Episode 243: root mealybugs
Transcript
Episode 243
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Jane: They're small, they're waxy, they live underground and they like to suck your plants' roots! Are root mealybugs the biggest houseplant horror of all? I find out in this week's On The Ledge podcast!
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Jane: Hello and welcome to the show! I am your host, Jane Perrone, bringing you all the info, tips facts and gossip about the world of houseplants! In this week's show I'm joined by entomologist, Professor Raymond Cloyd, who's got all the info you need to know about this particular, underground houseplant pest. Spoiler alert: I'm afraid it's not good news for those of us who have suffered from infestations of this pest, but we get into all the different aspects of looking for root mealybugs and what to do when you find them! Plus, I answer a question about braided plants.
Small housekeeping note: my British Library appearance, which was due to take place earlier this week, has actually been postponed and it's now happening on 2nd December, so if you didn't get around to purchasing a live stream, or in-person, ticket, then you have not missed the boat! Look for details of that at the top of the show notes at janeperrone.com. And a brief reminder that if you are still using Elon Musk's play-thing, aka Twitter, then you can join me and my US counterpart, Lisa Eldridge Steinkopf, aka The Houseplant Guru, every Tuesday night for Houseplant Hour. It's at 21:00 UK time, that's 16:00 ET. It's an hour of chat about all things planty! You can ask questions, flex your plants and generally shoot the breeze with other houseplant enthusiasts. Just follow @houseplanthour on Twitter to get involved!
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Jane: If you've been listening to On The Ledge for a while, you may have heard my cries of despair about root mealybugs. I know some of you have suffered with this pest too, so it felt like time to devote an interview to finding out more about this particular pest. Joining me, once again, is Professor Raymond Cloyd, of Kansas State University based in Manhattan, Kansas. Professor Cloyd is a Horticultural Entomologist, so mealybugs are his bread and butter, if I can put it that way! The first thing I wanted to know was: are root mealybugs just regular mealybugs, that you might see above ground, that have just decided to go underground for some reason, or are they something entirely different?
Raymond: That is true, Jane. It is not the same as the citrus mealybug, a longtail and our above-ground mealybug, but this is actually a different species of mealybug that inhabits the root zone. People often have this perception that the above-ground mealybugs go into the soil and they start feeding on the roots. That's not true. They are primarily feeding on above-ground leaves, stems, flowers and fruits, so there are actually two different species based on location and where they feed on the plant.
Jane: That makes sense to me. I assumed that that wasn't the case because, otherwise, why would they be suddenly turning up in the roots? Obviously, you do get mealybugs on the surface, but it's a different species we're dealing with here. I think the reason why I find these particularly difficult, is the fact that, unlike mealybugs, you really don't know you've got them until the infestation is quite severe, or you happen to take the plant out of the pot, it's all happening under the surface and then it's gone badly wrong by the time you realise that you've got this problem.
Raymond: No, absolutely, you don't notice you have a problem until your plants are wilting or stunting and they're not responding to water, or fertilizer. You take them out and you see these clusters of white, cottony masses around the roots.
Jane: Those are the things that I noticed, was the plant just suddenly not looking great, just looking generally dull and starting to look as if it was thirsty. Those were the first things that I spotted, in the worst cases, where I hadn't repotted. Then, when I did take those plants out, they obviously had those cottony masses.
Raymond: They feed on the food-conducting tissues, the phloem, especially in the root zone because the phloem is up and down movement from the leaves down, that's how roots get their food, so they're robbing the plant of its nutritional content and that's why you see the stunting and wilting. The plants just can't grow, they're not obtaining enough nutrition to maximise growth production.
Jane: The other thing I noticed, which I did find useful to know, was about watering and finding, I guess the non-technical term is crawlers, the young root mealybugs coming up to the surface. Does that sound like I'm getting the right diagnosis of root mealybug, when you get these, kind of rice grain-like little babies coming up and appearing on the surface of the soil when you water?
Raymond: You have the same life-cycle, you have the eggs and then nymphs or crawlers, are what you're observing, and then the adults. So when you're watering, or you're over-watering, the crawlers can't survive in water while in growing medium, so they'll try to escape. But if you've got well-drained growing medium they can probably stay there because the medium will dry out. The crawlers, as well as the adults, the females in particular, are feeding on the roots, and so they're basically removing the nutritional content and so the plants display stunting and wilting, don't respond to fertility in water, but yes, the crawlers are what you see. Again, if it's waterlogged, there's too much water, they will migrate up to the top, but they will likely go back down because they have evolved, or been designed in some way, to just feed off the roots.
Jane: Even if you do get them out of the pot, sometimes I find it's not necessarily easy to distinguish between a little bit of fungal growth and the mealybugs. I guess this is where my hand lens comes out and now I obsessively look at every fleck of perlite in the soil to check whether it's a root mealybug. I have to say I've become paranoid now, but that is what you're looking for, isn't it? Those masses on the roots? And I find I'm increasingly putting things into clear pots, so I can keep an eye on them. Is the life-cycle like the mealybug, where it's quite a swift turnaround? They're reproducing quite swiftly once they get going in a pot?
Raymond: The life-cycle, from egg to egg-laying female, and this of course is really contingent on growing -medium temperature, can vary from about two weeks, to maybe 30 days. Also, plant growth, plant life stage, growing-medium type may also influence that. That research probably has not been done and it would be useful. Mealybug has a much more extended life-cycle, Jane, than, say aphids, or thrips, or whiteflies. It's not like a two-week life-cycle. It's probably two weeks to three, maybe four weeks.
Jane: Am I right in thinking that they favour plants where the substrate tends to stay slightly on the drier side? I'm thinking of the things that have been affected in my collection, particularly cacti, succulents, Hoyas, that kind of thing, where they don't experience as much moisture as they might do, say, in a fern pot?
Raymond: I'm not sure there's enough data. I do know that Azaleas and Chrysanthemums are susceptible, but does that mean that's where they've been found? So I'm not sure there's been enough studies that show that they have a preference for certain plants. The question I would always have is how do they get there? We know that cacti are susceptible to above-ground mealybugs, for sure, which is why they're difficult to deal with because they get in those tight, enclosed areas of hens and chickens and others, but whether they have a preference for succulents... Most of your mealybugs are very polyphagous, meaning they feed on a wide variety of plant types. I would say, with so much confidence, with minimal evidence, that even the root mealybug probably is a generous feeder and really doesn't have much preference. Whatever it's infesting and feeding upon, it's going to use as a food source.
Jane: From what you were saying earlier, the solution to root mealybugs is a scorched earth approach, shall we say? There really aren't any particular pesticides that are going to be hugely helpful and it maybe a case of throwing the plant away. Let me tell you what I've done with the ones that I've had, and certain plants have been easier than others. When it's a succulent, where I can do this, literally cut the succulent off at ground level, washed it off really carefully and re-rooted it, disposing of all of the substrate, washing the pot out with hot, soapy water and that has worked. It seems like that's the best way forward with most of these, which for people with a lot of plants, like me, is not great. Does this affect commercial crops in a kind of disastrous way, on occasion?
Raymond: Yes. I had experience working with nursery production systems, even green roots, root mealybug became a problem. There are some materials available, but it's a timing issue. If you wait until it's too late and mealybugs have developed large abundance of population and large densities, then it becomes more difficult to deal with it. Most of your contact insecticides, when you're dealing with a growing medium, it gets very complex. Some of these can be bounded up by the soil particles and of course, where they're feeding, it's hard for them to be exposed to lethal concentrations of the solution and rates. What are the rates for either drenching or sprenching, sprenching meaning a high volume spray application where you get some into the growing medium? So, with minimal research done, there has been research basically, but we still don't know sufficient rates that are going to give us adequate mortality, but again that's going to be contingent on getting them early on, proactively, before they build up the numbers. That's why one of the recommendations that I have been alluding to is releasing biological control agents, such as the Rove Beetle, Dalotia coriaria. I have no data on this, we'd like to study it, but it's a generous predator that the larva don't seed on fungus and larvae Western Flower thrips pupil stages and so it "might" feed on the mealybugs and even root aphids, although we just don't have any quantitative data to substantiate that. Thinking of how the biology of that insect is, it's at least something to try and I know the cannabis and hemp growers that deal with root aphids and mealybugs, that's pretty much their only option, other than like you mentioned, cutting the plants, starting new plants or just throwing the plants away.
Jane: Yes, it's brutal, isn't it? Was it Rove Beetle you were mentioning for biological control there?
Raymond: Yes, Dalotia coriaria, formerly Atheta, I've been rearing it for probably 15 to 20 years, it's very easy to rear or treat colonies and you can buy them, they're commercially available. You release them as adults, they reside in the growing medium, both the larva and the adults, and they feed on a wide variety of insect pests, we know fungus gnat larva and thrips because graduate students that I've mentored have proven that, we just don't know, at this point, their efficacy against root mealybugs and root aphids. These insects are covered with a frothy, waxy material and it's a possibility that the Rove Beetles don't like that or can't get in to feed on them, which may negate their potential effectiveness as biocontrol agents in use against root mealybugs.
Jane: I can imagine that's not that palatable, that waxy layer. I wonder whether they're working at the soil depth that's deep enough. Would they be going right down to the bottom of the pot? Perhaps it's just the ones I'm seeing, but I seem to find most of the root mealybug right down at the base of the pot when I'm looking at infestations.
Raymond: There may be a spatial distribution difference between the two. We do know Rove Beetles, because they require oxygen to breathe, they're around the upper surface growing-medium layer and they may not get down where root mealybugs are feeding, especially if you have deep pots, like Easter Lily containers, or mature plants. They just don't go down that deep. Again, that would be something interesting to quantify that. We know that fungus gnat larva also will go deeper in the growing medium and that may allow them to escape exposure of Rove Beetle, adults and larva. So, yes, there may be a spatial aspect associated, where the Rove Beetles may not provide the effective and mortality-wise killing mealybugs because they're not in the same area where the root mealybugs are feeding.
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Jane: More root mealybugs realness to come, but now it's time to hear from this week's sponsor.
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Jane: I've not been doing it in a scientific way, so who knows, but what seems to have worked for me on the plants where I've just thought to myself, "Oh my gosh, I cannot face cutting the tops off, it's just too big a plant!" what I've done is a soil drench of pyrethrin and that seems to have, if not killed off all of the mealybugs, certainly knocked back the population quite considerably. Obviously, the problem with cacti and succulents is, right now, it's the period where I'm not going to be watering them for quite some time because of allowing them to have their dormancy period. My plan with most of my plants where I really do balk at taking cuttings and chucking the whole thing, is that I keep going with these pyrethrin soil drenches. I guess it's better than nothing. That was one of the chemicals listed on the list of things that could work, that I've seen. I don't know whether you've got any thoughts on using that particular pesticide?
Raymond: Pyrethrin is derived from the chrysanthemum plant, Tanacetum cinerariifolium. It is a broad-spectrum insecticide/miticide. It kills everything that you come in contact with. It's widely used outdoors in organic production systems because of very short residual activity. I think, in sunlight, it's gone after an hour; short post-harvest interval. One of my concerns is, in the soil or growing medium, we don't know if it's going to bind to the soil particles and again the residual is so short, Jane, I don't see how that's going to work very well overall, especially when you've got this cottony mass that's protecting the mealybugs from exposure to those. So, without the quantitative data, my hypothesis is that those are not going to be effective and they have to be applied multiple times because of their short residual activity. Now, in the growing medium where there's no UV light exposure, they might last longer, but we don't know how they're interacting with the growing medium. We do know that certain growing media, especially with a 30% organic content, will bind to certain insecticides and consequently reduce their efficacy. I'd have to do the testing to get a reliable quantitative data, but my hypothesis is it's probably not going to provide overall long-term effectiveness against root mealybugs.
Jane: Oh well, that's not the news I was hoping to hear, but interesting nonetheless!
