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House plant pests (Part 1)

David Hurrion introduces three of the most common house plant pests: mealybug, scale and spider mite, and explains how and when to treat infestations.
Now, thankfully, with house plants, there are relatively few pests that affect plants because of the protected conditions in which we grow them. But equally because of those protected conditions, pest numbers can get high very, very quickly and they can quickly get out of hand. So it’s really important that you check plants regularly for signs of pests and deal with them as quickly as possible. And also looking out for any eggs that would obviously hatch into the pests and cause more problems. The sooner you can deal with these pests, the better.
So the first three that we’re going to look at are things that are often introduced with new plants that you might buy from certain nurseries or which you might get on plants that are given to you. And possibly the worst of all these pests is the mealybug. And this is a bug that is covered with a grey meal, hence the name, whitish grey meal, is particularly virulent on certain bulbs and also on cacti and a number of succulent plants feeding on the sap. It’s covered in a white waxy secretion, which helps to make it proof to various different predators that might eat it. It stops them eating it, and it also makes the pest waterproof.
They exude honeydew because they’re feeding on the sap of the plant. This honeydew is a sweet substance that’s exuded from them and that in turn can cause sooty mould. And we’ll talk more about that in a moment. It’s really easy to see as adults, they’re quite large, it lays plentiful eggs, which spoils their numbers very quickly. And they’re very difficult to hand pick off, actually. But that’s the best way to control them, because they tend to congregate, as I said before, in the leaf axils and other inaccessible parts of the plant. Now, a wooden toothpick is really useful for levering them out of those hard-to-get-at places.
And you really need to dispose of fallen leaves that might have bugs or eggs attached to them. And if you’re growing in a glasshouse or in a conservatory or even indoors, you could use the predatory ladybird Cryptolaemus to control their numbers during the summer. There are a number of biological control methods that you can use for pests as long as you’re happy to use them indoors. There’s no reason why you shouldn’t. Severely affected plants with mealybug may need to be destroyed because sometimes it’s impossible to get rid of it completely. Now, the second one on this slide is scale insect, and this is quite tricky to deal with as well.
But this forms almost like small shields on the stem, and that has an insect underneath, that shield-like structure is protecting the insect underneath, which is sucking the sap from the plant, again, it can produce honeydew. And there are different life stages. So the insects themselves lay eggs which turn into crawlers and these crawlers then develop into the scale-like structures. It’s easy actually to remove them with a thumb or a fingernail to pry them off the stems, but they tend to get down right deep into the the union between the leaf and the stem. And that can sometimes make it quite difficult, certainly, to get rid of the eggs. And those eggs may then hatch out and develop on into adults.
Again, there’s biological control methods that can be used to control these with Metaphycus, which is useful in a conservatory or a glasshouse condition. But it might not be something that you want to have in the home. And then lastly, red spider mite, tiny sap sucking pests, which are related to spiders. They are pale green, really in colour for much of the year, but then they turn orangey red in the autumn months as the light levels start to decrease. And that’s what gives them the name red spider mite. They thrive in hot, dry conditions, can breed all year round. And you really need to boost the humidity around plants with tepid water to reduce their incidence.
You can certainly keep their numbers down by that. And there is a predatory mite, Phytoseiulus, which can be used to help their control. Chemical pesticides are available for all of these insect pests. But you should follow all the instructions carefully on the packet and store them out of reach of children and animals.
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