摘要:

Summary.An experiment was made to determine the effect of the removal of grasses on the behaviour of populations ofPlantago lanceolata, P.mediaand P.majorin three grassland habitats. Treatments included the addition of seed of all three species to the existing vegetation. The grasses were removed by treatment with 2,2‐dichloropropionic acid (dalapon), a herbicide selective against the Gramineae. The chemical appears to be slightly toxic to thePlantagospecies at the dose used (12 Ib/ac a.e.). The removal of the grasses was followed by a marked increase in the plantain populations shown both in counts of the numbers of plants and seedlings and in increased seed output per unit area. Deliberate sowing of seed into the habitats in autumn resulted in increased numbers of seedlings in the following spring, particularly in those plots where the grasses had been removed. Species of Plantago not occurring naturally in the communities were frequently established by sowing seed, if the grasses had been removed, but not otherwise. The overall results of the experiment suggest that in two of the communities the grasses played an important role in determining the presence or absence of particularPlantagnspecies and also in controlling the size of the existing plantain populations. The experiment is discussed in the wider context of population control in plants.Tentative de modification de populations naturelles de Plantago lanceolata, P. major et P. medi

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Summary.Two means of reducing soil contamination resulting from the leaching of spray residues of dalapon from plant foliage were tested: use of volatile forms of the herbicide, residues of which slowly evaporate from the foliage; and use of formulations that congeal to a solid film to retain the herbicide against leaching. Rates of evaporation from glass slides at 20° C for the ethyl ester,nbutyl ester, acid, and diethyleneglycol bisester of dalapon were respectively 15, 1‐6, 0′27 and 0.01 mg/cm2. As foliar herbicides the ethyl and butyl esters were ineffective and the acid of limited effectiveness due to rapid evaporation. The glycol ester was as effective as the sodium salt. With its evaporation rate of approximately 1 kg/ha/hr at 20°C, application of dalapon in the form of the diethylrneglycolbisester is considered promising as a means of limiting soil contamination. Mixtures of the diethyleneglycolbisester of dalapon with polyvinylacctate emulsion dry to form films that greatly reduce leaching of the herbicide at the expense of minor reduction in herbindal activity. Such formulations afford a means of limiting soil contamination.Formulation du dalapon pennettant de rédiuire la contamination

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Summary.Eight experiments were carried out on a range of pasture lypes under different management and in different years to lest the reaction of white clover (Trifolium repensin grasstand to doses of up to 4 lb/ac of the herbicides MCPA‐sodium or‐potassium and 2,4‐D‐amine. The initial effect of the treatments was to reduce the amount of dover in the sward, the size of the reduction varying greatly from field to field for any one dose. In general, the higher the dose, the more severe was the depression of the clover 1 month after spraying. Both herbicides at 2 and 4 lb/ac caused substantial depressions on some of the fields. The growth of the treated clover was examined during the year following spraying. The ability of the clover to recover from the initial depression varied considerably in the different fields; on some, recovery started in the year of spraying and on others in the following year. Quick recovery was usually associated with a high initial resistance but there were fields in which the clover showed contrasting rates of recovery following similar depressions. The experiments produced no clear‐cut evidence as to why the initial resistance and speed of recovery varied in different fields. In one experiment the effects of MCPB‐sodium and 2,4‐D‐amine on white clover were compared separately and in a series of mixtures. An examination made 6 weeks after spraying showed that MCPB at up to 8 lb/ac had no significant effect on the clover, whereas 2,4‐D at 1 lb/ac caused a 22% reduction. Mixtures containing up to 0.37 lb 2,4‐D and up to 6 lb MCPB caused no reduction while those containing 0.75 lb 2,4‐D and 4 lb MCPB were not significantly different from 1 lb 2,4‐D alone.Reaction deTrifolium repens (L.)en prairie au 2,4‐D, au MCPA, et aux mél

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Zusammenfassung.Samen vonSinapis arvensis(Ackerscnf) undAvena fatua(Fiughafer) wurden indirekt liber die Wurzeln in Wasserkultur aufwachsender Pflanzen mil S‐35 markiert. Die spezilische Aktivität der Nährlösung betrug fürSinapis0,75 μ C.cm−3und fürAvena1,0 μ C.cm−3. DieSinapis‐Samen besassen bei der Ernte (0,88 Halbwertzeiten nach der Markierung) einc Aktivitat von 0,11 μC pro Einzelsame und 59,4 μC pro Gramm Samen. Die entsprechenden Werte fürAvenawaren nach 0,91 HWZ 0,24 μC und 21,2 μC. Die aus den markierten Samen aufwachsenden Keimpflanzen konnten ohne vorherige Präparation unter einem dünuwandigen Endfensterzählrohr von nicht markierten Keimpflanzen eindeutig unterschieden werden. Dabei betrug die Aktivität der Keimblätter vonSinapisnach einer HWZ ca. 1000 Imp./min., diejenige vonAvenanoch nach mehr als 4 HWZ 60‐80 Imp./min. Em sicherer Nachweis (doppelter Nulleffekt) von S‐35 in den unpräparierlen Keimblättern ist beiSinapisfür einen Zeitraum von 5 HWZ, fürAvenavon 4 HWZ nach der Markierung möglich. Die beschriebene Markierungs‐methode eignet sich daher auch für Samen mit längerer Keimruhe, wie am Beispiel vonA. fatuagezeigt werden konnte. Um die Brauchbarkeit der markierungsmethode auch unter Feldbedingungen prüfen zu können, wurden im Herbst 1960 auf 4 Parzellen von je 2 m2Grösse eincs abgeernteten Gerstenfeldes jeweils 2000 markierte Samcn vonSinapis arvensis, die kurz vorher im Gewächshaus zur Reife gelangt waren, eingesät. Die einzelnen Parzellen wurden anschliessend einer verschiedenen Bodenbearbeitung unlerworfen und danach die aufgehenden markierten Keimpflanzen zu verschiedenen Zeitpunkten ausgezählt. Dabei ergaben sich folgende Keimprozente: Unbearbeitete Parzelle: 11,8%; Schälpflug: 4,7%; schwere Egge: 48,7%; Scheibenegge: 31,1%. Auch bei diesen Versuchen war es mit Sicherheit möglich, eine Unterscheidung der aus unmarkierten und markierten

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

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

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Summary.Studies on weed control in groundnuts grown with summer irrigation in the sandy coastal plain of Tripolitania (Libya) are described. These conditions favour rapid vigorous weed growth which competes severely with the crop; nearly 10 tons/ac of herbage was gathered from unweeded plots, on which groundnut yields were under half those from land kept effectively weeded. Early planting is desirable but may aggravate weed problems, due to inadequate time for cultivation and labour for weeding, through conflicting demands of other crops. It was therefore decided to investigate the possibilities of chemical control. Herbicides applied pre‐emergence included TCA, PCP, monuron, propham and 2,4‐D‐esters. Control of the predominant annual dicotyledons (Portulaca oleracea, Thlaspi arvenseandAmaranthus retroflexus) comparable to that from hand‐weeding during early growth was obtained from PCP (10 lb/ac), the crop was not damaged by rates up to 20 lb. and the highest groundnut population was consistently established on plots treated with this herbicide. Effective control was obtained from 2,4‐D‐ester at 0.5 and 1.5 lb/ac, but the higher rate severely checked the groundnuts. Crop damage also occurred from monuron (3 lb/ac) which destroyed all vegetation, TCA (24 lb/ac) which was effective only againstCynodon dactylon; and propham (up to 10 lb/ac) which failed to control weeds. Post‐emergence treatment with MCPB (1.8 lb/ac) and 2,4‐DB (2.5 lb/ac) controlled some 50% of broad‐leaved weeds, but was slow to act and also damaged the crop. A combined PCP + 2,4‐D spray applied pre‐emergenceprovedto be the best chemical treatment, but maximum persistence was only about 10 weeks; after this, perennial monocotyledons such asC. dactylonandCyperussp., not effectively checked by any of the selective herbicides, became a serious problem. Under these conditions good yields depend on weed suppression late into the growing season and excellent results were achieved when an efficient pre‐emergence herbicide was followed, as its persistence waned, by careful handweeding. Early cultivation often damaged the crop, and a comparison of plots where this was omitted and the initial weeding delayed over several weeks, with those hand‐weeded throughout growth, showed no significant advantage from the extra operation. If no pre‐ernergence herbicides can be applied it may therefore be better to postpone the first cultivation for 5–7 weeks after planting. Observations on varieties representing the four broad morphological groups of groundnuts suggest certain differences in susceptibility to herbicides; further studies are required on this subject.Expériences sur le désherba

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1961.tb00022.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY