Originally Posted by jamesqf
I wonder, though, why alfalfa itself isn't considered a weed, at least in the context of introducing a non-native plant to the back country. While it's not exactly prolific, I do find the occasional plant growing in my garden, presumably having come from the horse manure I use as fertilizer.
Alfalfa is almost always cut pre-bloom. If the plant has not blossomed yet, It can't have any seeds. It is really easy for an ag inspector to look at a field of alfalfa and recognize if there is a blue/purple hue from blossoms. If it's all green the plant has not blossomed and no seed are possible.
Where most grass plants don't usually have a blossom or at least not one you identify from the corner of a field. And the variety of grass in a field may go to seed at different dates. Making it much more difficult for an inspector to tell if there are any seeds in the standing grass.