Dear Plant Doctor, how do I kill aphids?

The leaves of a White bird of paradise flower infested with woolly aphids. The Plant Doctor recommends spraying the pests with water mixed with neem oil. Photo: Visualhunt.com

Dr Christopher Teh, soil biologist and senior lecturer at Universiti Putra Malaysia answers gardening questions in Star2’s monthly gardening column, Ready, Set, Grow!, which is brought to you by social enterprise Eats, Shoots & Roots. Go to questions.eatsshootsandroots.com to send in your queries.

Can you please tell me how to get rid of those tiny white pests that dwell on the underside of leaves? The whole leaf gets coated with them and then it withers and drops soon after. – Lee Kok Tham