Hello, I have had a bonsai tree for three years. It is called a Chinese Buddhist Pine, or Japanese Yew. For the past several weeks I have noticed leaves that have brown segments, get very brittle, then drop off. Under my microscope I see that the underside of the leaves have “crystals” all over them, the occasional brown lump (that looks like it may be the entry for the insects) and possibly a few very tiny cream colored eggs. Do you have any suggestions for what I can use to rid the bonsai of this problem? I see no actual insects. (By the way, my Christmas cactus also has leaves that are drying up and dropping off.)
Thank you very much for your assistance.
So sorry to hear that your Chinese Buddhist Pine, or Japanese Yew (Podocarpus macrophyllus) is not doing well.
Based on the information you have provided it may be that your tree has scale which is a sucking insect common to Japanese Yew . While there are literally thousands of species of scale with many different shapes and colours it sounds like the brown lumps could be the hard-shelled scale exterior and the crystals may be the honeydew or by-product of their feeding on the plant. Their infestations do cause leaves to yellow and fall as you describe.
If the infestation is not too far along the plant can be saved but it will take some care on your part. First, cut off any heavily infested branches or where leaves are dropping. If your plant has just a few scale you might be able to pinch them off with your fingernail. Then spray with water to wash them off. Keep a close eye on the plant and pick off new scale as they appear.
Another option is to use an organic mineral oil to coat and kill the scale although this is best done when the plant is dormant. The simple process for applying oils is described in this excellent piece on bonsai scale. https://kitsunebonsai.blogspot.ca/2009/07/closer-look-bonsai-pests-scale.html
Once your tree is pest-free the trick will be prevention and early intervention if the scale comes back. Keep good air circulation around the plant, water well but keep the drainage good and use only slow-release, low-nitrogen fertilizer. Make sure to keep the interior of the tree open enough to allow light and air to penetrate.
While scale is a common pest of Christmas Cactus (Schlumbergera) it is usually a soft-sided scale and more attracted to the roots, which may not be the same as the scale on the Yew. Please feel free to submit an additional inquiry with more detail about the condition of the Christmas Cactus.