摘要:

SUMMARYThe distribution ofRhopalosiphum padion spring barley plants in the field and the laboratory is described. Aphids fed mainly on the lower parts of the plants in both the field and the laboratory. A relatively large proportion of the field population was found beneath the soil surface early in the season. In the laboratory, aphids preferred the stem base and auricles of young and old plants respectively. The highest soluble nitrogen concentration was found in the stem base of young plants. The aphids avoided temperatures above 25°C in a temperature gradient (20°C‐40°C). The soil surface temperature in a barley stand can reach lethal levels for aphids during clear days early in the season. It is concluded that the preference ofR. padifor the lower part of young spring barley plants is mainly a consequence of the stem base being the most nutritious part of the plant and that a harsh microclimate possibly forces the aphids beneath the soil surface. This tendency to feed near or below soil level must be taken into account when assessing field densities ofR.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03226.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe population density of the bird cherry‐oat aphid (Rhopalosiphum padi) was monitored in spring sown barley and in grasslands (leys and pastures) and a suction trap was used to monitor the flight periodicity of the aphids. Emigrants from the primary host (bird cherry) colonised both grass and cereals in spring and a migration from cereals to grasses took place in mid‐summer. There was a negative correlation between the sizes of summer and autumn migration. There was a positive relationship between late summer growth in leys and the size of autumn migrations. It is concluded that the size of the autumn migration is mainly dependent on aphid population growth in grasslands during late summer and aut

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03227.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYUsing a soil debris isolation method, populations ofRhizoctonia solaniwere monitored over a 4 ‐yr period in four fields which were initially cropped to sugar beet and in which four areas of Rhizoctonia crown rot diseased beets (DA) and four areas of apparently healthy beets (AH) had been selected and precisely located. Soil from these areas was assayed during the subsequent crops, which included sugar beet, tomato, cucumber, maize and soybean. No significant differences in colony counts were found between the soils in DA and AH on any of 30 sampling dates.R. solanipopulation counts were, in general, quite low, except under sugar beet and following tomato harvest. Areas of diseased beet and highR. solanisoil populations that developed in subsequent sugar beet crops did not necessarily coincide with the previously selected diseased areas. HighR. solanipopulations developed from parasitic activity on sugar beet or saprophytically on tomato crop residues. Of the other crops, both maize and soybean may have slightly increased the lowR. solaniresidual populations in soil. The monitoring ofR. solanipopulations in the season prior to, and during the early season of sugar beet cropping did not provide a basis for forecasting disease in fields or sites within fields. The initiation of disease patches in these sugar beet fields was therefore governed by factors other than inoculum densit

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03228.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYMany spores ofPhoma aquilinaandAscochyta pteridiswere rinsed from dry infected litter obtained from a site where curl tip was prevalent. More spores were released from litter which had been incubated under moist conditions for 24 h before rinsing.P. aquilina, known to cause curl‐tip symptoms in bracken when inoculated via wounds (McElwee, 1983), did not damage healthy plants when spores were applied to intact tissues.A. pteridisappeared to infect undamaged plants under humid conditions causing the initial ‘fleck’ symptoms associated with the disease. Flecks formed on plants byA. pteridismay permit subsequent infection byP. aquilina.For bracken control, treating plants with fungal inoculum in disease‐free areas may result in disease if inoculum supplements can be found which permit initial infection byA. pteridisor damage plants sufficiently to allow colonisation byP. aquilinad

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03229.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe effect of net blotch on the growth and yield of cv. Beatrice spring barley was examined in a greenhouse experiment. Separate inoculations at growth stages 21 and 34 reduced green leaf area, root weight, leaf sheath and stem weight and tiller number. The early inoculated plants, which responded and recovered more rapidly than later treated ones, suffered a loss in grain yield and this was related to the amount of disease, the loss in green leaf area and the reduction in unit leaf rate.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03230.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn pot tests, MEMC, quintozene, captafol, carboxin, thiabendazole, carbendazim, benomyl and thiophanate‐methyl used as seed treatments gave much better control of cowpea seedling rot in light‐textured sandy and loamy sand soils than in heavy‐textured loam and silt loam soils inoculated withRhizoctonia solani.Disease control by chloroneb was not altered by soil texture. Amendment of sandy soil with montmorillonite reduced disease control with all fungicides, except chloroneb and carboxin; similar amendments with kaolinite decreased efficacy of MEMC and captafol. Green manuring with cluster bean reduced disease control by MEMC, captafol, benomyl and thiophanate‐methyl; sunnhemp reduced efficacy of MEMC. Most fungicides gave poor disease control when farm yard manure or biogas sludge was added to soil, the sludge having the more marked effect. All the fungicides tested, except carboxin, were inactivated to different extents by humic acid extracted from farm yard

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03231.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA precise, reproducible and easy‐to‐handle glasshouse test is described for the evaluation of the systemic activity of chemicals for the control ofPlasmopara halstedii, the downy mildew pathogen of sunflower. Four‐day‐old sunflower germlings were inoculated by immersing them in a zoosporangium suspension. Seedlings were then immersed in appropriate concentrations of the chemicals to be tested. Plants were grown in a glasshouse and assessed on three occasions to determine successively antisporulant, curative (systemic fungistatic), and eradicant effects.Sporulation in general was inhibited by lower concentrations than those required to exert an eradicant effect. There was a highly significant correlation between the ED50values for visually recognised disease symptoms (stunting, dampingsff and leaf chlorosis) and for both curative and eradicant effects.Among 13 compounds tested, metalaxyl, RE 26745, furalaxyl, LAB 149202F and cymoxanil showed sufficient eradicant activity, to justify field evaluation for eradication of seed inf

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03232.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAfrican cassava mosaic virus (ACMV) was detected in cassava leaves by ELISA. Some normal constituents of cassava leaves interfered with virus detection but leaf extracts ofNicotiana benthamianadid not. The symptom pattern was determined early in the growth of a leaf and subsequently changed little. ACMV was found only in the yellow or yellow green areas of the mosaic pattern. Virus content of the leaves increased with increasing symptom intensity, but decreased with leaf age and ACMV was not detected in mature leaves. Most whiteflies were found on young growing cassava leaves and the number decreased progressively with leaf age. This distribution will aid both the acquisition and inoculation of the virus.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03233.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYWatercress chlorotic leaf spot virus (WCLV) caused a yellow leaf spot disease of watercress at Pickering, Yorkshire. The virus was mechanically transmitted to and maintained inChenopodium quinoa, C. amaranticolorandPetunia hybridain which it caused systemic symptoms. It could not be mechanically transmitted, however, from infectedC. quinoatoChrysanthemum, Gynura aurantia, potato, tomato, watercress or nine other species ofCruciferae.WCLV could be partially‐purified after extraction in weak (0.05–0.1 M) but not strong (0.5 M) phosphate or tris/HCl buffer after clarification with diethyl ether and acidification to pH 3.9–4.0. Preparations were non‐infective if treated with 5% (vlv) ethanol or n‐butanol or if stored at — 12°C for 1 day or heated for 10 min at 54°C. Preparations were non‐infective after treatment with RNase or proteinase K but not after treatment with DNase.The virus was present in roots of diseased watercress plants which also contained the watercress crook root disease fungusSpongospora subterraneaf. sp.nasturtii.Tests showed that WCLV was transmitted byS. subterraneazoospores and that it persisted in the resting spores of the fungus.The crook root disease was controlled by adding 0.3–0.5 μg Zn/ml to the inlet water supply to the crop. The water that had flowed through the crop contained 0.05–0.10 μg Zn/ml. Although this increased the zinc content of the watercress from 8–9 in untreated beds to 16–48 μg Zn/g in treated beds, this was below the tolerance recommended by the Food Standards Committee.A method is described of obtaining accurate dilutions of solutions of zinc sulphate (20% w/v ZnSO4.H2O) in the water supplying the crop using solutions of th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03234.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYMethods of processing and storing lettuce mosaic and cucumber mosaic virus infected tissues prior to ELISA have been examined. Virus antigen detection was highest in samples homogenised in phosphate inoculation buffer (1% K2HPO4, 0.1% Na2SO3) and stored at either — 20°C or — 196°C. Detection was poor in samples homogenised in phosphate buffered saline prior to storage and in samples of all treatments stored at 4°C. Freeze‐dried leaf segments retained a high concentration of antigen, as did freeze‐dried homogenates of samples prepared in inoculation buffer.Higher levels of antigen were detected in samples stored as whole leaves at 4°C for 24 h before processing, than in samples stored as leaf segments during

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb03235.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY