caterpillar clinic (plus magnolia scale), with the morton arboretum’s julie janoski


TODAY’S GUEST, Julie Janoski, answers even more Urgent Garden Questions each year than I do, in her role as Plant Clinic manager at The Morton Arboretum in Lisle, Illinois. The inquiries include lots about caterpillars galore, from bagworms to gypsy moths (above, their caterpillar) and fall webworms.

Besides being an arboretum and public garden, The Morton is a world-class 1,700-acre research center, conservation and education organization, and it’s preparing to mark its centennial in 2022.

Last year, 17,000 questions arrived by phone, email, or in person at the plant clinic, questions representing consumers from 48 states. Julie is a former landscape designer who has managed the arboretum’s free plant clinic for three years, after volunteering there for five years before that.

Julie and I talked about the most common questions we each get from gardeners, including ones about Magnolia scale and about all those hungry caterpillars.

Read along as you listen to the Sept. 6, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).

caterpillars and more with julie janoski


Margaret: It’s good to speak to you again, Julie. I really enjoyed getting to know you and The Morton Arboretum a little better, as part of a recent “New York Times” column we did together. So the arboretum’s stated mission is to act as a champion of trees, right? And tell us a little bit about it, just briefly.

Julie: So our mission is to try and study, and promote the care and appreciation of trees. And we do that in a lot of ways. We have a number of scientists on staff who are studying trees and climate change and how that affects them. We have the 1,700 acres that you mentioned. And we also provide a lot of education for homeowners and green professionals in the best practices in tree care, based on that scientific background.

Margaret: Right. Always science-based, yes. I mean, I hope that when the Times column came out that the readers didn’t overwhelm you with more questions than you already get [laughter]. By the way, we should say that questions can be emailed in, or phone calls and so forth. We’ll give the how to contact you, how to contact the Plant Clinic information. So people will be able to do that. What’s your email for the Pant Clinic?

Julie: Our email address is plantclinic @ mortonarb dot org.

Margaret: O.K., so the clinic team is you and I think another full-time staff colleague, and then who else?

Julie: So we also have between 45 and 60 volunteers, depending on the year, who are well-trained. They’re either master gardeners or have horticulture degrees, or have been avid gardeners and have gone through a lot of the arboretum training. And they come in and help us answer questions via email or phone.

In addition to whatever their background is, we put them through about 30 hours of training ourselves, before they can even pick up a phone for us. So these are extremely well-trained volunteers, and they are really the core of our team. They spend thousands of hours volunteering here.

Margaret: Right. So I’ve been writing about gardening for a long time, and like the doctor at the cocktail party who gets asked medical questions [laughter], I get a lot of plant questions wherever I am. And I suspect you do, too. So greatest hits: For me, for instance, one that always comes up over and again, year after year is, “When do I prune my…” And it’s usually fill-in-the-blank. But often, it’s hydrangea or lilacs. Those are two really popular ones.

And related is, “Why didn’t my fill-in-the-blank plant,” usually a shrub, “bloom? What went wrong?” And that’s often lilacs. It could be hydrangeas. And pests and disease questions in season come up, year after year. What are the ones that you’re getting?

Julie: Well, we certainly get all of those as well. But a key thing that we do here is plant identification for people. People can send us or bring us samples of plants that they have in their yard, or that they found, and we can help them identify them. A lot of people aren’t aware of all the different types of plants we have in the area, or even how to figure out what they are. So we do a lot of that.

We also help people select plants for specific areas in their yard. So we get a lot of questions about, “Hi, I’ve got this circle in the middle of my driveway and the tree there died, and what should I put back in there?” And we spend time with them, trying to figure out what the conditions are in that area, how big a plant they can put there, what they’re looking for. And then we can make recommendations to help them figure out what to put in a space like that.

This year, we’ve been very dry in the Upper Midwest. And so we have spent an enormous amount of time talking about how to water properly. And the fact that even big trees need to be watered when you have a 12-week drought, because it’s just so important for the longevity of the tree to get some sort of regular moisture.

Margaret: Yes. And we talked about that in the “New York Times” story, was one of the points that you made was that people will go and water their vegetables, or water their pots of annuals. But what about the trees? And it may not be showing the signs right away, some big old tree especially, but it is suffering, like you said, in a prolonged dry spell. So I believe you told me if more than 10 days to two weeks of dry, or something, is there a protocol that you recommend to people?

Julie: Yeah. That’s usually exactly the timeframe that we recommend. If it hasn’t rained in 10 days to two weeks, you should water your trees and shrubs, not just your pots and your annuals. Trees and shrubs lose those fine feeder roots when the soil dries out completely. And it takes them a long time to build that back.

So if you have a prolonged period of dry weather, these plants will lose a lot of their root system. And that has very long-term implications, especially for big old trees.

Margaret: Right. Now, we’re going to get into some creepy-crawly things [laughter]. For the first time this year, I saw magnolia scale on a magnolia in my yard. Very small number of the… Well, they’re scale insects, so they’re like little dots underneath the leaves. And I had never seen them before. And I have read about it, and so forth. Is that something you’re hearing about? Is that a trending pest?

Julie: Magnolia scale [below] has been a big pest here for the last five or six years. And you can identify magnolia scale by white fuzzy spots on the stems and branches of your magnolia trees. They only feed on magnolias. So if you find something like that on a different plant, it’s not magnolia scale. But yeah, we spend a lot of time trying to help people identify it, and then figure out what to do with it.

Margaret: And so I just said undersides of the leaves, and I guess I meant right by where the leaf is attached, the little buds and twigs and so forth.

Julie: Yeah, exactly.

Margaret: Yeah. Right. Because it was the only time I’d ever seen it. It was maybe six weeks ago, or something. Very few of them. And so it’s on the twigs and branches, stems and branches. O.K.

Julie: Right.

Margaret: And what’s to be done?

Julie: Well, so magnolia scale, if it’s just a minor infestation and you’re only seeing a few of them, you can maybe cut those little branches and twigs out, just throw them away.

A lot of times, people don’t notice it until it’s really covering the tree. And at that point, there has to be a chemical intervention—horticultural oil, or there are some systemic pesticides you can use. That’s going to vary, what’s legal from state to state. So you would want to contact your local cooperative extension for specific pesticide information.

Margaret: Right. And the interesting thing about these scale insects is, again, it looks like a little bump [laughter] underneath. But it then goes into a crawler stage, doesn’t it? Does it start moving around, or what happens next?

Julie: Yeah, it does. The life cycle of Magnolia scale is really cool, if you’re into that sort of thing, I guess. [Laughter.]

Margaret: If you like icky, creepy things, yeah.

Julie: Because basically, the white part that people notice is actually a waxy covering that is over the adult scale. And they build that so that they can hatch their babies, which we call crawlers. And I say hatch loosely, because magnolia scale actually produce live young. And once the young are born, they crawl out from under the waxy covering and start to move around. And they’re the only part of the insect that actually moves. So that’s why we call them the crawlers.

Margaret: That’s funny. The other thing about treatment, even with horticultural oil, is timing is everything. And it works on one life phase and not another. And again, I’m not an expert in this; I’ve read a little bit about it. But that’s why it’s so important to not just, again, ready, shoot, aim with what you think you might’ve heard about the thing, because it has to be timed properly as well, doesn’t it?

Julie: Yes, absolutely. Once they’re under that waxy covering, nothing is going to harm that insect underneath there. So you have to wait until the crawlers come out from underneath it. And that’s true for almost any pest or disease, that the timing is nearly as important as the product that you use.

So you always want to clearly identify what problem that you have, which disease, which pest, and then find a product that works on that pest or disease. And then really read the labels for timing, to make sure that you’re spraying at the right time. Because if you’re not, you’re wasting product, you’re putting chemicals into the environment that don’t need to be there.

Margaret: Right. And again, even if it’s oil, it doesn’t mean you should just do it indiscriminately or waste it, even if it’s oil. Yeah.

Julie: Correct.

Margaret: So dare I veer into the world of caterpillars [laughter]?

Julie: O.K., if you must.

Margaret: Did you have a gypsy moth year there? Now, I did not. I’ve never had them in the 35 years I’ve been at this property. I’ve never had an infestation. I see the adult moths, sometimes when I look for moths at night. I love to go mothing and put out a CFL blacklight and put up a sheet, and see what moths are around and so forth.

I know they’re here. But not far from me, there were large tracts of land that were heavily infested this year. And I don’t know if you had that also, from callers in the Midwest and so forth.

Julie: So this year, we did not see as much of an infestation. Last year was a particularly bad year. And the State of Illinois has a spraying regimen, where they put traps out all over the state. We’re part of that process. And then they monitor how many moths they catch in the traps, which indicates what the populations are. And if the populations are high in certain areas, then they’ll come and do aerial spraying for us.

For those of you who don’t know, this is a pest that got introduced into the country in the 1860s. And it’s a serious pest, because it can eat leaves off a tree and completely defoliate a tree, if the populations are high enough. Which of course, over time, would kill the tree. So we have been fighting gypsy moth for a long, long time.

Margaret: Right. So earlier in the year, people would have been seeing caterpillars and hearing—you can actually hear them chewing, if there’s enough of them. It’s a noise, yeah? I mean, the crunching.

Julie: Exactly. Yeah. And the caterpillars usually hatch out in May, usually mid- to early May. And of course, that’s dependent on the weather. It’s a temperature thing; it’s not a date. They suddenly look at their calendar and say, “Oh, it’s time to hatch.”

And what they need to do, in order to turn into the adult moth, is eat constantly, until they’re ready to pupate, or turn into the adult moth. Once they’re a moth, they’re not a problem, except that they’re out there laying more eggs. It’s that caterpillar phase that’s really, really damaging.

Margaret: Right. So I believe with these, that even if the aerial spraying, like you just said, if your government agency says, “Hey, we’re going to spray,” the timing is everything, once again. And they go after the young caterpillars, not when they’ve reached close to the end of their larval life phase.

And so if people are calling now, and people called up and said, “What can I do?” There are some things you can do in your home environment, your garden environment now, looking for egg masses, I think, can’t you, to sort of reduce the population somewhat.

Julie: Exactly. So the egg masses you can look up, they look like strips of mud [above]. And they will lay their eggs on tree bark, on lawn furniture, on firewood, on pretty much anything. And they’re pretty obvious. So if you can go, and if you find those and can scrape them off, there could be thousands of eggs in one of those masses. And if you can scrape them off the tree and throw those away, you’re going to prevent that many caterpillars from hatching.

Margaret: Right. And you don’t do this with your fingers, folks. That’s an important thing, I think. We don’t touch them. We use a putty knife, or something to scrape them. And we put them in a bucket of warm water, or soapy water, or something like that.

Julie: Hot, soapy water, or with household bleach, ammonia. Yeah. The gypsy moth hairs, which are part of all of their life stages, can actually cause an allergic reaction, a skin rash. So you really want to be careful, and wear gloves and long sleeves.

Margaret: O.K. All right. And use a tool to scrape them. So that is something that we can do, monitoring and reducing the potential very localized infestation, of course. If callers are calling now, you’re not telling them that there’s anything they could do to the caterpillars. It’s about these egg masses, because the caterpillars are done. Their life phase is done.

Julie: That’s correct. They became the moths already, about mid-summer.

Margaret: There are other caterpillars, like right now, fall webworms [above] are happening. And I think people, especially if they were shell-shocked by gypsy moths this year, any caterpillar looks really like something to be afraid of. But dot, dot, dot, not the case. I mean, some are native, benign—in effect, just good bird food, right? [Laughter.] They’re just part of the ecosystem. So what about fall webworms, for instance?

Julie: Yeah. Fall webworm, we really don’t worry about much, because they don’t hatch out until very late in the season. And that’s when they start eating. The trees are nearly done with what they need to do with the leaves for the year. And so any kind of damage that happens late in the summer, or early in the fall is really not going to affect the tree at all. So they’re not attractive; their webs are really gross and ugly, but they’re not going to permanently harm your tree.

Margaret: Right. They look like these big, gauzy enclosures on the ends of branches, and they can be on lots of different plants. And I think that’s the other thing that makes them not a big problem, is that they’re not host-specific. They don’t have a narrow target, where they go on the same kind of trees or the same kind of shrubs, and decimate that crop. They are generalists in their diet. So they’ll be on everything.

I’ve even had them on perennials, on large-leaf perennials some years. But mostly, you’ll see these gauzy things on the ends of branches. And people, a lot of times, think it’s a recurrence, at least here, of Eastern tent caterpillars, which come early in the spring. And of course, it’s not. It’s something different.

Julie: Right. Absolutely. The Eastern tent caterpillar is going to show up in the spring. And just like gypsy moth, it can do a lot of damage, because it’s eating leaves off a tree in the spring, and the tree hasn’t had all season to make food for itself with its leaves. That one is really focused on fruit trees, and trees in the rose family, especially like crabapples, apple trees, cherry trees. Those are really the hosts for that one.

In either event, you can clip these tents out. You can just open them up with a stick, and the birds will work on them. You rarely need to treat either of these infestations, unless you have a serious infestation of Eastern tent caterpillar, because that one is capable of defoliating a tree.

Margaret: Yeah. What else are you hearing about at the moment? Anything trending there on the hotline [laughter]?

Julie: Well, if you’re talking about gross bugs, we are seeing a lot of bagworm right now. Bagworm is an insect that takes the leaves or needles of the plants that it’s on, and it not only feeds on it, but then it winds it together with a piece of silk and attaches it to a branch. So it looks like you’ve got a little hanging bag of dead leaves or dead needles on there [above].

Bagworm infestation, same thing. They can defoliate. They do tend to like evergreens, which have a harder time re-needling than deciduous trees do. And the bags look different, depending on which tree they’re on. So if they’re on an arborvitae, they look very different than they would be on something with an actual leaf on it.

So same deal. You have to treat them at the right time. Once they’re tied into their little bags, it’s almost impossible to get any pesticide on them. So you have to wait until they hatch out in the spring, before you can actually treat them.

The other thing you can do is if you find these bags and they’re fully formed, and they’re tied to the branch, you can just snip them off and throw them away. We had a gentleman in here about three weeks ago, who said he spent a whole day snipping bagworms. And he showed me pictures of a 5-gallon bucket of bagworm bags that he had pulled off of his arborvitae [laughter]. So the good news is he should not have a problem next spring. But yeah, that was dedication.

Margaret: It cracks me up in a way, because I used to work for Martha Stewart for many years. And so we did cooking and we did crafting, and bagworms are kind of like culinary experts and crafting experts [laughter], because they eat their favorite meal, and then they also use part of it to make a decorative, this enclosure or this thing. They’re kind of wild. They almost look like tiny little pine cones on some of the species, hanging down like these little ornaments, or something. Very strange.

Julie: You’ve got the Martha Stewart of the bug world.

Margaret: There you go. There you go. Yeah. Do you get a lot of questions about weeds and weed ID, and so forth? I get a lot of questions about that.

Julie: We absolutely do, mostly in the spring, where people will send us pictures of, “I don’t remember planting this and it’s coming up all over in my garden.” A lot of times, it’s too early to specifically identify something. But if you didn’t plant it and it’s now all over your garden, the likelihood is, is that it’s fairly aggressive and you may want to get rid of it.

Margaret: [Laughter.] Yeah. I think it’s so important to learn about what your weed seedlings, the local weed seedlings look like, so that you can get ahead of things earlier. And that’s hard information to find sometimes, but it’s proactive to be able to learn that.

What else are you hearing about right now? What other hit items? [Below, a section of the arboretum.]

Julie: Well, we’ve had a lot of heavy storms in the area, so we’ve seen a lot of broken branches, a lot of trees down. We’re getting a lot of questions about, “What should I do about this branch that’s hanging in my tree?” or “I lost this half of the tree, is the other half going to live?” We’re seeing a lot of questions about that right now.

We try and deal with each situation, but my best advice on that is to really observe your trees and have them taken care of. The best time to protect against a storm or against an ice storm, and make sure that your tree is structurally sound, is before the storm happens. So developing a relationship with a good arborist, who can help you take dead wood out of your tree on a regular basis and structurally prune it every five to seven years, or something like that, is really the best thing you can do to protect a tree in a storm.

Margaret: Right. And of course, the hesitation is always—it’s easy to put it off, because it’s not inexpensive. However, compared to what can happen if it goes wrong, if a large tree comes down or large branches come down in a storm and so forth, it can be even more costly. So again, getting ahead of it and having a regular, as you say, relationship with an arborist, who walks the perimeter of your place, looks around, checks all the trees, etc. And helps you stay ahead, to be aware of their condition.

I have a number of trees in decline. I’m in a state forest and parkland surrounding me. And there’s a lot of old trees. And knowing which ones are declining and so forth is better than having a giant tree fall at some time.

Julie: Exactly, exactly. And it’s not that you have to take them out. These arborists are trained in how to protect and care for trees, and stabilize them if necessary. And then tell you the truth if something really does need to come down.

We got pictures from our last storm, where a client sent us pictures that she had two big trees in front of her house from the 1800s. We suspect the trees were that age.

Margaret: Wow.

Julie: And the one tree, there were two frame trees on each side of her sidewalk, and one fell down. Missed the house, fortunately. But took the other one down, and took the power lines down for about a quarter of a mile. So just keep up with it, and make sure you’re observing your plants and observing your trees.

Margaret: Well, Julie Janoski from The Morton Arboretum Plant Clinic, I’ve been so happy to meet you. I hope we’re going to have regular conversations. And thank you again for helping me with the Times story and with this podcast today. And I hope I’ll talk to you again soon.

And I’ll give lots of links to all of your great resource materials and how people can use the website, and of course, get in contact with you. Thank you.

(Photos except fall webworm from The Morton Arboretum.)

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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Sept. 6, 2021 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify
or Stitcher (and browse my archive of podcasts here).


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