Types of Bonsai Tree Pests and How to Protect Your Trees from Them

Bonsai tree pests can cause severe damage to your plant that, if not dealt with properly, can lead to loss of leaves and branches, and possibly even death. Certain trees are more susceptible to particular pests than others, and the type of insects you will encounter will also depend on your location and climate.

The best way that you can protect your plant from pest infestation is to learn what “enemies” are common to your area and are known to be attracted to your specific type of tree. This way, you will recognize the signs and be able to catch the problem early, before these pests cause any permanent damage.

Also, insects are more likely to attack weaker, unhealthy trees. So, you can protect your bonsai by following the proper steps when pruning, re-potting, fertilizing, and watering.

Treatment: Most pests can be eliminated by either picking them off by hand or treating the plant with an insecticide. Your choice will often depend on the type of pests you are dealing with.

A systemic insecticide is usually poured onto the soil where it is absorbed by the roots and then distributed to other areas of the tree. Some products can also be sprayed onto the foliage, where they are absorbed and carried throughout plant. Any insect that chews on the leaves or bark will also be eating these poisonous substances.

A contact insecticide is sprayed directly onto the plant and will kill pests on “contact”. Any insect that is not sprayed will not be affected.

You can either treat your bonsai with a chemical solution purchased at a nursery or bonsai store, or you can use an organic or environmentally friendly option such as pesticide soaps or other “natural enemy” insects that are safe for your bonsai.

Types of Common Bonsai Tree Pests

Aphids:

These are one of the most common bonsai tree pests and are sometimes referred to as “plant lice”. Aphids suck important juices or sap from the plant and also carry many viruses or diseases that can be transmitted to your tree. While they are usually green, they can also be grey or black and are most often found on the stems or underside of the leaves. Since aphids can cause significant damage, it is important that you check your bonsai regularly for these pests.

Symptoms: You will notice weak leaves and branches, and possibly some curling or deformed shoots. Aphids also leave behind a sticky, sugary substance called “honeydew”, which attracts ants and causes the growth of a fungus known as “black sooty mold”.

Treatment: Aphids can often be removed without the use of insecticides. Usually showering the plant or spraying the undersides of the leaves and stems with a hose will remove these pests. However, you can also apply a soft soap spray or use a systemic pesticide such as plant pins. Some people also prefer to use lacewing larvae, since one larva can eat more than 300 aphids.

Remember to check your plant for root aphids when re-potting, and spray with a systemic insecticide if necessary.

Red Spider Mite:

These are one of the most dangerous bonsai tree pests and can kill your plant quite quickly if not treated. Red spider mites are almost microscopic and are often very difficult to spot. The best way to identify an infestation is to shake a branch over a piece of white paper, and the mites will fall like a fine red dust. Since they prefer a warm, dry climate, red spider mites are more common on indoor bonsai.

Symptoms: As the mites feed off the plant, they will cause the foliage to turn from green to yellow, then eventually brown. They will also weave very fine webs between branches and leaves. Conifers are more often attacked, although other types of trees are not exempt.

Treatment: Applying a systemic insecticide or organic soap spray to the undersides of leaves usually works quite effectively.

Scale Insects:

These insects will most often appear as small white, yellow, or brown bumps on the trunk, branches, or leaves. As they suck sap from the tree, they produce a sticky secretion and will sometimes have protective shells around them. They are most commonly found in clusters.

Symptoms: Branches will droop and foliage will often wilt and turn yellow.

Treatment: The best solution is to remove scale insects by hand. You can try using an insecticide, but this is not always effective due to the protective shell. For small outbreaks, painting the shells with alcohol sometimes works well.

Caterpillars:

Caterpillars can be very destructive and can quickly strip your bonsai of its leaves and shoots. It is very important to watch carefully for these bonsai tree pests and to eliminate them on first sight.

Symptoms: Since caterpillars feed on foliage, you will usually notice leaves that appear eaten or have holes. There may even be branches that have been stripped completely.

Treatment: Since caterpillars are usually very visible, it is often most effective to remove them by hand. You can also use either a contact or systemic insecticide, or an organic spray such as Di-Pel. These bonsai tree pests have a tendency to “re-appear” so even when you think that the problem has been taken care of, keep checking for a few more day to make sure that you have removed them all.

Vine Weevils:

Vine weevils are very destructive and, unfortunately, can do the most damage before you even notice that they are there. The larvae will eat the root systems and can often cause irreparable damage before visible symptoms appear.

Symptoms: Leaves will start to wilt as if the plant is lacking water, and you may notice U-shaped notches around the edges of the foliage. Adult weevils are quite large and very noticeable, although it is the larvae that cause the most damage because they feed off the bonsai root systems. By the time your tree begins to wilt, the problem is usually already quite extensive.

Treatment: As with any bonsai tree pests, prevention is the best treatment against the vine weevil. If you notice an adult insect on your plant, remove it immediately to prevent it from laying eggs on your bonsai. You can also add soil insecticides to your mixture when re-potting or water your tree with a pesticide that is recommended for the prevention of vine weevils. Rubbing your bonsai bench legs with a barrier glue is also an effective way to stop climbing weevils from getting to your plant.

Mealy Bugs:

Mealy bugs will appear as little cotton balls sitting on the leaves and branches of your bonsai. The insects hide within the little “balls” and are protected by wax-like coverings. They can commonly be seen in patches or clumps. During re-potting, and any other time when you notice symptoms, you should also examine your plant for root mealy bugs.

Symptoms: Your tree's growth will be slowed or stunted and leaves will droop and turn yellow. Mealy bugs can also cause the development of black sooty mold.

Treatment: You can treat your bonsai with either a contact or systemic insecticide. If you have a recurring issue with mealy bugs, an initial contact solution will be effective, but you may wish to use a systemic treatment to prevent re-infestation.

Bonsai tree pests can cause damage, disease, and even the death of your plant. But, being able to recognize the symptoms and knowing the proper treatment can help you protect the health and beauty of your bonsai.

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