STUDIES OF THE RESPONSE OF PLANTS TO ROOT-APPLIED HERBICIDES

Summary. Applications of several herbicides -were made to roots and to the bases of shoots of peas, cucumber, mustard and barley grown in soil, sand or water culture.
Localized applications (variation horizontal) of atratone and MCPA to roots of peas and barley in soil produced effects similar to those observed in water euluire, described in Pan I. Airatone killed the plants whether available to the whole or to only a portion of the root system whereas MCPA affected only the roots with which it was in direct contact, and growth continued when a portion of the root system was in herbicide-free environment.
In water culture, MCPA was more effective when applied to the lower (younger) roots with the upper (older) roots kept dry than when twice the concentration was applied evenly to the whole root system in water. When all the roots were kept wet the effect of application to the upper roots was greater than the effect of application to the lower roots. The response of plants to atratone was not appreciably altered whether applications were made to the upper or lower parts of the root system in water culture. Variations in water level had little effect.
Even when the herbicide solution was confined to the stem or hypocotyl, atratone and DNOC were little, if any, less effective than when applied to roots. MCPA, both as ester and sodium salt, was significantly less effective.
Partial replacement of solution in the root zone by sand and air did not reduce the activity of atratone at a given concentration. Similar replacement in the zone of the stem or hypocotyl greatly reduced the effectiveness of all herbicides. When sand of low water content was used, atratone and MCPA-sodium became quite ineffective via the stem, but DNOC and MCPA-ethyl ester remained active.
Études sur les réactions de certaines plantes á des herbicides appliqués aux racines II. Observations nouvelles sur l'effet de l'application localisée.     

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     

Joint action of sulfonylurea herbicides and MCPA

The joint action of mixtures of the sulfonylurea herbicides chlorsulfuron, metsulfuron and tribenuron and MCPA as a dimethylamine salt was assessed on Stellaria media L. and Lamium purpureum L. Two statistical analyses, and appropriate experimental designs, were used—the additive dose model (ADM) and the principle of parallel dose-response curves. The ADM analyses revealed that mixtures of the sulfony-lureas and MCPA were less potent than expected on Stellaria while the parallel-line assay analyses showed that activity of the sulfonylurea herbicides on Stellaria and Lamium was reduced in mixtures with MCPA. The antagonism was found to be dependent on the ratio of the two herbicides. Activity decreased with increasing MCPA ratios in the mixtures. Sequential spraying and selective placement of droplets revealed that MCPA only antagonized the sulfonylureas when the herbicides were in physical contact with each other. The benefits of applying both statistical methods when studying the joint action of two herbicides both possessing activity on the test plants are discussed. Action de melanges d'herbicides sulfonylurées et de MCPA L'action de melanges des herbicides sulfonylurées chlorsulfuron, metsulfuron et tribénuron avec le MCPA formulé en sel de diméthylamine, a été etudiée sur Stellaria media L. et Lamium purpureum L. Deux analyses statistiques asso-ciées a deux systèmes expérimentaux appropriés ont été utilisés: le modèle à doses additives (ADM) et le principe du parallélisme des cour-bes dose-effet. Les analyses ADM ont montré que les melanges de sulfonylurées et de MCPA ont été rnoins efficaces qu'attendu sur Stellaria. Les analyses en courbes parallèles ont montré que 1'activité des herbicides sulfonylurées sur Stellaria et Lamium était réduite dans des mélanges avec le MCPA.L'antagonisme dépendait du rapport entre les doses des deux herbicides, 1'activité décroissant avec 1'augmentation du taux de MCPA. Des traitements séquentiels et des dépôts localisés de gouttelettes ont montré que le MCPA n'était an-tagoniste des sulfonylurées que lorsque les herbicides étaient physiquement en contact. L'intérêt est discuté, d'utiliser les deux méthodes statistiques de concert pour étudier les interactions entre deux herbicides actifs sur les plantes test. Gemeinsame Wirkung von Sulfonylharnstoff-Herbiziden und MCPA Die Wirksamkeit von Mischungen der Sulfonyl-hamstoff-Herbizide Chlorsulfuron, Metsulfuron und Tribenuron mil MCPA als Dimethylamin-salz wurde an Stellaria media L. und Lamium purpureum L. bestimmt. Die Versuche wurden so angelegt, um 2 statistische Analysen anzuwen-den: das Additiv-Dosis-Modell (ADM) und das Prinzip paralleler Dosis-Wirkungs-Kurven. Die ADM-Analyse ergab, daß diese Mischungen gegenüber Stellaria weniger wirksam als erwartet waren, während die Parallel-Analyse zeigte, daß die Wirksamkeit der Sulfonylharnstoff-Herbiz-ide in Mischungen mil MCPA gegeniiber den beiden Arten herabgesetzt war. Es ergab sich, daß der Antagonismus vom Verhältnis der Mischungspartner abhängt. Die Wirkung nahm mit steigenden MCPA-Anteilen in den Mischungen ab. In Spritzfolgen und bei separater Applikation zeigte sich, daß MCPA nur dann gegenüber Sulfonylharnstoffe antagonistisch wirkte, wenn sich die Herbizide vermischten. Die Vorzüge der Anwendung der beiden statistischen Methoden zur Untersuchung des gemeinsamen Effektes von 2 Herbiziden ähnlicher Wirkung werden diskutiert.     

Effects of broadleaf herbicides on imazamet habenz-met hyl performance on wild oat (Arena fatua L.)

The influence of broadleaf herbicides on imazamethabenz-methyl performance on wild oat (Avena fatua L.) plants grown outdoors in pots was examined. The foliar activity of imazamethabenz-methyl was reduced when applied in mixture with salt formulations of MCPA and mecoprop, salt and ester formulations of bromoxynil and bentazone. In contrast, chlorsulfuron had no influence and ester formulations of MCPA and mecoprop either had no effect or promoted imazamethabenz-methyl performance. A comparison of the activity of imazamethabenz-methyl in mixture with the ester formulation of MCPA and the corresponding formulation blank revealed that the antagonistic effect of MCPA active ingredient in the salt and ester formulations were similar. However, because of an enhancing effect of the formulation constituents in the ester formulation antagonism was masked in mixture with the latter. Similarly, addition of a mineral oil adjuvant only masked but did not eliminate the antagonistic interaction between the two herbicides. Volume rate did not affect imazamethabenz-methyl activity nor the antagonistic effect of the salt formulation of MCPA. The ester formulation of MCPA, however, promoted imazamethabenz-methyl performance significantly more at the low than at the high volume rate. Sequential application reduced antagonism of the salt formulation of MCPA on imazamethabenz-methyl. Selective placement of droplets revealed that antagonism occurred only if imazamethabenz-methyl and the salt formulation of MCPA were applied in the same droplet but not as separate droplets. Neither foliarnor root-applied MCPA reduced the performance of root-applied imazamethabenz-methyl. The results indicate that antagonism of MCPA was caused by a reduced uptake. The implications of the results of the present study in relation to the performance of tank mixtures of imazametha-benz-methyl and broadleaf herbicides under field conditions are discussed. Effet d'herbicides antidicotylédones sur l'efficacité de l'imazaméthabenz-méthyle contre la folle avoine (Avena fatua L.) L'effet d'herbicides antidicotylédones sur l'efficacité de l'imazaméthabenz-méthyle contre la folle avoine (A vena fatua L.) a étéétudié sur des plantes cultivées en pot à l'extérieur. L'activité foliaire de l'imazaméthabenz-méthyle était réduite quand il était appliqué en mélange avec des formulations sel de MCPA, et de mécoprop, et des formulations sel ou ester de bromoxynil et de bentazone. Par contre, le chlorsulfuron n'avait aucun effet, et les formulations ester ou sel de mécoprop et de MCPA, soit n'avaient aucun effet, soit augmentaient l'efficacité de l'imazaméthabenz-méthyle. Une comparaison de l'efficacité de l'imazaméthabenz-méthyle en mélange avec une formulation ester de MCPA et avec le blanc de formulation correspondant, a montré que l'effet antagoniste de la matiére active MCPA était similaire dans les formulations sel et ester. Cependant à cause de l'effet stimulateur de constituants de la formulation ester, l'antagonisme était masqué dans le mélange. De mßme, l'addition d'une huile minérale masquait mais ne supprimait pas l'antagonisme entre les deux herbicides. Le volume d'application n'affectait pas l'efficacité de l'imazaméthabenzméthyle non plus que l'effet antagoniste de la formulation sel du MCPA. L'augmentation d'efficacité de l'imazaméthabenz-méthyle par la formulation ester du MCPA était significativement plus élevée à bas qu'à haut volume. Une application séquentielle réduisait l'antagonisme de la formulation sel du MCPA sur l'imazaméthabenz-méthyle. Des applications sélectives de gouttelettes ont montré que l'antagonisme ne se produisait que si l'imazaméthabenz-méthyle et la formulation sel de MCPA étaient appliquées dans la même gouttelette mais non dans des gouttelettes séparées. Le MCPA, qu'il soit appliqué sur le feuillage ou par les racines, n'affectait pas l'efficacité de l'imazaméthabenz-méthyle appliqué par les racines. Les résultats indiquent que l'antagonisme était provoqué par une réduction de la pénétration. Les implications pratiques des résultats de cette étude sur l'efficacité des mélanges d'imazaméthabenz-méthyle et d'herbicides antidicotylédones au champ sont discutées. Einfluß von Herbiziden gegen Dikotyle auf die Wirkung von Imazamethabenz-methyl auf Flug-Hafer (Avena fatua L.) Der Einfluß von Herbiziden gegen Dikotyle auf die Wirkung von Imazamethabenz-methyl auf Flug-Hafer (A vena fatua L.) wurde im Freiland in Topfversuchen untersucht. Die Wirkung von Imazamethabenz-methyl über das Blatt war herabgesetzt, wenn es in Mischung mit Salzformulierungen von MCPA und Mecoprop sowie Salzund Esterformulierungen von Bromoxynil und Bentazon ausgebracht wurde. Chlorsulfuron dagegen hatte keinen Einfluß, und Esterformulierungen von MCPA und Mecoprop beeinflußten die Wirkung von Imazamethabenz-methyl weder positiv noch negativ. Ein Vergleich der Wirksamkeit des Imazamethabenz-methyls in der Mischung mit der Esterformulierung von MCPA und der entsprechenden Leerformulierung zeigte, daß der antagonistische Effekt des Wirkstoffs MCPA in der Salz-und der Esterformulierung ähnlich war; die wirkungsfördernden Bestandteile der Esterformulierung maskierten jedoch den Antagonismus. In ähnlicher Weise wurde der Antagonismus zwischen zwie Herbiziden durch den Zusatz von Mineralöl nur überdeckt, aber nicht aufgehoben. Die Aufwandmenge blieb sowohl auf die Wirksamkeit des Imazamethabenz-methyls als auch auf den Antagonismus der MCPA-Salz formulierung ohne Einfluß. Aber bei der niedrigen Aufwandmenge förderte die Esterformulierung von MCPA die Wirkung von Imazamethabenz-methyl signifikant mehr als bei der hohen. Aufeinander folgende Anwendung mäßigte den Antagonismus der MCPA-Salz-formulierung auf Imazamethabenz-methyl. Der Antagonismus trat nur auf, wenn Imazamethabenz-methyl mit MCPA-Salzformulierung zusammen, nicht aber in getrennten Tröpfchen nebeneinander appliziert wurde. Weder übers Blatt noch über die Wurzeln appliziertes MCPA minderte die Wirkung von wurzel-appliziertem Imazamethabenz-methyl. Die Ergebnisse zeigen, daß der Antagonismus von MCPA durch eine reduzierte Aufnahme zustande kam. Die Untersuchungsergebnisse werden hinsichtlich der Wirksamkeit von Tank-mischungen von Imazamethabenz-methyl mit Herbiziden gegen Dikotyle unter Freiland-bedingungen diskutiert.     

