SOME PHYSICO-CHEMICAL INTERACTIONS OF PARAQUAT WITH SOIL ORGANIC MATERIALS AND MODEL COMPOUNDS

Summary. The adsorption equilibria of paraquat were investigated on a range of organic materials including an organic soil, various humic fractions of that soil, model polymers prepared by the oxidative coupling of benzoquinone, ion-exchange resins (Zeo-Karb 216 and 226) and a polystyrene resin (Amberlite XAD-2). Isotherms were prepared for adsorption on the H⁺ and on some of the Ca²⁺ saturated materials. Measurement of the counter-ion in solution at equilibrium, and correlation of the adsorption with exchange capacity for H⁺ adsorbents showed that ion exchange was the primary adsorption mechanism. Significant amounts of non-exchange adsorption were also detected, especially at low concentrations, but generally the results followed the Rothmund-Kornfeld isotherm equation fairly accurately. The Rothmund-Kornfeld plots for the Ga²⁺ forms were complicated by the hydrolysis by water of some of the exchange sites. Other types of isotherm equations were tested and found to be unsatisfactory.
Desorption of paraquat with HCl from organic soil preparations was less than expected, and the isotherms did not conform to the Rothmund-Kornfeld or to the mass action equations. The probable reasons for this behaviour arc discussed.
Quelques interactions physico-chimiques du paraquat avec des matériaux de sol organique et des composés modèles
II. Adsorption, désorption et équilibre dans les suspensions aqueuses     

COMPLEX FORMATION AS AN ADSORPTION MECHANISM FOR LINURON AND ATRAZINE

Summary. Measurements were made of the effect of exchangeable cations on the adsorption of linuron and atrazine by an ion-exchange resin, cellulose phosphate powder, bentonite and a peat soil. The cations studied were Ca²⁺, Ni²⁺, Cu²⁺, Fe³⁺ and Ce⁴⁺. The results with linuron were consistent with the hypothesis that complex formation with exchangeable cations is a possible mechanism of adsorption. This was not so with atrazine due to complications arising from pH effects, and it seems unlikely that adsorption of atrazine by this process is significant.     

Studies on herbicidal carbamoyltetrazolinone derivatives: Selection of fentrazamide

1-Phenyl-5(4 H )-4-dialkylcarbamoyltetrazolinones represent a new class of herbicides that are active against barnyardgrass ( Echinochloa spp.) in paddy fields. To select the most favorable compound as a paddy herbicide, herbicidal activity and selectivity of the carbamoyltetrazolinone compounds to transplanted rice were determined in greenhouse tests. Higher herbicidal activities were associated with the compounds having a 2-Cl- or 2-Cl-6-Me-substituted or an unsubstituted phenyl ring, and a combination of C_2–3 linear alkyl group and a C₄ branched-chain alkyl or a C_5–6 cycloalkyl group on the nitrogen atom in the carbamoyl structure. In addition, the compounds carrying a total of seven to nine carbon atoms in the substituents on the carbamoyl nitrogen exhibited a good selectivity between barnyardgrass and transplanted rice plants. From the results of soil thick-layer chromatography, the good crop compatibility of carbamoyltetrazolinones was correlated to the mobility of the compounds in paddy soil. The investigation resulted in the selection of an excellent compound, 4-(2-chlorophenyl)- N -cyclohexyl- N -ethyl-4,5-dihydro-5-oxo-1 H -tetrazole-1-carboxamide (common name: fentrazamide), as a rice paddy herbicide for controlling barnyardgrass.     

THE PHYTOTOXICITY OF SOME HERBICIDES IN FIELD AND POT EXPERIMENTS IN RELATION TO SOIL PROPERTIES

Summary. The phytotoxicities in a number of soils of lenacil, linuron, prometryne and simazine to two indicator plants were determined in field and glasshouse experiments. The results were compared with estimates of the adsorption capacity of the soils obtained by two methods using dimethylaminobenzaldehyde as a model adsorbate. The possible influence of other soil properties was also considered.
One of the adsorption measurements had some predictive value for glasshouse behaviour but was not markedly superior to soil organic carbon content for this purpose. None of the factors studied was usefully correlated with field performance. Results from field experiments in spring were poorly correlated with those from similar experiments in autumn. Neither set of field results related closely to those obtained in the glasshouse. It is concluded that the influence of climate was more important than that of soil type.
La phytotoxiciti de quelquts herbicides dans des experiences en pots et en plein champ, en relation avec les propriétés du sol     

THE ADSORPTION OF UREA AND SOME OF ITS DERIVATIVES BY A VARIETY OF SOILS

Summary. The absorption of urea and a number of its derivatives by different soils was investigated using a slurry-type procedure. The materials could be listed in the following order of increasing tendancy to be adsorbed: urea, fenuron, methylurea, phenylurea, monuron, monolinuron, diuron. linuron, neburon and chloroxuron. Both N -aryl and N -alkyl substituents appeared to play a part in adsorption. Increasing chain length in the alkyl substituents and chloro- and chlorophenoxy substitution in the aryl substituent increased adsorption. There was no relationship between adsorption and water solubility.
Organic matter content was the only soil property that could be related to adsorptive capacity. The evidence of Langmuir isothermal equilibrium plots suggests that only a fraction of the total soil surface is available for the adsorption of substituted ureas.
L'adsorption Je l'uré de ses dérivés sur dfférents sols     

THE ADSORPTION OF FOUR HERBICIDES BY DIFFERENT TYPES OF ORGANIC MATTER AND A BENTONITE CLAY*

Summary. A bioassay was used to study, adsorption of prometryne, simazine, linuron and pyrazon by fibrous peat, sphagnum moss, muck soil and bentonite as 1 % mixtures with quartz sand. Of these bentonite caused least reduction in bioactivity, and sphagnum moss reduced it only slightly more. Fibrous peat and muck soil were the most adsorptive. Prometryne, simazine and pyrazon were more highly adsorbed by fibrous peat than by muck soil, while for linuron the opposite occurred. Fibrous peat was approximately three, seven, thirteen and three times more adsorptive than bentonite for pyrazon, linuron, prometryne and simazine, respectively, while for muck soil the corresponding values were two, fourteen, seven and two. Studies with prometryne and five different soils indicated that percentage organic matter, cation-exchange capacity and specific surface area were all highly correlated with adsorption.     

SOME PHYSICO-CHEMICAL INTERACTIONS OF PARAQUAT WITH SOIL ORGANIC MATERIALS AND MODEL COMPOUNDS I. EFFECTS OF TEMPERATURE, TIME AND ADSORBATE DEGRADATION ON ARAQUAT ADSORPTION

Summary. Some investigations were carried out on the adsorption of paraquat by a range of organic materials which included an organic soil, various humic fractions from that soil, model polymers prepared by the oxidative coupling of benzoquinone, the ion exchange resins Zeo-Karb 216 and 226, and Amberlite XAD-2. The time required for the adsorption process to reach equilibrium ranged from about 3 h (for the soil and humic preparations) to about 48 h (for the more highly cross-linked materials). Adsorption by Amberlite XAD-2, a cross-linked polystyrene resin, was very small, presumably because it lacked ion-exchange sites.
The results suggested that particle diffusion control was operating and the different equilibrium times reflected different degrees of molecular complexity within the adsorbents.
Temperature, within the 20°–70°C range, did not affect the adsorption equilibrium, and this is indirect evidence for ion exchange as the primary adsorption mechanism. No evidence was found for decomposition of paraquat in the adsorption systems studied.
Quelques interactions physico-chimiques du paraquat avec des inatéaux de sol organique et des composes modéles I. Effets de la température, du temps et de la dégradation sur I'adsorption du paraquat     

CHLORAMBEN (AMIBEN) DEGRADATION JN SOIL

Summary. When columns of three soil types were perfused with a microbial medium containing 5·7 and 26·9 ppm ¹⁴COOH-labelled chloramben, there was a rapid decrease in the ¹⁴C activity remaining in solution, attributable to soil adsorption. Soil pH and organic matter content were the primary factors controlling chloramben adsorption. Soil pH may enhance adsorption through its effect on the number of soil anion exchange sites, and sites for polyvalent cation bridging and H bonding. Following adsorption, liver decreases in solution ¹⁴C-chloramben activity were attributed to degradation; ¹⁴CO2 evolved during perfusion amounted to 25–30% of the total decrease in ¹⁴C-chloramben from solution. It was concluded that more than 90% of the ¹⁴C-activity remaining in solution could be attributed to intact chloramben. Thus, decarboxylation appeared to be the primary mechanism of chloramben degradation in soils. Lag phases observed during degradation and subsequent investigations with re-amended solutions implicated the soil microflora; even at chloramben concentrations of 26.9 ppm no toxic effect on the chloramben-degrading micro-organisms was apparent.
Dégradation du chlorambène [amibène) dans le sol     

SHOOT ZONE UPTAKE OF SOIL-APPLIED HERBICIDES IN PISUM SATIVUM L.

