Episode Transcript
Tyler Hale Garden Futurist
Sarah Beck: You're listening to Garden Futurist. I'm Sarah Beck, here with Adriana López-Villalobos. Hi, Adriana.
Adriana López-Villalobos: Hey, Sarah.
Sarah Beck: I'm so excited that we've had this series of three Garden Futurist podcasts that have really focused on invertebrates.
This is a really interesting area of science, I so encourage students who are looking for areas of study, especially if you love plants, if you love forests, if you love ecology and you’re really interested in the urban forest, the urban canopy, there's just so many aspects that can be great areas of research.
We know that we are going to make our shared green spaces so much healthier if we're paying attention to growing plants in the right place and looking at plant health. Forest health is just so incredibly important to human enjoyment. Our well-being is really enhanced by health, the health of our forests.
Adriana López-Villalobos: We can't separate the insects from the plants. You can have the negative aspects of pests to plants, but most of the time are actually beneficial relationships, like what we find in nature between insects and plants.
So that is that's also an area that I would encourage students or the younger generation, ourselves, to just dig deep into it, because it's just fascinating and you can learn so much and then you learn to appreciate nature better.
Sarah Beck: Tyler Hale is program manager of the Plant Protection Program and Sentinel Plant Network at the American Public Gardens Association.
Sarah Beck: We've talked a lot about the urban forest on Garden Futurist, mostly because there's so many relevant pieces in terms of climate resilience. We talk a lot about the forest canopy in urban spaces, yet we have never really talked about the work that you do, this element of forest health focusing on invasive pests.
This doesn't need to scare anyone, but I would love for you to frame this issue for us, so we have just like a sense of, in the broadest strokes, what are we really talking about when we talk about invasive pests in terms of the urban forest?
Tyler Hale: It's a pretty wide-ranging topic, and there is a lot of doom and gloom. If we do a crash course, essentially, we want to protect our healthy ecosystems. In terms of urban landscapes, a lot of that is going to be cultivated, but some will be native plants.
The importance here with urban landscapes is that urban centers are often the sites of first introductions of some of these pests, because of the ways that they move around, because of the ways that we move them around. So that's why it's so important to keep this in mind when we're gardening, when we're planning public garden plantings, things like this, in urban spaces. These things might start in an urban landscape, but they move out into agricultural settings or into forest settings, they can do even more damage.
Sarah Beck: I love that term ports of call. It harkens back to some sort of like nautical era or something.
When we're talking about pests coming in through urban ports, I mean, really, we all became very familiar with this idea, because I remember those early days during the pandemic going, “Oh my gosh, where are there cases of COVID happening?” And you're like, “Oh, right, that's the major city over here. And I bet it, oh, it just popped up there.”
It's a similar concept here, because things globally move around and things come in in some of those places that are that are big areas of trade and movement.
Tyler Hale: Yeah, absolutely. We all sort of became armchair epidemiologists during the pandemic.
A lot of those parallels are really clear. There's, sure, the introduction side and wondering where it's going to move next, but there's also, similar to how we dealt with the pandemic, there are various management strategies. There’s no one silver bullet but taking them all as part of a larger management strategy can buy time to research better strategies, can slow the spread of these things and reduce damage.
So, yeah, a lot of a lot of really interesting parallels in the last few years.
Sarah Beck: Wow, no, that's scary.
So let's just jump into maybe an example or two that really nicely illustrates what you're talking about. I thought emerald ash borer (Agrilus planipennis) might be one to start with. As a person in the Pacific region, what's something that is a really good example of this concern for specifically trees?
Tyler Hale: It's interesting looking at what folks are most concerned about on the West Coast, absolutely. Emerald ash borer is a major pest of concern. There was an introduction two years ago in Portland, Oregon. It's a very difficult one to control. So it can be devastating to forests and urban forests.
It's hard to catch. It takes a little while before an ash tree starts to show symptoms, and then once it does, it's essentially too late to save that ash tree. In terms of large-scale prevention, also very difficult.
This is part of that doom and gloom. So what they're saying in Oregon is that if with current management strategies or doing nothing, you could lose 99 percent of ash trees in Oregon, and that means Washington and California as well.
This is a relatively slow-moving pest on its own. It gets moved around by humans, but once it's established in an area, it just slowly expands and expands.
Sarah Beck: Why is it so hard on the trees, could you explain? This guy's a beetle.
Tyler Hale: We have a lot of beetles. We have a lot of a lot of insects that are important to ecosystems. This one is sort of perfectly out of its element and in our element. So beetles and trees are supposed to evolve together and evolve defenses against one another so trees can defend themselves against infestations from insects that have other natural predators in our landscapes.
When you take something out of its natural environment—so emerald ash borer came over from Asia, it's got plenty of natural enemies in China. But when you take it and you put it in New York or in Oregon, there's nothing that's really predating it, and so its population can just boom. That’s essentially what happens.
The way that it kills trees is that it creates its galleries, it burrows under the bark of the tree. It creates areas where it can lay eggs, and where it wants to lay eggs is right in the vascular tissue under the bark of the tree. It essentially just girdles the tree and reduces its ability to transport water and nutrients until the tree can no longer sustain itself.
Once it lays eggs in there, the eggs hatch and the larvae will eat all of the vascular tissue that they can, they'll go to an adult stage, and continue the process onto the neighboring ash tree.
Sarah Beck: That is so sad about the emerald ash borers. So they are actually eating parts of the outer layer that's just under the bark. Are there other pests that have that specific characteristic? I'm assuming some of these pests are hurting a tree just inadvertently by doing something.
Tyler Hale: The significant pests that we talk the most about fall into a couple categories.
So emerald ash borer, things like Asian long-horned beetle (Anoplophora glabripennis) fall into this bark beetle or boring bark beetle category. The mechanism is pretty similar, where they're boring through the bark and creating these egg laying galleries beneath the bark of the tree, and that destroys the vascular tissue.
There are also significant pests that that we look at that are defoliators. So things like spongy moth (Lymantria dispar)—so this is the pest that was formerly known as gypsy moth. What this does is essentially just defoliate a tree. It goes through outbreak cycles where the conditions are right for a large number of spongy moths to hatch that year, and it essentially just cuts leaves off of trees. So that is obviously an issue when it comes to things.
Sarah Beck: Trees like photosynthesizing.
Tyler Hale: Exactly, and then there are some other some other pests that will feed directly on soft tissue, like leaves or younger stems. So insects that have, they call them piercing-sucking mouthparts, that will suck the juices right out of a leaf. That does a similar thing to defoliating, just has a negative impact on the plant's ability to photosynthesize.
So you mentioned insects that might not be eating the tree. So we also see things like disease complexes, so disease insect complexes would probably fall into that category.
There are some situations where the insect is not actually an issue, but it may be harboring a pathogen will actually cause issues for the host plant. And we see that in various places.
Sarah Beck: What's the climate change component of all of this? Can you describe where that fits in?
Tyler Hale: Climate change brings up another interesting part of this issue.
When we hear about emerald ash borer, Asian long-horned beetle, Japanese beetle (Popillia japonica), things like this, we're always thinking about insects that have been introduced to North America from other places. That is not always the case when we're looking at major pest infestation issues in urban landscapes or in forests.
So you can have native insects that, due to things like climate change or poor forest management, can have outbreak cycles and cause similar types of large-scale deforestation as some of these introduced insects do. So that's part of that climate change issue.
As things get warmer and drier, you see more unpredictable wildfire situations. All of these things stress forests out, and pests are generally attracted to plants that are already stressed for some reason. As the climate changes and that plant no longer feels comfortable in the climate that it finds itself in, it'll be stressed from drought, it'll be stressed from ash or fire or something like that, and that can be the entry point for an insect to take advantage of what would otherwise be a healthy tree.
Sarah Beck: That makes a lot of sense, and I think we can get into this topic a little bit in terms of our own gardening stewardship and our own care for trees, because I think that’s really a key point.
Aaron Anderson told us recently that in your garden, most of the insects are not doing anything troublesome. In terms of invasives, how does that play?
Tyler Hale: For the most part, things that you find in your garden, things that you see in the forest are not going to be an issue. Generally, they're part of a healthy ecosystem.
