Re: What makes holes in walnut trees?

David E. Ross <nobody@nowhere.invalid> wrote:

On 7/10/2025 10:48 PM, Michael Uplawski wrote:

bp@www.zefox.net wrote in rec.gardens:

>
http://www.zefox.net/~bp/walnut/

 
        [snipped]
 

Anyway. No chemical product exists which could act against an
ongoing infestation. Usually you have to get rid of the beetle.

 
        [more snipped]
 
There are actually two chemical methods of eliminating borers in trees.
 
One involves a drench of Imidacloprid.  The amount depends on the
diameter of the trunk at the height of your chest.  The drench is
applied in the root zone.  DO NOT use Imidacloprid while the tree or any
adjacent plant is blooming because it is very harmful to bees.  On the
other hand, it is harmless to birds and mammals; thus, nuts from the
tree would still be edible.
 

Last I heard imidocloprid has been banned in California as of this
year (or thereabouts), at least for retail sale.

The other involves a small plastic capsule containing a systemic poison.
 I don't remember the name of the poison or the brand name of the

Perhaps AceCap? It's banned in California also.
https://www.amleo.com/acecap-systemic-insecticide-tree-implants-50-pack/p/AC450
The capsules seem rather large, 3/8" (10 mm), so using them will do some
appreciable damage. The holes looked small, less than 2 mm.

I tried probing the holes with a wire, it went in, seemingly straight,
about 9 or 10 millimeters and stopped firmly. If there was an egg at
the bottom, now it's an omelete 8-) I'll certainly keep an eye out for
more damage.

Searching via https://ipm.ucanr.edu/#gsc.tab=0&gsc.q=walnut%20borers&gsc.sort=
turned up three candidates, flathead borer, shothole borer and twig beetles.
My best guess is shothole or flathead borer. All are commercial pests in
California walnut groves and apparently the usual remedy is cultural: Keep
trees healthy, remove damaged wood and sterilize the debris. The bugs are
here to stay amd a chemical warfare stalemate isn't very attractive, at
least not for an ornamental tree.

Out of seven trees in my walnut hedge only this one seems affected. Perhaps
significantly, it also has the smoothest and likely thinnest bark. If one
tree is lost out of the seven that's acceptable attrition. Four trees,
evenly spaced, would provide ample shade when the city trees (Pistacia
chinensis) come out, and I could be dead by then 8-)

Thanks for everybody's attention and thoughts!

bob prohaska