Mature bark is falling off - symptom of borers?

Mature bark has been peeling off several of my trees - the most concerning are a black pine and a larch. The larch has lost almost all of its flaky bark on its trunk and the black pine has lost all of it on the bottom few inches of the tree. I have found what looks like the remains of small cocoons

on several of the bark pieces.

The larch does not show any signs of sap leakage or other holes in the trunk. And, for now at least, seems healthy and growing vigorously. The black pine is showing white residue that appears to be dried sap but I don’t see any holes in the trunk. The new growth is strong but older needles are yellowing.

I also have a cork bark pine that is showing the same white residue and is actively leaking sap from one of the smaller branches. I’ve inspected with a magnifying glass and don’t see any obvious infestations - an occasional spider, some fungus gnats.

My fear is that this is the early signs of borers but I don’t really know. Interested in any thoughts on causes or recommendations on an insecticide that might be broadly useful even in the absence of a specific identification.

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Hi Bill, welcome to the forum and the Mirai family. If it is borers you would normally see the waste from the borer mixed with resin. There is a film in the library on borer removal where Ryan shows how, and the tell tale signs. Sometimes bark simply fall off. Ryan uses Kyano to stick it back in place.

Thanks Keith-in-UK - I’ll give that a watch. Another video where Ryan took the bark off a juniper as a preventive for borers made a real impression on me too. I’m starting to lean away from the borer theory towards there might be two or even 3 issues going on. There’s maybe some bug that happens to like to make cocoons in tree bark and as it grows the fine bark of a bonsai pops off. It’s not eating the tree, it’s just creating mechanical damage. And the browning needles are due to a fungus infection. and maybe there is some low level of bug activity that I have tolerated but shouldn’t. I have decided to give the affected trees a spray with Bayer 3 in 1. I’d prefer to reach a definitive conclusion before spraying but I’m out of ideas.

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I have heard from Ryan that if the tree is growing extremely vigorously that it is possible to “make a old tree young again.” The sap leakage looks like pine pitch, the result of rapidly growing vascular tissue with sap production and movement. The expansion of the cambium combined with a nesting insect can result in shedding of mature bark. Thereby making the established bonsai appear young again. I would clean the nest off and apply liquid cut paste to it and re attach to the trunk. As stated earlier borers usually leave a trail of saw dust and sap. Keep an eye out, I wouldn’t apply any insecticide until you know for sure. Also, borers are largely unaffected by the applications of systemic insecticides.

I have a sandwich baggie half full of Ponderosa bark this summer. Some just falls off. My large ponderosa has half inch+ plates of bark.
Some might be from birds or squirrels. Have NOT seen any borers. Have seen some bug or spider cocoons.
Smaller amounts of J. Larch and other pine bark, too.
Not too concerned yet. Will freek out later.
I’ve looked for borers under juniper bark while removing it. None seen. I want to think the trees LOOK better without the bark…
Just fyi, large wild Ponderosa shed bark every year. Piles of it next to the trunk… Some an inch thick the size of your hand. Oh ya, Ponderosa shed cones big enough to really hurt… falling from 150+ feet.:confounded::grin: