Episode 102: spider mites
Red spider mites suck the sap from the undersides of leaves. Photograph: Gilles San Martin on Flickr.
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Transcript
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Red spider mites may not be visible with the naked eye, but they damage they can do to our houseplants is considerable. I get an insight into the world of the spider mite with entomologists Jules Howard, who is the author of books including Death on Earth; and Andrew Salisbury, who is principal entomologist for the RHS, and look into the various options to keep mites under control. And I answer a question about easy trailing plants that are non-toxic to cats.
Check out the notes below as you listen to find out more about the fascinating world of mites, and how to control the red spider mite.
Spider mite specifics
The red spider mite, Tetranychus urticae, is also known as the two spotted spider mite.
its lifecycle lasts only up to a month: check out this video for a look at the spider mite all stages. The RHS has an excellent information page on red spider mite that is worth checking out too.
The red spider mite is the main mite that will attack houseplants, although the mite family is enormous. (Patreon subscribers of $5 a month or more can hear more mite insights from Jules Howard in An Extra Leaf 30).
It seems to favour papery-leaved plants of the Maranta group but can attack just about any houseplant.
Spider mite symptoms
The first signs of an infestation are the plant starting to droop and generally look miserable.
If you can use a hand lens, a magnifying glass or even your mobile phone’s camera is really useful to check the backs of the leaves - mites are not visible to the naked eye but can be seen with a bit og magnification. This is the one I have - a double botanist’s hand lens made by Ruper.
The leaves will develop pale mottling as the mites begin to suck sap from the plant cells.
The undersides of the leaves will display a grainy white substance, and more severe infestations may exhibit webbing.
The leaves will eventually turn yellow and die off, leading to total plant collapse.
Treating spider mite
Prevention is better than cure: making sure your plants are in good health will help prevent pests from taking hold. Pests tend to target specimens that are already undergoing stress: they love hot, dry conditions so are a particular problem in summer.
When it comes to pesticides to treat red spider mites, Acetamiprid is a systemic pesticide that is suitable for use on houseplants, although I don’t use it because I take an organic approach. Acetamiprid contains neonicotinoids which have been linked to bee decline.
Neem oil is a popular treatment for spider mites and other houseplant pests: however it is not licensed for use as a pesticide in the UK so I don’t use it. It is meant to be effective, but if you use it, please don’t assume that because it’s “natural” (it is extracted from the neem tree, Azadirachta indica) can be sprayed indiscriminately: you still need to follow the instructions closely.
There are a number of pesticides available that are based on plant oils or fatty acids: they work really well, but may need repeated treatments to work fully.
There are a number of ‘plant invigorator sprays’ on the market which contain a mix of nutrients and surfactants, such as SB Plant Invigorator, Neudorff Plant Invigorator and Ecofective Houseplant Defender.
When you first see spider mite symptoms, isolate your plant, and start treating it immediately. Washing or wiping down with a damp cloth daily will help remove mites and eggs: focus on the underside of the leaves.
Biological controls such as the predatory mite Phytoseiulus persimilis are best used early on in infestations, and for larger collections.
My Pilea libanensis, as mentioned in episode 99. Photograph: Jane Perrone
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This week's show featured the tracks Roll Jordan Roll by the Joy Drops, InsectifEYE by KidNNasty and Lonely Spider by Cullah. Ad music is by the Heftone Banjo Orchestra: Dill Pickles and Whistling Rufus. All tracks licensed under Creative Commons.
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