%hashA = ( '11.5'  => [ 1723478, 1734789, 1798761, ],
           '11.12' => [ 1700123, ],
           '11.01' => [ 1780345, ]       
         );

##</code><code>##

@{$hashA{q/11.5/}} = [ grep { $_ != 1734789 }, @{$hashA{q/11.5/}} ];

##</code><code>##

my $id = q/11.5/;
@{$hashA{$id}} = [ grep { $_ != 1734789 }, @{$hashA{$id}} ];