Eastern Hemlock: Pests, Benefits and the Pennsylvania State Tree

Lou Meyer, regional business developer in Davey's mid-Atlantic region, talks about the Pennsylvania state tree, the Eastern hemlock, as well as its beauty, benefits and threats it faces from the hemlock woolly adelgid. 

In this episode we cover: 

• History of the Eastern hemlock (1:03)
• Horticultural oil for pest control (2:18) (5:56)
• What are other treatment options for these trees? (4:04)
• Signs of hemlock woolly adelgid (6:47)
• Does fertilization help Eastern hemlocks? (8:07)
• How weather and temperature affect these pests (8:31)
• Can these pests kill hemlocks? (10:08)
• Hemlock woolly adelgid damage treatment (10:48)
• The wonder and beauty of Eastern hemlocks (11:41)
• Are they easy to grow? (13:32) (14:06)
• Shade-tolerant evergreen (13:40)
• Physical description and genus of the tree (14:52)
• These trees need room to grow (16:20)
• Eastern hemlock cultivars (17:03)
• Are all hemlock cultivars susceptible to hemlock woolly adelgid? (18:33)
• Can deer damage these cultivars? (18:56)
• Other uses for the Eastern hemlock (19:16)

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Connect with Doug Oster at www.dougoster.com. 

Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!

Transcript

Doug Oster: Welcome to The Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much, much more. Tune in every Thursday to learn more because here at the Talking Trees podcast, we know trees are the answer. Well, he's back again, our friend, Lou Meyer, a regional business developer for the Mid-Atlantic region for the Davey Tree Expert Company based in Baltimore, Maryland. Today, in our occasional series on species, we're talking about the Pennsylvania state tree.

Lou Meyer: That's right, Doug, the eastern hemlock, the mighty tsuga canadensis. Fun spelling there. It's got a silent T at the front, so it's a good Scrabble word if you've got a floating T out there.

Doug: [chuckles] Well, I've got them all over my property, Lou. I've got at least 40, 50 of them. I guess we can start off with maybe one of the problems with hemlocks, which for us here is hemlock woolly adelgid, or would you rather talk about something more positive right now?

Lou: No, let's lead with the adelgid and end on the positive. Yes, it is a prevalent pest of our eastern forest. The hemlock woolly adelgid was introduced in 1924. It came here. It's a pest from East Asia. It definitely came here on a boat at that time. Probably hooked into a pallet or shipping container. Maybe nursery stock, but usually not. Interestingly, there is a hemlock woolly adelgid for the western hemlocks that has been on the continent for thousands of years. Like the hemlocks of Asia that have evolved to live with the hemlock woolly adelgid there, our western species have also. Our eastern species are just getting decimated.

Doug: Yes, tell me about it. Here, we had a brutal stretch of winter, which it's tough during the time, but it also knocks back those hemlock woolly adelgid. In my situation, I have so many hemlocks, they can't all be treated. Anything that I can reach, I'm covering that pest with horticultural oil.

Lou: That's your best approach. That's the first step. We like using horticultural oil for a lot of reasons. Number one, it's a non-toxic product that is safe for birds. You don't want to directly spray a bird with it on purpose by any means, of course. It's a non-toxic approach to pest control. Utilizing horticultural oil for hemlock woolly adelgid is great for a whole variety of pests. You want to apply hort oil when it's between 40 and 60 degrees. For hemlocks like yours, we like doing that in the springtime or in the fall. Actually, both springtime and fall, for good control.

You don't want to do it. You do not want to apply it when it is hot out. It is an oil. It will fry your trees, like steak in a pan. [chuckles] If you mix in oil in the summer, it's bad news. Now, professionally, we can water it down. There are times where we can stretch that time usage by tweaking it, but you really don't want to use hort oil in the summer.

Doug: If you had a 40-foot-tall tree, like in the case of me, a homeowner that couldn't get horticultural oil up there, what are other treatments for a tree like that?

Lou: Yes. We can use systemic products that we either spray onto the trunk of the tree, drench over the root system of the tree, or in rare instances, inject into the tree. We inject all sorts of products into trees when we need to. We drill into the cambium, the vascular system of that tree. You put a one-way stopper valve, you hammer it into that hole, and then into that valve, you inject the product. The tree's vascular system, the cambium, uptakes it, and it works through the tree. One of the benefits for hemlocks for utilizing that is the control lasts between three and five years.

It's usually a more costly approach upfront, but the long-term effect outweighs that. You really have to decide. What you don't want to use is those pesticides near water. If you're near a lake, in hemlocks-like wet spaces, you find them growing over creeks and rivers, especially in Pennsylvania, the brook trout, a favorite. I think you said you might go fishing today. The brook trout loves to spawn under the shade of the hemlock tree in those creeks. We want to protect those trees for the trouts. We do not want pesticides washing into there.

For those purposes, drilling into the tree where it's close to waterways so it's contained into that tree system is a really important approach.

Doug: All right. I'm writing down that fishing tip. Let's see. Brook trout underneath hemp. Got it.

Lou: There you go, buddy.

Doug: Would it be cost-effective or effective in general to get up high with horticultural oil?

Lou: Yes, absolutely.

Doug: Is that something you would do?

Lou: Yes. First of all, the trucks we use have pumps on them. You can put horticultural oil pretty high up with those. I've seen 50, 60 feet. For above that, you can go up in bucket trucks. We will do that occasionally, especially on sensitive properties where they don't want any pesticides being used. Think of government properties. Here, I'm in the capital region. A lot of those DC properties that have really big trees, they don't want systemic pesticides being used. In those instances, yes, we use bucket trucks to spray horticultural oil up high.

Doug: What does it look like if you have hemlock woolly adelgid?

Lou: The adults are these tiny brown specks. Because they're tiny and brown and the hemlock twig is brown, they're really hard to see. The telltale sign when you know you've got adelgid is the egg sac. The egg sac is this white, woolly, that's why it gets the name, is this woolly fluff that shows up on the twigs of, especially new growth, so on the outer twigs of the tree. It'll look like you've got these little cotton balls, these tiny little cotton balls, holding onto the twigs. The damage to the tree, you'll see the needle start to yellow.

The damage to the tree from this pest is it's a sucking pest. The adults pierce the leaves and the twigs-- I think they pierce the twigs, too. I know they pierce the leaves. They're sucking the sugars out, the carbohydrates. That's what they're feeding on. When you're losing that, when you're losing those deep green carbohydrates that are created through photosynthesis, the chlorophyll, you see the yellowing of the leaves. Then the canopy begins to thin. Then you've just got a thin yellow canopy on what should be a very thick green canopy.

Doug: Before we move off the hemlock woolly adelgid, would fertilization help, or is it more of the treatment of the insect?

Lou: Fertilization helps the health of the tree. However, I don't think that we recommend heavy fertilization on trees with woolly adelgids because you just create more sugars, and you create an overabundance of the pest. I do want to return briefly, though, to what you said about cold snaps. That's absolutely true. These pests are very affected by cold, which is one of the reasons why they haven't-- They're in 90% of the range of the hemlock, which is pretty much the eastern United States and southern Ontario. 90% of that range has hemlock woolly adelgid. The southern half is what's really being crushed by it, though, because we have those warm summers.

We've had a number of years where we've had really cold snaps down south. We've seen new growth on previously infested hemlocks. We've seen them rebound momentarily. This is one of those pests that when we talk about climactic change and how it affects tree species and the environment as a whole, these are the ones that we see, those long, warm summers really being beneficial. The warm winters, more than the long hot summers, those warm winters that we've talked about in past shows, how those affect tree species that leaf out when it's 70 degrees in February when it should be 30 degrees. Then they're getting zapped back and the rest.

Those winters are letting these pests cycle longer and grow in numbers.

Doug: Well, 10 below is going to help my hemlock woolly adelgid population decline. I'll start here pretty soon with the horticultural oil and hope for the best. Again, before we move on, is this a pest that can eventually kill a hemlock?

