Robot farmers? Machines are crawling through America's fields. And some have lasers.

It uses three high-resolution cameras to peer down at the ground below. Lit by synchronized strobe lights, an onboard computer creates a digital image of each seedling as it glides by, comparing them with all the greenery it might reasonably find in a field of rich Salinas valley farmland two hours south of San Francisco. "It puts a dot on the stem and maps around it," says Todd Rinkenberger of FarmWise, the robot's maker. "Now it knows what's plant. Everything else is a weed."