We should carefully look after trees to ensure they grow well. For young trees, we need to provide irrigation and fertilising for early growth, give them support by staking, control weeds around them and carry out formative pruning to create a balanced and healthy tree form, which could help reduce the tree risk in the future. For mature trees, we need to be more aware of potential risk and carry out inspection by trained personnel, especially in areas where there are greater numbers of people and traffic.
We can all take care of trees in the community and make Hong Kong a greener place. Below are some practical tips:
Phauda flammans are found in southern China, Hong Kong, Malaysia, Thailand, Indonesia and India. Phauda flammans larvae (larvae) feed on leaves to survive and are commonly found on Ficus trees. After a larva matures, it will form a cocoon, pupate, and then emerge from the pupal case and turn into an adult. The adult will then lay eggs on leaves after mating, which will hatch into larvae and start feeding on leaves. There can be more than two generations of larvae per year.
It is a natural phenomenon that larvae feed on leaves of Ficus trees. However, this phenomenon was more apparent in Hong Kong in the summer of 2020. Though the appearance of infested Ficus trees has deteriorated due to defoliation, the infestation did not have a serious impact on their overall health and structural conditions. The affected trees recovered from infestation gradually in late 2020 and early 2021 and no trees have to be removed.
To ensure the effective implementation of integrated pest management, specific measures should be adopted having regard to different stages of the life cycle of the insect (eggs, larvae, pupae and adults), followed by monitoring, evaluating the effectiveness of the control measures and making adjustments whenever necessary. Private property owners or management personnel can monitor affected trees on their properties on a regular basis, and take appropriate control measures according to the infestation extent of the trees, their surrounding environment, as well as different stages of the life cycle of the insect. Pest control work for trees involves arboricultural knowledge and requires professional input. Private property owners or management companies should engage qualified professionals to advise, supervise and handle all matters in relation to tree work. Appropriate control measures include:
To wrap the tree trunk with bamboo/straw mats or hessian bags to catch active larvae on the trunk; and to regularly remove and replace bamboo/straw mats or hessian bags that are drenched, so that the trunk will not be weakened in a humid environment for a long time, which will affect its health and structural conditions.
To step up the clearance of pupae inside the tree bark, crevices in roots, top soil and fallen leaves when larvae are forming cocoons, so that fewer larvae will emerge as adults in the next stage; and to properly handle yard waste such as dead leaves and pupae to prevent pest transmission due to improper transportation.
To spray soap water or chilli water on the affected tree crown and tree trunk to remove larvae on the leaves or the trunk.
To consider engaging a professional pest control agent if necessary, as advised by the qualified arboricultural professionals, for pest prevention and control work, particularly the application of agricultural pesticides*.
(*Note: Since pesticides will cause environmental pollution, priority should be given to other methods in preventing and controlling plant pests, and appropriate pesticides should only be used after all other methods have been found ineffective. As regards pesticide application, appropriate pesticides that are the safest, most effective with lower toxicity and approved under the Hong Kong legislation should be used to reduce their impact on the environment and ecology. After applying pesticides, relevant warning signs should be displayed conspicuously. For more information on the safe and proper use of pesticides, please visit the webpage of the Agriculture, Fisheries and Conservation Department at: