what's wrong with my lemon tree?

[sandspider]

Hi folks.

As above, really! See pic of lemon tree below. Black deposits on the leaves, and little brown creatures / casts. Anyone know what these are, and what to do about them?
Cleaning the leaves would help, i assume?

Thanks.

[ameno]

The brown things are scale insects, and are the main problem here. They suck the sap of the plant, much like aphids do, and it can weaken the plant in a bad infestation.
They need rubbing off by hand, as their waxy shell protects them from pesticides.

The black stuff is sooty mould. It is growing in the sugar the scale insects secrete as a waste product, so is not harming the plant directly. However, it does reduce the amount of light getting to the leaves, so you should wipe it off where you can.

[sandspider]

Thank you sir or madam, I'll go and give it a rub and a scrub.

[Plot70]

I have found that wind driven wind will get them off.
Pick a night that is cold but not freezing with high wind and driving rain. Chain the pot to a flag stone.
Citrus leaves turn to an angle in wet windy weather naturally for the purpose of clearing infestations.
Indoor ones always end up with scale insects.
You have reminded me that I need to get some citrus feed for mine.

[sandspider]

That's interesting, thanks. Cleaning them off manually is quite hard work. Having said that, the tree originally got the scale insects and soot outside! Maybe it wasn't windy enough. I'll put it back outside when wet and windy but not below 6C or so.
Cheers.

[Plot70]

Yes it needs to be cool so that the scale insects are less active so that they come off more easily.