Hi Master Gardeners,
My beautiful, very loved, little Japanese maple tree (Acer palmatum) is in trouble and I don’t know what to do. We planted it 5 years ago and it has grown and thrived, but I have just noticed that its leaves have all turned brown and dry at the edge and are curling up. Interestingly, there is one branch with brand-new, bright red leaves, but the rest of the little tree is in a horrible state. The tree is planted in a north-facing bed, but at the east side of the bed, at the side of the house next to the garage. In the middle of the day, at least half of the tree gets direct sun. I have looked at the trunk and it looks healthy. I have looked for insects or insect damage and it does not have any. Thank you for your research.
Hi gardener, I am truly distressed to see a well-loved tree in such distress. Three Toronto Master Gardeners have now looked at your problem, and we believe that your tree has “leaf scorch”. Thank you for the clear photographs, details, and information on the location of your tree. These have helped us identify the problem. I have walked around my neighborhood and have noticed that a number of the Japanese maple trees are also showing similar problems. What is interesting, is that the trees with very feathery, laceleaf, leaves are expressing the problem way more than the leaves that are more like a palm of a hand.
The reasons for leaf scorch are environmental. This growing season in Toronto has seen an unprecedented amount of rain, high humidity, high temperatures, and high winds. Since your tree is on the edge of the bed and hence more exposed, it is suffering from these extreme temperatures and exposure to the direct sunlight. The other possible causes of leaf scorch can be that you are not watering your tree at its base adequately, and the leaves are exposed to drying water on the leaves. For very detailed instruction on how you should be watering your tree, please go to this website. Other possibilities are that perhaps the soil is not rich enough in organic matter (the heavy rains could have caused runoff of the soil), and because the tree is planted on the edge of the bed, that the wind has been causing the plant stress. For more information about leaf scorch, also take a look at this website.
The good news is that leaf scorch will not kill your tree. Next year is another year, and when your tree gets new leaves next spring it starts another season anew. But in the meanwhile, add rich organic matter (compost) to the soil (in a donut shape so that the compost does not touch the tree), make sure that you are giving your tree a good soaking (if it has not been raining), and watering at the base of the tree and not on the leaves, and if possible, try to set up a barrier at the edge of the bed to provide at least some wind and snow protection.
When it comes to identifying a problem with a plant, you have to be a bit of a detective, and go through a process of exclusion.
- Is the source of the problem environmental. Is the plant getting too much or too little light, cold damage from last winter or heat damage from a very hot wind, or getting too much or too little water? This has been a record-breaking wet July in Toronto, so we should be able to exclude underwatering, but is it possible that the tree is shaded from the rain, and hence is underwatered? What about the other environmental stressors?
- Is it a pest or a disease? Is there any insect damage or signs of insect droppings, bites, or eggs on the underside of the leaves?
- Could it be a fungal, bacterial or viral infection? Besides the brown curling, do the leaves show any black or red spots?
- Is it transplant shock (not likely in this case since your tree is already five years in your garden)?
- Is there any chance that there is a nutrient deficiency? Does the tree need more organic matter in the soil? The opposite of this problem, is whether you have been using the wrong, or too much, fertilizer. Fertilizing your tree is often a problem in itself and can cause shock, and should be avoided.
So depending upon the cause, you have some solutions available to you.
- If after looking at the tree’s location you determine that it has not received enough water, start soaking it at the roots, and encourage the new growth that you can see.
- If you find that an insect is the perpetrator, then getting rid of the insect is a path that you can take. We mostly recommend physically removing or squishing the eggs that you see and drowning the insects in a bucket of soapy water. Keep in mind that weak plants are attacked by insects. Strengthening the plant must be your priority. Ensure that it has the rich soil filled with micronutrients and organic matter that it needs and the plant will be able to fight off the insects.
- Looking at the pictures online of the different common diseases affecting Japanese Maples, none seem to fit well. Your leaves do not have any spots on them. The two most common scary options are Phytophthora Root Rot or Verticillium wilt (caused by six different fungi). We really hope that is not the issue, although they are common diseases of Japanese Maples. These diseases thrive when the tree has been soaking in water (if the tree is planted in a boggy area of your garden) for long periods of time, which I hope is not the issue. You said that the stem of the tree is looking healthy so hopefully we can exclude root rot.
- Is your plant suffering nutrient deficiency. A strong plant is a warrior and can fight off diseases and insects, but it can only do as well as the medium you have planted it in. This website has great pictures to help identify nutrient deficiency by looking at changes in the colouring of the leaves, but looking at the pictures, your tree does not have any particular nutrient deficiency. That being said, add compost and you will have a stronger tree.
So wishing you and your tree a good growing season. As this sweet post from the Durham Master Gardeners says, no one but you will come close enough to your tree to notice its leaf scorch, and it will still can continue to be a focal point of your garden.