Talking Trees

Erwinia amylovora

Subscriber Episode • • Arboricultural Academy • Season 2025 • Episode 126

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In this episode of Talking Trees, we dive into the bacterial disease Erwinia amylovora, commonly known as fire blight. Listeners learn about the origins, biology, and symptoms of this aggressive pathogen that primarily affects apple and pear trees. The discussion covers essential practices for managing outbreaks, including preventive measures, proper sanitation, pruning techniques, and considerations for chemical control. A comprehensive episode providing valuable insights for arborists and horticulturalists dealing with fire blight.

Background information:

  • Doolotkeldieva et Bobusheva. 2016. Fire Blight Disease Caused by Erwinia amylovora on Rosaceae Plants in Kyrgyzstan and Biological Agents to Control This Disease.pdf
  • IPPC. 2016. Erwinia amylovora.pdf
  • Pedroncelli et Puopolo. 2023. This tree is on fire_ a review on the ecology of Erwinia amylovora, the causal agent of fire blight disease.pdf


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Roger:

Talking Trees with Lillian Jadd. Welcome to Talking Trees. Today we explore the research surrounding Erwinia amelovora, the causative agent of fire blight in rosaceae. We'll discuss diagnostic protocols, including symptom identification, isolation methods and molecular and serological tests as outlined by IPPC standards. We'll also review studies focusing on antagonistic actinomycetes in Kyrgyzstan, ecological interactions and the possibility of using bacteriophages and biological control agents for sustainable plant protection. Let's dive in. Let's dive in.

Jad:

All right arborists, welcome back. It's time to tackle something you probably see out there in the field pretty often fire blight and we've got two really great resources to help us out here. One is the International Plant Protection Convention's Diagnostic Protocol for Erwinia amylovora.

Lilly:

Okay.

Jad:

And the other one is a recent academic review on the ecology of Erwinia.

Lilly:

Oh, very cool. These are great sources yeah.

Jad:

So we want to make sure that everyone listening, you know. If you find yourself out there looking at a tree and you think it might be fireplate, you know what to do.

Lilly:

Absolutely.

Jad:

So I guess, just to start out I mean we've all seen the damage, right. So I guess, just to start out, we've all seen the damage right, yeah, the scorched leaves. The scorched leaves, the oozing cankers.

Lilly:

The shepherd's crook, shepherd's crook. Yeah, you can't miss it.

Jad:

But you know, sometimes looks can be deceiving, right.

Lilly:

Absolutely. Other bacteria can mimic Fireblade, so we need to be sure. So how do we make sure? Well, the IQPC protocol that you mentioned lays out a really clear path. It recommends a three-pronged approach, starting with PCR tests.

Jad:

Okay, so PCR tests.

Lilly:

Not one, but two.

Jad:

Why two?

Lilly:

Well, it turns out that some erwinia strains can cause a lot of damage, but they lack a specific DNA sequence that's often used for identification. Okay, identification. So one PCR protocol checks for the common sequence, and then the second one targets a different part of the bacteria's DNA, just to make sure we're not missing these sneaky strains that don't have that particular plasmid.

Jad:

Gotcha. So two different areas to look at Exactly. What about the other two tests?

Lilly:

Okay. So the second test is docilisa, which is kind of a mouthful, but think of it as a molecular bloodhound sniffing out very specific proteins that are produced by erwinia, and it's very accurate.

Jad:

Okay.

Lilly:

And then finally there's a pathogenicity test, and in this test you literally inoculate a healthy plant and then you watch to see if it develops those characteristic fire blight symptoms.

Jad:

Oh, so you're proving it.

Lilly:

Proving it.

Jad:

That it's Arwinia. You got it by actually giving it to a plant and seeing if it gets sick.

Lilly:

Okay Well, so then what makes Arwinia such a tough adversary?

Jad:

in the first place.

Lilly:

Well, one word biofilm, biofilm, biofilm. It's like a microscopic fortress that Arwinia builds Right Using complex sugars like amylobin 11 and cellulose, and it's this sticky shield that protects the bacteria from everything we try to do to get rid of it.

Jad:

So these sugars, what do they do Like? How do they help it survive?

Lilly:

Well, amyloverin and leaven are particularly interesting because they enhance the bacteria's resistance to stress Things like drying out or high salt conditions, like tiny umbrellas shielding it from a harsh environment.

Jad:

So it's not even just hiding in the tree, it's like actively fighting back.

Lilly:

Oh yeah, it's, very clever.

Jad:

Wow.

Lilly:

And then it gets even more challenging because Erwinia has another trick up its sleeve, which is the VBNC state, and this is a dormant state where the bacteria essentially goes into hibernation. Oh wow, it becomes undetectable to standard lab tests.

Jad:

So even if you hit with copper treatments or, like you know, starvative nutrients, it can just kind of lay low.

Lilly:

It just waits it out, yeah.

Jad:

So that makes eradication super difficult.

Lilly:

Very, very difficult.

Jad:

Okay, so let's say we've got a confirmed case of fire blight. Now what's the game plan? Okay, what do we do?

Lilly:

So, as arborists, we need to act fast.

Jad:

Okay.

Lilly:

And the first thing we have to do is accurately assess how far that infection has spread. Okay, so when you're collecting samples for testing, you want to focus on what we call the leading edge of the disease lesion. Okay, the leading edge, so like that's where the bacteria are most active.

Jad:

Oh, okay.

Lilly:

Like the front lines of an advancing army.

Jad:

Gotcha. So that's where they're doing the most damage, exactly, and so you're sampling there.

Lilly:

Yes, to get a really accurate picture of how far it's gone.

Jad:

Okay, so we've confirmed it's fire blight. What's next? Pruning, pruning, okay.

Lilly:

Pruning is our primary weapon here. Right, we need to surgically remove those infected branches and you have to cut well below any visible symptoms.

Jad:

Yeah, I imagine sanitation is really crucial here.

Lilly:

Oh, absolutely. You have to sterilize your tools meticulously.

Jad:

Why.

Lilly:

Just like a surgeon in an operating room. Yeah, we don't want to be spreading this bacteria around with our tool.

Jad:

No, that makes sense.

Lilly:

Okay. Okay so we've pruned those infected branches. Now what do we do with all the debris? This is so important. Do not compost this material.

Jad:

Okay.

Lilly:

Erwinia can persist in compost, oh wow. And it can potentially reinfect your plants.

Jad:

Oh no.

Lilly:

The IPPC recommends either burning the debris or sending it to a landfill to make sure that bacteria is completely destroyed.

Jad:

So you want to break the cycle.

Lilly:

Exactly we want to break the cycle, we don't want to keep it going.

Jad:

Right yeah.

Lilly:

We want to get rid of it.

Jad:

Don't put it in your compost.

Lilly:

No, absolutely not.

Jad:

Okay.

Lilly:

It needs to be gone.

Jad:

So we've talked about how to contain it, but how about how to prevent it?

Lilly:

Yeah.

Jad:

You know what can we do to reduce the risk of fire blight outbreaks in the first place.

Lilly:

Well, the research you provided highlights just how important these ecological factors are.

Jad:

Okay.

Lilly:

Like temperature, rain, even insects.

Jad:

It's like the perfect storm.

Lilly:

Exactly, and warm, wet weather during bloom yeah, that creates like the ideal conditions for Erwinia to really thrive and spread.

Jad:

Oh so those nice spring rains.

Lilly:

Right.

Jad:

They could backfire.

Lilly:

They could.

Jad:

Oh man.

Lilly:

Yeah.

Jad:

Okay, but what about insects? How do they get involved?

Lilly:

Well, insects, even some that we think of as being beneficial, can act as vectors, carrying that bacteria from tree to tree as they're moving around foraging and pollinating.

Jad:

So even the good guys can be bad guys sometimes.

Lilly:

Sometimes yeah, it's a harsh reality.

Jad:

Yeah, so we're fighting a battle on multiple fronts here.

Lilly:

We are.

Jad:

So how do we manage all that?

Lilly:

Well, knowledge is power.

Jad:

Okay.

Lilly:

So by understanding how these factors work together we can kind of anticipate those high risk periods and take proactive steps.

Jad:

Okay, so like what would an example of that be?

Lilly:

So, for example, during those warm, wet spells in the spring, we need to be super vigilant about monitoring for any signs of fire blight, and then we might even consider some preventative measures like copper sprays.

Jad:

Oh, ok, that makes sense.

Lilly:

We need to empower our clients yeah, to be our partners in fire blight management. So educate them about the disease, the symptoms, the environmental conditions.

Jad:

So we're not just treating the trees, we're treating the tree owners too.

Lilly:

Yes, exactly, we need to explain to them how important it is to prune properly, to sanitize properly.

Jad:

Yeah.

Lilly:

And even to think about the role of microclimate.

Jad:

Oh yeah.

Lilly:

In their own landscapes.

Jad:

And how those could be affecting things.

Lilly:

Exactly, and even small wounds on a tree can become entry points for erwinia.

Roger:

Oh, wow.

Lilly:

So we need to really emphasize careful pruning and minimizing damage during other landscaping activities.

Jad:

So it's like a whole big picture approach.

Lilly:

It is. It's a holistic approach to fire blight management.

Jad:

OK, and so the research paper. You mentioned that there are other organisms that can influence fire blight outbreaks. Can you tell us more about that?

Lilly:

Yeah, so research indicates that certain fungi and bacteria can actually make trees more susceptible to getting infected with Erwinia. Really so it's like this complex web of interactions where some of these organisms are actually paving the way for Erwinia to come in and succeed.

Jad:

So it's not even just Erwinia we're dealing with.

Lilly:

No, it's a whole community.

Jad:

It's a whole team of bad guys.

Lilly:

It is. It's a whole microbial community.

Jad:

Oh man, this is complicated. It is complex, OK, but maybe that complexity also means that there's more that we can look into to figure out how to manage this.

Lilly:

That's right. So, for example, if we can understand these microbial interactions, yeah that could lead to developing biocontrol agents. Ok, that can actually suppress Erwinia, oh wow. Or enhance the tree's own natural defenses. So that's promising. It is very promising.

Jad:

So the more we learn about this, the better we can be at managing it.

Lilly:

Absolutely.

Jad:

OK, are there any other like new things on the horizon that we should be looking out for that give us hope that we can be more targeted in combating this.

Lilly:

Well, scientists are working really hard to develop fire blight resistant cultivars.

Jad:

OK.

Lilly:

Imagine apple and pear trees that can just naturally fend off these Erwinia attacks.

Jad:

That would be a game changer.

Lilly:

That would be huge.

Jad:

Yeah.

Lilly:

For orchards and for landscapes.

Jad:

Yeah, for sure, what else?

Lilly:

Well, remember how we talked about other bacteria coexisting with Erwinia? Uh-huh, some of those bacteria might actually be our friends.

Jad:

Really.

Lilly:

They could be natural antagonists that inhibit Erwinia's growth and spread.

Jad:

So they're fighting the bad guys for it. So if we can harness the power of those beneficial microbes, that could give us a more sustainable and more targeted approach to controlling fire blight.

Lilly:

I like that approach Fighting fire with fire.

Jad:

Right.

Lilly:

Or, in this case, bacteria with bacteria.

Jad:

Exactly.

Lilly:

Are there any other really cool things on the research horizon that you're looking forward to?

Jad:

Well, the research into bacteriophages is super exciting. What are those? These are viruses that specifically infect and kill bacteria.

Lilly:

So researchers are looking at whether we can use these as a very targeted weapon against Erwinia.

Jad:

So they're like tiny assassins.

Lilly:

Tiny assassins.

Jad:

Going after the Erwinia.

Lilly:

That's right, going in and destroying it within the plant.

Jad:

Without harming the plant.

Lilly:

That's the goal.

Jad:

That's amazing.

Lilly:

It's pretty amazing stuff.

Jad:

That's like science fiction.

Lilly:

It is, but it's really promising.

Jad:

Yeah.

Lilly:

And it really speaks to just how dedicated and ingenious these researchers are all over the world who are working to find innovative ways to fight plant diseases and protect these precious plants.

Jad:

That's great. Okay, so we've been talking about. You know how these other organisms can help us fight erwinia, but the research paper also mentioned that, or when you can actually survive outside of its host plant. So, like, what does that mean for us?

Lilly:

yeah, so that does complicate things a little bit okay so, or when you can persist out in the environment even without a host plant really so research suggests it can survive in the soil, in water oh, wow even on the surfaces of plants that it can't actually infect.

Jad:

Oh, so it's like just hanging out waiting.

Lilly:

It's waiting for its chance.

Jad:

To strike.

Lilly:

To strike yeah. Wow so this is where understanding those ecological factors really comes into play, because temperature and humidity play a big role in whether Erwinia survives outside of its host or not.

Jad:

Okay, so dry conditions it might die.

Lilly:

Right.

Jad:

But if it's wet, then it's happy. It can thrive Wow Okay, so it's wet, then it's happy it can thrive Wow Okay, so it's a delicate balance.

Lilly:

It is.

Jad:

So we need to be mindful of those factors, not just when we're managing a tree that's already infected.

Lilly:

Yes.

Jad:

But the whole area around it.

Lilly:

Absolutely the whole landscape. So sanitation practices Like cleaning up fallen debris.

Jad:

Yeah.

Lilly:

Minimizing wounds on trees.

Roger:

Right.

Lilly:

That's important, not just to prevent erwinia from spreading from infected trees, but also to reduce the amount of erwinia that's just hanging out in the environment in general.

Jad:

So it's all about prevention and good hygiene.

Lilly:

Absolutely.

Jad:

Inside the plant and around the plant.

Lilly:

Inside and out. So if we take that holistic approach that considers the plant, its environment and all these interactions going on, we can really make a difference in reducing the risk of fire blight outbreaks.

Jad:

That sounds great. It seems like we need to be on our toes all the time with herwinia.

Lilly:

Yeah.

Jad:

You know, with all these different factors at play, yeah. Is there anything else that we should be aware of when it comes to how herwinia survives?

Lilly:

Well, the review paper also pointed out that herwinia can form biofilms on non-host plants.

Jad:

Wait. So you're telling me that it can build its little fortress, even on plants it can't infect.

Lilly:

That's what the research suggests, yeah.

Jad:

Wow, so it's just hanging out there.

Lilly:

Yeah, waiting Could be For the opportunity. Yeah, oh, man, okay. So that complicates things. It does a little bit, but I think the key takeaway here is just awareness.

Roger:

Okay.

Lilly:

So if we understand that Erwinia can persist on all these different solfaces, then we can implement some more comprehensive sanitation practices.

Jad:

Right, so not just focusing on the trees that are infected, but thinking about what's around them as well.

Lilly:

Yes, the surrounding vegetation.

Jad:

Okay, so it's all about being proactive.

Lilly:

Absolutely.

Jad:

Thinking ahead.

Lilly:

Thinking ahead.

Jad:

Trying to figure out where erwinia might be hiding.

Lilly:

Yes.

Jad:

Okay, so let's talk a little bit more about the infected tree itself.

Lilly:

Okay.

Jad:

The research paper talked about these different kind of waves of infection. Can you walk us through that a little bit?

Lilly:

Sure, so the first wave usually happens during bloom, okay, when those flowers are the most susceptible.

Jad:

Right, because those nectarines are wide open.

Lilly:

Exactly, they're like welcome mats.

Jad:

Yeah, for erwinia to just come right on in, and so once those first flowers are infected, then it's like a domino effect.

Lilly:

It is. Those infected flowers become like erwinia factories.

Jad:

Wow.

Lilly:

They produce a huge amount of bacteria that can then be spread to other parts of the tree by rain, wind, insects. Okay, and so then, as the season goes on, there's more waves of infection, exactly. That are affecting the shoots and the leaves, even the fruit.

Jad:

That's right.

Lilly:

And I imagine those secondary infections are the ones that cause the most serious damage.

Jad:

They can be. While flower infections are significant, okay, the real danger is when it spreads to the branches in the trunk, right, because then you start getting those large cankers.

Lilly:

Yeah.

Jad:

That can girdle the tree and lead to dieback.

Lilly:

Or even death of the tree.

Jad:

Exactly.

Lilly:

So that's why it's so important to catch it early.

Jad:

Early intervention is key.

Lilly:

When it's just those flower infections.

Jad:

Yes, targeting those early infections is critical.

Lilly:

Okay.

Jad:

Because it can significantly reduce the risk of it spreading.

Lilly:

To those more critical parts of the tree, that's right. So you really got to keep an eye out during bloom.

Jad:

You do, even if you just see subtle symptoms. Okay, it's important to be vigilant.

Lilly:

It's like you know, catching a fire when it's just a small ember.

Jad:

Great analogy. Yeah, rather than letting it become a huge raging fire.

Lilly:

That's right.

Jad:

Okay, so we've made it through the season, but Erwinia doesn't just disappear when it gets cold, right.

Lilly:

No, unfortunately not. It can overwinter it can overwinter in infected tissues.

Jad:

In those cankers.

Lilly:

In those cankers. Yeah, okay, yeah, those cankers and those cankers, yeah, okay, yeah, just waiting for spring to come back around.

Jad:

So even when the trees are dormant, the threat is still there the threat remains so what do we do about that?

Lilly:

so as temperatures start to warm up in the spring, yeah, or when you wakes back up okay and it starts producing ooze oh yeah and that ooze can spread to new flowers and shoots starting the whole cycle over again starting the whole cycle over again.

Jad:

Starting the whole cycle over again, oh man, okay. So what can we do to target those overwintering populations?

Lilly:

So preening out infected branches and cankers.

Jad:

Okay.

Lilly:

Even during the dormant season.

Jad:

Okay.

Lilly:

Can really help to reduce the amount of owenia that's present in the spring.

Jad:

Okay, so it's like removing the enemy's stronghold before they have a chance to attack. And, of course, sanitation is still super important.

Lilly:

Always.

Jad:

Making sure we're getting rid of that infected material.

Lilly:

Yeah, whether by burning or sending it to a landfill.

Jad:

Okay.

Lilly:

It's crucial to prevent those overwintering bacteria from reinfecting.

Jad:

Okay, so it all comes back to those basic things.

Lilly:

Yes, the fundamentals.

Jad:

Staying vigilant. Good sanitation.

Lilly:

Absolutely.

Jad:

And really understanding how Erwinia works.

Lilly:

Understanding the biology and how it interacts with the environment.

Jad:

Okay, well, this has been super informative.

Lilly:

It's been a pleasure.

Jad:

Thank you so much for sharing your expertise with us, you're welcome. And to all of our listeners out there. Thank you for joining us on this deep dive into the world of Erwinia amylovora.

Roger:

Thank you for joining us on this episode of Talking Trees. Today, we examined Erwinia amylovora, the bacterium behind fire blight, by discussing the IPPC's diagnostic protocols covering symptom recognition, isolation techniques and serological and molecular tests. We also reviewed research on actinomycetes with antagonistic and plant stimulating properties, explored the ecological interactions of E amylovora and considered strategies for enhancing plant resistance through genetic improvements and biological control measures. We appreciate your attention and look forward to our next discussion.

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