Summary. The effects of localized herbicide placement at different internodes of pea ( Pisum sativum L. cv. Alaska) shoots below the soil surface after plant emergence were studied by removing the soil from around the shoots and replacing with herbicide-treated soil. The first internode proved insensitive to linuron, diuron, atrazine and simazine at 4·5 kg/ha, while treatment of the second and third internodes markedly reduced plant growth 4–6 days after treatment. Separate exposure of the first internode alone, and the second and part of the third together to ¹⁴C-labelled atrazine indicated no difference in herbicide metabolism. However, a two- to threefold increase in ¹⁴C uptake and movement to the foliar parts occurred when the second and part of the third internode was treated, as compared to first internode treatment. Thus the differential sensitivity of the internodes to atrazine, and possibly to the other herbicides, may be because the more mature first internode allows less uptake and subsequent movement to the foliar parts.
Absorption dans la zone des tiges des herbicides appliqués dans le sol chez Pisum sativum L.     

Response of black, cranberry, kidney, and white bean to linuron

Dry bean producers in Ontario, Canada, have few herbicide options available for annual broad-leaved weed management and there is little information on the tolerance of dry bean to linuron. The tolerance of black, cranberry, kidney, and white bean to the pre-emergence (PRE) application of linuron at the rates of 0, 500, 1000, 1500, 2000, and 2500 g ai ha⁻¹ was evaluated in field studies conducted in 2005 and 2006 at Exeter and in 2006 at Ridgetown, Ontario. The four market classes differed in their response to linuron. Cranberry and kidney bean were more tolerant to the PRE application of linuron than black and white bean. Linuron applied PRE caused as much as 12% injury in cranberry and kidney bean, 47% injury in black bean, and 56% injury in white bean. Linuron applied PRE at 500–2500 g ai ha⁻¹ had no effect on the height of cranberry and kidney bean but decreased the height by 7, 8, and 15% in black bean and by 10, 13, and 23% in white bean at 1500, 2000, and 2500 g ai ha⁻¹, respectively. Linuron applied PRE at the rates evaluated did not cause any adverse affect on the yield of cranberry, kidney, and white bean but black bean yield was reduced by 16% at 2500 g ai ha⁻¹. Based on these results, there is not an adequate margin of crop safety for the PRE application of linuron in black and white bean at rates >1000 g ai ha⁻¹. However, there is a potential for the use of linuron PRE for weed management in cranberry and kidney bean at the rates evaluated.     

INFLUENCE OF SOIL PROPERTIES ON PHYTOTOXICITY OF 4–AMlNO-3,5,6–TRICHLOROPICOLINIC ACID (PICLORAM)

Summary. Effective dosages of picloram (4–amino-3,5,6–trichloropicolinic acid) required to reduce fresh weight of sunflowers ( Helianthus annuus L. var. Menonite) were determined for seven Saskatchewan soils under controlled environmental conditions. The relationships between ED₅₀ value and clay content, organic matter content and cation exchange capacity were evaluated by correlation and regression analysis for possible usefulness in predicting dose requirements. ED₅₀ values were also determined for Weyburn loam and in culture solutions adjusted to various pH levels.
There Was no significant correlation between ED₅₀ values of picloram and soil clay content or cation exchange capacity. ED₅₀ values were highly correlated with soil organic matter content, and they increased as the soil pH was lowered or raised from pH 6.5. The increase in ED₅₀ values in the acidic range was attributed to adsorption of the unionized molecules of picloram on the organic matter in the soil. The increase in ED₅₀ values in the alkaline range may be mainly due to reduced uptake of the ionized acid by plant roots.     

VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: SHOOT COMPARED WITH ROOT UPTAKE

Summary. Turnip, lettuce and ryegrass seedlings showed toxicity symptoms following shoot exposure to atrazine, linuron and aziprotryne at soil concentrations less than would be obtained from normal field applications. Responses following shoot exposure to simazine and lenacil were much less. Root exposure to all five herbicides caused seedling death at concentrations lower than those required for 'shoot-zone' toxicity. Pronamide and chlorpropham were tested against ryegrass only and at the concentrations examined were toxic only when localized in the shoot zone. Root exposure suppressed root growth, but the shoots were able to grow normally if the soil was kept sufficiently moist. Shoots contained more ¹⁴C-atrazine at emergence after shoot exposure compared with root exposure, but there was little subsequent uptake from the shoot zone. There was extensive uptake from the root zone after emergence. In the shoot-zone treatments, concentrations in the plant were high at emergence but were rapidly diluted by plant growth, whereas with root exposure, they increased throughout the experiments. The possible significance of these results to herbicide bebaviour under field conditions is discussed.
La distribution verticale des herbicides dans le sol et leur disponibilité pour les plantes: absorption comparée par la partie aèrienne et par les radnes     

Control of Avena fatua and Fagopyrum tataricum with tank mixtures of linuron or linuron + MCPA and sequential applications of linuron, and post-emergence A. fatua herbicides

Linuron (0.21 and 0.28 kg/ha) and linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture with field rates of barban, difenzoquat and flamprop-methyl reduced the phytotoxicity of these herbicides to Avena fatua. When linuron was applied immediately following or 6 days after the A. fatua herbicides no reduction in phytotoxicity to A. fatua occurred, suggesting that the antagonism may be occurring as a result of physical or chemical incompatability when the herbicides are mixed together. The possibility of obtaining broad-spectrum weed control with one trip over the field by applying linuron and one of these wild oat herbicides separately but at the same time using a double-boom, double-tank system deserves evaluation. When linuron was applied in a tank mixture (0.21 and 0.28 kg/ha), immediately after, or 6 days after diclofop-methyl (0.70 kg/ha), there was no reduction of A. fatua control, and wheat tolerance to the tank mixture was good. This tank mixture offers potential for control under field conditions of A. fatua and some broad-leaved weeds in one spray operation. Linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture severely reduced A. fatua control with diclofop-methyl. No loss of phytotoxicity to Fagopyrum tataricum occurred when the A. fatua herbicides tested were tank mixed with linuron or linuron + MCPA. Lutte contre Avena fatua et Fagopyrum tataricum avec des mélanges extemporanés de linuron ou de linuron + MCPA et des applications successives de linuron et d'herbicides de postlevée actifs contre A. fatua     

VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: TREATMENT OF DIFFERENT PROPORTIONS OF THE TOTAL ROOT SYSTEM

Summary. Uptake of atrazine and linuron by wheat seedlings was measured from different initial distributions of herbicide in the soil. Uptake of both compounds was proportional to the fraction of the total root system exposed to herbicide-treated soil. It was calculated that under the conditions of the experiments, this factor would offset the reduction in concentration of herbicide in the soil following incorporation of 1 kg/ha to 3, 6 or 9 cm, so that after the same time, the concentrations of herbicide in the plants in the different treatments would be similar.
La distribution verticale des herbicides dans le sol et leur disponibilité pour tes plantes: traitement de différentes fractions de l'ensemble du système racinaire total     

AN AUTORADIOGRAPHIC STUDY OF THE DISTRIBUTION OF 14C LABELLED ASSIMILATES AT DIFFERENT STAGES OF DEVELOPMENT OF OXALIS LATIFOLIA H.B.K. AND O. PES-CAPRAE L.

Summary. An autoradiographic study of the distribution of ¹⁴C-labelled assimilates, derived from ¹⁴CO₂ fed to the aerial parts, was made at ten different developmental stages of Oxalis latifolia H.B.K. and Oxalis pes-caprae L. Changing patterns of distribution of labelled assimilates to the underground parts of both species were revealed. These patterns are discussed in the context of the timing of control by defoliation and by foliageapplied herbicides.
Etude autoradiographique de la distribution des métabolites marqués an ¹⁴C à différents stades de développement de l'Oxalis latifolia H.B.K. et de l' O. pes-caprae L.     

The degradation of simazine, linuron and propyzamide in different soils

Simazine, linuron and propyzamide were incubated in 18 different soils at 25°C and field capacity soil moisture content. The degradation of each herbicide followed first-order kinetics. The half-life of simazine varied from 20 to 44 days, that of linuron from 22 to 86 days and that of propyzamide from 10 to 32 days. The rate of linuron degradation was highly significantly correlated with soil organic matter content, clay content, soil respiration and the extent of herbicide adsorption by the soil. The rate of simazine degradation was significantly and negatively correlated with soil pH, but the rate of propyzamide degradation was not related with any of the soil factors examined.     

