Episode 176: biological controls part one

Fungus gnats aka sciarid flies are treatable with two different biological controls. Photograph: Andermatt UK.

Transcript

Episode 176

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Jane: Hello and welcome to the podcast for people with a propensity for plants... or On The Ledge, for short! I'm your host, Jane Perrone, and in this week's show we're talking about predators on your plants. Yes, biological controls. Plus I'll be answering a question about a Prickly Pear that needs support and we have our youngest ever Meet the Listener! You are going to love her!

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Jane: I've just discovered that I'm number one on the Russian Home and Garden charts, so 'Privet!' to any Russian listeners out there! Thanks to Juniper and Jessica, both became Ledge-ends in the last few days, and Raker who became a Crazy Plant Person. Do check the show notes for details of how to become a Patreon of the show or make a one-off donation via ko-fi.com It is simple, easy and very, very beneficial for On The Ledge because while this show is free to listen to, it isn't free to make. From podcast hosting fees, to equipment, to the work of my assistant Kelly and transcribing the podcast, all of these things have to be paid for through advertising and crowdfunding and that is where Patreon comes in. So support the show! If you become a Ledge-end, or at Super Fan level, then you get to unlock exclusive episodes of the show and you get a mail-out every December and there's going to be a Patreons-only Zoom coming up once I reach 300 Patreons and I'm only ten away from that, so it's getting close, so sign up now!

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Jane: When you start bringing houseplants into your home, it is inevitable that there will be some livestock that either comes in with the plants or arrives on your plants in due course. Whether it's mealybugs, those fluffy white terrors of the cacti and succulent world, spider mites, those invisible assassins of your Maranta group plants, or fungus gnats, the floaty but oh-so-annoying flies that lay their eggs in your compost. All of these pests will, in their own unique way, drive you into the ground. So it's not surprising that many of us have been turning to biological controls. We're trying to avoid using synthetic chemicals in lots of areas of our lives and houseplant care is no exception, but it's very confusing from what to buy, to how to apply. This is one of those topics that really needs looking at. So I got two experts to answer all of your questions about biological controls. The interview was such a good one that I've decided to split it across two episodes. In this episode we'll hear about what biological controls actually are, why it's vital that you read the label and how to get the best out of biological controls for fungus gnats, aka Sciarid Flies.

Tessa: I'm Tessa, I own Ladybird Plantcare and sell bugs that eat the bugs you don't want on your plants.

Andy: My name is Andy Brown, I'm the managing director of Andermatt UK who are a global manufacturer and retailer of biological control products.

Jane: Lots of listeners have been desperate for us to talk about this topic in the show because it seems increasingly popular, the idea of biological controls, that we can avoid using chemical sprays and instead rely on a small tiny army of creatures to sort out our problems, but I'm not sure that all of us have quite got a handle on what the phrase biological control actually means. Does one of you want to start off, maybe Andy? Just give us a definition, as closely as you can, of what biological controls actually are?

Andy: Yes certainly. As you say, it can be complicated and one of those complications is because there is no one definition of what biological control is, so, depending on where you are in the world, you come across terms like "natural", or "found in nature", or "living organisms", or "chemically identical", but as a general rule, it's using a natural solution to control a pest or disease problem. To get around this issue, there not being one definition, there's a trade association called the IBMA, International Biocontrol Manufacturers Association, and they've come up with this term of 'bioprotection' as an umbrella term for biological control. They talk about biological control as originating from nature and then either being "sourced from nature", or "nature identical" if it's synthesised.

Jane: Tessa, when you're marketing your products, do you find that customers need a bit of education about what they're actually buying? Is that starting to filter through to the growing community, do you think?

Tessa: Yes, I think it is, I think people tend to hear about it from someone else, or often from a site or a forum. A lot of the time they'll pick on the most popular or well-known predators, like ladybirds, for example, and they'll just think that ladybirds are going to answer all of their problems. I think the main education piece is around the fact that there's an ideal predator for each pest and there's ideal conditions for that that predator. If you want to get it right, if you want it to do its job, then you need to be using the right thing and you need to be using it at the right time of the year, or in the right light and heat conditions, for it to work effectively. Also, giving people the understanding that it's not a bug spray, so you can't just liberally throw it around and it's just going to work, and that they're live creatures and we have to give them some encouragement and make sure that we're giving them the right conditions for them to do their job.

