FACTORS AFFECTING PERSISTENCE AND INACTIVATION OF DIQUAT AND PARAQUAT

Summary. The adsorption of diquat cation was found to be 0.3, 2.0–2.5 and 80–100 mg/g on a sandy loam soil, Grade Hydrite 10 Georgia kaolinite and National Standard Bentonite, respectively. Bentonite (113 lb/surface ac) applied to plastic pools previously treated with 1 ppm paraquat reduced the concentration of paraquat to less than 0–05 ppm within 24 hr of application. Only bentonite appeared to hold either diquat or paraquat in a form unavailable to wheat. Appreciable uptake by wheat from soil treated with diquat or paraquat (16 lb/ac pre-emergence) occurred only in soil or sand in which the herbicide leached below the 05 in. zone. A 12 hr dark period following foliage application did not appear to enhance movement of either herbicide in wheat. Loss of radioactivity was observed when diquat or paraquat was exposed to ultraviolet light (2537 Å).
Facteurs agissant sur la persistence et l'inactivation du diquat et du paraquat     

Analytical method for the simultaneous determination of diquat and paraquat residues in potatoes by high-pressure liquid chromatography

A novel method was developed for the simultaneous determination of diquat and paraquat residues in potatoes. Potato tissues were spiked at several levels and extracted with acid using a micro-reflux procedure with 5 g of sample; this was followed by adjusting the hydrolyzate pH to 9 to 10 and using a silica Sep-Pak for rapid clean-up and preconcentration. Aliquots of the final eluate were taken to dryness, dissolved in the h.p.l.c. mobile phase and analyzed as their heptanesulfonate ion-pairs by u.v.-h.p.l.c. (reverse phase column chromatography) at 254 and 313 nm for paraquat and diquat, respectively. A detection limit of approximately 0.05 mg kg^?1 dication in a 5-g sample of spiked potato (i.e. 0.25 μg ml^?1 final extract) was achieved. Recoveries of 79.5 to 97.6% were obtained at spiking levels of 0.05 to 5.0 mg kg^?1 for diquat and paraquat with coefficients of variation not greater than 8.27%. The method was developed and validated using ¹⁴C-radiolabelled diquat and paraquat; u.v.-h.p.l.c. recoveries were comparable with recoveries determined by radioassay. Several parameters affecting the extraction, adsorption and chromatography of diquat and paraquat were evaluated. The formula weights of diquat and paraquat were determined and their importance described; they were determined as mono- and tetra-hydrates, respectively.     

Applying the double knock technique to control Conyza bonariensis

Sequential applications of glyphosate followed by another postemergent herbicide, known as the "double knock" technique, were trialled for their effectiveness in controlling Conyza bonariensis . Combinations of glyphosate with and without 2,4-D followed by paraquat plus diquat, paraquat, or 2,4-D were tested at a range of follow-up application times in two field and two pot experiments. The results showed that paraquat plus diquat or paraquat following glyphosate or glyphosate plus 2,4-D provided highly effective weed control compared to glyphosate alone. The optimum timing for follow-up applications of paraquat or paraquat plus diquat was between 5 and 7 days after the initial glyphosate application. Combined applications of glyphosate and 2,4-D, compared to split applications, were not significantly different. However, following glyphosate application with 2,4-D >1 day later considerably reduced the level of control. This study showed that the double knock technique is highly effective in controlling C. bonariensis and is rapidly becoming an important tool in the management of this problem weed.     

Paraquat-resistant biotypes of Hordeum glaucum from zero-tillage wheat

There has been a significant increase in the area seeded to minimum- and zero-tilled crops worldwide over the past two decades. These cropping systems rely primarily on the non-selective herbicides glyphosate or paraquat/diquat to control weeds before seeding the crop. Both glyphosate and paraquat/diquat are regarded as low-risk herbicides in the ability of target weeds to develop resistance to them. Following 10–15 years of once annual applications of paraquat and diquat for weed control in zero-tilled cereals, failure of these herbicides to control Hordeum glaucum Steud. in two separate fields occurred. Dose–response experiments demonstrated high-level resistance to paraquat and diquat in both populations; however, the resistant biotypes are susceptible to other herbicides. This is the first report, worldwide, of paraquat resistance following the use of this herbicide in zero-tillage cropping systems and is therefore a harbinger of future problems in minimum-tillage systems when there is exclusive reliance on a contact herbicide for weed control.     

