摘要:

The harmful effect of molybdenum on animals is well established, but there is comparatively little knowledge of the conditions in which molybdenum is poisonous to plants. Obvious differences in response to molybdenum poisoning in different soils have been previously noted, but no adequate explanation has been put forward.Tomatoes grown in ordinary loam showed little outward sign of poisoning with heavy doses of sodium molybdate, but some depression of crop occasionally occurred, especially when the dose was divided into early and late treatments. The response varied with season and variety. On certain light and fen soils the plants were killed at an early stage with the heavier dressing of molybdate, and seriously injured with the lighter dose, the leaves showing the golden colour characteristic of molybdenum poisoning in various plants.The reaction of different crops varied considerably in the same soil with similar treatments. On old cucumber soil tomatoes showed no sign of toxicity even with the heavy dressing, flax was progressively damaged with increasing doses, whileSolanum nodiflorumwas most seriously affected even with the lighter dressing of molybdate. It was impossible to predict the reaction between soil, poison and crop without actual experiment.The growth of flax was greatly impeded on a manganese‐deficient fen soil, and the molybdenum toxicity was masked in consequence. When the deficiency was corrected the poisonous effect of molybdenum on this soil was very marked, even with the lower dressing.The composting of loam with peat usually, but not invariably, resulted in a reduction of the toxicity of molybdenum. The different results obtained with several crops on a variety of soils still yield no definite clue to the factors which determine the relative toxicity of molybdenum to plant growth and such points as soil acidity, response to climatic conditions and nutritive deficiencies are among those which need further investigatio

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07358.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

In a four‐year study of winter lettuce cultivation, attention has been given to the effects of variety, dates of sowing and transplanting, method of preparing seed‐beds, nature of field soil, and fungicidal treatments upon percentage survival and date of maturity of the cropThe inferiority of the variety Trocadero Improved to such a winter variety as Imperial is due mainly to its susceptibility toPythiumroot rot. This disease often causes severe thinning of the stand of Trocadero seedlings and dwarfing of many of the survivorsLate autumn plantings of Imperial and other winter varieties survived better overwinter on a medium‐heavy loam than on a light sandy soil. The disparity varied in different seasons and was not associated with severity of winterThe dates of maturity of the crop in relation to dates of sowing and transplanting have been determinedoverthe four‐year period. On the basis of these, and on the records of survival and of market prices, an estimate can be obtained of the financial aspects of different cultural methodsFungicidal treatment in the seed‐bed of plants set out in the field in November gave little improvement in survival; but pronounced benefit was obtained by February or March dusting of seedlings which had overwintered in the seed‐bedThe onset of disease in overwintering seed‐beds was found to be influenced by the nature of the soil and by the manner of preparation of the seed‐bedThe interrelations of overwintering and soil type are briefly discussed, with special reference to the effects of soil type (i) on the root system, and (ii) on microbiological interference with invasion of die

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07359.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Observations on earthworm populations in the Carse of Stirling indicate that there are definite differences according to soil type both in total population numbers and in the relative numbers of each species present. The light and medium loams appear to carry higher total populations than the heavier clay types or the more open gravelly sand or alluvial types. Within and between the respective soil‐type populations, species numbers are variable, but the actual numbers present on a soil type do not necessarily indicate the relative importance of each species. In all casesAllolobophora caliginosais the dominant species, being more numerous on the light loam than elsewhere.A. longais subdominant and forms a substantial percentage on the medium loam and clay. On the light loamA. longais high in number, but forms a smaller percentage of the total population because of the abundance ofA. caliginosa. A. longais also of reduced importance on the open soils—gravelly sand and alluvium. This species does not differ very much fromLumbricus rubellusandL. terrestris, as a percentage of the population on these two later soils and the light loam. The percentages of these two species are similar within populations, though much lower on the clay than on the other soils, and the totalLumbricuspopulation number is highest on the light loam and lowest on the clay. There is a fair similarity between the two populations on the two open‐textured soils, in both numbers and percentages.Areas of acid, natural pastures contain earthworm populations low in number and species variety. Some of the species typical of these areas are small active species, e.g.Dendrobaena rubida, D. octaedraandBimastus eiseni, which are not found in well‐established field populations. When agricultural treatment improves an area the acid‐pasture species eventually decrease in relative number and importance as the species normally associated with good pasture land become established and build up their po

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07360.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

It is well known that infestation is only one of a number of factors which determine the amount of wireworm damage occurring in a field. As an attempt to analyse the conditions under which crops fail from wireworms, thirteen fields showing both damaged and undamaged areas were studied. Data were collected on wireworm populations, chemical and mechanical composition of the soil, feeding reactions of the wireworms collected, agricultural history and treatment of the different plots and fields. In six only of the fields did the damaged areas coincide with areas of higher infestation. In the remainder, the failures occurred at low populations, and no marked differences in population could be detected between the failing and successful plots. The levels of population at which the failures occurred varied between wide limits in the different fields. Two of the edaphic factors investigated were associated consistently with the failing and successful plots; CaCO3was consistently higher and sand content consistently lower on the failing plots. Differences in these factors were particularly noticeable in those fields where differences in infestation were not detected. There is a suggestion from four of the fields that wireworm attack commonly follows sainfoin. None of the other factors showed significant relationships. Although the results suggest that differences in one or more of the factors, infestation, CaCO3and sand, are associated with differences in wireworm damage within fields, the differences between the fields cannot be explained so simply. Evidently, other factors, relatively uniform within single fields but varying from field to field, also influence the amount of wireworm damage. Consideration of the results in relation to wireworm and plant populations brings out the need for greater attention to the role of wireworm activity and the environmental factors which influence it. The importance of reliable methods for predicting wireworm damage to any methods of control is stressed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07361.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

One part of metaldehyde in thirty parts of bran by volume is the minimum effective concentration for obtaining aneconomickill of slugs under average weather conditions. For use againstMilax gracilisLeydig. heaps of bait should not be normally more than 2 yd. apart and againstArion hortensisFer. not more than 3 ft. apart. The mortality of slugs attracted to metaldehyde‐bran baits is dependent on the drying property of the soil and atmosphere around the baits. D.D.T. flea‐beetle dust and powdered pyrethrum flowers are sufficiently distasteful to slugs to prevent their consuming a lethal dose of the poison mixed with bran. The addition of 10%, by volume, of dried blood to metaldehyde‐bran bait increases the catch of some slugs under certain conditions but does not increase the mortality. The addition of 10%, by volume, of dextrose increases the mortality produced by metaldehyde but does not increase the numbers attracted to the bait. A metaldehyde‐bran bait compacted into ‘biscuit’ form with anhydrous calcium sulphate catches more slugs than an ordinary metaldehyde‐bran bait, but almost completely counteracts the effect of the metaldehyde. A metal‐dehyde‐bran‐casein glue bait in ‘biscuit’ form increases the catch and kill ofMilax gracilisandAgriolimax reticulatusMüll., but not ofArion hortensis. Metaldehyde‐bran‐casein glue bait broadcast in ‘broken biscuit’ form is effective over a longer period, thus producing a greater kill of slugs, than a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07362.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

The success of size and gelatin as pretreatments was not confined to films of pyrethrins in oil. Pretreatment of cement with 10 % w/v size and 5 % w/v gelatin greatly prolonged the toxic life of films formed by other insecticides in oil solution.The effects of adding different substances to size and gelatin solutions as pretreatments were investigated. 5 % w/v size or gelatin solutions containing suspended lime or distemper powder were, with the exception of gelatin containing distemper, less effective pretreatments than size or gelatin solutions alone. Magnesium silicofluoride, benzoic acid and salicylic acid, at concentrations up to 0.5 % w/v, appear suitable as preservatives for 5 % w/v gelatin. These three substances are, however, unsuitable for inclusion in size solutions, as they cause precipitates to form. Glycerin or turkey‐red oil at concentrations of 0.5 % v/v, appear suitable as plasticizers for inclusion in both 5 % w/v size and 5 % w/v gelatin solution

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07363.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Cotton flour sacks, jute flour sacks, jute bran sacks and jute grain sacks have been impregnated with 1 and 5 % by weight of D.D.T. Treated and untreated sacks, each containing 1 cwt. of a mixture of grain (5 parts) and weatings (1 part), were exposed to severe infestation by adults ofCalandra granaria, Tribolium castaneum, Ptinus tectus, Oryzaephilus surina‐mensisandEphestia elutella. After storage for 15 weeks at a mean temperature of 21.3d̀ C. and a mean relative humidity of 65 %, the numbers of adult insects in each sack were determined by sieving the contents.The results withEphestia elutellawere inconclusive. The results with the four species of beetles showed that the eventual degree of infestation of the contents of the sacks was dependent upon the closeness of weave and the D.D.T. content of the sacking material. Impregnation of sacking with 1 % of D.D.T. should afford adequate protection against insect infestation to clean bagged goods stored in stowages which are not heavily infested. Impregnation with 5 % of D.D.T. should offer a very high degree of protection at all times and can almost entirely prevent infestation, if the treated material is of sufficiently close weave to afford some mechanical hindrance to penetration by insec

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07364.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

An account is given of the methods used to determine the relative pathogenicity of isolates ofVerticillium albo‐atrumfrom fluctuating and from progressive outbreaks of the wilt disease of hops. Isolates from fluctuating outbreaks were less pathogenic to young hop plants than those from progressive outbreaks, and it is suggested that this is the main cause of the differences in symptom incidence and intensity between the two types of outbreak in the fiel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07365.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

The success of seed certification schemes in controlling the aphis‐transmitted viruses that cause leaf roll and rugose mosaic has greatly increased the relative importance of potato virusX, in spite of the value of such schemes in reducing the prevalence of the most virulent strains. VirusXoccurs throughout commercial stocks of most varieties and is responsible for many of the uncertainties and difficulties encountered in field inspections, for the production of leaf symptoms by many strains depends on the weather. Also, the predominating virus strain in a stock may change from season to season.Methods of testing for the presence of avirulent strains in potatoes are described. These include transmission to suitable indicator plants, plant‐protection tests, and serological methods. The virus content of different parts of the plant varies widely, but is everywhere high enough for transmission to indicator plants at all times of the year. The virus content of immature tubers is too low to give a precipitin reaction, but extracts from developing sprouts contain nearly as much virus as those from foliage, and can be used reliably.Infection of virus‐free stocks of the varieties Majestic and Arran Banner with four different strains of virusXreduced their yields by amounts varying from 5 to 24%. Scotch Stock Seed Majestic, however, cropped better than the virus‐free seed, and the need for considering additional factors to freedom from viruses when selecting clonal lines for propagation is stressed.VirusXwas not transmitted by cutting healthy tubers with a knife previously used to cut infected ones, and cut tubers whose storage parenchyma was rubbed with infective sap gave rise to virus‐free plants. Infection occurred when sprouts were rubbed with infective sap, and the virus also spread from infected to healthy sprouted tubers stored in the same sack.Spread of the virus under natural conditions is slow, and it is concluded that the maintenance of virus‐free stocks under commercial conditions is feasible, provided that precautions are taken to prevent contact with infected plants. The relative importance of volunteer plants and other sources of infection is discussed, and methods of testing the virus‐free stocks

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07366.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Experiments on the spread of five strains of potato virusXwere made with seven potato varieties and with tomato plants both under glass and in the field. Spread by leaf contact between healthy and infected plants was confirmed, and it was also found that spread could occur between plants whose only contact was below ground.The rate of spread was much greater in tomato than in potato plants, and virulent strains of the virus, which achieve a high concentration in infected plants, spread more rapidly than avirulent strains. In only one experiment with potatoes did more than 10% of the healthy potato plants exposed to infection become infected during one season.Datura stramoniumand tomato plants became infected when growing in soil containing sap or residues fromX‐infected plants.It was common in the field for potato plants whose foliage gave no reaction for virusXat the end of the season to yield a mixed progeny of healthy and infected tubers. Such infections are thought to result from underground spread.Attempts to transmit virusXfrom infected to healthy potatoes by means ofRhizoctonia solanifailed. No examples of infection were found except when healthy plants came into direct contact with sources of the viru

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07367.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY