I live in La Selva Beach CA (near Santa Cruz) and have 4 Shin deshojo maples with what my landscape contractor believes to be powdery mildew. I have tried two different fungicides but the new red growth continues to be blighted and to die. The trees leafed out nicely but now the trees are slowly defoliating. I have the Vertrees book, which I have read and am concerned that the trees are untreatable. The trees are about 5 feet tall and are planted in the ground in openings in my brick patio. The openings are about 18 inches square. The trees grow almost entirely in the shade except for early mornings. I have other japanese maples growing successfully on my property but not in patio openings (numerous bloodgoods, oshio beni, harpstring, several sangos, seriyus). What can or should I do?
Can you post any pictures? Powdery mildew is normally a white or grayish film on the leaves present mainly during warm damp weather or hot and dry weather, it can be slowed or controlled using a fungicide such as Funginex (triforine) or Benomyl (benlate). When you say that the new red growth is blighted and dying it makes me think that powdery imldew is not the problem. I would guess you may have some issues with verticillium wilt or possibly anthracnose, which a picture would help the web-board users identify for you. With maples (and all plants really) it is essential that you sterilize your tools between work on plants, clean with a 10% bleach to water solution when moving from one tree to the other to help curb disease spread.
powdery mildew?? I appreciate your response. Only one image can be attached. The weather has been unusually warm here in Santa Cruz County this year. There is some white material on the the green leaves which I have been assuming is also mildew. The red leaves eventually turn brown/black and die.
Well, I would say the powdery mildew diagnosis definately looks correct. I would use a systemic fungicide (Benomyl) if possible, and I would prune a bit to encourage more air flow through the plant, if the plants are quite shaded consider getting them more light, maybe you could trim a larger tree that is shading them? Shindeshojo is my favorite japanese maple, I would hate to see someone lose one. The new growth color is outstanding.
benomyl or phyton 25 Thanks for the good news. After reading some messages in this forum, I ordered Phyton 25 (I think that is the number) from Minnesota. It has not yet arrived. Which fungicide would you pick of the two? Also, the trees get almost no sun...just in the early morning. They are shaded by my house so there are no overhanging trees. I can thin them out a bit and will do that. In the spring, they are absolutely spectacular...I don't want to lose them either.