Effect of the herbicides EPTC and linuron on cotton diseases caused by Rhizoctonia solani and Fusarium oxysporum f. sp. vasinfectum

The herbicides EPTC and linuron applied to soil in the field at three different concentrations X₂X, 1X, and 2X of recommended dose) decreased post-emergence, but not pre-emergence daraping-off in cotton incited by Rhizoctonia solani. Both herbicides at the two high concentrations significantly reduced wilt incited by Fusarium oxysporum f. sp. vasinfectum. Both herbicides reduced germination of chlamydospores of Fusarium in natural soil, but not in steamed soil. The 2X concentration of EPTC and linuron reduced the saprophytic activity of R. solani in soil. The effects of EPTC and linuron on post-emergence damping-off and wilt were attributed Ic their ability to suppress the saprophytic ability of R. solani and chlamydospore germinability of Fusarium in soil, respectively.     

Analysis of fatty acids in lipids of Verticillium dahliae and induction of lubimin accumulation in eggplant

The unsaturated fatty acid pattern and content of the main lipid fractions of three isolates of Verticillium dahliae were investigated, Oleic (C_18:1), linoleic (C_18:2) and linolenic (C_18:3) acids were the unsaturated fatty acids detected in the polar lipids and in the free fatty acids extracted from myceha of three isolates of the fungus. The concentration of the three fatty acids in polar lipids was about double that in free fatty acids, Linoleic acid was the predominant fatty acid in both lipid fractions. The capacity of linoleic and linolenic acids to induce lubimin accumulation in eggplant fruit discs was evaluated in comparison with that of the polyunsaturated fatty acid arachidonic acid, which is a known elicitor of phytoalexin synthesis in potato tuber. The accumulation of moderate levels of the phytoalexin was induced by arachidonic and linolenic acids, A higher induction was observed when browning of the tissue was inhibited by phenylthiourea. Under these conditions, linoleic acid induced only a slight accumulation of lubimin. The possible role of linolenic acid in triggering defence reactions in eggplant is discussed.     

A SPLIT-ROOT TETRAZOLIUM METHOD FOR EVALUATING EFFECTIVENESS AND PHYTOTOXICITY OF ROOT-ACTIVE HERBICIDES

Summary. Copper sulphate (GUSO₄.5H₂O) and sodium hydroxide (NaOH) were used to test the performance of a split-root method for evaluating the effectiveness and phytotoxicity of root-active herbicides. This method involves a vertical separation of the root system of weeping willow ( Salix babylonica L.) cuttings. One section is treated with the herbicide dissolved in half-strength Hewitt's medium while the other remains in medium without herbicide during the test period. Roots are assayed with 2,3,5-triphenyttetra-zolium chloride 24 h after treatment to determine their viability. Both herbicides satisfactorily reduced the viability of the treated roots as measured by the quantity of formazan extracted. Copper sulphate was systemic and injured untreated plant parts; sodium hydroxide affected only treated roots. The split-root tetrazolium method is relatively rapid and does not require sophisticated laboratory equipment.
Méthode au tétrazolium sur portions de racines pour l'évaluation de l'efficacité et de la phytotoxicité des herbicides agissant par les racines     

Premiers résultats de lutte biologique par les souches K84 et K1026 contre Agrobacterium radiobacter var. tumefaciens, agent du crown-gall des rosacées fruitières et du rosier au Maroc

Une collection de 206 souches marocaines d' Agrobacterium radiobacter var. tumefaciens a été testée vis-à-vis des souches antagonistes Agrobacterium radiobacter K₈₄ et K₁₀₂₆ in vitro . Ce test d'antagonisme a montré que la sensibilité des souches varie en fonction de la souche antagoniste, du biovar et de la plante-hôte d'origine. La K₁₀₂₆ s'est avérée meilleure que la K₈₄ aussi bien par le nombre et par le diamètre plus élevé. Des essais au champ ont montré une bonne efficacité de la souche antagoniste K₈₄ en seaux ou en sol naturellement infesté. La réussite de la lutte biologique avec la K₈₄ varie entre 70% et 95% sur GF677, rosier, amandier amer et pêcher par rapport aux témoins sans K₈₄, alors que l'abricotier s'est montré résistant au crown-gall aussi bien en sol inoculé qu'en sol naturellement infesté. Nous pensons généraliser cette lutte dans tous les foyers marocains à crown-gall avec une souche mutante de la K₈₄, la K₁₀₂₆, qui a donné aussi une satisfaction meilleure in vitro dans d'autres pays méditerranéens comme l'Espagne, la France et l'Italie.