Bonsai: Detect and combat diseases and pests

Bonsai: Detect and combat diseases and pests

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Bonsai trees are naturally very robust. And yet, improper care can lead to various diseases. Here is a brief overview of the most common diseases and pests and how to combat them.

A bonsai needs the right care in order not to get sick. You always keep an eye on your bonsai pupils. You simply need special care so that they can develop splendidly. The regular assessment also has its positive aspects. Illness symptoms are quickly noticed and you can intervene accordingly.

The most common maintenance errors occur in the water supply. With the sheet diagnosis, small errors can be recognized immediately:

Your bonsai suddenly gets yellow, withered or dry leaves that eventually fall off - then it clearly receives too little water. However, if the leaves gradually turn yellow and die, too much water, too much fertilizer or a lack of nutrients are responsible.

»Reading tip: Fertilize bonsai - This way the plant gets all the important nutrients

Viral and fungal diseases in bonsai trees

Bonsai can catch a virus or contract a fungus. You can recognize the diseases by pale, yellowish leaves or needles. The branches die. Quarantine and hygiene are the first measures. The triggers are often transmitted by touch, which is why separate, clean handling is extremely important.

Remove the infected parts and separate the affected plant. Fungi can usually be combated well with a fungicide (my recommendation: bestseller no. 1 Compo Duaxo Universal Fungus-Free) as long as the disease has not yet spread to the entire bonsai.

➜ stem rot and root rot


Root rot and stem rot are caused by bacteria and fungi. The stem rot destroys the bonsai from the inside. The trunk and branches turn reddish brown from the inside. The disease mainly affects yew, walnut, horse chestnut, pine, box and olive. Waterlogging and poor air exchange favor stem rot.

The root rot occurs on the root ball and destroys the bonsai from below. Brown, withered leaves and a foul smell are usually the first signs. The roots become soft and mushy, the water transport no longer works. Waterlogging is also a factor here that affects root rot. So always think of good drainage and carefully regulate the water balance of the bonsai!


It is often advised to completely dispose of bonsai trees affected by stem or root rot. You can also remove affected parts generously. Then place the bonsai in fresh substrate and make sure to place it separately until you can be sure that it has recovered well. Fungicides (see above) work against fungi that cause root and stem rot.

If nothing helps: remember not only to remove the bonsai, but also to clean the planting bowl thoroughly, preferably with alcohol.

➜ Dangerous: fire on the bonsai

The fire blight is triggered by bacteria. The leaves turn brown to black, the tree dies. There is no antidote, unfortunately the bonsai must be destroyed.

Pests on bonsai trees

➜ aphids:

Aphids often spread on the bonsai. Bathe the bonsai upside down in a mixture of detergent and water, ideally repeat several times.

➜ scale insects:

Scale insects also damage the bonsai. Use a biological spray based on paraffin oil, e.g. the expectorant from Bayer.

➜ Aphid:

The aphid is the most dangerous louse. It sucks the woody parts and causes malignant ulcers. You can also use the biological spray agent just mentioned here.

➜ Spider apple tree moth:

The apple tree spider moth is another well-known bonsai pest. It is a butterfly that lays its eggs on the shoots. The hatched caterpillars eat the bonsai completely bald in no time. The infestation shows itself visually by a gray-white web between the leaves. You can try scraping off the eggs and collecting the caterpillars. Again, place the bonsai separately so that the pests do not spread to other plants.