Jane: Yes, it's the old thing about read the label, isn't it? I think with biological controls, it's really vital because I know lots of people who are thinking about, in the garden, people who spend money buying the nematodes that work on say vine weevil and then say, "Oh, it didn't work!" and you question them further and it turns out that they've not really applied them when the soil's at the right temperature, or in the right way, and lo and behold, it hasn't worked! So, yes, it's the old thing of read the label, isn't it?

Tessa: It is and I think it's really important to identify that you really have got to get to grips with what pests you've got in the first place and that you know, therefore, what predator you need, and the conditions, and the way in which to apply them, before you purchase them, as well, because once you've got them, there's nothing you can do! You can't send them back - they're live!

Jane: Let's just go through some of the main products that you can get for the pests that houseplant growers will be encountering. I guess the one that I get the most questions about are fungus gnats and often it's people who think they've got fruit flies and don't realise that they're actually a completely different species of fly that is affecting their plants, I think that's the one that most people ask about. Back a couple of years ago, right at the start of my podcast, I did an episode on fungus gnats and back then, I think the main biological control that was being recommended was the nematodes, I've forgotten the species name, but now mites seem to be on the agenda as well. Can we just talk a little bit about what the fungus gnat options are for biological control?

Andy: Fungus gnats, it's actually the larvae that cause the damage to the plants. The larvae live in the soil, in damp soil is what they like, which is what the plant likes. So if you're keeping the soil nice and moist for your plants, you're also creating an environment that the larvae would like. But it's often the adults that people see more, so the actual flying adult, and they're more of a nuisance than actually causing damage to your plants and they're just a nuisance flying around you and your house. By far the most commonly used biological control products for home use for control of fungus gnats, or Sciarid Fly, is nematodes and it's the nematode species Steinernema feltiae and it's in a number of different products, this is put onto the soil in water to control the larval stage.

Jane: It really does work! I use that treatment twice a year on my houseplants. I think one of the things that people want with pests, is they want there to be a silver bullet that they're going to do something and it's going to fix the problem forever, which is not really how pests work, or how biological controls work, but it certainly is effective, I find the nematode treatment for fungus gnats, but you do have to do it a couple of times a year for it to be effective. Is there anything you can do to really get the best out of your nematodes once you have applied them, in terms of keeping them going as long as possible while there are still fungus gnats around? I imagine they need some moisture level in the soil to work?

Tessa: That's a question we get asked a lot, 'How moist does the soil need to be? How wet does the soil need to be? I like to keep my plants really dry'. That kind of question. A really good test that I was told is that - you don't have to actually do it - but imagine if you squeezed that pot, you would want a couple of drops to come out the bottom. So you wouldn't want it to be dripping and you don't want it to be dry that no water would come out of that pot if you squeezed it, but you just want it so that, through the holes in the bottom of the pot, a couple of drops would come out.

Jane: That's a really useful guide because that's a question that has crossed my mind many times. Let's just mention the other biological control for Sciarid Fly. I can't really say this word, Hypoaspis? Is that right?

Tessa: Aspis, yes, I find that they're really good for people that are using a growing material that's not going to be suitable for nematodes. So, for example, orchids in bark, you can't really use nematodes because there's nothing for them to live in and they're more expensive, so some people won't want to use those. They're really good because they will eat away and get rid of the larvae and then they can last up to 60 days without being fed. So they do the job and they fill their tummies and then they are around for that period of time afterwards, which therefore offers that level of protection that nematodes won't because they'll stop working as soon as there's no more prey for them to eat.

Jane: I think we're all a bit scared of the idea of mites because of spider mites but, obviously, as we've discussed on the podcast before, there are many, many species of mites and not all of them are going to be damaging your plants and indeed these ones are doing good in destroying fungus gnats.

Tessa: There's loads of great mites, yes.

Jane: Which brings us on to spider mites. Is there a good biological control for spider mites? Please god, let there be a good control!

Tessa: Yes, there's a couple of really good controls for spider mites, if you're looking to prevent spider mites. So, you know that you get spider mites, say, when it's warm in your in your house or in your glass house, you know that, come mid-May, you start to see spider mite. Then you can introduce the slow-release product, which is the Andersoni sachets. They can tolerate temperatures a bit cooler than the spider mites, so they can be there ready to pounce on them as soon as they crawl out from wherever they've been hiding and because they're in the slow-release sachets, they'll crawl out over a period of four to six weeks and offer you that protection. They'll also feed on small amounts of sap and spores, so they can last while there's no spider mite present. A lot of the time, as much as you try, you're going to have spider mite at a higher level and you've got the beginnings of an infestation. As soon as you see any webbing, then you want to be getting the Phytoseiulus, which is just amazing. The Phytoseiulus mites are way faster than the spider mites, so they can overcome their prey very effectively. They also tolerate lower temperatures and higher moisture levels, so if you're introducing the Phytoseiulus and spraying the plant with water, then you're just doing the double whammy and you're getting rid of them,

Jane: I've heard people say, "Oh well, you know, now that we're only - that nurseries are mainly - using biological controls to control pests, such as spider mite, we all need to expect that, when we buy a plant, there's a good chance there's going to be a few spider mites on it because, actually, in order for biological controls to work there needs to be a low base-level of pests around." Is that true or is that just something that plant sellers say?

Andy: I think there's a level of education there for everyone in the supply chain. It's true we're moving away from using chemical products that annihilate everything and so destroy anything living on the plant, good or bad. I'd take there being a few spider mites on a plant I bought as a good thing, as a sign that the plant hasn't been treated with a harsh chemical.

Jane: That's a really good point, actually, and I think that's something that many new houseplant owners have got to get to grips with. For a start there's already lots of tiny creatures in your house anyway, but by bringing plants in, you're inevitably bringing living things with living things on them and that's just something we have to get used to. You're not going to be able to have a plant that's completely free of any creatures because, as you say, the only way to do that is by using a lot of chemicals which, hopefully, we're realising aren't so great. Somebody wanted to know if there are advantages and disadvantages to biological control compared to conventional methods? We've touched on this already in terms of some of these chemical sprays are not that great, what are the pros and cons? Obviously, you're going to be saying biological controls are great but are there any disadvantages of using biological controls?

Andy: Yes, I think we've touched on it and as Tessa was saying earlier, there's a level of education and knowledge and you have to understand what it is you're trying to target and how to get the best out of the product you're using. Because you're dealing with living organisms, they can be less forgiving if you don't do it correctly. That's not to scare off people. I see that as an exciting part of using them, understanding them, and how to get the best performance out of them. You are dealing with living organisms on the whole and so an understanding of how to get them to work best, yes, an advantage and a disadvantage.

Jane: One of the other questions that came in was about using biological controls as a preventative measure. We've touched on this with spider mites already, but I'd always assume that it's not worth getting them unless you've got the problem, as in, if you go and buy a load of mites, or whatever, or nematodes, and there's nothing for them to eat because you're pre-empting a situation, then you're just wasting your money, but is that wrong?

Tessa: It depends across the spectrum of products really. So yes, nematodes will not survive if there's nothing for them to eat. Also, nematodes aren't a super swimmer, great, fast creature. They're quite lazy, so you tend to have to apply them where the pest is. They're not going to go in search of it. The slow-release product for spider mite, the spurious product for thrips, they both are supplied in a sachet that has grain mites in there, so they've got some food inside the sachet and they crawl out over a period of time, as I said, with their spider mite product, they will feed on other things. On the whole, I think if you want to get your money's worth, you're right, you want to introduce those products once you've got something for them to eat, their prey is present. I think, if you know your plants, and you know the problems that you've had the previous years, I always say to people it's almost a good idea to keep a pest diary. So from year to year, you know when certain things started to appear and you get your predators in, either as soon as the first signs of problems are there, or just before. If you know every year you get spider mite on your particular plant when the sun starts shining through that window, then get it in early. Get it nipped in the bud.

Jane: I've got a Ctenanthe, a member of the Maranta family, which has just always got a bit of spider mite on it and, for that reason, I keep it on its own. I'm wondering, if I wanted to use a biological control on that, whether there would be enough on the plant for the biological control to be effective, or do I need a whole mini-jungle of foliage houseplants for the mites to snack on, or is one plant enough?

Tessa: One plant is enough. On most suppliers' websites, there'll be information about how much you need per square meter, or per plant, so it's quite easy to work out how much you need. With the nematode products it's a bit tricky because they come in very specific sizes and that's just due to the way that they're produced. For something like the Andersoni, you can order as few as five sachets and for one plant you might just put one sachet on there and then put the other ones on plants that are susceptible to spider mite and change it every six weeks, or every eight weeks, if you really don't think there's much of a problem. But you might, with that, want to just use something like a horticultural soap every fortnight, if it gets a bit worse every week, a couple of times a week, to keep the spider mite under control. That might be a much more effective way for you to do that.

Jane: Andy, somebody wanted to know about how we get these biological controls in the first place. I can't imagine what the what the factory looks like where you produce nematodes. Can you give us an insight into how these biological controls are mass-produced for the market?

Andy: There's not a lot of knowledge out there because it's something that is so alien to people, but there's an incredible amount of research that goes into developing these technologies. We talked earlier about the Steinernema feltiae for controlling Sciarid Fly. That's been around for 30 years and it's probably the first true example of successful biological control, certainly here in the UK, on a commercial scale. The level of technology that goes into manufacturing these living organisms is incredible. The nematodes, for example, they're bred in stainless steel fermenters, some of them three storeys high, massive vessels, like a beer brewing fermenter or a wine fermenter, and getting the conditions just right inside that fermenter, to effectively create the environment they reproduce in within an insect, then getting them out of the fermenter and separating them and making a pure product, and then putting them in a formulation that they're happy to live in until the customer gets them, there's an incredible amount of technology and history and research money that's gone into these.

Jane: Well, I wasn't expecting you to describe a three-storeys-high metal fermenting tube while describing how these things come about! That's amazing! When you get them, the first time I used a biological control was many years ago now, whichever the nematode that's used for slugs I would imagine, but I remember getting the pack and having to put it in the fridge and having to put a big sign on it so my husband didn't try and put it on toast or anything, and getting it out and it looks like a sort of brown, powdery, semi-sticky stuff, which you've then got to dilute in water and I think that sort of blew my mind because I'm thinking, "I can't see what I'm dealing with here!" which was slightly disturbing! I wonder if that's why, when you're talking about people's ideas about what biological control is, they want to think about a ladybird because we all know what a ladybird looks like and what it is? It's quite hard to think about a nematode in a useful way when you've never actually seen what they look like and you get this brown powder, and it's all very mysterious, but I guess that's why you have to follow the instructions very closely!? One of the things that people are really concerned about, Andy, is "biological controls gone mad!". I think they're worried that they're going to break out of our homes and do something terrible in the environment or, indeed, one listener was very worried about lacewings getting in her hair! Can you offer some reassurance here? I would presume, after many decades of using nematodes and so on, that we've got a good handle on the fact they're not going to break out and cause any damage to the native environment, or are there any ones that we are concerned about for that reason?

Andy: Very much so. As well as the amount of research that goes into them, these products are heavily regulated, and rightly so for any product that's used to control a pest. Are they going to cause problems outside in the environment? No, is the answer. Product registration varies from country to country. Here in the UK, the products are regulated and part of what a manufacturer has to do, is to ensure that the product isn't going to cause any problems to the wider environment once it is released. As for them getting into a listener's hair, I have less and less hair as the years go by! I don't see it as a problem for me but maybe people with more hair do see it as more of a concern? If it did get in your hair, it's not going to do any harm to you. I imagine the lacewing, being about a centimetre-and-a-half wide is probably more scared of you than you are of it!

Jane: I love lacewings, I think they're gorgeous, but I know not everyone's keen on flying things.

Tessa: Lacewing are predominantly looking after aphids for you, so there's not an awful lot of aphids in people's houseplants. I get a lot of people buying lacewing because they're beautiful and they want them to do all the good things in their house when, actually, they're more of a product that we tend to recommend for outdoors in the summer. Also, the fact of them reproducing in your house and getting out of control, they'll only really reproduce in perfect conditions and with the right amount of prey, so it depends how much pest you've got really.

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Jane: Thanks so much to Tessa and Andy and my interview with them will be continuing in next week's show. In the meantime, do check out the show notes at janeperrone.com for links to both Andermatt UK and Ladybird Plantcare - more information about the biological controls we've talked about today and lots of resources for you to check out.

It's now time for Question of the Week, which comes from Jane - great name, Jane! I've never met a bad Jane! Jane is a new listener to the show, having binged through the episodes over the last few months, and has a Prickly Pear Cactus from her husband which came as a birthday present, but unfortunately, it arrived looking droopy and sad-looking. This is interesting. Jane has handily attached some pictures to her email and I can see that the specimen in question looks like it's Opuntia monacantha which has the common name of the Drooping Prickly Pear, so, maybe we're on to something here. When the plant arrived, she gave it a good soak and trimmed off a mushy leaf and the soil was dusty dry at the time. After the drink the top leaf is still very soft but the bottom two have firmed up and Jane is using wooden kebab sticks to prop it up but she's wondering what else she can do to help it thrive.

So, Opuntia monacantha, as the common name suggests, this particular Prickly Pear is particularly prone to drooping and if you've got a Prickly Pear that has drooped over the wintertime, the main thing you need to establish is the cause of the drooping. It could be the plant is short of water, or it could be that the plant is rotting. So how have you been treating your Prickly Pear over the winter? Check that potting mix. Is it dry and hard and completely dried up, or is it moist and gooey? That will give you a good guide as to whether your plant has had too much water or too little. If it's had too much water, it's a dire state of affairs. There's probably not that much you can do to save it if it's already gone very soft and droopy. If, on the other hand, the potting mix is dead dry and the plant is lacking water, it's a lot easier to deal with. In fact, I'm sitting here and to my left there is my very own Opuntia monacantha and I'm looking at it - I'm just going to give it a little bit of a... be careful because it's quite spiny - yes, that's pretty droopy, I'd say. It's about 50 centimetres tall and the top ten centimetres is drooping, but I'm not too worried. The reason why I'm not too worried is because this plant will revive quite nicely once it has some more water come, well, I'll probably start properly watering it in the next month or so. Over the wintertime in the office here, about 15C to 18C, that is about 63F/62F or so, 61F at a push? Out here, it does get a bit of water during the winter, but it stays very much on the dry side and therefore it does droop. If I start watering that and give it a good soak, it will perk up very quickly and it's interesting because I also have my Opuntia microdasys, the one with the lovely velvety pads covered with yellow glochids, those tiny spines, that did droop, but when I watered that, it perked up completely and that's completely upright, so it just shows you that Opuntia monacantha is particularly prone to drooping.

So, basically, the message is don't worry too much! What's happening on a cell level here is that, in each cell of a plant there is a thing called the vacuole which is basically a big old bag of liquid, and when the vacuole is full of water, the cell is turgid, it's firm and steady, and therefore the vacuole is pressing against the cell wall and making everything stand upright. When the vacuole isn't full of water and it collapses in a bit, that means the plant isn't turgid, those cells aren't turgid, and as a result the plant droops over. As soon as the plant is watered and can get a good supply of water to those vacuoles, it will re-inflate itself, a bit like a balloon, and be absolutely fine. It's much more of a concern, as I say, if it's wilting because of rot because that means the roots are rotted and you may have to start again. I would try and rescue any firm pads and cut away everything else if you've got rotting roots and start that as a new cutting, but that's not the case here, Jane. You just need to worry about getting your cactus through the next few weeks and then it will perk up. Once you're into April, and if it's getting good sunlight, you can start watering that cactus every week, provided that you've got a good potting mix there which will let the water drain away quickly.

So, in addition to having a look at the plant and how it's doing, if it's a new plant and you've only just got it, do have a look at what it's potted into and consider changing that potting mix if you think it's going to hold on to too much water and prevent you from watering it regularly during the growing season. Monacantha is native to South America, although it has become naturalised in places like South Africa and Australia and is, in fact, an invasive weed in some parts of the world. So, if you live in a part of the world where this one's naturalised, it is worth taking care not to let this loose in your garden but if you're growing this as a houseplant in the UK, as I am, then that is absolutely fine.

The particular cultivar of Opuntia monacantha that seems to be very much the most popular, is the Monstrose variegated form. Monstrose: what does that mean? Well, it just means that it's twisted and elongated, basically showing etiolation even when the sunlight isn't lacking. And the variegation, how does that show up? Well, on the Opuntia Monacantha, it's quite subtle. There's silvery areas randomly speckled across the surface of the pads which, as I say, are stretched and elongated in a way which, if you look at the parent species of Opuntia monacantha is just completely different. If you're getting in Opuntia monacantha from a shop, this is probably the form you're going to get. The reason why it's popular is because it is much more compact than the parent species, mine is pretty big, it's about 50 centimetres tall then it might get to one metre, but the species would get to about six meters in the wild, so it's a much smaller form, much easier to handle in a domestic situation.

If you want to propagate this plant, if you're worried that your plant is not doing well or you just want to make new plants, it is very easy. You can just take one of those pads, twist it off very carefully and leave it on the side for a couple of days, let that cut callous over, pop it on the surface of some very gritty potting mix, just allow that cut to be slightly buried and you'll find that will root beautifully and you can make new plants.

Now, Opuntias, generally, are a bit lethal. As I've already said on the microdasys species, you get these glochids, which stick in your fingers, and the Monacantha, well, it doesn't have a huge amount of spines but it does have some and they are a little bit sharp, to say the least. But if you're looking for an Opuntia that won't do you any harm, I've recently seen a cultivar of Opuntia Microdasys, called Caress. You can guess from the name what that means: there are no glochids or spines on that one, so do look out for Opuntia Microdasys Caress. I like saying that, 'Caress'! If you want a plant that won't do any harm, or if you've got a small child who's into cacti and succulents and wants one of these but you're worried about them getting stabbed. Speaking of children, it's time for Meet the Listener and, this week, I was absolutely blown away to hear from a young houseplant enthusiast called Susie. Listen to this...

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Susie: Hi, my name is Susie and I'm seven years old. I got into houseplants last year during the first lockdown and I really love them. It's my birthday soon and, hopefully, I will get some new plants and I just learned how to say plant in Latin, which is "planta".

Jane: Question one. You've been selected to travel to Mars as part of the first human colony on the Red Planet. There's only room for one houseplant from your collection on board! Which plant do you choose?

Susie: I would really like to take my Money Tree to Mars because it's really easy to care for and I think it could survive a little while on Mars without oxygen. Also, I spent a whole £59.99 on it, with my own money, and it's been really happy and even pushed out some new growth for me a few times, so I would definitely choose my Money Tree, Pachira aquatica, because there's lots of other common names for Money Tree.

Jane: Question two. What is your favourite episode of On The Ledge?

Susie: My favourite episode of On The Ledge is definitely the episode when you interview Maria Failla because that's quite a funny episode, in my opinion, and I just really like the episode. I listen to it almost every night and I just really like the episode.

Jane: Question three. Which Latin name do you say to impress people?

Susie: I definitely like to say Rhaphidophora tetrasperma because it's a long name and it sounds like a tongue twister to lots of non-plant people. I really like that plant and I'm hoping for one for my birthday.

Jane: Question four. Crassulacean acid metabolism, or guttation?

Susie: I definitely prefer guttation to CAM because I can actually physically see guttation happening all around me on my plants. CAM is really cool, lots of plants that have adapted to it, but I think I like guttation slightly more because I can see it and also it looks like a crystal hanging off my plants' leaves.

Jane: Question five. Would you rather spend £200 on a variegated Monstera, or £200 on 20 interesting cacti?

Susie: I would definitely choose the cacti because, as much as I like Monstera**s, I don't even know if my mum would spend that much money on just one plant. So, I think she would just about be able to spend it on 20 cacti because I love cacti and even though I really like Monsteras, our first one that we tried didn't go too well. Even though it's so beautiful, I'd definitely choose more plants rather than just one beautiful one.

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Jane: Thanks to Susie's mum for helping her take part and to Susie! Kid, you are going to go far! That was amazing. There are lots of adults who wouldn't have had the confidence to do what you have just done, so well done to you! Wow! It was a little bit like listening to myself as a child, except Susie was way more clued up than I was at that age! If you want to take part in Meet the Listener, age, location and background are immaterial. Just drop a line to ontheledgepodcast@gmail.com That's all for this week's show. I'll be back next Friday for more planty pest control! Bye!

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Jane: The music you heard in this episode was Roll Jordan Roll by The Joy Drops, An Instrument the Boy Called Happy Day, Gokarna by Samuel Corwin and Lonely Spider by Cullah. All tracks are licensed under Creative Commons. Visit janeperrone.com for details.

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I’m joined by two biological control experts to tackle your questions about dealing with infestations on your plants. Plus I answer a question about a droopy prickly pear, and we hear from a seven-year-old fan of the show in Meet The Listener.

This week’s guests

Tessa Cobley of Ladybird Plantcare sells biological controls to UK gardeners for pest control on plants inside and outside. She is on Instagram as @ladybirdplantcare.

Dr Andy Brown is managing director of Andermatt UK. a manufacturer and seller of biological controls. Follow Andermatt UK on Twitter here.

Want to skip on to part two of our interview, in episode 177? Click here.

Check out the notes below as you listen…

An introduction to biological controls

• There’s no one definition of what a biological control is - it varies from country to country, but as a general rule it means using a natural solution to control a pest or disease problem. The IBMA (International Biocontrol Manufacturers Association) have come up with the term bioprotection as an umbrella term.

• When you are thinking about using a biological control, it’s vital that you figure out what pest you are dealing with, as different biological controls work for different pests.

• When your biological control arrives, read the label very carefully, as biological controls require specific methods of application and conditions to thrive.

• If you’re interested in how nematode production happens, there’s an interesting blogpost about a trip to a nematode production plant in the UK here.

Nematodes for fungus gnats come in a pack like this: the powder is disoolved in water before being applied to the soil. Photograph: Andermatt UK.

Fungus gnats

• Fungus gnats aka sciarid flies are the tiny, floaty black flies you’ll find floating around your houseplants. See the top of this post for a picture.

• They lay eggs into the potting mix around your plants and it is the larvae that can do damage, although the main plants that will be adversely affected are young seedlings.

• The two options for biological control are the nematode Steinernema feltiae. Read more about this nematode and its use on fungus gnats on Andermatt’s website. It’s put onto the soil in water to control the larval stage of the fungus gnat. Sticky traps can be used to catch the adult flies and stop them laying more eggs.

• Once applied, the nematodes need damp soil to work effectively.

• The other treatment for fungus gnats is the predatory mite Stratiolaelaps scimitus aka hypoaspis mites. These are particularly useful for treating plants where the soil is too dry for nematodes to work, but they are generally more expensive to buy. They can last in the soil up to 60 days without being fed, offering a level of protection beyond that of nematodes in the weeks after an outbreak.

• Check out my episode on fungus gnats here.

Spider mites

• Red spider mites are a common pest of houseplants, and seem to particularly love members of the Maranta group, such as Calathea, Ctenanthe and Stremonathe.

• They are too small to see with the naked eye, but look out for white grainy stuff close to the midribs on the underside of leaves - this is their shed skins. In severe outbreaks, webbing may be present.

• Spider mites are treated with predatory mites called Amblyseius andersoni  which are usually supplied in slow-release sachets. The mites will crawl out over a period of four to six weeks.

• Phytoseiulus persimilis are another predatory mite that can be used to treat red spider mite.

• Check out my episode on spider mites here.

QUESTION OF THE WEEK

Listener Jane’s prickly pear was a birthday present - but it has begun to droop alarmingly, as shown in the picture to the left. One of the common names of this species is drooping prickly pear. The majority of this species on the market for houseplants are the more compact monstrose variegated form, with its elongated pads and paler markings.

Opuntias droop for two reasons: either they are too dry, or they are starting to rot. As its common name suggests, this species is particularly prone to drooping, and in fact my own specimen is doing this right now, as it often does during winter, when I keep it more or less dry. It will recover quickly when I start watering regularly in March or April, and in the meantime I stop it from drooping too seriously with occasional drinks. When Opuntias rot, it is usually because they have had too much water at root level, often when the substrate is too moisture-retentive. This is usually the death knell for the plant.

I suspect Jane’s plant is suffering from dryness, although as it’s a new plant I’d suggest repotting in a really gritty potting mix this spring (50/50 grit, perlite or other drainage material/houseplant potting mix).

When a plant is drooping, it’s because the vacuole within each cell is not turgid. If you’re interested in finding out more about the role of the vacuole in botany, there’s more info here.

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!

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CREDITS

This week's show featured the tracks Roll Jordan Roll by the Joy Drops, An Instrument the Boy Called Happy Day, Gokarna by Samuel Corwin and Lonely Spider by Cullah.