It's not just herbicide that kills field weeds, they can be shredded too, not by a lawn mower but by grit. USDA agronomist Frank Forcella uses bits of corn cob to battle his weeds.
In collaboration with university researchers he devised a tractor mounted system that uses compressed air to shoot high-speed particles of half millimeter sized grit in-between crop rows.
The machine shoots in a cone at the ground at the rate of about 300 pounds per acre using 100 pounds per square inch of compressed air. Crop plants aren't hurt because they're taller than weeds at the time of application and have thicker stems.
It's an effort to help organic growers control weed infestations.