Raymond: Insecticidal soaps, potassium salts and fatty acids have been used but, again, those are short residual contact. So unless they come in contact with the root mealybugs, they're providing no mortality. The same with horticultural oils, mineral-based oils, so that requires multiple applications. So what you have to do, is you have to take the plants out, look at them and see are you getting a reduction in populations, not just waiting until the plants are wilting. Just because the plants are looking fine, it doesn't mean that you've got management. You still have to look and see if there's numbers increasing in the growing medium. I do know that homeowners have tried to use those and they're not robust studies, mostly anecdotal information, so at this point it's hard to make a recommendation without some type of quantitative data, to substantiate there's going to be a level of efficacy because you don't know where they're at, you can't see the growing medium. The plants can be shipped in. If you're going for, like, a nursery or garden centre, they get their plants, they could have root mealybugs. Now, the extent of the infestation, we wouldn't know, so whenever you buy a plant, I recommend not only checking the above ground parts but also, if you can, take the plant out of the pot and just look at the roots. Make sure the roots are healthy, for one, making sure there's none of these frothy or cottony masses in there because you really don't want to bring that plant home, obviously, once you've seen that.
Jane: Exactly. I've learned my lesson now, but you're absolutely right, if the problem comes into your collection, it's dire. I've also learned my lesson, as well, with how these creatures have been spreading through different plants in my collection where I either have reused substrate, or I haven't cleaned pots thoroughly enough when I'm reusing them. I'm guessing that's how they're spreading from pot to pot?
Raymond: It could be. That's why we recommend using new growing medium or using new pots. Not just for root mealybugs, but for pathogens - fungi that can reside in debris, or on a container or even in a growing medium. The way that I have read that they spread, is they can come out of the drainage holes and move around, or people are touching growing medium and going from plant to plant. It's not the same as like an above-ground mealybug, moving or crawling from one plant to next. These are in the growing mediums, so more than likely they're either coming out through the drainage holes or somebody's using a growing medium that's infested and pots a plant in that and that's how they're getting the root mealybugs, that way.
Jane: Yes, a fellow cactus grower did say to me, "One thing you can do is make sure that your plants are not all standing on the same tray" but they've got their own individual trays because of that very reason - that they could be coming out at the bottom of the drainage hole and floating along on the surface of a rivulet of water and ending up going into another pot, which I guess kind of makes sense. As you say, if you can avoid them coming into your collection in the first place, that is the major issue. One other treatment that I'm seeing bandied around on the internet, such as it is, that I wanted to ask you about, is this hot water bath technique, where you're getting water up to a temperature of around 49C / 120F and you're dunking the whole plant in there at that temperature, with the idea that you're killing off the pest in question without killing off the plant. Have you heard of that and have you got any thoughts on its effectiveness for root mealybugs?
Raymond: One of the concerns I have, is the temperature is 149F in one minute, but it'll start to decline. Unless you're maintaining a consistent level of hot water, you're not exposing all your plants to the same temperature. The other one is the effect on plants. You can kill the mealybugs, but if it negatively affects your plants, that's not what you're looking for. It's very short-term and you'll kill them, maybe, but you can get a re-infestation somehow, either inadvertently, or basically on your own. So those are just some of the concerns, being a scientist, I looked at. It's a very quick and easy way to get rid of things like invasive insects that come in, but insects that are established in areas, it may be less so. Again my concern is how long do you leave them in there? How consistent is that hot water? Are you maintaining it somehow? If not, is it going to decline? So your first couple of plants may be exposed, but your later plants may not, and so, if they're not getting exposed to lethal temperatures, you're not having any control overall.
Jane: This feels like a bit of a depressing conversation because there really, clearly aren't many easy answers to this root mealybug question!
Raymond: There are pests that we deal with, indoor and outdoor, that the options are minimal. Root mealybugs is one that we have. Where do we go from here? If it becomes a more severe pest, I'm sure there will be, hopefully, an uprising moment to start working on that, but funds are tight, we're living in different times. I think, at this point, what I could provide is guidelines, or recommendations, is when you buy plants, you look at the roots. You can't take, like, a five gallon container, but, like, a 4/6/12 inch, look at the root zone, you should actually be doing it anyway to make sure that the roots are not girdling and they're healthy because you don't want to bring a sick plant in because you're going to be spending labour and time trying to save it. Obviously, use clean containers and growing media every time you repot plants, whether it be succulents, or orchids, or other plants, to minimise, mitigate or reduce the possibility of moving mealybugs from one plant to the next. If it's, like, a prize plant, take them out, wash the root zone off and wash the mealybugs off the roots and replant it into a fresh growing medium. That would be an option if you've got this, what's the term I'm thinking of? They use it all the time now? This escapes me right now, but anyway, a prize plant, basically, that your grandmother, your great-grandmother passed down to you. So that would be one way to salvage it, as opposed to throwing it away, or trying to start cutting, is just clean that root zone off, get rid of the mealybugs that are there, as best you can, with the force of water-spray, dunk it in water, shake it, maybe try to apply maybe a soapy water, that might help somewhat. Then just start with the new growing medium and, like you said, provide water, proper fertiliser, growing conditions, those go a long way in maintaining healthy plants. Even if you have a low level of root mealybugs, if your plants are mature and healthy, then you probably can tolerate low infestation, as long as that infestation doesn't start increasing in density, or abundance, to becoming a problem.
