Treated oak wilt pruning

[Brando CalPankian]

I got a question regarding oak wilt treatment that I had no answer for.

If I treat someone's oaks for oak wilt, can I prune them during peak transmission time?

My knee jerk reaction was no, as it isn't fool proof. But, shouldn't it protect regardless?

 

[The Green One]

Brando,

Give this a read. https://extension.psu.edu/stay-alert-for-oak-wilt

"Insects are responsible for spreading oak wilt over slightly longer distances, roughly within a mile of an infected tree, particularly sap beetles (Nitidulidae) and to a lesser extent, oak bark beetles (Curculionidae). These insects are particularly attracted to fresh wounds – they can arrive at a fresh wound within 10-15 minutes! Wounds must be less than 72 hours old in order for oak wilt transmission to occur."

I personally would not wound during the peak season (Red Oak Group)

Perhaps some have more "experience/trial and error" with this, and use a dressing like Lac Balsam directly after each cut.

Would love to hear some real world "feedback" on this topic too.

 

[Tom Dunlap]

For a few years I worked with Dr. Jenny Juzwick on her oak wilt research.

She used to work out of a USFS lab on the U of Mn St Paul campus. Google her...

Ask her or maybe @KTSmith might chime in

 

[Brando CalPankian]

Brando,

Give this a read. https://extension.psu.edu/stay-alert-for-oak-wilt

"Insects are responsible for spreading oak wilt over slightly longer distances, roughly within a mile of an infected tree, particularly sap beetles (Nitidulidae) and to a lesser extent, oak bark beetles (Curculionidae). These insects are particularly attracted to fresh wounds – they can arrive at a fresh wound within 10-15 minutes! Wounds must be less than 72 hours old in order for oak wilt transmission to occur."

I personally would not wound during the peak season (Red Oak Group)

Perhaps some have more "experience/trial and error" with this, and use a dressing like Lac Balsam directly after each cut.

Would love to hear some real world "feedback" on this topic too.

This is the research I had in mind when I said no. Deliberately introducing the risk of transmission is logically an inappropriate risk to take.

But it's a bit like having An "immunity" to the pathogen. If I have an immunity, am I worried about getting it? I'm not worried about getting smallpox...

Most of this conversation came from a client wanting treatment and a crown clean as well, very little exposed sapwood in the pruning objective.

Still, when climbing the risk of damaging bark and encouraging sap beetles is there.

@Tom Dunlap I'll check out her research. I want to reach out to my local DNR Forester about it as well. It's a valid question from a thinking customer, my favorite kind.

 

[Tom Dunlap]

But it's a bit like having An "immunity" to the pathogen. If I have an immunity, am I worried about getting it? I'm not worried about getting smallpox.

Be careful about crossing biology and botany.

Unless there were an imminent high safety risk I would never prune outside of the DNR accepted dates.

I think that you'd be in an indefensible position if the tree were to get infected.

 

[ATH]

Is there a reason you can't push that pruning for at least 6 weeks? We flat out say "no" to Oak pruning until October... But even if you could get into mid-August you are a lot safer than right now... In every passing week gets better and better.

 

[Brando CalPankian]

Is there a reason you can't push that pruning for at least 6 weeks? We flat out say "no" to Oak pruning until October... But even if you could get into mid-August you are a lot safer than right now... In every passing week gets better and better.

Oh absolutely. That's what I said. This is strictly an inquisitive question.

I told the client no but that I didn't have any other information.

I have a ton of work scheduled for fall, precisely because of this point.

I wanted to see if there WAS a study regarding efficacy of pruning post treatment and transmission rates.

I didn't know if we'd progressed enough yet research wise to see the outcomes. It would make sense that treated trees are safe (not promoting this, thinking aloud). It's treated, it should be resistant to infection though overland transmission.

 

[Brando CalPankian]

Be careful about crossing biology and botany.

Unless there were an imminent high safety risk I would never prune outside of the DNR accepted dates.

I think that you'd be in an indefensible position if the tree were to get infected.

Definitely not going to prune right now. Just want to know if there's been a study on this topic.

 

[Brando CalPankian]

I'm not one to say "no because they said so" without having tangible statistics to back it up. I also don't like to waffle on an opinion, so I start searching. My searches didn't turn up much, so now I'm reaching out to universities, DNR, and y'all (my favorite source) to see what they have to say.

 

[Rusticus]

Because oak wilt treatments don't make a tree immune; they're still able to be infected by normal means and pass along the wilt through root grafts. Treatments just suppress that tree's symptoms. I get the reasoning behind the question if it's a therapeutic treatment, but with a preventative treatment, unnecessary pruning would just roll another dice in whether or not it may contract or persevere through the disease.

 

[Brando CalPankian]

Because oak wilt treatments don't make a tree immune; they're still able to be infected by normal means and pass along the wilt through root grafts. Treatments just suppress that tree's symptoms. I get the reasoning behind the question if it's a therapeutic treatment, but with a preventative treatment, unnecessary pruning would just roll another dice in whether or not it may contract or persevere through the disease.

If the tree already has it (white, bur), then it shouldn't make a difference (therapeutic).
Red oaks can't be treated therapeutically, but it is extremely effective at preventing infection...
It'd be interesting to see if there's been a study on this in particular.

 

[Brando CalPankian]

From Dr. Jenny Juzwick



Hi Brandon,

You asked a good question: If trees are injected with propiconizole for preventative purposes, then why wouldn't arborists "be able to perform pruning operations post propiconazole injection?"

I do not know of any research that addressed that question directly. However, one field research project conducted by one of my former grad students (Ryan Blaedow, 2004 - 2007) as part of his PhD program does shed some light on what is happening post PPZL injection. A couple of his key findings and my experience defining periods of different levels of risk give me some support for my bottom-line response.
* PPZL does not eradicate the oak wilt pathogen (B. fagacearum or Bf) within a tree if it is already infected. Rather, it suppresses disease progression (Ryan has an article in Tree Clippings -- fall 2010).
* PPZL is a growth regulator, as well as a fungistat.
* PPZL injected trees produce small diameter springwood vessels for at least 2 years following treatment. Small diameter vessels are part of the reason white oaks exhibit tolerance of oak wilt compared to high susceptibility to the disease. [One unpublished chapter in Ryan's PhD thesis presents this story quite clearly.]
* Thus, PPZL treatment would reduce the chance of disease development if a freshly pruned wound is visited by Bf-contaminated nitidulid beetles. The chemical may also have some fungicidal effect (i.e., kill) on propagules that are deposited on wound surfaces.
* In general, the risk of infection between mid-July and the end of October in Minnesota is "low" for overland transmission of Bf by these beetles (see 2015 U of MN Extension bulletin on oak wilt -- available on-line). In contrast, the risk for OW development in red oaks following beetle visitation of fresh wounds is highest in April through mid-July, partly because of large diameter springwood vessels found during that time period.

My bottom-line points: 1) a Yes, theoretically PPZL may indeed prevent Bf propagule germination or spread within a tree during the "low risk" period of the year in which injection was done. The following year, however, the PPZL levels (in ppm) in above portions of the tree will have dropped due to degradation (primarily due to higher temps) by the following spring. [Nancy Osterbauer M.Sc. thesis work & published in ISA journal] showed 18 months is maximum length of time PPZL was detectable in above ground portions of the tree. In other words, the residual concentration may or may not be sufficient to kill the pathogen in pruned branches. Furthermore, the springwood vessels would have been mostly laid down by the time injection is done in late spring or early summer -- their diameter has already been "set" for the growing season
2) So, it would not be totally unreasonable to prune PPZL treated trees during the low risk period following injection treatment in late May through end of June. Seems like it comes down to the customer's risk tolerance.

Hope you find the above helpful!

 

[Brando CalPankian]

I'll find time to dig up her referenced publications as well. The modality of PPZL seems to be an enigma. It's not a sterilant, but because of that it MAY be effective in this scenario, but mostly in the first year.

Is this something I could test on container grown red oaks to eliminate below ground spread and inoculation? I'd like to start testing this theory.

 

[Basswood]

Way too much room for error with macro injections alone would stop me from doing this. From applicator error to the tree itself causing inconsistent distribution of product.

 

[Brando CalPankian]

Way too much room for error with macro injections alone would stop me from doing this. From applicator error to the tree itself causing inconsistent distribution of product.

Without more research, yes.