Bonsai Diseases

Part 7 of a series by Eugene Howell

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Japanese White Pine Zui-sho pinus parviflora}Many bonsai enthusiasts and gardeners in general, have a tough time diagnosing plant disease and then have trouble deciding how to treat it. The reason may be because there are so many diseases, some of which have unusual or often very subtle symptoms, many of which are similar. So the average bonsai artist looks at a diseased leaf and doesn’t know what the problem may be or how to treat it.

There are three broad categories of bonsai diseases. They are fungus, virus and bacteria. Unfortunately there are no cures for viral and bacterial diseases in plants. But it’s critical that you know and recognize them because it’s very easy to inadvertently spread the disease from bonsai to bonsai as you work on your trees. Learning to recognize plant disease when it occurs will allow you to quarantine the tree away from your other bonsai. Remember to wash your hands thoroughly after handling the diseased tree before working on any other bonsai.

You may also need to wash your clothes and tools as well. Experiments done by the Univ. of Florida have shown that after introducing a single infecting tomato plant to a field of tomatoes, a worker in the same field can spread the disease throughout the whole field.

But don’t panic, the majority of bonsai diseases are caused by fungus, which is treatable. The Univ. of Florida estimates that about 97% of plant disease falls into this category.

In general, diseases caused by fungus are fairly easy to prevent. The key action that a bonsai artist can take is to maintain environmental conditions that are not conducive for fungus to grow. Don’t allow dead leaves and weeds to accumulate around the base of your bonsai trees. And whenever possible, try to water only the bonsai soil as opposed to spraying water over the entire tree. Fungus require approximately 14 hours of continual wetness to begin growing and spreading. Because we often need to water our bonsai daily, it’s easy to create these conditions on the trunk and branches of the tree. By watering only the soil and keeping the surface of the soil clean, we can eliminate places where fungus are able to grow and thrive.

Japanese White Pine ‘Zui-sho’ {pinus parviflora} by Drew Avery

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