The citrus red mite, Panonychus citri (McGregor), is a relatively new pest to South African citriculture, the first recorded injury to citrus trees was from Rustenberg, Transvaal in 1950 (Smith 1953). In the U.S.A. the biology of this mite has been studied by Quayle (1938), Prendergast (1938), English and Turnipseed (1941), DeBach (1947), DeBach et al. (1950), Ebeling (1959) and Jeppson et al. (1957,1961). However, in South Africa little information is available concerning the ecolopy of the citrus red mite. The majority of the literature pertaining to P. citri in Republic, (Smith (1953), Mentz (1954), Stofberg (1959), Schwartz (1965) and Brodrick (1965) is of a descriptive nature, and mainly concerned with the chemical control of the mite. The only biological investigation on the development of P.citri, and the effect of insecticides and insect predators on its biology, under South African conditions, was made by van Rooyen (1966) at Zebediela, Transvaal. In the control of citrus pests, such as the citrus red mite, that need for a better understanding of their ecology has been well emphasised by DeBach (1951) and Griffiths (1951). DeBach (1951) in particular, stressed the danger of the continued reliance on insecticidal treatment as the only method of nest control, and has pointed out that persistent chemical applications may only serve to intensify the pest problem. He has suggested that a closer study of the environment of the pest species could provide a solution to the problems now encountered as a result of insecticidal control measures. Intro., p. 1-2.

Thesis (PhD )--Stellenbosch University, 1981. / EKSERP: Vanwee die voortdurende probleme wat die valskodlingmot, Cryptoph lebia leucotreta (Meyr.), by die verbouing van nawels in die Oos-Transvaalse Laeveld daarstel, is 'n indringende studie van hierdie insekprobleem onderneem. Die biologie van die insek is onder sowel laboratorium as natuurlike toestande nagevors. Daar is bevind dat temperatuur 'n belangrike rol in die ontwikkeling van die insek speel. By 20 tot 30°C het temperatuurstygings die ontwikkeling van die insek laat versnel. By 35°C het die lewensduur van die volwasse motte afgeneem en is geen eiers gelê nie . Die valskodlingmot is deur middle van 'n kunsmatige metode geteel om genoegsame proefmateriaal te verkry. Verskeie verbeteringe is in die bestaande tegniek aangebring.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Planococcus citri (Risso) (Hemiptera: Pseudococcidae), the citrus mealybug, is a highly destructive pest of citrus in South Africa. The ability of mealybugs to develop resistance to chemicals, as well as their cryptic nature and protective wax coverings, all individually and combined, impair the ability of insecticides to control them. Furthermore, chemicals deplete natural enemy populations that usually establish control over mealybug populations well before harvest in March to May. The inability of chemicals to control P. citri successfully and the growing public awareness of the detrimental environmental effects and health risks that are associated with pesticides are pressuring citrus growers to find alternative methods to chemical control. Entomopathogenic nematodes of the Rhabditida order, belonging either to the families Heterorhabditidae or Steinernematidae, have proven to be valuable biocontrol agents of a variety of insect pest species. These nematodes are, however, not yet commercially available in South Africa. Various laboratory bioassays were conducted to determine the potential of entomopathogenic nematodes to control P. citri. Adult female P. citri were screened for susceptibility to six indigenous nematode species. Planococcus citri was found to be most susceptible to Steinernema yirgalemense and Heterorhabditis zealandica, causing 97% and 91% mortality, respectively. Both H. zealandica and S. yirgalemense completed their life cycles inside adult female P. citri. Under optimal conditions, H. zealandica and S. yirgalemense, at an application rate of 170 infective juveniles (IJs) / insect (LD90), were able to control P. citri efficiently with a discriminating dosage of 11(LD50). The water activity (aw) bioassay indicated that S. yirgalemense was two times more tolerant to lower levels of free water than H. zealandica, with aw50 = 0.96 and aw90 = 0.99, compared to H. zealandica with aw50 = 0.98 and aw90 = 1.01. Furthermore, S. yirgalemense proved able to locate and infect P. citri at a faster rate than H. zealandica. Nematode activity was not significantly affected when exposed to 15°C, 20°C and 25°C. Results of the exposure trial also showed that the first 2−4 h post-application was the most decisive time for establishing successful infection of mealybugs. Further experiments were conducted to determine the ability of two polymer products, Zeba® and Xanthan gum, and a surfactant, Nu-Film-P®, to improve nematode application suspensions. Despite not being as effective as Xanthan gum, Zeba® still retarded sedimentation significantly. The addition of 0.02% Xanthan gum did not improve the ability of nematodes to control P. citri at 60% and 80% relative humidity containing H. zealandica and 0.03% Zeba® increased mortality by 14% at 60% RH and by 22% at 80% RH. The same polymer formulation was tested with S. yirgalemense, with mortality being found to have increased by 21% at 60% RH and by 27% at 80% RH. The combined addition of Nu-Film-P® and Zeba® was able to retard sedimentation significantly, increasing the average number of nematodes deposited on 2-cm2 leaf discs. To illustrate those factors that should be taken into consideration before applying nematodes in an integrated pest management (IPM) programme for citrus, the compatibility of H. zealandica and S. yirgalemense with biological control agents and agrochemicals to which they are most likely to be exposed was determined. Bioassays showed the coccinellid beetle, Cryptolaemus montrouzieri, to be susceptible to both nematode species. Beetle larvae proved to be highly susceptible, with H. zealandica obtaining 80%, and S. yirgalemense obtaining 92% control. Adult beetles were found to be twice as susceptible to S. yirgalemense, with 64% mortality recorded, as to H. zealandica, with 30% mortality recorded. Tolerance of H. zealandica and S. yirgalemense infective juveniles to the affect of aqueous solutions of an insecticide (Cyperphos 500 E.C.®), two biopesticides (CryptogranTM and HelicovirTM), and two adjuvants (Nu-Film-P® and Zeba®) on the infectivity and survival of H. zealandica and S. yirgalemense was evaluated. Heterorhabditis zealandica proved to be highly compatible with all products tested. Significant increase in mortality of S. yirgalemense was recorded after 12 h exposure to CryptogranTM, HelicovirTM and Cyperphos 500 E.C.®, and after 6 h exposure to Nu-Film-P®. However, there was no decrease in the ability of S. yirgalemense to infect the insect hosts. Towards selecting the appropriate nematode species for field studies, the ability of S. yirgalemense and H. zealandica to control P. citri was first evaluated under less harsh simulated glasshouse conditions. The ability of both the above-mentioned nematode species to control P. citri, with and without the addition of 0.03% Zeba® and 0.06% Nu-Film-P®, was evaluated in a growth chamber at 75 ± 8% relative humidity and 22°C. All treatments resulted in significantly higher mortality of adult female P. citri than did the control. The addition of 0.03% Zeba® and 0.06% Nu-Film-P® to an H. zealandica and an S. yirgalemense suspension increased resultant mortality from 26% to 30%, and from 34% to 45%, respectively. This increase in mortality was, however, not significant. The ability of this formulation to prolong the ability of S. yirgalemense to infect P. citri and to prolong nematode survival was also evaluated under the same conditions and showed the formulation to improve both infectivity and survival for up to 2–3 h post-application. In the semi-field trial, S. yirgalemense was unable to obtain significant control of P. citri without the addition of 0.03% Zeba® to nematode application suspensions. However, with the addition of 0.03% Zeba® S. yirgalemnse was able to obtain up to 53% control. The study established that the polymer product Zeba® improves the ability of S. yirgalemense to infect P. citri by retarding desiccation and by buffering nematodes from suboptimal environmental conditions. / AFRIKAANSE OPSOMMING: Planococcus citri (Risso) (Hemiptera: Pseudococcidae), die sitrus witluis, is ʼn baie skadelike pes van sitrus in Suid Afrika. Die vermoë van witluise om weerstand teen chemiese middels te ontwikkel, hul kriptiese lewenswyse en die beskermende waslaag wat hul liggame omhul inhibeer gesamentlik en individueel die vermoë van insektisiede om witluis bevolkings te beheer. Chemiese middels verminder ook die natuurlike vyande wat gewoonlik witluis bevolkings beheer voor die sitrus oestydperk in Maart tot Mei. Die onvermoë van chemiese middels om P. citri suksesvol te beheer en verhoogde bewustheid van die publiek rond om die vernietigende omgewings impak en gesondheidsrisiko’s verbonde aan chemiese insek beheer, noodsaak sitrus produsente om alternatiewe beheermetodes te ontwikkel. Entomopatogeniese nematodes, van die orde Rhabditida wat aan die families Heterorhabditidae of Steinernematidae behoort, is bekend as effektiewe biologiese beheeragente van ʼn verskeidenheid insek pes spesies. Hierdie nematodes is egter tans nie kommersieel beskikbaar in Suid- Afrika nie. Om ten einde die vermoë van plaaslike nematode spesies te bepaal om P. citri te beheer, is verskeie biotoetse in die laboratorium uitgevoer. ʼn Vinnige siftings proses is uitgevoer om vas te stel watter plaaslike nematode spesies die hoogste persentasie mortaliteit van P. citri wyfies veroorsaak. Daar is bevind dat P. citri die mees vatbaarste is vir Steinernema yirgalemense en Heterorhabditis zealandica wat 97% en 91% mortaliteit respektiewelik veroorsaak het. Die ontwikkeling van beide H. zealandica en S. yirgalemense na die infektering van volwasse P. citri wyfies is gevolg en daar is bevind dat beide nematode spesies hul lewensiklusse kon voltooi in insek kadawers. Onder optimale toestande was H. zealandica en S. yirgalemense in staat om P. citri effektief te beheer, as hul teen ʼn konsentrasie van 170 infektiewe larwes (JIs) per insek (LD90) toegedien word, met ʼn diskriminerende toedienings dosis van 11 (LD50). ʼn Water aktiwiteit biotoets het gewys dat S. yirgalemense twee keer so verdraagsaam is teenoor laer vlakke van vrye water as wat H. zealandica is met aw50 = 0.96 en aw90 = 0.99, in vergelyking met H. zealandica met aw50 = 0.98 en aw90 = 1.01. Resultate van ʼn blootstellings toets het ook gewys dat S. yirgalemense die vermoë het om P. citri vinniger op te spoor en te infekteer as H. zealandica. Die blootstellings toets was uitgevoer teen 15°C, 20°C en 25°C en daar is bevind dat die aktiwiteit van H. zealandica nie beduidend verhoog het met ʼn verhoging in temperatuur nie. Resultate vir die blootstellings toets het ook gewys dat die eerste 2 tot 4 uur na toediening van nematodes die mees kritieke tyd is om suksesvolle infektering van witluise te bevestig. Verdere eksperimente is uitgevoer om te bepaal of die byvoeging van twee polimeer produkte nl. Zeba® en Xanthan gum en ʼn benatter Nu-Film-P®, nematode toedienings suspensies kan verbeter. Deur 0.02% Xanthan gum by nematode toedienings suspensies te voeg is die vermoë van nematodes om P. citri by 60% en 80% relatiewe humiditeit (RH) te beheer nie beduidend verhoog nie, terwyl die byvoeging van 0.03% Zeba® wel ʼn beduidende verhoging in mortaliteit veroorsaak het. ʼn Suspensie van H. zealandica en 0.03% Zeba® het beheer met 14% by 60% RH en met 22% by 80% RH verhoog. Die invloed van dieselfde polimeer formulasie was ook getoets op S. yirgalemense en mortaliteit het verhoog met 21% by 60% RH en met 27% by 80% RH. Ten spyte daarvan dat “Xanthan gum” nie so effektief was om afsakking van nematodes te verhoed nie, het die byvoeginging van 0.03% Zeba® by toedienings suspensies steeds ʼn beduidende invloed gehad. Die gekombineerde byvoeging Nu-Film-P® en Zeba® was in staat om die gemiddelde aantal nematodes gedeponeer op 2-cm2 blaar skyfies te verhoog. Om te wys watter faktore in ag geneem moet word voor EPNs as deel van ʼn geïntegreerde pes beheer program toegedien word, is die verenigbaarheid van H. zealandica en S. yirgalemense vir biologiese beheer agente en landbouchemikalieë, waaraan hulle heel waarskynlik blootgestel gaan word, bepaal. Biotoetse het gewys dat die liewenheersbesie, Cryptolaemus montrouzieri, vatbaar is vir beide nematode spesies. Die larwale fase was hoogs vatbaar met mortaliteit van 80% en 92% verkry deur die toedeining van H. zealandica en S. yirgalemense respektiewelik. Daar is ook bepaal dat volwasse besies twee maal so vatbaar is vir S. yirgalemense wat 64% mortaliteit veroorsaak het, as vir H. zealandica met 30% mortaliteit aangeteken. Verdraagsaamheid van IJs van H. zealandica en S. yirgalemense met oplossings van ʼn insektisied (Cyperphos 500 E.C.®), twee bio-plaagdoders (CryptogranTM en HelicovirTM), en twee byvoegmiddels (Nu-Film-P® en Zeba®), vir infektiwiteit en oorlewing is bepaal. Resultate het gewys dat H. zealandica hoogs verenigbaar is met alle produkte wat getoets is. ʼn Beduidende verhoging in mortaliteit van S. yirgalemense is aangeteken na 12 ure se blootstelling aan CryptogranTM, HelicovirTM en Cyperphos 500 E.C.®, en na 6 ure se blootstelling aan Nu-Film-P®. Resultate het egter ook gewys dat die vermoë van S. yirgalemense om om gashere te infekteer nie deur beinvloed word nie. Om ten einde te bepaal watter een van H. zealandica of S. yirgalemense die beter isolaat sou wees om te gebruik in veldproewe, is hul vermoë om P. citri te beheer eers evalueer onder minder ongunstige gesimuleerde glashuis toestande. Die vermoë van beide nematode spesies om P. citri te beheer is bepaal in ʼn groeikamer by 75 ± 8% (RH) met en sonder die byvoeging van 0.03% Zeba® en 0.06% Nu-Film-P®. Mortaliteit verkry deur alle behandelings was beduidend hoër as die kontrole. Deur 0.03% Zeba® en 0.06% Nu-Film-P® by toedienings suspensies van H. zealandica en S. yirgalemense te voeg is die gevolglike mortaliteit van P. citri verhoog van 26% na 30% en van 34% na 45%, respektiewelik. Hierdie verhoging in mortaliteit was egter nie beduidend nie. Die vermoë van die bo-genoemde formulasie om oorlewing van S. yirgalemense en infeksie tydperk van P. citri te verleng was bepaal onder dieselfde toestande en daar is gevind dat die formulasie beide die infektiwiteit en oorlewing van nematodes met 2 tot 3 uur na toediening verleng het. Tydens die semi-veldproef was S. yirgalemense nie in staat om beduidend hoër mortaliteit van P. citri te verkry, in vergelyking met die kontrole, sonder die byvoeging van 0.03% Zeba® by toedienings suspensies nie. Met die byvoeging van Zeba® is daar tot 53% beheer verkry. Die studie het onweerlegbaar gewys dat die polimeer produk Zeba® die vermoë van S. yirgalemense om P. citri te infekteer verbeter deur die uitdroging van nematodes te vertraag en deur hul te beskerm teen ongunstige omgewings toestande.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Paecilomyces Ii/acinus, ras 251 (geregistreer in terme van wet 36 van 1947 as Suid-Afrika se eerste natuurlike nematisiede en kommersieel beskikbaar as PI Plus) is as biologiese beheer agent getoets by aartappels en in geïntegreerde beheer programme by sitrus en wingerd teen respektiewelik Me/oidogyne species, Ty/enchu/us semipenetrans en verskeie ektoparasitiese nematodes. Die swam toon belofte vir die beheer van hierdie nematodes en het terselfdertyd nie 'n nadelige effek op nie-teiken, voordelige organismes in die grond nie. Veral in kombinasie met chemiese middels, as deel van geïntegreerde programme, kan dit lei tot verminderde gebruik van hoogs toksiese middels en dus meer omgewingsvriendelike landboupraktyke. Biological control of plant parasitic nematodes on potatoes, citrus and grapevine with the fungus, Paecilomyces liIacinus. Paecilomyces liIacinus, race 251 (registered in terms of act 36 of 1947 as South Africa's first natural nematicide, commercially available as PI Plus) was tested as a biological control agent on potatoes and in integrated control programs on citrus and grapevine against Me/oidogyne species, Ty/enchu/us semipenetrans and various ectoparasitic nematodes respectively. The fungus shows promise for the control of these nematodes, without having a harmful effect on non-target, beneficial organisms in the soil. Especially in combination with chemical products, as part of integrated programs, this can lead to less use of highly toxic compounds and thus to more environmentally friendly agricultural practices. / AFRIKAANSE OPSOMMING: Sedert die ontdekking van die swam, Paeci/omyces Ii/acinus (Thom.) Samson as 'n effektiewe eierparasiet van Meloidogyne incognita acrita en Globodera pal/ida (Jatala et al., 1979) het verdere veldproewe in Peru tot die effektiewe beheer van M. incognita en Tylenchulus semipenetrans gelei. Na verskeie suksesse in Peru is die swam onder verskillende klimaat- en grondkondisies in verskeie ander lande beproef. Die sukses behaal in die Filippyne het gelei tot die kommersiële produksie van die swam onder die handelsnaam Biocon. Anders as met chemiese middels vind die werking van biologiese agente stadig oor tyd plaas. Biologiese beheer sal nie chemiese beheer sonder meer kan vervang nie. Dit behoort egter deel te vorm van geïntegreerde nematode bestuur. Inkorporering van die natuurlike organismes, die oordeelkundige gebruik van chemiese nematisiedes, moontlik in kombinasie met die biobeheer agente, weerstand, en ander kulturele praktyke moet ernstig oorweeg word as ons hoop om die steeds groeiende wêreldbevolking te voed (Jatala, 1986). Paecilomyces liIacinus, ras 251, Suid-Afrika se eerste geregistreerde natuurlike nematisiede, kommersieel beskikbaar as PI Plus, is in die Olifantsrivier besproeiingsgebied geëvalueer vir die bestuur van ekonomies belangrike plantparasitiese nematodes by aartappels, sitrus en wingerd. Hierdie gewasse is belangrike bedryfstakke van die streek en is onderhewig aan skade deur nematodes wat die opbrengs nadelig beïnvloed. Chemiese beheer bied slegs 'n korttermyn oplossing vir nematode probleme en skadelike getalle word in 'n kort tyd weer opgebou. Boonop lei dié hoogs toksiese middels tot agteruitgang van die omgewing en sy waterbronne. Die toenemende besorgdheid hieroor en die groot potensiaal van biologiese beheer agente (Jatala, 1986) was die hoofrede vir die werk waaroor hier gerapporteer word.

South Africa is the world's second largest exporter of fresh citrus and is ranked 14th in citrus production. Fungal pathogens such as Phytophthora and Pythium cause economic losses as a result of root rot and brown rot. Mycorrhizal fungi are specialized members of the fungal community forming a mutualistic relationship with plant roots. Mycorrhizal fungal structures are known to associate with other soil microorganisms and these may contribute to improved plant growth. A diverse group of bacteria that interact with the mycorrhizal fungi are known as Mycorrhizal Helper Bacteria (MHB). The aim of this study was to investigate the role of arbuscular mycorrhiza and associated bacteria isolated from spores and determine whether they had any plant growth promoting potential. A total of 19 bacteria were isolated from arbuscular mycorrhizal spores and were molecularly identified as belonging to several Bacillus, Micrococcus, Onchrobactrum and Staphylococcus sp. All bacterial isolates were tested for plant growth promotion abilities. One Bacillus isolate was able to solubilise phosphate. Four isolates Micrococcus sp, Micrococcus leteus, Ochrobacterum sp and Ochrobacterum antropi were able to produce Indole Acetic Acid and three isolates showed potential to reduce growth of Phytophthora nicotianae, P. citrocola and P. citrophthora in in vitro plate cultures. Further tests using culture supernatants of the Bacillus sp, Micrococcus sp and Bacillus cereus confirmed their ability to inhibit or reduce growth of the three Phytophthora species in a 96 well bioassay. Bacillus sp and Bacillus cereus were able to inhibit Phytophthora spp by 95 to 100 % and Micrococcus spp was able to decrease pathogen growth by 60 to 94 %. These bacterial isolates were further evaluated for plant growth promoting abilities on citrus rough lemon seedlings alone or in combination with arbuscular mycorrhizal inoculum. Bacterial and mycorrhizal inoculants influence the increase in shoot and root biomass. Bacillus cereus in combination with mycorrhizal inoculum significantly increased seedling shoot to root ratio while root biomass was significantly increased with mycorrhizal inoculation. Due to the short duration of the trial mycorrhizal colonisation could not be assessed. It is evident that selected combinations of bacteria and mycorrhizal fungi could promote citrus seedling growth and potentially improve seedling health. Further studies under nursery conditions are recommended.

Two ant species, Pheidole megacephala (Fabricius) and Anoplolepis custodiens (Smith) reach pest status in citrus orchards through precipitating outbreaks of homopterous pests. However, predacious ants, including these two ant species, play an important role in pest suppression in agroecosystems and are therefore beneficial to these systems. If A. custodiens and P. megacephala are important natural control agents in citrus, using ant bands to break the mutualism between the ants and the Homoptera as a method of ant control is preferable to poisoning. Ant communities were sampled by pitfall trapping in three experimental subunits of 2-, 4-, 15- and 30-year-old citrus orchards, in the Grahamstown area of the Eastern Cape. In one subunit in each orchard, populations of P. megacephala and A. custodiens were suppressed by poison applications. In a second subunit, trees were banded with trunk barriers so that ants were prevented from foraging in the trees and a third subunit served as the untreated control. Bait pupae of bollworm, false codling moth and fruit fly were planted in bait trays in all of the subunits to investigate predation on these citrus pests in the relative absence of predacious ants and where they were excluded from the trees. Pheidole megacephala dominated exclusively in all of the plots. Community composition did not change dramatically with increasing age of the trees, but species diversity and species abundance did. Rank-abundance curves showed that community diversity was highest in the 2-year-old plots and lowest in the 30-year-old plots. The Simpson and Shannon-Wiener diversity indices and their evenness measures indicated that diversity and equitability were highest in the poisoned subunits and lowest in the banded subunits. Principle component analysis revealed that the poisoned subunits were similar and distinct in species composition, that there was significant monthly variation in species composition and that community stability increases with an increase in orchard age. The presence of P. megacephala was significantly negatively correlated (rs = -0.293; p < 0.001) with pest pupal survival. Pupal survival was significantly higher for bollworm (p < 0.001), FCM (p < 0.001) and fruit fly (p < 0.001) in the poisoned subunits, than in the banded and control subunits. There was a general trend for survivorship to increase with an increase in the age of the trees. A significant difference (p < 0.001) was found between the months in which the trials were carried out. Pupal survival was significantly lower (p < 0.001) for FCM than for bollworm and fruit fly. In citrus orchards, ant communities are organised by ecological processes and interactions and are influenced by methods of ant control. Ant bands are preferable to poisoning as a method of ant control, so that beneficial species are left on the ground to prey on pests that pupate in the soil. Maintaining high ant species diversity in citrus orchards would be beneficial as predation on the pupae was more effective where ant species diversity was higher.

There is a growing recognition globally that many agrochemicals are hazardous to humans, animals and the environment. Therefore, there is a need to substitute these chemical products with biological and physical treatments, and to change agronomic practices in order to control pests and diseases in agriculture. The primary objective of this thesis was to develop and test in laboratory, field and commercial packhouses trials as alternative control measures against green mould of citrus (caused by Penicillium digitatum Pers: Fr. Sacc) and Penicillium molds of litchi (caused by several Penicillium). A South African isolate of P. digitatum, isolated from an infected orange fruit, was found to be resistant to imazalil (the standard postharvest fungicide used in South Africa). Sixty yeast and 92 Bacillus strains were screened for their antagonistic activity against this isolate of P. digitatum. None of the yeasts or Bacillus isolates produced a curative action against P. digitatum on oranges. However, yeast Isolate B13 provided excellent preventative control of P. digitatum, superior to all the Bacillus isolates, when it was applied to citrus fruit prior to artificial inoculation with P. digitatum. Electron microscopy showed that yeast Isolate B13 inhibited conidial germination of P. digitatum. For the control of P. digitatum pre-harvest, trees were sprayed with a yeast, Isolate B13, a few months or a few days before harvest. However, this treatment alone proved to be ineffective in providing preventative control of green mould on Valencia oranges. For the control of P. digitatum preharvest, trees were treated with potassium silicate for a full season. Regular potassium silicate treatments resulted in a significant preventative control of P. digitatum infection on both navel and Valencia oranges. Treatment of Eureka lemons with potassium silicate as a postharvest treatment for the control of P. digitatum resulted in reduced disease lesion diameters when applied preventatively or curatively. Electron microscopy showed that potassium silicate inhibited germination of P. digitatum conidia and growth of its mycelium. Hot-water dip treatment at 50-58°C for 60-180 seconds (in increments of 15 seconds), significantly reduced infection development in inoculated wounds of Valencia oranges compared with control fruit treated with tap water, without causing any rind damage. The integration of the yeast, a hot water dip and potassium silicate pre-and postharvest applications provided control of P. digitatum control in multiple packhouse trials. The control achieved by the yeast Isolate B13 or hot-water, and potassium silicate in the packhouse alone was superior or equivalent to that provided by imazalil. A similar study was also carried out to determine possible control measures for Penicillium sp. on litchis. In this study, a total of 23 yeast and 13 Bacillus isolates were obtained from litchi fruit surfaces. Ten yeast and 10 Bacillus isolates that had shown good efficacy against P. digitatum of citrus were added to these for screening against Penicillium sp. of litchis. None of the yeasts or Bacillus isolates produced a curative action against Penicillium sp. infection on litchis. However, several yeast isolates (YL4, YL10, YLH and B13) resulted in reduced severity of the pathogen, when applied preventatively, compared with an untreated control. The yeast isolates were superior to all the Bacillus isolates, when applied to litchis prior to artificial inoculation by Penicillium infection on litchis. Potassium silicate as a postharvest treatment for the control of the pathogen caused reduced lesion diameters when applied preventatively or curatively to naturally infected litchis. The results presented in this thesis highlight the use of biological, physical and agronomic practices singly or in combination as an alternative control strategy against citrus postharvest green mould. This thesis also provides an insight into expanding these strategies, partly or fully, for the control of other postharvest Penicillium infections using litchi as an example. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Includes bibliographical references (leaves 102-114) The highly successful biological control of the citrophilous mealybug Pseudococcus calceolarie (Maskell) (CM) by the parasitic wasp Coccophagus gurneyi Compere in several countries led to the release of this parasitoid in the Riverland of South Australia as part of an integrated pest management program. However CM has not been successfully controlled in this region. The results of this study may help to explain the lack of effective biological control of CM in Riverland citrus.

Mealybugs (Planococcus citri) and thrips (Scirtothrips aurantii) are common and extremely damaging citrus crop pests which have proven difficult to control via conventional methods, such as chemical pesticides and insect growth regulators. The objective of this study was to determine the efficacy of entomopathogenic fungi against these pests in laboratory bioassays. Isolates of Metarhizium anisopliae and Beauveria bassiana from citrus orchards in the Eastern Cape, South Africa were maintained on Sabouraud Dextrose 4% Agar supplemented with Dodine, chloramphenicol and rifampicin at 25°C. Infectivity of the fungal isolates was initially assessed using 5th instar false codling moth, Thaumatotibia leucotreta, larvae. Mealybug bioassays were performed in 24 well plates using 1 x 107 ml-1 conidial suspensions and kept at 26°C for 5 days with a photoperiod of 12 L:12 D. A Beauveria commercial product and an un-inoculated control were also screened for comparison. Isolates GAR 17 B3 (B. bassiana) and FCM AR 23 B3 (M. anisopliae) both resulted in 67.5% mealybug crawler mortality and GB AR 23 13 3 (B. bassiana) resulted in 64% crawler mortality. These 3 isolates were further tested in dose-dependent assays. Probit analyses were conducted on the dose-dependent assays data using PROBAN to determine LC₅₀ values. For both the mealybug adult and crawlers FCM AR 23 B3 required the lowest concentration to achieve LC₅₀ at 4.96 x 10⁶ conidia ml-1 and 5.29 x 10⁵ conidia ml-1, respectively. Bioassays on adult thrips were conducted in munger cells with leaf buds inoculated with the conidial suspensions. Isolate GAR 17 B3 had the highest mortality rate at 70% on thrips while FCM AR 23 B3 resulted in 60% mortality. Identification of the isolates, FCM AR 23 B3, GAR 17 B3 and GB AR 23 13 3, were confirmed to be correct using both microscopic and molecularly techniques. ITS sequences were compared to other sequences from GenBank and confirmed phylogenetically using MEGA6. Mealybug infection was investigated using scanning electron microscopy, mycosis was confirmed but the infection process could not be followed due to the extensive waxy cuticle. These results indicate that there is potential for the isolates FCM AR 23 B3 and GAR 17 B3 to be developed as biological control agents for the control of citrus mealybug and thrips. Further research would be required to determine their ability to perform under field conditions.

False codling moth (FCM), Thaumatotibia leucotreta is an extremely important pest of citrus in South Africa and with the shift away from the use of chemicals, alternate control options are needed. One avenue of control which has only recently been investigated against the soil-borne life stages of FCM is the use of entomopathogenic fungi (EPF). In 2009, 12 entomopathogenic fungal isolates collected from South African citrus orchards showed good control potential during laboratory conducted bioassays. The aim of this study was to further analyse the potential of these isolates through concentration-dose and exposure-time response bioassays. After initial re-screening, concentration-dose response and exposure-time response sandconidial bioassays, three isolates were identified as exhibiting the greatest control potential against FCM in soil, Metarhizium anisopliae var. anisopliae (G 11 3 L6 and FCM Ar 23 B3) and Beauveria bassiana (G Ar 17 B3). Percentage mycosis was found to be directly related to fungal concentration as well as the amount of time FCM 5th instar larvae were exposed to the fungal conidia. LC50 values for the three isolates were not greater than 1.92 x 10⁶ conidia.ml⁻ₑ and at the LC₅₀, FCM 5th instar larvae would need to be exposed to the fungus for a maximum of 13 days to ensure a high mortality level. These isolates along with two commercially available EPF products were subjected to field persistence trials whereby net bags filled with a mixture of autoclaved sand and formulated fungal product were buried in an Eastern Cape citrus orchard. The viability of each isolate was measured on a monthly basis for a period of six months. All isolates were capable of persisting in the soil for six months with the collected isolates persisting far better than the commercially used isolates. Two of the isolates, G 11 3 L6 and G Ar 17 B3, were subjected to small scale laboratory application trials. Two formulations were investigated at two concentrations. For each isolate, each formulation and each concentration, FCM 5th instar larvae were applied and allowed to burrow into the soil to pupate before fungal application or after fungal application. Contact between fungi and FCM host is essential as, in contrast to pre-larval treatments, percentage mortality in post-larval treatments was low for both formulations and both isolates. For isolate G Ar 17 B3, a conidial suspension applied as a spray at a concentration of 1 x 10⁷ conidia.ml⁻ₑ obtained the highest percentage mortality (80 %). For isolate G 11 3 L6 however, both formulations performed equally well at a high, 1 x10⁷ conidia.ml⁻ₑ concentration (conidial suspension: 60 %; granular: 65 %) The results obtained thus far are promising for the control of FCM in citrus, but if these EPFs are to successfully integrate into current FCM control practices more research, some of which is discussed, is essential