The image posted by the OP is in color, which means the camera is in day mode, and the DCS-5020L doesn't have the ability to independently disable the IR illuminstors.
I'm not sure what you mean by "independently disable", but for clarity, you can turn the IR illuminators on and off manually, if you want.
Interesting observation about "image is in color, thus day IR=off". I actually had not had occasion to turn the IR on in daylight to see, but you are correct: you get a grayscale image that way. I had posted my comment because I have an IP camera from another manufacturer where this is not true: if you turn the illuminators on in good light, you get a washed-out color picture of exactly the sort that the OP posted. Curious that the behavior is different between cameras.