The effect of repeated applications of 2,4-D and MCPA on their breakdown in soil

The effect of repeated applications of 2,4-D and MCPA in a long-term field experiment on their subsequent degradation was investigated. The herbicides had been applied annually since 1954, Comparisons were made with plots treated once and then retreated the following year. Repealed applications of the two herbicides resulted in a reduction in degradation lime from 10 weeks for 2,4-D and 20 weeks for MCPA after one application to 4 and 7 weeks respectively after 19 years of annual application. In spite of an increased capability of the soil microflora lo degrade 2,4-D and MCPA 9 months after a previous treatment. no change in numbers of organisms capable of utilizing the substances as carbon sources were found in treated plots as compared with the control. It is obvious that there is a cross adaptation between 2,4-D and MCPA. It seems most likely that two different ‘enrichment’ been induced, each capable of decomposing both herbicides, but with different efficiencies. Effet d'applications répétée de 2,4-D et de MCPA sur leur degradation dans le sol L'effet d'applications répétée de 2.4-D et de MCPA sur leur degradation uléerieure a étéétudié dans une expérience au champ de longue durée. Les herbicides ont été appliqués chaque année depuis 1954. Des comparaisons ont été effectuées avec des parcelles traiées une fois et traitées à nouveau l'année suivante. Les applications répétées des deux herbicides ont provoqué une réduction du temps de dégradation qui est passé de 10 semaines pour le 2,4-D et 20 semaines pour le MCPA après une seule application, à 4 et 7 semaines respectivement, après 19 années d'applications annuelles. En dépit d'une capacité accrue de la microflore du sol à dégrader le 2.4-D et le MCPA, neuf mois après un traitement préalable, aucun changement n'a été constaté dans le nombre des organismes capables d'utiliser les produits comme sources de carbone dans les parcelles traitées, par rapport au témoin. II est évident qu'il y a une adaptation croisée entre le 2,4-D et le MCPA. II apparait très probable que deux ‘enrichissements’ de Hores ont été induits, chacun d'eux étant capable de décomposer les deux herbicides mais avec des efficacités différentes. Die Wirkung wiederholter Behandlungen von 2.4- D und MCPA auf ihren Abbau im Boden Die Wirkung wiederholter Anwendungen von 2,4-D und MCPA auf ihren Abbau wurden in einem Freiland-Versuch untersucht. Die Herbizide wurden jährlich, sell 1954 ange-wendet. Es wurden Vergleiche mil Parzellen angcstellt, die zum erstenmal und im folgenden Jahr nochrnaK bchandelt worden waren. Die widerholien Behandlungen mit den beiden Herbiziden bewirkte elne Verringerung der Ab-bauzeit von 10 Wochen fur 2,4-D und 20 Wochen fiir MCPA nach einer Behandlung, auf 4 bzw. 7 Wochen nach 19 Jahren jahrlicher Anwendung. Trotz der erhohten Ffihigkeit der Bodenmikroflora 2,4-D und MCPA neun Monate nach einer vorhergehenden Behandlung abzubauen, war die Zahl der Organismen, die diese Herbizide als Kohlensloffquelle verwerten konnen, in den behandelten und unbehandelten Parzellen gleich gross. Zwischen 2.4-D und MCPA existiert ofVensichtlich elne Kreuz-Adaplalion. Sehr wahrscheinlich wurden zwei versehiedene ‘enrichment’-Floren induziert, von der jede in der Lage ist beide Herbizide, aber mit unterschiedlicher Effizienz, Hbzubauen.     

Interaction between benzoylprop ethyl, flamprop methyl or flamprop isopropyl and herbicides used for broadleaved weed control

A marked antagonism of A. fatua control was found when 2,4-D, dicamba, 2,4-D-dicamba-mecoprop or bromoxynil were added to benzoylprop ethyl, flamprop methyl or flamprop isopropyl. Because of the much poorer control of A. fatua by these mixtures obtaining broad spectrum weed control with them in one spray operation would not be possible. The A. fatua herbicides did not affect the activity of the added herbicides on Fagopyrum lataricum. In eight out of nine mixtures tested there was no significant antagonism in the field conditions when MCPA or bromoxynil-MCPA was added to the A. fatua herbicides. There were significant antagonistic effects, however, in six out of nine such mixtures in glasshouse experiments. This suggests that under farm use conditions benzoylprop ethyl, flamprop methyl or fiamprop isopropyl can be mixed with MCPA amine or ester or with bromoxynil-MCPA to obtain broad spectrum weed control from one spray operation, though slightly poorer A. fatua control may be expected with these mixtures.     

THE CONTROL OF WEEDS IN SPRING CEREALS WITH MCPA, MCPB AND 2,4-DB

Summary. Eighteen experiments were carried out over a period of 4 years jointly by the National Agricultural Advisory Service and the Agricultural Research Council Unit of Experimental Agronomy to compare the effects of spraying spring cereals with MCPA, MCPB, 2,4-DB and mixtures of MCPA and MCPB, at two different times. The first applications was made before the cereal crop had reached the five-leaf stage and when it was judged that most of the weeds had germinated. The second application was after the crop had reached the five-leaf stage, which is the time normally recommended in Britain for the application of MCPA to spring wheat or spring barley. The earlier applications produced better crop yields and gave a better control of weeds except where conditions for spraying were unsatisfactory or where a considerable number of weeds germinated subsequently. Mild deformity of the ears of the crop occurred in some experiments following early applications of MCPA, otherwise there were no marked differences in the effect on the crop of the different herbicides at the doses used; the dose of MCPA was less than that of the other herbicides. In view of these results and the lower cost of MCPA, it is concluded that MCPA applied early is the most efficient of the treatments tested except where the risk of malformed ears occurring is not acceptable.
Le désherbage dans les céréales de printemps avec le MCPA, le MCPB, et le 2,4-DB     

Effect of MCPA on the phytotoxicity of imazamethabenz-methyl applied to wild oats (Avena fatua L.)

Greenhouse studies were conducted to determine the effect of both ester and amine formulations of MCPA on the phytotoxicity of imazamethabenz applied to wild oats (Avena fatua). The MCPA ester antagonized activity of the liquid concentrate (LC) formulation of imazamethabenz but not the suspension concentrate (SC) formulation of imazamethabenz when the combination was applied to wild oats at two-to three-leaf stage without tiller. The MCPA amine antagonized the efficacy of both formulations of imazamethabenz on wild oats at the two-to three-leaf stage. When the herbicides were applied at the three- to four-leaf stage with one or two tillers, the antagonism was found only with MCPA amine and imazamethabenz-LC. In general, antagonism is most likely to occur at an early stage of wild oats. MCPA amine was more antagonistic than MCPA ester on the phytotoxicity of imazamethabenz. Imazamethabenz-SC can be tank mixed with MCPA ester but should not be tank mixed with MCPA amine. Imazamethabenz-LC should not be tank mixed with either ester or amine of MCPA because of antagonism, especially when herbicides are applied at early stage. When MCPA was applied at intervals of from 2 to 24 h following applications of imazamethabenz-LC, there was no antagonistic effect of MCPA and the same level of phytotoxicity was produced as with imazamethabenz-LC alone. In the reverse sequence of MCPA followed by imazamethabenz-LC, the greatest antagonism of phytotoxicity of imazamethabenz-LC occurred when 2 h separated the two applications. This effect was lessened when the elapsed time increased. Effet du MCPA sur I'efficacitée de l'imazaméthabenz-méthyle sur la folle avoine (Avena fatua L.) Des études en serres ont étéé réalisées pour déterminer I'effet de formulations ester et amine du MCPA sur l'efficacité de l'imazaméthabenz contre la folle avoine (Avena fatua L.). Lorsque le mélange était appliqué sur des folles avoines au stade 2–3 feuilles sans talle, l'ester de MCPA était antagoniste de la formulation de l'imazaméthabenz en concentré liquide (LC) mais pas de la formulation en suspension concentrée (SC). Le MCPA amine était antagoniste des deux formulations d'imazaméthabenz. Quand les herbicides étaient appliqués au stade 3–4 feuiles avec 1–2 talles, l'antagonisme ne s'observait qu'avec le MCPA amine et l'imazaméthabenz- LC. En général, l'antagonisme se produisait surtout aux stades précoces de la folle avoine. Le MCPA amine était plus antagoniste de l'activité de l'imazaméthabenz que le MCPA ester. L'imazaméthabenz-SC peut étre mélangé au moment du traitement avec le MCPA ester mais pas avec le MCPA amine. L'imazaméthabenz- LC ne doit pas étre mélangé au moment du traitement avec le MCPA, qu'il soit sous forme ester ou amine, surtout quand les herbicides sont appliqués è un stade précoce. Quand le MCPA était appliquéè des intervalles de 2 è 24 h après l'imazaméthabenz-LC, il n'y avait pas d'antagonisme du MCPA. Si l'ordre des applications était inversé, l'antagonisme était le plus important lorsque 2 h les séparaient et il diminuait lorsque l'intervalle augmentail. Beinflussung der Phytotoxizität von Imazamethabenz-methyl auf Avena fatua L. durch MCPA In Gewächshausversuchen setzte MCPA-Ester die Wirkurlg der Flüssig-Formulierung von Imazamethabenz-methyl auf Avena fatua L. im 2- bis 3-Blatt-Stadium herab, aber nicht die der Suspensions-Formulierung. MCPA-Amin war gegenüber beiden Formulierungen antagonistisch. Im 3- bis 4-Blatt-Stadium bei 1 bis 2 Bestockungstrieben trat die Wirkungsminderung durch MCPA-Amin nur bei der Flüssig- Formulierung ein. Also scheint der Wirkungsantagonismus in frühen Avena-fatua- Entwicklungsstadien und für MCPA-Amin am stärksten zu sein, so daé es von Tankmischungen mit der Suspensions-Formulierung ausgenommen werden sollte. Die Flüssig-Formulierung sollte weder mit MCPA-Amin noch -Ester gemischt werden. Bei Applikation von MCPA 2 bis 12 h nach Imazamethabenz-methyl in der Flüssig-Formulierung wurde die Wirkung nicht beeinträchtigt. Umgekehrt ergab sich bei Anwendung der Flüssig-Formulierung 2 h nach einer MCPA-Ausbringung der gröte Antagonismus, der sich mit längerem Abstand zwischen den Anwendungen verringerte.     

DEGRADATION OF SEVERAL HERBICIDES IN A SOIL PREVIOUSLY TREATED WITH MCPA

Summary. Soil which had received nine previous field treatments of MGPA (33 kg/ha) at intervals of about 6 months, and which had become able to detoxify MCPA more rapidly than untreated control soil, was able to degrade MCPB with equal facility. In contrast, the disappearance rates of phytotoxic residues of dichlorprop (2-(2,4-dichloro-phenoxy)propionic acid), mecoprop (2-(4-chloro-2-methylphenoxy)propionic acid), fenoprop (2-(2,4,5-trichlorophcnoxy)propionic acid) and dicamba (2-methoxy-3,6-dichlorobcnzoic acid), as determined with a bioassay technique, were unaffected by previous treatments of the soil with MCPA. Indirect evidence from these studies suggests that β-oxidation of MCPB to MCPA did not occur to any significant extent either in the soil to which the roots of the indicator plant were exposed or in the roots themselves. Dégradation de quelques herbicides dans un sol préddenvnent traté avec le MCPA Résumé. Un sol ayant reçu 9 traitements au MGPA (3,3 kg/ha) à des intervalles d'environ 6 mois et qui est devenu capable de dégrader le MCPA plus rapidement qu'un téntoin non traité, s'est montré capable de diégrader le MGPB avec la mêmefacilité. En revanehe, les taux de disparition de résidus toxiques déterminés par des testsbiologiques, du dichlorprop (acide 2-(2,4-dichlorophenoxy)propionique), du mécoprop(acide 2-(4-chloro-2-méthylphénoxy)propionique), du fénoprop (acide 2-(2,4,5-trichlorophénoxy)propionique) et du dicamba (acide 2-méthoxy-3,6-dichlorobenzoique) n'ont pas été affectés par les traitements antérieurs avec le MCPA. Comme conclusion indirecte de ces travaux il est suggéré que la β-oxydation du MGPB en MCPA ne se produit pas à un dcgré significatif dans le sol où les racines desplantes servant d'indicateurs sont plongées, pas plus que dans les racincs elles-mêmes. Abbau von verschiedenen Herbiziden in einem vorher mit MCPA behandelten Boden Zusammenfassung. Boden, der auf dem Feld in Abstanden von sechs Monaten neunmal mit MGPA (3,3 kg/ha) behandelt wurde und dadurch in der Lage war, MGPA schneiler umzuwandeln als der unbchandelte Kon troll boden, konnte MCPB gleichermassen abbauen. Mit Hilfe von Biotests wurde ermittelt, dass vorausgehende Behandlungen des Bodens mit MCPA dagegen keinen Einfiuss auf die Abbaurate phytotoxischer Rückstände von Dichlorprop (2-(2,4-Dichlor-phenoxy)-propionsäurc), Mecoprop(2-(4-Ghlor-2-methyl-phenoxy)-propionsäure), Fenoprop (2-(2,4,5-Trichlorphenoxy)-propionsaure) und Dicamba (3,6-Dichlor-2-methoxy-benzoesaure) hatten. Die Ergebnisse lassen darauf schliessen, dass der β-Oxidation von MCPB zu MGPA weder im Boden, dem die Wurzein der Testpflanzen ausgesetzt waren, noch in den Wurzeln selbst Bedeutung zukam.     

STUDIES OF THE RESPONSE OF PLANTS TO ROOT-APPLIED HERBICIDES

Summary. Peas, barley and linseed were grown in water-cuture. Roots were divided into two portions and contained in separate vessels. The effect of herbicides applied to one-third of the roots was compared with their effect when applied to the whole root system.
Propham, chlorpropham, atratone and 2,3,6-TBA killed the plant whether application was to one-third or all of the roots. Roots in direct contact with propham, chlorpropham and 2,3,6-TBA were deformed or killed, while roots in uncontaminated solution remained healthy. The effect of atratone and high concentrations of chlorpropham on a portion of the roots was transmitted to roots not in the toxic solution.
Certain concentrations of MCPA and DNOC applied to the whole root system killed the plant while three times the concentration to one-third of the roots caused local damage but had little effect on the plant as a whole. Sufficient herbicide may be taken up by one- third of the roots from high concentrations to kill the whole plant.
TGA gave variable results with respect to the health of the aerial portion of the plant but had no obvious direct effect on root growth.
Propham, chlorpropham, atratone and 2,3,6-TBA reduced transpiration rates whether applied to part or whole root systems. MCPA and DNOC prevented water uptake by roots with which they Were in direct contact.
Etudes sur les réactions de certaines plantes à des herbicides appliqués aux racines I. Effet d'une application localisée     

Synergistic joint action of MCPA ester and metsulfuron-methyl

MCPA is antagonistic to a range of herbicides but there is limited research on its compatibility with other broad-leaved weed herbicides. In this study we assessed the joint action of MCPA ester and metsulfuron-methyl on Brassica napus L. using the additive dose model (ADM). The fresh weight responses for selected ratios of the mixture were plotted on the ADM and compared to the predicted mixture response at three assessment levels - 50, 75 and 90% control. The mixture demonstrated increasing synergism as the response level increased from 50 to 90%. This result for MCPA ester is in marked contrast to that of the MCPA amine formulation, which was shown in previous studies to be antagonistic towards sulfonylurea herbicides. Formulation is the major deciding factor in determining the compatability of phenoxy herbicides with other herbicides.     

Yield responses of spring cereals to reduced herbicide doses

Reduction of the dose of MCPA/mecoprop and MCPA/fluroxypyr mixtures to half or one-third of the recommended rates still provided good weed control efficacy in spring wheat (Triticum aestivum L.) and particularly in spring barley (Hordeum vulgare L). The average yield of treated plots was 8% higher in wheat and 1% higher in barley compared with untreated plots. However, yield reductions were observed in 32% of wheat plots and in 43% of barley plots treated with herbicides. The yield responses were poorly correlated with the weed density of mixed weed flora at the time of spraying. No reliable threshold density for chemical weed control was found. Réponses au rendement de céréales de printemps, à des doses d'herbicides réduites La réduction de la dose de MCPA/mecoprop et MCPA/fluroxypyr a la moitié ou au tiers des taux recommandés a encore assure une bonne efficacité herbicide chez le blé de printemps (Triticum aestivum L.) et specialement chez l'orge de printemps (Hordeum vulgare L.). Le rendement moyen des parcelles traitées était de 8% plus élevé chez le blé et de 1%élevé chez l'orge que dans les parcelles non traitees. Cependant, des reductions de rendement ont été observées dans 32% des parcelles de blé et dans 43% des parcelles d'orge traitées aux herbicides. Les reponses du rendement étaient faiblement liées a la densité en adventices d'une flore mixte au moment du traitement. Aucune densité seuil-sérieuse pour le desherbage n'a été trouvée. Ertragsbildung von Sommergetreide bei reduziertem Aufwand von Herbiziden Eine Reduzierung des Aufwands von MCPA-Mecoprop- und MCPA-Fluroxypyr-Mischungen auf die Halfte oder ein Drittel des empfohlenen Aufwands ergab in Sommerweizen (Triticum aestivum L.) und besonders in Sommergerste (Hordeum vulgare L.) noch eine gute Unkrautbekampfung. Im Mittel war der Ertrag der behandelten Parzellen beim Weizen um 8% und bei der Gerste um 1% höher als in den unbehandelten, aber in 32% der Herbizidparzellen mit Weizen und in 43% der mit Gerste wurden Ertragsminderungen beobachtet. Die Ertragsbildung stand kaum in Beziehung zur Unkrautdichte zur Zeit der Behandlung. Es wurde keine verläßliche Schadensschwelle gefunden.     

Yield losses in weed-free wheat and barley due to post-emergence herbicides

The tolerance of weed-free wheat and barley to a range of herbicides (bromoxynil, methabenzthiazuron, MCPA, bromoxynil + MCPA. linuron, prometryne, diuron, 2,4-D ester and 2,4-D amine) when applied at the crop three-leaf stage, was examined over the 5-year period 1968–72. All chemicals lowered grain yields to some extent, but the variation between chemicals was greater for wheat than for barley. In both crops, methabenzthiazuron was the safest chemical causing only small (<2·0%,) yield losses at rates up to 2·25 kg a.i./ha. At this rate of application yield losses of up to 36% were recorded for the substituted urea derivatives. Both crops had a low tolerance to 2,4-D ester and amine. Yield losses from bromoxynil, bromoxynil + MCPA and MCPA were similar, varying from 4 to 8% al 0·5 kg a.i./ha to 9–24% at 2·25 kg a.i./ha. Pertes de rendement dans le blé et l'orge provoquées, en l'absence de mauvaises herbes, par des herbicides de postlevée Pendant une période de 5 années (1968–1972) les auteurs ont examiné la résistance du béet de l'orge. Traités, en l'absence de mauvaises herbes, au stade 3 feuilles, avec une série d'herbicidcs (bromoxynil, méthabenzthiazuron, MCPA, bromoxynil-i-MCPA, linuron, prométrync. ditiron, 2,4-D ester et 2,4-D a mine). Tous ces produits ont diminué les rendements en grains dans des proportions variées, mais la variation entre produits a été plus grande pour le blé que pour l'orge. Pour les deux céréales, le méthabenzlhiazuron a été le produit le moins toxique, provotjuant seulement de faibles penes de rendement inférieurcs à 2,0%, à des doses allant jusquà 2,25 kg/m.a/ha. A cette dose d'application, des pertes de rendement allant jusquà 36% ont élé enregistrées avec des urées substituées. Les deux éréles ont manifesté uoe faible resistance au 2,4-D estr et amine. Les pertes de rendement provoquées par le bromoxynil, le bromoxynil + MCPA, et le MCPA ont été analogues, variant de 4 à 8% pour 0,5 kg/m.a./ha, jusqu’à 9 à 24% pour 2,5 kg/m.a./ha. Ertragsverluste durch Nachaufiatifherbizide in unkrautfreiem Weizen und Gerste In unkrautfreien Weizen- und Gerstebestánden wurde in fünfjáhrigen Versuthcn (1968–72) die Toleranz der beiden Arten gegenüber folgenden Herbiziden untersucht: Bromoxynil, Methabenzthiazuron, MCPA, Bromoxynil + MCPA. Linuron, Prometryn, Diuron, 2,4-D-Eister und 2,4-D-Amin- salz. Die Behandlung erfolgte jeweils im 3-Blattstadium. Alle Verbindungen erniedrigten zu einem gewissen Grad den kornertrag. Beim Weizen waren aber die Unterschiede zwischen den verschiedenen Herbiziden grösser als bei der Gerste. Methabenzthiazuron war bei Aufwandmengen bis zu 2.25 kg A.S./ha in beiden Getreidearten das sicherste Herbizid und verursachte nur geringe Ertragsdepressionen (<2%). Bei dieser Aufwandmenge wurden bei den Harn-stoffherbiziden bis zu 36% Ertragsverlust festgestellt. Gegen 2,4-D-Ester und 2,4-D-Aminsalz waren Weizen und Gerste wenig tolerant. Die Ertragsverluste durch Bromoxynil, Bromoxynil + MCPA und MCPA waren etwa gleich und betrugen 4–8% bei 0.5 kg A.S./ha bis 9–24% bei 2,25 kg A.S./ha.     

Glasshouse trials with controlled drop application of some foliage-applied herbicides

MCPA, mecoprop, dichlorprop, dicamba, 2,3,6-TBA, bentazone, ioxynil/bromoxynil (a mixture), barban, difenzoquat and chlorfenprop-methyl were applied by spinning disc in controlled drop sizes from 150-350μm and at very low volume rates (5–45 1/ha), to the foliage of some dicotyledonous weed species or wild oats (Avena fatua L.). The same herbicides were also applied by means of conventional hydraulic nozzles at volume rates of about 200 1/ha. Most of these herbicides performed as well at very low volume rates as with the conventional application, the major exceptions being bentazone, ioxynil/bromoxynil (both of which have distinct contact effects) and dichlorprop. Comparisons between oil and water as the diluent at a very low volume rates suggest that there may be situations when oil is preferable and others when water is.     

Herbicide Effects on Sugarcane Growth, Pythium Root Rot, and Pythium arrhenomanes

ABSTRACT Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.     

CONTROL OF SONCHUS ARVENSIS (L.) WITH CHEMICALS

Summary. Pot experiments concerning the control of Sonchus arvensis with chemicals showed that the time of application of MCPA or 2,4-D has a dominant influence on the results obtained. Foliage applications at late rosette to early bud stage gave considerably better effects than did earlier or later applications as assessed by the. weight of roots, this assessment being considered the most reliable for final effects. Increasing the rates from 1 to 3 kg/ha was of less significance than the time of application. A good wetting ability of the spray solution is also essential for an effective control of this weed, which has very waxy leaves. The addition of a wetting agent to aqueous solutions of various salts of 2,4-D had a great and significant influence on the effects. This was not the case with 2,4-D acid in Carbowax. When wetter was added, there was no difference in the effects of the sodium, ammonium and triethanolamine salts. The latter were also slightly more effective than MCPA. 2,4-D-ester was much more effective than MCPA by foliage application. When the chemicals were applied to the roots through sub-irrigation pipes, however, MCPA was at least as effective as 2,4-D-ester. The maximum effect by this method of application was obtained at a somewhat later stage of development than by foliage application. By foliage application of MCPA and dinoseb or DNOC at various rates used alone or in mixture, an antagonism between the growth regulator and the contact herbicides was demonstrated as regards the reduction in root weight of S. arvensis . The scorching effects of dinitro compounds were, on the contrary, increased when applied in combination with MCPA. Amitrole at rates of 5, 7.5 and 10 kg/ha applied at late rosette stage gave a complete kill of S. arvensis.
La destruction du Sonchus arvensis L. à l'aide de produits chimiques     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Herbicidal potential of pyrenophorol isolated from a Drechslera avenae pathotype

A pathotype of Drechslera avenae (Eidam) Scharif exhibited host‐specificity, being pathogenic to Avena sterilis L but not to a number of related or unrelated species tested. In culture, the fungus produces a metabolite which was identified as the macrodiolide pyrenophorol (5,13‐dihydroxy‐8,16‐dimethyl‐1,9‐dioxa‐cyclohexadeca‐3,11‐diene‐2,10‐dione). This compound at a concentration of 320 µM was phytotoxic to A sterilis and considerably less so to Avena fatua L. The phytotoxicity was expressed as leaf necrosis on seedling cuttings partially immersed in pyrenophorol solution and as ‘green islands’ on detached leaves on which droplets of the solution were placed. Seed germination and seedling growth of A sterilis were not affected. Pyrenophorol at concentrations up to 640 µM did not cause any symptoms of phytotoxicity to a number of other monocotyledons or dicotyledons tested, with the exception of Lycopersicon esculentum Miller on which leaf necrosis was observed after application of the substance through the vascular system to seedling cuttings. These findings are discussed in relation to the exploitation of such compounds of natural origin as wild oat herbicides. © 2000 Society of Chemical Industry     

Effects of dose and application timing on the seed production of three weed species treated with MCPA or tribenuron-methyl

The seed production of Fallopia convolvulus (L.) A. Love, Galium spurium L, and Thlaspi arvense L., treated with MCPA or tribenuron-methyl, was studied in a pot experiment. The herbicides were applied in doses from 1/16 to 1/l of a full dose at five different growth stages. The largest reduction of seed production was observed on plants treated when one true leaf had developed (F. convolvulus, both herbicides) or at the beginning of the generative phase (G. spurium treated with tribenuron-methyl and T. arvense treated with either herbicide). Tribenuron-methyl (0.375 g a.i. ha^?1) or MCPA (0.1875 kg a.i. ha^?1) applied at bolting stage was enough to reduce the seed production of T. arvense by 83% and 100%, respectively. The seed production of F. convolvulus, treated with 0.75 kg MCPA at the cotyledon stage, was reduced by 70%. Plants of G. spurium with 5–9 axillary shoots, treated with 3 g tribenuron-methyl, produced 45% fewer seeds than the control. Both herbicides (at least at the highest doses) reduced seed production of all three species more than shoot dry matter.     

Pesticides and the Honey Bee

Abstract

In wheat fields, irrigated with treated sewage water, the performance of six herbicides: bromoxynil/MCPA; bentazon/ dichlorprop; diclofop‐methyl; tralkoxydim; pendimethalin and bromophenoxim; and some their combinations were assessed at two different locations around the city of Riyadh. The common weeds include: Lolium spp.; Phalaris spp.; Avena spp.; Malva spp.; Chenopodium spp. and others. The best weed control treatments were: bentazon/dichlorprop followed by bromoxynil/MCPA for the broad‐leaved, and diclofop‐methyl followed by tralkoxydim for the grassy weeds. The combinations of bromoxynil/MCPA with either pendimethalin or tralkoxydim were far more effective against the broad‐leaved weeds, and significantly improved the wheat growth and yield, compared with the single treatments. However, bromoxynil/MCPA combination with diclofop‐methyl was less effective against the grassy and broad‐leaved weeds than each of them. Bromophenoxim showed an effective control of the whole weeds, with appreciable improvement in the wheat growth and yield.