It would be interesting to see what the local rules says.
. We had a similar discussion years back in my small airfield after an aircraft did land while one of us was mowing the runway grass. In practice, frequency was not manned , we did not issue a NOTAM. and the guy mowing wears ears protections and looks at the grass. So only the eyeballs of the pilot on finals can save the day. But if the small mower color is green and the guy wears dark clothes the chances of spotting it on time is small... We learned from that.