[Umbrian]

When staying with a friend in London last week he asked me what this "pest" is. They are on his pot grown Lemon and occur either singly or in small groups on the woody parts of the plant - mainly on the branches but some on the trunk. My guess was wooly aphids but he was not convinced so now it is up to the experts.
Also what is the best way to eradicate them? 

[Umbrian]

Sorry seem to have posted the photo twice!
Interesting to note how the pest seems to mimic the flower bud?

[Alisdair]

Carole, It looks like a wingless female woolly aphid, as you'd thought. In the UK they are minor pests of apples and pretty ubiquitous, but do love potted citruses and seem to find their way on to them quite quickly
When we had a small Meyer's lemon in London we kept the aphids under control by picking them off individually with an artist's paintbrush soaked in methylated spirits. On our full-size citrus trees in Greece we have sprayed them with soft soap, which does work, but may not give such lasting results as a more persistent insecticide.

[ezeiza]

Methylated spirits, 90%, water 10%. mixed when it is about to be used. Spray on the pests, kills instantly all insects and mites. Of course chemical insecticides can not be used on something that will produce fruit unless this is not eaten.

[JTh]

It is often useful to repeat this treatment around 10 days later, not all stages of these parasites are equally susceptible to the treatment, it helps to attack those that survived the first treatment before they have reached the mature stage and start producing a new generation.

[Umbrian]

Many thanks Alasdair, ezeiza and Jorun and good to see that you all recommend the same treatment, makes life so much simpler Will pass on the advice post haste.

[Umbrian]

Three cheers for the Forum for being so useful in gaining expert advice that can be passed on to others. The other day another friend, here in Italy this time, asked me what was attacking her Lemon tree (white,wooly infestations) I was immediately able to say, with compete confidence, Oh that's woolly aphids, you need to treat them with Methylated spirits.

[ezeiza]

Umbrian, it works once the pest is present and provided you can spray the spirits directly on the beasts.

[John]

I think that these are scale insects not aphids. They occur on all sorts of woody plants around London.

[John]

These are the flightless females. We used to have them on our Cornus kousa var. chinensis. I suspect that they are relocated by ants which possibly are farming them. They are particularly common on Lime trees. I managed to get rid of them on this small tree with a trunk diameter of about 30cm by regularly jet washing them off with my thumb on the end of the hose.

[ezeiza]

They are postively farmed and distributed by ants.

[Umbrian]

Now I am thoroughly confused Are the blighters wooly aphids or scale insects? and have I given out wrong information and am going to have to eat humble pie? 
No ants were present on the tree in London that I inspected on several different days if that is any kind of clue

[John]

Carole I can only say that I'm pretty sure they are scale insects so we will have to wait for other opinions to come through!

[Alisdair]

I'd stick with the woolly aphids, Carole. The flightless females do look just like your picture, and do walk around like that if the ants haven't shifted them. Scale insects are a bit different. (But the meths would still deal with the scale insects too, anyway....)

[David Bracey]

I cannot tell from the photo; it is quite fuzzy when I blow it up. Do you have another pic?

Anyhow you should not go around spraying methylated spirits.  It is not green nor organic nor biologically proven.  I gives conventional pesticides a good name.  As Alisdair suggests use a soapy solution and spray as often as convenient and where practical wipe the infested branch between your fingers.

A follow up spray will control those eggs which have hatched in the meantime.