Our present knowledge, as indicated by the above data, proves that fire blight is due to a specific organism, a bacterium known in science as Bacillus amylovorus, which manifests itself in the following ways: 1. Blossom blight, due to the bacterial infecting the nectary of the flower and multiplying therein, later passing down into the stem by way of the ovary and pedicel. Apparent by the browning of the flowers, which later become blackened. 2. Twig blight, due to inoculation infections through wounds made by insects or other agencies on the young and tender shoots, blighting from the tips downward, the leaves turning brown and appearing as though scorched by fire. 3. Fruit blight, due to the progress of the bacteria up the pedicel into the pulp of the fruit; appearing as brownish or much darkened areas, later involving the entire fruit. 4. Canker blight, due to the entering of the larger branches by bacteria, conveyed by insect, bird, or mechanical agents, or by the bacillus working back from infected twigs, fruit-spurs, or water-sprouts. These cankers vary in size from barely visible areas to a girdling of the entire limb; they appear roughened and depressed with a distinct line separating the canker from the apparently healthy tissue. They are called "hold-over cankers." 5. Collar blight is nothing more than canker blight which attacks the base of the trunk usually through an infected water-sprout, borers, or mechanical injury. Trees afflicted with collar blight soon take on the sickly appearance of half starved trees, prematurely defoliating (partially or wholly), and finally dying. 6. Leaf blight, due largely to insect injury, the majority of infections the margin, either lateral or terminal, although central lesions are found. The blighted portion of the leaf being a light or yellowish brown with a faint purplish border at the advancing edge, which when active shows a narrow watery zone. During the warm sunny days soon after rains, when the trees are in blossom and the pollen gathering insects are busy visiting the flowers, and the hold-over cankers are exuding drops of the blight bacterial, fire blight begins its havoc. Insects come in contact with this gummy substance and later visit the blossoms, thereby inoculating the flowers with the active organism, blossom blight resulting. Bees are awarded first place in spreading the blight to the flowers but flies and all other insects which visit the bloom are also liable to spread the germ. Later on in the season, as long as the tree is in a vigorous stage of growth, the aphids, ants, leaf hoppers, borers, beetles, and in fact any of the biting or sucking insects which inhabit the apple tree, may spread the organism to the succulent tissue, causing twig blight, fruit blight, leaf blight, or body blight. It is a fact that the insect, which in one section of the country is most troublesome in disseminating blight-bacillus, may not be so important an agent in another section. Different varieties of apple trees may also vary in different sections as to their powers of resistance or susceptibility; the York Imperial being listed as a susceptible variety in Pennsylvania and Virginia while in West Virginia it seems to be quite resistant. We cannot control weather conditions which play so important a part in the spread of blight. The weather may put a tree in a responsive or susceptible condition to inoculation and may also control insect life to a great extent. And it is indeed difficult to try to "harden up" a tree by the application of phosphate and potash fertilizers and by the discontinuing of cultivation, especially when the soil is strong and rains are frequent. Hence the more practical methods must be followed: 1. Fight the insects which spread the disease. Spray with nicotine sulphate or some other tobacco extracts in combination with the early scab or codling moth sprays. Where "Black leaf 40" is used, the recommended strength is 1 to 800 parts of water. 2. Cut out the source of infection,- the hold over cankers--cutting back an inch or two into healthy bark, and disinfect the wound with bichloride of mercury (1-1000). Prune out all blighted branches and if possible cut out all blighted twigs, cutting back several inches into the healthy wood. A severe winter often kills the germs in the twigs. All the waste material should be hauled out of the orchard and burned. 3. It is well to discontinue cultivation and application of manure or nitrogenous fertilizers as soon as blight its appearance. 4. The trees are most susceptible to the attack when planted in low wet ground; hence drain the low spots in the orchard. Many bulletins have stated that winter pruning is inducive to wood and thus favors fire blight. Little attention should be paid to such recommendations for we need trees with good growth which will carry a crop of fruit and allow the sun to penetrate throughout the tree and color up the apples. Many fruit growers have bearing orchards and are not anticipating new ones, so to such,the talk of susceptible and resistant varieties means little. Then too, some of the susceptible varieties are the best commercial apples to raise, and when such is the case it means careful inspection for the hold-over cankers. It is however well to pay some attention to this fact when planting an orchard. What is needed badly is community spirit or cooperation in this difficult work of controlling fire blight. For if one's neighbor does not keep the disease out of his orchard, it is sure to spread to the adjoining orchard. So everyone should "pull together" and control blight which has and is now causing the apple grower heavy losses. / Master of Science

Errata and addenda attached. Bibliography: leaves 195-211. This thesis is concerned with the biology of Eriosoma lanigerum (WAA) and its parasitoid (Aphelinus mali), the impact of the pest on the crop and the effects of pesticides used routinely in South Australian orchards on both woolly apple aphid and the parasitic wasp. The study identifies current management practices of apple growers in South Australia. Aspects of the biology of WAA and A.mali are examined. Work is also done on the toxicity against WAA and A.mali of insecticides used in the control of codling moth and phytophagous mites. The effects of WAA infestation on the growth of young trees are investigated. The seasonal activity of WAA on mature trees is determined over a two season period.

Errata and addenda attached. / Bibliography: leaves 195-211. / xviii, 211 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis is concerned with the biology of Eriosoma lanigerum (WAA) and its parasitoid (Aphelinus mali), the impact of the pest on the crop and the effects of pesticides used routinely in South Australian orchards on both woolly apple aphid and the parasitic wasp. The study identifies current management practices of apple growers in South Australia. Aspects of the biology of WAA and A.mali are examined. Work is also done on the toxicity against WAA and A.mali of insecticides used in the control of codling moth and phytophagous mites. The effects of WAA infestation on the growth of young trees are investigated. The seasonal activity of WAA on mature trees is determined over a two season period. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Apple (Malus x domestica Borkh.) is an important horticultural crop worldwide and in the Western Cape. The income generated from apple and other deciduous fruit production amounts to approximately 25% of the gross total value of horticultural production in the Western Cape. Unfortunately diseases and pests adversely affect fruit production in this region. Woolly apple aphids (Eriosoma lanigerum L. (Hausmann» have a significant effect on the apple industry in the Western Cape. Damage caused is two-fold, occurring aerially and terrestrially. Insects colonise the plants, feeding off the phloem sap. Aphid infestation around the root system results in repeated infestation of the foliage as it serves as a reservoir of aphids. In extreme cases, the apple cores are also infested, thus affecting the sale of apples. In 1962, Northern Spy was identified as a woolly apple aphid resistant rootstock and has since then formed the basis for traditional rootstock breeding programmes. The Er1 gene in Northern Spy confers resistance. According to one report, the natural resistance of Northern Spy was overcome in South Africa in 1968, but this was not confirmed in an independent study. The main objectives of this study was to firstly identify molecular markers more closely linked to the woolly apple aphid resistance gene, Er1, than existing markers, by applying AFLP technology to selected seedlings, identified to be resistant by conventional phenotyping. If identified, these markers can be incorporated into existing breeding programmes. Secondly, previously identified RAPD and SCAR markers were tested to determine their applicability in local populations for use in breeding programmes. Ultimately the segregation of the Er1 gene in South African populations can be determined if tightly linked markers are identified. Three families were derived from crosses of each of three resistant genotypes, namely Northern Spy, Rootstock 5 and Russian Seedling and a susceptible cultivar, Braeburn. For the three successive years of the study, each resistant genotype was allowed to cross-pollinate in isolation with the susceptible parent. Two hand-pollinated families, Russian Seedling x Liberty and Russian Seedling x Northern Spy, were also included in the study. The amplified fragment length polymorphism (AFLP) technique was used in an attempt to identify markers in the resistant and susceptible seedlings. No markers were identified using this technique. Known sequence characterised amplified regions (SCAR) and random amplified polymorphic DNA (RAPD) markers were used due to their suitability in marker-assisted selection for woolly apple aphid resistance. Varying results were obtained with these markers and no conclusive information was acquired with regard to the segregation of the Er] gene in any of these rootstocks and crosses. This underlines the need for the development of markers that can readily be applied in local breeding programmes. The identification and integration of such markers will greatly benefit the local and world wide apple industries. / AFRIKAANSE OPSOMMING: Appels (Malus x domestica Borkh.) is wêreldwyd en in die Wes-Kaap 'n belangrike landbougewas. Inkomste gegenereer deur appels en ander sagtevrugte vorm bykans 25% van die bruto inkomste uit vrugte in die Wes-Kaap. Siektes en insekpeste verlaag egter die produksie van vrugte in hierdie streek. Appelbloedluise (Eriosoma lanigerum L. (Hausmann» het 'n groot invloed op appelproduksie in die Wes-Kaap. Skade word bogronds en ondergronds aangerig. Insekte koloniseer die plant en leef op floeëmsap. Besmetting van die wortels lei tot herhaalde besmetting van bogrondse dele aangesien die insekte aanteelop die wortels. In uiterste gevalle word die vrugte geaffekteer, wat vrug-verkope beïnvloed. 'Northern Spy' is in 1962 geïdentifiseer as 'n onderstam met natuurlike weerstand teen appelbloedluis en het vir lank die basis gevorm vir tradisionele telingsprogramme. Weerstand word verleen deur die Erf geen. Volgens een verslag is die natuurlike weerstand van Northern Spy egter in 1968 in Suid-Afrika oorkom, maar dit is nog nie in 'n onafhanklike studie bevestig word nie. Die hoof doelstellings van hierdie studie was om eerstens deur middel van die AFLP tegniek molekulêre merkers te identifiseer wat nouer gekoppel is aan die appelbloedluis weerstandsgeen, En, as bestaande merkers. Hierdie tegniek is toegepas op saailinge wat deur konvensionele fenotipering geselekteer is. Indien merkers suksesvol geïdentifiseer is, kan dit in bestaande telingsprogramme geïntegreer word. Tweedens is bestaande RAPD en SCAR merkers ook getoets om hul toepaslikheid te bepaal vir gebruik in plaaslike teelprogramme. Oplaas sal die segregasie van die Erf geen in Suid- Afrikaanse populasies ook deur middel van nou gekoppelde merkers bepaal kan word. Kruisings van elk van die drie weerstandbiedende genotipes, naamlik 'Northern Spy', 'Rootstock 5' en 'Russian Seedling', en die vatbare kultivar, 'Braeburn' , het drie families daargestel. Elke weerstandbiedende genotipe is toegelaat om in isolasie te kruisbestuif met die vatbare ouer. Twee hand-bestuifde families, 'Russian Seedling' x 'Liberty' en 'Russian Seedling' x 'Northern Spy', is in 'n latere stadium van die studie ingesluit. Die AFLP tegniek is gebruik vir die identifikasie van polimorfiese merkers tussen vatbare en weerstandbiedende populasies. Geen merkers is egter geïdentifiseer nie. Bestaande SCAR en RAPD merkers is vervolgens gebruik om te bepaal of hulle geskik is vir gebruik in merker-bemiddelde seleksie vir appelbloedluis weerstand. Wisselende resultate is verkry ten opsigte van amplifikasie, herhaalbaarheid van resultate was swak en geen onweerlegbare bewyse oor die segregasie van die Erfgeen is bekom nie. Dit beklemtoon die noodsaaklikheid om merkers wat geredelik in plaaslike teelprogramme toegepas kan word, te ontwikkel. Die identifikasie en integrasie van sulke merkers sal die plaaslike en wêreld-wye appel industrieë aansienlik bevoordeel.

Thesis (MScAgric)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Various aspects of the biology and ecology of woolly apple aphid, Eriosoma lanigerum, were investigated, including initial galling damage caused by E. lanigerum to the roots of apple trees, the possible relationship between E. lanigerum and Xiphinema and Pratylenchus nematodes and the effectiveness of Biostart 2000® and Furfural® as possible control agents of E. lanigerum in the orchard. Preliminary root damage by first instar E. lanigerum feeding was characterized by the mechanical injury of endodermis and parenchyma tissues. Damage by second, third and fourth instar E. lanigerum was similar, but the symptoms were more pronounced. Damage caused by adults included a pronounced swelling at infected areas of the root. Cell walls hardened until the root was radially strengthened with sclerenchyma tissue and nonconducting xylem vessels while the cuticle expanded greatly through the growth of corklike cambium tissue. There was no direct relationship between the population dynamics of E. lanigerum and those of Xiphinema and Pratylenchus nematodes. The occurrence of E. lanigerum appeared to be seasonal while P. penetrans and Xiphinema numbers fluctuated erratically. Undamaged root nitrogen levels seemed to correspond with the normal root growth cycle. Nitrogen levels from galled roots were significantly lower than those of undamaged roots, probably due to E. lanigerum feeding. Soils rich in fine sand and clay sustained higher populations of E. lanigerum and Xiphinema than sandy soils. The number of E. lanigerum found in soil samples correlated well with the damage index allocated to the samples. The numbers of Xiphinema found in soil samples also correlated well with the damage index allocated to the samples according to suspected Xiphinema damage symptoms. Both Biostart 2000® and Furfural® were effective as control agents of woolly apple aphid. Furfural'Ï, a chemical waste product of the sugarcane industry, was however not as effective as Biostart 2000®, a product that includes an activator and three bacterial species, Bacillus laterosporus, B. chitinosporus and B. licheniformis. The bacteria in the Biostart 2000® treated pots could replicate themselves under suitable conditions while Furfural® dilutes with each watering. Biostart 2000® is also easier to prepare than Furfural® since the components of Biostart 2000® readily mix to form a paste easily thinned by water, whereas Furfural® is an oily substance that does not easily disperse in water. Root damage was initiated soon after E. lanigerum started feeding, however there was no apparent relationship between E. lanigerum and the nematode species. The most promising, environmentally friendly control measure was Biostart 2000®. / AFRIKAANSE OPSOMMING: Verskeie aspekte van biologie en die ekologie van die appel bloedluis, Eriosoma lanigerum, was ondersoek insluitende aanvanklike galvorming veroorsaak deur E. lanigerum op wortels van appelbome, die moontlike verwantskap tussen E. lanigerum en Xiphinema en Pratylenchus nematodes en die effektiwiteit van Biostart 2000® en Furfural® as moontlike beheeragente van E. lanigerum in die boord. Aanvanklike wortelskade deur eerste ins tar E. lanigerum voeding was gekenmerk deur die meganiese beskadiging van endodermale en parenchiem weefsel. Skade veroorsaak deur tweede, derde en vierde instar E. lanigerum was soortgelyk alhoewel die simptome meer beklemtoond was. Skade deur volwassenes het 'n meer duidelike swelsel by geïnfekteerde wortelareas ingesluit. Selwande het verhard totdat die wortel radiaalsgewys versterk was met skierenchiem weefsel en nie-geleidende xileemvate terwyl die kutikula grootliks toegeneem het deur die groei van kurkagtige kambiumweefsel. Daar was geen direkte verwantskap tussen die bevolkingsdinamika van E. lanigerum en dié van Xiphinema en Pratylenchus nematodes nie. Die voorkoms van E. lanigerum was seisoenaal terwyl P. penetrans en Xiphinema se getalle onvoorspelbaar gefluktueer het. Onbeskadigde wortel stikstofvlakke het ooreengestem met die normale wortel groeisiklus. Stikstof vlakke van galwortels was noemenswaardig laer as dié van onbeskadigde wortels, heel waarskynlik as gevolg van voeding deur E. lanigerum. Grond ryk aan fyn sand en klei het groter bevolkings van E. lanigerum en Xiphinema onderhou as sanderige gronde. Die aantal E. lanigerum in grondmonsters het goed ooreengestem met die skade indeks wat aan die monsters toegeken was. Die aantal Xiphinema in grondmonsters het ook goed ooreengestem met die beskadigingsindeks wat aan die monsters toegeken is weens vermoedelike Xiphinema skade simptome. Beide Biostart 2000® en Furfural® was effektief as beheeragente van die appelbloedluis. Furfural'", 'n afvalproduk van die suikerriet industrie, was egter minder effektief as Biostart 2000®, 'n produk bestaande uit 'n aktiveerder en drie bakterie spesies, Bacillus laterosporus, B. chitinosporus en B. licheniformis. Die bakterië in die Biostart 2000® behandelde potte kon vermeerder onder gunstige toestande terwyl Furfural® na elke besproeiing verdun het. Biostart 2000® is ook makliker om aan te maak as Furfural® aangesien die bestanddele van Biostart 2000® geredelik meng tot 'n wateroplosbare pasta, terwyl Furfural® 'n olierige vloeistofis wat moeilik 'n waterige suspensie vorm. Wortelskade het plaasgevind kort nadat E. lanigerum begin voed het, alhoewel daar geen duidelike verwantskap tussen E. lanigerum en nematode spesies voorgekom het nie. Die mees belowende omgewingsvriendelike beheermaatreël was Biostart 2000®.

The rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) is the most serious pest apple aphid in view of the scale of damages inflicted to the fruits by a small number of individuals. Although numerous natural enemies have been associated with D. plantaginea, they are unable to halt infestations soon enough in most commercial apple orchards obliging fruit growers to control it chemically to prevent severe economic losses. In order to reinforce the contribution of indigenous aphidophaga in regulating rosy apple aphids, the use of insectary plants selected to support two groups of specialist aphid antagonists, notably aphid parasitoids and aphidophagous monovoltine syrphids, was investigated. 1. A first step consisted in selecting appropriate plant species. The rowan tree Sorbus aucuparia L. and the common elder Sambucus nigra L. were selected for their ability to support substitute aphids for the rosy apple aphid parasitoid E. persicae Froggatt (Hymenoptera: Braconidae, Aphidiinae) and monovotine syrphids (Diptera: Syrphidae) respectively. 2. Next, trials were conducted to induce substitute aphid infestations on their host plants by introducing eggs of Dysaphis sorbi Kaltenbach on rowan and small colonies of Aphis sambuci L. on elder. The resulting aphid populations which developed on their respective host plants in spring proved to be exploited by the natural enemies expected, i.e. E. persicae and monovoltine syrphids of the genus Epistrophe. Besides, diapause mummies of E. persicae and diapausing last-instar Epistrophe larvac were recorded on rowan and in the elder litter respectively, indicating the successful settlement of the antagonists in the orchard environment. A complementary investigation devoted to syrphid adults indicated that females of all species recorded ovipositing on the eider shrubs, including Epistrophe spp. had consumed a large majority of apple pollen grains as a protein source required for egg maturation. 3. To comfort our choice in the two groups of aphidophaga considered, a study dedicated to their respective phenology versus the one of D. plantaginea showed that they could both potentially halt rosy apple aphid infestations by attacking the aphids while the latter still occupied the primary, fundatrix-induced rosette leaf colonies, i.e. a critical moment in rosy apple aphid control. 4. Finally, marking methods were tested to label E. persicae internally and the egg load of gravid syrphids. These trials were intended to pave the way towards future mark-release-recapture experiments aimed to evaluate the antagonists’ activity range and thus strategically position the insectary plants for optimal aphid biological control in the whole orchard. The first step of new approach in the biological control of D. plantaginea has been set with this study. Its originality lies in the induction of economically indifferent aphid infestations on selected plants introduced in the orchard to encourage well-targeted groups of specialist aphid antagonists. Further trials are still needed to validate the field efficacy of the insectary plant systems developed and evaluate their possible integration within the whole array of pest management tools in both organic and integrated apple production. / Doctorat en sciences, Spécialisation biologie animale / info:eu-repo/semantics/nonPublished