THE HERBICIDAL CONTROL OF BROAD-LEAVED AND GRASS WEEDS

IN ESTABLISHED GRASSLAND

STANLEY EVANS

National Agricultural Advisory Service Liaison Officer, A.R.C. Weed Research Organization

INTRODUCTION

Herbicides have been used on grassland forthe past fifteen years, but attempts to reviewfully their place in grass husbandry in thiscountry have been few (21, 25). The majorgrassland text-books published in the U.K. inrecent years and the bulletin on Grasslandprepared by the National Agricultural Ad-visory Service dismiss weeds and herbicidesin a few sentences. Surveys of herbicide usagehave shown that weedkillers are not widelyused on grassland (14). There is a singular lackof interest in grassland spraying.

THE DIFFICULTY OF DEFINING WEEDSOF GRASSLAND

Broad-leaved plantsA weed is defined as 'a plant out of place'.

There are however few plant species which areundesirable in all situations in grassland. Theseare mainly broad-leaved weeds such asCirsium arvense. Ranunculus acris and R.bulbosus, which supply nothing to the grazinganimal and may even be harmful. Other broad-leaved weeds such as Bellis perennis andAchillea millefolia provide scant grazing butdespite low output could be considered desir-able because of their contribution to themineral nutrition of the grazing animal (27).

GrassAll grass species have some nutritive value

and a grass can usually be defined as a weedonly in a particular habitat. For exampleAgrostis spp., which may be considered weedsof fertile lowland pasture, can be valuedconstituents of upland swards.

The traditional view of grassland workersis that, for the improvement of swards.

management should lead to the elimination ofcertain grass species with at the same timean increase of those species considered moredesirable. This is a view which, although itpermits the concept of weeds, tends to be abotanist's view. The farmer is interested inanimal output per acre and his methods ofimprovement are measured in these terms.The use of botanical analyses of swards as anindication of their worth is valid only if adirect correlation between grass species andproductivity can be shown.

The experience of advisers and researchworkers has led them to classify certain speciesof grass as generally undesirable. Baker (7),reporting on a survey of English grassland,used the method of classification of Davies(20) where swards are graded as follows:

1. Ryegrass swards2. Kye,grsiS,slAgrostis swards3. Agrostis swards4. Fescue swards5. Molinia or Nardus swards6. Rush communities.

Poa thvialis, P. pratensis and Holcus lanatusare mentioned by Baker in his survey as weedsonly, although P. trivialis, for example, hasbeen strongly recommended for use in seedsmixtures (44). A questionnaire on grasslandcompleted by N.A.A.S. Regional GrasslandOfficers (4) indicates that P. trivialis is a wide-spread constituent of swards on fertile soils;that Agrostis species are of very commonoccurrence in swards on poorer soils; and thatboth species are generally considered as weeds.Other species classified as weeds by N.A.A.S.officers include Holcus lanatus, Deschampsiacaespitosa, Molinia caerulea and Nardus stricta.

The most rapid way in which species may be

205

206 THE HERBICIDAL CONTROL OF BROAD-LEAVED AND GRASS WEEDS IN ESTABLISHED GRASSLAND

eliminated and others established is by plough-ing and resowing, the result of which is oftento improve productivity. Davies and Williams(22), comparing leys and permanent grass,concluded that the productivity of much of ourgrassland could be greatly increased byploughing and resowing. The comparisonshowever were between old and new swardswhich were manured differently. They were indifferent but adjacent fields which had differenttreatments in the previous year. The densityof stocking was arrived at subjectively by anassessment by the experimenters as to what theswards would carry. The amount of nitrogen-ous fertilizers used was small, and although thedata do not clearly indicate the botanicalanalyses of the swards, the advantage shownby the leys might have been due, in somedegree, to their higher clover content. Re-sowing of course, involves much more thansimply replacing some grass species by others,and it is impossible to say from the work byDavies and Williams how much, if any, of theincreased output from the leys is due to havinga different type of grass. Indeed, when leysfrom contrasting seeds mixtures (i.e. commer-cial seed and seed of leafy grass strains) werecompared, there was, in general, not a greatdeal of difference in output.

More recent work at Great House Experi-mental Husbandry Farm (3), in a high rainfallarea of the hills of Lancashire, has shown thatgrassland established from a simple leymixture may give no more output than anestablished sward of mixed 'inferior' species.Three experiments on fields of differentfertility, under a system of generous nitrogen-ous fertilizer usage and running for four years,have shown no clear-cut advantage of a leyover a permanent pasture. In the conditionsof these experiments, however, the newly-sown leys seem to be soon invaded by indi-genous species.

Recent reports from the Grassland ResearchInstitute have shown that under comparableconditions the total annual dry-matter pro-duction from a pure stand of Agrostis tenuiscan be similar to that obtained from S23 orIrish perennial ryegrass, over a range ofnitrogen applications (17).

In Wales the productivity of ryegrass, cocks-foot, timothy, meadow fescue and Agrostistenuis, each sown with white clover, have beencompared under different levels of fertilizeruse over three years (32). The plots were cuttwo or three times a year and the DM esti-mated. The annual yield of the A. tenuis swardwas sometimes greater thari that of the meadowfescue, cocksfoot and perennial ryegrassswards, and the Agrostis sward always had,with the exception of one cut, the highest crude-protein content. Agrostis differed from theother species in having a higher proportionof the annual yield in the second and thirdcuts.

The value of a grass is determined by manyfactors in addition to its annual dry-matterand protein production. The season of maxi-mum production, the palatability and digesti-bility at different stages of growth, and theability to persist under various managementregimes and habitats are some of them. Eco-types of the same species may show widedifferences in these characteristics. Recentresearch suggests, nevertheless, that somespecies of grass which have often been con-sidered, at least in lowland pastures, as'inferior' species are not necessarily so. Thebotanical analysis of a sward perhaps may notalways be a satisfactory criterion of its worth.

BROAD-LEAVED WEEDS

The advantages of controlling broad-leavedweeds

Advantages of controlling broad-leavedweeds in grazed pastures have been demon-strated (8, 9, 30) but it is evident that thepotentially greater production from a weed-freesward is only achieved where the standard ofmanuring and grazing management is high.Gutsell (30) showed, over 4 years at 5 siteswhere buttercups were controlled with MCPA,an average increase of 11% in the productionof weed-free herbage as a result of spraying,an increase of 83% from the application ofnitrogen, and an increase of 106% from acombination of these treatments. Phillips andPfeiffer (48) have shown a close correlationbetween the degree of control of buttercups

STANLEY EVANS 207

from spraying and the intensity of grazing bybeef cattle. The inefficiency of grazing by stockwhere thistles are present is apparent to thecasual observer, and areas of undergrazingmay be foci for the spread of undesired species.Some weeds are poisonous, and apart from thedeath of stock which consume them, there maybe insidious losses, less easily estimated, froma lack of thriftiness of animals or a decline inthe milk yield, following the consumption ofsub-lethal amounts. Harper (31) has observedthat inexperienced stock may graze Ranunculusbulbosus and R. acris, with consequentblistering of tongue and lips and possiblestomach ulceration, leading in extreme casesto death. Most animals normally avoid thesespecies, but R. repens is often found bitten bylivestock and this species contains lower con-centrations of the glycoside ranunculin thanthe other species.

Herbicides for the control of broad-leaved weeds

The present recommendations for thechemical control of a number of perennialbroad-leaved weeds of grassland are given inthe Weed Control Handbook (50). MCPA and2,4-D are frequently recommended herbicides,but at the doses required to give a reasonablecontrol of broad-leaved weeds they can beharmful to clover in the sward. Elliott (24)has shown that the reduction in the amount ofclover in a sward following identical treatmentscan vary from field to field and that recoveryof the clover can also vary and is sometimesvery slow.

There is little evidence on how this checkto clover may be minimized. Proper manuringand management, designed to encourageclover growth, is usually quoted as beingeffective in producing a rapid recovery, butElliott's work raises doubts about this. Thetime of application may be important in itseffect both on initial depression and subse-quent recovery, but there appears to be littlepublished work on this. Tn New Zealand,emphasis is given to spraying outside the timesof peak growth of the clover. Thus earlyspring and autumn and the midsummerdecline in growth are suggested as suitable

times for spraying (42). Emphasis has beenlaid on the management of the field in reducingill effects on the clover. Eor example anapplication of basic slag during the winterprevious to spraying, with hard grazing of thesward a fortnight before spraying (to removemuch of the clover foliage) and hard grazingagain a fortnight after spraying (to encouragethe clover to spread), has been recommended

(1).In controlling some grassland weeds, low

doses of MCPA or 2,4-D are likely to havelittle effect on established clover. To obtain theadvantages of safety to clover and the maxi-mum control of weeds, commercial mixtures ofMCPB or 2,4-DB with small amounts ofMCPA or 2,4-D are available. Elliott (25) hasquestioned the advisability of placing relianceon a single treatment and quotes several reportswhere repeated applications of low doses ofMCPA or 2,4-D are stated to have givenbetter results than single large doses. This may,in the long term, be a more satisfactoryapproach to grassland spraying, both from thepoint of view of weed control and cloverdamage, and it parallels the experience of thearable farmer, who expects to spray his fieldsmore than once.

