Ask the Plant Doctor! How to correctly identify and deal with pests that attack your plants

Insects that frequently attack jasmine trees are spider mites, mealybugs and whiteflies. Photo: 123rf.com

Do you have a question about plants or how to maintain your garden? Send your questions to the Plant Doctor! Email your questions to [e-mail] with "Plant Doctor" in the subject field. Questions may be edited for brevity and clarity.

Q My jasmine plants are frequently attacked by insects that damage their leaves and lay green-coloured eggs on the leaves, especially the young shoots, resulting in their inability to flower. How do I remove them? – Dr Sanjeev Janardhanan

Several insects, such as spider mites, mealybugs and whiteflies, may attack jasmine plants. The symptoms you have described suggest that moths or butterflies are the likely culprits, since these pests usually lay coloured eggs and target young shoots.

Aphids may also be responsible, as they tend to favour new growth, but typically produce live offspring rather than eggs.

Even then, their eggs are usually black, brown or grey, unless they are recently laid, in which case they produce light yellow to greenish eggs.

To effectively manage these pests, it is best to first correctly identify the insects. You can do this by inspecting your plants, insects and eggs, and taking photos. You can seek help from professionals, such as a local extension service, nursery or online entomology forum.

Once a pest is known, the most suitable control method can be applied.

These strategies may include the manual removal of insects and eggs if the infestation is not too severe.

It is also possible to use insecticidal soaps, horticultural oils and biological pesticides.

They are made from naturally occurring substances that control pests through non-toxic mechanisms, such as bacteria, viruses or fungi. For example, Bacillus thuringiensis (popularly known as Bt) produces proteins that are harmful to several types of insects.

All of these biology-based products can be purchased online. Be sure to spray these products on both sides of the leaves, following the instructions. Regular pruning of plants and clean-up of the plant environment can discourage infestation.

You can also cover your plants with netting to prevent adult moths or butterflies from laying eggs on them. If these methods are ineffective, chemical pesticides are used as a last resort because of their potential environmental impact.

Finally, monitoring and repeated treatments may be necessary to fully control some infestations. The most effective pest control usually involves a combination of methods.

Dr Christopher Teh heads the Dept of Land Management, Faculty of Agriculture, Universiti Putra Malaysia and coordinates the Healthy Garden series. The views expressed are entirely his own.