ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01428.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe results of field trials designed to evaluate the resistance of carrots to carrot fly (Psila rosae) attack were influenced by plant density and position within trials. Five trials are described, their results analysed and implications for future work discussed. Density effects were of major importance when the range of densities within a trial was greater than about three‐fold. Density and damage were associated, carrot cultivars and families with the most roots having the least damage; plant densities achieved should therefore be as close as possible to the targets set. Positional effects were often very important, so trials should ideally have no more than about 10 plots in a block, possibly by using an incomplete block design. Conventional analyses of variance removing block effects may be sufficient but it is desirable, especially with large blocks, to use some form of nearest neighbour analysis for which the various possible techniques gave similar result

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01429.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe effect of chlorosis induced in needles of Sitka and Norway spruce by the green spruce aphid on growth of the aphid is investigated, and the effect of infestation of the aphid on amino acid levels in Sitka spruce foliage is reported.On both Sitka and Norway spruce green spruce aphids were heavier when reared on chlorotic (previously infested) needles than when reared on green (previously uninfested) needles. The effect was more pronounced on Sitka than on Norway spruce. Infestation of the aphid altered the amino acid balance of Sitka spruce foliage but not the concentration of total amino acids. Possible causes of chlorosis, the influence of individual amino acids on aphid growth, the potential effect of chlorosis on outbreaks of the aphid and the differences in susceptibility of Sitka and Norway spruce to damage by the aphid are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01430.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYLaboratory experiments were conducted to measure the feeding rates, preferences, survival rates, maturation times, and weight gain of four common species of grasshoppers (Orthoptera: Acrididae) on four lines of safflower (Carthamus tinctorius). When safflower lines were presented individually, all were readily consumed although consumption differed significantly according to grasshopper species, age and sex, and to safflower line. Consumption was greatest on a safflower line devoid of spines. However, grasshoppers also fed readily on spiny lines, and results of experiments in which all safflower lines were presented together indicated preferences that did not necessarily correspond to the results of the single‐line feeding trials.Camnula pellucida, a graminivorous species, did feed on safflower, but restricted feeding almost exclusively to stem cambium, whereasMelanoplus bivittatus, M. packardiiandM. sanguinipesfed mainly on the heads, flowers and leaves.Highly significant differences in grasshopper maturation time and weight gain were apparent among grasshopper species, and among safflower lines. Seedtec‐5, the line which was least digestible, least consumed and least preferred nevertheless yielded rapid development and the greatest body weights of grasshoppers. All species ofMelanoplusdeveloped more quickly and gained more weight on safflower than on wheat. One species,M. packardii, was more able to utilise safflower than its congeners, and may gain competitive advantage if safflower becomes widely gr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01431.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe numbers of cereal aphids on the soil surface was assessed by soil samples and by counting the numbers captured in pitfall traps. A relationship was found by both methods between the density of aphids on the plants and the numbers of aphids on the soil. This relationship indicated that a higher proportion of the aphid population was on the soil surface at the lower densities on the plant. Reasons for this relationship are suggested and discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01432.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSeeds from 53 of 64 collections ofLolium perennefrom its centre of origin or from old pastures in Europe were found to be infected with endophyte whereas only four of 16 commercial cultivars had infected seed. Almost two thirds of seed samples ofL. multiflorum, Festuca arundinaceaandF. pratensiscollected from plants growing in the wild in Italy contained endophyte but none of the eight commercial cultivars ofL. multiflorumand only two of five cultivars ofFestucaspp. produced by the Welsh Plant Breeding Station were infected. At least one seed sample from each of six species and varieties of annual ryegrasses contained endophyte mycelium. Endophytes in annual ryegrasses could not be cultured axenically and are probably a different species to theAcremonium loliipresent inL. perenne.A correction to the spelling of the specific epithet ofA. loliiis explained.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01433.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe initial incidence of the disease caused byPhytophthora fragariaein healthy stock of strawberry, cv. Merton Princess, was not affected by different systems of cultivation or by no cultivation for several months before preparing infested soil for planting.In disease development studies, healthy plants which were planted in infested soil in April and sampled at 35‐day intervals showed symptoms of red core on 1 September. Disease severity (mean % number of diseased roots) increased with time and, when averaged over intervals of 70 days, the greatest increases occurred between the end of July and the beginning of October and between December and February. Whereas the former was due to infection of plants in which the total numbers of new roots were low, the latter was due to an increase in the numbers of diseased roots. Most primary roots were produced in October and early November and 75% of the final total were formed by 15 December.Healthy plants of the cvs Cambridge Favourite and Redgauntlet, dug from the field at monthly intervals and challenged with zoospores, were less susceptible in May and June than in other months.It is suggested that a fungicide applied in late September or October would protect the maximum number of new roots and achieve the optimum effect for a single applicatio

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01434.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe insecticidal properties of the foliar fungicide pyrazophos were investigated in autumn‐ and spring‐sown barley crops using several methods to estimate the density of non‐target arthropods and by using manipulative experiments. In autumn‐sown crops, pyrazophos significantly reduced densities of cereal aphid natural enemies relative to pre‐treatment levels compared to areas of crop that were left unsprayed. These significant differences persisted in most groups for over 45 days after treatment. Groups most affected were aphid‐specific predators, polyphagous predators, (Carabidae, Staphylinidae but not Araneae) and parasitoids. Insects known to be preferred food items of wild gamebird chicks and other non‐target groups such as the Collembola were also significantly reduced in density on plots sprayed with pyrazophos, the effects again persisting for over 45 days. Densities of beneficial and non‐target insects were also reduced in plots of spring barley sprayed with pyrazophos. However, the experimental design meant that levels of reductions were not significant for most arthropod groups.Removal of prey items (Drosophilapupae) placed in sprayed and unsprayed spring barley plots showed that the proportion predated was significantly lower on pyrazophos‐treated plots compared to those remaining unsprayed, the difference persisting for at least 7 wk after treatment. Removal of cereal aphids from colonies introduced to sprayed and unsprayed plots was also significantly lower on plots treated with pyrazophos. Difficulties of data interpretation associated with experimental design are discussed together with the consequences of the use of broad‐spectrum pesticides in I.P.M. pr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01435.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe effects of four fungicide treatments for the control of mildew on spring barley were assessed in three field experiments, one in each of the years 1981, 1982, 1983. The fungicide treatments (+/ ‐ triadimenol seed treatment and +/ ‐ triadimefon foliar spray applied during early booting) were chosen to control mildew, and hence affect yield determining processes, at different times in the life of the crop. Two of the experiments also tested different nitrogen amounts and the third tested four varieties differing in their degree of mildew resistance. Mildew appeared too late to affect the production and survival of spikelets and shoots, but reduced average grain weight by reducing the rate of grain growth. Grains in the upper part of the ear had a considerably lower growth rate and final weight than grains in central and basal positions but there was no evidence that the effects of mildew on grain size depended upon grain position within the ear. Mildew incidence increased with increasing nitrogen and varietal susceptibility but there were few significant interactions between these factors and fungicide treatment for grain yield. The degree of mildew control achieved by the seed treatment varied with barley variety. Use of the two successive fungicide treatments did not yield more barley than use of either alone. Amongst varieties, grain positions within the ear and fungicide treatments there was a close correlation between rate of grain growth and final grain weight. Duration of grain growth was not related to rate of grain growth or final grain weight but was inversely correlated with mean temperature during the period of rapid grain growth. The temperature sums during the period of rapid grain growth were similar for the three years and it is suggested that a more precise knowledge of the relationships between mildew incidence, varietal susceptibility and rate of grain growth may enable more accurate predictions to be made about likely yield responses to fungicide treatme

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01436.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe effect of plant genotype, soil temperature, and moisture on recovery ofRhizobium leguminosammserogroups WA01 and WA02 from soil, was evaluated in the greenhouse using three plant genotypes (Pisum sativumcv. Alaska,Pisum sativumcv. Paloma andLens culinariscv. Rechief), three temperatures (12, 20 and 24°C) and soil from two different slope positions. The impact of moisture was followed by assessing pea nodulation after incubation of soil at different preplanting moisture levels. Isolates were also evaluated for serogroup, response to low levels of antibiotics and efficacy of symbiotic characters.Of the 33 antibiotic‐strain combinations showing growth, 10 permitted 50% or more of the isolates to grow. Of the 24 clusters obtained, all except one were dominated by isolates in either serogroup. WA01 or WA02. There was no relation between either serogroup or cluster groupings and N2fixation. Serogroup recovery was influenced by plant genotype and temperature. At root temperatures of 12 and 24°C, serogroup WA02 occurred in a significantly lower fraction of the lentil nodules as compared to the pea species. At 12°C, recovery of WA02 was higher for the Paloma than Alaska pea. Recovery of WA02 in pea nodules generally increased as the soil moisture was preconditioned to drier levels of ‐0.5 and ‐1.5 MPa water p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01437.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY