Pg. 29-30 Die beheer van vrugtevlieë by lietsjies

Lietsjievrugte word gedurende die vrugrypwordingsfase deur twee vrugtevliegspesies aangeval, nl Mediterreense- en Natalse vrugtevliee. Hoewel vrugtevliegeiers dikwels op die vrugvlies by ‘n steekplek waargeneem word, vind ontwikkeling van die larwes selde plaas. Die meeste skade word aangerig deurdat gisting in die vrug by ‘n steekplek plaasvind en die skil kan laat bars. Dit lei tot sekondere bederf. Vrugtevliegskade moet voorkomend beheer word deur die aanwending van ‘n giflokaas, wat een of twee keer per week op ‘n gedeelte van elke boom gespuit word. Die hoeveelheid giflokaas kan varieer van 250 mf tot 1 f/boom en moet in groat druppels gespuit word. Die giflokaas bestaan uit ‘n mengsel van ‘n proteienhidrolisaat of suiker, ‘n insekdoder soos trichloorfon of merkaptotion en water. ‘n Tweede metode om die vrugte teen vrugtevliee te beskerm is om die vrugte na die Novembervrugval toe te maak met, lietsjiesakkies. Die uitroei van nuttelose gasheerplante soos die luisboom word aanbeveel. Die gebruik van lokvalletjies met sintetiese geslagsferomoon kan help om die bevolkingsopbou van vrugtevliee in boorde te bepaal.

Summary:

• Litchi fruit are attacked during the ripening phase by two fruit fly species, the Mediterranean fruit fly (Ceratitis capitata) and the Natal fruit fly (Pterandrus rosa).
• Although fruit fly eggs are often found on the flesh at puncture sites, larval development rarely occurs.
• Most damage is caused by fermentation at puncture wounds, which can also cause cracking of the skin and secondary fruit rot.
• Preventative control is essential and involves regular application (once or twice a week) of poison bait sprays to parts of each tree.
• The poison bait spray is applied in large droplets and typically consists of a mixture of protein hydrolysate or sugar, an insecticide such as trichlorfon or mercaptothion, and water.
• The amount of bait spray varies from 250 ml to 1 liter per tree, depending on tree size, and must be freshly prepared each time.
• Bait sprays are applied high on the trees, only on one side, ensuring large droplets fall onto leaves to be effective.
• If rain occurs soon after application, reapplication is recommended, especially if the fruit has developed red skin.
• For control of overwintering flies, two or three bait applications in winter on surrounding evergreen trees on warm sunny days are advised.
• A very effective alternative is enclosing fruit clusters in specially made litchi bags after the “November fruit drop,” protecting fruit from fruit flies, litchi moth, fruit bats, and sunburn.
• Fruit are harvested 6 to 8 weeks after bagging and transported to cold storage still in the bags; some bags can be reused in the following season.
• Removal of useless host plants that harbor fruit flies near litchi orchards is advised, such as the woolly nightshade tree (Solanum mauritianum), which provides food and breeding sites.
• Other host plants to be eradicated include wild guavas and brambles.
• Population monitoring of fruit flies can be done using traps baited with synthetic sex pheromones.
• Weekly counts in traps indicate the success of bait applications; a sudden increase in flies suggests a need to intensify control measures.
• One or two pheromone traps per hectare are sufficient, to be hung in shaded parts of the orchard in spring.
• Pheromone should not be applied outside the traps to avoid flies gathering on the outside, leading to inaccurate counts.
• The pheromone (Capilure) is mixed with a small amount of an insecticide (such as dichlorvos) to kill trapped flies.
• The bait mixture is prepared fresh every season and old mixtures should be disposed of well away from orchards to prevent contamination.