Physiological effects of methyl 2-[4(2,4-dichlorophenoxy)phenoxy] propanoate on oat,wild oat,and wheat

Methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]propanoate (dichlofop-methyl) is a selective herbicide for wild oat (Avena fatua L.) control in wheat (Triticum aestivum L.). Dichlofop-methyl inhibited IAA-stimulated elongation of oat and wheat coleoptile segments by 51 and 13%, respectively, at 10 μM concentrations. Dichlofop-methyl alone had no auxin activity at concentrations of 0.1, 1.0, and 10 μM. The inhibitory effect of dichlofop-methyl was overcome partially by increasing the IAA concentration or by application of 3,6-dichloro-o-anisic acid (dicamba), a herbicide with weak auxin activity. The de-esterified free acid metabolite, 2-[4-(2,4-dichlorophenoxy)phenoxy]-propionic acid (dichlofop), at 10 μM inhibited auxin-stimulated oat coleoptile elongation by 23%, but it did not affect wheat coleoptile elongation at the same concentration. Both dichlofop-methyl and dichlofop inhibited root growth in excised shoots and seedlings of wild oat but had no effect on wheat. Dichlofop was a more effective inhibitor of root growth than dichlofop-methyl. The results suggest that dichlofop-methyl functions as a strong auxin antagonist, while the metabolite, dichlofop, inhibits root growth and development by another mechanism. The herbicidal effect of dichlofop-methyl may be the net effect of two biologically active forms of the compound each with a different mode of action acting at different sites within a susceptible plant.     

Analysis of soils for diclofop-methyl and diclofop

A method is described for the analysis of soils for residues of the herbicide diclofop-methyl, methyl (RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionate, and its breakdown product diclofop, (RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid. Diclofop-methyl undergoes hydrolysis in the soil to diclofop, which also has herbicidal activity. A procedure, using a 1% phosphoric acid solution for extraction purposes, has been developed and gives good recoveries of both diclofop-methyl and diclofop at the 0.5 and 0.05 mg kg^?1 levels. After methylation, gas-liquid chromatography with electron-capture detection is used to determine total residue concentrations.     

In vitro sensitivity of wheat and oat mitochondria to the selective herbicide,diclofop-methyl

Compared to diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate), diclofop (the demethylated derivative) was a more potent inhibitor of polarographically monitored state 3 respiration of mitochondrial preparations isolated from shoots of dark-grown wheat (Triticum aestivum L. cv. Neepawa) and oat (Avena sativa L. cv. Terra) seedlings. Wheat and oat mitochondria demonstrated essentially similar concentration-response patterns for the uncoupler-like stimulation of state 4 respiration and the inhibition of state 3 respiration by diclofop, thereby intimating that differential mitochondrial sensitivity was not a selectivity factor between these species. Diclofop suppression of unconstrained oxygen utilization elicited by the respiratory uncoupler FCCP indicated that inhibition of state 3 respiration involved interference with some site(s) on the mitochondrial electron transport chain and not with energy transfer directly. Cytochrome c oxidase activity was not affected by diclofop, but succinate- and malate-PMS oxidoreductase activities were inhibited by diclofop. Enhanced rates of passive mitochondrial swelling in isotonic KCl medium in the presence of diclofop pointed to a direct influence on the permeability properties of the inner mitochondrial membrane and indicated that membrane disruption could have been a factor in the effects elicited by diclofop on mitochondrial respiration. However, it does not appear that specific interference with mitochondrial functionality is the primary mechanism of phytotoxicity in susceptible plants.     

Catalytic hydrolysis of diclofop-methyl on Ca-, Na- and K-montmorillonites

The decomposition of the herbicide diclofop-methyl (methyl (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionate), on homoionic Ca-, Na- and K-montmorillonite in hydroalcoholic suspension was investigated. The results show that the solvolysis of the pesticide affords two products: diclofop (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid) and diclofop-ethyl (ethyl (RS)-2-(4-(22,4-dichlorophenoxy)phenoxy)propionate). The former is always the main product of hydrolysis on the Ca-, Na- and K-clays, whereas the latter, arising from a transesterification reaction, is favoured only by the presence of Ca-and Na-clays. The solvolysis reaction follows the adsorption of the herbicide on the clay, as evidenced by the shift of the IR stretching value of the ester group of the molecule, depending on the polarising power of the saturating ions.     

Interaction between diclofop-methyl and 2,4-D in wild oat (Avena fatua L.) and cultivated oat (Avena sativa L.), and fate of diclofop-methyl in cultivated oat

Influence of 2,4-D on toxicity of diclofop-methyl to Avena sativa (cv. Selma) and Arena fatua at 2·5 leaf stage has been evaluated under controlled conditions. Effects of 2,4-D on the fate of diclofop-methyl in cultivated oat have also been studied. Mixture with 2,4-D reduced the toxicity of diclofop-methyl to both species. When applied immediately after diclofop-methyl treatment, 2,4-D still reduced herbicide toxicity to wild oat. This reduction was smaller in cultivated oat. and was only observed at higher phytotoxicity. No interaction was observed when a 10-day period separated the two applications. In mixture, 2,4-D enhanced diclofop-methyl penetration and diclofop acid conjugation in cultivated oat, and it slightly increased conjugation when applied separately. None of these effects clearly explain the reduction of diclofop-methyl toxicity by 2, 4-D in cultivated oat. Other processes are possibly involved and could be connected with the site of action of diclofop-methyl.     

A root bioassay procedure for the determination of chlorsulfuron, diclofop acid and sethoxydim residues in soils

Measurement of the root lengths of pre-ger-minated oat seedlings (Avena sativa L. var. Sioux) grown in the dark in treated soils was used to assay residues of diclofop acid (2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate) and sethoxydim (2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propy]-3-hydroxy-2-cyclohexene-1-one). Similar measurements involving maize seedlings (Zea Mays L. var. Sunny Vee) were also used to determine residues of the herbicide chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbony]benzenesulfonamide) in soils. The procedure appeared to be reproducible with residues of chlorsulfuron, diclofop acid and sethoxydim being detectable at amounts of 0.001, 0.2 and 0.05 μg g^?1 respectively.     

Comparison of physiological effects of fluazifop-butyl and sethoxydim on oat (Avena sativa L.)

Laboratory experiments were conducted to compare the physiological effects of two herbicides: fluazifop-butyl {butyl ( RS )-2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy]-propionate} and sethoxydim {(±)-2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on oat ( Avena sativa L. cv. Zenshin). The herbicides strongly inhibited growth of oat and induced chlorosis at the basal part of shoots and ethylene production from the seedlings. The phytotoxicity of these herbicides in oat seedlings was alleviated by 2,4-D (2,4-dichlorophenoxyacetic acid), but not by IAA (indole-3-acetic acid). Coleoptile elongation induced by 2,4-D or IAA was inhibited by fluazifop-butyl and sethoxydim, suggesting both herbicides possess the activity to inhibit this auxin action. Fluazifop (free acid) and sethoxydim inhibited proton excretion from oat roots but fluazifop-butyl did not. This proton excretion was not restored by 2,4-D or IAA. Furthermore, cellular electrolyte leakage in oat shoots was increased by both herbicides, indicating that the membrane permeability was increased. We conclude that fluazifop-butyl and sethoxydim may have the same mechanism of action which leads to disruption of membrane integrity, although fluazifop-butyl acts as a free acid after hydrolysis (fluazifop).     