You need different types of insects to break down organic material, so plants that have died or died back overwintering, things like that. Insects and other microorganisms help break that down. And help build up soil.
Sarah Beck: They're doing good things most of the time, right?
Tyler Hale: Exactly. Absolutely.
Sarah Beck: Even when they're munching on some of your plants there, we kind of love that food web.
Tyler Hale: Yeah. You see things that are eating your leaves, often all it's going to be is an aesthetic issue. There are, of course, things that will completely skeletonize your leaves, but often something's going to come in, munch on a little bit of your garden, and then move on.
They use this thing called the 10 percent rule. So of all non-native insects, animals, plants that get introduced, or escape cultivation, they say that around 10 percent of them end up actually establishing themselves in a way that's a nuisance or would be considered invasive. Even of the things that we bring in from overseas that might come through ports or other places, those things don't always end up being a major issue.
There's a lot of proactive research being done to look at plant health issues, in other countries, overseas, to try to figure out what, if it were to be introduced, would cause the most issues. So there's a lot of work being done there as well.
Sarah Beck: Is it mostly beetles that we should be concerned about?
Tyler Hale: I think I think having at least a good mental picture of some of these major invasive species is super helpful, but also just understanding a little bit about insect morphology and the way that they feed on things can help make you a better gardener for sure.
It's rare that you'll see the insect in the act of doing the damage. You might see an insect and see some damage. If you understand a little bit about how insects feed and what they're feeding on, you can make some judgment calls about whether or not this thing actually did this damage, because a lot of times you just have some circumstantial evidence.
Sarah Beck: They’re like, “I was just sitting here. I had nothing to do with that.”
Tyler Hale: Exactly. Just at the scene of the crime on that day, which is suspicious. But yeah, I think having a good mental picture of what an Asian long-horned beetle is, what an emerald ash borer is.
Go look up what a spotted lanternfly (Lycorma delicatula) looks like, which is another major pest of concern across the US. They have not yet been introduced to the West, there are no uncontrolled populations, but they do get moved around pretty easily. They lay eggs on things like trucks and shipping pallets and things like this that get moved around the country. They also get moved through nursery stock and would be a major issue on the West Coast.
They have a wide range of host plants that they like to eat, but some of the big ones are apples and grapes. So a major agricultural pest for some major agricultural crops on the West Coast. So definitely something that folks should be looking out for.
Just while on that topic, another one that is super important on the West Coast is one of those insect disease complexes that I mentioned before.
It’s called an Asian citrus psyllid (Diaphorina citri), and the insect itself is not super damaging but it vectors a disease called citrus greening or huánglóngbìng (Liberibacter spp.). And this is this is a disease that has done a huge amount of damage.
Sarah Beck: It’s devastating. Like this is the orange industry, right, or citrus industry, generally?
Tyler Hale: Absolutely. It's out in commercial groves in Florida and doing a huge amount of damage. Not yet doing that scale of damage on the West Coast. The eradication efforts are swift, and the quarantines are pretty strict in California.
The introductions that they do see often are in retail and homeowner citrus. So if you're buying a citrus plant, a lemon or something from Home Depot or another box store, it's important to know the signs of this, because if it gets off of your citrus and into commercial fields, it would be it would be a disaster.
Sarah Beck: Wow. That is very serious. We will make sure that we have all the resources that you mentioned attached to the transcript for this episode.
I had no idea that there was a component of potential spread through, I mean I use lemons and limes on a daily basis here whenever they're available, because they're so good, and having one right outside your house makes a great deal of sense. We're going to have to be very careful to be alert to this. Is this something you'd see damage on the actual foliage of the tree?
Tyler Hale: The Asian citrus psyllid is a very small insect. The symptoms of citrus greening I think are it's worth just looking up and looking at pictures of it, it does basically what it says, it causes the fruits of otherwise healthy citrus to turn green.
Important to know what that looks like and make sure that if you see it, if you're in California, reporting it to CDFA.
Sarah Beck: What does CDFA stand for?
Tyler Hale: CDFA is the California Department of Food and Agriculture.
Sarah Beck: The other thing you mentioned was this sort of movement and I was reminded of, I know there's a couple of rules out there about, “You don't move firewood.” Every now and then, when you're crossing a border, sometimes there's a checkpoint around this.
Can you talk just a little bit about moving things, if you ever didn't take that seriously?
Tyler Hale: Absolutely. Yeah, if you've ever driven into the state of California on a major highway, you probably have been stopped and asked if you're transporting any fruit. That citrus psyllid is one of the one of the big things, but California produces a huge amount of food for the rest of the country, and so they are understandably pretty strict about what you can and can't bring into the state.
Moving firewood is never a good idea. Some of these bark beetles that I mentioned earlier could still be viable and under the bark of firewood, even after it's been chopped up. That's not going to take care of insect pests. So moving them from places where they don't have those pests to places where they do, that's how things are vectored or moved around.
Management strategies change all the time. USDA has a department called APHIS, or the Animal Plant Health Inspection Service. They deal with a lot of the agricultural commodities and creating management strategies for some of these pests. The Emerald Ash Borer Program falls under that umbrella. They have actually moved away from a quarantine and toward a management strategy of releasing biocontrols.
Sarah Beck: Oh, I love this. tell us about some of the biocontrols. This is really neat stuff.
Tyler Hale: This is really interesting research. So essentially you go to the source. So for emerald ash borer, you work with researchers in China, or you send researchers to China, and look at emerald ash borer in its native habitat.
It, in Asia, will have evolved with the ash trees or other plants that are its hosts and they'll have some defense mechanisms, or there will be other insects around, or animals, or something else that keeps the emerald ash borer population in check.
The idea of biocontrols is looking at what those, in this case, it's insects. They're looking at a few different types of wasps that lay their eggs in the emerald ash borer. So what they do is they bring those back to North America. They rear them, so that they can essentially put them in a box and send them to places where there's an active emerald ash borer infestation, and you can release those biocontrols and they do the work for you.
It's definitely one of the more sustainable management strategies. Definitely something that we like to see because the other the other methods are probably going to involve pesticides, which are expensive, they have side effects that we don't like, and in the case of emerald ash borer, they're not terribly effective.
Yeah, if you've got an ash tree that you really love in your front yard, you might get away with treating that continually for many, many years, and keeping that one tree alive, but as far as the urban landscape in sum total, those types of treatments are too expensive to really be effective.
The biocontrols are some of the most exciting management strategies that are being researched right now.
Sarah Beck: Well, and after we talked to Aaron Anderson and just learned the extent to which a lot of these insecticides and pesticides are so toxic, and they're tenacious.
One of the things that Aaron said was about just the pure number of parasitic wasps that exist. There are so many species of parasitic wasp and I think if nothing else, I would love for us to cultivate among gardeners a real appreciation for the parasitic wasp. There's so many of them, and some of them are little, tiny, and they're clearly an important part of our ecosystems. They're really a magical little creature.
Tyler Hale: Absolutely. They really are. They're kind of all over the place in terms of biocontrol as well. When I used to work in greenhouses, we would release a parasitic wasp to cut down on aphid populations.
There are so many different ones. People hear the word wasp, I think, and immediately sort of cringe and recoil because wasps have gotten a bad rap.
Sarah Beck: Those are different ones, though.
Tyler Hale: Yeah, not as nice to be around. But yeah, a lot of these wasps are so small that you wouldn't even see them. Either can't sting you or have absolutely no interest in doing so. They're incredibly important parts of a healthy ecosystem. They're the things that keep our native insects in check.
Sarah Beck: This question does, I know, come up when we talk about biocontrols. Is there a sense that you have one problem, and then you think you're adding a solution, but ecology is so complicated.
I'm assuming these researchers are paying really close attention and are concerned about, “Well, what if this new thing we introduced caused a problem that was unforeseen?”
Tyler Hale: That is definitely an important part of the research, is figuring out once this once this wasp depletes its source of emerald ash borer, will it go after some of our native beetles in the same family or closely related?
So it's something that researchers look at. A lot of these biocontrols, they’re also not adapted to North America, right? So the emerald ash borer has found its niche here, but a lot of these biocontrols can't overwinter in North America.
Sarah Beck: That interestingly reminds me of what you were saying about climate change, too, because if we are having these strange shifts in what our typical weather pattern is, that really opens up this vulnerability to something that might be able to fill into that space.
Tyler Hale: It opens up vulnerabilities for everything. It creates situations where native plants, native insects have a hard time adapting, just because of the speed at which the climate is changing and how erratic some of these weather patterns are becoming.
Sarah Beck: I do want to circle back to all the wonderful things that we can do to care for our urban forests, generally, as gardeners in these spaces, because clearly there are ways we can minimize the impacts of a lot of these issues, right? What is your advice to gardeners and folks in urban spaces, whether as professionals or as individuals, they're caring for some landscapes?
Tyler Hale: I would say these major significant pests or invasive pests are something that you should take as part of your overall strategy to cultivate a healthy landscape.
This all falls under this umbrella of IPM or integrated pest management. Whether it's a common garden pest or one of these major invasives, there are things that you can do to give your landscapes a helping hand. Planting native plants or just understanding what wants to live where you want to plant is one of the most important things that you can do. Just understanding your conditions in your area.
Get a soil test done. See what kind of soil you have in your garden. That can go a long way to helping you pick plants that will thrive and be healthy, and healthy plants are less likely to have pest issues.
Understanding your plant material, understanding what it looks like when it's healthy, understanding what it looks like when it's stressed, and understanding what different types of insects and disease damage look like are also super helpful.
I think having an awareness of the resources at your disposal is also important. Understanding who works at your local extension. A lot of extensions will have somebody who specializes in ornamental horticulture. If you're a master gardener, you're obviously pretty familiar with this already, but that's another great resource to keep in mind.
But yeah. Plant what wants to be in your garden, and I think you're in pretty good shape. That’s the big piece of advice that I would give.
Sarah Beck: Oh, absolutely. What you said also reminded me, because we have had a lot of great expert advice from a lot of researchers working on drought. And looking at just explaining what you should be doing in terms of irrigation establishment.
Irrigation doesn't mean you're supposed to be just pouring tons of water on a plant that's adapted to a summer-dry climate. So I think you really made some great points there about your climate-adapted plants need climate-adapted maintenance, as well. We’re not just like pouring water on them during their dry time.
Tyler Hale: On that point, when I talk to folks at some of these diagnostic labs where homeowners send in samples of diseased and dying plants, overwatering is one of the biggest killers of residential landscapes and houseplants. Yeah, you're probably watering too much.
Sarah Beck: I just had one other question, just thinking about the roles that professionals play in the world that you're in. I think this is such an interesting slice of a horticulture-allied profession. There are some government agency roles and obviously there's all kinds of interesting research going on. What are some of the career opportunities in this field?
Tyler Hale: There are a lot of careers in forestry, in maintaining healthy forests.
There's just a ton of research being done in this field right now, from testing the genetics of plants to see if they're resistant to some of these issues, to identifiers who work in ports of entry who just comb through all the plant material that gets imported every day and look for pests at the state level. Folks do this at nurseries and farms.
Within the small sphere of pest detection, there are a lot of great careers. I work with public gardens, and there are also a lot of great jobs at public gardens that do similar things, whether it's education or caring for the landscape at gardens. They’re also a great place to work.
Sarah Beck: I agree. Your programs have had some success in this way. Do you want to share a couple of highlights of what you've achieved over the years with working with public gardens?
Tyler Hale: I've been working with the American Public Gardens Association since 2016. Coordinating and managing various programs in this field, we've educated nearly a thousand public garden professionals on these topics, brought them to workshops and talked about these different issues, helped them with strategies for talking to the public about these issues, how to monitor.
We've also done some targeted pest trapping at gardens around the country, just looking for these specific pests, looking at where they’ve been introduced into different landscapes. We've got a youth education program that that works through our public garden membership. So, if you're near a public garden, and you want your kids to get interested in this, ask them if they participate in the Plant Heroes program, or you can check us out at plantheroes.org.
Sarah Beck: There have been first detections where somebody saw something. It’s like, “If you see something, say something.”
Tyler Hale: Absolutely. A lot of times it's homeowners who find these things. One of the first introductions of emerald ash borer in Texas was discovered by some teenager using one of these apps on his phone to identify insects and found an emerald ash borer and reported it to a state agency.
So it could be you. Be a real-life plant hero.
Sarah Beck: If you're a gardener, I feel like there are certain things that should be common knowledge within these areas. I'm not saying that everybody needs to know deep detail, but just to have that awareness. Because if you think about just all the times that you're traveling and, hey, your family's going camping. And you're like, “Huh, should I throw some wood in the back of the car and take it with me?”
Pests and pathogens and chemical threats to pollinators, all of these things. I think there's a certain amount of common knowledge that once you have an awareness, you realize how important it is, as a community member of the world.
Adriana López-Villalobos: For me, what are the conditions that might help the spread of X or Y pathogen, insect? That's not clear to anyone, right? There are some things that we know, oh, these things might help with life cycles. Because there's a lot that is not known, it's better to take precautions and be more careful.
Like what example he gives with introducing firewood from one place to the other. You might not see it, but it could be there in different life stages.
This theme is definitely interesting for the community that we serve. It is definitely important and globally it threatens biodiversity, right?
Sarah Beck: I honestly was quite surprised by the citrus psyllid information. I mean, I had been aware of citrus psyllid in terms of the citrus industry. I was very aware that quarantines have happened a number of times.
When it comes to commercial or academic situations, there's so many regulations and people are being so cautious and professionals are involved.
This is gets me back to thinking about the individual being aware of these things, because they're most concerned that it's going to be someone purchasing a citrus plant, a sweet little lemon tree that you want to put in your yard, that that could end up being the vector, that could end up being the infected plant that then impacts, say, a massive area of agriculture in our areas. It's a little bit terrifying.
Adriana López-Villalobos: It is, and a lot of it honestly comes down to the economic impacts.
Like we think of the impacts on agriculture are huge, and those translate to money—the interference with the productivity of the forest, the social aspects, the aesthetic impacts on urban areas.
Sarah Beck: Something that I really took away from really both talking to Aaron Anderson and Tyler Hale was, not that we need to be patting ourselves on the back, but a little bit of a feeling that the things that we have been working on at Pacific Horticulture all this time—talking about climate-appropriate selections and really finding the right plant for the place. This idea that if we make careful choices about the plants we are putting in the ground and that those plants are going to thrive because we paid attention to the soil type and we paid attention to moisture needs and we didn't overwater.
I think that there is something to really say about the strength of a plant and the resistance to disease, pests, and pathogens that a plant has. I think there's something really great to say here about the rewards of the work of thinking about, how do we select plants that are really going to be happy where we place them? And how do we give them natural immunity?
Adriana López-Villalobos: Like if you're choosing the right things that are going to be happy in that environment, we're not stressing the plants to the point where they can get sick and infected and be potential vectors for pests and other insects that might be harmful.
Sarah Beck: We had a really nice webinar event last week with Kurt Wilkinson, who is a is a designer, a garden designer in Adelaide, Australia, and I was really taken aback with his comments about this.
Kurt Wilkinson was talking about how, of all the mediterranean climates of the world, the one that he's in is probably the most difficult. It made me actually feel like we're really lucky in the West Coast region of North America, because in Adelaide, Australia, he was talking about, first of all, very low air moisture. He said that experienced 50 and 60°C temperatures. I thought he was using Fahrenheit.
He's only selecting plants that.do well in his climate, but he feels very strongly that with the pathogen pressures that he deals with where he is, he feels like having a plant that is resilient and can fend for itself is really the only answer.
Adriana, when you think about advice for the gardener or for a designer or a professional horticulturist, what do you think are the high-level takeaways from this? Other than those basic selection ideas? Are there other things to take away from this that people should have in mind?
Adriana López-Villalobos: I think learning about the plants they want to grow. We need to know what we're going to grow, how it looks at different stages from seedlings all the way to reproductive individuals, and learning how they spread, how they reproduce, because that gives you an insight of when things are not right.
Sarah Beck: Yes, I think you're absolutely right. Like understanding what the healthy version of the plant you’re caring for should look like.
