摘要:

SUMMARYA damage model was used to take into account the effect on winter wheat yield of the size, duration and timing ofSitobion avenaeinfestation in summer, and the influence of insecticide applications. It was validated as far as possible using available data, and appeared to be sufficiently accurate to be useful. The model was applied to a total of 32 winter wheat fields over the period 1975 to 1983 in eastern England and the Netherlands, to obtain estimates of yield losses associated with not applying insecticides at the end of ear emergence (G.S. 59), mid‐anthesis (G.S. 65) or the end of anthesis (G.S. 69). These estimates of future yield losses were related in multiple regressions to the number ofS. avenaeper tiller at the time the insecticide was applied, and the rate of population increase over the previous few days.Basing the decision about whether to apply insecticide on forecasts from the multiple regression equations appeared to be slightly more profitable than prophylactic spraying when the chemical cost alone was considered, but substantially more profitable when the application cost and wheeling loss were also taken into account. The strategy minimising losses involved forecasts at all three crop growth stages. It was validated using a further 21 fields studied in 1984 and 1985, and gave better results than the EPIPRE system, which over‐estimated the number of fields requiring spraying, and the economic threshold of George&Gair (1979), which under‐estimated the number requiring spraying. However, the accuracy of the damage model needs to be checked against measured yield losses in order to establish the success of the multiple regression strategy conclus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02007.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThree cultivars of Italian or hybrid ryegrass were exposed to frit fly attack at varying frequency in the laboratory. Initially a Westerwolds and a hybrid cultivar showed greater yield reductions than an Italian ryegrass cultivar, although they did not usually suffer a higher proportion of damaged tillers. The differing effect on yield appeared to be due mainly to greater impact of first or infrequent attacks on cultivars producing fewer tillers. After two to six attacks in approximately 7 months the Westerwolds and hybrid cultivars appeared to become tolerant to attack and were subsequently the least affected, although continuing to suffer tiller damage at a rate at least as high as the Italian ryegrass. All cultivars recovered fully when attack ceased, and their exclusion from attack did not improve their persistence.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02008.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn years of relatively high frit fly activity the control of all generations produced increases averaging 0×44 t d.m. ha‐1in annual yield of Italian and hybrid ryegrass. A cutting programme designed to make the sward especially vulnerable to frit fly attack did not increase the total annual effect of pesticide treatment but accentuated the periods at which damage occurred. The annual yield increase was almost entirely obtainable by controlling the second and third frit fly generations, but even one treatment for this purpose was of doubtful economic justification. The prospect of augmenting the response to control of later‐occurring pests, such as leatherjackets or eriophyid mites, by including the part of the frit fly response which is recoverable by the same treatment, was a more probable justification for pesticide usage.There was some evidence that a Westerwold and a hybrid cultivar suffered more damage than an Italian ryegrass cultivar, but pesticide treatment did not improve the persistence of any cult

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02009.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYCulture‐produced conidia ofDrechslera incurvatafrom coconut failed to germinate on the leaves of coconut seedlings incubating under the dry conditions of a greenhouse. Viability and rate of appressorium formation of artificially‐dispersed, culture‐produced conidia fell significantly during extended incubation of inoculated seedlings in the greenhouse, when 43% of conidia germinated after 90 days incubation compared with 62% at 59 days and 90% at 24 days. Field‐produced conidia on excised leaves also lost viability upon storagein situon the laboratory bench; germination fell from 60% at 3 months storage to 0×5% at 5 months and no germination at 6 months.Shading of seedlings in the field with saran cloth producing 30% shade or 50% shade depressed the amount of dew forming on leaves of young coconuts and significantly reduced both the number of infections from artificial inoculations and the severity of leaf spot disease developing subs

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02010.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn studies on the infection of potato cultivars with different field isolates ofPhoma exiguavar.foveata, cultivar × isolate interactions, although sufficiently large to influence the relative pathogenicities of isolates on different cultivars, were not substantial enough to affect cultivar ranking order. Cultivar rank was markedly influenced by pathogen isolate only when both field and culture collection isolates were compared. This suggests that the complications of cultivar × isolate interactions can be avoided in cultivar screening tests by the use of recent field isolates of high pathogenicity. It was found that cultivar was considerably more important than isolate in determining gangrene lesion size. The need to consider both lesion diameter and depth when estimating rot size following point inoculation of different cultivars was confirme

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02011.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA hand‐held apparatus, produced by modifying a veterinary multiple dosing gun, was used to pressure‐inject aqueous solutions of imazalil into the trunks of plum or apple trees after harvest, before bud burst or during flowering. Bioassay showed that post harvest injection led to movement of imazalil up and down the trunk and into branches of both apple and plum trees. Movement in the trunk after injection before bud burst also occurred in plums but was limited in apples and fungicide was detected in branches only in apples and only at the end of the season. Injection at flowering time resulted in movement of imazalil into branches of apple, but not plum, trees. Imazalil was detected in twigs of apple, but not plum, trees but only after flowering time injections.The technique could be useful for control of tree diseases provided due attention is paid to dose, to the number and siting of injection holes and to the linking of injection time with the epidemiology of the target dise

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02012.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA bioassay procedure was developed as a means of assessing the fungicidal efficacy of post‐harvest citrus dips containing the fungicide guazatine. The method is designed to overcome certain inaccuracies associated with the existing method of chemical analysis. The technique involves assessment of actual fungicidal activity by the inhibition of growth of aGeotrichum candidumculture. Comparisons are made between results of chemical analysis and this method, and the usefulness of the procedure is demonstrate

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02013.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe competitive ability of effective and ineffective isolates ofBradyrhizobiumto form nodules on four peanut (Arachis hypogaea) genotypes from which they were originally isolated was investigated in a greenhouse study. Pregerminated seeds of each genotype were inoculated with five ratios of ineffective effective bradyrhizobia: 104:0, 104:102104:104102:104and 0:104. Plants were harvested 35 days after planting and nitrogenase activity, total nodule number per plant, plant shoot dry weight and the proportion of nodules formed by eachBradyrhizobiumisolate were determined. Nodulation suppression occurred on plants inoculated with the mixed cultures, especially on those inoculated with the 104:102ineffective effective inoculum ratio. More than 85% of the nodules on plants inoculated with the 104:104and 102:104ineffective effectiveBradyrhizobiummixtures were formed by the effective isolates. The number of effective nodules per plant, nitrogenase activity and plant shoot dry matter production all increased with the proportion of the effective bradyrhizobia in the inocula.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02014.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe acquisition and transmission of cauliflower mosaic virus (CaMV) by six aphid species and three clones of aphids was studied and compared with that of turnip mosaic virus (TuMV) withMyzus persicae.Two clones ofAphis fabaewere unable to transmit CaMV, but the other species,Acyrthosiphon pisum, Brevicoryne brassicae, Megoura viciae, M. persicaeandRhopalosiphum paditransmitted in a bior multi‐phasic manner. There was no statistical evidence of a bimodal transmission pattern.R. padiis recorded as a vector of CaMV for the first time.The transmission efficiency of CaMV varied with time of acquisition and suggested that accumulation of the virus occurred with two peaks of efficiency within the anterior region of the insect gut. The time at which these two peaks occurred varied between the species, but the basic pattern was common to all transmitting aphid species in this study. This pattern contrasted with that of TuMV. The transmission data are discussed in terms of bimodal transmission, the influence of feeding behaviour, the role of a helper protein associated with both TuMV and CaMV and the evidence for site specific attachment of CaM

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02015.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYMeasurements were made of respiration in the roots of tomato cultivars susceptible and resistant toMeloidogyne incognita.Nematode infestation of the susceptible cv. Roma VF caused an initial stimulation of the total respiration with an increase in the CN‐sensitivity; the effect decreased and then disappeared as the seedlings aged. In the resistant cv. Rossol nematode infestation initially caused an inhibition of total respiration and a decrease in the CN‐sensitivity; respiration and CN‐sensitivity increased with seedling age. The activity of the alternative respiration pathway (m‐chlorobenzhydroxamic acid‐sensitive) was unchanged by nematode infestation in the resistant cultivar and increased markedly in the susceptible cultivar during the early stages of in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb02016.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY