Enter Lettuce Bot, the brainchild of Stanford-trained engineers, Jorge Heraud and Lee Redden. Their diligent robotic labourer, pulled behind a tractor, takes pictures of passing plants. Computer-vision algorithms devised by Mr Redden compare these to a database of more than a million images, taken from different angles against different backdrops of soil and other plants, that he and Mr Heraud have amassed from their visits to lettuce farms. A simple shield blocks out the Californian sun to prevent odd shading from confounding the software.
When a plant is identified as a weed—or as a lettuce head that is growing too close to another one—a nozzle at the back of the unit squirts out a concentrated dose of fertiliser. If this sounds bonkers, it turns out that fertiliser can be as deadly as a pesticide, which is why farmers usually sprinkle it at a safe distance of 10-15cm from the plants to be nourished, so as to dilute its effect. So the robot not only kills weeds and excess heads, but feeds the remaining crops at the same time.