Degradation of the herbicide [14C]-diclofop-methyl in soil under different conditions

The degradation of the herbicide diclofop-methyl, ( ± )-methyl 2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate, was investigated in two agricultural soils under aerobic and anaerobic conditions. Using two differently labelled forms of [¹⁴C]-diclofop-methyl the qualitative as well as the quantitative formation of extractable metabolites was followed for 64 days. The mineralisation of the uniformly labelled aromatic rings was pursued by monitoring the ¹⁴CO₂ generated for 25 weeks. As a first step of the degradation a very rapid hydrolysis of the ester bond was detected under all conditions. Diclofop, the corresponding substituted propionic acid formed, was extensively degraded under aerobic conditions, the final product being ¹⁴CO₂. As an intermediate, a compound later identified by GLC/MS to be 4-(2,4-dichlorophenoxy)phenol, was found in the extracts. Furthermore, traces of six other unknown metabolites were detected. Under anaerobic conditions the degradation proceeded to a small extent. At most 3% of the applied radioactivity was accounted for by the degradation product 4-(2,4-dichlorophenoxy)phenol. No other metabolite, including ¹⁴CO₂, was observed, implying lack of any further degradation.     

The response of resistant and susceptible plants to diclofop-methyl

Wild oat (Avena fatua L.) plants sprayed at the 2-or 3-leaf stages of growth with diclotop-methyl developed chlorosis over the entire leaf blade of all leaves. The leaves became necfrotic ⁷days after spraying Shool growth was inhibited. In wheat (Triticum aesicum L cv.Waldron) discrete chlorotic areas developed only where the herbicide convicted the 2nd or 3rd leaf with no visible injury so new growth uf'ter treutment. Growth inhibition of susceptible oat (Avena sativa L. cv. Garry) was sensitive to placement of diclutop-methyl near the upica and meristematic sites of the plant. Chlorosis and necrosis were independent of herbicide placement. Selective herbicide placement induced chlorosis only or both chlorosis and growth inhibition Root growth in wild oat and barley (Hordeum rulgare L. cv. Dickson) was strongly inhibited by 1–0 μM diclofop-methyl. Wild oat shoots were killed when seedlings were root-treated with 10 μM diclofop-melhyl. The 100 μM rool treatment killed barley shoots but only stunted the growth of wheat shoots by approximately 50%. In root-ireated wheat plants the shoots were turgid and developed a light purple colour, whereas in foliar-treated plants the shoots developed discrete chlorotic areas.     

Selectivity and mode of action of ethyl (±)-2-(N-benzoyl-3,4-dichloroamiino)propionate in the control of Arena fatua in cereals

The activity of foliar applications of ethyl (±)-2-(N-benzoyl-3,4-dichloroanilino)—propionate(benzoylprop-ethyl)to oat was dependent upon its degradation to the biologically active acid (benzoylprop). The acid, unlike benzoylprop-ethyl, showed some movement via the phloem from the foliage to the stem where it inhibited stem elongation through an effect on cell expansion. The resulting stunted wild plants oat were unable to compete successfully with the cereal crop. Selectivity of the herbicide was dependent on its relative rate of de-esterification, and the subsequent detoxication of the acid to inactive conjugates. De-esterification was fastest in oat and slowest in wheat. The rate of detoxication in wheat prevented the accumulation of the acid to phytotoxic levels but in oat, although the rate of detoxication was higher, it failed to prevent the occurrence of phytotoxic levels of benzoylprop. In barley de-esterification was slower than in oat, and detoxication again failed to prevent some accumulation of the acid.     

