Bonsai Pests & Diseases Care Guide

Bonsai trees can occasionally suffer from pests, diseases, or other health problems — just like any other plant.

The good news is that most problems are relatively easy to manage when they are noticed early.

Regularly looking at your bonsai is one of the best forms of prevention. Check the leaves, branches, trunk, soil surface, and especially the undersides of leaves. Changes in colour, unusual spots, sticky residue, webbing, or small insects can all provide useful clues.

One important thing to remember: not every unhealthy-looking bonsai has a pest or disease.

Problems with watering, light, temperature, soil, roots, or seasonal changes can produce very similar symptoms.

Is My Bonsai Actually Sick?

Before reaching for a pesticide or fungicide, take a closer look at the tree and its growing conditions.

Yellow Leaves

Yellow leaves can be caused by many things, including overwatering, underwatering, poor drainage, insufficient light, nutrient deficiencies, root problems, seasonal leaf changes, or pests.

A few yellow leaves are not necessarily a reason to worry.

If large parts of the tree suddenly turn yellow, however, investigate the cause.

Brown or Crispy Leaves

Brown leaf tips or crispy leaves are often associated with insufficient watering, very dry air, excessive heat, strong sun exposure, wind damage, root problems, or excessive fertilization.

Check the soil before assuming that the tree needs more water.

Leaves Falling Off

Leaf drop can occur because of seasonal changes, sudden changes in environment, overwatering, underwatering, insufficient light, temperature stress, root damage, or pests and disease.

Some deciduous bonsai naturally lose all their leaves in autumn.

Evergreen species may also occasionally shed older foliage.

Sticky Leaves

Sticky leaves are often a sign of sap-feeding insects such as aphids, scale insects, mealybugs, or whiteflies.

These insects produce a sugary substance called honeydew.

Check the undersides of leaves and along branches carefully.

White Substance on Leaves or Branches

White material can indicate several different problems.

A powdery coating across the leaves may be powdery mildew, while small cotton-like clusters are more likely to be mealybugs.

Always identify the problem before treating it.

Black or Brown Spots

Spots on leaves can result from fungal infections, bacterial infections, sun damage, water stress, or physical damage.

A small number of damaged leaves may not be serious, but rapidly spreading spots should be investigated.

Fine Webbing

Very fine webbing between leaves and branches is one of the classic signs of spider mites.

Spider mites are extremely small, so the webbing may be easier to notice than the mites themselves.