FIELD EXPERIMENTS TO INVESTIGATE LONG-TERM EFFECTS OF REPEATED APPLICATIONS OF MCPA, TRI-ALLATE, SIMAZINE AND LINURON: REPORT AFTER 6 YEARS

Summary. In five long-term field experiments begun in 1963, each of four herbicides was applied to plots either planted with the same crop each year or uncropped. The following treatments were applied annually: MCPA at 24 oz/ac to barley at the 5-leaf stage, triallate at 24 oz/ac to barley pre-emergence, simazine at 24 oz/ac to maize pre-emergence, linuron at 12–24 oz/ac to carrots preand post-emergence. The main assessments reported in this paper are crop yield and persistence of herbicide residues. In the fifth experiment, these herbicides were applied twice each year at about double the above these to plots kept as far as possible free from all vegetation. MCPA did not affect the yield of barley and disappeared from the soil within 2–3 weeks of each application. In the uncropped plots, the time for the applied dose (3 lb/ac) to reach the limit of detection was reduced from 3 weeks in 1964 (after three previous applications) to 4 days in 1968 (after ten previous applications). Tri-allate did not affect the yield of barley. Soil residues could be detected for 5–6 months following each dose of 24 oz/ac. When applied at 48 oz/ac twice yearly, a residue persisted but with no progressive build-up during the 6-year period. Agreement between bioassay and CLC methods of determining residues varied from good to a factor of 4, with CLC usually, but not always, providing a higher figure. No residues of pre-allate could be detected in the barley straw or grain. Simazine did not influence the yield of maize during 1963–67. In 1968 there was a significant reduction in yield of foliage and stems but not in grain yield. Simazine applied to maize disappeared from the soil rapidly during the first 6 weeks; after this period 20–25% of the applied dose could be recovered. The remaining residues declined slowly and 1–2 oz/ac could be detected 23–50 weeks after application. No residues were found below the 0–2 in. soil level. When 48 oz/ac was applied twice annually a residue persisted varying from 8 to 27 oz/ac/6 in. There was no accumulation from year to year and no evidence that repeated treatment influenced breakdown rate. Most of the simazine remained in the 0–2 in. soil level. In three out of four determinations there was good agreement between CLC and bioassay results. Linuron reduced the yield and % dry matter content of carrot roots in 1965 and 1966 probably because of exceptional short-term phytotoxicity, otherwise there was no effect. Half the applied dose of 8–16 oz/ac disappeared from the soil within 8 weeks and residues were undetectable after 6 months. The residues in the uncropped plots did not fall below 11 oz/ac. Most remained in the 0–2 in. layer of soil but some herbicide was found in the 2–4 and possibly 4–6 in. layers. Progressive build-up of residues did not occur and repeated treatment did not influence breakdown rate. No linuron could be detected in carrot roots in 1965; in 1966, following an abnormally late application, 05 ppm was found. Chemical analyses of soil samples taken at regular intervals during 1964–67 showed that no major changes had been caused by the herbicide treatments in the levels of available potassium, nitrate nitrogen, ammonium nitrogen, available phosphorus or in pH. Information is presented on the variation in the deposit on the soil surface of applied herbicides immediately after spraying, also on subsequent distribution in the soil. It is concluded that this work provides an encouraging contribution to the evidence that these four herbicides, when used at the recommended rates, are unlikely to have any injurious effect on the capacity of soil to produce healthy crops. Six armies d'expériences au champ pour étudier les effets & long terme d'applieations répétiés de MCPA, tri-allate, simazine et linuron Résumé. Dans cinq expériences de longue durée effectuées en plein champ depuis 1963, chacun des quatre herbicides fut appliqué sur des parcelles, soit replantées chaque année avec la mème culture, soit non cultivées. Les traitements suivants furent appliqués chaque année: du MCPA à 1,680 kg/ha sur de I'orge au stade 5 feuilles; du tri-allate à 1,680 kg/ha en pré -levée sur de I'orge; de Ia simazine à 1,680 kg/ha en pre-levee sur du mais; du linuron à 0,840 et 1,680 kg/ha sur des carottes en pre-levee et en post-levée. Les principaux résultats mentionnés dans cette publication concernent les rendements et la persistance des résidus herbicides. Dans la cinquiéme expéerience, les herbicides ont été appliqués deux fois chaque année, à des doses approximativement doubles de celles indiquées ci-dessus, sur des parcelles maintenues autant que possible sans végétation. Le MCPA n'affecta pas le rendement de l'orge et disparut du sol dans les 2 à 3 semaines qui suivirent chaque application. Dans les parcelles non cultivées, le temps pour que la dose appliquée (3,3 kg/ha) décroisse jusqu à la limite de detection fut réduit de 3 semaines en 1964 (aprés trois traitements) à 4 jours en 1968 (aprées dix traitements). Le tri-allate n'afFecta pas le rendement de l'orge. Les résidus dans le sol purent étre détectés durant les 5 à 6 mois qui suivirent chaque traitement à la dose de 1,680 kg/ha. Quand ce produit fut appliqué 2 fois par an à 3,360 kg/ha, un résidu persista, mais sans qu'il en resulte une accumulation progressive, durant les 6 années de l'expérience. Entre les essais biologiques et les méethodes chimiques de détermination des résidus, la concordance fut tantôt bonne, tantôt correspondant à un coefficient 4, les méthodes chimiques fournissant généralement, mais pas toujours, des ehiffres plus élevés. Aucun résidu de tri-allate ne put être décelé dans la parcelle ou les grains de l'orge. La simazine n'influenca pas la production du mais durant la péeriode de 1963 à 1967. En 1968. il y cut une réduction significative de la production de tiges et de feuilles, mais non de la production de grain. La simazine appliquée sur le mais disparut du sol rapidement durant les six premiéres semaines; aprés cette période 20 à 25% de la dose appliquee pouvaient être retrouvês. Les résidus restants diminuérent lentement et 70 à 140 g/ha purent être de'celes 23 à 50 semaines apres l'application. II ne fut pas trouvé de résidus au-dessous de la couche située entre 0 et 5 cm à partir de la surface du sol. Aprfes les traitements à 3,360 kg/ha, appliqués deux fois par an, un résidu persistant, variant de 0,560 kg/ha à 1,890 kg/ha sur une profondeur de 15 centimétres. 11 n'eut pas d'accumulation d'une année à l'autre et pas d'indice de modification du taux de degradation resultant de la repetition des traitements. La plus grande partie de la simazine resta localisee entre 0 et 5 cm au-dessous de la surface du sol. Dans trois essais sur quatre, il y cut une bonne concordance entre les dosages chimiques et les dosages biologiques. Le linuron réduisit le rendement et le pourcentage de matére séche des racines de carottes en 1965 et 1966, probablement en raison d'une exceptionnelle phytotoxicitéà court terme. Les autres années, il n'y eut pas d'effet. La moitié de la dose appliqué e (dc 0,560 kg/ha 1,12 kg/ha) disparut du sol durant les 8 premieres semaines et il ne fut plus possible de detecter des résidus apres 6 mois. Les résidus dans les parcelles non cultivées ne descendirent pas en-dessous de 0,770 kg/ha. La plus grande partie restait entre 0 et 5 cm au-dessous de la surface du sol, maia des traces d'herbicide furent retrouvees dans la couche 5 à 10 cm et peut-être dans la couche 10 à 20 cm. II n'y et pas d'augnientation progressive des résidus et la répétition des traitements ne modifia pas le taux de dégradation. II ne fut pas décelé de linuron dans les racines de carottes en 1965; en 1966; à la suite d'une application anormalement tardive, il en fut trouvé 0,5 ppm. Des analyses chimiques d'échantillons de sols préieves à intervalles réguliers entre 1964 et 1967 montrirént que les traitements herbicides n'avaient pas provoqué de changements importants dans les taux de potassium utilisable, d'azote nitrique ou ammoniacal, de phosphore utilisable; le pH ne fut pas non plus affecté. Des informations sont présentées, eoncernant la variation du depot en surface des herbicides appliqués, immédiatement aprés le traitement, et aussi sur la distribution qui en résulta dans le sol. En conclusion, ce travail apporte une contribution encourageante à la preuve que ces quatre herbicides, quand ils sont utilisés aux doses recommandées, n'ont trés probablement pas d'effet nuisible sur la capacié du sol à produire des récoltes saines. Feldversuche zur Untersuchung der langfristigen