摘要:

In view of the favourable reduction in the weed‐seed population on Broadbalk wheat field (Rothamsted Experimental Station) by the 2‐year fallows between 1925 and 1929 a cyclic fallowing of one section out of five per year was adopted to maintain control over the weeds. Annual samples for determining the weed seeds were taken from plots receiving farmyard manure, minerals and sulphate of ammonia together, and minerals and sulphate of ammonia in alternate years.The numbers of seedlings obtained were grouped to show the reduction in weed‐seed population during fallow and the behaviour of various species in succeeding years. By this grouping the effect of the variable seasonal and cultivation factors is greatly reduced, as several years are included in each figure.Most species are reduced by fallow, rise more or less rapidly during succeeding years, and are again reduced by a later fallow, usually to a lower level than by the first.Alopecurus agrestisshowed the greatest variation from year to year.Papaver rhoeaswas the outstanding exception to the general rule, as, once reduced by fallow, it failed to reassert itself except in a few cases, and was further reduced by the later fallow. These two species, withAlchemilla arvensis,Veronica arvensisandMedicago lupulina, contributed about 90% of the total seeds.Alternate manuring with minerals and sulphate of ammonia greatly influenced the production of weed seeds. With most species nitrogen induced heavier seed production, as was shown by the average number per section compared with those produced with minerals.Alopecurus agrestis, Alchemilla arvensis, and usuallyPapaver rhoeasresponded thus,Veronica arvensiswas the only one of the main species to behave irregularly, whereasMedicago lupulinashowed a reverse response, being more benefited by minerals than nitrogen.In the first year after fallowing the crop and weeds alike were usually able to benefit by the stored fertility and did not appear to interfere with one another except where farmyard manure was used, when the competition of the crop at first prevented the weed‐seed population from rising. In the later years the crop tended to decrease, and the weeds to increase, until the balance was restored by another fallow.Field observations, as well as laboratory samples, have shown a steady improvement in the cleanness of Broadbalk field, the most noticeable reduction being in poppies. The various weed species fall into definite groups, in two of which the reduction or increase in numbers induced by fallowing is maintained, while in the third there is an irregular increase and decrease in numbers over a period of years.The general conclusion is that the fallowing of one section per year has fully justified itself, as the total weed‐seed population has not only been kept in check, but has also been gradually decreased during the 15 years the system has bee

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06259.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The effect of eyespot throughout the season on wheat receiving different amounts of nitrogen was studied in pot experiments. Plants inoculated in December showed chlorosis of outer leaves in February. Among plants with high nitrogen, eyespot killed 11%, caused straggling of 31% and whiteheads in 14% of the surviving ear‐bearing straws, reduced yield of straw by 8% and of grain by 16%. The loss in straw yield was due to reduction in plant number, that of grain was about half due to reduction in number of ears and half to production of lighter grains. Among plants with low nitrogen the disease killed 23% of the plants, caused straggling of 86% and whiteheads in 18% of the surviving ear‐bearing straws, and reduced yield of straw by 23% and of grain by 44%. The loss in straw yield was due to death of plants, that of grain was about two‐thirds due to the production of fewer ears and one‐third to that of lighter grains. In the high‐nitrogen series the number of shoots at the time of maximum tillering was reduced by 29%; in the low‐nitrogen series the disease caused reduction in height, a very uneven crop, delay in ear and anther emergence, and an increase in tail corn from 4% in the controls to 30% in the inoculated plants.All inoculated plants became infected, but those receiving high nitrogen had only 49% of the ear‐bearing straws with severe lesions at harvest, while those receiving low nitrogen had 86%. The larger number of tillers produced when nitrogen was applied may have enabled the less severely diseased shoots to survive and bear ears while the most severely

