Ask the Experts – Issue 22


Question My mango tree is about two-storeys high. The tree fruited twice but on both occasions, the mangoes had black spots on the flesh and worms were present. Can you please advise how I can eradicate the worms so that I can enjoy the mangoes? Thank you. – W.F. Chow I have a mango tree almost two storey in height. During the recent dry spell, it flowered profusely. When the small fruits appeared, I sprayed it with a water-based permethrin solution. Despite spraying three times over a period of three weeks, the fruits had worms inside. How can I overcome this problem? – W.L. EngAnswer Female fruit flies lay their eggs just beneath the skin of the developing fruit. Spraying the fruits with water-based permethrin solution would generally not be effective, as the pesticide is a contact insecticide, meaning it needs to be sprayed directly on the insects in order to kill them. The most environmentally friendly way of dealing with this problem is to protect the fruits from being infested. This would involve covering the fruits with fine netting or newspaper. However, this of course requires that it can be done safely and would be easier accomplished if the plant is a dwarf or of a small-growing variety. You could refer to this webpage and scroll to the section on making a fruit fly trap (Lynfield or bucket trap). You can replace the vinegar used in the webpage’s suggested ingredients with fruit fly attracting solution available at major nurseries. Some people drop insecticide such as malathion into the solution to poison the fruit flies. You will often find that a variety of management methods have to be applied rather than just one solution in order to better control pest infestations. – Dr Wilson WongPhoto of mango tree from NParks Flora and Fauna WebAsk the Expert team is made up of NParks horticultural and gardening experts. If you have any questions on plants or plant-related subjects, please send your question to Ask the Experts at

Total Comments: 2

Margie Lim 6/15/2015 7:29:09 PM

Dear Dr Wilson Wong, I have been recommended to grow Eugenia Oleina trees (EO) in my garden as they provide plenty of shade and block traffic noise from the road. Furthermore, I was told they are hardy and easy to maintain. I observe that these trees are commonly seen in public areas such as in schools, roadside, parks etc. throughout Singapore. However, I have a few concerns and hope that you could help better understand the nature of these trees before I decide to plant them: 1. EO seems to have blue berry-like fruits at times. Do these fruits secrete juice and expel from the stems/branches when they are ripen or do they simply fall to the ground? If they do how far do they expel? Basically this is to ascertain how far away these trees should be planted away from the boundary walls and house walls to avoid staining. 2. If the fruits do not expel from the stems/branches, do they attract animals such as birds and fruit bats to eat them and later defecate on the walls? 3. Are these fecal stains permanent or can they be easily washed off by water &/or soap? 4. Finally, may I know how often do EO flower and fruit each year? Many thanks! Regards, Margie

Li-San 6/23/2015 8:41:13 AM

Hi Margie, The fruits drop around the tree's root zone and birds do enjoy feeding on them - this is good for biodiversity to flourish in our urban areas. The stains can be washed away. We currently do not have the information on the frequency of the Eugenia Oleina flowering and fruiting in Singapore, but do note that if the plant is pruned frequently to function as a screening plant, it can reduce the intensity of the flowering and fruiting to a certain extent.

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