368 Trees vs. Invasive Shot Hole Borers

Show Transcript

368 Invasive Shot Hole Borer TRANSCRIPT

Farmer Fred   

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Welcome to the Garden Basics with Farmer Fred podcast. If you're just a beginning gardener or you want good gardening information, you've come to the right spot.

Farmer Fred

Today, we venture into the critical realm of invasive pests, zeroing in on the invasive shot hole borer (ISHB), a formidable newcomer from southern Asia threatening California's trees. We navigate through the fascinating biology of the ISHB, discussing its rapid spread and dire consequences for urban and native forests alike, not only threatening California’s tree canopy, but over 65 species of trees throughout the country. 

We are joined by Dr. Beatriz Nobua-Behrmann from the University of California Cooperative Extension, who sheds light on the pest's impact, including essential native varieties. And, one of this pest’s target trees will bring a frown to guacamole lovers throughout the land: avocado trees.

Now that I have your attention, stay tuned to find out what you can do. We will emphasize the importance of monitoring and early detection of the Invasive Shot Hole Borer, with Dr. Nobua-Behrmann outlining diagnostic signs and mitigation strategies. We highlight integrated pest management techniques and the potential of biological controls, such as the introduction of parasitoid wasps. 

As the conversation unfolds, the significance of diversifying tree species is emphasized, advocating for resilient urban landscapes - as well as practical solutions - for homeowners and gardening enthusiasts, in the battle against the Invasive Shot Hole Borer.

We’re podcasting from Barking Dog Studios here in the beautiful Abutilon Jungle in Suburban Purgatory, it’s the Garden Basics with Farmer Fred podcast, brought to you today by Smart Pots and Dave Wilson Nursery. Let’s go!

INVASIVE SHOT HOLE BORERS, Pt. 1

Farmer Fred

There are a lot of insects in California, and for that matter, across the country and around the world, that are so infamous, they're just known by their initials. Like ACP, which is the Asian citrus psyllid, which spreads citrus greening disease, which has decimated the Florida citrus industry. It spread to California, but we've kind of learned the lessons of what happened in Florida and applied it to California, and it is probably under control. 

Another one famous for its initials is a really strong flyer and an excellent hitchhiker now found in a majority of states. It's called the BMSB, the Brown Marmorated Stink Bug. There are some reports in Pennsylvania that have indicated that peach growers have lost as much as 50 to 60 percent of their crop to BMSB, which feeds directly on the fruit. Other fruits that the BMSB attacks include apples, pears, and also vegetable crops such as corn, beans, peppers, and tomatoes, and many ornamental plants as well. 

Another one, RGLP. That's the red gum lerp psyllid, which is a pest of certain varieties of eucalyptus trees. And it's an aphid-like insect that was found here in the Sacramento area back around the turn of the century, around 2000 or so, but was unintentionally introduced in Los Angeles and now occurs on plant hosts throughout California and in very many Mediterranean and Asian climates as well.

Now, guess what? There's a new infamous pest known by its initials, ISHB, the Invasive Shot Hole Borer. And they're small. They're tiny. They're less than two millimeters long, and they range from black to brown in color, and they live in the trees.

And the thing is, you'll never see them, probably, until you notice something wrong with your trees. Both males and females spend most of their lives inside trees within channels that are called galleries that the females create by boring into trunks or branches. And once the larvae grow into adults, the beetles will mate inside those galleries, and then the females will disperse, ready to start their life cycle all over again. They don't eat the wood, but what they do is they farm a disease that we've talked about on this program before, fusarium. These fungi infest the tree tissue causing that disease, fusarium dieback. You probably know it in relation to our chats about tomatoes.

So, what's going on with the invasive shothole borer? The death of thousands of trees. It can totally decimate a tree population. And down in Southern California, they've found a lot of these invasive shothole borer damaged trees. And now that pest has spread to Northern California in the San Jose area of the San Francisco Bay Area. Is it going to get here? Is it going to get to where you live?

Let's find out, and find out what we should do about it. We're talking with Dr. Beatriz Nobua-Behrmann. She is with the Urban Forestry and Natural Resources Department. She's an advisor for the University of California Cooperative Extension down in Southern California. So, doctor, this invasive shothole borer, it has come on strong and it's very hard to locate. And sometimes the only way you know you have a problem is when the trees are dying. And this pest does affect a lot of tree species, doesn't it?

Dr. Beatriz Nobua-Behrmann

It does. It really likes to go for many, many different species of trees. In here in California, there's about 65 species of plant that these beetles can attack and can actually reproduce in these trees. They can even attack even more species. It's just they might not be able to reproduce in them. But in here, 65 actually work as what we call reproductive hosts. So the beetles can make a gallery in them. They're able to grow the fungus and they're able to make more beetles. So a lot of our landscape, common landscape trees get affected. And sadly, a lot of our native California species also get affected.

Farmer Fred

]I guess this pest came from Southeast Asia in shipping materials. This is not an uncommon way for pests to travel around the world. Where else in the world is the invasive shothole borer a problem? Is it spread throughout the United States or maybe just in USDA Zone 9 or 10?

Dr. Beatriz Nobua-Behrmann

So within the U.S., we have them in California, and then we have their sort of sister species. I mean, this is what we call species complex, where there's several species of beetle that basically look the same. And the only way we can distinguish them is through DNA analysis, right? And so that includes two species that we have in California, they're called the polyphagous shot hole borer and the Kuroshio shot hole borer. And we call them, we group them in what we say, the invasive shot hole borer, because you need a term for both of them. In Florida, we have the Tea Shot hole borer, , which is another one of the same complex, but is a little bit less of a concern. It's not as aggressive for the trees. This group is from Southeast Asia, is here in California and in Florida, the Tea Shot Hole borer. And then around the world, we found them in so many other places. So it's a problem in Israel with avocado growers. It's in India. It's in South Africa. It's in Australia. It's now down in Argentina and Brazil. It's present in many, many places. And the thing is, they can move so easily with woodpacking materials.

Dr. Beatriz Nobua-Behrmann

]And the way they reproduce makes it easy for them to colonize a new place. Because you actually only need one female to start a population. Because that female can lay an unfertilized egg that turns to be a male. All the unfertilized eggs are males and the fertilized eggs are female. And so if she doesn't, let's say she's not made it, but she made it to a new area, a new country, that female can lay an unfertilized egg or a couple that will become males and she can mate with them and start making more females. You know, very sneaky. It's easy for them to start new populations. So sadly, we can find them in many, many places around the world.

Farmer Fred

I'm sure a lot of ears perked up when you mentioned that they were attacking avocado trees in Israel. And avocados are a very popular crop here in California. In commercial avocado groves, they've been found, the invasive shothole borer. Let's talk about some of the tree species that are affected by the invasive shothole borer. Some trees are more susceptible than others. Some species, it will kill the tree. Others, it can just damage the tree. And I guess the first line of attack would be to aim your controls, and we'll call them controls, they're not a cure, they're just controls, at those trees that could completely die. And the thing is, the symptoms you would see, you could easily just say that, oh, it was caused by fusarium, without actually looking for their entry holes. And that is one of the keys, isn't it?

Dr. Beatriz Nobua-Behrmann

Absolutely. So the key here to management, the first thing you need to do is to do monitoring, right? You need to know if you have that beetle infestation in your trees and how bad that is. And constant or periodical monitoring of your trees would be in any integrated pest management program.

Monitoring will be the first thing that you do, and in this case, it's not an exception. It is the most important thing to do. So if you're looking at your trees, you're going to be looking for those perfectly round entry holes. They are very small because this beetle is about the size of a sesame seed. So imagine they're just drilling a gallery (tunnel), and they drill a gallery of the size of their body. So in order to identify if the hole I'm looking at in a tree belongs to invasive shothole borders or any of the many other borers that could affect the tree, the best thing is look for perfectly round entry holes. And the size is about the tip of a medium ballpoint pen. And this is important. I always bring a pen with me. When you find something, really, you should put a pen next to it and look if it just matches the size. There's things that, holes that are perfectly round, but a little bit smaller or a little bit bigger. So you really want that size to match what you're expecting.

But you're not going to just go looking for holes. There's other things that are in the trees that will make you go and look, right? So off of those holes, when you damage a tree, They basically bleed like we do, but in their own way. So you'll see usually wet staining. There's liquid oozing out of those holes. And so that stains the bark and you see the bark kind of darker in wet stains. So when you see that, that is a sign that you should go and look closer at that tree and see if you find the exit holes. We call them entry or exit holes because they enter and exit from the same hole. The hole is why we'll tell you this is the borer. But the staining or sometimes you can see frass or gumming, all of those symptoms is what is going to make you go and look for that hole, right? The hole is so small that you have to be close to the tree to see it. So, it's going to make you check that tree is if you see the staining.

Farmer Fred

We'll have a link in today's show notes about the invasive shothole borers from the University of California, which will include a host list of the trees most susceptible to tree death due to the invasive shothole borer.

The trees that may die from this are very, very popular trees like the big leaf maple, the trident maple, the box elder, the palo verde, the California sycamore, London plane tree, cottonwood trees... if you have a lot of country. Also valley oak, several varieties of willow. And those are the ones that probably need to be removed, whereas there are even more trees that can cause dieback. And maybe just the branches have to be removed if they find a heavy infestation. And that includes things like acacia, more maple varieties, including the Japanese maple, the California buckeye, tree of heaven...well, they can go ahead and kill that. Mimosa trees, the king palm, camellias, chestnut trees, Australian pine.

Strawberry trees, the Japanese beech, black mission fig, the honey locust, jacaranda tree, the Chinese flame tree, sweet gum, southern magnolia. You get the idea. There are a lot of trees. 

And yes, the avocado is on that list where it can cause dieback, which means basically that branches have to be removed. So, like I said, we'll have that link in today's show notes on which trees are most affected and can give you some good knowledge about the invasive shot hole borer as well. You mentioned about how, I won't say it's easy, but at least if you just put your nose right next to the tree and start looking, you can probably spot these holes with a pen in your hand, a medium ballpoint pen, and look for those small entry holes. Where along the trunk, and at what height, are those holes usually found?

Dr. Beatriz Nobua-Behrmann

Well, that really depends on the species of tree. In most of the species, you'll find it in the trunk and it could be anywhere from, wherever you can see them and even up high in the canopy. They can also attack the branches. So it's kind of anywhere. I've even seen it when the roots kind of come out of the ground a little bit, I've seen them attacking those roots as well. So it could be anywhere. 

For some of the species, they attack the branches and not the main trunk. And that is usually the case for oaks and the avocado. But for other species, they attack almost anywhere. But we use this information that we have, that we know about how the beetles attack different species of trees and what do they do in order to think about management strategies, right? So you mentioned avocado. Avocado is one of the few, at this point, I guess it's the only agricultural species that they attack. You know, the only crop species that they attack.

And it was the Avocado Commission, the California Avocado Commission, was one of the first ones that provided a lot of funding for the first research that we did on invasive shothole borers. And rightfully so, they were very concerned. And that funding and that research that came from that funding gave them integrated pest management strategies that they can use to effectively manage invasive shothole borers without using much pesticides. So that's how we learned about the beetle's life cycle and how they prefer the branches versus not so much the trunk in avocados. And that's how we learned that then, since avocado goes through a pruning every year, especially in groves where they're growing avocado commercially, they do some quiteheavy pruning every year. And so we were able to give them management recommendations. And when you do that pruning, you should prune the infested branches.

And even if you have a couple of needles left in your growth, they're not going to do significant damage. As long as every year you make sure you take most of them out with your pruning. So we were able to provide them with a solution to their problem. And then, of course, we always say, if you're pruning away, if you're removing something that is infested, you have to be very responsible. What do you do with that infested plant material, right? Whether you're removing a tree or a branch or anything else, you need to manage that infested material so you're not spreading the pest. And for that, we also did some research and came up with what you can do. You can chip that infested material. If the chips are less than one inch in diameter, you will kill 99.9% of the beetles present in that material. But even if you cannot reach that size, which is quite tricky sometimes, it's not that easy to get to less than one inch chips, the smaller you can do, the smaller the chip, the more clean or the more beetles you're killing. Like if the chips are three inches and smaller, that kills 98% of the beetles. So, it's pretty, pretty good. So you're going to be chipping and then those chips, you don't want to move them, give them to your friend that lives in the other city or, you don't want to move those chips and use them anywhere else. You want to compost them before you're able to move those chips. 

You can use them in your own property. If you're a homeowner and you removed a heavily infested branch and you were able to chip it, you can spread those chips as mulch in your own property. That's fine because you know that the beetle is already there. And maybe if you get one more beetle from those chips, that's not a big deal. But you don't want to be moving it because you don't want to start a new infestation.

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INVASIVE SHOT HOLE BORERS, Pt. 2

Farmer Fred

We'll have a link in today's show notes to a video that talks about the chipping process, as well as another strategy for being sure to killing off what might be still alive in those branches. And especially if you're removing the tree and you have big trunk parts, is to solarize it. And it points out that in the summertime, by putting sheet plastic over a pile, a small pile, not a tall pile, but a very low pile, maybe just one layer thick, have clear plastic over it, seal the edges around. That can kill off any remaining invasive shothole bores with six weeks of solarization in the summertime. In the wintertime, it would take like three or four months. Yeah, you mentioned about the problems of chipping to less than an inch. That was the first question I had when I was reading about this is, how the heck do a chip to an inch or less?

Dr. Beatriz Nobua-Behrmann

Yeah. So before I answer that, I want to clarify something. If you want to solarize, the tarp has to be under and over the pile.

Farmer Fred

Okay.

Dr. Beatriz Nobua-Behrmann

So it has to be completely sealed. The idea will be no beetles can escape from there. And think about this, beetles are the size of a sesame seed. So they can find little crevices. You have to be very careful on how to solarize. It's an option, but it's not a very practical option. But it is if that's what you want to do.

Farmer Fred

It's not only moving chips around, it's moving firewood. And I think that's one of the big takeaways from this conversation is don't be moving firewood around the state. Burn it where you found it.

Dr. Beatriz Nobua-Behrmann

Oh, absolutely. So that is great advice, not only for this pest, but for any pest that attacks tree. Firewood can have pests inside of them and then you're buying firewood in one place and moving it to another place where you're going camping or whatever and you're moving that pest to this new location. And so in general, the best advice is to buy firewood in the place where you're going to be using it, ideally within a couple of miles of that location. And when you're done using your firewood and you have leftovers, don't bring them back home. You either leave them there, give them to your fellow camper that is there, and is going to stay a couple more days there. Just give it to them so they can use it. But don't bring it back home,  because it will be exactly the same problem. You're bringing a pest from wherever you were camping to your city. So not moving firewood is absolutely the best way to protect your trees against shothole borers and against a plethora of other invasive pests that move on firewood.

Farmer Fred

I had mentioned at the beginning of our chat about the Asian citrus psyllid, which spreads the citrus greening disease. It's here in California, but first it hit Florida back in the 1990's or so, and they didn't know what they had. So they were flying blind trying to control it. By the time it got to California, we had studied what Florida had did and the strategies that they employed, studying what worked, what didn't work, and took it from there. And as a result we have maintained better control over the Asian citrus psyllid here in California,

]although there are still quarantine zones all around the state on that. Andsort of the same thing has happened with the invasive shot hole borer, because it started in Southern California and probably not too far from where you are. 

But I heard about trees at UC Irvine, thousands of trees. There's 30,000 trees on campus, and that's where the problem was noticed first?

Dr. Beatriz Nobua-Behrmann

Well, that would be within Orange County, I guess. But the problem was noticed first in L.A. County. So in the area of Whittier-Narrows, that's where they found the first bunch of trees suddenly declining and dying. It was interesting. It was around 2003 where they found a beetle in a trap. And if you remember what I was saying, that they're this cryptic species, right? And so when they looked at it and it didn't do a DNA analysis, it looked like the Tea shothole borer that we have in Florida. And they were like, okay, well, this is not a pest of much concern, and no action was taken. 

But then years passed and we kept finding trees infested here and there. People were not paying too much attention to it. But then eventually, especially in LA County, we started seeing full streets of sycamores die. That's when we started looking at it closer. 

Dr. Akif Eskalen was able to do DNA analysis on the beetle and the fungus and determined that this was a different species. We're dealing with something different. And that was in 2012. So it took almost 10 years since we knew that beetle existed here until we figured out it was a different species and it was worse than we thought. And that's because this beetle is sneaky that way. So the populations grow kind of under the radar for quite some time. 

So you can think that your tree is fine because it would look kind of fine. Your tree, you have a sycamore and it's going to have green leaves and everything that's staying on the trunk, you know, the tree seems to be fine. Meanwhile, the populations of the beetles are growing and growing and growing and growing. By the time your tree is showing signs of dieback and decline, that's when that tree is severely infested. By then, you have like thousands of beetles coming out of that tree. It's a very sneaky pest, and that's why it's very important to monitor your trees. Because if you find the infestations in the early stages, there's things you can do. There's branches you can trim. And if you want, there are options for some chemical management. If that's something you want to do, there's something you can do. But once the tree is severely infested and it's showing signs of dieback and it has more than 150 exit holes, that tree is probably not going to survive.

Farmer Fred

Ah, there's the key for you then. 150 exit holes. Yeah, that would be a problem. I can see that.

Dr. Beatriz Nobua-Behrmann

You have to, that's why it's very important to do regular monitoring with all of this, for any pest, right? The main thing is to catch the infestations early so you can take action early and manage the problem. So here in Southern California, we've been dealing with this pest for a long time. It was very bad, especially at the beginning because we didn't know we had it. Then after we knew a lot of land managers were like, eh, it's not a big problem. So we were not taking care of it for a while. And by the time they were calling us and saying, hey, my trees are dying. It was kind of too late, you know, because they were dying. 

The trees were severely infested. Because the beetles make all these galleries and sort of between the damage that the physical damage that the beetles do and the damage that the Fusarium fungus does, it's kind of like irreversible eventually, right? So once your trees are dying, that's quite too late. And that's why we lost so, so many trees in here. But then once we get our ducks in a row and decided to start doing good integrated pest management for this pest, and we as researchers found out new things and what we can do, what works. 

Right now in Southern California, we still have it as a problem, but it's something that if you're on top of it, you can manage it, which is a good thing.

Farmer Fred

What is the progress of finding a biological control for this? In many situations where a pest has come from another country, I'm thinking of the red gum lerp psyllid, they found a beneficial in Australia that actually attacked this red gum lerp psyllid, and they imported it here to California. Then there were years and years and years of testing before they released it, and in this case, in eucalyptus groves for the red gum lerp psyllid. And that seems to be a problem now that we can live with, thanks to this biological control, this garden good guy, if you will, who attacks the red gum lerp psyllid. Has there beenan insect found that does attack the invasive shothole borer?

Dr. Beatriz Nobua-Behrmann

Yeah, we have several candidates. So there is at least three species of parasitoid wasps that can be used as natural enemies. So what a parasitoid does is they lay their eggs together on the beetles or the beetle larvae, and then the eggs sort of hatch and the wasp larvae feeds on the beetle and kills it.

And imagine if they're teeny tiny wasps, right? Because they have to match the size of the beetles. So there's these three species that were identified as potential good biocontrols. We have been, and by we, I mean other researchers. I haven't done that, but researchers from UC Riverside have gone to Southeast Asia looking for natural enemies. They found these three species, they brought them back, and they're still kind of figuring this thing out because those wasps are, we still haven't figured out how to raise them in the lab to do any kind of testing. And that's because we have several sort of hoops to go through. 

We need beetles for the wasps to parasitize and make more wasps. And so we need to learn how to raise the beetles in the lab. But these beetles live inside a tree. So what are we going to do? Are we going to have a bunch of trees in the lab? That doesn't seem very practical. So first, there's been all of this research to figure out how to raise the beetles in the lab withoutneeding trees. So they figured that out. That took several years. Now we can raise the beetles in sort lab tubes. And now we have to figure out how to raise these wasps in the lab. We haven't been very successful. After a couple of generations, the populations crash. And that happens a lot with insects. They're not that easy to raise in the lab, not every species at least. And so that's something that we're still working on. 

The funding that we had for that kind of research is gone. And so we're now waiting to get more funding to finish those projects in which we're going to keep trying to figure out how we can raise those wasps in the lab. And that way, once we have that nailed down, then we have all the testing, right? Because you really don't want to release something here in California that could be maybe attacking a native beetle. You don't want to create another problem, right? So we need to do a lot of testing to make sure it's safe for us to release those wasps. And then once all the testing is done, that can be used as a biocontrol. So we still have a long way to go. That's going to be like a very long term solution.

Farmer Fred

In the meantime, there are a lot of integrated pest management controls that people can employ to take care of their trees and also come tree planting time, avoid certain situations. I don't know about avoiding certain trees or not. That's an interesting topic on its own. But try to avoid monocultures. You've heard me say on this programa lot: Mother Nature abhors a monoculture. And that is so true with this pest. Don't plant a row of willow trees. Why would you plant a row of willow trees, anyway? Don't plant a row of sycamores or anything that is susceptible to this pest. Mix it up.

Dr. Beatriz Nobua-Behrmann

Absolutely. And that's good for this pest and any other pest, right? Because let's say, this shothole borer doesn't attack pines. So I'm going to plant all, Canary Island pines in here.

But then the next couple of years, we might get a pest that attacks your Canary Island pines and then you planted all that and now all your pines are gone.

So plant trees thinking about the invasive shothole borer, but also thinking about any other pest. The more diverse your urban forest is, the more resilient we'll be. 

It's a bit different issue if you are restoring our natural areas. You might not have a pallet that is that big, right? Because you're restricted to only natives that live in that area. And that could be a little bit more tricky because most of our native riparian trees are hosts for the invasive shothole borer. 

But, I wanted to share this, it's exciting. There is probably a medium term solution that will come up hopefully fairly soon. It is that there's other research that has been done regarding another aspect of biocontrol. Let me set the scene here. Inside the trees, there is fungi and bacteria that live inside the trees and are beneficial for them. Which is very similar to our gut flora and fauna, right? So we want those good bugs in our gut. Trees want the good bacteria and fungi inside of them. They're called endophytes, like inside a plant, endophytes. They're there. And apparently some of those can give the trees some protection against fusarium.

So Dr. Shannon Lynch and Dr. Akif Eskalen from UC Davis have been studying this and they've been collecting samples from inside the trees and growing all these endophytes and putting those endophytes against Fusarium and noticing that several of those have like an antagonistic relationship with the Fusarium. So wherever that endophyte grows, Fusarium doesn't want to grow. That is very interesting, right?

Farmer Fred

Yes.

Dr. Beatriz Nobua-Behrmann

And so now we have this set of potential good candidates for this. Of these endophytes that actually fight fulsarium. Now they're figuring out, and this is research that is kind of ongoing right now, is how to grow them. And they call it brewing them. And then once we have them, it's like basically like probiotics. Now you eat your yogurt. How do you give the tree their yogurt, right? So that's what they need to figure out. And it seems like it might be a little bit more difficult to add those to a tree that is already mature, but it's probably a lot more simple to inoculate seedlings.

So that could be in the near future, I'll say, a good option for replanting, especially in these areas that are natural areas and are limited to what species they can plant. But if we can figure out how to effectively inoculate seedlings with this good endophytes that will give them some protection against fusarium, they're not the total shield, but they're probably going to allow these trees to survive or withstand infestation a lot better. Maybe we could use those seedlings in the future to replant in our riparian areas. So this is super, super exciting. And I wanted to share this with you because I think this is going to be coming hopefully in a few years, maybe a couple of years, maybe earlier. I don't know exactly, but soon. That's why I'm saying it's a couple of years in the future because there's so many steps in between, right? You need to learn how to get those seedlings with the endophyte. So then you have to make sure that they will keep it and not lose the endophyte that you gave them.

Farmer Fred

Years of testing and then distribution to all the growers to start growing these trees.

Dr. Beatriz Nobua-Behrmann

Yeah, but it's something, you know, that is it's a light at the end of the tunnel or at least in the middle of the tunnel. ]So hopefully this, I think, this will help once we get it nailed down.

Farmer Fred

Well, this also brings in that if you spot a problem in your tree, you ought to bring in a professional like a certified arborist or a consulting arborist or a pest control professional, because maybe in a few years they'll be able to give trees an injection that could slow the spread of this strain of fusarium. But I like the idea of treating the seeds first and just give it that resistance from birth.

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Farmer Fred

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INVASIVE SHOT HOLE BORERS, Pt. 3

Dr. Beatriz Nobua-Behrmann

The one thing that you need to think about is you still need to protect your trees now with the resources we have now, right? Because you want your tree to be alive by the time we have natural enemy that we can release or anything like that. So again, monitor, monitor, monitor. Make sure you look at your trees. Make sure you find the infestations early. And then if you want, you can remove infestations that are located in branches, you can just remove those branches. And if the infestation is in the main trunk, you could keep monitoring. And if the infestation becomes moderately infested, you might want to treat it if that's something you're willing to do. And if you want to go that route, you definitely need to hire a professional to do it. There's no home remedies that we have tested that works. And all the pesticides that can be used to manage this pest, they have to be applied by a licensed professional. The ones that you can buy at the store, they don't really work. And if you're not trained on how to do this properly, you can be causing more damage than good. So as general advice, get a professional to do that.

Farmer Fred

That is very good. And yeah, home remedies such as add more water or add more fertilizer are not necessarily good pieces of advice.

Dr. Beatriz Nobua-Behrmann

No, actually overwatering and underwatering are usually the main problem that I find in our trees, the urban trees. It's either too much water or too little water. And it's good to have someone to tell you, or at least with some knowledge on how are you managing that tree, it's good to have the tree well irrigated and healthy. Absolutely.

Just adding more water because the tree looks sad might not be necessarily the issue. You have to look, you know, touch the ground. Is the ground wet or dry? You might be overwatering your tree. Are you doing deep irrigation or are you just using the hose like when you might water your lawn? Trees need deep irrigation, not shallow irrigation. They usually need deep and infrequent irrigation. So all thosegood cultural practices to keep your trees healthy is a good thing. And you mentioned fertilizer. I'll give you a word of caution on fertilizing trees.

Most mature trees do not need to be fertilized, at least not with a regular fertilizer. They do not tend to be nitrogen deficient. So fertilizing for the sake of fertilizing might actually cause more damage. With some pests, actually, fertilizing the tree encourages creation of a lot more new shoots, which for a lot of the defoliating pests, that's a flag saying like, hey, here's a buffet for you. Here's good food. And you're attracting defoliating pests to your tree. So unless there's a reason like you tested the soil or you tested the leaves and you realize that the tree needs a specific kind of nutrient, usually trees don't need to be fertilized.

Farmer Fred

All they need is love and mulch.

Dr. Beatriz Nobua-Behrmann

Yeah, and a good irrigation. Yeah.

Farmer Fred

By the way, we'll have a link in today's show notes regarding how you can help determine if you do have the invasive shothole borer on one of your trees. There's the ISHB detection assessment page that I'll be linking to that can give you more information on a step-by-step basis of how to check before you call somebody and say, hey, I think my tree's got this borer. So you can do that little test and walk through first before you advance further on in the world of the invasive shothole boar. Yeah, trying to wrap this up with a pretty little bow on it, the integrated pest management controls for this pest, the invasive shothole borer, does include things like avoid monocultures, keep trees healthy, check the trees, confirm those suspected infestations with that tool I just talked about. There are management options you can choose. Call in a professional, take care of the waste, and replant wisely. There's one little sentence on this one about replanting wisely that I have not considered, and it's really good advice. It says, "consider the current concentration of tree species in your neighborhood when deciding what types of trees to plant". That's great advice.

Dr. Beatriz Nobua-Behrmann

Absolutely, yes. And replant early, right? Like if you know that there's a lot of trees there, you know, you're removing a lot of trees in a property, start replanting early so the tree has time to grow and replace that canopy, right? Definitely. And as you said, just aim for increased diversity. You want more different species of trees in your urban forest.

Farmer Fred

Thank you, Mother Nature. We've been talking about the invasive shothole borer, a pest in Southern California now spreading to Northern California. And it's throughout the world and they're working on finding a cure for it. In the meantime, just take care of your trees. Dr. Beatriz Nobua-Behrmann has been with us from Southern California. She is an urban forestry and natural resources advisor for the University of California Cooperative Extension in Los Angeles and Orange Counties. Thank you so much for telling us more about the invasive shothole borer.

Dr. Beatriz Nobua-Behrmann

Thank you so much for having me there, and cheers to trees, I guess.

Farmer Fred

Garden Basics with Farmer Fred comes out every Friday and it's brought to you by Smart Pots and Dave Wilson Nursery. Garden Basics is available wherever podcasts are handed out. For more information about the podcast, as well as an accurate transcript of the podcast, visit our website, gardenbasics.net. And thank you so much for listening and your support.