Holden Arboretum Studies Resistant Beech and Ash Trees

Herein lies a post about the long, patient work that begins when something goes wrong with the world. With the introduction of beech leaf disease into North America, things have gone very wrong. Another noble, native tree species, towering and strong, is proving no match for a microscopic nematode. When this happens--yet another example of collateral damage from international trade--scientists mobilize to seek understanding and possible remedies.

In recent blog posts about beech leaf disease, I've mentioned Holden Arboretum. Holden happens to be located east of Cleveland, close to where the disease was first noticed back in 2012. Visiting family in Cleveland this summer during a band tour, I reached out to Holden staff to see if I could stop by to witness their research on the disease. 

Tucked behind some 3000 acres of gardens and ponds, forests and fields, is a research station where Holden is devoting staff and greenhouses to a collaboration with the U.S. Forest Service and others to test resistance not only beech leaf disease, but also to the introduced insects that have decimated two other native trees--ash and hemlock. 

I learned primarily about their research on beech and ash trees.

AMERICAN BEECH

Where did the nematode that causes beech leaf disease come from? According to Rachel Kappler, Holden's Forest Health Collaborative Coordinator, who generously came in on a Saturday to give me a tour, they have identified the island in Japan from which the nematode came. It was not a species from Asia's mainland. 

Holden's main endeavor is to seek out beech that show some resistance to the disease, and test that resistance. 

Rachel first grows seedlings that can be used as root stock for these tests. The root stock serves as the bottom half of a graft.

When trees are found that have lingered in the landscape while others succumb, Rachel then grafts cuttings from these "suspiciously healthy" trees onto the prepared rootstock. 

Once the grafts heal,

the trees can be tested for resistance. Measured numbers of nematodes are applied to the buds, documented with colored tags, and the tree's resistance to the nematodes is then observed.

The nematodes are small enough to enter the buds between the overlapping bud scales. The tiny worm-like creatures inhabit the leaves all summer. Then in fall, exiting the leaves through the stomata--the openings on the undersides of the leaves through which the tree breathes--the nematodes transfer to the new buds to overwinter.

Each step in the process of testing resistance takes time and consistent attention. Rachel says some promising means of speeding research are in the works. Promisingly resistant trees can be propagated using only their leaves. The leaves are cut, a particular root hormone applied, then the leaf is stuck in soil medium to grow. This approach could potentially avoid the need to grow root stock, grafting, and the time it takes for grafts to heal.

As for treatments for the disease, she says soil applications of phosphite have mostly been experimented with on smaller trees because it's easier to study at these smaller scales. Similarly, using chemical sprays on the trees' foliage requires just the right timing, and a thorough coating, which makes larger trees very difficult and expensive to spray. They are experimenting with pruning to allow better air circulation and thereby reduce the moisture that the nematodes like.

ASH TREES

Research on resistant ash trees is a little farther along. Rachel showed me a grove of young green ash--protected by a deer fence--that are being tested for resistance to the Emerald Ash Borer (EAB), which spread through Ohio nine years before Beech Leaf Disease. This is the same introduced insect that has decimated Princeton's ash trees.

Rachel explained that the ash can defend themselves from the burrowing insects in three ways. One is a blockage that prevents entry. Another is to react by building a wall around an ash borer that has gotten in under the bark. Another is to somehow deprive the ash borer of nutrition, so that it becomes stunted. 

Sticky boards are used to monitor the presence of Emerald Ash Borers at the site.

When I told her that I had only seen one adult Emerald Ash Borer in my life, despite the hundreds of millions of ash trees killed, she pulled one off of the sticky board.

In this closeup, the Emerald Ash Borer is on the left; a native ash borer, far less destructive, is on the right. Though they are similar in appearance, it's the difference in behavior of the introduced species that has proven lethal.

She said that ash trees become vulnerable to EAB attack fairly early in life, certainly under ten feet high. While some of the ash trees being tested in the grove are dying due to EAB (perhaps these are the controls in the experiment), 

many are doing well, showing some degree of resistance. 

The green ash that have proven resistant to the EAB must not only be able to survive at low EAB levels, but also when the Emerald Ash Borer is present in high numbers. Rigorous testing helps avoid later marketing an ash variety that ultimately could prove vulnerable. 

This scar is evidence of an inner struggle by the ash to fend off the borer. The tree tries to build walls around the EAB larvae. 

Rachel described an autoimmune reaction, observed in black ash up north, in which the tree is too aggressive in blocking off passages, interfering with its own circulation. 

She talked about the physical aspects of doing research on trees and their pathogens. The wooly adelgid that plagues our hemlocks is hard to study, in part because it can be hard to apply the soft insect to test trees without squashing its soft frame, so they use its eggs. Nematodes are much easier to count and apply to branches.

Expanded greenhouses suggest Holden is expanding its efforts to nurture trees resistant to imported insects and disease. 

One bonus from my visit was that Rachel took an interest in our efforts in Princeton to bring back the native butternut (Juglans cinerea), and has put us in touch with someone studying the species.

If, as beech leaf disease takes its toll on beech trees in Princeton, we see some trees that "linger" and remain "suspiciously healthy," we'll want to notify Holden Arboretum, to aid their ongoing search for resistant trees. 

A thunderstorm prevented me from exploring the many gardens at Holden that day, including a treetop walk and tower. And then there's the Cleveland Botanical Garden closer into town, with which Holden recently merged. These are some good botanical destinations in Cleveland, with a mission that extends far beyond the city, and an engaging origin story.

Botanical Threats to Greenway Meadows--Neighbors Raise Concerns

Over the years I've sung the praises of Greenway Meadows, the park in western Princeton with an asphalt trail running down the middle of an expansive meadow. One post describes the beauty of broomsedge and cross country racers "testing inner nature in a natural setting." Another describes the exhilaration of riding a bike through the meadow on the way to an art exhibit opening at the Johnson Education Center.

More recent visits to Greenway Meadows have focused on the threats to the park posed by invasive species, and the need to act quickly, before the problem gets overwhelming. This past April, it was dramatic to see how lesser celandine is beginning to invade the meadow and the lawn.

Then this summer, Mimi Schwartz, who lives near Greenway Meadows, reached out about the park. She had noticed some attrition among trees along the Poetry Trail, and wondered if competition from the tangle of invasive shrubs growing beneath them might be a cause.

Another neighbor of the park, Jennifer Widner, is focusing on threats to the meadow--threats that surely go unnoticed by the many people who walk or jog down the asphalt trail, see a pleasing green, and look no closer.

Still apparent to all are the many native wildflowers in the field, among them common milkweed and wild bergamot. 

But on a visit to meet Jennifer, I was astonished to see the extent to which Sericea lespedeza (aka Chinese bushclover, Lespedeza cuneata) is beginning to dominate. This is an invasive species that has become a big problem in the southeast U.S. and the plains states, but was comfortingly rare in Princeton when I first moved here in 2003.

There are various species of native bushclover that can sometimes be found mingling with other wildflowers in a field, but Sericea lespedeza doesn't, as they say, "play well with others." It's behavior is more that of a bully.

In understanding the threat posed, it helps to have lived elsewhere in the country where Sericea lespedeza has had a longer track record of aggression. Living in Durham, North Carolina, near where the species was first introduced, in 1896, and is still widely used for erosion control despite many efforts to have it banned from seed mixes, I witnessed its capacity to displace native species. 

For those who say live and let live, and let it be, consider the ecological consequences if the meadow ultimately becomes a monoculture of an introduced plant with indigestible seeds and inedible foliage. Here's one fact sheet's description:

"Sericea contains a high concentration of tannic acid, which causes wild and domestic animals to avoid eating it, unless no other food is available. Animals then forage more intensely on native plants, which depletes the desirables and allows invasives to increase. Tannic acid leaches from sericea into surrounding soil, creating a toxic environment that prevents or slows the growth of other plants, giving it yet one more advantage."

Mimi and Jennifer have had some success engaging public officials on these threats, and the land managers at DR Greenway's headquarters nearby are potential allies. 

The project with the clearest solution is the freeing of trees from the invasive shrubs growing beneath. A greater challenge, requiring intervention and vigilance for years to come, will be stopping uber-invasives like lesser celandine and Sericea lespedeza. 

My experience, though, is that the work can get easier year to year, as steady effort makes the invasives less numerous. Down the road, or down the trail, as the threat recedes, those involved may get to experience that wonderful "walk in the park" feeling, where the botanical bullies have been sent packing, and require only a bit of ongoing vigilance and mild intervention to prevent their return.

For more information on Sericea lespedeza, try these: BlueRidge and Oklahoma State.

Related post:

Monocultures in the Making - 2013

Fuel Tank Raingarden Losing Out to Weeds

Maintenance is looked down upon and taken for granted in our culture. One reason for this is that, done well, maintenance is invisible. Our human tendency is to notice what is wrong, not what is kept right. At home, we are more likely to notice dirt and disarray than the cleanliness and order a housemate worked hard to achieve. 

In landscaping, the tendency is to fund and celebrate design and installation, then leave maintenance to the vicissitudes of chance, undertrained and undermotivated staff, and perennially strapped budgets. But even with the best designs, maintenance is what ultimately matters. Maintenance is destiny. 

Maintenance at its best is a form of love. In gardening, what we call maintenance is really more akin to the nurturance of parenting--an ongoing process of encouraging what is desired, and discouraging what is not. A garden can also be thought of as a playground. When maintenance is done right, plants that exhibit bullying behavior, like mugwort, don't get to play in the garden. 

Environmental groups encourage people to dig up some lawn and plant native wildflowers. These meadow plantings are characterized as low-maintenance, but that is true only if the weeds are caught early. Once the weeds get firmly established, maintenance becomes very difficult.

The only gardens I've seen flourish are those that are loved, like a child is loved. Love leads to knowledge and steady attention, and early intervention when things go wrong. 

Just off Witherspoon Street in Princeton there are contrasting examples of loved and unloved public gardens. 

The loved garden in this instance has almost no weeds--a standard few of us achieve. For years, near the entrance to the Community Pool, gardens around the Princeton Recreation Department offices were taken care of by "Vikki C. and Team PRD," as the sign proudly declares. That would be employee Vikki Caines. Vikki's glorious plantings expanded over the years well beyond the Rec. Dept. building. She retired in 2023, but when I asked her, she assured me that her gardens would continue to be well kept. 
 

By contrast, just down the street, past the Princeton First Aid and Rescue Squad, lies a rain garden that collects water from hard surfaces around the town's fuel storage tank. Regulations require that raingardens be dug and planted to collect and filter runoff from new paved areas. In a series of posts, I've tracked the destiny of this very public but largely unnoticed raingarden, whose extended limbo in 2020 ended with planting in 2021. But in gardening, as when a baby is born, the birth of a garden is not the end but rather just the beginning. In 2022, it was still full of color and easy to weed, but by 2023 the weeds were getting entrenched. 

I alerted town staff that the raingarden was losing out to the weeds, and was told that the municipality was weeding it once or twice a year, and was working "towards a system of regular maintenance, while balancing many, many other priorities."

This year, the original plantings are beginning to disappear beneath waves of mugwort, nutsedge, and other botanical bullies that don't play well with others--

weeds like foxtail grass, 

and wild lettuce--to name just a few of the species that maintenance crews would need to be able to recognize and remove. Note that the designer of a garden must know only the intended plants, while the maintainer, typically underpaid and underappreciated, must additionally know and recognize the many weeds that can invade.

This is the difference between loved and unloved gardens. Imagine a child being notified that a parent was "working towards a system of regular visits, while balancing many, many other priorities."

Now, a town's public works department does of course have many other priorities. Job one is to serve people, not gardens. But that being the case, the aim would be to keep the raingarden in the easy-to-maintain stage by catching the weeds early. Vigilance and early intervention--a form of love--save time. 

The only way Vikki Caines could maintain beautiful gardens while also doing her job in the recreation department was to stay on top of the weeding. 

Well-designed raingardens are easier than most gardens to maintain. The runoff they collect keeps the soil soft for easy weeding, and many native species of wildflowers and shrubs are adapted to flourish in the wet ground. Regulations can call for the digging and planting of raingardens, but the fate of the planting is left to chance. Weeds grow 24/7, while people are easily distracted. If the weeds take over, the ultimate response will be to mow it down and manage it as lawn. Nature's complexity, unloved, unnurtured, will once again be simplified and suppressed, the better to pursue other priorities.

Related posts: 

To Save a Raingarden, Know Your Weeds 

The Work Behind a Natural-Looking Meadow: Smoyer Park in Princeton

Evolved Coexistence in Nature

What is "natural" in nature? I remember a 1990 column entitled "Bug Wars," in which NY Times columnist Anna Quindlin wrote about the gypsy moths that, back then, were defoliating vast areas of eastern forest. She used the destructive moths as fodder for reflections on nature and its ways, not knowing that the moths can hardly be thought of as natural. They were introduced from another continent, then escaped and multiplied, consuming forests that had not evolved any defenses against them. Fortunately, scientists found a very low-toxicity way to limit the gypsy moth's numbers, though sustaining that balance requires ongoing human vigilance and action.

With introduced insects and diseases having decimated first our ashes and now our beech trees, it's worth noting the more sustainable relationships between plants and animals that have co-evolved over millennia on the same continent. 

Tent Caterpillars and Black Cherry

This spring, tent caterpillars defoliated some of our black cherry trees. Were the caterpillars a threat to the trees? Well, they finally got their fill and wandered off to pupate and become moths, leaving the trees to sprout new leaves and grow unhindered for the rest of the summer. The trees may grow more slowly, but their survival (and therefore the survival of the tent caterpillars that depend upon them) is not in peril. 

 

Hibiscus Sawfly and Rose Mallow Hibiscus

Near the gazebo in the Barden at Herrontown Woods grows the local native hibiscus (H. moscheutos). Earlier this summer, its leaves were getting eaten. 

Some internet research suggests that these are larvae of the hibiscus sawfly. 

If the culprit had been an introduced insect, I might have worried. For instance, each year I see more evidence of our arrowwood Viburnums being eaten by the Viburnum leaf beetle, an insect introduced from Europe. Because the beetle's arrival is fairly recent, we don't know if it poses an existential threat to Viburnums.

But given that the native hibiscus sawfly has been interacting with the native hibiscus for thousands of years, that long track record of coexistence is reassuring.

 

Though many leaves were partially eaten, the hibiscus grew new ones that remained unaffected. I think of this relationship as akin to someone who donates a percentage of their income to good causes each year. 

An Aphid-like Insect and Hickory Trees

Earlier this year, some leaves of a young hickory tree developed these green bumps. They appear to be hickory leaf galls, caused by an aphid-like insect in the genus Phylloxera. 

The hickory leaves ultimately curled up. The insect's lifecycle sounds much like that of the introduced nematode that causes beech leaf disease. Should we be worried for the future of hickories?

Again, the aphid-like Phylloxera and the hickory tree "go way back," and through those millennia a balance seems to have been struck. Only the lower portions of the tree appear affected. The hickory continues to grow. 

Psyllids and Persimmon

Lastly, a twig on a native persimmon in Herrontown Woods was showing symptoms of contorted leaves similar to those proliferating on nearby beeches. Might we be losing our persimmons? Again, some internet research points not at apocalypse but at coexistence, between the native persimmon and a native insect called the persimmon psyllid. 

According to a NC State website,

"On native persimmon, these psyllids can be temporarily abundant; but their populations soon decline naturally, as they are attacked by their natural enemies, including parasitic wasps."

For some, even small blemishes on a plant will be annoying, but in a nature preserve, the long-sustained give and take between the plant and animal worlds is part of a complex food web to be celebrated. 

We could wish that the beech and the introduced nematode that threatens it would ultimately come into a balance that allows coexistence, but other native tree species laid low--chestnut, elm, ash--remain marginalized, even, as in the case of the American chestnut, more than a century later.

Finding Pawpaws in Paw Paw, Michigan

When the Lunar Octet, a latin/jazz band I've been in for 40 years, performed this past weekend in PawPaw, MI, a jazz naturalist like me was naturally curious about whether there are any pawpaws growing there. 

The town, named after the PawPaw River, which in turn was named by the indigenous people after the pawpaw trees that grew along it, has a population of about 3500.  Though the downtown preserves some historic feel, the town has not exactly embraced its namesake. Grapes ornament the town logo on the water tower and elsewhere, not pawpaws. 

Upon arrival, I asked my phone where I might find a pawpaw in Paw Paw, and was directed to the post office, where I navigated past redbuds and callery pears before finding this pawpaw tucked around the side. 

The tree had fruit, but none ripe as yet. I asked around, at the sandwich shop and down along the beautiful lake where we performed. Most people were unfamiliar with this native tree. The post office worker I ran into said he didn't know anything about pawpaw trees in PawPaw, except that he doesn't like the taste. 

The flavor of a pawpaw, a rich, creamy combination of mango, banana and pineapple is appealing to some but not everyone. Our host was more generous with her knowledge and assessment, mentioning a couple places the pawpaw grows in town, including at one of the schools.

The town of Pawpaw sprouted along the Territorial Road, one of the three main east-west routes of pioneer days. That history is documented next to the lake, but the native tree remains largely unknown and uncelebrated in a town that bears its name. 

My theory is that, since Asimina triloba primarily grows in floodplains, the pawpaw trees were lost when the river was dammed to make Maple Lake. Its fruit, with fragile skin and a taste less universally appreciated than other tropical-tasting fruits, resisted mass marketing. That, and the general drift away from plant knowledge, consigned the pawpaw to obscurity. 

Still, it remains a singular fruit, the only member of the tropical custard apple family, Annonaceae, to adapt to northern climates. And some of us still remember the song: "Way down yonder in the pawpaw patch"--a pawpaw patch that, in PawPaw, Michigan, became a lake with a lovely breeze to carry our music. 

Update: Turns out that, if you live in PawPaw Michigan, you'd have to drive to southern Indiana or Ohio to find a festival celebrating the pawpaw. PawPaw's festival celebrates grapes.

New: Field Guide to Mushrooms in Herrontown Woods

Thanks to Peter Ihnat and his daughter Raisa for sharing their extensive knowledge of mushrooms in a Field Guide to the Wild Mushooms and Fungi of Herrontown Woods. 

Peter and Raisa return today, Sunday, August 4, to Herrontown Woods to lead a mushroom walk from 11am - 1pm. 

Raisa posts about the mushrooms she encounters on her instagram account, foragingwithraisa.

How Are Monarchs Doing in 2024?

Several times a year, the question of "How are the monarchs doing?" rises in my mind. An internet search typically ends up at Chip Taylor's blog on Monarch Watch. There you will find thoughtful commentary and deep analyses, a mixture of good news and bad news, as this extraordinarily resilient species faces ever greater challenges. In 2024, overwintering numbers in Mexico were the second lowest ever recorded, with 2013 having been the lowest. Chip's more recent posts tell of a rebound this summer, as this robust and prolific species has increased its numbers during its migration, following the growth of milkweed north in a tagteam of successional generations, spreading into all corners of the eastern U.S.. 

I've had maybe five sightings of monarch butterflies this summer--a typical number. One appeared frantic, as if it had been searching the great outdoors in vain for a partner. Another was laying eggs on a patch of common milkweed at Mercer Meadows--a beautiful and hopeful sight. Another, pictured, was in my front yard on busy Harrison Street in Princeton, gathering nectar on a swamp milkweed. 

A few days ago, one was nectaring on a patch of narrow-leaved mountain mint near Herrontown Woods. I was treated to a surprising display of butterfly aggression, as several skippers suddenly ganged up to chase the monarch away from the mountain mint. 

Part of that competitive fervor may have to do with the scarcity of pollinator plants. In a 4.5 acre field, there were only two small patches of mountain mint. Since forests don't supply summer nectar, meadows like this are where monarchs and other pollinators are going to find food and each other. Many meadows and roadsides are being taken over by mugwort, Chinese bushclover, and other invasive species with limited utility for pollinators. Add that threat to all the others: habitat loss, climate change, indiscriminate herbicide use in people's yards and along roadsides. This meadow is preserved, but that's really just the first step in realizing the meadow's potential as habitat that can help sustain species like our beloved Danaus plexippus, aka monarch butterfly.

Related posts:

Growing Monarchs

Do Praying Mantises Eat Monarch Butterflies?

Other previous posts about monarchs

The Wineberry Tease

Wineberry (Rubus phoenicolasius) is a non-native bramble common along woodland edges. 

Because its berries are tasty, I have in the past hesitated to remove it from our various wild garden areas. But this year, the hesitation is fading fast. One reason wineberry is getting cut down and pulled out is the cumulative impact of thorns on my sympathies. Repeated prickling sensations from running up against a wineberry or even a native blackberry gets old.

Another reason is that the dreamed of harvest of delicious wineberries is very nearly all intercepted by the birds, particularly catbirds. The early bird gets the wineberry. leaving us a disappointing display of "too late" and "too soon."

Another good reason to remove wineberry is that it will take over your garden. Here's a wall of wineberry along a road in Kingston, more than holding its own amidst other invasives like mugwort and multiflora rose. 

Even wineberry will lose out to the mobbing behavior of the uber invasive porcelainberry vine. You can see wineberry's last gasp at the bottom of the photo. 

A Followup on Beech and other Threatened Native Trees

Having grown despondent about the devastating toll beech leaf disease will likely take on Princeton's beech trees, I was surprised and somewhat heartened by what I found on the Princeton University campus. 

A friend from childhood was visiting me for the first time, and as I showed him and his wife around campus, I began to feel as if we had somehow been transported back to an era before introduced pathogens and insects had marginalized many of our native trees.

An American white ash towered over us, healthy as can be. American elms, too, grew as if Dutch elm disease had never arrived.

Unlike the ailing beech trees up along the Princeton ridge, the beeches on campus appeared unfazed by beech leaf disease.

I looked for signs that these trees had been injected with chemicals to ward off invasion, but found none. Surely, though, this improbable survival depends heavily on medicinal intervention.

Since I first alerting the community to the presence of beech leaf disease in Princeton in a blog post and letter to the editor, some articles have been written in the local press--one in TapInto Princeton and one in Town Topics. 

Both mention phosphites as the primary treatment available thus far. Applied to the soil, phosphites are a biostimulant that improves the tree's immune system response. I was skeptical that this could make much of a difference, but the University appears to be having good results. Grounds supervisor EJ May said they started seeing signs of beech leaf disease two years ago. Speaking generally about efforts to save native trees, he acknowledged some losses but some success as well.  

Another lead I had checked out was a kind of beech mentioned in a list of special campus trees.  Called a fern-leaved beech (Fagus sylvatica 'Asplenifolia')--a variety of European beech with unusual foliage--the university had gone to great lengths to save this extraordinary specimen during construction of the new chemistry building. The tree's described online as having "no serious insect or disease problems." Was the text written before beech leaf disease was discovered in 2012, or might this variety have some sort of natural immunity? I stopped by to take a look, and could find no visible symptoms. 

There remains, too, an uncertainty as to the origin of the nematode that causes beech leaf disease. It is most similar to a species found in Japan, but differs in some ways.