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How to get rid of mealybugs

These fluffy white bugs are a common pest on houseplants. They suck sap and hide in places that are difficult to reach
Ceri ThomasEditor, Which? Gardening

Mealybugs are small, oval, sap-sucking insects up to 4mm long. They look like tiny, pinkish or grey woodlice close up, but are usually covered with a fluffy layer of protective wax. Colonies resemble blobs of sticky cotton wool and may be accompanied by sooty mould.

What damage do mealybugs do?

Glasshouse mealybugs suck the sap of their host plants which weakens and can kill them. The colonies of mealybug with their associated wax, honeydew and sooty mould can be very disfiguring to specimen plants.

Root mealybugs prevent the roots from operating properly and the plants may appear stunted, or wilt, especially in pots. Damage is usually worse if the plants are in dry compost or soil. With phormiums, heavy mealybug infestations will weaken the plant and eventually kill it.

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How do I prevent mealybug infestations?

Check new plants thoroughly before bringing them home. If you have a precious collection of, say, cacti, African violets or orchids, it is worth quarantining new plants for a month or so before mixing them with the others. Stripping old bark off indoor vines in winter helps to dislodge incipient mealybug colonies. Keeping the compost moist will deter root mealybug, though unfortunately this will not suit some of the most vulnerable plants.


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How do I treat mealybugs?

Eradicating mealybug requires persistence and it may be better to discard badly infested plants. Quarantine any pot-grown plants you are going to treat and put them outdoors if it is mild enough. In fact, leaving plants outdoors over winter is a good way to destroy colonies on plants that are hardy enough, such as camellias. Scrape, hose or brush off as many adults as you can, or cut out badly affected shoots.

You can spray with a suitable insecticide. Some people report good effects by spraying with SB Plant Invigorator.

Organic treatments for use during the growing season include fatty acids or plant oils or extracts. These organic pesticides have a contact action and short persistence and so may require more frequent use. They can be used on edible plants if the plants are washed thoroughly before consumption. 

What about biological control for mealybugs?

If mealybug gets established in a heated greenhouse or conservatory, biological control using Cryptolaemus montrouzieri beetles or Leptomastix dactylopii, a parasitic wasp, should do the trick. Cryptolaemus is a black and orange ladybird from Australia. Its larva looks rather similar to a mealybug but is twice as big. An adult will consume about three mealybugs a day, and a larva nine. They only search a small area so you need to release at least one on each plant.

Leptomastix dactylopii is a wasp about 3mm long that kills mealybugs by laying their eggs in them. They are much better at finding small colonies than cryptolaemus but only attack citrus mealybugs.

Screen opening doors, windows and vents with fine netting so the adults won’t escape. Both controls thrive only in the summer as they need good light and temperatures above 21ºC.

Suppliers of biological controls include: 

Dragonfli dragonfli.co.uk

Ladybird Plantcare ladybirdplantcare.co.uk

Green Gardener greengardener.co.uk

Which plants do mealybugs affect?

There are three main groups: Glasshouse mealybugs (pseudococcus, planococcus and nippaecoccus) mostly come from the tropics and only survive here in protected environments (though one mealybug from Northern Europe can be found outdoors on shrubs in favourable districts). They attack a wide range of houseplants and greenhouse ornamentals, plus vines. Cacti and succulents, African violets, ferns and orchids are particularly vulnerable.

Root mealybugs (rhizoecus) build up into dense colonies on the roots of greenhouse ornamentals. They are 1-2.5mm long, greenish-yellow and surrounded by white wax. They tend to be most troublesome when the potting compost is kept on the dry side, so vulnerable plants include cacti and succulents as well as abutilon, African violet, begonia, ficus, hoya, hippeastrum, dracaena, ferns, fuchsia, palms and pelargonium.

Phormium mealybugs (Trionymus diminutus) attack phormiums and cordylines. They are 4-5mm long, grey or dark red, with a white wax covering. Unlike other mealybugs, they can survive low winter temperatures.

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