Many reports on experimental work on thecontrol of perennial weeds are concerned withfield spraying trials, and there has been littleattempt to study the growth behaviour of theweed and relate this to herbicide treatment.Inconsistent results have been obtained fromspraying, which have not been satisfactorilyexplained. A considerable effort has been putinto finding a satisfactory herbicide for brackenand inconsistency in results has been an out-standing feature of the work (33). It has beenpointed out (15) that there may be six or sevenreserve frond buds underground to eachbracken frond which has emerged; moreoverthe majority of these frond buds are carried onrhizome branches that do not carry an ex-panded frond. Repeated spraying in consecu-tive years has not markedly improved resultswith bracken. Although creeping thistle cansometimes be well controlled with a singleapplication of MCPA, repeated spraying ineach of three consecutive years in a trial has

208 THE HERBICIDAL CONTROL OF BROAD-LEAVED AND GRASS WEEDS IN ESTABLISHED GRASSLAND

failed to eradicate the weed (2). The physio-logical condition of the plant is probablyimportant. Natural increase and declineoccur in the shoot population of weeds: theresults of spraying at a time when populationsare decreasing might be different from those ofspraying when the density of the weed is build-ing up. Most assessments in experiments onperennial weeds have been on visible shoots,which may not be the most satisfactorymeasure of the lethal effects of a herbicide.The botanist has an important role to play inthis aspect of weed control.

SELECTIVE CONTROL OF GRASSES

The balance of grass species within a swardis readily altered by many management factors(39) and herbicides are only one of severalmethods of changing the grassland communityinto something considered more desirable. Itappears however that, while managementfactors may change the proportion of thevarious constituents of a sward, they seldomlead to the complete elimination of a species.Van Slijcken and Andries (49), comparingreseeding methods with improvement byfertilizing over five years, found that a markedbotanical change of the sward was observedonly where the original sward was destroyed.Gang mowing can produce marked changesin a sward, but seldom appears to eliminateany species entirely (12).

Herbicides can provide a means of hasteninga change in sward composition (13) and maybe able to eliminate selectively an unwantedspecies. Paraquat and dalapon are the chemi-cals which have been most studied, becauseboth show some degree of selectivity betweengrass species. Fryer (28) has listed some speciesin the following order of increasing suscepti-bility to paraquat:

(i) Lolium perenne, Dactylis glomerata andFestuca rubra,

(ii) Festuca pratensis and Phleum pratense,

(iii) Poa trivialis and Holcus lanatus,

(iv) Agrostis stolonifera.

Fryer and Chancellor (29) have put thefollowing species in order of increasing sus-ceptibility to dalapon:

(i) Poa trivialis,

(ii) Cynosurus cristatus, Holcus lanatus andLolium perenne,

(iii) Agrostis tenuis,

(iv) Festuca rubra;

(v) Agrostis canina,

(vi) Molinia caerulea, Anthoxanthum odor-atum, Nardus stricta and Deschampsiacaespitosa.

Such lists can be somewhat misleading,however, because the re-action of grasses varieswith the time of spraying. Timothy, forexample, has been killed at a lower dose inSeptember than in June, whilst at the same siteperennial ryegrass required a higher dose inSeptember than in June to produce a kill. Ateach time of spraying timothy was more sus-ceptible than ryegrass, but the selectivitybetween the two species was much greater inSeptember than in June. Lolium multijiorum,however, was more susceptible than Poaannua when sprayed in September but lesssusceptible when sprayed in June (34). The testswere done on species grown in isolation.

The effect of paraquat is to scorch all foliage,following which recovery of surviving grassesoccurs. The rate of recovery differs quitemarkedly between species and competition in amixed sward at this stage may reinforce ordiminish the selectivity of the herbicide.

Instances of remarkable and valuablechanges in sward composition following theuse of herbicides have been recorded, but theresults are unpredictable (37, 38). We requiremore knowledge on the behaviour of grasscultivars and ecotypes in swards and of theirresponse to the herbicides, under a widevariety of influences—seasonal, biotic andhabitat—before much progress is likely withexisting chemicals. Chemicals showing moreconsistent selectivity are required at this stageto produce a reliable treatment. In any eventthe practical value of the selective control of

STANLEY EVANS 209

grasses seems to hinge largely upon the re-assessment ofthe potential ofthe various grassspecies.

THE TREATMENT OF SWARDS WITH HERBICIDESBEFORE RESEEDING

The killing of swards with chemicals beforereseeding offers attractive possibilities. If newspecies are required in a sward it appears thatoften they must be introduced and the diffi-culty of introducing new species into a livingsward Is well known (26, 46). Ploughing beforeresowing is the traditional method for re-creating a sward; but inversion of the soil bythe plough may have disadvantages. Theappearance of rushes in fields ploughed andresown, where rushes had not been knownbefore, has been a common experience (45).Any soil disturbance is likely to inducegermination of buried seeds. Loss of soilconsolidation from ploughing may be detri-mental, particularly on soils high in organicmatter or on peat bogs (35). Crompton (18)has shown that, on some soil profiles, plough-ing, by inversion of the soil, puts a spongy matbelow a relatively unstructured sub-soil. Thisproduces conditions most unsuited for pro-ductive grasses. There may also be areas whereploughing is impossible or highly expensivebecause ofthe contour or the presence of rocksnear, or on, the soil surface.

The term 'chemical ploughing', sometimesused in reference to herbicides used for killingswards, is very misleading and should be dis-carded. The plough does more than kill asward; it exposes the soil which can act as aseedbed. Some trouble has been encounteredwhere herbicides have been used, because it isnot easy to establish grass and clover in deadtrash, particularly when there is an acid 'mat'beneath the trash. From a series of N.A.A.S.trials it was concluded that, as the landbecame more difficult, so the technique ofsward renovation with herbicides combinedwith minimum cultivations became less practic-able (47). To improve the chance of success indifficult situations, some improvement of thesward and soil profile may be a necessaryprelude to the use of a herbicide. It seemsessential under British conditions that the

sown seed should come into contact withmineral soil. Burning of the surface trash andthe treading of stock have helped seed-establishment (36, 41). The protection of seed-ling grasses and clover from desiccation andfrost by the dying litter ofthe old sward, suchas has been favourably reported from NewZealand (43), has not met with success in theU.K. Indeed the migration of slugs and otherdamaging fauna from the dying sward to thenew seedlings is a distinct hazard (10).

Some form of cultivation generally seemsnecessary after spraying to ensure a satisfactoryestablishment of the sown grasses. The rotarycultivator has been cited as the best implement(6) but this is as expensive as the plough touse and can itself be effective in destroying asward (19). The principal herbicides used forkilling swards are dalapon, amino triazole andparaquat. None will kill seeds in the soil andthe regeneration of grasses such as Festucarubrci from seed and the germination of broad-leaved weeds can occur after no residues oftheherbicides remain in the soil (40). This is likelyto occur more particularly when the soil hasbeen disturbed, and so far as broad-leavedweeds are concerned may necessitate the useof a selective herbicide such as MCPB whenthe sward has established itself. Rapid estab-lishment of the new sward is desirable tominimize the invasion of weeds from seed andfrom incompletely killed plants.

The only precise commercial recommenda-tion for the use of a herbicide in sward renewal(1963) is with paraquat. Treatment has to befollowed by rotary cultivation and must beconfined to lowland swards, which generallyare suitable for normal ploughing and re-seeding methods, and the process is as costlyas normal reseeding methods.

Charles (11) has recently reviewed surface-sowing methods of establishing new pastures.His conclusion was that the techniques, withthe machinery and herbicides available, werenot as reliable as the conventional methodsof ploughing and sowing. For progress, hesuggests that attention be given not only toherbicides but to machinery designed forsurface sowing, and in this connection thereis a report of an experimental machine which

210 THE HERBICIDAL CONTROL OF BROAD-LEAVED AND GRASS WEEDS IN ESTABLISHED GRASSLAND

drills seed in a fluid into a small slit in thesoil (5). Charles stresses that successful surfacesowing can be achieved only by subsequentgood management, including adequate controlof the grazing animal.

In many aspects of herbicide use in grass-land there is need for a great deal of researchand development and it is perhaps not sosurprising that many authors, advisers, andfarmers show little interest in herbicides forgrassland.

REFERENCES1. ANON, Pasture Management at Thurgarton, pub.

Boots Pure Drug Co, Ltd., Nottingham,2. ANON. N . A , A , S , Unpublished data.3. ANON, 1962. Great House Experimental Hush. Farm

Review, Min, of Agric, Fish, and Food,4. ANON, 1963, A.R.C, Symposium on Grassland

Improvement, Oxford—January 1963.5. ANON. 1963, Better grass without the plough,

Fmr's Wkly, Lond, 14.6,63 p. 45,6. ALLEN, H, P, 1963, Guide to the use of'Gramoxone

W for pasture renewal. Pub. Plant Protection Ltd,7. BAKER. H, K. 1963, A survey of English grasslands.

Proc. 6th Brit. Weed Contr. Conf. i962, pp. 23-̂ 30,8. BAKER, H, K, and EVANS, S. A, 1960, The control of

weeds in permanent pasture by MCPA and thesubsequent effect on herbage productivity, Proc.4th Brit. Weed Contr. Conf. 1958, pp, 16-20.

9. BAKER, H. K., JONES, L. and CHARD, J. R, A, 1961,The control of weeds by MCPA in permanentpasture under different management and the effecton herbage productivity, Proc. 5th Brit. Weed Contr.Conf. I960 pp, 141-9,

10. BLACKMORB, L . W, 1957. Chemicals as an aid tooversowing and crop establishment, Proc. iOth N.Z.Weed Contr. Conf. pp, 18-23,

11. CHARLES, A. H, 1962, Pasture establishment bysurface sowing methods. Herb. Ahstr. Vol. 32. No. 3.pp, 175-81,

12. CHIPPENDALE, H . G . and DAVIES, T . H . 1962, Theuse of the forage harvester in the improvement ofrough grazing, J. Brit. Grassl. Soc. Vol. 17, pp.315-21,

13. CHIPPENDALE, H, G , and MERRICKS, R, W, 1956,Gang-mowing and pasture management. J. Brit.Grassl. Soc. Vol. 11, pp, 1-9,

14. CHURCH, B, M. . KINSEY. C, and POWELL, T . R, W .1963, Surveys of herbicide practice in four dairyfarming districts, 1961-62, Proc. 6th Brit. WeedContr. Conf. 1962 pp, 387-94,

15. CoNWAY, E, 1961, Considerations on judgingcontrol methods of Pteridium aqualinium. Proc. 5thBrit. Weed Contr. Conf i960, pp, 187-90,

16. CoPEMAN, G. J, F, and ROBERTS, H , W . I960, Thedevelopment of surface reseeding. / . Brit. Grassl.Soc. Vol, 15, pp. 163-8,

17. COWLING, D , L, , LEIGH, J, H, and LOCKYER, D, L.1962, Recovery of N by grass species, Grassi. Res.Inst. Rep. Expts. in Progr. 1960-6i, pp. 19.

18. CROMPTON, E, 1953, Grow the soil to grow thegrass. / , Min. Agric. Vol, 60, pp, 301-8.

19. DAVIES, J, and EVANS, S, A, 1955, Sward destruc-tion by TCA. Proc. 2nd Brit. Weed Contr. Conf.1954, pp, 205-11.

20. DAVIES, W . 1941, Grassland map of England andWales. / . Min. Agric. Vol, 48, pp, 112-21.

21. DAVIES, W , 1963. The place of herbicides in grass-land management, Proc. 6th Brit. Weed Contr. Conf.1962, pp. 37^2.

22, DAVIES, W, and WILLIAMS, T . E, 1948, Animalproduction from leys and permanent pasture. J.R. agric. Soc. Vol, 109. pp, 148-65,

23, ELLIOTT, J. Cl, 1957. The effect of MCPB and 2,4-DB on seedling and established clovers, Proc. 3rdBrit. Weed Contr. Conf i956, pp, 465-76,

24, ELLIOTT, J,G, 1961. T'he reaction of 7>//o//Hm repe/Min grassland to 2,4-D and MCPB, Weed Res. Vol. 1,pp, 184-95,

25, ELLIOTT, J, G. 1963, Chemical possibilities ingrassland, Proc. 6th Brit. Weed Contr. Conf. i962,pp, 31-6.

