In article , Slugs&snails
says...

Hi

Could anyone give me some advice please - my lime bush (which was on my
window sill but i've moved it outside and is still in its pot) has lost
a lot of leaves, there are little bumps now all up the stem which i'm
guessing is some kind of infestation?. Since i moved it outside it has
starting growing leaves but they are reddy/brown - does this mean it
has a deficiency?

any thoughts?

Did you move it from indoors directly into full, outdoor sun?

Red brown in the leaves suggests sun stress. Lots of plants when sun-
stressed will develop a red colour in the leaves.

Follow David's recommendation regarding the possibility of scale.

I wonder, after you rule out scale, if the little bumps are dormant buds
activating.