Ilya, I do not know whether you are placing the Czech Republic in Eastern or Central Europe, but here is what you write no one knows. I do not think of myself, but also of other growers who are my friends. (you probably know - Petr Broza, Zdeněk Černoch and many others). Besides, I am the moderator of a Czech forum devoted to citrus growing. "Meyer's disease" I hear really for the first time. Meyer has a number of various problems in Eastern Europe, but this is new, quite different. For me totally unknown.
But I do not know it does not mean it does not exist!!
Symptoms on my Meyer (EU-Czech Republic) are similar of matt_citrus (USA, Los Angeles) and Mtlgirl (Canada).
I have been growing citrus since 1981. My oldest Meyer is from 1984. I have 4 diffrent Meyer plants. Until 2010 they were all without disease. Since 2010, all of my Meyers have been reported to be ill.
Appears exclusively in the second half of summer. Is only on old leaves, never on new additions. It does not spread to other varieties of citrus.
Plants only significantly weaken, but will not die.
Testing fungicides had no effect at all.
At the same time, it must be said that effective fungicides are forbidden in the European Union. Or they are subject to strict regulation. For normal humans they are inaccessible. You know that.
I managed to get a bit of a highly efficient fugicide subject to regulation. I will try it this year. It is (cyproconazole 160 g / l + trifloxystrobin 375 g / l).
This "Meyer disease" belongs together with the hybrid (unshiu x P.T.) ITSZ Prague among my two biggest mysteries about citrus.