Richard Cline wrote:

In article , "O.B."
wrote:

This is a long shot but it may be part of the problem. It sounds like
one tree is badly diseased. It may be better to remove it to prevent
the spread of the disease. The others may be a variety that is poorly
suited to your climate. The tree may require more or fewer hours of
chilling.

The trees should not require fertililzer. The trees normally benefit
from robust pruning.

I think proper pruning would be more beneficial.
--
Travis in Shoreline Washington