growlnotify not showing when shellscript run from launchd

Question

I have a back up bash script that I launch when a particular volume is connected. I used Lingon to create a job that runs the script when a volume is mounted. I have added:

growlnotify -a terminal -t "Backup Done" -m "Backup done"

to my script and it works if I run the script manually from the terminal but the growlnotify fails to register if the script is launched via the daemon. Can anybody help with this problem?

ps very basic bash skills