摘要:

The chief aim of the investigation was to find an effective non‐corrosive spray for killing potato haulm.Certain tar acids were nearly as effective as sulphuric acid, but as some samples of such compounds were highly irritant, only those proving both effective and relatively harmless to the human skin were passed as suitable.The chemical composition of a sample of tar acids is largely dependent on the method of carbonization employed. The samples examined were from horizontal‐retort, coke‐oven, vertical‐retort and low‐temperature processes. At present, suitable compounds which can be produced commercially have been obtained from the two last‐named only. Fractionation at intervals of 10° C. indicated that, as a rule, high‐boiling fractions (250–290° C.) were more effective haulm‐killing agents and less irritant to the skin than low‐boiling fractions (190–250° C.).Various methods of emulsification are discussed. An emulsifier, consisting of a mixture of gum arabic and casein, was developed, yielding a stable concentrate, easy to dilute with water of any degree of hardness. The spray when applied formed a tenacious rain‐resistant film on the leaves. The action of sulphuric acid was considerably reduced by rain falling shortly after application.Sodium chlorate gave a fair leaf kill but a poor stem kill and is, therefore, far less effective than sulphuric acid. Restricted trials carried out with calcium cyanamide dust indicated that this compound is even less efficient than sodium chlorate.Di‐nitro‐cresol derivatives were only moderately effective and have objectionable staining properties.Of the copper compounds tested, copper chloride and nitrate proved the most effective but were not as good as sulphuric acid and are relatively expensive. A mixture of copper sulphate and salt was moderately effective on senescent haulm only. Like sodium chlorate it has the advantage of being inexpensive.Tar‐oil winter wash proved effectìve, but is expensive and slow in action.Young haulm is readily killed but becomes more resistant as the season advances and finally again susceptible during senescence. Individual, leaves on a plant show the same age/susceptibility relation. Varietal differences in susceptibility appeared to be largely the result of varietal differences in maturity.Control of blight in tubers was related to the extent of haulm kill obtained by spraying. Unless the fungus was actually wetted by the spray, it continued to sporulate freely on the leaves until the tissues died. For this reason slow‐acting compounds, such as tar‐oil winter wash and those which are ineffective on stems, provide less adequate control than quickacting, highly effective compounds such as sulphuric acid and tar acids.‘Setting’ of the skin of tubers is accelerated by killing the haulm, but the kill must be virtually complete. Therefore, to obtain maximum resistance to lifting injury, the crop should be left in the ground as long as possible after spraying. Methods of assessing ‘skin setting’ are described.Cooking tests on the produce of plots where the haulm had been killed by various tar derivative and other compounds showed no deleterious effect on quality. Neither was there any indication of detrimental residual effects in the soil following spraying with various tar‐acid and copper compounds, tar‐oil winter wash, sodium chlorate (3 %) or sulphuric acid.A low‐temperature tar‐acid compound, T.A.C. 36c, incorporating a gum emulsifier, gave satisfactory results in large‐scale tests made by War Agricultural Executive Committees in 1945. This compound, with a slightly improved emulsifier (gum arabic + casein), reference T.A.C. 46, and a vertical retort tar‐acid compound, T.A.C. 42, proved equally successful in a restricted field trial and are regarded as satisfactory for commercial use. Because of present cost of materials (40s.per acre for a 100 gal./acre application of 10% spray) their use is likely to be restricted. Comparative costs of the more effective compounds are given.The most effective non‐corrosive substitutes for sulphuric acid on vigorous haulm are certain tar‐acid sprays. For killing haulm at the end of the season some of the less effective and cheaper compounds, such as sodium chlorate or copper sulph

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06339.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06340.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

In the present paper an account is given of observations and experiments on the influence of the casing soil on the cropping of beds of the cultivated mushroom,Psalliota campestris.It is shown from the results of a survey of cropping at thirty‐nine mushroom farms that when the compost and cultural conditions are suitable for cropping, the production of mushrooms may be largely determined by the soil used for casing. Casing soils are classified into four grades depending on the numbers of sporophores formed, their rate of growth and the type of mushroom produced. A laboratory method of assessing the cropping potentialities of soils is described, and examples are given of its use for investigating field factors affecting the selection of soils for casing and the nature of the soil factors affecting cropping. It is suggested that chemical substances or specific surfaces in soils may promote cropping, but that close contact with air is necessary for them to be effective. It is concluded that direct trial is the only reliable method of assessing the value of a material for casing and that considerable fundamental research is needed on casing soil

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06341.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Calonectria rigidiusculahas been found associated with an acute and a chronic form of dieback of cacao. It can also infect cankers caused primarily byPhytophthora palmivora, and the lesions following attack by the capsidsSahlbergella singidarisandDistantiella theobroma.The association with the capsid lesions is of great economic importance since it appears that capsids alone are capable of killing only green shoots, and that the severe damage caused to woody shoots followsC. rigidiusculainfection of the capsid lesions. Acute dieback occurs only in certain districts after exceptional drought and may be considered primarily the result of environmental conditions. The main importance of chronic dieback is that it prevents the recovery of cacao which has been seriously weakened from other causes.C. rigidiusculainfection retards the healing ofP. palmivoracankers and also produces a lesion in the xylem tissue which may be extensive.C. rigidiusculahas been established in wounded cacao stems of all ages without difficulty. The spread of the fungus is slow, but is more rapid in the xylem than in the cortical tissues. Spread is greatest in the unlignified tissues.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06342.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

