In all of my time in Brazil, I have only seen one lawnmower, and that was a tiny little lawnmower being used to mow the lawn of this rich guy's house. Everyone else uses weed wackers, and when the lawn crew is out and cutting grass along the highways or public roads, they have these helpers who hold up this shield. I guess the idea is to keep the grass from flying onto cars, etc, but it doesn't seem to be so effective.
They really seem to take their grass cutting seriously, with masks, full on clothing cover ups, boots and the shields. Another example of how they do things differently here. Is it a more effective technique? Well, it's hard to say, but I think they spend a lot more manpower than we do in the US. But then again excessive manpower is the name of the game here, given that the minimum wage is R$400 per month. That's about the price of a nice end cell phone. Try feeding a family of four on that.