Because bonsai are made from normal plants and trees, they are subject to the same types of bugs and pests as those in your yard and garden. You should monitor your bonsai regularly to make sure that it has not been infested by any of these tiny but destructive forces of nature. They can cause stress and damage to all your hard work and even kill the tree if not caught promptly.
Sometimes known as plant lice, aphids are one of the most common enemies of bonsai. They appear as green (occasionally black or gray) and can be found under the leaves or on stems. They suck the sap and can spread disease to your plant.
It is possible to remove them by spraying the plant with water, but you can use systemic insecticide if preferred.
Red spider mite
These nearly invisible little pests can destroy a bonsai fast and are hard to see, sometimes making it necessary to shake the plant over a piece of paper. Found more often on indoor bonsai, the mites feed on the tree, causing the leaves to turn yellow and brown.
Spray the bottom side of the leaves with an organic soap mixture or use systemic insecticide such as pesticide pins.
These look like tiny balls of cotton on the branches and leaves and frequently gather in clumps. The insects are actually inside the balls, and can cause yellow leaves and slow growth. Not only do they feed on the juices from your bonsai, they also introduce a spectrum of diseases.
Insecticide should be used to rid your bonsai of these pests.
They can be removed manually, as they have a shell that can protect them from chemical insecticides. If there aren’t too many bugs you can brush alcohol onto them to kill them.
They tend to come back even when you think you’ve gotten them all so keep checking regularly.
Unlike most pests, vine weevils can cause significant damage to the root system of a plant, because that’s where the larvae feed. While adults are bigger and more noticeable, the larvae are the most destructive and by the time you notice wilted leaves, it may be too late. If you can see adults, remove them by hand and apply a soil pesticide.
The important thing to remember about bonsai pests is that checking your plant regularly can prevent extensive damage. Always check the roots when repotting to make sure there are no unwelcome guests.