Weeelll... It's just cheap paintbrush

I buy packs of large cheap stiff bristle paint brushes from $2 shops and chop them up (i.e. grip a little clump, chop with scissors, glue to base). To keep them upright I use super-glue and put a dab on the bristles before i put them on the base to keep the bottom stiff, for spread out ones I use PVA and just stick straight to the base (then you can tease them a bit).
What I really like about this method is that you can make the bristles as long or short as you like, and you get slightly different effect from using the tips of the bristles as opposed to the chopped off bits (more grassy vs more reedy/wheaty)
For the colour on these guys I used a brown wash and some green ink at the base, which the bristles will naturally suck upward from the bottom giving that gradiated look.