Episode 176: biological controls part one
Fungus gnats aka sciarid flies are treatable with two different biological controls. Photograph: Andermatt UK.
Transcript
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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.