hydrolytic activity is identical, but can be increased by starving the mycelium either for carbon, nitrogen, or both carbon and nitrogen. The enzyme which is responsible of this activity is of the aryl acylamidase type (EC 3.5.1 aryl acylamine amidohydrolase). It is also active on propionanilide and acetanilide, two structural analogs of propanil. A value of K_m = 0.13 mM has been obtained for propanil. Temperature optimum is 40°C, when assayed with propanil as substrate. Although the pH optimum is 8, there is a relatively high enzyme activity over a wide range of pH values between 7.8 and 10.2. Carbaryl has been found to effectively inhibit the enzyme activity on propanil (K_i = 0.03 mM). The results indicated that the properties of this aryl acylamidase from A. nidulans are very similar to those of enzymes isolated from a variety of organisms such as rice, mammals and the fungus Fusarium solani.     

The degradation of the herbicide benzoylprop-ethyl following its application to wheat

The herbicide benzoylprop-ethyl [SUFFIX,^a ethyl (±)-2-(N-benzoyl-N-3,4-di-chloroanilino) propionate] has been applied in a radiolabelled form to spring wheat and winter wheat growing both indoors and outdoors. During the application the compound also fell onto the soil. The plants and corresponding soils were examined at harvest at 71-98 days from treatment. Conversion of the herbicide occurred in plants and soil predominantly by a hydrolytic reaction to form benzoylprop^b followed in plants by its conjugation with sugars. Small amounts of N-benzoyl-3,4-dichloroaniline and benzoic acid were also detected in plants. There was no evidence for the presence of 3,4-dichloroaniline in the crops or soils nor was there evidence for 3,4,3′,4′-tetra-chloroazobenzene which has been implicated as a degradation product of some 3,4-dichloroaniline herbicides in soils. Residues on plants were greatest in the straw and consisted mainly of benzoylprop-ethyl and benzoylprop in free and conjugated forms. There was no evidence for appreciable movement of the compound within the plant from the treated foliage. Residues were particularly low in the grain and were not detected in the crop grown outdoors (limit of detectability 0.01 mg/kg). Residues in the soils were mainly in the 0-7.5 cm layer and there was no evidence for leaching below 15 cm.     

Resistance to paraquat in Mazus pumilus

Mazus pumilus is an annual self‐pollinating weed that is commonly found in arable land, vegetable gardens and roadsides. This weed harbours insects and pathogens that attack vegetables. The mechanism of resistance to paraquat of M. pumilus found in Ohita, Japan, was studied. Whole plant bioassays revealed that the resistant (R) biotypes were four to six times less susceptible than controls. Chlorophyll destruction of leaf discs by paraquat treatment in R biotypes was 4–20 times lower than those of susceptible (S) biotypes. Ferric reducing antioxidant power (FRAP) values in R biotypes were higher than those of S biotypes before and after paraquat treatments. The activity of superoxide dismutase (SOD) was also higher in R biotypes than those of S biotypes before and after treatment with paraquat, but the activities of ascorbate peroxidase (APX) and catalase (CAT) were not different between R and S biotypes. Change of ascorbate (AsA) contents before and after paraquat treatment was equivalent in both biotypes. These results indicate that the increased SOD activity and antioxidant capacity in R biotypes contribute to the resistance to paraquat of M. pumilus.     

Propanil metabolism in rice: A comparison of propanil amidase activities in rice plants and callus cultures

Propanil amidase is an enzyme found in rice, which hydrolyzes the herbicide 3,4-dichloropropionanilide, propanil. The activity of the enzyme as measured in rice plants was found to be two to four times greater in plants with four leaves than in plants with fewer than four leaves. The higher amidase activity of the four-leaf plants was localized in the unexpanded leaves.Rice root callus suspension in cultures also demonstrated propanil amidase activity. In vivo experiments indicated that the herbicide was metabolized by the tissue culture. Propanil amidase activity as determined in vitro, however, was detected only after the culture had developed to late stationary phase.     

Degradation of the herbicide benzoylprop-ethyl in soil

The degradation of [¹⁴C] benzoyl prop ethyl (SUFFIX,^a ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate) in four soils has been studied under laboratory conditions. The major degradation product of benzoylprop ethyl at up to 4 months after treatment was its corresponding carboxylic acid (II). On further storage this compound became firmly bound to soil before it underwent a slow debenzoylation process which led to the formation of a number of products including N-3,4-dichlorophenylalanine (IV), benzoic acid, 3,4-dichloroaniline (DCA), which was mainly present complexed with humic acids, and other polar products. Although these polar products were not identified, they were probably degradation products of DCA, since they were also formed when DCA was added to soil. No 3,3′,4,4′-tetrachloroazobenzene (TCAB) was detected in any of the soils at limits of detectability ranging from 0.01-0.001 parts/million. Since N-3,4-dichlorophenylalanine (IV) and 3,4-dichloroaniline were transient degradation products of benzoylprop ethyl, the metabolism in soil of radiolabelled samples of these compounds was also studied. In these laboratory experiments the persistence of the herbicide increased as the organic matter content of the soil increased and the time for depletion of half of the applied benzoylprop ethyl varied from 1 week in sandy loam and clay loam soils to 12 weeks in a peat soil.