Jane: Well, that's interesting. I have found that there are a couple of my plants, which I know I haven't completely eradicated the root mealybugs, but the plant seems to be doing well at the moment. They're specimens that are big enough that they seem to be able to cope. It's so interesting to hear about this pest and, hopefully, this will be a warning for anyone who hasn't yet fallen prey, to keep a really close eye on their plants and look out for the first signs of it because you don't want to end up with a big infestation in your houseplant collection, that's for sure! Thank you so much for joining me today, Professor Cloyd. It's been a pleasure and, hopefully, you can come back on the show at some point in the future with better news about some more treatments for this particular pest! Thanks so much.
Raymond: You're welcome, Jane. Any time!
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Jane: Thanks to Professor Cloyd for giving me all that much-needed information about root mealybugs. If you've suffered, tell me what you've done, what's worked and what hasn't worked and I'll keep you posted as to how my own experiments go with this tricky pest.
Now it's time for Question of the Week and it comes from Kathleen, in the US, who brought a whole host of Ficus benjamina questions to me, common name the Weeping Fig, a real OG houseplant, I think you could say. Very popular as an indoor tree, maybe it's lost a bit of ground to Ficus lyrata, the Fiddle-Leaf Fig, but still so popular. Now, this is one of those plants that does have the ability to be manipulated in all kinds of different ways and you can see it sold in everything from tiny plants that are just a few centimetres tall. Plants grown as lollipop-like standards, where they've got a bare stem and then a ball of growth at the top and sometimes these standards have got braided stems. It's an interesting one, this. It's very popular with the species Pachira aquatica, the Guiana Chestnut, also known as the Money Tree. That's probably the most popular houseplant species that comes with braided trunks, but Ficus benjamina is another one that you sometimes see with this particular set-up. I guess the reason is that it's probably quicker to grow three much thinner trunks and braid them together, than it is to grow one thicker trunk. Of course, time is money in the nursery trade, so that way they can grow three trunks, braid them together and hey presto you've got a much thicker looking trunk that would be much more time-consuming and expensive to produce if it was just a single trunk with that lollipop-like top on it.
Here's Kathleen's problem though: one of those three trunks of her braided Ficus benjamina is dead. Kathleen didn't like the aesthetic and she wanted to undo it anyway. This is often what happens with this braided set-up, is that the plants are kind of scrunched together and one will get out-competed by one of the others and you'll end up with a dead branch. So what can Kathleen do? If she doesn't unbraid, then what's going to happen? I suspect, ultimately, in the long, long, long run, you could face a scenario where two of the trunks die back and you're left with one trunk that stays healthy. If you can unbraid them, particularly now that one's dead that's not going to look aesthetically great, I would definitely try to unbraid them, Kathleen. The dead roots from the dead trunk are not going to help your soil particularly. They probably won't do that much harm but I would say if you can get that dead trunk separated out and make two separate trunks, then you could train them in whatever way you wanted to. You could stake them, to try to straighten them out. They're probably going to always be a bit twisted because they've been trained in that braided way in the first place.
Kathleen wanted to check if the third trunk is actually dead. She's done what I would usually suggest, which is scratching the bark at the base of the plant just to see if it looks green or whether it looks completely dead - if there's no sap or greenness showing there, then the plant is probably dead. To be honest, do you really need three Ficus benjamina, anyway? You're probably going to end up with one decent plant at the end of this process, maybe two, so get unbraiding and see what you're left with. You may look at those two trunks once they're potted up individually and be able to visualise a shape and it may be that you have to accept that it's not going to be totally straight but you're going to have a characterful Ficus benjamina that's got some twisting to it and that's fine, but the plants will inevitably do better once they are potted individually and given that space. That's not to say that braided trunks can never work, but I think, on the whole, oftentimes they are for the benefit of the nursery rather than for the long-term health of the plants.
The other species that you sometimes see braided is one of the Sansevieria, specifically Sansevieria cylindrica, there'll be a whole bunch of cuttings of this plant that are placed into soil, individually rooted and then they will be plaited into an elaborate design. Again, particularly with this plant, it's really not sustainable in the long term, you should separate those plants out and get them unbraided and you'll find you've basically got a heck ton of cuttings which can then be potted up separately and the plant will be much happier. Ultimately, that's just not how the plant grows in the wild and it's just not going to be happy like that in the long term. It will grow out of the braiding and look a mess. If you do have a braided Cylindrical Snake Plant, then, like the Weeping Fig, the damage that's been caused by that braiding will remain, but the plant will at least start to grow some new growth, which will eventually grow past the problem. It's a trend that I'm not that fond of, I have to say, but it's something that you can help a plant with if you put a bit of time into it.
Kathleen has the advantage of living in San Diego, California, so nice weather for a Ficus benjamina. The humidity in her home is 60% to 90% - nice! I think your Ficus benjamina is going to be pretty happy once you get this braiding issue sorted out. Just be aware, with this particular plant, it can lose a lot of leaves when it is moved about, so you may find that the stress of the separately potting is that you get some leaf loss, but I think it's going to be okay. Certainly, come spring, it should start to re-sprout. Just make sure that the pot has plenty of drainage and that it's not sitting in too much water over the winter and that soil is free-draining and that will set you up for success with your plant. Good luck, Kathleen, and let me know how you get on! If you've got a question for On The Ledge, do drop me a line ontheledgepodcast@gmail.com is the best address to use and be like Kathleen - send me loads of information and pictures and I will do my best to help!
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Jane: That is all for this week's show. Thank you so much for joining me! I'll be back next Friday, so until then, set your hand lenses to magnify and enjoy your plants this weekend! Bye!
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Jane: The music you heard in this episode was Roll Jordan Roll, by The Joy Drops, The Road We Used To Travel When We Were Kids, by Komiku and Overthrown, by Josh Woodward. The ad music was Holiday Gift, by Kai Engel. All tracks are licensed under Creative Commons. Visit the show notes for details.
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I find out how to spot and treat root mealybugs with entomologist Professor Raymond Cloyd, plus I answer a question about braided houseplants.
This week’s guest
Professor Raymond A Cloyd is a horticultural entomologist at Kansas State University. You can also hear him talking about root mealybugs in On The Ledge episode 143.
Dates for your diary
On December 2 2022, I'm taking part in a panel discussion on houseplants at the British Library, along with James Wong, Carlos Magdalena and Mike Maunder. Indoor Jungles: The Story of the Houseplant starts at 7pm, and livestream and in person tickets can be booked here.
My Hand Lens Gang merch is available now! Check it out here.
Check out the notes below as you listen…
What are root mealybugs?
They are a different type of pest to the mealybugs you’ll find above ground. Root mealybugs from the genus Rhizoecus, whereas regular mealybugs are from the genera Pseudococcus and Planococcus.
Root mealybugs use their mouth parts to suck the sap from roots via the phloem - the food conducting tissues, so they gradually rob the plant of its nutritional content.
Root mealybugs’ life cycle is longer than aphids or thrips, lasting around two to four weeks, depending on a number of factors including soil temperature and substrate.
They make themselves unpalatable and hard to kill with a waxy coating to their bodies.
Root mealybugs will eat anything, but personally I have found that they are particularly keen on members of the Gesneriad family, Hoyas, and cacti and succulents.
Root mealybugs are often confused with root aphids: you can read more about these two pests and the differences between them in this article by Prof Cloyd.
Symptoms of an infestation
In severe infestations, plants may appear to suddenly wilt and collapse, as the root mealybugs deprive the plant of nutrients. In less severe cases, plants will start to put out stunted growth.
If you take the rootball out of the pot, cottony masses around the roots will be visible (see the photograph above).
If you soak the rootball in water, look for white specks the size of small rice grains coming to the surface: these are the ‘crawlers’ or young nymph stage root mealybugs. These will escape from the drainage holes of plants and spread to other plants that way.
How to treat root mealybug
Prevention is better than cure! Check the roots of all new plants you add to your collection, and initially quarantine them away from your other plants until you are sure they are clear of an infestation.
In severe infestations, it is best to take cuttings of your plant - or cut the plant off at the base in the case of many succulents - and re-root them in fresh substrate, disposing of the old substrate and scrubbing the pot in hot soapy water before reuse.
If that isn’t possible, wash off the substrate, soak in soapy water for a few minutes, and repot in fresh substrate, using a clean pot.
The rove beetle (Dalotia coriaria), a biological control that predates on some other houseplant pests including thrips and fungus gnats, may be able to make an impact on root mealybug populations, but not enough research has been done yet to show how successful rove beetles are at controlling root mealies.
You can use pesticides like pyrethrin as a soil drench (this is what I have tried) but its efficacy is not yet clear to Prof Cloyd and other entomologists. I have found pyrethrin can knock back populations of root mealybug, but repeated applications are necessary: and remember that this is a wide spectrum pesticide will kill all the soil fauna, not just root mealies. Horticultural soap sprays can be used, but may have the same issues.
Hot water baths - 10 minutes soaking at 120F/49°C - has been practiced with success by some growers, but the challenge is to keep the temperature steady - and this treatment may damage some plants, too.
Other things I’ve found helpful
Keeping susceptible plants in clear plastic pots allows you to keep an eye out for infestations so you can deal with them at an early stage.
Do not sit groups of plants on a communal tray: instead give them individual drip trays or cachepots, as this will discourage them from migrating to new plants.
Do not reuse substrates and prioritise hygiene for your equipment and pots.
The braided trunk on Kathleen’s Ficus does not set up the plant for long term success.
QUESTION OF THE WEEK
Kathleen’s Ficus benjamina (weeping fig) has a braided trunk but one of the three sections has died off. This is a common practice with certain houseplants including Pachira aquatica (guinea chestnut) and Sansevieria cylindrica, the cylinder snake plant: I suspect it’s a way of making a houseplant look like you’re getting a more mature plant than you actually are.
I suggest Kathleen untangles the stems and pots them up separately to grow, as ultimately only one of the trunks is likely to survive anyway due to overcrowding. They probably won’t straighten out completely but Kathleen may be inspired by their shape to choose a particular form for the plant.
Want to ask me a question? Email ontheledgepodcast@gmail.com. The more information you can include, the better - pictures of your plant, details of your location and how long you have had the plant are always useful to help solve your issue.
THIS WEEK’S SPONSOR
COZY EARTH
This week’s show is supported by Cozy Earth, the premium bedding company that helps you get the deep restorative sleep you need. Bedtime is literally my favourite time of day, so it’s really important that my bed is the most comfortable place it can be. I got to try out a set of Cozy Earth sheets and they really are so comfortable! Cozy Earth’s high quality bedding is responsibly sourced and made from soft and sustainable viscose that comes from bamboo fabrics. Bundle up in Cozy Earth pajamas made from ultra-soft viscose from bamboo this holiday season. Now available in holiday hues! Want to give the gift of a good night's rest with Cozy Earth? On The Ledge listeners can take up Cozy Earth’s exclusive offer today - get 40% off site wide at cozyearth.com using code LEDGE now.
HOW TO SUPPORT ON THE LEDGE
Contributions from On The Ledge listeners help to pay for all the things that have made the show possible over the last few years: equipment, travel expenses, editing, admin support and transcription.
Want to make a one-off donation? You can do that through my ko-fi.com page, or via Paypal.
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CREDITS
This week's show featured the tracks Roll Jordan Roll by the Joy Drops, The Road We Use To Travel When We Were Kids by Komiku and Overthrown by Josh Woodward. The ad music is Holiday Gift by Kai Engel.