By: Tonya Barnett, (Author of FRESHCUTKY)
Hardy to USDA growing zones 5-8, Japanese maple trees (Acer palmatum) make beautiful additions to landscapes and in lawn plantings. With their unique and vibrant foliage, diversity, and ease of care, it is easy to see why growers gravitate towards these trees. Once established, Japanese maple plantings usually require little attention from homeowners, with the exception of a few common tree issues – tar spot on Japanese maples being one of these.
Known for their beautiful color changing foliage, growers may be understandably alarmed by the sudden change in appearance of the leaves of their maple trees. The sudden appearance of spots or other lesions may leave gardeners wondering what could possibly be wrong with their plants. Luckily, many foliar issues such as Japanese maple tar spots, can be easily identified and managed.
Tar spot of maples is fairly common and, like many other foliar issues in trees, spots on Japanese maple leaves are most often caused by various types of fungus. Initial signs of tar spot manifest as small pin-sized yellow dots on the surface of the tree’s leaves. As the growing season progresses, these spots become larger and begin to darken.
While the color and appearance of these spots is generally uniform, the size may vary slightly depending upon which fungi has caused the infection.
The presence of tar spots on Japanese maple trees is frustrating for growers due to their appearance, but the actual disease does not usually pose a significant threat to the trees. Beyond the cosmetic appearance, most incidences of leaf spot will not cause permanent damage to the tree. Due to this, treatment for a Japanese maple with tar spot is generally not required.
A variety of factors contribute to the spread and recurrence of this fungal infection. Some factors, such as weather, may be beyond the gardener’s control. However, there are some ways in which growers can work to prevent infection over several years. Most notably, proper garden sanitation will help reduce the spread of tar spot.
Overwintering in fallen leaves, the removal of leaf debris from the garden each fall will help to remove infected plant matter and encourage overall health of trees.
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You might want to consider planting a larger growing tree that will eventually provide some shade in the afternoon for the Japanese maple. To achieve this, the larger tree would need to be positioned to the west of the Japanese maple.
The heavier sun this year could very well have what lead to the fungus problem.
The best fungicide to use is Propiconazole. Here are two brands that contain this systemic fungicide.
Bonide Systemic Fungicide
Fertilome Liquid Systemic Fungicide
Your local independent garden center should have one of the two. You could call around to make sure before making a trip. You won't need to spray them until next year as the tree should be going dormant at this time. Best time to spray is next year when the temperature gets near about 80 degrees.
Let me know if you need any other questions answered.
Here's what the problem may be:
Botrytis blight, also called gray mold, sometimes affects red Japanese maple leaves. The fungal pathogens (Botrytis) thrive during wet weather conditions in spring and summer. Signs include brown spots appearing on the maple leaves. Some infected leaves develop silvery spore masses on dead tissue. Botrytis blight disease spreads by splashing water and wind gusts. Control includes pruning out and discarding affected leaves, improving air ventilation and applying fungicides.
With fall setting in the leaves are probably already dropping. Remove all infected leaves existing on the tree and from under and around the base of the Japanese Maple.
A fungicide should be applied next year, preferably a systemic fungicide that will absorb in to the plant. Some fungicides can damage the leaves of Japanese Maples. Make sure to read the label or get advice from a nurseryman to make sure you are getting a suitable product. It's best to find the right fungicide at a local independent garden center.
I have observed Red Japanese Maples that turn a little grayish looking on damaged foliage from too much sun, late freezing temperatures during the spring months, water scald, and insect damage. Water, sitting on Red Japanese Maple foliage while the sun is beaming on it, will scald and burn the foliage. Always water Japanese Maples at the base of the plant, and only during significant drought periods. If you use an overhead irrigation system water early in the morning just before the sun begins to rise. This will allow the foliage to dry before the sun can cause scalding.
To control tar spot, you need to rake up the affected leaves in the fall and destroy them. Some fungicides can also help, but because you have to apply them carefully and evenly, Cornell doesn’t recommend them as a first line of defense.
RIULHP recommends treating sooty mold in two steps: Control the insect infestation by applying an insecticidal soap or a stronger chemical remedy. Then blast the leaves of the maple tree with jets of water, to wash away the mold.
Japanese garden landscape need suggestions
Help! the leaves on my coral bark japanese maple look like this after
Need help with japanese maple bonsai
October Glory maple bare branches
The spring foliage on J. maples is pretty tender and easily damaged. This looks to me a bit like sun damage amplified by water drops remaining the leaves. Not serious - pretty much just a cosmetic issue. FWIW, this can happen just as easily on young J. maples planted in the ground although older, established trees tend to grow out of it.
There's no harm to growing your maple in a pot, but it does make them more susceptible to leaf spotting and drying out. You might consider repotting it in a larger container. It might just be running out of space for the roots, so it dries out quicker. It might also just be what gardengal mentioned -- spotting caused by water drops on leaves. One of my maples got leaf spotting real bad this spring, even though it's in a fairly shady location on my deck and it's a sun-tolerant variety (Emperor). I had just repotted it and moved it out of the shade too quickly. The leaves burned around the edges, but otherwise it's OK.
This looks like a disease to me. My daughbors japanese maple got it then her other tree beside it got it then my huge silver maple got it accross the street. This sucked and we put up with it for two years, finally she dug the thing up and got rid of it, this year everything is just fine so far. For some reason her tree had it bad.
Your maple has frog eye leaf spot. Caused by Phyllosticta minima. I had the same problem last year and did ALOT of research on finding out what it was and how to fix it. Bad news is this is a disease and not caused from too much sun. The good news is that this rarely does any damage to the tree, it's just ugly to look at. But since we all want beautiful trees, I had to find a way to get rid of this. The consensus everywhere I looked, was to make sure come fall you clean up all dropped leaves and dispose of them so the disease doesn't come back. Chemical treatment is rarely needed. I cleaned up my debris last fall, and so far this year, I do have it on a couple of my maples, but it is far less than last year, so I feel like I'm getting some where with it. Good luck to you!
Thanks for the info, guys. Guess I'll keep an eye on this one. Would this small tree be benefitted by my removing the spotted leaves, in case they're fungal?
If it's just a few leaves, I would cut them off, but if it's alot, I wouldn't defoliate the whole tree. You can defoliate a tree completely in the summer, believe it or not, and get a whole new flush of growth by the end of the season. This is often done in bonsai, but cannot be done back to back seasons. I have a very young Hogyoku that had the leaf spot on every leaf this time last year. I defoliated it in August, and the tree has responded great. Here are some pics of the transformation in just one year. The tree has really taken off this year and if you look closely at todays pic, I only have about 5 leaves with the spot as opposed to the entire tree last year. I'm going to cut these off shortly.
Hogyoku April 2004 -- Was covered in spots a month later
Hogyoku Oct 5th after complete defoliation in August