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?
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