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Plant Pests and Bonsai

Growing bonsai? Knowing plant pests comes with the territory!

Juniper bonsai tree, bonsai tree pictures

Because we use many different kinds of plants to create bonsai trees, there are many different problems to watch for.

Any article about bonsai plant care is not complete without this discussion.

Not all plants are susceptible to the same problems.

Each time you adventure to another species, research the potential pests and diseases for that plant.

Junipers such as this cascade by Ed Trout, Ft. Lauderdale, FL are susceptible to red spider mites.

If you don’t know what’s crawling on your tree, or why your tree is doing something weird (like wilting or dropping leaves), always ask!

Remember, just as there are good reasons for some plants to wilt or drop leaves; there are also many more “good bugs” than bad.

If you don't know, never spray pesticides first!

These are some of the bad ones:

Aphids - are one of the most common problems for people growing plants in general. Many bonsai are susceptible to this ‘plant lice’ with piercing-sucking mouthparts.
If that sounds scary, read more about Aphids here.
Mites - In the world of bonsai, mites also rank pretty high on the bad bug scale. They appear on temperate, tropical, indoor and outdoor plants.
The type of mites we see most often are what we call red spider mites. They are barely visible, but can be easily spotted on a piece of white paper.
Greatly enlarged illustration by Eduardo Varona.

We often assume they only attack our juniper bonsai, not so! I have seen them on everything from regular house plants to trees in the yard.
Their feeding causes the plant to appear off-color and eventually turn completely brown. Another symptom is the webs they weave (where they lay eggs).
Mites can kill plants quickly. When you have a bonsai that just doesn’t look quite right, suspect spider mites!

Boring insects - are truly horrible pests.

One that is often missed! Virtually all woody plants and trees are subject to borer attacks. Borer damage, juniper bonsai, plant pests
If you're growing bonsai trees, you can have borers!

Borers nearly always attack unhealthy or stressed plants or trees.

Although you may think your tree is healthy, what about the injuries from cutting? These 'wounds' can be entry places for borers.

Not as common as many other plant pests; they are something to always be aware of.

Some bore deeply into the wood however, many bore just under the bark. Sometimes you will see small holes in the trunk or limbs with fine sawdust directly beneath them. When you see these signs, find the soft area.

Try to gouge out the area as soon as possible. Don't stop digging around soft spots until you find something. Beetle and/or larvae are almost always still there!

You may end up with a terrific shari or (as in the ugly damage shown here) -- you may not be so lucky! Read more about borers.

Not Too Common Plant Pests

Every once in a while you may come across something really odd, be sure to check it out! One example that rarely shows up is "pit scale".

When it does appear, it can be devastating. Nashia inaguensis is one species it is particularly attracted to.

Another terrible invasion can come from root mealy bugs!

They are worse than the above ground kind, and very difficult to see! Root mealy bugs are often misidentified! Be sure to read about them.

More Common Plant Pests

Details on some of the other most common plant pests including:
galls, leafminers and thrips can be found at the

Institute of Food and Agricultural Sciences web site.

IFAS may become one of your favorite pest information sources.

If you can’t find what you’re looking for there, contact your local Cooperative Extension Service. I’m always pleased with their friendly and helpful response.

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