Lou: Oh, yes. Great question. In 4 to 10 years of infestation, those trees will be dead. When you come down south here, you go to Shenandoah Valley, Virginia. It's a national park. It's a spectacular park. It's been inhabited for tens of thousands of years by humans. George Washington used to hang out there. Lewis and Clark both came from there. There's a tremendous amount of importance to that. That park is mainly, I would say, mainly, I say, hemlocks, and they're all dead. You look into these valleys, and it's just standing cadavers, and it's awful.

Now, like I said, the pest showed up in 1924. It showed up in the eastern ranges in the 1960s. I think 1951 was the first positive ID in the eastern United States, but really, the '60s. We started to treat a lot of these trees. We're not going to save entire forest stands. Here, in Maryland, for instance, we have an old-growth stand of hemlocks in Swallow Falls, which is in western Maryland. It's a gorgeous park. To walk amongst these giants is something different. It's really cool. They're treating those trees. They're choosing select stands of these to protect. They're also identifying some of the more important species, so large hemlocks or high-visibility hemlocks.

Doug: All right, enough of the doom and gloom. Let's talk about this beautiful tree and what a wonder it is in our landscape and in the forests.

Lou: Oh, it's a stunner. It's a huge tree to begin with. It's the largest of the eastern conifers. The white pine is close, but both of them are neck and neck, with the hemlock being slightly larger. It's mature height than your typical landscape. It's 40 to 70 feet. The spread's 25 to 30 feet. The tallest living hemlock is called the Noland Mountain tree. It's about 170 feet tall. The largest on register I saw elsewhere is 175 feet tall. Could be the same tree. When they talk about massive trees, we, the tree community, don't usually publish their locations.

The largest tree on the continent is Hyperion. It's not published where that's located because we don't want people going there to mess with them. We want to protect those. Those could be the same tree measured at different times. The biggest one on register is 175 feet tall with 194-inch circumference, which is about a 5-foot diameter. That's a big honker of a tree. The oldest living hemlock in the United States, and these are long-lived trees, is actually in your home state of Pennsylvania, in Tionesta.

Doug: Yes, Tionesta.

Lou: About two hours northeast of where you are in Pittsburgh there. They estimate that tree between 500 and 555 years old. That's an old one.

Doug: Pretty easy tree to grow?

Lou: Beyond the adelgid, yes. Actually, one of the neat things about these is it's a shade-tolerant evergreen. That's something that I wanted to be sure to mention, that this is one of the few shade-tolerant evergreens that we have. Because of that, there are a lot of cultivars. In the gardening community, we're always looking for that shade-tolerant evergreen. I want something underneath the oak tree. Well, I don't want to tell you. You're not going to plant much. Hemlocks can handle that. They're easy to grow if you keep them somewhat shady. They can handle sun, but they also handle shade.

They like moisture. Again, they like living by creeks, rivers, lakes, and bottomlands. They're beautiful structure. They can look like a Christmas tree, but they can also be very dangly. I've got probably 10 hemlocks on my little 0.6-acre property. Clearly, they planted them along the edge. I've got them along the backyard as a screen. There's not much structure to them. They reach everywhere. They do have a single leader. Rarely do they split into two leads. They're a good structured tree. The bark is a beautiful cinnamon-colored brown. Really pretty.

I know you and I have talked a lot about four-season trees. Generally, we're talking about deciduous trees when we talk about four-season because they've got the spring flowers, the summer leaves, and fruit, the fall color, and the winter. The winter interest on those is always the bark, the cinnamon flaky bark. These guys have it all year round, too. It's just inside that canopy. Really pretty trees that way. They're part of the pine family, the pinaceae. If we're getting scientific here, just to give that back, they do have cones. They're conifers. Their cones are very tiny. They're about an inch long and half an inch wide at the most.

I think they're really cute cones. They're adorable little things. They're great for crafts for that reason. My daughter Maggie loves to collect them. We'll glue them together to make winter ornaments or little figurines. They're great for that. The needles are also very small. The leaves of the needles are about an inch long at the most. They're a dark green glossy top. When you flip them over, they're paler. What really makes them stand out is, A, they're flat. They're not a round needle. They're a flat needle. They've got two bands that run lengthwise down them. They're easy to identify that way.

Doug: You discussed it a little bit, but they're a great tree for screening if you have the room. Don't put a hemlock in because it's going to get big, right?

Lou: It is, unless you find a cultivar. Like I said, there's about 300 cultivars out there. They do have dwarf versions. Now, I will caution anyone. It depends who loads the truck that day if you really get the dwarf cultivar. The number of houses I've shown up to, and homeowners have said, "Ah, this river birch I bought 15 years ago. It was a dwarf cultivar. It was supposed to be 10 feet tall." Now, it's 60. I go, "Yes. Well, I can't tell you what happened." There are many cultivars. Two of my favorites. The most popular cultivar out there is the sargentii.

I've seen this in a lot of botanical gardens. It's a weeping shrub. It's about 10 feet tall by 20 feet wide at most. As far as beautiful trees goes, this one blows me away. It's that weeping form. It's really fun for kids to play under because it's almost like a fort underneath there. It's contained. You use them a lot near water features. I see them in cemeteries a lot near water features. That weeping form looks like a waterfall. It's that cascading effect. In landscape design, we use those a lot around water features to mimic that. That's a favorite.

Another interesting one that I came upon recently is Gentsch White, G-E-N-T-S-C-H. It's a shrub. It's 4 feet tall by about 4 feet wide, globe-like. It's not a tight globe, but it's a globe. What's interesting about it is that the new growth that comes out each year is a silvery white color. You've got this green interior with this silvery white exterior, especially in the late fall through the winter. It looks like it has snow on it year-round, or at least through the winter, even when there's no snow there. It's a really pretty cultivar to use. You don't want to put it in full sun, that one especially. It burns easy, but something neat to use.

Doug: Are all cultivars susceptible to the hemlock woolly adelgid?

Lou: They are, yes. As far as I know, they are. You got to protect them.

Doug: Those smaller ones would be a lot easier to protect, though.

Lou: Oh, yes. Spraying horticultural oil on a 4-foot shrub is way easier than an 80-foot-tall tree.

Doug: How about deer?

Lou: Deer browse on it. They don't damage it like arborvitae. Arborvitae is their favorite. You got an emerald green, and you have deer, it's game over. They'll browse on it during heavy seasons. Like I said, I've got 10 in my backyard, and we've got a lot of deer. They don't get too bad. Not too bad. Some other uses, some interesting stuff about it. Wood uses. It is a dominant tree of the eastern United States. It's used for construction lumber, used for crates, and paper. The pulp is very important. It's really popular for railroad ties.

It's not a good fuel source. Most conifers are not. You never want to burn evergreens in your house because of-

Doug: Creosote.

Lou: Creosote, thank you. I was going to say creatine. Your creosote, so you don't want to burn it. No one has those uses. Some of the more natural uses, Native Americans and early pioneers, and people today, use the needles to make tea. I think it's real high in vitamin C. Arborvitae is the tree of life. Arborvitae is tree of life because of the high vitamin C content, it offsets scurvy. The hemlock is the same. You use the needles for tea. The inner bark also can be eaten, which is interesting. You can use the inner bark. You can eat it raw or boiled, or you could dry it and mill it into flour. I have not tried that, but it's helpful.

Doug: Great stuff, Lou. That's more than I ever thought I would learn about hemlocks. Even though I've got 40 or 50 in my property, now I've been schooled on hemlocks. I appreciate it. As always, it was great to talk to you, buddy.

Lou: Doug, great talking to you, too. Have a great day.

Doug: It's always a treat to talk to Lou Meyer, that's for sure. Now, tree lovers, I want you to tune in every Thursday to the Talking Trees podcast from the Davey Tree Expert Company. Do me a favor, subscribe to the podcast so you'll never miss an episode. Do you have a question for an arborist? I'd love to put together a show featuring your questions. A couple different ways to do that. Send us an email to podcasts@davey.com, that's P-O-D-C-A-S-T-S @ D-A-V-E-Y.com, or you can just click the link at the end of our show notes to text us a fan mail message.

Your question could be on a future show. We'd love to hear from you. As always, we like to remind you on the Talking Trees podcast, trees are the answer.

[00:21:37] [END OF AUDIO]