The problem is that you have blindly put in 'my' to keep strict happy. Unfortunately, you did so *everywhere*, including places where it isn't appropriate. The key bit that's causing your current problems is this:

foreach my $subdir (my @dirlist) { 
#...
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The my @dirlist creates a new (and empty) @dirlist. You mean to refer to the one you tried to create earlier with this bit:

my @iresdir = readdir IRESDIR;
foreach my $dir (@iresdir) {
    push (my @dirlist, $dir);
}
closedir IRESDIR;
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...however, that code also has an error. The code "push (my @dirlist, $dir);" pushes the current $dir onto a lexically scoped @dirlist. The problem is that the scope for @dirlist goes away once you hit that next closing brace on the next line. So effectively, you push the directory onto an array, then throw the array away.

I suggest two things. One, read up on scoping. In particular, Dominus' Coping with Scoping article. Two, you're reinventing the wheel here. It would be best to use File::Find for this sort of thing.