β-Oxidation of certain growth regulators by plant tissues

The growth-regulating activity and metabolism, in pea and wheat tissues, of y-(chloro-phenoxy)-, y-(2,4-dichlorophenoxy)- and y-(N, N-diniethylthiocarbamoylthio)-substituted butyric, β-hydroxy-butyric, crotonic and vinylacetic acids have been investigated. With the exception of y-(2,4-dichlorophenoxy) vinylacetic acid in pea tissue, members of the two phenoxy series were degraded to the corresponding phenoxyacetic acid. Although members of the 2,4-dichlorophenoxy series were less easily metabolised, both series exhibited similar activity. Other than with the y-phenoxyvinylacetic acids, there were no appreciable differences in metabolism or growth-regulating activity between members within a series. No evidence for the metabolism of y-(2,4-dichlorophenoxy)vinylacetic acid in pea tissue was found and this acid was also less active in the pea tests. Members of the N, N-dimethyl-thiocarbamoylthio series of acids, however, were less regular in their metabolic and growth-regulating patterns. The substituted crotonic acid was inactive and unstable whilst pea tissue was found to metabolise the substituted acetic acid to inactive N-methylcarbamoylthioacetic acid. The results with all active acids fit the accepted theory of metabolism by β-oxidation.     

Compatible and antagonistic mixtures of diclofop-methyl and flamprop-methyl with herbicides used to control broad-leaved weeds

In glasshouse experiments, the addition of four ‘pyridine herbicides’ (substituted picolinic and pyridyloxyacetic acids) to either diclofop-methyl or flamprop-methyl had little effect on wild oat (Avena fatua) control. This contrasts with the serious antagonisms which occur with 2, 4-D and 2, 3, 6-TBA. With wild and cultivated oat, l'-methylheptyl (4-amino-3, 5-dichloro-6-fluoro-2-pyridyl)oxyacetate (Dowco 433) was completely compatible with diclofop-methyl and flamprop-methyl, and there was evidence that its presence improved the control of wild oats. Picloram, 3, 6-dichloropicolinic acid and triclopyr had only slight effects on phytotoxicity. The control of cleavers (Galium aparine) by picloram, triclopyr and Dowco 433 was not significantly reduced by addition of flamprop-methyl. Preliminary metabolism studies suggest that picloram does not greatly increase the rate of diclofop detoxification as do 2, 4-D and 2, 3, 6-TBA, and the observed compatibility could well be a direct consequence of this. The absence in these greenhouse experiments of serious antagonism between the pyridine herbicides and diclofop-methyl or flamprop-methyl suggests that ‘tank mixes’ of these herbicides could be used for the control of both broad-leaved weeds and wild oats.     

Interaction between difenzoquat and other herbicides for wild oat and broadleaved weed control in barley

