Flat Headed Fir Borer

[Tree Lady]

I have three customers with infested mature Douglas fir. They seem to be only in the limbs so far. I dead-wooded them in the summer and now they have 3-8 more dead limbs each. I think cutting the dead limbs in early winter might get rid of some/most of the pupae.
I'd like to inject a systemic insecticide.
Any ideas or advice?

 

[evo]

I have three customers with infested mature Douglas fir. They seem to be only in the limbs so far. I dead-wooded them in the summer and now they have 3-8 more dead limbs each. I think cutting the dead limbs in early winter might get rid of some/most of the pupae.
I'd like to inject a systemic insecticide.
Any ideas or advice?

Are they in the collar? Sounds like your on the right track

 

[Tree Lady]

Are they in the collar?

Branch collar? No.

 

[evo]

Branch collar? No.

That’s good, sanitation pruning of any limbs that look off in the winter could be very helpful. As far as chemicals I’m unsure of how effective uptake is in Doug, but likely trunk injections of systemics.

 

[Brando CalPankian]

How high up are they infesting??? Are they mature trees??

 

[Tree Lady]

How high up are they infesting??? Are they mature trees??

Scattered through out. Very mature.

 

[Brando CalPankian]

Is it a wooded area? There could be more cultural issues happening that are influencing their populations.

 

[evo]

Scattered through out. Very mature.

Often flathead borers come in waves. A population can bloom much like a rot pocket in a stand (and can be result of a rot pocket). Taking over a few stressed trees building population levels where they can start overcoming healthy trees. Thus chemical injections might not do much overall good, and would likely need to be reapplied.
Maybe trying to figure out what stage the borer infestation is at could be a good place to start. What is the near by stressor that the bugs took advantage of? Can that be corrected, which might include removal of the stressed trees?
Chipping is effective at breaking down the wood to small enough sizes, but if left on site can attract more. Look into bait trees. Basically picking a sacrificial tree, wounding or partly girdling it making a feast for the bugs, then mid winter removing the tree off site.

 

[evo]

Is it a wooded area? There could be more cultural issues happening that are influencing their populations.

Beat me to my follow up thoughts. Been on the road, so fragmented replies.

 

[Tree Lady]

These are yard trees in different locations. They are each the only Doug fir in the yard. They are stressed. One is in a hotel parking lot, so paved all around with cars driving over. One is up against a house, has a driveway on one side and just had a septic system installed near it. One has sap suckers attacking it.

 

[Tree Lady]

Drought.

 

[Brando CalPankian]

Oof. That's going to be a tough one. Imidacloprid (like you were saying), soil test, and do what you can to improve conditions for the trees. Since they're mature they may not have the vigor to recover well. Keep us updated!