Auswirkung wiederholter Applikationen von MCPA, Triallat, Simazin und Linuron. Bericht nach sechs Versuchsjahren Zusammenfassung. In fünf 1963 angelegten langfristigen Feldversuehen wurden vier Herbizide jeweils auf Flächen mit permanenter Monokultur und auf Brachflächen ausgebracht. Foigende Behandlungen erfolgten jährlich: 1,68 kg/ha MCPA zu Gerste im 5-Blattstadium, Vorauflaufbehandlung mit 1,68 kg/ha Triallat 2u Gerste, Vorauf-laufbehandlung mit 1,68 kg/ha Simazin zu Mais, Vorund Nachaufiaufbehandlung mit 0–84 bis 1,68 kg/ha Linuron zu Mohren. Die in dieser Arbeit berichteten Aus-wertungen beziehen sich vorwiegend auf den Ertrag und die Persistenz der Herbizid- Rückstände. Im fünften Versuch wurden die Herbizide zweimal jährlich in ungefähr doppelter Aufwandmenge auf weitgehend vegetationslosen Fläehen angewandt. MCPA beeinflusste den Ertrag von Gerste nicht und verschwand aus dem Boden innerhalb von zwei bis drei Wochen nach jeder Behandlung. Auf den Brachflachen war die Zeit des Abbaus bis zur Nachweisgrenze der ausgebrachten Menge (3,36 kg/ha) von drei Wochen im Jahr 1964 (nach drei vorausgegangenen Applikationen) auf vier Tage im Jahr 1968 (nach zehn vorausgegangenen Applikationen) zurückgegangen. Triallat beeinflusste den Ertrag von Gerste nicht. Rückstände im Boden waren fünf bis sechs Monate lang nach jeder Applikation von 1,68 kg/ha festzustellen. Wurden 3,36 kg/ha zweimal jährlich ausgebracht, so war eine permanente Ruckstandsmenge, jedoch keine Akkumulation im Verlaufe der sechs Versuchsjahre festzustellen. Die Oberein-stimmung zwischen Biotest und GLG-Methode zur Riickstandsbestimmung variiertc von gut bis zu einem Faktor vier, wobei mit GLG gewohnlich, jedoch nicht iminer, ein höherer Wert ermittelt wurde. Keine Triallat-Ruckstande waren in Stroh und Korn von Gerste nachzuweisen. Simazin beeinflusste den Ertrag von Mais in der Versuchszeit von 1963 bis 1967 nicht. 1968 war eine signifikante Ertragsminderung bei Blatt und Stengel, nicht jedoch beim Korn, eingetreten. Simazin verschwand in den Maisparzellen innerhalb der ersten sechs Wochen rasch aus dem Boden; danach konnten noch 20 bis 25% der ursprunglich ausgebrachten Menge wiedergefunden werden. Die verbliebenen Rückstandsmengen verschwanden nur langsam und 0,07 bis 0,14 kg/ha konnten noch 23 bis 50 Wochen nach der Behandlung nachgewiesen werden. Keine Ruckstande waren unterhalb 5 cm Bodentiefe festzustellen. Wurden 3,36 kg/ha zweimal jährlich ausgebracht, so war eine permanente Ruckstandsmenge von 0,56 bis 1,89 kg/ha ca. 15 cm vorhanden. Es konnte jedoch keine Akkumulation und kein durch die wiederholte Behandlung bedingter beschleunigter Abbau beobachtet werden. Das Simazin blieb vorwiegend in den obersten 5 cm des Bodens. In drei von vier Analysen war die Üereinstimmung zwischen Biotest und GLG-Methode gut. Linuron beeinträchtigte 1965 und 1966 Ertrag und % Trockengewicht der Möhren-wurzeln vermutlich wegen einer aussergewohnlichen, kurzfristigen, phytotoxischcn Wirkung des Mittels. Sonst war keine Beeinflussung der Möhren zu beobachten. Die Hälfte der ausgebrachten Menge von 0,56 bis 1,12 kg/ha verschwand aus dem Boden innerhalb von acht Wochen und nach sechs Monaten waren keine Rückstande mehr festzustellen. Die Ruckstande auf Brachflachen fielen nicht unterhalb 0,77 kg/ha. Linuron verblieb weitgehend in den obersten 5 cm des Bodens, doch war eine gewisse Menge auch in 5 bis 10 cm und möglicherweise auch in 10 bis 15 cm Bodentiefe nachzuweisen. Akkumulation trat ebensowenig auf wie beschleunigter Abbau nach wieder-holter Anwendung. 1965 waren keine Linuron-Rückstände in Mohrenunrzeln nachzuweisen; 1966 wurde nach einer anomal spaten Applikation eine Ruckstandsmenge von 0,5 ppm gefunden. Die chemische Analyse von Bodenproben, die von 1964 bis 1967 in regelmassigen Abstanden gezogen wurden, ergab keine grosseren herbizidbedingten Veranderungen im pH sowie im Gehalt an veräugbarem Kalium, Nitratund Ammonium-Stickstoff sowie Phosphor. Es werden weiterhin Informationen gegeben über die Variation der Herbizidmengen auf der Bodenoberfläche unmittelbar nach der Behandlung und über die anschliessende Verteilung der Herbizide im Boden. Es wird gefolgert, dass diese Arbeit einen ermutigenden Beitrag zu der Tatsache darstellt, dass diese vier Herbizide in praxisüblichen Auiwandmengen kaum negative Auswirkungen auf die Bodenfruchtbarkeit haben.     

CHEMICAL CONTROL OF FERTILE SPARTINA TOWNSENDII (S.L.) ON THE CHESHIRE SHORE OF THE DEE ESTUARY I. FIELD TRIALS ON SPARTINA SWARD

Summary. Trials with dalapon, paraquat and fenuron in 1963 and 1964, and with bromacil and amitrole-T in 1964, were carried out on mature Spartina sward. Dalapon, paraquat and fenuron all gave complete kill on some plots in 1963. In 1964, paraquat gave variable results and lower percentage kills than in 1963, whereas dalapon and fenuron were more consistent. Fenuron allowed a greater degree of regeneration than dalapon and was uneconomic at the high dose (60 lb/ac) required for complete kill. Dalapon gave the best results and with 100 lb/ac there was 98–100% kill 2 years after treatment. At 50 lb/ac results were initially good, but there was more regeneration in the second season after spraying. Bromacil at 5 and 20 lb/ac and a mixture of 5 lb/ac bromacil and 4 lb/ac amitrole-T maintained more than 99% kill lor 2 years after application.
La lutte chimique contre les formes fertiles de Spartina townsendii (s.l.) sur la cóte du Cheshire dans l'esluaire de la Dee I. Essais au champ sur des pelouses de Spartina     

THE EFFECT OF POST-EMERGENCE HERBICIDES ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF CENTROSEMA FUBESCENS BENTH. IN QUEENSLAND

Summary. 2,4-D-amine, 2,4-D ethyl ester, 2.4-DB-potassium. MCPA-sodium, diquat and a 1:1 mixture of 2,4,5-T butyl ester and 2,4-D ethyl ester were applied to the tropical pasture legume Centrosema pubescens Benth. (centro) grown either alone or with Panicum maximum Jacq. (guinea grass). Even at 0.5 Ib/ac (total) the 2,4,5-T/2,4-D mixture caused severe damage to seedling and mature centro. 2,4-D-amine, 2,4-D ethyl ester and 2,4-DB-potassium were less damaging and there were only slight differences in response to these. Diquat at 0.25 Ib/ac desiccated centro seedlings, but most plants survived and grew satisfactorily. There was some evidence that the growth of mature centro was depressed least when the herbicides were applied during vegetative quiescence.
Application just after the start of flowering altered the flowering pattern but did not reduce seed yields significantly. 2,4-D-amine at 0.75 and 1–5 lb/ac and 2,4-D ethyl ester at 1.5 Ib/ac decreased the percentage germination of abraded seed. Diquat 0.25 Ib/ac applied at the start of flowering caused significant increases in top growth and seed pod numbers, possibly the result of modification of the normal flowering pattern.     

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     

GENETIC VARIATION IN SIMAZINE RESISTANCE IN WHEAT, RAPE AND MUSTARD

Summary. The resistance to simazine of a range of varieties of wheat ( Triticum aestivim L.), rape ( Brassica napus L.) and mustard ( Sinapis alba L.) was assessed in glasshouse tests Varietal differences in survival and final weight of survivors were found in all three crops Variability m the time for which individual plants survived was greatest in the two out-breeding crops, rape and mustard. The 1 % of mustard plants that survived 10 oz/a csimazine were allowed to produce seed in a polycross. These progenies showed a very marked increase m resistance over the unselected controls.
There is thus appreciable genetic variation in resistance to simazine both within and between varieties. This is readily available for selection, and could he valuable in extending the selectivity of herbicides.
Variation génétique de la resistance á la simazine chez le blé, le colza et la moutarde     

STUDIES ON THE BIOLOGY AND CONTROL OF VAUCHERIA DICHOTOMA FOUND IN FRESHWATERS IN BRITAIN

Summary. Vaucheria plants collected from a ditch near Crowland and from the River Cherwell at Oxford in the first week of October 1970 were identified as V. dichotoma Ag. A nutrient medium is described which allows the growth and the production of organs of sexual reproduction of this alga. Preliminary studies on the control with diquat show that it must be exposed to a concentration of 2 mg/1 for 6 h for the herbicide to be effective. The presence of mud reduces the rate at which chlorophyll disintegrates and hastens the inactivation of diquat.
Etudes sur la biologie et la destruction de Vaucheria dichotoma. Ag. dans les eaux doucei de Grande-Bretagne     

A REVIEW OF EXPERIMENTAL WORK WITH DIQUAT AND RELATED COMPOUNDS

Summary. Published literature on diquat (9,10-dihydro-8a, 10a-diazonia phenanthrene dibromide; 1,1'-ethylene-2,2'-dipyridylium dibromide) and related dipyridyl herbicides is reviewed. Their activity is probably connected with the formation of stable free radicals on reduction and both photosynthetic and respiratory processes may be associated with free radical formation in the plants. These herbicides are rapid-acting translocated desiccants and kill the aerial parts of most plants, but are safe as soon as they touch the ground, having no residual effect through the soil. Possible uses are as desiccants, in place of cultivation to clear fallows and seedbeds before sowing, in pre-emergence weedkilling, for weeding round trees and bushes and, with directed spraying, for inter-row weeding in row crops.
Revue des essais effectués avec le Diquat et des composés apparentés     

THE EFFECTS OF SUB-LETHAL DOSES OF MCPA ON THE MORPHOLOGY AND YIELD OF VEGETABLECROPS

Summary. The effects of sub-lethal doses of MCPA-sodium on the morphology and yield of red beet, turnip and onion and on the morphology of spinach were studied in field and glasshouse experiments. Epinastic responses of beet were seen at 0.003 lb/ac a.c., but no serious formative effects or yield reductions occurred below 0–07 lb/ac and plants were only killed by doses above 0–1 lb/ac. Spinach was affected at 0–06 lb/ac, the lowest dose used, but the plants were not killed at 0–33 lb/ac. Epinasty in turnip occurred at 0–002 lb/ac, and at 0–01 lb/ac many of the roots were abnormal, while spraying with 0–1 lb/ac and above resulted in severe distortion or death of the plants. Onion was the least affected of all the crops studied. When a welting agent was included in the spray epinasty occurred at 0–3 lb/ac, but there were no serious formative effects or yield reductions below 1–0 lb/ac. The symptoms of injury in onion were often transitory because the affected parts were replaced as the bulb developed.
Effets de doses sub-léthatles de MCPA sur la morphologie et If rendement des cultures légumiéres. V. Betteraves, Epinards, Navets et Oignons     

THE EFFECTS OF SUB-LETHAL DOSES OF MCPA ON THE MORPHOLOGY AND YIELD OF VEGETABLE CROPS

Summary. The effects of sub-lethal doses of MCPA-sodium on the morphology, yield and maturity of French beans, and on the morphology of broad beans, were studied in field and glasshouse experiments. Epinasty in French beans developed at 0.002 lb/ac a.e., but formative effects were not seen at less than 0–1 lb/ac. With doses up to 0.4 lb/ac there was no significant reduction in yield or haulm weight, but at 1.0 lb/ac and above, yield was reduced and some of the plants sprayed at an early stage of growth were killed. There were characteristic modifications of the roots and stems and of those leaves which were at a susceptible stage of development when sprayed. Broad beans were only slightly injured by 0.2 lb/ac but were generally killed by 2.0 lb/ac. Abnormalities were noted in the germination of seed produced by affected plants.
Effets de doses sub-léthales de MCPA sur la morphologic et le rendement des cultures légumières IV. Haricots verts et fèves     

DIRECT-DRILLING OF CEREALS AFTER USE OF PARAQUAT

Summary. Cereal crops were grown at Jealott's Hill in 1962 and 1963 without cultivations, following the use, before drilling, of paraquat to kill unwanted vegetation. This investigation was extended with a series of trials at outside centres. Three trials with winter wheat were drilled in the autumn of 1963, two into pasture and one into stubble. Three barley trials were drilled into stubble in spring 1964.
All the autumn trials and one spring trial compared direct-drilling with normal cultivations at two levels of nitrogen. The other two spring trials compared rates and times of application of paraquat without any plough comparison.
Individual trials showed significant yield differences between direct-drilling and ploughing, but there was no consistent advantage in favour of either technique.
Spraying in advance of drilling generally resulted in similar yields to spraying and drilling on the same day. Winter wheat drilled into pastures showed some retardation of spring growth when spraying and drilling had been carried out on the same day.
When averaged over times of application, yields after spraying paraquat at 2 lb/ac were significantly higher than after 1 lb/ac.
In the trials where two levels of nitrogen were included crops responded to an increase from 60 to 120 units nitrogen/ac as top dressing for winter wheat and from 60 to 90 units nitrogen/ac combine-drilled for spring barley; the response was not always significant.
Semis direct de céréales après application de paraquat     

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     

A RE-EXAMINATION OF THE INFLUENCE OF LIGHT AND DARKNESS ON THE LONG-DISTANCE TRANSPORT OF DIQUAT IN LYCOPERSICON ESCULENTUM MILL.

Summary. Using autoradiographic techniques, the long-distance transport of 'ethylene'¹⁴C-labelled diquat dibromide was studied. It was confirmed that a period of darkness after diquat application was necessary for reliable systemic action during a subsequent light exposure. Darkness was necessary in the region where the herbicide was applied, and then only to allow adequate penetration of diquat. This was its only role.
Desiccation following death, with the transfer of free water containing diquat to other leaves are the primary forces of long-distance transport; light is essential only for rapid toxic action and not directly for transport. Orthophosphate-³²P and urea-¹⁴C applied topically with unlabelled diquat were distributed in the same pathway as the herbicide and not in the phloem. These results are discussed.
Nouvelles recherches sur l'influence de la lumière et de l'obscurité sur le transport à longue distance du diquat dans Lycopersicon esculentum Mill .     

THE EFFECTS OF SUB-LETHAL DOSES OF MCPA ON THE MORPHOLOGY AND YIELD OF VEGETABLE CROPS

Summary. The effect of sub-lethal doses of MCPA-sodium on the morphology, growth and yield of carrots and parsnips was studied in twenty replicated field experiments. Slight epinasty was produced in carrots by doses as low as 0.002 lb/ac a.e., but formative effects were not usually seen below 0.01 lb/ac. Crop weight was only reduced by doses greater than 0.1 lb/ac, but abnormalities rendered a proportion of the roots unmarketable at doses below 0.05 lb/ac. Small plants were sometimes killed by 0.3 lb/ac, but larger plants survived treatment with up to 0.5 lb/ac. Tests on carrots which were unmarketable on grounds of appearance failed to reveal any effect of MCPA on flavour, sweetness or texture of the roots. The effects of MCPA on parsnips were similar to those on carrots, but the expression of injury symptoms was generally less marked.
Les effets de doses sub-létales de MCPA sur la morphologie et le rendement des cultures légumières III. Carottes et panais     

THE EFFECT OF JULY APPLICATIONS OF DALAPON ON THE GROWTH AND BOTANICAL COMPOSITION OF AN AGROSTIS/LOLIUM PASTURE

Summary. Dalapon–sodium at 3.3–7.5 Ib ac/a.e. was applied in early, mid– and late July 1964 to an Agrostis/Lolium pasture for selective control of the weed grasses Agrostis stolonifera, Poa trivialis and Holcus lanatus. These species were significantly more susceptible than Lolium perenne to dalapon at all doses regardless of the time of spraying. The most promising treatment was 33 lb/ac applied on 4th July, which increased the ground cover of L. perenne and substantially reduced Agrostis stolonifera and Poa trivialis. The total yield of herbage 12 weeks after spraying was only 50% of that from the unsprayed control, but the yield of Lolium perenne was not affected. When cut on 21st May and 5th August 1965, total yield was only slightly reduced and that of L. perenne was increased by 60–90%. The successful practical utilization of this selectivity is likely to depend largely on the spacing of the plants of L. perenne in the pasture. Simazine at 0.75 Ib/ac applied to half of each plot 3–4 weeks alter dalapon treatment had no lasting beneficial effect on the composition of the sward.     

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 MCPA ON THE AMINO ACID AND SUGAR COMPOSITION OF VICIA FABA LEAVES

Summary. The effect of spraying Vicia faba leaves with 5000 ppm MCPA is described. Three to 4 days after spraying, a marked increase (× 5 approx.) was found in the concentrations of leucine iso -leucine and valine in the leaves. No significant changes were detected in the other amino acids. Treatment with MGPA also caused a significant increase (× 4 approx.) in the glucose and fructose content of the leaves. Detached leaves (sprayed and unsprayed), when kept in a moist atmosphere for 3–4 days, exhibited very similar increases in amino acids and sugars to sprayed intact plants. Experiments using ¹⁴CO₂ revealed that in short term photosynthesis (30 min) of sprayed and unsprayed plants, 80–90% of the radioactivity was incorporated in sucrose, with about 5% in each of glucose and fructose. Over photosynthelic periods of 4 days, glucose and fructose were found to be almost as heavily labelled as sucrose in sprayed plants, but in the controls the distribution of radioactivity was similar to that in short term photosynthesis. It is suggested that the build up of amino acids and sugars in plants treated with MCPA is due to an interruption of the translocatory flow from the leaves, and that this build up of metabolites may be a contributory factor in the toxic action of this herbicide.
Effet du MCPA sur la composition en amino-acides et en sucre des feuilles de Vicia faba     

THE EFFECT OF DEPTH OF BURYING AND FREQUENCY OF CULTIVATION ON SURVIVAL AND GERMINATION OF SEEDS OF WILD OATS (AVENA FATUA L. AND AVENA LUDOVICIANA DUR.)

Summary. Seeds of Avena fatua and A. ludoviciana were sown at a depth of 15 cm or mixed into the top 5 cm of soil in small field-plots at Rothamsted and subjected to 5 different regimes of depth and frequency of cultivation for 3 years, after which all plots were dug to 15 cm in spring and autumn for a further 4 years. Seedlings were counted and no plants were allowed to produce seeds. After 7 years, soil-samples showed that very few intact seeds of A. fatua and none of A. ludoviciana remained, although less than 20% of the seeds sown had produced seedlings. Laboratory tests after 4 to 8 years'dry slorage showed seeds of both species to be viable. The maximum survival of viable seeds, estimated by seedling-emergence, was 61 months for A. fatua and 33 months for A. Indoviciana . Seeds of A. fatua survived slightly longer at 15 cm than in the top 5 cm of soil. Survival of A. ludoviciana was less affected by depth and cultivation, except that birds ate some shallow-sown spikelets in the first fortnight after sowing. A. fatua germinated in spring and autumn, and A. tudoviciana in winter, irrespective of age of seed and cultivation of soil. Frozen soil delayed emergence of A. ludoviciana seedlings lor varying periods between December and March. Seedlings of A. ludoviciana were slightly more winter-hardy than A. fatua . More seedlings of A. fatua appeared in the second spring than at any other time, but 80% of the seedlings of A. ludoviciana appeared in the first autumn and winter.
Effets de la profondeur d'enfouissement des graines et de la fréquence des façons culturalles sur la longévité et la germination des semences de Folle-Avoine (Avena fatua L. et A. ludoviciana Dur .)     

COMPETITION OF WILD OATS (AVENA FATUA L.) IN WHEAT AND FLAX*

Summary. This project was designed to study various aspects of wild oat competition in spring wheat and flax. From ten to forty wild oat plants/yd² were sufficient to cause significant yield reductions in wheat when grown on summerfallow land or when ammonium phosphate fertilizer was added to stubble land. However, when wheat was grown on stubble land without the benefit of a fertilizer treatment, seventy to one hundred wild oat plants/yd² were needed to suppress wheat yields significantly. This would suggest that on stubble land, soil fertility was a more important factor than moderate densities of wild oats in determining eventual crop yields. In these experiments, wild oats reduced the number of tillers per plant, but did not significantly affect the protein content of the harvested grain. Only ten wild oat plants/yd² were sufficient to reduce flax yields significantly on both summerfallow and stubble land. The only exception was in 1966, when flax grown on summerfallow land was not significantly affected until the density of wild oats reached forty plants/yd2. This confirms the general observation that flax is a poor competitor with wild oats. The results suggest that wild oat competition had already commenced prior to emergence of wheat, particularly with the higher densities of wild oats. In general, competitive effects increased with time and with wild oat density. In flax, severe competition had already taken place prior to the 2–3-Ieaf stage of the weed in 1964, but did not become severe until after the 2–3-leaf stage of wild oat growth in 1965 and 1966. Again, competitive effects increased with time and with wild oat density. Results of a final series of experiments, suggested that the optimum seeding date for flax in Manitoba is the latter part of May or the first week of June. Yield reductions due to wild oat competition became very severe as seeding dates were delayed. La compétition de la folle avoine (A vena fatua L.) avec le blé et le lin     

Seed longevity and seedling establishment of Bromus diandrus Roth.

Some aspects of the seed and seedling biology of Bromus diandrus Roth. were investigated with the aim of formulating non-chemical control methods. B. diandrus seeds remained viable for at least 2 years when dormancy was enforced by environmental conditions, although 95% of seed was capable of germinating within 27 days of shedding from the parent plant when conditions were favourable. Seeds buried at 50 or 150 mm depth in field soil germinated or lost viability within 6 months. Seedling establishment was greatest and most rapid from seeds buried at 50 mm with 97% of total seedling emergence occurring within 1 month of burial. Less than 1% of seeds buried at 150 mm produced seedlings. Establishment of seedlings from surface-sown seed occurred over 18 months. The prevention of seeding by the application of paraquat to flowering plants of B. diandrus in the field led to a significant reduction in the population in the following year. Control methods based on these results are suggested. Longévité des graines et installation des jeunes plants de Bromus diandrus Roth. Certains aspects de la biologie des graines et des jeunes plants de Bromus diandrus Roth. ont fait l'objet d'une étude dans le but de formuler des méthodes de lutte non-chimique. Les graines de B. diandrus sont restées viables pendant au moins 2 ans lorsque la dormance résultaient des conditions ambientales, bien que 95% des graines ait été capables de germer dans un délai de 27 jours à partir de la séparation de la plante mère, étant donné des conditions favorables. Des graines enfouies à une profondeur de 50 ou 150 mm dans le champ ont perdu leur viabilitié au bout de six mois. L'installation la plus importante et la plus rapide de jeunes plants a eu lieu à partir de graines enfouies à 50 mm, 97% de la levée globale se produisant dans un mois après enfouissement. Moins de 1% des graines enfouies à 150 mm n'a produit de jeunes plants. L'installation de jeunes plants à partir de graines semées sur la surface du sol a continué pendant 18 mois. L'application de paraquat lors de la floraison de plantes de B. diandrus, pour empêcher la chute des graines dans le champ, a amené une baisse significative dans la population de l'année suivante. A base de ces résultats, l'auteur propose des méthodes de lutte contre cette espèce. Lebensdauer und Keimung der Samen von Bromus diandrus Roth. Im Hinblick auf die Bekämpfung dieser Trespe auch ohne Herbizide wurde die Keimungsbiolo-gie in einigen Aspekten untersucht. Unter kühlen und trockenen Bedingungen blieben die Samen im Lager nach einer Keimruhe mindestens 2 Jahre keimfähig, aber unter günstigen Bedingungen keimten 95% der Samen innerhalb von 27 Tagen unmittelbar nach dem Abreifen. Von ganz flach ausgesäten Samen wurden über 18 Monate hin Keimpflanzen gebildet. Am besten keimten die Samen aus 5 cm Tiefe (97% innerhalb eines Monats). Aus 15 cm Tiefe keimten jedoch weniger als 1%. Die Verhinderung der Samenbildung durch Applikation von Paraquat auf die blühenden Pflanzen verringerte die Population im Folgejahr significant. Bekämpfungsmethoden aufgrund der Ergebnisse werden vorgeschlagen.     

EFFECT OF TEMPERATURE ON THE ACTIVITY AND PERSISTENCE OF AMITROLE AND 2,4-D

Summary. One leaf of each of several tomato plants 5–6 weeks old maintained at 55, 70 or 85° F was dipped in 0.05 M amitrole or 0.005 M 2,4-D solution. The treated leaf was removed 1 week later. Scions taken from untreated plants were grafted to the treated plants at intervals up to 4 months after treatment.
Amitrole-treated plants maintained at 55° F were killed within 1 month but those at 70 and 85° F recovered.
Plants treated with 2,4-D showed typical symptoms when maintained at 70 and 85° F but no symptoms at 55° F. Scions grafted on plants maintained at 55, 70 and 85° F for 60 days after 2,4-D treatments exhibited typical symptoms. Grafts made more than 60 days following the 2,4-D application did not exhibit symptoms except a slight malformation on the plants held at 55° F.
New growth on the scions grafted up to 103 days after amitrole treatment on plants which had been maintained at 70 and 85° F exhibited typical amitrole symptoms (i.e. white foliage) but scions grafted after this lime did not. New shoots developing from buds on the treated plants also produced green growth 115 days after treatment but produced white foliage prior to that time.
Effet de la température sur l'activi'ité et la persistance de l'aminotriazole et du 2,4-D