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06260.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Fusarium avenaceumis reported for the first time as a cause of rotting of potato tubers in Britain. The progress of rotting in tubers infected with F. avenaceum has been compared with dry rot due toF. caeruleumin the laboratory, clamp and potato store. Of the four varieties, Majestic, King Edward, Doon Star and Arran Pilot, tested for susceptibility, King Edward was the most susceptible toF. avenaceumand Doon Star toF. caeruleum.Optimum temperatures for growth on potato‐dextrose agar were 20‐25d̀ C. forF. avenaceumand 20d̀ C. forF. caeruleum; maximum temperatures were>30 and 30d̀ C. respectively. For infection of wounded potato tubers, cardinal temperatures forF. avenaceumwere similar to those on agar, but forF. caeruleumthe optimum was 15d̀ C. and the maximum 25d̀ C. The optimum temperature for rotting tended, with both species, to be higher in the more susceptible potato varieties. At low temperaturesF. caeruleumcaused quicker rotting than didF. avenaceum, even though its rate of growth on agar was scarcely more than half that of the latter.High humidity favoured rotting especially byF. avenaceum; F. caeruleumwas more tolerant of relatively low humidity. Both species caused quicker rotting in the clamp than in store, even though there was no appreciable difference in mean temperature between the clamp and the store. This was attributed to the higher atmospheric humidity in t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06261.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The effect of bruising and of disinfecting (‘dipping’) seed potatoes with a proprietary organo‐mercury preparation on the incidence of dry rot in them was tested in field trials during three seasons. The tubers used were of the susceptible variety Ninetyfold, taken from crops grown in contaminated soil, harvested immature in July to early August each year under farm conditions, and stored in boxes.Seed tubers not deliberately bruised, whether dipped or not at lifting time, remained practically sound until planting time in the fallowing season, if left undisturbed in their boxes.Tubers deliberately bruised, either at digging time or 1‐2 weeks later, but not dipped, developed severe dry rot with few exceptions. The disease had run its course by mid‐October. When undipped, sound tubers were bruised in October, they contracted severe dry rot, but dipping such tubers immediately before bruising reduced the loss satisfactorily in five out of six trials.Tubers bruised at digging time and immediately dipped suffered little from dry rot in almost all cases. Delayed dipping of bruised tubers checked the disease in some trials but not in others. Seed tubers severely bruised 1‐2 weeks after being dipped remained practically sound except in one instance, whereas tubers severely bruised approximately 3 months after being dipped, subsequently developed severe dry rot in four out of six tests, unless they had been redipped immediately before they were bruised.Inoculation of healthy tubers with soil samples showed that the fungus is widely distributed in potato fields in Cheshire. Dipping killed all, or almost all, of the fungus in the soil adhering to the seed tubers.The results are discussed and suggestions are made for further investigations and for practical contr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06262.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Results are given of eight replicated‐plot trials of a number of copper fungicides in comparison with standard Bordeaux mixture under relatively severe conditions of potato blight incidence, in Devon and Cornwall during the years 1941‐4.Recent methods of disease measurement on foliage were applied and developed; characteristic curves were obtained defining the conditions of trial and the relations between spray timing and progress of blight attack. The time interval between half‐decay dates for sprayed and unsprayed foliage was taken as a numerical criterion of the direct protective effect of spraying.A linear relationship was found to hold between probit foliage decay and time, and this was accounted for by the close correspondence of the probit curve to that derived from a growth law,da = Ca(A ‐ a)dt, whereadenotes the percentage foliage area affected by blight at timetafter the beginning of the attack.Methods were found for preparing dispersible mixtures of bentonite with active copper compounds for use in spraying. With such admixture, to improve adhesion, both cuprous oxide and copper oxychloride preparations nearly equalled Bordeaux mixture at the same copper dosage. Without sticker, and compounded with water‐soluble dispersing agents, these materials were equalled by Bordeaux mixture at half their copper dosage.Suspensions of metallic copper were found to have pronounced fungicidal effect againstPhytophthora infestans.A bearing of this result on the fungicidal mechanism of cuprous oxide is discussed.Results from 103 pairs of twice‐sprayed and unsprayed plots of main‐crop potatoes in Devon and Cornwall in 1941‐4 showed a mean prolongation of growth due to spraying of 16 1/2 days, and a mean gain in total yield of 2 3/4 tons/acre; but the gain in yield resulting from a given prolongation of growth varied greatly, according to the stage of crop development at which the prolongation of growth began.Spray retention data, for correlation with foliage protection and yields, were obtained in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06263.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

A short account of the present state of knowledge regarding the disease is given. Methods for the examination of seed samples for the estimation of infection withPhialea temulentaare described; the most suitable is the examination of each seed microscopically after the removal of one or both glumes, for the presence of macroconidia. The causal organism was isolated by germinating macroconidia and ascospores and also from mycelium within the seed. Its growth on media confirmed previous indications thatPullularia pullulanswas not the parasite responsible for the disease. Growth in culture is slow, and the production of numerous mucilage‐cove red macroconidia, the formation of which was observed, gives a slimy appearance to the culture on most media.The fungus and its life history are described. Inoculation experiments carried out in 1940 and 1941 proved the pathogenicity ofPhialea temulentaand the saprophytic nature ofPullularia pullulans.Italian rye‐grass, commercial perennial rye‐grass and two strains of pedigree perennial rye‐grass were all found to be susceptible to attack when inoculated at flowering time with either macroconidia or ascospores. Using commercial perennial rye‐grass the amount of infection was very much reduced when inoculations were carried out after flowering had ceased. The correlation coefficient between percentage infection and germination was calculated from the results of inoculation experiments carried out in 1941 and for samples of pedigree perennial rye‐grass (S24) seed received for examination in 1940, 1942 and 1943. In all cases there was a highly significant, negative correlation indicating that infection withPhialea temulentaresulted in reduced germination. The fungus has been isolated fromFestuca ovinaL.,Agrostis caninaL.,A. palustrisHuds.,Poa pratensisL.,Holcus lanatusL. andCynosurus cristatusL., whileFestuca elatiorL. andPoa trivialisL. were successfully inoculated in 1943 using macrospores of the fungus.The control of the disease by the breeding of resistant strains and by crop management is discussed. There is little possibility ofPhialea temulentabeing viable in the seed if an over‐year sample is sown. In field experiments hot‐water treatment of the seed prevented the production of apothecia, but infection occurred owing to the dispersal of ascospores from other plots. A later experiment indicated that the disease is widespread in pastures, waste ground and hedgerows so that the sowing of disease‐free seed will not guarantee a resultant healthy seed crop. It has been shown that contaminated and diseased seed may be freed from infection by hot‐water treatment, whereas the use of organo‐mercury disinfectants applied dry or by the short wet method were only partially effective. Treatment with hot water for 15 min. at 50d̀ C. following a 4 hr. pre‐immersion in tepid water, or for 30 min. at 50d̀ C. without pre‐immersion provided complete control, and the germination of the seed was in no case impaired when it was thoroughly dried

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06264.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Although epidemics of bee disease have been repoited in Europe for hundreds of years it was not until recent times that detailed notes on the incidence and distribution of one of these epidemics, the so‐called ‘Isle of Wight disease’ epidemic, were made.Since 1918 four complaints of the adult honeybee, acarine disease, Nosema disease, Amoeba disease and bee paralysis, have been recognized in this country.Surveys in England and Wales to determine the incidence and distribution of acarine disease, Nosema disease and Amoeba disease were carried out during the winters of 1941‐2 and 1943‐4. These surveys showed that none of these diseases is clearly confined to any definite areas of England and Wales. Acarine disease is, however, apparently more abundant in the west and south‐west; and Nosema disease appears to be most prevalent in Buckinghamshire, Hertfordshire, Middlesex and Surrey, and also has other areas of heavy infection in Leicestershire and Cumberland, Lancashire and Yorkshire.Sufficient cases of Amoeba disease have not yet been recorded for it to be possible to conclude that any one area is more heavily infected than another. It is estimated that approximately one out of every five or six of the colonies of bees in England and Wales is suffering from acarine disease. Less than 1% are likely to be suffering from Nosema or Amoeba disease. Bee paralysis is both common and widespread, but probably does little s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06265.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Between 1934 and 1936 beet eelworm was found to be prevalent on a farm in the Isle of Ely. The virtual absence of other species of Heterodera and the workable nature of the soil made the farm ideal for the study of soil populations. In 1937 a sampling technique for estimating the cyst, viable cyst and egg content of soil was developed and standardized. The first part of the paper deals with the sampling technique and the investigation of the various steps of which it is composed. When put into operation, the technique gave consistent results, but difficulty was experienced with counts of viable cysts and eggs owing to bias between different observers.The second part of the paper gives the results obtained by the application of the technique to twenty‐four fields during the period 1937‐42. There appears to be a correlation between the general level of the eelworm population and the frequency with which susceptible crops are grown, and also between the general level of the population and the amount of damage to the crop, ‘beet sickness’ being most extensive and most severe where populations are greatest. Marked increases in the eelworm population follow the planting of susceptible crops upon heavily infested land, while smaller increases occur in fields with low eelworm populations. Fields which were completely ‘beet sick’ required very long periods of rest from susceptible crops (more than 10 years) before the eelworm populations in them fell to a low level and before they could be regarded as safe to grow sugar beet once more. The general effect of non‐susceptible root crops is to bring about a lowering of the eelworm population. Cereals have the same general effect, but to a lesser extent. In some instances, rises were recorded after the growing of cereals. These appeared to be due to weeds, or to susceptible crops growing as weeds amongst the cereal crops. Claying had a beneficial effect.The results of the investigation indicate the difficulties which may arise where close cropping is practised with crops susceptible to beet eelworm, and the desirability of avoiding widespread ‘beet sickness’ in important beet‐growing areas. Brassicae are capable of increasing beet‐eehvorm populations, although they do not as a rule show signs of distress when growing on land where sugar beet develops the symptoms of ‘sickness’.A strong correlation was observed between the viable cyst and egg content of bulk samples. This suggests that viable cysts are a better measure of the general level of the eelworm population than might have been supposed. Cysts decay slowly and remain in the soil long after they are devoid of living contents. For this reason cysts alone are better as a guide to the past history of an infestation than as a measure of its present intensity. The eehvorm population of any field is complex and has highly individual characteristics. The best measure of this population so far devised is an estimate of the encysted egg population. While this may be adequate where it is desired to note changes in the level of the population following a particular crop or treatment, it is not nearly so satisfactory where a forecast of damage to an ensuing crop is required.In examinining cysts for viability, fungal hyphae and the fruiting bodies of other organisms were found inside. One of these, a fungus of the OrderChytridiales, had fruiting bodies similar to microcysts (Triffitt, 1935), and it is concluded that some part at least of the microcyst population of soils is composed of the fruiting bodies of fungi of this Order. Another organism, probably a fungus, caused blackening of the eggs. This was almost certainly a parasite, and its rather high incidence suggested that it might be of importance in reducing egg populations.In conclusion, a number of suggestions are made for the adaptation of the technique for advisory purposes. Experience suggests that the general level of the egg population above which it is unsafe to grow sugar beet or mangolds on Fen soils is about 10 eggs per g. of air‐dried soil or approxima

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06266.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY