Disabling Akonadi Tray in Kubuntu

https://bugs.launchpad.net/ubuntu/+source/kdepim-runtime/+bug/868970

System settings -> start and shutdown -> autostart -> add programm -> Utilities -> Akonaditray -> ok -> tick status checkbox to disable

or

sudo nano /usr/share/autostart/akonaditray.desktop
Change "Exec=akonaditray" to "Exec=".