No description available.

No description available.

Thesis (MSc)--Stellenbosch University, 1981. / ENGLISH ABSTRACT: No abstract available / AFRIKAANSE OPSOMMING: Die aard, omvang en beheer van voelskade by wyndruiwe is ondersoek in die streek Stellenbosch - Simonsberg. Die Mossie (Passer melanurus, Willer) en die Europese spreeu (Sturnus vulgaris, Linnaeus) veroorsaak die meeste voelskade aan.wyndruiwe in die streek. Die kultivars gebruik in die ondersoek Was Chenin blanc, Pint noir, Riesling, Cinsaut, Clairette blanche en Cabernet Sauvignon. Die laagste suiker- en tic.ogsbasuurgehaltes waarby voelskade voorgehom het was onderskeidelik 11,2° Balling en 25,9g per l,- terwyl vreetskade by gemiddelde 12,4°. Balling en 19,1 g per l totale suur begin het. Die belangrikste enkele faktor wat t rol gespeel het by beskadiging was die suikerkonsentrasie. Die patroon van vreetskade oor t wingerdry is bepaal en het getoon dat die eerste 30 stokke aan weerskante van die wingerd die meeste beskadig word. 'n Metode is vasgestel cm die hoeveelheid skade aangerig te bepaal met behulp van tellings van beskadigde korrels in verteenwoordigende wingerdrye. Die skade in die streek is op 2,5% van die totale opbrengs per hektaar bepaal. Die bespuiting van wingerdblokke en alternatiewe buffer-kantrye met die afskrikmiddel metiokarb (Mesurol) teen 'n konsentrasie van 0,1% or genoemde kultivars, asook Muskadel, het onvoldoende beheer gebied. Bespuitings teen hoer konsentrasies word aanbeveel.

Dissertation (PhD (Agric))--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use. / AFRIKAANSE OPSOMMING: 'n Studie van die basiese biologie van ondergrondse bevolkings van , Eriosoma lanigerum (Hausmann) is in appelboorde in die Weskaap Provinsie van Suid-Afrika uitgevoer. Die afwesigheid van kornikels en die aanwesigheid van 'n vulva kon gebruik word om die 1ste instar nimfe en volwassennes onderskeidelik te identifiseer. Liggaamslengte, liggaamsbreedte en die lengte van die agterste femur kon gebruik word om die 2de , 3de en 4de instars van mekaar te onderskei. Onderskeiding tussen 2de en 3de instar nimfe was egter baie onbetroubaar. Maksimum bevolkingsgroei het by 23°C plaasgevind, terwyl dit nul was by 30 °C. Die beraamde minimum en maksimum temperature vir ontwikkeling was by 4.32 en meer as 30°C onderskeidelik. Getalle van ondergrondse E. lanigerum in grondmonsters wat geneem is met gebruik van meganiese en hand bore was eenders. Getalle plantluise in monsters is egter beïnvloed deur die afstand vanaf die stam waarby die monsters geneem is en die teenwoordigheid van wortelmateriaal in die monsters. Meer plantluise is aangeteken as daar wortelmateriaal in die monsters was, en veral as daar galle op die wortels was. Die appelbloedluis was dwarsdeur die jaar ondergronds aktief. Bevolkingsvlakke het gedurende die vroeë somer (November, Desember) en vroeë herfs (Februarie, Maart) toegeneem, en gedurende die winter afgeneem, veral as die winterreënval hoogwas. Embrio's was ook teenwoordig dwarsdeur die jaar. Daar was meer embrio's in die 4de instar en volwasse plantluise as in die ander instars. Die hoogste aantal embrio's in die 4de instar en volwasse plantluise het in die lente voorgekom, wat saamgeval het met piek stikstofvlakke in die wortels van appelbome. Stikstofvlakke in wortelmateriaal aangrensend aan wortels en in wortels sonder galle was hoër as in wortelgalle. Talle entomopatogeniese swamme, insluitend spesies van Conidiobolus, Hirsufella en Beauvaria IS gevind. Hulle huidige bydrae tot biologiese beheer is nie bekend nie. 'n Strooideklaag het ondergrondse bevolkingsvlakke van E. lanigerum tot ten minste dieselfde mate as die grondinsektedoder, imidacloprid, wat tans in gebruik is, onderdruk.

No description available.

Thesis (MSc)--Stellenbosch University, 1992. / One copy microfiche. / ENGLISH ABSTRACT: The effects of synthetic pyrethroids on the spider mite, Tetranychus urticae Koch, and its natural enemies was investigated. The pyrethroid cyfluthrin, sprayed for the control of fruit weevil Phlyctinus callosus, did not cause mite outbreaks and was not harmful to the predators when sprayed before they appeared on the apple trees. This spray also gave good control of thrips, bollworm (Heliothis armigera) and fruit weevil (P. callosus). A late season spray of deltamethrin against codling moth, caused an increase in the phytophagous mite population. This was assosiated with a temporary reduction in the population level of the predatory beetle, Oligota fageli. The plants found on the orchard floor were examined. The plant diversity was low and plants that acted as hosts of phytophagous mites during the winter were scarce. However, Solanum nigum carried high mite populations and infected the adjacent apple trees. The plants were too few to have an effect on the whole orchard. Eight synthetic pyrethroids were tested for repellency in a leafdisk dip and spray bioassay using T. urticae. Deltamethrin and fenvalerate caused no walk-off. Cyfluthrin and fluvalinate caused moderate walk-off and bifenthrin, cyhalothrin and lambda-cyhalothrin caused high walk-off. / AFRIKAANSE OPSOMMING: Die invloed van sintetiese piretroIedes op die rooispinmyt, Tetranychus urticae Koch en hul natuurlike vyande is ondersoek. Die piretroIed, cyfluthrin, gespuit vir die beheer van snuitkewer, P4ctinus callosus, het the mytuitbrake veroorsaak the en was ook the skadelik vir predatore nadat dit vroeg in die seisoen, voordat myte in die appelbome verskyn het, gespuit is the. Die bespuiting het ook goeie beheer van blaaspootjies, bolwurm (Heliothis amdgera) en P. callosus gegee. Deltametrien wat later in die seisoen toegedien is vir die beheer van kodlingmot, Cydia pomonella, het 'n mytuitbraak veroorsaak. Dit word geassossieer met die tydelike onderdrukking van die populasievlak van die predatoriese kewer, Oligota fageli. Die plante in die dekgewas is ondersoek. Die plant-verskeidenheid was laag en plante wat kon dien as oorwinterings gashere vir fitofage myte kon dien was skaars. Solanum nigrum het egter groot bevolkings myte gedra wat die appelbome naaste aan hulle eerste besmet het. Daar was egter te min van hierdie plante om 'n invloed op die hele boord te he. Agt piretroIedes is vir afwering van T. urticae in 'n blaarskyf doop en spuit bioessal getoets. Deltamethrin en fenvalerate het geen afwering getoon the. Cyfluthrin en fluvalinate het 'n redelike afwering, terwyl bifenthrin, cyhalothrin en lamda-cyhalothrin het 'n hod mate van afwering getoon

The within-field spatial distribution of F₁, F₂, and F₃ pink bollworm (PBW) (Pectinophora gossypiella Saunders) generations were modeled with Taylor's power law (TPL), Iwao's patchiness regression (IPR), and the geostatistical semivariogram. Kriging interpolation was used to grid data for the generation of isarithmic maps. Distributional patterns and movements within a field are displayed in a time series of three maps depicting density across the field. The sampling protocol was replicated in eight commercial cotton fields in south-central Arizona during 1985 and 1986. Permanent sample stations were situated throughout the fields on a regular grid pattern. Samples were collected during the peak larval population and handled so as to maintain the integrity of site-specific samples (spatially identified by X,Y coordinates). TPL and IPR could not be used satisfactorily to model the F₁ generation. TPL fit the observed F₂ and F₃ data better than IPR. Both methods predicted the F₂ to be more highly aggregated than the F₃. For a given precision, optimum sample size increased when TPL and IPR model parameters were incorporated into sample size formulae relative to a formula which assumed random distribution. Ninety-five percent of the modeled PBW distributions were autocorrelated in 2-dimensional space and shown to conform to regionalized variable theory by the successful application of geostatistics. The semivariogram models are in conceptual agreement with traditional models and represent a worthy alternative to traditional modeling methodology. The semivariogram models have a large nugget effect proportion (average = 67%) which, in combination with low PBW density in commercial fields, limits the applicability of geostatistics in this system. Isarithmic maps showed that F₁ larvae are either localized near a field edge or generally scattered throughout the field. No consistent inter-generational dispersal pattern was identified. The use of systematic grid sampling is most advantageous (relative to random sampling) when density and the spatial dependence of samples is high, or many samples can be taken. Systematic sampling and kriging estimation yielded more precise estimates than random sampling and classical statistics, but the advantage was buffered by low PBW densities and large nugget effect.

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Bibliography: leaves 81-100. Entry of inoculum into a crop and disease development in the crop cannot be prevented because spores are airborne and there is a lack of highly resistant varieties. This makes complete control of chocolate spot unlikely. It should however, be possible to improve current levels of disease control through the integration of the factors identified in the study.

Bibliography: leaves 169-185.