Thrips management in mango orchards

Grove, Tertia (1999-03)

Dissertation (PhD) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: Thrips associated with mango trees {Mangifera indica L. (Anacardiaceae)} were collected over a five year period in the main mango production areas of South Africa. Fifteen species were identified, eleven belonging to the family Thripidae and four to the family Phlaeothripidae. The citrus thrips, Scirtothrips aurantii Faure and the red banded thrips, Selenothrips rubrocinctus (Giard) were the only two species found to cause lesions on the fruit. Scirtothrips aurantii was the economically most important species found. There was a tendency for lesions caused by S. aurantii to decrease in prominence as the fruit matured. Some lesions that were prominent at the beginning of the season appeared less clearly defined at the end of the season. However, badly marked fruit did not recover to the extent that it could be exported. Sticky traps (140mm X 76mm X O.2mm) of various colours were tested in mango orchards for the attraction of S. aurantii adults'. Yellow was superior to blue, white, red and green. Yellow traps can be used effectively for assessing activity levels of S. aurantii in mango orchards. Cumulative insect-days were computed for S. aurantii on the traps and on the fruit and were correlated with the percentage fruit with lesions making it unacceptable for export. Fruit with such lesions should not exceed 5%. Chemical intervention should be used when S. aurantii on the traps exceed 2326 cumulative insect-days and when numbers on the fruit exceed 24 cumulative insect-days. By using a two stage sampling system for determining S. aurantii population levels in mango orchards, the optimum combination of the number of trees per orchard (primaryunits) and fruit per tree (secondary units) was estimated. The recommendation is to sample 5 fruit from 10 trees. Hoerl's function (Y = aXbecX) was used to describe the relationship between the number of S. aurantii on the fruit and fruit size, as well the number on the traps and fruit size. Fruit size when the maximum numbers of S. aurantii occurred ranged from 20.22mm to 40.33mm, while the ·fruit size at maximum numbers on the traps was from 2.94mm to 36.82mm. Therefore, for the management of thrips S. aurantii it is essential that they are monitored until fruit are at least 40mm in length. Scirtothrips aurantii numbers started to build up during September which is the end of the flowering period and reached a peak usually during October or November when small fruit were present. Scirtothrips aurantii was only present on the fruit for a short period and the population survived on new growth that was present throughout the year. Low numbers were present from June until August. The highest number of S. aurantii was observed on the cultivar Sensation. Different insecticides were evaluated in the field· for control of S. aurantii on mango fruit. The insecticides tested were formetanate, formetanate plus sugar, tartar emetic plus sugar, methamidophos, sulphur, phenthoate, cypermethrin, fipronil, fenthion, isophenfos and prothiofos and an extract of Syringa [Melia azedarach L. (Meliaceae)]. A non-toxic, garlic based insect repellent and feeding depressant was also evaluated. The best control was obtained with formetanate and fipronil. The garlic based substance showed potential, but not the Syringa extract.

AFRIKAANSE OPSOMMING: Blaaspootjies wat op mango bome {Mangifera indica L. (Anacardiaceaej)} voorkom, is oor 'n tydperk van 5 jaar in die belangrikste mango produksie gebiede van Suid-Afrika versamel. Vyftien spesies is geidentifiseer, waarvan elf behoort aan die familie Thripidae en vier aan die familie Phlaeothripidae. Die sitrusblaaspootjie, Scirtothrips aurantii Faure en die rooibandblaaspootjie, Selenothrips rubrocinctus (Giard) was die enigste twee spesies wat letsels op die vrugte veroorsaak het. Scirothrips aurantii was die ekonomiese belangrikste spesie wat voorgekom het. Letsels veroosaak deur S. aurantii het 'n afname in prominensie getoon namate die vrugte volwasse geword het. Sommige letsels wat prominent aan die begin van die seisoen was, was ligter en nie so duidelik aan die einde van die seisoen gedefinieer nie. Vrugte met letsels het egter nie in so 'n mate herstel dat dit vir uitvoer aanvaarbaar was nie. Taai kaartvalle (140mm X 76mm X O.2mm) van verskillende kleure is in mangoboorde getoets vir die aanlokking van volwasse S.aurantii. Geel het meer aangelok as blou, wit, rooi en groen. Geel valle kan effektief aangewend word vir die bepaling van die aktiwiteitsvlak van S. aurantii in mangoboorde. Kumulatiewe insek-dae is vir S. aurantii op die vrugte en op die valle bereken en met die persentasie vrugte met letsels wat dit onaanvaarbaar vir uitvoer maak, in verband gebring. Vrugte met sulke letsels moet nie 5% oorskry nie. Chemiese ingryping moet geskied wanneer S. aurantii op die valle 2326 kumulatiewe insek-dae en op vrugte 24 kumulatiewe insek-dae oorskry. Deur gebruik te maak van 'n twee stadium mosternemingstel is die optimum kombinasie van die aantal bome per boord en vrugte per boom bereken. Die aanbeveling is om 5 vrugte van 10 bome te monster. Hoerl se funksie (Y = aXbecX) is gebruik om die verhouding tussen die aantal S. aurantii op die vrugte en die vruggrootte asook aantal op die valle en die vruggrootte te beskryf. Die vruggroote waarby die maksimum aantal S. aurantii op die vrugte teenwoordig was, was vanaf 20.22mm tot 40.33mm, terwyl die die vruggroote waarby die maksimum aantal op die valle teenwoordig was, gewissel het van 2.94mm tot 36.82mm. Vir die bestuur van blaaspootjies is dit dus belangrik om te moniteer vanaf vrugset tot vrugte ten minste 40mm in lengte is. Scirtothrips aurantii se getalle het begin opbou gedurende September, wat die einde van die blomperiode is, en het gewoonlik 'n piek gedurende Oktober of November bereik wanneer klein vrugte teenwoordig was. S. aurantii was slegs vir 'n kort periode gedurende die seisoen op die vrugte teenwoordig en die bevolking het oorleef op nuwe groei wat reg deur die jaar teenwoordig was. Lae getalle het vanaf Junie tot Augustus voorgekom. Die hoogste getal S. aurantii is op die kultivar Sensation waargeneem. Verskillende insekdoders vir die beheer van S. aurantii op mango vrugte is in die veld geevalueer. Die insekdoders wat uitgetoets is, was formetanaat, formetanaat plus suiker, braakwynsteen plus suiker, metamidofos, swael, fentoaat, sipermetrin, fipronil, fention, isofenfos and protiofos en 'n ekstraksie van Sering [Melia azedarach L. (Meliaceae)]. 'n Nie-toksiese knoffel insek-afweermiddel en voedingsdepressant is ook geevalueer. Die beste beheer is verkry met formetanaat and fipronil. Die knoffelsubstraat het potensiaal getoon, maar nie die Sering ekstrak nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/51528
This item appears in the following collections: