Some 20 years ago I planted a row of 33 Leyland (leylandii) trees of 18 inches high. They now form a barrier of some 10 feet high but well cut into a box shape. Some 2 years ago I noticed a browning or blotching of dead fronds in part of the hedge. The problem has become much worse and now half the hedge is very brown and half almost untouched. Is there a remedy to this problem? I have noticed a number of hedges and other leyland trees suffering the same fate in various parts of the country.

Mike