It doesn't answer your question, but may we assume that

a) the script which calls your script can't erase those files
b) you cannot have the script run as root say from cron, or otherwise have a program running as root user to watch that folder for changes.
c) prod and dev are different user groups, and/or prod does not want to set g+w to the files it moves into there.
d) you cannot get someone to run a shell script from cron that chowns the files that get moved in there before calling the backup program
e) your script doesn't have access on prod server that would allow you to grab the files with Net::FTP instead of having prod copy them over himself.
f) prod is unwilling to maybe upload these things to your script in some fashion.

I'm sure you've thought of most of these but just want to make sure we are on the same wavelength. :)