don't use the "ssh_args" specifically. )

my %ssh_options = (options => "StrictHostKeyChecking no");

my %login = (user      => $user,
             password  => $pass,
             debug     => 1,
             \%ssh_options
            );

#########################################################
#or

my %ssh_options = (
 StrictHostKeyChecking => "no"
);

my %args = (
 username  => $user,
 password  => $pass,
 debug     => 1,
 ssh_args  => (options => \%ssh_options)
);

my $sftp = Net::SFTP->new($host, %args)

Normally you should be able to fold this in, as so:

my %args = (
 username  => $user,
 password  => $pass,
 debug     => 1,
 ssh_args  => (options => { StrictHostKeyChecking => "no"} )
);