How to treat a bonsai: Pests and diseases

Most of the trees or shrubs used for the cultivation of bonsai, can be infected by diseases or pests, if there are not the special care and attention that need, daily.

Almost all bonsai that are infected because the living conditions were not suitable, the most common problems are:

  • Wrong irrigation
  • Lack of light
  • Wrong location

Ants can attack trees at random, but by recognizing the problem they no longer become a danger.

Even if the trees are not immune to disease at all, they will still be able to better resist problems and react strongly to the treatment given to them.

The purchase of various insecticides must be taken into consideration, to act as soon as you become aware of the problem.

But what to do when the bonsai is infected?

The first thing to do is to try to understand the real problem. Has it lost its leaves? Has the foliage discolored?

Observe every part of the plant with extreme care, even to see if there is any parasite on the surface of the tree or around it.

The second thing to do after understanding the problem is to put the bonsai as long as it is no longer attacked by the same insect (eg caterpillars).

If the bonsai loses its leaves, there are only three causes:

  • GELO: tropical and subtropical species should not be exposed to frost
  • SPEED: it is a very rare cause, but if the bonsai is in close contact with other plants of different species and you use the herbicide, there is a small chance that the plant is exposed to a spray of poison.

Dehydration is one of the main causes for which a bonsai suddenly loses its leaves. Once the soil is not moist, after several hours the plant will start to lose some leaves. Make a healthy watering.


Here is a list of the parasites that appear most frequently on bonsai trees:

Caterpillars: Caterpillars can be very dangerous for the entire bonsai, especially for growing leaves. They are very difficult to find because they blend in with the leaves. If the bonsai has hollow or yellow leaves, check them carefully and closely. In these cases, insecticides should be used immediately.

Snails: Snails and slugs are very destructive and cause great problems of defoliation. They are very common, especially in wet evenings. They are killed with a liquid solution or with a pellet-shaped bait.

Red mites: Red mites, commonly called only come out of their hiding place a few days a year, especially when temperatures are 20°C and the sun is quite mild. Apparently harmless, they feed on larvae that can be found on your bonsai.

Ladybugs: they are insects that feed on sap and stick to the bark of bonsai covering themselves with a protective brown shell. The only way to remove these insects is by manual operation, as the taste offers total protection, even to insecticides.


Viruses can be noticed by the lack of color in some leaves or flowers.

If a plant is contaminated by a virus, it is good to move it to a place where there are no other bonsai to avoid contamination. After treating the bonsai is good to sterilize all the instruments.

Mould, rust and black spots are the most common viruses on weak and particularly stressed trees.

Mould: Mould is a fungus that grows in damp and poorly ventilated environments, causing the presence of a white mold on the foliage. These fungi extract sap from the plant, causing loss of vigour and abnormal growth.

Rust: Rust causes the leaves to look brown/orange. It should be treated with a fungicide and placed in a place where there is good air circulation.

Black spots: Black spots are viruses similar to mould or rust. Care should be taken not to spray the foliage as water helps the spores by travelling around the plant. Avoid exposing the tree in the rain and treat with fungicide.