In Bolivia, tomato acreage is 6717 and has a yield of 12005 kg/ha and the total production is 80,636 TM. Departments that harvest tomato are Santa Cruz, Cochabamba and La Paz, Santa Cruz being the department that shows the highest rates of production with 40653 TM in comparison with La Paz which has a production of 3109 TM and Cochabamba of 2420 TM. The principle factors in affect are, the best climatic conditions in Santa Cruz, while Cochabamba and La Paz have differences in seasonal changes (National Institute of Statistics, 1998). The importance of the tomato harvest lies in consumption preference, for the nutritional properties, as they provide a rich source of Vitamins A and C, principally for its qualities of high productivity in terms of yield per area, being a factor of great importance in the economy of the farmer. The repeated production of tomato in the same area or locality tends to create problems phytopathologicals caused by fungi, bacteria and viruses, that at times become difficult to handle, thus becoming serious limiting factors that are able to seriously affect the yields, as such the investigation of sickness control is of extreme importance. The community of Carmen Pampa belonging to the municipality of Coroico, Nor Yungas, constituting a suitable area for the cultivation of tomato, but the attack of diseases caused by fungi, principally Phytophtora infestans, with an incidence of rate of 98%, which is increased by high temperature, humidity, precipitation and fog, all of which favor the spread of this fungus. For this reason farmers are forced to use chemical products that cause problems of resistance of the causal agent of the illnesses. The FAO (1992) estimates 3 million poisonings annually at a global level of farmers and families as a result of chemicals, which cause in turn a residual effect, environmental pollution and creates and additional cost in production. In the investigation of intoxication by agrochemicals in Bolivia, in a population of 870 persons studied mentioned that, 88% are unaware of the risks associated with the use and management of using them; the cases of poisonings are more frequent in tropical plains with 46%, the valleys with 26%, the inter-Andean valleys with 14% and the high plains with 12%, without mentioning those of suicide origin. For this reason, the object of the present investigation is to try to control the late blight disease (Phytophtora infestans) in the cultivation of the tomato (Lycopersicum sculentum), with biocides, to eliminate or diminish the use of agrochemical products.

No description available.

Direct dissemination of expert knowledge to agricultural producers through computer programs will increase product quality as well as profit margin. The construction of an expert system to help farmers manage apple orchards is reported. The system provides advice regarding specific pest management, treatment of winter injuries, drought control and general pesticide selection. The knowledge structures employed in the construction of the system are explained, and some sample interactions are provided. A model of the apple scab disease cycle is incorporated into POMME to give the system a more fundamental reasoning capability than available from the use of infection tables. Extension experts who have run trial cases on the system have approved its release for use by commercial apple growers. / Master of Science

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Grey mould, caused by Botrytis cinerea, is the most important foliar disease of rooibos seedlings. Although the disease is primarily controlled with applications of fungicides, the improvement of cultural methods of disease management should lessen this dependence on chemical control. Such improvements would, however, not be possible without knowledge of the inoculum sources and dispersal of the pathogen. The aim of this study was to investigate the inoculum ecology of B. cinerea in rooibos nurseries in order to identify primary sources of inoculum and to improve the environmentally friendly management of the disease. The study was conducted in four nurseries over two production seasons (March to July 2003 and 2004). Levels of airborne inoculum of B. cinerea were monitored on a monthly basis inside and around the nurseries with spore traps. Samples of plant material and organic debris were taken in the corresponding areas to determine the incidence of plant material infected by the pathogen and the incidences of grey mould in the nurseries were recorded. Low numbers of B. cinerea colonies were observed on the spore traps. Similar levels of airborne inoculum were observed inside and around the nurseries. The incidence of plant material yielding B. cinerea was higher outside the nurseries than inside, indicating the importance of such materials as potential sources of inoculum. Since patterns of airborne inoculum observed in this study confirmed reports of the local dispersal of B. cinerea, the removal of possible hosts outside the nurseries could aid in the management of grey mould in rooibos nurseries. Resistance to dicarboximide fungicides is a genetically stable trait in B. cinerea, and therefore has the potential to be used as a phenotypic marker. This marker can be used to gain knowledge on the dispersal of B. cinerea inoculum inside and outside rooibos nurseries. Isolates of B. cinerea collected from the air and from plant material in and around four rooibos nurseries were assessed for resistance to iprodione at 1 and 3 μg/ml a.i. Some of the isolates showed resistance to iprodione at 1 μg/ml a.i. However, none of the isolates showed resistance at 3 μg/ml a.i. iprodione. The initial incidence of dicarboximide-resistance at the nurseries was slightly higher than expected. As the season progressed, the incidence of iprodione-resistant isolates decreased towards May, after which an increase was observed towards July. A relatively high percentage of isolates collected outside the nurseries was found to be dicarboximide-resistant. Two of the nurseries had a significant higher incidence of resistant isolates on plant material collected inside, than on plant material collected outside the nursery. However, when looking at resistance levels of airborne isolates, no significant differences were found in the incidence of resistant isolates sampled inside and outside the four nurseries. The data indicated the importance of organic debris and seed-borne infections in the survival and dispersal of dicarboximide-resistant isolates of the pathogen. With the current emphasis on organic agriculture the knowledge gained in this study presents valuable possibilities of improving the cultural management of grey mould in rooibos nurseries. / AFRIKAANSE OPSOMMING: Vaalvrot, veroorsaak deur Botrytis cinerea, is die belangrikste bo-grondse siekte van rooibossaailinge. Alhoewel die beheer van die siekte hoofsaaklik op die gebruik van fungisiede berus, behoort die verbetering van verbouingspraktyke hierdie afhanklikheid van chemiese beheer te verminder. Sulke verbeteringe sal egter slegs moontlik wees indien voldoende kennis van die inokulumbronne en verspreiding van die patogeen beskikbaar is. Die doel van hierdie ondersoek was om die inokulum ekologie van B. cinerea in rooibos kwekerye te ondersoek sodat primêre inokulumbronne opgespoor en omgewingsvriendelike siektebestuurspraktyke verbeter kan word. Die ondersoek is in vier kwekerye oor twee produksie seisoene (Maart tot Julie 2003 en 2004) uitgevoer. Vlakke van luggedraagde inokulum van B. cinerea is op ’n maandelikse basis met behulp van spoorvangers binne en buite die kwekerye gemonitor. Monsters van plantmateriaal en organiese materiaal is in ooreenstemmende areas geneem om die voorkoms van B. cinerea geïnfekteerde plantmateriaal vas te stel en die voorkoms van vaalvrot in die kwekerye is aangeteken. Min B. cinerea kolonies is op die spoorvangers waargeneem. Soortgelyke vlakke van luggedraagde inokulum is binne en buite die kwekerye waargeneem. Die hoër voorkoms van B. cinerea geïnfekteerde plantmateriaal buite die kwekerye as binne, dui op die belang van sulke materiaal as potensiële inokulumbronne. Aangesien die patrone van luggedraagde inokulum, soos waargeneem in hierdie ondersoek, ander berigte van B. cinerea se beperkte verspreidingsvermoë bevestig, kan die verwydering van moontlike alternatiewe gashere buite die kwekerye die bestuur van die siekte binne die kwekerye verbeter. Weerstand teen dikarboksimied fungisiede is ’n geneties-stabiele kenmerk in B. cinerea en het daarom potensiaal om as ’n fenotipiese merker gebruik te word. Hierdie merker kan gebruik word om kennis aangaande die verspreiding van B. cinerea in en om rooibos kwekerye in te samel. Botrytis cinerea isolate in lug en op plantmateriaal in en om vier rooibos kwekerye is gedurende 2003 en 2004 versamel. Die isolate is vir weerstandbiedendheid teen iprodioon by konsentrasies van 1 en 3 μg/ml aktiewe bestandeel (a.b.) getoets. Isolate met weerstand teen 1 μg/ml a.b. iprodioon is waargeneem, maar nie teen 3 μg/ml nie. Die aanvanklike voorkoms van dikarboksimiedweerstand by die kwekerye was hoër as verwag. Hierdie vlak het egter gedaal met die verloop van die seisoen tot in Mei, waarna ’n toename tot in Julie waargeneem is. Die persentasie dikarboksimied-weerstandbiedende isolate buite die kwekerye was relatief hoog. In twee van die kwekerye was die voorkoms van weerstandbiedende isolate op plantmateriaal in die kwekerye betekenisvol hoër as op plantmateriaal buite die kwekerye. Daar was egter geen betekenisvolle verskille in die voorkoms van luggedraagde weerstandbiedende isolate nie, ongeag van die kwekery of posisie. Die data dui op die belang van organiese materiaal en saadgedraagde infeksies in die oorlewing en verspreiding van dikarboksimied-weerstandbiedende isolate van die patogeen. Met die huidige klem op organiese landbou bied die inligting wat in hierdie ondersoek versamel is moontlike praktyke wat geïmplementeer kan word om die beheer van vaalvrot in kwekerye met behulp van verbouingspraktyke te verbeter.

Thesis (PhD (Agric) (Conservation Ecology and Entomology))--University of Stellenbosch, 2005. / Six tortricid species are of major economic importance to the South African fruit industry. They are the codling moth Cydia pomonella, the oriental fruit moth Grapholita molesta, the false codling moth Thaumatotibia leucotreta, the macadamia nut borer T. batrachopa, the litchi moth Cryptophlebia peltastica and the carnation worm Epichoristodes acerbella. For phytosanitary purposes and to aid the management of population levels of the aforementioned species, their identities at species and population level were investigated using morphological and molecular genetic techniques. Morphological characteristics were used to distinguish and differentiate between the final instar larvae and pupae of the six species. For this purpose the morphology of the final instar larvae and pupae of the Afrotropical species T. leucotreta, T. batrachopa, Cr. peltastica and E. acerbella was described and illustrated using line drawings and scanning electron micrographs. Taxonomic characters found to be useful for the identification of the larvae were the presence and structure of the anal comb and the number and arrangement of crochets on the prolegs. The pupae could be distinguished based on the presence or absence of a distinct cremaster, the shape of the spiracle, the position of the setae on the anal rise, the structure of the mouthparts and the length of the procoxa in relation to that of the protarsus. These characters were used to develop keys to distinguish between the tortricid species occurring on tropical and subtropical fruit (T. leucotreta, T. batrachopa and Cr. peltastica) and deciduous fruit (E. acerbella, C. pomonella, G. molesta and T. leucotreta). At population level, molecular techniques were employed to compare geographic populations of each of the six species. Amplified fragment length polymorphism (AFLP) analysis with five selective primer pairs was used to investigate genetic diversity. In addition, host populations of species were compared where relevant. No evidence was found to suggest that populations from different hosts were genetically differentiated. However, geographic populations were found to be genetically distinct in each of the six species, with extensive genetic divergence apparent over local geographic scales and significantly high estimates of population differentiation ranging between Gst = 0.2625 and 0.3778. Factors influencing the genetic population structure of the six species were investigated by comparing the amount and distribution of genetic variation between oligophagous and polyphagous species as well as introduced and native species. Results indicated that host range and population history did not have a major effect on population genetic structure. It was therefore suggested that other factors such as limited dispersal were responsible for the extensive genetic divergence observed between geographic populations of each of the six tortricid species. These results should be incorporated into existing pest management programs and taken into consideration when designing new control strategies. This is the first report of its kind to identify, with a high level of accuracy, the aforementioned tortricids and the first to determine the population genetic structure of these species.

Dissertation (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A survey was conducted in the Western Cape Province during the 1999/2000 and 2000/2001 seasons on mealybugs occurring in vineyards. P/anococcus ficus (Signoret) was the dominant mealybug in vineyards during this time. During this study P. ficus was recorded for the first time on roots of grapevines, which has far reaching implications for the control of this important vine leafroll virus vector as control actions were focused on above ground control. Other mealybugs presently recorded in local vineyards included Pseudococcus /ongispinus (Targioni) and Ferrisia ma/vastra (McDaniel). Pseudococcus viburni (Maskell) and Ps. so/ani Ferris were found on weeds in vineyards. Natural enemies of P. ficus recorded most frequently were species of Nephus predatory beetles, and the parasitaids Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. and Leptomastix dacty/opii (Howard). Developmental studies on P. ficus and C. peregrinus indicated that the intrinsic rate of increase (rm) was similar, peaking at 25°C (rm = 0.169 for P. ficus; rm = 0.149 for C. peregrinus). The net replacement rate (Ra) was higher for P. ficus than for C. peregrinus at all five temperatures tested. The Ra for P. ficus reached a maximum at 21°C (308.87) and C. peregrinus at 25°C for C. peregrinus (69.94). The lower and upper thresholds for development of P. ficus were estimated at 16.59 and 35.61°C respectively. The lower threshold for development of C. peregrinus was 8.85°C. These parameters indicated that both insects were well adapted to temperatures in the Western Cape Province. The lower minimum threshold temperature of C. peregrinus in relation to that of P. ficus suggests that C. peregrinus should be more active during winter and early spring than P. ficus. A central systematic presence-absence sampling system was developed for P. ficus. Monitoring three different plant parts on the vine indicated that new growth areas on vines adjacent to the main stem could serve as an early warning system for pending P. ficus bunch infestations. Intervention should be planned when 2 % of the stems are infested with P. ficus when using this system. Seasonal population studies of P. ficus and its natural enemies showed that stem infestation by P. ficus reached peak levels during January in Robertson and Stellenbosch and during February in the Hex River Valley. Vine mealybugs colonised new growth early in the season, followed by the leaves and eventually the bunches towards the end of the season. High stem infestations early in the season resulted in high bunch infestation levels at harvest. A density dependent relationship was evident between P. ficus populations and parasitoid populations, suggesting that the parasitoids played a mayor role in the biological control of P. ficus populations. Biological control was however only achieved towards the end of the season when damage to the crop had already occurred. Mass releases of C. peregrinus on P. ficus populations were done in order to augment biological control as an alternative to chemical control. Between five and six releases of 20 000 C. peregrinus per release were done at monthly intervals in three grapegrowing areas. Mass released C. peregrinus controlled P. ficus adequately in the Hex River Valley. Control of P. ficus using this approach was no worse than using chemical control in Robertson and Stellenbosch. C. peregrinus is commercially available and can therefore be used as an alternative to chemical control by producers. Degree day estimation was used to predict development of P. ficus populations. This information was used as an input in a P. ficus pest management model. Data acquired from P. ficus and ant monitoring were used as components to construct a decision chart. This chart can be used by producers to optimise the control of P. ficus populations using either chemical control or mass releases of C. peregrinus. / AFRIKAANSE OPSOMMING: "n Studie is gedurende die 1999/2000 en 2000/2001 seisoene gedoen met die doelom die witluisspesies wat in wingerde voorkom, te identifiseer. Planococcus ficus (Signoret) is tans die dominante witluisspesie in wingerde in die Wes Kaap Provinsie. P. ficus kolonies is op wingerdwortels gevind. Dié bevinding kan verreikende gevolge hê vir die beheer van dié plaag as "n belangrike rolbladvirus vektor aangesien beheer tot dusver gefokus het op bogrondse gedeeltes. Ander witluisspesies wat in wingerde gevind is, sluit in Pseudococcus /ongispinus (Targioni) en Ferrisia malvastra (McDaniel). Pseudococcus vibumi (Maskell) en Ps. so/ani Ferris is op onkruide in wingerde gevind. Dominante natuurlike vyande van P. ficus sluit predatoriese kewertjies van verskeie Nephus spp. en die parasitoïede Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. en Leptomastix dacty/opii (Howard) in. Ontwikkelingstudies op P. ficus en C. peregrinus het aangetoon dat die inhirente voortplantingstempo (rm) soortgelyk was vir beide insekte met "n maksimum by 25°C (0.169 vir P. ficus, 0.149 vir C. peregrinus). Die netto vervangingstempo (Ra) was in vergelyking met C. peregrinus hoër vir P. ficus by al vyf temperature getoets. Die Ra van P. ficus het "n maksimum bereik teen 21°C (308.87) en die van e. peregrinus by 25°C (69.94). Die teoretiese hoër en laer drempels vir ontwikkeling van P. ficus was onderskeidelik 16.59 en 35.61 oe. Die teoretiese laer drempelwaarde van ontwikkeling vir e. peregrinus was 8.85°e. Hierdie parameters dui aan dat beide insekte goed aangepas is by temperature in die Wes Kaap Provinsie. Die laer minimum drempel vir ontwikkeling van C. peregrinus in verhouding tot P. ficus impliseer dat C. peregrinus in die winter en vroeë lente meer aktief sal wees as P. ficus. 'n Sentrale sistematiese aan-afwesig moniteringsisteem met bekende vlakke van steekproefnemingsfout is ontwikkel in kommersiële wingerde vir P. ficus. Monitering van drie verskillende dele op die wingerdstok het aangedui dat die nuwe groei areas kan dien as 'n vroeë waarskuwing vir latere P. ficus trosinfestasies. Dié sisteem sal produsente in staat stelom te bepaal wanneer optrede noodsaaklik is. Daar word voorgestel dat optrede noodsaaklik is by 'n P. ficus besmettingsvlak van 2 % op die nuwe groei areas op stokke. Stambesmetting deur P. ficus het in Januarie piekvlakke bereik in Stellenbosch en Robertson, en in Februarie in die Hex Rivier Vallei. P. ficus koloniseer nuwe groei vroeg in die seisoen waarna blare en trosse aan die einde van die seisoen gekoloniseer word. Dié data dui aan dat P. ficus besmetting op nuwe groei vroeg in die seisoen 'n aanduiding kan gee van hoë trosbesmetting aan die einde van die seisoen. 'n Digtheidsafhanklike verwantskap was waarneembaar tussen P. ficus plaagpopulasies en parasitoïed populasies. Dié verwantskap dui aan dat parasitoïede die belangrikste rol speel in biologiese beheer van P. ficus populasies. Biologiese beheer van witluis is egter eers aan die einde van die seisoen bereik toe die oes reeds beskadig was. Massavrylatings van C. peregrinus is in P. ficus besmette blokke gedoen om biologiese beheer aan te help en sodoende as alternatief tot chemiese beheer te dien. Tussen vyf en ses vrylatings met 20 000 C. peregrinus is een keer per maand gedurende die seisoen gedoen. Die vrygelate C. peregrinus het P. ficus populasies voldoende beheer in die Hex Rivier Vallei. Beheer van P. ficus deur massavrylatings van C. peregrinus was soortgelyk as chemiese beheer in Robertson en Stellenbosch. C. peregrinus is kommersieel beskikbaar en kan om hierdie rede as alternatief tot chemiese beheer gebruik word. Graaddag bepaling is gebruik om die ontwikkeling van P. ficus populasies te voorspel. Hierdie inligting is gebruik as 'n verdere hulpmiddel in die P. ficus plaagbeheermodel. Inligting verkry vanuit P. ficus en mier monitering is gebruik as komponente in die opstel van 'n besluitnemingstabel. Hierdie tabel kan gebruik word deur produsente om beheer van P. ficus plaagpopulasies te optimaliseer deur chemiese beheer of massavrylatings van C. peregrinus.

Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: During a survey in the greater Cape Flats Heterodera schachtii was found to be widespread on cauliflower, Brussels sprouts, beetroot and cabbage. The numbers present were above two eggs and juveniles per gram of soil, generally regarded as the economic threshhold level of infestation and requiring control. The damage potential of H schachtii on vegetables, as well as the ability of certain weeds to serve as a source of infection on subsequent crop plantings was studied under greenhouse conditions and resulted in a reduction of yield and root weight of crops. Population densities of H schachtii increased significantly under favourable hosts like cabbage where densities of 198 eggs and juveniles per gram of soil were reached. The most commonly occurring weeds maintained nematode development and increased their population densities. They can thus serve as alternative hosts in the absence of susceptible hosts and should be routinely controlled. The life cycle and biology of H schachtii was also studied. Penetration of plant tissue and subsequent development on vegetables, weeds and trap crops were observed. Penetration was successful on all crops tested reaching 37% and 52% at inoculum levels of 22 and 11 juveniles per gram of soil, respectively. Subsequent development of H schachtii on weeds and vegetables was similar, but in the case of cauliflower and black nightshade as hosts, their life cycle was shorter in comparison to other crops. The possible existence of varying susceptibility of crops to different populations of H schachtii was examined by comparing the rates of penetration in crops and reproduction of geographically isolated populations of H schachtii in the greater Cape Flats. When root penetration, virulence and juvenile emergence were examined, populations from Lynedoch and Philippi were distinct from the other populations. Subsequently, representative individuals of these populations were subjected to PCR-RFLP, but with these techniques real differences between the various populations could not be adequately detected. The environmental parameters such as soil texture, temperature and pH on H schachtii were investigated as to their influence on the root weight and yield of crops. Reductions in the yield of beetroot and cabbage were observed with soil temperatures ranging between 15 to 30°C. Migration and penetration of H schachtii juveniles declined with an increase in clay and silt content of the soil. Above a 34% silt and clay content of soil, no migration and penetration took place. Root penetration levels of 30% and higher were reached with pH varying between 4.5 and 7.4. This resulted in a significant reduction in yield of crops. Crop rotation is an essential component of non-chemical control. In the case of H schachtii, it required one host crop in four non-host rotational cycles to maintain the population of the nematode in the soilless than three eggs and juveniles per gram of soil. The inclusion of a trap crop reduced the population densities to below two eggs and juveniles per gram of soil. It therefore also forms an integral part of a control strategy. Solarization proved successful as a physical control method. Best results were obtained in summer with clear polyethylene which led to a 97% reduction of infective juveniles. This method can be applied during the late summer in the greater Cape Flats, just before the onset of winter. This may safeguard future spring plantings. The need for effective control strategies in order to reduce the numbers of H schachtii is of the utmost importance to ensure vegetable production in the future. Small-scale farmers should therefore be educated in this respect. / AFRIKAANSE OPSOMMING: Heterodera schachtii het wydverspreid in 'n opname in die groter Kaapse Vlakte voorgekom op beet, blomkool, Brusselse spruite en kopkool. Die nematode getalle by alle lokaliteite was bo die algemeen aanvaarbare ekonomiese drempelwaarde van twee eiers en larwes per gram grond wat beheer regverdig. Die skadepotensiaal van H schachtii op groente, sowel as die vermoë van sekere onkruide om as infeksie bronne te dien vir opvolgende gewasse, is in glashuise ondersoek en het tot 'n verlaging in opbrengs en wortelmassa by gashere gelei. Die populasie digthede van H schachtii het met die aanplant van geskikte gashere tot vlakke van 198 eiers en larvae per gram grond gestyg. Die mees algemeen voorkomende gasheeronkruide het nematode ontwikkeling in stand gehou en selfs tot 'n populasie verhoging gelei. Hierdie onkruide is 'n beperkende faktor vir die verbouing van groente aangesien die onkruide as alternatiewe gasheer kan dien in die afwesigheid van gashere en onkruidbeheer moet dus op 'n gereelde basis toegepas word. Die lewenssiklus en biologie van H schachtii is ondersoek deurdat die penetrasie van gasheer wortels en die daaropvolgende ontwikkeling op groente, onkruide en vanggewasse vergelyk is. Penetrasie, vyf dae na inokulasie, is met alle gashere verkry met 37% en 52% penetrasie met inokulum vlakke van 22 en 11 larwes per gram grond onderskeidelik. Daaropvolgende ontwikkeling van H schachtii was soortgelyk op groente en onkruide, maar blomkool en nastergal het as gashere 'n verkorte lewenssiklus tot gevolg gehad. Die moontlikheid van verskille in die virulensie van H schachtii is ondersoek deur die penetrasie van gewasse en reproduksie vlakke van nematodes van nege verskillende geografies geskeide populasies in the groter Kaapse Vlakte te vergelyk. Die Lynedoch en Philippi populasies het onderskeibare resultate gelewer ten opsigte van die populasies uit die ander lokaliteite, maar geen verskille kon met PKR-RFLP aangetoon word nie. Die invloed van omgewings parameters, grondtekstuur, temperatuur en pH, is op H schachtii ondersoek ten opsigte van opbrengste en wortelmassa van gewasse. Grondtemperature tussen 15°C - 30°C het tot die grootste daling in opbrengs gelei op kopkool en beet. Migrasie en penetrasie het afgeneem met 'n toename in klei en slik inhoud tot en met 'n klei en slik inhoud van 34%, waarna geen penetrasie en migrasie voorgekom het nie. Wortelpenetrasie van 30% en hoër het voorgekom by pH vlakke van tussen 4.5 - 7.4 met die gepaardgaande verlaging in opbrengs van gewasse. Afwisseling van gewasse is 'n essensiële metode van nie-chemiese beheer van nematode getalle in die grond. Die mees optimale rotasie ten opsigte van H schachtii beheer is met die aanplanting van een gasheer gewas in vier gewas aanplantings verkry. Die insluiting van 'n vanggewas in die gewas rotasie siklus het die nematode populasievlakke tot onder twee per gram grond laat daal. Solarisasie is suksesvol uitgevoer met deurskynende poli-etileen in die groter Kaapse Vlakte gedurende die somer met gevolglik 'n 97% vermindering van die getalle infektiewe nematodes. Effektiewe beheermaatreëls ten opsigte van H schachtii moet in die groter Kaapse Vlakte ingestel word om groente-produksie in hierdie gebied te verseker. Kleinboere moet in hierdie tegnieke opgelei word.

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.

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Striga, a genus of obligate parasitic weeds in the family Orobanchaceae, has been identified as the most important biological factor limiting agricultural productivity in sub-Saharan Africa. Germination of Striga seeds is triggered by strigolactone root exudates from host plants. Strigolactones also induce hyphal branching in arbuscular mycorrhizal (AM) fungi, which are important for plant uptake of phosphorus in low phosphorus soils. Mechanisms of Striga resistance based on reduced strigolactone production may also convey resistance to AM fungi which would require higher inputs of phosphorus fertilizer to attain optimal crop growth. There is evidence for genetic differences in mycorrhizal responsiveness in other grain crops; therefore it is beneficial for breeders to be aware of these differences when developing Striga-resistant sorghum cultivars. This research aims to determine phosphorus and mycorrhizal responsiveness of sorghum genotypes important for or developed by breeders working on Striga resistance. Phosphorus response curves were determined for twelve sorghum genotypes using pasteurized low phosphorus soil amended to achieve four different phosphorus levels. Simple linear regression was performed on root and shoot dry weight data. Results indicate variability in phosphorus responsiveness within Striga resistant and susceptible genotypes. Seven of these genotypes were selected for continued research, which analyzed responsiveness to phosphorous and differences in mycorrhizal responsiveness in relation to reported mechanisms of Striga resistance. Treatments included three levels of phosphorus amendments and the addition of Funneliformis mosseae inoculum. All genotypes were strongly responsive to P amendment when grown without AM fungi and showed a decrease in responsiveness to P when inoculated with F. mosseae. Trends for all genotypes indicate a greater uptake of P, Zn, and Mg by mycorrhizal plants as compared to nonmycorrhizal plants. All seven genotypes were responsive to mycorrhizae, with a significant increase in biomass for all genotypes, especially at the lowest phosphorus level. The responsiveness to the mycorrhizal fungus does not appear to be directly related to the susceptibility of genotypes to the parasitic weed Striga. / Graduation date: 2012