26, ELLISON, W, 1963, Machines for better grassland.J. Min. Agric. Vol. 70, pp, 6-11.

27, FAIRBURN. C, B, and THOMAS, B, 1959, The potentialnutritive value of some weeds common to north-eastEngland, J. Brit. Grassl. Soc. Vol, 14, pp, 36-46,

28, FRYER, J, D, 1962. Studies on the selective toxicityof paraquat to grasses, made by the A.R.C, WeedResearch Organisation 1960-62, Rep. Symposiumat Elvedon Hall 19-20 Nov, 1962. Plant ProtectionLtd.

29, FRYER, J, D, and CHANCELLOR, R, J, 1959, Toxicityof daiapon and amino triazole to some commonBritish grasses: a progress report, Proc. 4th Brit.Weed Contr. Conf i958, pp, 197-202,

30, GUTSELL, R, J, 1963, Field experience in combiningMCPA and fertilisers for the control of Ranunculusspp, (Buttercup) in permanent pasture, Proc. 6thBrit. Weed Contr. Conf i962, pp, 105-20,

31, HARPER, J, L, 1958. Famous plants—8 The Butter-cup, P^ew Biology, No. 26,

32, HENDERSON, J, L,, EDWARDS, R, S, and HAMILTON,J. L, 1962, The productivity of five grass species atsix levels of compound fertiliser application, J.agric. Sci. Vol, 59, pp, 5-11, 199-206.

33, HODGSON, G , L, 1963, N.A.A.S. Quart. Rev. Vol.14, No. 59, pp. 100-5,

34, HOLROYD, J. 1962, Private communication,35, HUNT, I, V, 1960, The improvement of grassland

by oversowing, Proc. ist Brit. Conf. on the improve-ment of marginai lands by oversowing after dalapontreatment, organised by Dow Agrochemicals Ltd.,pp. 33-45,

36, JONES, J, 1963. Dalapon as an aid to sward renova-tion. Proc. 6th Brit. Weed Contr. Conf. 1962, pp.65-74.

37, JONES, L, 1962, Herbicides to aid pasture renovation,J. Brit. Gra.tsl. Soc. Vol, 17, pp, 85-6,

38, JONES, L, 1963. Personal communication.39, ,|ONES. M, G, 1933. Grassland management and its

influence on the sward, Emp. J. cxp. Agric. Vol. I,pp, 43-57, 122-8, 223-34, 361-7,

40, KYDD, D . D . 1959, Grassl. Res. Inst. Rep. Exp. inProgr. 1957-58, pp. 23-5.

41, LAWSON. H . 1963, Dalapon for hill land improve-ment without reseeding. Proc. 6th Brit. Weed Contr.Conf 1962, pp, 57-64,

42, MATTHEWS, L, J, 1962, Private communication,43, MATTHEWS, L. J, and BLACKMORE, L,, W . 1958.

Pasture renovation by the use of weedicides. Proc.N.Z. Inst. agric. Sci. 1958, pp, 74-80,

44, MOORE, H , I, 1943, Grassland Husbandry, pub,Geo, Allen & Unwin.

45, MOORE, H , I, and BURR, S, 1948. The control ofrushes in newly reseeded land in Yorkshire, J. Brit.Grassl. Soc. Vol, 3, pp, 283-90,

46, NORMAN, M, J. T. and GREEN, J, O, 1957. Therenovation of downland permanent pasture. / .Brit. Grassl. Soc. Vol, 12. pp. 30-8, 74-80.

47, ORMROD, J, 1961, The use of chemicals in therenovation of difficult sward in the east midlands ofEngland. Proc. 5th Brit. Weed Contr. Conf 1960,pp. 151-6,

48, PHILLIPS, J. D. and PFEIFFER, R, K, 1960, Anexample of the relation between palatability ofpastures and selective buttercup control, Proc. 4thBrit. Weed Contr. Conf. 1958, pp, 15-6.

STANLEY EVANS 211

49. VON SLIJCKEN, A, and ANDRIES, A. 1960, A com- 50. WOODFORD, E, K, and EVANS, S. A, 1963, Ed,parative study of different methods for grassland Weed Control Handbook, British Weed Controlimprovement. Proc. 8th int. Grassl. Congr. I960, Council, pub, Blackwelis Scientific Publications Ltd,pp. 399-401.

(Received for publication 10 October 1963)