Escallonia hedge

Last year our Escallonia hedge (in Wexford) lost all its leaves. It had similiar black spots to the Black Spot on Roses. I sprayed it with Dithane 945 as advised by a garden centre about 3 weeks ago when the new leaves were growing. Should I repeat the procedure or use something else. The new leaves seem to have spots again this year. The hedge is about 8 years old and about 6ft tall. I dont put any fertilizer on it.