Sudden Leaf Loss in Japanese Maple - Ask Extension
We have a mature Japanese Maple in our backyard that is about ten feet high by 15 feet wide. For the last six years seven years, it has lost the maj...
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Sudden Leaf Loss in Japanese Maple #710794
Asked August 07, 2020, 7:13 PM EDT
We have a mature Japanese Maple in our backyard that is about ten feet high by 15 feet wide. For the last six years seven years, it has lost the majority of it's leaves mid to late in July. In years past when this excessive leaf drop occurs, new leaves will grow back before fall. For example this last week, it had all of it's leaves on a Monday before we left town. When we arrived home Saturday, about 80% of the leaves had turned brown, dried up and dropped. The only remaining leaves are those on the furthest ends of the branches. The maple grows under a very large cherry tree (taller than our house) and receives filtered sunlight. I water with a slow stream of water every week. I do not regularly fertilize the tree.
I have tried to research this issue, and I keep drawing a blank. I do not believe that this can be Verticillium wilt as the leaves of the tree grow back during the season and then proceed with a normal fall drop and spring regrowth. And since it is irrigated regularly, I can't see that it is a drought issue. The ferns, hostas and hydrangeas under and nearby are all thriving. Do you have any suggestions as to what is causing this severe leaf drop? I imagine that this is a stressful cycle for the tree, as well as a pitiful specimen to look at in the garden for some weeks.
I have tried to research this issue, and I keep drawing a blank. I do not believe that this can be Verticillium wilt as the leaves of the tree grow back during the season and then proceed with a normal fall drop and spring regrowth. And since it is irrigated regularly, I can't see that it is a drought issue. The ferns, hostas and hydrangeas under and nearby are all thriving. Do you have any suggestions as to what is causing this severe leaf drop? I imagine that this is a stressful cycle for the tree, as well as a pitiful specimen to look at in the garden for some weeks.
Multnomah County Oregon
Expert Response
Thank you for your question. It would be helpful to have photos of the tree, as well as the leaves before they brown and drop, as well as mid-leaf color change. How many plants are under it? Have you mulched the soil out to the extent of the leaf canopy? It really sounds as if your tree is getting too little water in this drought. Japanese maples have shallow, fibrous root systems. Planting ferns and hostas--both with deep root systems that suck up a lot of available moisture--is depriving the maple of water, and it's competing with the cherry tree and the hydrangeas.
I suggest that you put a soaker hose around it, remove ferns and hostas this fall, and purchase an inexpensive water meter so you know whether and when the soil is dry at 6 inches. And apply mulch (larger is better) and/or leave the leaves in the fall, since they both hold in moisture and provide nutrients as they decompose. Good luck!
The tree is well mulched. I do have a moisture meter and will check the level in different areas around the tree. As the tree had not shown these symptoms for the first five or so years we have lived here, I had not considered that it could be a watering issue. I water the area twice a week in the heat of summer. I am including some photos of the tree. One is of the entire tree, some of the leaves that are remaining but are browning and then a final pic of the greener leaves at the end of the branches. I do not have pictures of the leaves prior to drop as we were out of town when it happened. In previous summers, the turning and dropping happens so fast that it’s quite remarkable to see.
Thank you again for your assistance.
Thank you again for your assistance.
Thank you for the photos. The browning at the tips of the leaves is a textbook watering issue. The mottled leaves appear to have a viral or nutrient issue that our diagnostic handbook doesn't list. I have referred it to our diagnostic group to get input, and I will get back to you once I get feedback. One other question: it is difficult to see from the first photo whether the tree exhibits exfoliation from generalized areas of the tree or from distinct branches. As you appear to know about verticillium wilt, flagging (loss of foliage on branch after branch) is common. Last thing: are any branches clearly so dead that you can dissect them to see if the internal vascular system is dark, rather than the normal light color? Thanks!
Yes, I had a difficult time getting a photo that would show the overall tree well enough. The leaf loss is throughout the entire canopy. It is not limited to only a few branches. There were three, very small, twigs that were entirely dead. But the rest of the limbs have good movement to them. I did trim off one branch a couple of days ago and scraped off some of the bark to examine the interior. It looked healthy. No signs of streaking green or brown.
Thank you for the input about the irrigation needs. I will work to water the tree more sufficiently and keep a better look at how well the soil is holding moisture in following seasons.
The discoloration/mottling of the leaves is new. This spring they were a vibrant, solid green.
While I'm waiting for some input, here is the diagnostic page for maple tree diseases in the PNW that you can read: https://pnwhandbooks.org/plantdisease/host-and-disease-descriptions?title=maple
I can find none with this pattern, but will continue to search.
I can find none with this pattern, but will continue to search.
Our state pathologist suspects a nutrient deficiency, probably nitrogen. He thinks viral infection would show opposite coloration. He believes the reappearance of foliage means nutrients were again available. Your competing plants are probably using up available water as well as nutrients. Large trees planted too closely, so competition for sun, water and nutrients. Best we can offer.
Thank you for digging into this tree problem that has been plaguing me for the last few years! I had been stumped. I will look at moving the understory plantings this fall, but there is not much I can do about the larger tree/shrub plantings nearby. So I will make a better attempt at watering in the summer months. I will also look into having a soil test done to determine if there is a nutrient deficiency as well.
Thank you again. I really appreciate your help.
You're welcome. A reliable local lab is this one: http://www.al-labs-west.com/
Be sure to pay a few extra shekels for recommendations based on the plants you have there.
