Black soot, lemon trees and ants?

I read recently that black soot on a lemon tree indicates an ants net nerby. We have less ants nests in the lawn than ever this year but am wondering if there is anything I need to do to shift the black sooty stuff on fruit and tree.Although some of the affected lemons dont look pretty it is easily wiped off. Am I going to lose the tree ?

no you wont lose the tree, the black sooty stuff is the poo of white fly. The fruit is fine and the soot can be wiped off. You will need to spray your tree with an oil to suffocate thosw dam unborn white flys which are lying in wait under your existing leaves...

thanks Jilly...I shall get hubby to get the spray out!
What sort of oil do you reccomend?

If you have just one or two trees, then neem oil is good, if you have more, then a commercial spray is recommended. I will check the name of ours - I just call it 'that spray' -not very helpful really..... whatever you use, use at about 2 weekly intervals about 3x. and, spray upwards. more later!