I have standard form of Japanese maple. Three years ago I saw my cat using it as scratching post, to my horror . I have since put wire cage around trunk, however there are more and more brown leaves and dead branches thinning tree. I noticed there is damaged and dried gap where graft was made where rain water can collect and bugs could get in. How can I repair this hole to keep my tree alive?
Finding damage or injury to a prized plant is always difficult and very upsetting. It is hard to tell from your description how old the wound is, how deep it goes or exactly what might have caused it, so it may be tough to tell you how to repair it.
Japanese Maple (Acer palmatum) is a thin barked tree and is highly susceptible to problems including sunscald. If the hole or dead patch is on the south or southwest side, it is likely due to the sudden changes in temperature caused by exposure to strong sunlight. This happens in summer during dry periods of intense heat and also in winter when days may be warm and nights quite cold, much like the weather we have witnessed over the past couple of years. To avoid sunscald maples need to be planted where they receive morning sun and afternoon shade or dappled light all day. Once the bark is injured, there is little that you can do if the wound is deep and the tree’s cambium (vascular tissue) has been seriously impacted.
According to the University of Florida IFAS Extension, Japanese maple trees are also susceptible to scorch disease (light brown and dead areas of leaves) caused by hot temperatures, wind, poor root health and lack of water. To protect your tree from scorch you should provide ample shade and irrigation during dry spells.
It is possible that applying a grafting wax to the damaged area to seal it from the elements and prevent mold might be a possible solution but advisable to know what is causing the problem before treating it. I suggest calling a reputable arborist might be the best plan.
Here is a site with valuable information on Japanese Maples.
Good luck with your maple.