Hi, My wife and I live in Deep Cove, North Saanich and have just had an issue with borers in a young Japanese Emperor Maple tree that we purchased 2 years ago. The tree was doing great and it started to leaf this year when it was hit with caterpillars that destroyed the initial flush of leaves very quickly and completely. We treated it with BTK and killed the caterpillars and were hoping that the tree would put forth another set of leaves. Unfortunately we then realized a week later that the tree had a large number of borer holes. The tree has since died (we scratched the surface and there was no green under the bark). We’re looking to replace the tree but are afraid of putting something in that will be susceptible to the same pest. We’re having a hard time identifying the pest which is why we're turning to you in the hope that we can identify it and hopefully put in a more appropriate tree. We’ve uploaded some photos of the bug and the holes in the tree: We have natural hedgerow up the side of the property and think the original caterpillars came from the hawthornes in there. We have another maple on the other side of the property (Bloodgood) that seems to have escaped unscathed. Thanks for any insights you can offer! The Japanese maple was a memorial tree so it’s important we come up with a nice long term alternative.
I have meant to respond sooner, but didn't remember/ get a chance until now. Sorry for the late reply. Bores are not very common in Japanese maples. This type of bore attacks weak trees while leaving healthy trees alone. More information on bores: https://web.viu.ca/corrin/frst352/New_Folder/Wood Borers.htm Since this tree was getting established, then defoliated, it opened it up to an attack, being in a weak state, and at times bores invade after the tree has failed. Other things in the trees past may have contributed to the weak state like drought, lack of a water schedule during the first year, or even lawn chemicals like weed and feed, crabgrass preventer, round up (all compromise the trees immune system as levels build up in the tree over seasons of use). As far as a recommendation I have found Acer palmatum 'Trompenburg' and Acer shirasawanum 'Palmatifolium' to be very trouble free trees.
Hi JT, Thanks so much for the feedback, we so appreciate it. That totally makes sense about it being a result of the weak state following the caterpillar defoliation. Thank you for the tree recommendations, that's wonderful :)
Bores are not very common in Japanese maples. This type of bore attacks weak trees The word is borer of course, and not "bore". I mention this because the use of "bore" in place of borer seems to be gaining traction, yet remains incorrect. As do the use of "Hellebore" in place of Helleborus - as in "Hellebore niger" - or "Peony" instead of Paeonia - as in "Peony lactiflora" - that I have been hearing in later years. And cringing at.
Bores are very common in the maple world. I count myself among them, and almost everyone agrees. When I give a garden tour here I ask visitors to pick a boring level between 1-5. 5 is very boring and takes about 6 hours. Only bores like myself want a 5.
I have heared, that the Asian long-horned beetle (Anoplophora glabripennis) is damaging maples in North America. This is an invasive species and should be regarded as dangerous pest. Consider informing proper authorities. Asian long-horned beetle - Wikipedia The bug on your pictures seem to be a member of the Cantharis family and is most possibly not related with the damage. Cantharis - Wikipedia
As owner of a garden that is controlled by the government annually -- used to be bi-annual -- for the Long-horned Beetle, I think I can reassure you. The internal pockets dug out by the larvae are much larger. This seems clear also from the wikipedia page. That's good, because the Asian Long-horned is really a disaster scenario, an requires burning all trees within IIRC a 500m radius.
It's good to mention ALB to raise awareness, but I didn't include, because the furthest pocket of outbreak to the west in North America is near Cincinnati Ohio (Clermont County, OH) Next would be Worcester, MA; then New York City and Long Island. I believe it's been found in Ontario, CA. The OP is in SW CA if my memory serves me. Anyway here is a PDF showing pockets of ALB on page 41 of PDF viewer or page 33 of publication. These areas are prone to spreading of course, but as already mentioned pictures don't indicate ALB Attached: Major Forest Insect and Disease Conditions in the United States PS I blame the bore borer on auto correct! I did like your joke about it and maples though..lol! I'm sure your garden tours are great! Otherwise come to one of ours for some tips. My wife says "all the ladies love you" when we give tours. I guess she is biased, but I did once put one old lady to sleep during a presentation at the Master Gardeners' Year End Awards Dinner (1 out of 75 isn't too bad; I blame the Turkey dinner!).
According to Asian longhorned beetle | Natural Resources Canada the exit hole of ALB has 6...14 mm diameter. So the size may vary a lot. One thing is for sure, the bug on the photos in the beginning of the thread is not the borer of those tunnels. Very good Canadian publication about ALB: Canadian Forest Service Publications | Natural Resources Canada
The tunnel looks large in the first photo because the saw cut was running along the top of the tunnel, making it appear larger. Vertical holes show the true size, where as cuts along tunnels running horizontal or at diagonal appear larger.
I suspect, that the creator of this thread is not an enthomologist, and those cuts and photos are random, not scientifically the best selection to identify the pest. As much as I understand, the ALB makes different kind of tunnels into the timber. As suggested in the Canadian Forest Service's publication there are "look-alikes", but their exit holes should be less than 6 mm. My eye is not so good, to estimate without proper reference, if those exit holes on the photo are 6 mm or 5 mm. According to the publication, if those exit holes are 6mm or more, then it's ALB. Because one possible look-alike, the maple callus borer, makes exit holes, that are 3...4 mm in diameter, and the other, the gallmaking maple borer, has exit holes with 4...5 mm in diameter. And no other similar borer pest on maple! The Cantharis on those photos above was just attracted by the sugars, that left from the sap, that was oozing from damaged trunk. It was not guilty in those timber damages.
So you are an entomologist? You are an expert in ALB? You know enough about it that the original creator of the thread should "alert the authorities" based on your expert opinion?
No, I am not an entomologist, but I am a forester and studied entomology in the university (the ALB was not a problem then, yet, so I haven't studied the ALB). I can not say for sure, that this is ALB, but I tried to give to the initiator of this thread an idea, what to look to determine if this pest is ALB. And maybe an idea, how to cut the trunk to find a pupal chamber etc.
Thanks for all the comments! I'm definitely not an entomologist and yes the cuts and photos were relatively random. I just tried to cut through where it would show the holes well :) I didn't think of adding scale to the photos - of course that makes a big difference. They are 2-3 mm exit holes. The bore/borer conversation is fabulous!
Another thing, both the ALB and the gall making maple borer have life cycle of 2 years typically (in the temperate zone, at least). As the maple was bought ca 2 years ago, then this tree might be infested already since then. No maple borer could have a life cycle so fast, that a maple tree, that got caterpillar damage this spring, weakened so much, that the borer came onto the tree as a secondary infestant, lay eggs, those developed into larvae, they bored feeding tunnels into the timber, finally puped and reached through full life cycle (exit holes on trunk) till June. Note, that on pictures some of the tunnels have darkened walls - this means, that they already got fungal infection, that also takes time. No way this borer infested the tree this spring! Were caterpillars, that are suspected in leaf damages, actually observed alt all? ALB-s eat leaves of those same trees, where they get hatched, after they exit from the trunk as young adults.
A flatheaded apple tree borer (Chrysobothris femorata) may also bore maples. Both the flatheaded apple tree borer and the maple callus borer have one year life cycle. Just take a measuring tape and check the diameter of the exit hole. This may easily rule out the ALB. A random cut through the feeding tunnel does not say much about the size of the pest. Larvae are usually very small, when they hatch. And the more they grow, the larger tunnel they dig.
This is all great information. Of the 128 species, we are talking about Acer palmatum. Much of the borer information applies to the North American species. It's my opinion that borer infestation is not the cause of death. It most likely happened after the tree was in decline. I know of several Acer palmatum in my area that are 50+ years old, with many of those being closer to 100, and none have suffered a borer attack. I don't want anyone to start to believe borer attacks are common, because they are not. ALB is a concern in some areas of the world, including some areas of North America. Acer palmatum is listed as a host tree, but it seems most documented deaths are of large species of Acer or the species native to N America and those grown as street trees. I would like to see more information on ALB attacks in Acer palmatum. Again, I know they are listed as a host tree, but I know of no documented cases. @emery do you know of any from your area? It's my hypothesis that Acer palmatum may be less likely attacked much like native N American species of Betula are prone to borer attack where as European and many cross species are not prone to attack. Many are afraid to grow birch trees in our area because of the common knowledge they are prone to borer attack. Some are so brain washed they look cross eyed when you tell them to plant European birch instead. In a forum setting, tone and intentions can be interpreted in a variety of ways. I do appreciate all the information on borer insects and the time and effort to share, it is valuable information. I am not trying to put a claim on who is right and who is wrong. I'm just trying to offer clarity that the pest and disease that one species is subject to does not always apply to all species of that genus.
