Bonsai Pests and Diseases

Part 8 of a series by Eugene Howell

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Japanese ZelkovaIn part 7 of this series (linked to at the bottom of this page) we started talking about bonsai pests and diseases. Today we’ll continue the topic of fungus that can adversely affect your bonsai trees.

Although there are many variations in symptoms, if you see black or brown spots begin to develop on a leaf, and if these spots begin to grow in size, you very likely have a fungus problem. With some fungi, these spots will develop along the edges of the leaves and thus look very similar to water stress (this is one of those hard-to-diagnose symptoms). In most cases, however, the spots will appear across the entire leaf surface. If the spots penetrate completely through the leaf, from the top side to the bottom side, your plant definitely has a fungus. Keep in mind, however, that not all fungi produce these symptoms.

So what do you do about the problem? Luckily there are many excellent fungicides on the market. Having identified the problem, you just need to follow the directions on the container. In general, most will have you spraying the plant and then about seven days later repeating the process.

But not all fungicides defeat all fungi, each one is made to kill certain varieties of fungus. If after spraying the plant twice, the symptoms continue to spread then you need to switch to a different fungicide containing different active ingredients. If the plant continues to develop spots on formerly healthy leaves, then it may have either a virus or bacteria and should be immediately isolated from your other bonsai trees. Unfortunately, in such cases, the tree is likely to die since there is relatively little that can be done to cure plant viruses or bacterial infections.

Many books have been written about the subject of bonsai pests and diseases, so don’t consider this short article as being “all inclusive”. It should however, give you a beginner’s awareness of plant disease.

Part 7 of this series : Part 9 of this series

Japanese Zelkova {zelkova serrata} TD1984 by Drew Avery

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