We have some olive trees in pots 3 of which have these deposits of a white material in clumps. We have a launderette nearby and at first I thought it was soap powder that had been borne on the wind - that's the kind of appearance it has - but one of the trees which is at a fair distance from it is still showing these deposits. One of our trees is free of it.
Any ideas on what it is and how to treat it would be appreciated. Many thanks.