灭生性除草剂敌草快与百草枯杀草活性比较

本文在田间情况下比较了灭生性除草剂敌草快和百草枯的生物活性。试验结果表明,二者在作用方式、作用速度、表现症状以及在相同剂量作用于同一种杂草的效果相近,没有达到显著差异。     

苏门白酒草对草甘膦等除草剂的多抗性检测及防治药剂筛选

苏门白酒草Conyza sumatrensis是中国华南地区常见的阔叶杂草,在果园和非耕地常造成严重危害。本研究采用整株剂量反应法,明确了采自广东省广州市的苏门白酒草疑似抗性种群 (GZ-R) 对草甘膦、百草枯和敌草快的抗性水平,比对了GZ-R种群和采自广东省清远市的敏感对照种群 (QY-S) 的草甘膦靶标酶基因EPSPS2片段的差异,并测定了灭草松、氯氟吡氧乙酸等5种茎叶处理剂对不同叶龄苏门白酒草的室内防除效果。结果表明:GZ-R种群对草甘膦和百草枯分别产生了中等水平和高水平抗性,并已对敌草快产生交互抗性,3种药剂对GZ-R种群的LD₅₀值分别是对QY-S种群LD₅₀值的7.2、72.3和6.6倍;与QY-S种群相比,GZ-R种群的EPSPS2基因106位由脯氨酸突变为苏氨酸。在灭草松、氯氟吡氧乙酸或2甲4氯钠推荐剂量下,于4~5叶期施药,苏门白酒草死亡率均为100%,但于6~7叶期和10~12叶期施药,苏门白酒草死亡率显著下降至44.4%~91.7%;而在草铵膦或苯嘧磺草胺推荐剂量下,不同叶龄期施药苏门白酒草的死亡率均为100%,因此在植株生长早期可使用草铵膦和苯嘧磺草胺防除已对草甘膦和百草枯等除草剂产生抗性的苏门白酒草。     

Tolerance to paraquat-mediated oxidative and environmental stresses in squash (Cucurbita spp.) leaves of various ages

Paraquat is labeled for row-middle application on cucurbits, but drift to crop foliage is inevitable. Experiments were conducted to determine whether differential tolerance to paraquat existed among leaves of various ages in Cucurbita spp. (squash) and other plants, and to examine whether leaves tolerant to paraquat are also tolerant to other herbicides and abiotic stresses. Physiological responses to paraquat, including antioxidant activity, were investigated in squash leaves to identify mechanisms of paraquat tolerance. Although the level of paraquat tolerance differed by leaf age, cultivar, and species, the level of paraquat injury was lower in younger leaves than in older leaves in 14 of 18 squash cultivars and 5 of 12 other species tested. Cellular leakage and lipid peroxidation were consistently lower in the youngest leaf (leaf 4) than in the older leaves. Quantum yield and relative chlorophyll content were the same in all leaves of nontreated plants. Epicuticular wax content was higher in the youngest leaf than in leaves 1, 2, and 3 of cv. ‘Joongangaehobak’ and ‘Wonbiaehobak’. However, leaf cuticle content was not consistent with leaf ages. Differential leaf response to paraquat was partially correlated with the change in catalase, peroxidase, ascorbate peroxidase (APX), and glutathione reductase activities in nontreated and treated leaves. The APX activity in the youngest leaf was generally 2 times higher than in leaves 1-3 in both nontreated and treated plants. Ascorbate antioxidant levels were also higher in the youngest leaf than those in leaves 1-3. Leaves tolerant to paraquat were also tolerant to diquat and to abiotic stresses, low temperature and drought. However, tolerance to oxyfluorfen, which has a different mode of action than paraquat and diquat, was higher in older than in younger leaves. Higher tolerance to paraquat-mediated oxidative and abiotic stresses in young leaves of most squash cultivars might contribute to the differential prevention of oxidative damage in leaves of various ages.     

Effect of light environment on the activity and behaviour of diquat and paraquat in plants

The importance of controlling the light environment of experiments involving diquat and paraquat is shown in experiments where activity is markedly dependent on the light quality and intensity before treatment and on the time of day of treatment. Activity and uptake are not directly related since treatments after low light intensities give increased activity associated with reduced uptake; following afternoon treatments, reduced activity is associated with increased uptake. Uptake increased when plants were darkened after treatment but the increase was not directly related to its duration, because after a time, uptake decreased. Three possible explanations for this decrease are considered: diquat exudation from the leaves, downward movement into the roots, and the adsorption of diquat in plant tissue. Evidence did not support exudation from leaves or downward movement into the roots.     

THE BIPYRIDYLIUM QUATERNARY SALTS

Summary. In a number of plant species, the biological activity of diquat and paraquat was increased by an increase in environmental humidity. This improved activity resulted from an increase in both uptake and movement.
High humidity was more effective after treatment than before it, and durations of 8 hr or more were required to produce the maximum effect. When periods of low humidity of up to 16 hr were interposed between treatment and high humidity, there was no significant effect on the activity of diquat in darkened tomato or sugar beet.
The increase in activity occurred both in the dark and in the light, and it is therefore concluded that humidity does not exert its effect by modifying the degree of stomatal opening.
Experiments were carried out with wheat using two air humidities combined with different soil moisture contents, ranging from saturated down to only 30% of water-holding capacity. Greatest movement occurred where high air humidity was combined with low soil moisture, and least where low air humidity was combined with high soil moisture. It is concluded that diquat and paraquat would be most effective in the field when sprayed under dry soil conditions in late afternoon or evening when increased humidity (and darkness) can follow soon after treatment.
Les sels quatemaires de bipyridylium
Effet de l'humidité atmosphérique et de l'humidité du sol sur l'absorption et la migration du diquat et du paraquat dans les plantes     

EVALUATION OF PARAQUAT AND DIQUAT FOR WEED CONTROL IN RUBBER

Summary. In Malayan rubber plantations where the weed flora was dominated by grasses paraquat was superior to diquat as a herbicide. At the rates needed to give satisfactory grass weed control paraquat also gave an adequate control of broad-leaved weeds.
The rate of paraquat needed varied between 0.75 and 1.25 lb/ac depending on the weed flora and the growth stage of the rubber trees. In young rubber 1.0–1.25 lb/ac gave 8–10 weeks' control, but in mature rubber there was only 20% recovery 6 months after an application of 0.75 lb/ac. Where weed regrowth was very rapid after the initial spray, as in the case of Paspalum conjugation in young rubber, a second application some 2–3 weeks after the first was an advantage. The volume of water in which it was applied was not critical.
Rain falling soon after application did not reduce the herbicidal activity of paraquat. Paraquat did not injure rubber trees providing it was not sprayed onto green tissue and this feature combined with its inactivation by soil made it safe to use from a very early stage in the growth of the rubber trees.
L'évaluation du paraquat et du diquat pour la lutte contre les mauvaises herbes dans les plantations de caoutchouc     

全球非选择性除草剂市场分析及预测(2020年)(上)

全球非选择性除草剂主要为草甘膦、草铵膦、百草枯、敌草快,2018年这些产品市场规模为83.2亿美元,它们的市场份额占非选择性除草剂总量95%。计上其它小宗的产品,全球非选择性除草剂市场达到85亿美元左右,这块占全球除草剂市场的32%,可见,非选择性的需求"扮演"着除草剂市场基石的作用。虽然非选择性除草剂市场整体稳定,可产品间表现不一。目前草甘膦市场需求增长疲态已经出现,未来不可能在像其刚出现时那样经历持续增长。草铵膦具有杀草谱广、低毒、内吸好、活性高和环境友好等特点,也是全球第二大转基因作物耐受除草剂,市场份额9.2亿美元,同时,百草枯受到全球广泛性禁用,市场萎缩严重,敌草快市场表现的不温不火。     

A rapid sensitive bioassay for determination of paraquat and diquat in water

The change in cell-membrane permeability as indicated by leakage of electrolytes from treated fronds of Lemna minor was the criterion used to detect the presence of diquat and paraquat in solution. The minimum herbicide concentrations that could be detected ranged from 1.8 and 1.7 μg/ml diquat and paraquat cation respectively after 3 h treatment to 0.00018 and 0.000017 μg/ml after 72 h. Paraquat was more active than diquat in all treatments. Increase in cell-membrane permeability occurred without the appearance of injury such as, chlorosis or bleaching of fronds. Light was necessary for these herbicides to alter cell-membrane permeability, though a little herbicidal activity could be detected after 48 h in the dark at concentrations above 0.17μg/ml. Un test biologique rapide et sensible pour la recherche du paraquat et du diquat dans l'eau Des modifications de la perméabilité de la membrane cellulaire, révélées par la déperdition d'électrolytes à partir de frondes de Lemna minor, ont été utilisées comme critères pour révéler la prèsence de diquat et de paraquat dans des solutions. Les concentrations minimales d'herbicides qui ont pu être décelées se sont situées entre 1,8 μg/ml et 1,7 μg/ml des cations diquat et paraquat respectivement, apres 3 heures de traitement, jusquà 0,00018 et 0,000017 μg/ml après 72 heures. Le paraquat s'est montré plus actif que le diquat dans tous les traitements. Un accroissement de la perméabilité cellulaire s'est produit sans qu'il soit apparu de dégâts tels que la chlorose ou le blanchissement des frondes. La lumière a été nécessaire pour que ces herbicides altèrent la perméabilité de la membrane cellulaire, bien qu'une faible activité herbicide ait pu être décelée après 48 heures à l'obscurité, à des concentrations supérieures à 0,17 μg/ml. Ein schneller und empindlicher Biotest für den Nachweis von Paraquat und Deiquat in Wasser Veränderungen in der Permeabilität der Zellmembran in Form des Austretens von Elektrolyten aus behandelten Wedeln von Lemna minor wurden als Kriterium für den Nachweis von Deiquat und Paraquat in wässeriger Lösung benutzt. Die geringsten Herbizidkonzentrationen, die festgestellt werden konnten, lagen nach 3 h nach der Applikation bei 1,8 und 1,7 μg/ml Deiquatbzw. Paraquat-Kation und nach 72 h bei 0,00018 und 0,000017 (μg/ml). In allen Behandlungen war Paraquat wirksamer als Deiquat. Der Anstieg in der Zellmembran-Per-meabilität war nichi mit äusseren Symptomen wie Chlorose oder Ausbleichen der Wedel verbunden. Für die Herbizidbedingte Veränderung der Zellmembran-Permeabilität war Licht notwendig, doch konnte auch eine geringfügige Herbizidwirkung nach einer 48-h-Dunkelperiode bei Konzenlrationen > 0,17 μg/ml festgestellt werden.     

The effect of some herbicides on vesicular-arbuscular endophyte abundance in the soil and on infection of host roots

The effect of the herbicides di-allate, diquat, diuron, paraquat, tri-allate and trifluralin, at a range of application rates from 0.5 to 32 times that recommended by the manufacturers, on vesicular-arbuscular (V-A) endophyte spore abundance in the soil and on infection of wheat roots was investigated in field and glasshouse experiments. Paraquat and diquat had no measurable effect on V-A endophyte spore abundance. There was a slight trend to lower V-A endophyte spore numbers at high rates of application of di-allate and tri-allate but no trend for the other chemicals. Infection intensity (% root length infected) declined at high rates of di-allate and led to lower mycorrhizal root weights. The phosphorus content of the shoots was also reduced by di-allate. High doses of di-allate, diuron, tri-allate and trifluralin reduced most parameters of plant growth more than mycorrhizal parameters. It is therefore concluded that at normal application rates these chemicals are unlikely to affect adversely endomycorrhiza formation or function.     

THE INFLUENCE OF SIZE OF SPRAY DROPLETS ON THE HERBICIDAL ACTIVITY OF DIQUAT AND PARAQUAT

Summary. Single droplets ranging in size from 250 to 1000 μ diameter and concentrations of diquat and paraquat over the range 0–09–0.75% ion were examined for herbicidal activity. Size of droplet and concentration of herbicide in the droplet were shown to have a marked influence on activity. An increase in droplet size above 250 μ increased herbicidal efficiency. An optimum was reached between 400 and 500 μ while activity fell off with a further increase to 1000 μ.     

Studies of the adsorption of paraquat on soluble humic fractions by gel filtration and ultrafiltration techniques

The adsorption of paraquat dichloride (1,1′-dimethyl-4,4′-bipyridylium dichloride) on a soluble sodium humate fraction of a Fenland soil was studied by gel filtration (on Sephadex G10 and G100) and by ultrafiltration (through an Amicon Diaflo UM-2 ultrafilter). Both methods depend upon the separation, on a molecular weight basis, of the unadsorbed molecules of herbicide from the adsorption complex (consisting of polymeric organic materials and the adsorbed paraquat). Separations were obtained on columns of Sephadex G10 (Method I) and in the ultrafiltration experiments (Method II), and isotherms were prepared from data for adsorption in water (by Method II) and in sodium chloride (by Methods I and II) solutions. Results from the two methods were comparable over the concentration range examined. The increased adsorption of paraquat by Na⁺-compared with Ca²⁺-humate is explained on the basis of the selectivity sequence of humate for exchangeable cations. Attempts to prepare isotherms from gel filtration data, for the adsorption of paraquat on two soluble model humic polymers (polyacrylic acid and a polymer prepared by the oxidative coupling of benzoquinone and ammonium chloride) were unsuccessful because binding to the gel matrix did not permit quantitative recoveries of the adsorption complexes. Paraquat was adsorbed to the same extent on each of four fractions of Na⁺-humate separated on Sephadex G100.     

