What’s wrong with my Japanese maple tree?
In a 24 to 48 hour period, some of the leaves on my Japanese maple tree developed dry, brown patches. Leaves that fell to the ground were completely dried-up and crunchy. About 10% of the leaves on the tee were affected. The condition has not worsened since I first noticed the problem a couple of days ago. I am an organic gardener. I do not use any herbicides or pesticides. I have not applied any fertilizer or plant food to either the grass around the tree or to the tree itself in months. I do not see any signs of insect infestation on the tree. The attached photos show the condition of the leaves. Do you have any thoughts on what has/is happening?
Liz Stanley, Community Education Assistant, Horticulture
Your Japanese maple looks like ‘Bloodgood’, one of the most beautiful and hardy varieties.
Japanese maples are somewhat fragile trees, though York County is certainly more temperate than other parts of Maine. They benefit from being planted in a protected area in dappled sun with well-drained acid soil, rich in organic matter. If your tree is in a lawn area that’s been limed for good turf health (pH of around 6.5), the soil may be too alkaline. A soil test will tell you if this is the case.
The bark, stems and roots of Japanese maples are notoriously thin and delicate so the trees don’t take stress very well. Some stressors include: Swings in moisture and temperature, winter freeze and thaw cycles, winter sunburn on the trunk, the root flare being buried by soil or bark mulch, fertilizer burn, salt damage, overstimulation by late fertilizing or pruning (this keeps the tree from hardening off before winter), too much soil or mulch on top of the roots (which need oxygen) and leaf scorch during hot weather. My guess is that the tree was stressed after these record high temperatures, especially if it’s in full sun.
The worst-case scenario would be verticillium wilt. The only way to tell if this is the problem is to look at the tissue on dead branches. Here’s an article from Penn State about Verticillium Wilt of Woody Ornamentals.
Here’s a really nice article from UNH: How to Plant and Care for a Japanese Maple.
It’s too late to fertilize woody plants now, since it may keep the tree from slowly going to sleep before winter. Water gently and deeply once a week (depending on rainfall) and hopefully it will bounce back.