I DON’T GROW a lot of roses, just a few favorites, but birds plant the occasional multiflora rose seed here and there around the garden. One of the resulting seedlings looked really strange when I noticed it while weeding in an out-of-the-way spot the other day. It was all disfigured, and red, and—uh-oh—rose rosette disease comes to my corner of Nowheresville.
I hear from a lot of you who have encountered rose rosette disease not on some weed as I did, but on your prized rose bushes. I invited research scientist Christina King of Star Roses and Plants—known for more than a century for many favorite garden plants, including the most popular roses today, the Knockout series—to explain what this disease is all about, how to ID it and respond to it, and what promise lies ahead for fighting it longterm.
Read along as you listen to the June 18, 2018 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
rose rosette disease with christina king
Q. As background, Christina, can you tell us a little bit about Star Roses and Plants, and about yourself? Your journey there was a little different. You weren’t intending to be a rose person particularly; I think you did your PhD in some fascinating aspect of conifer reproduction, or something?
A. I did. I’ve been interested in plants since I was a kid, and then through college figured out how I could actually make a career out of plants.
I started at Star Roses about six years ago, and they had a research project in rose and it was similar—the molecular, kind of fancy-science part, was similar to my PhD work. So I got on board with them, and ironically my middle name is Rose, so it seemed to be the perfect fit.
Q. Oh, kismet, O.K. [Laughter.]
A. Roses can be a difficult thing, but I was used to it from working in conifers. Conifers certainly aren’t front and center and the hot new plants. But roses are much prettier.
Q. [Laughter.] And so Star Roses—as I mentioned in the introduction, is well known for many different plant series, including the Knockout roses. So a good part of Star’s business, I assume, is roses—meaning rose rosette disease is a big concern to this company, and to other companies in the industry.
And I think the industry’s kind of working together in recent years to try to figure out what to do, and you even hosted a webinar recently on the topic with various universities and other companies, I believe.
Let’s do a little short history of the disease. Where did it come from? When was it first discovered?
A. The disease, it’s not an invasive disease; it is part of America. They first noticed it on some species roses in the Rockies around the 1940’s, but it wasn’t a big deal. It wasn’t in someone’s prized rose garden, it was just in the mountains. But then it started to spread to the Great Plains when they started introducing multifora rose. It was planted a lot in the 60’s as a hedgerow, and just kind of spread across the country. It [rose rosette] followed multiflora rose across there. And as we all know multiflora rose got a little out of control.
A. So, then the disease was able to use that as a host, and then expand just moving up the Eastern seaboard in the last couple of decades. People really started noticing it because we love roses so much. It started popping up outside of these species roses.
Q. Now, just to backtrack a minute, not everyone may know multiflora rose. So, it was as you said, brought … I don’t remember where it’s native to [update: Asia], but it was introduced as a hedgerow, like for the boundaries of farms and so forth to be used as a hedge. Is that what it was for?
A. That was one of the big uses for it.
Q. And it really did, like many invasive plants over time, the first intention was good, but the result was bad. If you look at the maps of the range of multiflora rose, it’s sort of now the same map of the spread of rose rosette disease, right? It leaped and hopped-
A. Right, yes. There’s a little, there’s a slight time gap, but you can see it definitely follows the same progression across the country. [Above, green areas on map from RRD webinar identify range of multiflora rose; dates represent rose rosette disease timeline in its spread East since its first appearance in the West in the 1940s. Below, multiflora rose detail from roserosette.org website.]
Q. So what causes it? You said this is a native disease, this is not some imported insect, or imported pathogen from another country like we hear about so many times today with other things. This is a native disease; how does it work?
A. The disease is caused by a virus. There’s a tiny, tiny mite that carries the virus, that feeds and lives on roses. It’s a wind-blown mite, so a nice gust of wind moves it around, or we have problems sometimes if you’re in a landscape, and you’re using a leaf blower, that can also blow it around.
Q. Oh, gee.
A. So, the little mites can get the virus when they feed on the plants. Then when they go to the next rose, then when they feed on that plant then they move that virus along. Then the mites also lay their eggs in the roses and they’ll overwinter there. So then in the spring, when the new mites hatch they’ll feed, and then slowly can move the disease that way.