The interaction between barban and difenzoquat was additive upon application at the two-or four-leaf stage of wild oat. Wild oat control with a mixture of barban and difenzoquat at 0.14 + 0.42kg/applied at the two-or four-leaf stage was as effective as the recommended field rate of barban alone (0.28 kg/ha) at the two-leaf or difenzoquat alone (0.84 kg/ha) at the four-leaf stage. Barley yield increases with the mixture were comparable to those obtained with the full rates of the herbicides used alone their correct leaf stages This mixture offers the farmer excellent wild oat control, an extended Leaf-stage latitude (two-to four-leaf), excellent barley yield increases and the possibility of reduced operating costs. The herbicidal activity of difenzoquat or a barban + difenzoquat mixture was reduced on addition of amine formulations but not ester formulations of herbicides for broadleaved weeds. MCPA ester and bromoxynil plus MCPA were the most compatible broadleaf herbicides when mixed with difenzoquat Difenzoquat or difenzoquat + barban significantly stimulated the activity of various herbicides on Tartary buckwheat. A mixture of burban + difenzoquat + bromoxynil-MCPA or MCPA ester provided effective wild oat and Tartary buckwheat control The latter mixtures enable a farmer to eliminate one spray operation. The interaction between difenzoquat and diclofop methyl [4-(2,4-dichlorophenoxy) phenoxy propionic acid methyl ester was additive. Wild oat control with the mixtures was good and barley yield was increased over that obtained with a recommended field rate of diclofop methyl. Interaction entre le difenzoquat et d'autres herbicides pour la lutte contre la folle acoine et les mauvaises herbes dicotylédones dans l'orge L'interaction entre le barbane et le difenzonzoquat a été additive en ce qui concerne l'application aux stades 2- et 4- feuilles de la folle-avoine. L'efficacité contre la folle avoine avec un mèlange de barbane et de difenzoquat à difenzoquat à 0.14 + 0.42 kg/ha appliqué aux stades 2 ou 4 feuilles a été aussi bonne que la dose recommandée au champ de barbane seul (0.28 kg/ha) au stade 2 feuilles ou que le difenzoquat seul (0.84 kg ha) au stade 4 feuitles. Les augmentations de rendement de l'orge avec le mélange ont été comparables employès seuls au stade correct de développement foltaire. Ce folle-avoine. une latitude de stades plus grande (2 á 4 feuilles). de substantielles augmentations de rendement pour l'orge et la possibilité de réduire le prix de revient de l'opération. L'activité herbicide du difenzoquai ou d'un mèlange barbane + difenzoquat a été réduite par l'addition de formulat ions amine mais pas avec les formulations ester des herbicides pour les mauvaises herbes dicotylédones L'ester de MCPA et le bromoxynile plus MCPA ont été les plus compatibles parmi les herbicides anti-dicotylédones lorsqu'ils ont été mélangés avec le difenzoquat. Le difenzoquat ou le mélange difenzoquat + barbane ont significativement stimulé l'activité de divers herbicides vis-à-vis du Fagopyrum tartaricum. Un mèlange de barbane + difenzoquat + bromoxynil-MCPA ou MCPA ester s'est montré efficace contre la folle-avoine et F tartaricum Ces derniers mélanges permettent au cultivateur de faire l'èconomie d'un traitement. L'interaction entre le difenzoquat et le diclofop mèthyle (ester méthylique de l'acide 4(2,4 dichtorophénoxy)phénoxy propionique) a été additive. L'efficacite contre la folle-avorne avec les mèlanges a été bonne et le rendement de l'orge a été meilleur que celui obtenu avec la dose recommandée de diclofop méthyle. Wechselwirkungen zwischen Difenzoquat und anderen Herbiziden zur Bekämpfung von Flughafer und dikotylen Unkräutern in Gerste Wenn Barban und difenzoquat im 2-oder 4-Blattstadium des Flughafers appliziert wurden, konnte etne additive Wirkung zwischen den beiden Herbiziden beobachtet werden. Die Flug-haferbekampfung war mit einer Mischung von Barban und Difenzoquat bei Aufwandmengen von 0.14 + 0.42 kg/ha und Anwendung im 2- Oder 4-Blattstadium genauso gut wie bei alleiniger Anwendung von Barban mit der empfohlenen Aufwandmenge von 0.28 kg/ha im 2-Blattstadium. oder von Difenzoquat mit O.84 kg/ha im 4-Blattadium. Die Mehrerträge an Gerste die mit der Mischung erzielt wurden. entsprachen den Mehrerträgen bei alleibuger Anwendung der Herbizide im empfohlenen Entwicklungsstadium Diese Mischung beitet dem Landwirt eine ausgezeichnete Bekämpfung des Flughafers bei erweitertem Anwndungsbereich (2- bis 4-Blattstadium). deutlich Mehrerträge bei Gerste und die Möglichkeit geringerer Anwendungskosten. Die Wirkung von Difenzoquat oder der Barban + Difenzoquat-Mischung war schlechter. wenn Amin-formulierungen von Herbiziden zur Bekämpfung dikotlyer Unkräuter zugesetzt wurden, jedoch nicht bei Zusatz von Ester-formulierungen. MCPA-Ester und Bromoxynil plus MCPA waren die geeignetsten Mischungspartner für Difenzoquat gegen dikotyle Arten. Difenzoquat oder Difenzoquat + Barban steigerten signifikant die Wirkung verschiedener Herbizide gegenüber Fagoyprum tataricum. Die Mischung von Barban +Difenzoquat + Bromoxynil-MCPA oder MCPA-Ester ergab eine gute Bekàmpfung des Flughafers und von F. tataricum. Mit diesen Mischungen kann eine Spritzung emgespart werden Für Difenzoquat und Diclofop-methyl [2-[4-(2′,4′-Dichlorphenoxy)-phenoxy]-propionsäuremethylester wurde eine additive Wirkung festgestellt. Die Flughaferbekämpfung mit diesen Mischungen war gut und der Gersteertrag war höher als bei Anwendung der empfohlenen Aufwandmenge von Diclofop-methyl.     