Optimizing diquat efficacy with the use of adjuvants

Optimizing diquat efficacy with the use of adjuvants may broaden the spectrum of weed control, but relevant research towards this direction is limited. Field and greenhouse experiments were conducted to evaluate the effect of diquat applied alone and with six commercial adjuvants (surfactants and oil-based adjuvants) on various weed species. Diquat effect was evaluated in two field experiments on natural populations of common lambsquarters (Chenopodium album L.), prostrate knotweed (Polygonum aviculare L.) and burning nettle (Urtica urens L.) along with two greenhouse trials on rigid ryegrass (Lolium rigidum L.). In field or greenhouse experiments, all the adjuvants significantly increased the control of C. album, P. aviculare, and L. rigidum, from 48, 42 and 7%, up to 82, 74 and 67%, respectively, in terms of fresh weight reduction, but to a different extent for each adjuvant. U. urens was totally (100%) controlled in terms of visual estimation either with diquat or with diquat plus any adjuvant. The differences in the effect of diquat applied with adjuvants mainly depended on the weed species examined and they were not proportional to the surface tension reduction of the spray solution caused by the adjuvants. Overall, the surfactants and the oil-based adjuvants examined in this study considerably enhanced the effect of diquat; this can broaden the spectrum of weed control against broadleaf and grass weeds in orchards and non-crop areas. The results are discussed in relation with the classification of the adjuvants.     

Appearance of a biotype of the weed, Hordeum glaucum Steud., resistant to the herbicide paraquat

A biotype of the grass weed Hordeum glaucum Steud, infesting a site at Willaura, Victoria, Australia has resistance to paraquat. Application of the recommended rate of paraquat does not cause death of the resistant biotype at any stage of growth. The LD₅₀ for the resistant biotype is 6.4 kg active ingredient ha^?1 which is 250 times greater than for the normal susceptible biotype (25 g active ingredient ha^?1). Growth of the resistant biotype is checked by paraquat with a clear dosage response evident. The paraquat resistant biotype is also resistant to diquat but is normally affected by herbicides with different modes of action. In addition to continued foliage growth of the resistant plants after paraquat application, seeds of these plants can germinate and seedlings elongate in the dark whereas seeds of susceptible plants germinate but there is no further growth. This suggests that studies of the mechanism(s) conferring resistance will have to consider both the effect of paraquat on the chloroplast and a non-photosynthetic effect on cell growth. Un biotype de la mauvaise herbe Hordeum glaucum Steud, résistant à l'herbicide paraquat Un biotype de la graminée Hordeum glaucum Steud. à Willaura, Victoria, Australie, s'est montré résistant au paraquat. L'application de la dose préconisée de paraquat ne provoque pas la mort de ce biotype, quel qu'en soit le stade végétal. La LD₅₀ pour le biotype résistant est 6,4 kg matière active ha^?1, c'est-à-dire 250 fois plus grande que pour le biotype normal sensible (25 g matière active ha^?1). Le paraquat provoque chez le biotype résistant une inhibition de croissance qui se rapporte à la dose. Le biotype résistant au paraquat l'est également au diquat mais réagit normalement envers les herbicides à mode d'action différente. Non seulement la croissance foliaire continue normalement après une application de paraquat chez les plantes résistantes, mais les graines sont capables de germer et les jeunes plants de s'allonger à l'obscurité, tandis que les graines de plantes sensibles germent à l'obscurité mais ne croissent pas. II semble donc que les études des mécanismes qui produisent la résistance devront examiner l'influence du paraquat sur le chloroplaste ainsi qu'un effet nonphotosynthétique sur la croissance cellulaire. Ueber das Auftreten eines gegen Paraquat resistenten Biotyps von Hordeum glaucum Steud. Bei Willaura, Victoria (Australien) tritt ein gegen Paraquat resistenter Biotyp von Hordeum glaucum Steud. auf. Die Application der normalerweise empfohlenen Dosierung Paraquat tötet den resistenten Biotyp in keinem Wachstumsstadium ab. Die Ld₅₀ für den resistenten Typ beträgt 6,4 kg ai ha^?1; dies ist 250 mal mehr als beim normal sensiblen Typ (25 g ai ha^?1). Das Wachstum des resistenten Biotyps wird durch steigende Dosen von Paraquat beeinträchtigt. Der gegen Paraquat resistente Typ ist auch gegen Diquat unempfindlich, weist aber gegenüber Herbiziden mil anderen Wirkungsmechanismen die normale Empfindlichkeit auf. Resistente Pflanzen zeigen nach Paraquatbehandlung ein weitergehendes Blattwachstum. Ihre Samen keimen und die Sämlinge entwickeln sich im Dunkeln weiter, während die Samen sensibler Pflanzen zwar keimen, sich aber nicht weiterentwickeln. Diese Beobachtungen weisen darauf hin, dass bei Forschungen zur Aufklärung der Resistenzmechanismen, sowohl die Wirkung von Paraquat auf die Chloroplasten als auch einen nicht photosynthetiseh wirksamen Effekt auf das Zellwachstum berücksichtigen müssen.     

Near‐field air concentrations of pesticides in potato agriculture in Prince Edward Island

BACKGROUND: Pesticides in air have become of increasing concern in recent years. This study examined downwind air concentrations of carbofuran, methamidophos, mancozeb and diquat dibromide resulting from spray drift within 24 h of application, within 100 m of potato fields. RESULTS: Concentrations ranged from less than 0.05 µg m^?3 in prespray samples to 6.37 µg m^?3 for methamidophos at 3 h post‐spray. For most applications, air concentrations decreased with distance from the field and with time after application. Methamidophos concentrations in the air downwind continued to increase up to 3 h after spray. Air concentrations during spray were positively correlated with application rate (r = 0.904), and air concentrations at 1 h and 3 h post‐spray were positively correlated with vapour pressure (r = 1.000 and r = 0.999 respectively). Carbofuran, methamidophos and diquat dibromide concentrations during spray were above some Canadian and international health protection guidelines. CONCLUSION: Although pesticide air concentrations measured in this study are generally consistent with other studies, maximum concentrations are greater than those that have been measured elsewhere, and some are above published air quality guidelines. An evaluation of the degree of risk posed by these and other pest control products to human and wildlife receptors is recommended. Copyright © 2009 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Fungicide resistance: definitions and use of terms

A first proposal on definitions and use of terms was made by Delp & Dekker in Bulletin OEPP/EPPO Bulletin 15 , 333–335, following the EPPO Conference on Fungicide Resistance in Brussels in 1984. These definitions were reviewed by the EPPO Workshop on Fungicide Resistance Testing Methods, held in Changins (CH) in November 1986, which proposed the present version. This has been approved by the EPPO Working Party on Pesticides for Plant Protection, with the involvement of GIFAP, and has been approved by the Executive Committee and Council of EPPO.     

Effect of four herbicides and two oils on leaf-cell membrane permeability*†

Leakage of electrolytes from leaf discs of treated Phaseolus Vulgaris L. plants was the main criterion used to study the effect of several chemicals on the permeability of leaf-cell membranes. Paraquat, diquat, dinoseb and oxyfluorfen (2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(Trifluoromethyl) benzene) increased leaf-cell membrane permeability after exposure for 12 h or less. An‘aromatic’oil caused a large increase in permeability at 2–5 min after treatment. Increases in electrolyte release were also correlated with release of soluble amino acids from the leaf discs but the former method was the more sensitive. Increase in cell membrane permeability was always associated with injury symptoms such as appearance of necrotic areas in leaves. Chlorpropham, linuron, sodium azide, glyphosate and 2,4-D at 10^?3M, as well as 1% X-77 surfactant and a non-phytotoxic isoparaffinic oil did not alter leaf-cell permeability at 12 h after treatment. Light was necessary for paraquat and oxyfluorfen to alter leaf cell permeability. Paraquat and oxyfluorfen caused a greater increase in leaf-cell permeability of a soybean mutant with yellow leaves as compared with the normal green leaves. With oxyfluorfen this difference in permeability was greater than with paraquat, and was associated with the appearance of severe necrotic injury symptoms in the yellow mutant; paraquat caused no injury symptoms.