Q. Right. And windblown, I mean, you’re not kidding—it really moves. It can move distances, unlike the mite left to its own devices, which doesn’t walk along a million miles an hour, it really gets on a breeze and gets going. So, the mite is the vector, yes? And it kind of balloons on the wind from place to place?
A. Yes, they’ve even found it in snow. They did some studies on some rooftops, and found that it could travel in the little water droplets of snow. So, it’s a persistent little bugger.
Q. Yes, so I mentioned before that the rose industry has to get together to work on this, because how long has it been a problem in cultivated roses? What’s a little bit of history of that?
A. We first really started talking about it, just a little bit, about six years ago. We heard some reports, it really wasn’t a big deal yet. It just kind of sprung up, and some researchers had just started studying exactly what was causing it. So, Star Roses just jumped on it quickly, just so we could be ahead of the disease, because a lot of the time it’s when you’re starting to lose massive trees, or crops, or anything, that’s when people really start paying attention.
So, we tried to be as proactive as we could, and talk to other industries, talk to some government agencies, talk to universities. We held an RRD summit, it was five or six years ago, just to start getting all of these people together to start talking about them and put together an action plan. That actually led to a group of a bunch of different universities, were able to get a big research grant. It’s a specialty-crops grant from the USDA.
A. And we’re, Star Roses, is one of the industry supporters of it. And they have other rose growers in there, and then people from the USDA as well, so that we can tackle the disease, both from a research point and an industry point, and also then try and get consumers and growers and just people that are buying roses for their house to help report where they see it so we can stop the spread, get samples and do testing—and just really try to figure out what’s going on with the disease and how we can work to stop it.
Q. Right. On the recent webinar you guys hosted, and people can watch the YouTube file if they want more information, I think some universities that were involved in that research … I think what, University of Florida, Texas, Oklahoma, Delaware. I’m probably missing some. But I think those were some of the main characters as well besides Star and other industry players.
A. Yes and they’ve been able to do some great work.
Q. Tennessee. Yes maybe, is Tennessee another one? Maybe that’s another one.
A. Tennessee, yes. And Tennessee has been doing a lot of trials with cultivated roses to see is there anything on the market already that is resistant or can tolerate the disease a little better.
Q. So we’ll talk about that in a second because that’s really interesting. I think I learned on the webinar that, and you kind of alluded to this, you said in the last six or so years it’s kind of become more of an awareness. So even though in the 1940’s in the west there was this thing, this disease, it didn’t even … The virus didn’t even get identified until I think 2011.
A. Right. Yes that’s when they said: “This is caused by a virus.”
Q. Right. So kind of interesting the phenomenon had been observed, but it hadn’t even been fully understood.
So you were saying some places, like University of Tennessee, are looking into which roses do better or worse against it. We know that multiflora rose is a vector, are there other species or types of roses that seem to be more or less susceptible that we know already?
A. So we do know a few species roses that do appear to be resistant.
A. And they’ve been doing testing. They put them in with their trials. And it looks like there are some species. So it looks like in rose genetics there is resistance somewhere. We have some of our consultants that have been going to the same fishing hole [of genetics] for 20 years and have seen these roses and have never seen RRD on them. So there is hope that it’s there. The trials for the varieties that are the commercial ones we’re still waiting to hear. They want to make sure that they have a few years’ worth of data so that we know for sure that when they say yes or no, that it’s good solid data.
Q. What are some of the species that seem to have some promise, off the top of your head?
A. So there’s a couple of species, there’s the swamp rose, which is Rosa palustris…
A. …which looks like it has it. There’s some … I don’t remember the common names.
Q. That’s O.K.
A. Rosa setigera [the prairie rose] looks like it might be [resistant]. And there’s a couple others where they think so. The initial tests are looking good, so they’re trying to see there, and looking at the DNA too to see if they can actually determine: is there a gene? Is there something we can pinpoint genetically that would help with research?
Q. So I said in the introduction that I’m up weeding the outer reaches of my place—I have a few acres, and I’m out at the far boundary and I find a multiflora seedling, as I do many times, that the birds have ingested, I guess, some fruit of and you know pooped it out and planted seedlings. [Laughter.]
And I’m in an agricultural area, so that’s one of the things, along with bittersweet and barberry and who knows what else, that I have as a weed. And I noticed this strange one stem so to speak. It didn’t even look like a normal stem, it was kind of red and different looking.
Tell us about what this RRD—it has its own acronym, Rose Rosette Disease—what it looks like, how do we recognize it?
A. So in the early symptoms you’ll usually start to see a reddish kind of growth at the tops of the plants and they’ll start to get an excessive amount of thorns. And it’s kind of relative because some roses are a little thornier than others.
A. Because it looks like it has more thorns than it normally should, that’s usually a good sign in the early stages. And they’ll get a little overly tender. Usually as you know with roses, sometimes the leaves start out a little red when you get some new growth. We see it on Knockouts, that’s one of their characteristics. They’ll turn green once they start, once it’s later in the summer. But when the red doesn’t go away and they get really thorny and they, like you said, they just look weird. Something is off on them.
A. That’s usually a pretty good indicator. You’ll also see that, if they do have buds on them, the flowers don’t bloom right. They just kind of look a little smushed, and they don’t open all of the way. You might see that the shoots just get really long and scraggly looking. And there are some instances if you know you’ve been spraying some kind of weed killer or any herbicide, sometimes it’s mistaken for herbicide damage.
A. But that’ll just … You’ll just get a little red; it will just look a little roughed up. But with these, especially the thorniness and the deformed flowers, are usually a sign. But if you’re a homeowner you usually know when you’ve been spraying things. It’s a little easier.
Q. So I see this thing, or people see some disfigurement of the nature you just described on a cultivated rose they have in their garden, and then what? What do we do? What should we do? People write to me a lot and ask me this and so I’m asking you: What are the tactical steps that we need to take?
A. The best thing to do to stop the spread especially if you have other roses or your neighbors have roses, is just to remove the whole plant.
Just grab a garbage bag, stick it over the plant and you can cut the plant off at the bottom, tie those up and then you can dig out the roots after that, to make it a little easier.
We don’t recommend pruning out just the diseased shoot, because you can see that it’ll come back. It can live in the base of the plant.
A. We recommend you just remove the whole plant. You can plant a new rose right away. The disease can’t live in the soil, so at least that’s good news.
Q. Oh I didn’t know that. That is good news. I mean we have to look for the silver lining in some of these things, don’t we Christina? [Laughter.] We’ll take it.
A. You can go out and you can plant a new rose the next day. And it’ll be fine.
Q. O.K. Is there anything preventive besides immediately removing and destroying, as you just described, an infected plant? Is there any other preventive, tactical stuff that we should be doing? Or not so far, we don’t have any?
A. One of the best things, and it’ll help with other various diseases as well, is just giving your roses a nice prune. Either in late winter, early spring right after that threat of the hard frosts are gone, cut them back. You can go about a third of the way down so that they’re about 12 to 18 inches tall. It’ll remove all of the dead blooms and the old wood, which is where the mites like to overwinter.
A. So if you can get that source then hopefully then any of the eggs that are there, or the females that are resting there, then you’ll remove them and that can help just the spread. So you get rid of all that dead material.
Q. It sounds like we might want to destroy that material, also. Not compost or put it in our brushpile.
Q. So extra-good sanitation sounds important.
A. Yes, and just keeping your plants healthy. Keeping your roses healthy in general, can … It just gives them kind of a better fighting chance for rose rosette disease and other pests that are out there for rose as well.
Q. You just mentioned a little bit about pruning and I wonder about when. Just so I can sort of segue and say one group of roses—or I don’t know if we call it a class of roses—the climbers, do we prune those after they bloom? I’m in the Northeast, and people are listening from all over the country, but I’ve always heard with those we wait till after the bloom. I mean clean them up in the spring, but more let them do their thing and then have at them. Do you have any point of view on that?
A. Generally for climbers we just prune them just to keep their shape, or if they’re getting too tall for you. They don’t need that cutback to re-bloom. And you generally do need the tops for them to bloom so it is better to do it later in the season, so you don’t lose your bloom.
Q. Oh, that’s why. Oh it’s because … O.K., because I wondered, and course, I should have just thought it through, but yes.
Q. I have one that is turning into quite the behemoth, and it’s going to get a haircut in about two weeks, after it finishes its bloom cycle, I think. Not even a haircut; it’s going to get some of the oldest canes taken out to the base, I think.
Q. Because some of them are quite substantial in an old climbing rose.
A. They can keep going, yes.
Q. Yes. So what are some of the research [angles], and you touched on this a little bit, but what are the main things? There are some people who are looking into which species are resistant, and where in the gene pool to get good strong genetics to breed in. What else is being looked at? Any other angles on the rose rosette research?
A. So they’re looking at better ways just to diagnose rose rosette disease. So, whether it’s something where you just send in a leaf and they can do a genetic test on it. Or they’re working toward being able to send out test strips so we can send them to rose growers. They’re hoping maybe even you know you could take these little strips, use them in your backyard and you can say, “Oh yes this does or doesn’t.”
A. Just being able to easily diagnose it. So from the grower point, before it even gets to the store to buy, that they can say this does or doesn’t have rose rosette disease. So just trying to stop it as early as they can so that it’s not spreading.
Q. Would you call that virus indexing or something?
A. It would be part of the virus indexing.
Q. Because for instance cannas–there are viruses that affect cannas, and I think with a number of kinds of popular bulbs. So that’s always a big problem when a commercial horticultural crop has some virus, merchants and then below that the homeowner, the recipient consumer at the other end—they don’t want it. So we want to know something’s been virus indexed, that it’s been checked for viruses. So you guys are trying to do that at your end in order not to have it trickle down into the stream.
A. Exactly. So that we know from the beginning at each move we’re just moving clean material.
A. They’re working on that, and to just make it easier and more cost efficient to do on a wide scale. So there’s been a big push. I know they’re hoping they’ll have a lot more information during the summer. They’re doing some more testing, so hopefully they’ll be able to bring something to market by the end of the year, I think is their hope.
And then along with that is, of course, just looking at you had mentioned before about just seeing are there genes out there, are they able to breed for resistance? So there’s a few grad students at Texas A&M—that is one of the big places they’re looking at it. They’re making these huge populations, looking at the DNA, seeing what they can pull out to see if we can identify some varieties or some species that are resistant, and can we breed that into some of the more popular, aesthetically pleasing [roses]–into some of our commercial varieties. Some of the species can be a little wild-looking.
A. And then even going into what are the best manners or practices so that we can give information to landscapers and growers and homeowners on just what’s the best way to take care of your roses.
And then they’re looking into, since it is a mite that spreads the disease, are there treatments—can we actually fight the mite as well? So they’re looking at miticides and oils and things so we can make recommendations for people that are doing these big plantings. So landscapes, all the way down to you and me, where we just want a few in our yard.
A. Kind of everyone can help at whatever level they’re at.
And then just gathering information—part of this grant that we’ve been assisting on is just getting people when they see it to report it so they can track the spread. And just looking at creating these information pipelines. Looking at the economics of the whole thing. And just setting up a nice system for monitoring, which just kind of helps the industry as a whole, because it just gives you a piecework so then you know the next big disease that’s going to come in 20 years we can follow a similar idea.
Q. Is there a currently … I mean I know with many things there is like with a lot of the Downy Mildew diseases in basil most recently and some other crops, there are places where citizen scientists or professionals can post their data if they have an outbreak they can put it in and it’s a real-time mapping system and so forth for the scientists to use.
Does that exist for rose rosette yet? Or where do I say so, if I have it?
A. Yes. So, if you go to roserosette.org. There’s a tab on their page–and this is hosted by the universities that are part of this grant, who have put together this page.
And there’s all kinds of link. You can see all the people working on it and there’s a tab that says reporting. And you can go in and you can say where you found it, you can put a picture of it and then depending where you are this also gives the university researchers a chance … You could put that if you’d be willing to give them a sample if they would want it, especially if it’s somewhere new or somewhere they haven’t tested.
Because we also want to make sure with the virus, that’s there’s only one—if the virus mutates or something. There are maps and you can kind of see where it is if it is near you or if you’re just looking for more information. There’s a lot on that page.
Q. Well, it’s a good thing that I called you in time, Christina King of Star Roses and Plants to talk about rose rosette when I saw my first discovery, because maybe I can make a report in a new area, unfortunately—but maybe that could be of value.
(Photos provided by Star Roses and Plants, except as noted.)
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its ninth year in March 2018. 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 June 18, 2018 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).