摘要:

SUMMARYIn two experiments done in successive years to compare the growth and yield of Cappelle wheat either protected from or exposed to attacks by larvae of wheat bulb fly, the plots were previously fallowed, but egg laying was prevented on half of each plot by using Polythene soil covers. In the first season wheat was sown at the end of October, November and December and in the second season in late October and in early January, when there were two sowings, one with and one without a spring application of herbicide. The infestation rate was 1·1‐1·7 million eggs per acre, typical of a moderate attack. Larvae had little effect on the yield of October‐sown wheat as the plants had two shoots each when first attacked and few were killed. On plots sown late, yield was decreased by up to 22%, as plants had only a single shoot when attacked and many were killed.The main effect of wheat bulb fly was to reduce the number of ear‐bearing shoots by killing plants and restricting the production of new shoots. Surviving plants partially compensated by producing more ear‐bearing shoots with heavier ears and slightly heavier seeds than normal.Killed plants were not distributed uniformly but were often in patches several feet across. Wheat on the attacked plots ripened more slowly and unevenly than on the unattacked plots.Weather affects the growth of the plants and activity of the larvae and thus partly determines percentage shoot

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04504.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe available methods for determining leaf area are briefly reviewed: it is concluded that the most satisfactory method for determining the irregular areas of leaves eaten by chewing insects is likely to be the dot‐grid method. This method has been used: (i) to determine the areas of circular plastic discs of known area; (ii) to determine the areas of tea leaves eaten by various species of adult weevils; (iii) to determine the areas of pieces of maize leaf eaten by larvae of the armyworm,Spodoptera exempta(Walker).For each determination it was found that reliable estimates could be obtained by taking four counts when the number of dots to be counted is between ten and forty, and two counts for larger areas. Dots on the boundary are counted as 0·5. For areas including fewer than ten dots it is usually necessary to use a grid with dots half the distance apart. For armyworm larvae on portions of maize leaf, half the counts should normally be taken vertically and half diagonally to the venation of the leaf; however, for long, thin, uneaten portions of leaf, especially when straight‐sided, vertical counts are too variable, all the counts should be diag

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04505.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYIn pot experiments, root applications of dimethoate and phorate were made to plants of fuchsia, nasturtium and bean. Twenty‐five mg dimethoate applied to a 5‐in pot made nectar from fuchsia and nasturtium and nectaries of beans toxic to bees andDrosophila melanogaster.Similar amounts of phorate and disulfoton did not cause toxicity.Gas chromatography showed that 4 days after treatment there was at least 100 times more dimethoate than phorate in the nectar of fuchsia and nasturtium.The dimethoate in nectaries taken from bean plants treated at rates between 0·5 and 50 mg dimethoate per pot was assayed by gas chromatography. The concentration of dimethoate in the nectaries depended on the applied dose: it was greatest 4 days after treatment. Loss was more rapid with larger doses than with smaller d

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04506.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYTen arable fields and two apple orchards were chosen from a total of thirty‐five sites visited to represent typical soils, crop rotations and insecticide applications in the Huntingdon area of East Anglia. Pitfall traps were used to collect insects and other invertebrates during fortnightly periods from early April until harvesting and in one orchard until the following February. Estimates of active biomass were obtained for several groups of invertebrates and differences between the sites are discussed. Samples of beetles, earthworms and slugs were collected during June and were sent with soil samples to the Government Chemist for analysis of organochlorine residues. The soil residues are compared with those in respective invertebrate samples and with stated application rates. It is concluded that soil invertebrates could form a regular source of pesticide residues for ground‐feeding birds but that the levels are generally too low to cause acute poison

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04507.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYThe optimum conditions forPeronospora farinosa betaeto produce spores were temperature 8–10 °C and relative humidity 90 % or more, but many spores were produced between 5 and 20 °C and between 80 and 90 % R.H. Most spores were formed in darkness after leaves were exposed to light for 6–8 h. Spores survived exposure to 60 % R.H. for up to 5 days, but were soon killed by temperatures above 20 °C. The germination capacity of spores collected from the field was often very small, but this could not be related to the weather. Most seedlings were infected when inoculated at the growing point and incubated in a saturated atmosphere between 3 and 15 °C for at le

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04508.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYWinter wheat drilled directly into stubble or pasture treated with paraquat to kill the vegetation has been found to be less severely attacked by take‐all (Ophiobolus graminis(Sacc.) Sacc.) and eyespot (Cercosporella herpotrichoidesFron) than wheat drilled after cultivation. The reduction of take‐all is associated, not with a direct effect of the chemical, but with factors, resulting from the technique, which limit the rate of spread of the fungus in the undisturbed s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04509.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYIn laboratory trials on detached bean leaves, benzyladenine delayed both senescence and aggressive attack of chocolate spot disease.In field plots, over 80% of the aggressive spots were on senescent leaves and the distribution of aggressively attacked leaves was predictable from the distribution of senescent leaves. The total frequency of aggressively attacked leaves per shoot was apparently related to the frequency of senescent spotted leaves.Although benzyladenine significantly reduced leaf senescence in field plots sprayed in May, the senescent leaves were more frequently attacked aggressively. Wider plant spacing (14 in instead of 8 in) similarly increased the ratio of aggressive attack to senescence, and the individual fields retained until June the differences in infection earlier established by frost damage.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04510.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYInfection of chrysanthemum leaf discs by spores ofMycosphaerella ligulicolawas increased in the presence of concentrated leaf washings obtained from five plant species tested. On separation of leaf washings by dialysis the residue stimulated infection and caused aggregation of hyphae on leaf and cellophane surfaces. In the presence of the diffusible fraction an extensive branching network of hyphae developed but there was no increase in infection except in the presence of the chrysanthemum diffusate.Infection of leaf discs of certain plants normally resistant toM. ligulicolaoccurred in the presence of concentrated leaf washings.Leaf washings from a resistant variety of chrysanthemum had the same effects as those from a susceptible variety. An extract of chrysanthemum leaves was less effective in stimulating infection than was a leaf washing.Defined nutrient media and potato extract stimulated infection but caused the development of different growth habits on leaf surfaces.The active components of the dialysis residue of chrysanthemum leaf washings were heat‐stable but apparently volatile. Eluates from strips of certain regions of paper chromatographs of leaf washings and potato extract caused increased infection together with development of characteristic growth habits of the fungus on the lea

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04511.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYIn a simple, routine test developed to detect viableSeptoriaspp. in samples of celery seed, seed washings are inoculated on to celery seedlings. Viable infection was detected in fifty‐four samples between 1960 and 1966. The method can be used to detect viable infection on one seed in several thousand.Spore exudation during ‘blotter’ tests was shown to be associated with lesion production both in the seedling inoculation test and in growing‐on tests. A high incidence of saprophytic fungi indicates that seed has not been treated but a low incidence does not mean that the sample is

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04512.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

SUMMARYAutumn‐sown crops of broad beans (Vicia fabaL.) in England often contain plants with some leaves characteristically distorted and with a chlorotic mosaic. From some of these plants true broad‐bean mosaic virus was isolated in 1959 and 1960 but not in 1965 and 1966. From other plants a similar but distinct virus, which caused staining of the seeds and we call broad‐bean stain virus, was isolated in 1960, 1965 and 1966. The two viruses were readily distinguished in serological tests, and in some test plants. Both were seed‐borne, and spread in crops, but were not transmitted by several animal species tested as vectors.Both viruses have isometric particles about 25 mμ in diameter. Some of these particles contain about 35% ribonucleic acid, some about 26% and some of those of broad‐bean stain virus contain none; these three types of particles had sedimentation coefficients of about 120–130S, 100Sand 60Srespectively. The ribonucleic acid of each virus had molar base content of G 23%, A 26%, C 18% and U 32%.These two viruses are members of the cowpea mosaic group of plant viruses; broad‐bean strain virus was serologically related to cowpea mosaic, F I, red‐clover mottle, and squash mosaic viruses. The particles of all these viruses and of true broad‐bean mosaic virus were similar in appearance, sedimentation behaviour, and nucleic acid content and composition. The nucleic acid of red‐clover mottle virus had a molar base content of G 20%,

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1968.tb04513.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY