We Can Protect Plants from Invasive Pests with Garden Futurist Tyler Hale

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.