Growing citrus

Question ...

We have a lemon tree in a pot, about 4 feet high. We kept it outdoors till September, then brought it in to a very sunny dining room. For the past few months it has been covered with a sticky substance, and we think it has scale insect. A friend who has a nursery told us you could burst them with a pin! We have tried washing them off with a soapy solution but this hasn't worked so far. Is there a biological control? What do you suggest?

Answer ...

Scale is a common pest on any citrus plant. Small infestations can sometimes be wiped off, but the size of your plant would make this time-consuming and difficult. Try spraying the leaves and stems with a suitable organically acceptable product - available from the Organic Gardening Catalogue.

The biological control to use against scale is a parasitic wasp, but it is very hard to find a supplier. The wasp, Metaphycus helvolus, requires lots of sun in which to bask, and our summers have not been very sunny in recent years. Optimum temperature 20-30°C. This makes breeding less easy.

Sprays approved for use in the organic garden can be harmful to useful insects, so only use them as a last resort. Spray flowering crops at dusk when bees are not active. Read the label before you buy. Use pesticides carefully

Garden Organic members can see our expert factsheets for further advice on organic gardening. Access to factsheets requires a members' password.
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