A virus disease of cacao, discovered in Trinidad towards the end of 1943, is apparently confined to the north‐western corner of the is land and does not occur in the main cacaogrowing areas of eastern, central and southern Trinidad; nor has it been found in Venezuela, Tobago or the Windward Islands of Grenada, St Vincent, St Lucia and Dominica. The symptoms resemble those of West African swollen shoot disease, consisting of vein‐clearing or mosaic of the leaves and red‐mottle of the leaves and pods. No swellings are formed, but recent observations indicate that the disease may cause both dieback and reduction in yield. There are two strains closely resembling each other. The spread of the disease under field conditions has been demonstrated, and although the rate of spread has varied somewhat, a mean increase of 41 % over the original number of infected trees has been found over a 10‐month period. As with swollen shoot disease, existing diseased areas have increased in size and new outbreaks at short distances have occurred. Both strains were readily transmitted by budding, the incubation period varying from 34 to 136 days, with a mean around 90 days, but no insect vectors have been found. There is at present little reason to believe that any varieties of cacao are immune to the disease or are even symptomless carriers. The question of eradicating this virus, while its distribution remains limited, should be seriously con

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06343.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Six grass fields were sampled once a fortnight from July 1943 to September 1944, and the wireworms in the samples counted by the washing and flotation method.The counts from twenty standard samples showed huge fluctuations which rendered them practically valueless as estimates of wireworm populations when treated singly. When treated as running means of four consecutive samplings, the counts showed certain seasonal trends, with minimum populations in July and August, rising populations throughout the autumn, maximum populations in the months from January to April and a sharp decline to the minimum populations again from April to July. On the average, the counts taken in winter were twice as high as those taken in the summer months.The fluctuation was evident in all size groups based on larval length but was most marked in the wireworms ‘under 4 mm.’, ‘4 mm.’ and ‘5 mm.’Samples taken to depths of 12 and 24 in. showed that on the average about 75 % of the wireworms were found in the 0–6 in. layer and about 90% in the 0–12 in. layer. These proportions varied considerably with the seasons.The seasonal changes in wireworm populations observed do not correspond with those expected from the life history ofAgriotesspp. Possible explanations for this anomaly are discussed, but it cannot be attributed to any known technical or biological factor. Several possibilities remain

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06344.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Six permanent pastures broken up in the summer of 1943 were sampled once a fortnight after ploughing in order to study changes in the wireworm populations.The graphs of the running means of four consecutive counts showed the chief trends in population. On four of the fields, a slight increase in population was apparent up to December. Only in February and March was a definite decline apparent. On the other two fields, the counts declined by about 30 % during the autumn and winter.A marked fall in population (from 30 to 70%) was evident on all the fields only after the first crop had been harvested. The new population at this time was characterized by an absence of larvae less than 4 mm. in length.The results considered alone indicate that after summer ploughing the wireworm population remains unaffected until the following spring and summer during the cropping period. When the results are considered in relation to the grass ‘controls’, it appears that a net decline in population occurs during the autumn and winter and that the decline in spring and summer is not more marked than that which normally occurs at this time in grass fields. Unlike the grass fields, however, the reduction is perman

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06345.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

Changes in wireworm populations during a bare fallow were studied on twenty‐three fields in 1943 and 1944. In every case populations were much reduced, sometimes to less than 10% of the original level. Wireworms of all sizes were affected, but the larvae less than 5 mm. in length were practically eliminated from the populations.Evidence is presented that the reduction achieved is greater in fields ploughed in February and March than in fields ploughed in May.As the populations in the grass ‘controls’ decline during the same period the entire reduction cannot be attributed to the fallow. The reduction in the bare fallow, however, differs from that in the controls in that it is permanent and continues through the autumn when the counts on the ‘controls’ are rising.The practical implications of the results are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06346.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

By extraction and precipitation from several solvents the toxic principle present inAnnona reticulataandA. squamosaseeds and roots has been concentrated up to one hundred‐fold. A preliminary chemical examination of this concentrate is described, leading to the conclusion that the toxicity is due to a glyceride or glycerides of a hydroxylated unsaturated acid or acids of high molecular weight.These extracts have been examined for contact and stomach poison and ovicidal properties in a variety of media. When used as a contact insecticide againstAphis fabae, Macrosiphoniella sanborniandMacronphum solanifolii, the concentrate exhibited a toxicity of the same order as that of rotenone, but againstOryzaephilus surinamensisthe toxicity was considerably less. As a stomach poison the ether extract was both toxic and repellent toPlutella maculipennislarvae, but was neither toxic nor repellent toDiataraxia oleracealarvae. Ovicidal tests against the eggs ofPlutella maculipennisand ofEphestia kühniellawere inconclusive. The potency of this concentrate is therefore of a limited nature and although of roughly the same order as that of rotenone to certain aphides, it has neither the intensity of effect nor the range of insecticidal action of that compou

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06347.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY

摘要:

The results of an investigation into the relation between chemical constitution and the knock‐down activity and toxicity of thiocyanate insecticides are recorded. Linkage of the toxic thiocyano radical through a ketomethylene group to a lipoid soluble hydrocarbon residue gives rise to knock‐down activity. The most active α‐thiocyanoketonesR.CO.CH2.SCN and thiocyanoacetatesR.O. CO. CH2. SCN are too irritant to the eyes and nose for inclusion in domestic fly‐sprays. Thiocyanoacetates derived from saturated 10‐carbon alcohols, however, are non‐irritant to the mucous membranes while possessing moderately high activity. The mode of action of these compounds

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1947.tb06348.x

出版商:Blackwell Publishing Ltd    

年代:1947

数据来源: WILEY