Are the leaves on your beloved bonsai tree turning brown or breaking out in spots? To keep the tree healthy, be certain to identify and treat the problem as soon as you can---or you might risk losing the tree entirely.
Fungal infections called rusts can cause raised brown patches to appear on the undersides of bonsai leaves. Remove the affected leaves, and make sure your bonsai receives good air circulation.
Too Much Mist
Brown spots can develop on a bonsai's leaves if water droplets evaporate off them too quickly. If you use a plant mister on your bonsai, stop misting it for a while, and see if the brown spots disappear.
Small bugs called leaf miners will occasionally create thin brown trails across a bonsai leaf. Leaf miners don't cause lasting damage, but be sure to remove the leaves they've damaged.
If the edges of your bonsai's leaves are starting to turn brown and crispy, the plant could be drying out too quickly. Move it to a less sunny location, or away from any nearby air vents.
You can stop many bonsai illnesses before they start by dosing your trees regularly with garden fungicides and herbicides.