Lethal Bronzing Study

[ahosey01]

Curious for anyone's speculation on what was going on here.  Study on LB performed in 2016 showing the following data:

439 palms tested, 158 showing symptoms of lethal bronzing.

Of the 158 showing symptoms of lethal bronzing, only 50 (less than 1/3rd) actually tested positive for the phytoplasma alleged to cause LB.

Of the 281 palms showing no symptoms of lethal bronzing, another 50 tested positive for the phytoplasma.

Maybe I'm just stupid but this leads me to believe that either a.) what we are calling 'lethal bronzing' is actually a disease complex, or b.) what we are calling 'lethal bronzing' is not definitively caused by the phytoplasma it is allegedly caused by.  This would also explain the futility in trying to treat symptomatic palms.

Link: https://apsjournals.apsnet.org/doi/10.1094/PHP-06-20-0046-S

Also, disclaimer: if you respond to this with some technical details regarding statistics or isolation of cell-wall-less bacteria, please do it in a way that educates your audience rather than leads them to believe you're an elitist prick who would talk down to them for their lack of understanding.

[Merlyn]

@ahosey01 the symptoms of LB are similar enough to other diseases like Thielaviopsis and Phytophthora crown rot.  It's easy enough to look at a Dactylifera or Sylvestris and say, "that's LB."  But a severe Magnesium deficiency or Thielaviopsis can cause premature browning of old fronds too.  So the visible effects might not be as easy to distinguish as I thought.  Two good examples of this are:

• A row of three Sylvestris a few miles from my house.  The middle died with LB symptoms, and I ppsted at the time that I thought it was LB.  Threeish years later the other two are still fine, albeit with some lower frond browning that might be LB, or Magnesium deficiency from never being fertilized.
• A cluster of about 8-10 Sylvestris on RT417 about 3 miles East of I4 on the North end have rapidly all died from apparent LB...except one.  The remaining survivor has a huge full crown draping nearly 10 feet to the ground, and no visible signs of any problems.  It was in the middle of the cluster.  If the leafhoppers are the main vector, it seems impossible for it to have avoided infection.  So was it LB that killed the others?  Is this one immune?  Dunno...  https://www.google.com/maps/@28.7991402,-81.3066149,3a,75y,231.28h,97.05t/data=!3m7!1e1!3m5!1sGlflK5QbDBmF7_HPMnb2Zg!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DGlflK5QbDBmF7_HPMnb2Zg%26cb_client%3Dmaps_sv.share%26w%3D900%26h%3D600%26yaw%3D231.2827366804659%26pitch%3D-7.04563857310994%26thumbfov%3D90!7i16384!8i8192?coh=205410&entry=ttu

I noted in the study that they did not test for other pathogens, or at least I didn't see it listed.  I can't explain why they would test just for LB and not see if the affected palms had some other disease too.  Maybe LB is the "gateway disease" for Thielaviopsis?

[flplantguy]

That doesn't make sense to me either.  There must be a missing peice that has not been discovered yet. Im not educated enough on it to have much more to say but it does sound odd to me.

[ahosey01]

9 hours ago, Merlyn said:

@ahosey01 the symptoms of LB are similar enough to other diseases like Thielaviopsis and Phytophthora crown rot.  It's easy enough to look at a Dactylifera or Sylvestris and say, "that's LB."  But a severe Magnesium deficiency or Thielaviopsis can cause premature browning of old fronds too.  So the visible effects might not be as easy to distinguish as I thought.  Two good examples of this are:

• A row of three Sylvestris a few miles from my house.  The middle died with LB symptoms, and I ppsted at the time that I thought it was LB.  Threeish years later the other two are still fine, albeit with some lower frond browning that might be LB, or Magnesium deficiency from never being fertilized.
• A cluster of about 8-10 Sylvestris on RT417 about 3 miles East of I4 on the North end have rapidly all died from apparent LB...except one.  The remaining survivor has a huge full crown draping nearly 10 feet to the ground, and no visible signs of any problems.  It was in the middle of the cluster.  If the leafhoppers are the main vector, it seems impossible for it to have avoided infection.  So was it LB that killed the others?  Is this one immune?  Dunno...  https://www.google.com/maps/@28.7991402,-81.3066149,3a,75y,231.28h,97.05t/data=!3m7!1e1!3m5!1sGlflK5QbDBmF7_HPMnb2Zg!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DGlflK5QbDBmF7_HPMnb2Zg%26cb_client%3Dmaps_sv.share%26w%3D900%26h%3D600%26yaw%3D231.2827366804659%26pitch%3D-7.04563857310994%26thumbfov%3D90!7i16384!8i8192?coh=205410&entry=ttu

I noted in the study that they did not test for other pathogens, or at least I didn't see it listed.  I can't explain why they would test just for LB and not see if the affected palms had some other disease too.  Maybe LB is the "gateway disease" for Thielaviopsis?

This is interesting to me for a different reason.  Back when it was called TPPD and it had primarily been seen only in Texas, the general consensus was that groups of palms did not contract the disease simultaneously.  Generally, it was understood that a group of palms might catch it - but the way this was done was through a slow process.  One would die, then the leafhoppers would have another egg cycle and look for a new host and another would die, and so on.  A whole cluster of palms dying at once would have been a red flag that the planting was not dealing with a TPPD infection.  That no longer seems to be the consensus opinion but I can't find any evidence that either is true or where opinion changed.

Mechanically, however, it does seem strange to me that an entire cluster would catch LB at one time.  The way lethal yellowing works (which is supposed to be an LB analog, just a different phytoplasma) is that two hosts must be present - i.e. St. Augustine and a Coconut palm.  Then what happens is the leafhoppers lay their eggs at the base of a tree, which hatch and fly up into the canopy and begin to feed.  If any of the leaves they bite are connected to the apical meristem, the phytoplasma can enter the palm's circulatory system and the tree dies.  It seems suspect to me that leafhoppers colonizing a new area would simultaneously choose all of the palm trees to lay their eggs against, they'd all hatch at the same time and all their new leafhoppers would bite the apical meristems of all the trees right around the same time.  Certainly not impossible, but feels like more of an explanatory reach than, say, a string-trimmer-happy landscaper dusting up all the trunks in a specific planting on a Saturday and then they all wind up catching ganoderma around the same time.

Idk... this is bro science either way.  But I'm still trying to think this through.

[Merlyn]

@ahosey01 one thing I've noticed is that areas seem to get "groups" infected all at about the same time.  This may be in group plantings, like the apartment complex ~2 miles from my house.  They planted 5 Sylvestris and 4 out of 5 almost immediately started showing signs of LB...and died 3 or 4 months later.  Most likely they were infected prior to planting.  The complex replaced the 4 dead ones with 4 new ones...and they promptly died 3-4 months later.  This was, maybe not coincidentally, the first batch of Sylvestris in my area dying from apparent LB.  A year later they are dying all over the place.  Oddly enough all the Dactylifera on the highway are infected and dying, but a car stealership about a half mile away has ~20 Dactylifera with zero visible symptoms.

One important thing to note is that leafhoppers don't just sit in one place under one tree.  The research shows that they can feed on one tree for a while, get the LB into their digestive tract, and then feed on another tree and spread it.  So there doesn't need to be a complete life cycle.  Likewise, the leafhoppers sometimes take a ride on landscaper trucks.  So if a crew is trimming one batch of infected palms they might transport trimmed fronds AND leafhoppers in the truck to their next job.  To me this seems like a really easy explanation for why all the highway Dactylifera and Sylvestris are all dying at the same time.

I'd also note that I was unable to find any published study disproving the "transmissable by contaminated pruning tools" idea for either LB or LY.  There's a great Youtube talk on LB from one of the UFL scientists where he details the studies proving it can be transmitted by leafhoppers.

https://www.youtube.com/watch?v=CvJIkxxJzJ4

I'd love to see an actual study showing that you can't transmit it by lopping off an infected frond, turning over to a different plant, and lopping off a frond.  I couldn't find one.

No doubt...it's definitely brozilla science here. 

 

[flplantguy]

I guess thats my favorite kind of science then! I thought that theory volleying was great and a sound explanation. And if it saved nursery growers and landscapers money i think they wouldn't care where it came from as long as it worked. I bet some of them google it and read this one day.