Help With Trunk Boring Insect

[USFishin]

I have some wood boring insects in my foxtail palm trunk. I noticed it a couple months ago and applied Imidacloprid twice (probably two weeks or so apart) to the soil. It seemed to have stopped them after a while. Only one small hole seemed to still be active. I just looked at the palm again today and they've now moved up to another area. I just applied some more Imidacloprid. Any help would be greatly appreciated. Hopefully I can kill the bugs off before they kill my palm.

[Merlyn]

3 hours ago, USFishin said:

I have some wood boring insects in my foxtail palm trunk. I noticed it a couple months ago and applied Imidacloprid twice (probably two weeks or so apart) to the soil. It seemed to have stopped them after a while. Only one small hole seemed to still be active. I just looked at the palm again today and they've now moved up to another area. I just applied some more Imidacloprid. Any help would be greatly appreciated. Hopefully I can kill the bugs off before they kill my palm.

That's really odd-looking.  Have you spotted any of the insects?  I was wondering if it was a woodpecker making "insect traps" so that they could come back later and feed on bugs attracted to the holes...?

[USFishin]

No, it's definitely little bugs. Here's some pics of the the area that they have left (and the holes left behind).

 

 

Edited June 11, 2022 by USFishin

[USFishin]

I saw one on the trunk and it went back in the hole as I got close. It was a little light brown bug. Here's a pic of a little spot on the trunk that the outer bark is coming loose. Behind it has what looks kind of like some of those bugs. Maybe larvae? Not sure.

[Merlyn]

Yeah that is definitely not a woodpecker.  They leave kind of ragged holes about 0.5" diameter around here, but usually pick oaks to make "insect traps."  The "weeping trunk" looks superficially like a Thielaviopsis infection, but I don't know that it's caused by bugs.  If the trunk is squishy in that area then it might be Thielaviopsis, which is an incurable infection that could cause the trunk to spontaneously collapse.  So I'd definitely poke around there with your finger and make sure it is still solid.  If it is soft and mushy then the trunk is compromised and may be a safety hazard.  It *might* be that the bugs are a symptom of the disease (Thielaviopsis trunk rot) and are not the cause.

If it is firm all around that area it might just be an opportunistic bunch of bugs.  I'd probably mix up some Acephate or Malathion into a squirt bottle and inject some into each bore hole.  The systemic should work, but it might take a while to filter up through the area and kill off the bugs.  Those two organophosphates should kill off any beetles and larvae. 

[USFishin]

It's definitely bugs because the trunk is still solid. I have some bifenthrin. Would that work or the organophosphates you mentioned would be better? The weeping bumps of mush are from the bugs boring holes and pushing trunk material back out of the holes.

[Merlyn]

Bifenthrin is a good pyrethroid quick bug killer, I'd think it would work and it's got residual effectiveness too.  It's kind of a guess, since we aren't really sure what kind of bug it is.  I think Bifenthrin is good against beetles, maybe look it up online and see if it is listed against your best guess of the type of bug.  I'm just assuming it's some kind of small beetle.  It's definitely not the dreaded RPW (Red Palm Weevil) because those are big. 

With the open wounds, I would periodically inspect it for Thielaviopsis by just giving it a poke.  If it stays solid and you can get rid of the beetles/weevils then it has a good chance longterm.  A surface fungicide (Daconil, Mancozeb, sulfur powder) might help prevent a future infection.  Likewise a systemic fungicide (Banrot, Alliette, etc) might also help prevent followup fungal infections.  Here's the UFL info sheet on Thielaviopsis, just for reference:

https://edis.ifas.ufl.edu/publication/PP143

[USFishin]

Thank you for all the help. I'll give the bifenthrin a try and hopefully that will kill them off.

[Looking Glass]

If it’s not Theilaviopsis, (and it does share, the weeping characteristics except for the tiny holes) then you’d probably be thinking ambrosia beetles / bark / boring beetles.  Since they are under the bark, topical treatments likely will have limited effectiveness but could prevent future attacks They also tend to infect sick, stressed trees so the problem could be multi-factorial.  

Peel a little bit of that bark and see if you can collect some beetles or larva or find sawdust or frass.  
 

https://ufdcimages.uflib.ufl.edu/IR/00/00/42/56/00001/MG00700.pdf

 

 

[Merlyn]

@Looking Glass yep that sure looks like it!  I had never heard of the ambrosia beetle before, fortunately it looks like pyrethroid sprays are a recommended treatment.  I read it needs to be repeated every 2 to 3 weeks since it washes off and might not kill the larvae after they hatch.  I guess this was my new thing to learn for the day... 

[USFishin]

That Ambrosia Beetle is definitely what I have. The holes, little toothpicks that stick out, etc all match the description. I read Imidicloprid doesn't kill them because they don't actually eat the tree so they won't eat the Imidicloprid. They create and eat a fungus. Bifenthrin is supposedly good at preventing the beetles from attacking a tree but won't help much if a tree is already being attacked. I have nothing to lose so I'm going to give it a try anyways. Unfortunately it sounds like I might lose the tree eventually.

[Looking Glass]

34 minutes ago, USFishin said:

That Ambrosia Beetle is definitely what I have. The holes, little toothpicks that stick out, etc all match the description. I read Imidicloprid doesn't kill them because they don't actually eat the tree so they won't eat the Imidicloprid. They create and eat a fungus. Bifenthrin is supposedly good at preventing the beetles from attacking a tree but won't help much if a tree is already being attacked. I have nothing to lose so I'm going to give it a try anyways. Unfortunately it sounds like I might lose the tree eventually.

A couple of sources/studies have said that Permethrin was longer lasting (4 weeks) than Bifenthrin (10-14 days) for attack prevention.   This is odd to me, because Permethrin is normally considered less long-acting than Bifenthrin for general insecticidal purposes outside the home like foundation-door-window spraying.    The beetles are attracted to ethanol in wood, which is considered a stress/injury marker in trees.  Which explains why they attack injured and sick trees more often.  You can actually make monitoring stations by hanging a piece of hardwood, that you drilled on top and poured EtOH into, from a rope and look for the holes and frass tubes to appear, though it's not that useful in the residential, non-treefarm setting.   

If using Bifenthrin you should probably treat topically every 10 days.  This would kill emerging females who come out, and arriving new females.        

By the way, that's a lot of moss and lichen on that tree's trunk.   Any chance it's getting hit excessively by lawn sprinklers causing an initial insult that drew in the beetles?....   Just wondering.   I know that palms in Hawaii are covered in moss from all the rain sometimes.   Is that a normal trunk finding for your area?   

https://www.researchgate.net/profile/Christopher-Ranger/publication/322024963_Residue_Age_and_Attack_Pressure_Influence_Efficacy_of_Insecticide_Treatments_Against_Ambrosia_Beetles_Coleoptera_Curculionidae/links/5c75b64e92851c695043ae03/Residue-Age-and-Attack-Pressure-Influence-Efficacy-of-Insecticide-Treatments-Against-Ambrosia-Beetles-Coleoptera-Curculionidae.pdf

Edited June 12, 2022 by Looking Glass

[USFishin]

Thanks for the detailed response. I have 3 foxtails about 10' from each other in a line that have been there for about 10 years. The've had the moss/lichen on them for a long time. Also, there's several queen palms on the property line of my yard and the neighbor's that have the same moss/lichen. I don't think the trunks in that area get a whole lot of sun since they're blocked from one side by an oak tree and the other side by the pool cage.

One of the three palms recently died during the winter a year ago. I thought it was a cold snap that killed it but the other two weren't affected that winter. I did notice that it seemed like the palm got killed from Ganoderma Butt Rot since it had a conch appear at the bottom. I did remove the conchs when I saw them but left the tree up for a while (didn't know any better). Hopefully the Ganoderma didn't move on to another palm. I fully removed the palm and stump. I just read that it's not recommended to replant another palm in the same location. Once again, a little too late. Hopefully this isn't another learning experience.]

[Merlyn]

Yeah the shade could definitely promote moss/lichen growth.  Foxtails aren't super-hardy, so if you went under 30F there's a chance of death.  Larger palms are typically hardier than small ones.  It might have been Ganoderma that killed it, or that the freeze damaged it and Ganoderma was an opportunistic infection that finished it off, or just the freeze.  There's probably no way to know for sure.  Ganoderma can stay in the ground for years, so it's a good idea to not plant another palm in the same spot.  That strain of Ganoderma doesn't attack other types of plants, so you could put an oak, maple, viburnum shrub, or most other plants in that spot without worrying about an infection.