The sensor was plugged into the rainbird controller the same way (both sensor leads) and I tried to replicate that. The manual for my sensor also showed that as a valid setup.
The Irritrol manual also says white goes to common, is that not what the COM-COM leads are on the controller?
Moving white to GND worked, thank you. Next I want to know what the difference between COM and GND are, and why the manual made it seem like what I did was valid.