Resistance to diclofop-methyl in two Lolium spp. populations from Italy: studies on the mechanism of resistance

The mechanisms of herbicide resistance were investigated in two diclofop-methyl-resistant Lolium spp. populations from central Italy, Roma '94 and Tuscania '97. These two populations were compared with two susceptible Italian populations (Vetralla '94, Tarquinia '97) and a resistant and a susceptible population from Australia, SLR31 and VLR1. The activity of acetyl Co-A carboxylase (ACCase) extracted from susceptible (S) or resistant (R) individuals from the Italian populations was inhibited by both aryloxyphenoxypropanoate (diclofop acid and fluazifop acid) and cyclohexanedione (sethoxydim) herbicides. Diclofop-methyl was rapidly de-esterified to diclofop acid at a similar rate in both R and S populations. In all populations, diclofop acid was subsequently degraded to other metabolites. The rate of degradation of diclofop acid was not significantly faster in R than in S populations; however, diclofop acid was degraded more completely in Roma '94 and Tuscania '97 compared with the S populations. Application of the mixed-function oxidase inhibitor 1-aminobenzotriazole (ABT) significantly enhanced diclofop-methyl toxicity towards both R populations, but not in S populations. However, enhanced herbicide metabolism does not completely account for the measured resistance level. A mechanism other than an altered ACCase and enhanced herbicide metabolism appears to be responsible for resistance to diclofop-methyl in Roma '94 and Tuscania '97.     

Phytotoxic activity of clomeprop in soil and concentration of its hydrolysed metabolite DMPA in soil water

The relationship between the fate of clomeprop in soil and its phytotoxic activity on the growth of radish (Raphanus sativus) seedlings was investigated in the laboratory. The phytotoxic activity of clomeprop in sea sand was much higher than in non-autoclaved soil, and the phytotoxic activity in non-autoclaved soil was higher than in autoclaved soil. The phytotoxic activity of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolysed metabolite of clomeprop, was higher than that of the latter under both soil conditions. Clomeprop was adsorbed on soil to a greater extent than DMPA. The concentration of clomeprop in soil water of non-autoclaved soil decreased with increase of the DMPA concentration in the soil water in a time-dependent manner. It is suggested that the phytotoxic activity of clomeprop applied to soil is induced mostly by the DMPA concentration in soil water after hydrolytic degradation by soil microbes. © 1999 Society of Chemical Industry     

Metabolism of bifenox in soil and plants

The herbicide, methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate (bifenox), had a half-life of 3 to 7 days after preemergence application to a greenhouse soil mix. Metabolites identified included: 5-(2,4-dichlorophenoxy)-2-nitrobenzoic acid, 2,4-dichlorophenyl 4-nitrophenyl ether (nitrofen), and 5-(2,4-dichlorophenoxy)anthranilic acid over a 313-day sampling period. Comparison of the total ¹⁴C in the soil to that extractable by methanol showed an increase in the proportion of bound material. The major metabolite eluted from a Frederick clay loam soil column was identified as the acid of bifenox and its mobility was associated with the short half-life of bifenox in soil. In vitro studies with shoot-tissue macerates showed that bifenox was not degraded by corn (Zea mays L.) or soybeans (Glycine max (L.) Merr.) and was degraded to less than 1% by velvetleaf (Abutilon theophrasti Medic.).     

Tank-mix adjuvants and pesticide residues: some regulatory and quantitative aspects

Although it is well known that judicious use of adjuvants can increase the performance of foliage-applied sprays of many agrochemicals, little information is available in the public domain about their ultimate effects on pesticide residues in treated crops. In the present work, the influence of Agral (polyoxyethylene nonylphenols), Toil (methyl esters of rapeseed fatty acids) and Bond (styrene-butadiene copolymers) on surface and crop residues of diclofop-methyl/diclofop and propiconazole in wheat and field beans was investigated using a model system simulating field practice. Pesticides were applied as commercial formulations, diclofop-methyl 378 g litre(-1) EC (Hoegrass) and propiconazole 250 g litre(-1) EC (Tilt), at their maximum approved rates, 1135 g AI ha(-1) and 125 g AI ha(-1), respectively, both in the presence or absence of the maximum rate recommended for each candidate adjuvant. No detectable residues of diclofop-methyl or propiconazole were found in wheat 35 days after any of the four applications. However, residues of diclofop were present in this crop, and those from applications containing Agral (0.07 mg kg(-1) fresh weight (FW)) or Bond (0.08 mg kg(-1) FW) were significantly lower than those with no adjuvant (0.14 mg kg(-1) FW) or Toil (0.16 mg kg(-1) FW). Unlike wheat, residues of both diclofop and propiconazole were detected in field beans after harvest. Significantly higher residues of the former were recorded from the applications with Agral or Bond (ca 0.32 mg kg(-1) FW) than with those with no adjuvant or Toil (ca 0.15mg kg(-1) FW). All the propiconazole applications containing adjuvants showed a similar significant increase in residues (0.10-0.16 mg AI kg(-1) FW) over the no-adjuvant treatment (0.05 mg kg(-1) FW) in this crop. There appeared to be little agreement between the apparent amounts of uptake, as indicated by the rates of decline of surface residues up to 5 days after application, and final residues in either target species. On wheat, surface residues of diclofop-methyl decreased from initially ca 20 to as little as 0.02 mg kg(-1) FW using adjuvants; the corresponding values for propiconazole were ca 2 to ca 0.03 mg kg(-1) FW. Recoveries of diclofop-methyl from the surfaces of field beans were much higher than those from wheat, declining from ca 30 to only ca 6 mg kg(-1) FW during the course of 5 days; the corresponding residues for propiconazole were ca 2 mg to 0.15 mg kg(-1) FW. These findings are discussed in relation to uptake results obtained with radiolabelled pesticides and adjuvants in the laboratory, and to the mandatory requirements for pesticide residue data for the authorised use of adjuvants in the UK.     

A comparison of the dynamics of root growth and biomass partitioning in wild oat (Avena fatua L.) and spring wheat

The dynamics of early root growth and dry matter partitioning were compared in spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) grown in solution culture. Total root length was greater in wheat than wild oat throughout the experiment; a result of a greater number of seminal axes and greater production of lateral root length per axis. The final number of adventitious roots was greater in wheat than in wild oat, but their length was similar. Relative growth rates were also similar as was shoot:root dry weight ratio and rate of root respiration. However, wheat used the dry matter partitioned to its roots more efficiently, producing a greater specific root length (SRL, length per unit weight). Caution must be exercised when relating these results to plants growing and compet-ing in the field, but three general points are raised. First, the initial number of seminal axes can have a profound effect on the rate of early root development; second, the adventitious root system of wild oat is not inherently more vigorous than that of wheat; and third, future studies should compare SRL of wheat and wild oat in the field. If differences similar to those in the present study are found they may contribute to the greater competitive ability of wheat.     

Cyclopaldic acid, a major phytotoxic metabolite of Seiridium cupressi, the pathogen of a canker disease of cypress

A phytotoxic substance was produced in vitro in a relatively high concentration (c. 40 mg/1) by Seiridium cupressi , a fungus that causes a canker disease of cypress ( Cupressus sempervirens ) and other Cupressaceae in Greece and in other parts of the world. Structural investigations demonstrated that the substance was identical with cyclopaldic acid, an antibiotic known to be a metabolite of some species of Penicillium, Aspergillus and Pestalotiopsis . Absorbed by severed twigs of three species of Cupressus and by cuttings of two herbaceous non-host plants (tomato and mung bean), cyclopaldic acid at concentrations of 10-100 ug/ml induced leaf chlorosis and necrosis. Oat seed germination and root growth of oat seedlings were also reduced to about 50% at 75 and 100 jig/ml, respectively. The compound showed antifungal activity towards species of Botrytis. Fusarium and Geotrichum when assayed at a concentration range from 10 to 100 /ug ml. We believe this to be the first report of cyclopaldic acid as a non-selective fungal phytotoxin. However, its possible role in the pathogenesis of the cypress canker disease has not been established.     

Distribution of diclofop-methyl and metabolites in oat (Avena sativa L.) protoplasts

The metabolism of the herbicide diclofop-methyl and the distribution of it and its metabolites have been investigated in a system utilizing isolated oat protoplasts (Avena sativa L. ‘Cascade’). Accumulations of ¹⁴C-diclofop-methyl were found in membrane fractions of the protoplasts. Diclofop-methyl partitioned into the lipid phase of the protoplast plasma membrane. Comparatively small amounts of diclofop were found associated with the protoplasts. Diclofop-methyl was converted to diclofop in the treatment solution by hydrolytic enzymes associated with the external surface of the protoplast. Approximately 78% of the radiolabel recovered from the treatment solution was diclofop. The two major accumulations of radiolabel were found in the water insoluble portion (membrane fraction) of the protoplast as diclofop-methyl and in the treatment solution as diclofop. Repartition du diclofop-methyl et de ses métabolites dans les protoplastes d'avoine (Avena sativa L.) Le métabolisme de l'herbicide diclofop-methyl (DM) et la répartition du DM et de ses métabolites ont étéétudiés dans un système faisant appel à des protoplastes d'avoine isolés (Avena sativa L.) ‘Cascade’. Des accumulations de ¹⁴C-diclofop-methyl ont été trouvées dans la fraction membranaire des protoplastes. Le diclofop-methyl est passé dans la phase pidique de la membrane plasmique du protoplaste. En comparaison, de petites quantités de diclofop ont été trouvées en association avec les protoplastes. Le diclofop-methyl a été converti en diclofop par des hydrolases associées à la surface externe des protoplastes. Approximativement 78% des traces radioactives retrouvées dans la solution de traitement étaient du diclofop. Les deux principales accumulations de radioactivitéétaient trouvées dans la fraction insoluble dans l'eau des protoplastes (fraction membranaire) sous forme de diclofop-méthyl et, dans la solution de traitement, sous forme de diclofop. Verteilung von Diclofop-methyl und Metaboliten in Hafer- (Avena sativa L.)-Protoplasten Der Abbau von ¹⁴C-markiertem Diclofop-methyl und die Verteilung des Wirkstoffs sowie eines Metaboliten wurden in isolierten Protoplasten von Hafer (Avena sativa L. ‘Cascade’) untersucht. Der Wirkstoff war in den Protoplastenmembranen angereichert, wobei eine Anlagerung an die Lipidphase der Plasmamembran festgestellt wurde. Von Diclofop waren vergleichsweise geringe Mengen an die Protoplasten gebunden. Diclofop-methyl wurde in der Versuchslösung durch hydrolytische Enzyme, die an der Protoplastenaussenfläche lagen, zu Diclofop umgewandelt. Radioaktiv markierte Stoffe wurden hauptsächlich als Diclofop-methyl am Protoplasten-membransystem und als Diclofop (mit 78% der eingebrachten ¹⁴C-Aktivität) in der Lösung gefunden.