Bonsai Essentials
Diseases Affecting Bonsai: Cedar Rusts

by Nina Shishkoff, Ph.D. and Andy Walsh, M.S.

On the whole, bonsai are probably the healthiest trees on Earth. In experienced hands, they are well cared for, provided with appropriate environmental conditions, and supplied with adequate amounts of macro-nutrients (NPK) and micro-nutrients. While such good horticultural practices can avoid most pests and diseases, there are some diseases that can still strike even the healthiest of bonsai.

One of these is a trio of fungal diseases, called "Cedar Rusts", that affects Junipers and members of the Rose family. These diseases can seriously damage or disfigure a bonsai [ed: the diseases rarely kill the tree]. With an understanding of disease epidemiology and some precautions these diseases can be avoided. This trio of diseases are known as Cedar-Apple Rust, Cedar-Quince Rust and Cedar-Hawthorn Rust. They are caused by different species of the fungus genus Gymnosporangium. What is peculiar about all three is that the fungus lives alternately in Junipers and then in Rose family members. The three diseases are similar so only an explanation of Cedar-Apple Rust will be given. The differences between the three types can be seen in Table 1.

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Collecting & Training Crab-Apples

by John Biel


The crab apple of this article was collected for several reasons: its rootage and trunk line and its flowers. The roots were nicely placed, although not plentiful, and the trunk had a subtle movement to it. These features were determined the year before collecting when all the apples were in bloom. These desirable bonsai elements you can judge for yourself from the pictures accompanying this article.

Finding such material was a real treat because the area in which these apples were growing was overgrown with knee-high tall grass, weeds and shrubby trees. Apples, as well as many other trees that grew in this sort of environment, seemed to end up with straight trunks until they grew beyond the height of the surrounding grasses. That was the case with this apple as well. The trunk above the first branch, about 8 feet up, was a lot more interesting, and had an attractive, ready made branch structure as well. Considering the ordeal of collecting this apple, it might have been just as easy for me to try air layering the top! Anyway, it was decided that this tree, and a few others that my friends and I had staked out, were going to get dug. Among the friends in question was David Rowe, who is now the Editor of the Journal of the American Bonsai Society. David lived in Ontario then and had discovered an abandoned growing field of a local nursery. He got permission for all of us to dig whatever we wanted. He is also the one who assured us that "digging them would be a piece of cake; they are all growing in sand. Just bring a shovel." So arrangements were made to dig our trees in early spring of 1992.

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Eastern White Cedar - Pinching Technique

By Greg Cloyd, with Bruce Baker

At a recent advanced study group meeting, eastern white cedar, or arborvitae, (Thuja occidentalis) pruning, foliage plane maintenance, and pinching practices were discussed.

Thuja occidentalis is a fragrant, evergreen, false cedar of northern North America. It is differentiated from its western cousin (Thuja orientalis) by its smaller size, prominent resin glands, slight differences in cone morphology, and its un-winged seeds. It grows as a telephone-pole-straight tree of moderate height in its southern range. Farther north, in Canada, it is a twisted and contorted, wind- and snow-tortured, deer-browsed, small tree of bog and limestone lakeshore. Along the Niagara escarpment and in Quebec it is a cliff-dwelling ancient dwarf growing less than an inch in radius per century.


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