After a lettuce field is planted, growers typically hire a crew of farmworkers who use hoes to remove excess plants to give space for others to grow into full lettuce heads. The Lettuce Bot uses video cameras and visual-recognition software to identify which lettuce plants to eliminate with a squirt of concentrated fertilizer that kills the unwanted buds while enriching the soil.
Blue River, which has raised more than $3 million in venture capital, also plans to develop machines to automate weeding — and eventually harvesting — using many of the same technologies.
Another company, San Diego-based Vision Robotics, is developing a similar lettuce thinner as well as a pruner for wine grapes. The pruner uses robotic arms and cameras to photograph and create a computerized model of the vines, figure out the canes' orientation and the location of buds — all to decide which canes to cut down.
Fresh fruit harvesting remains the biggest challenge.
Machines have proved not only clumsy, but inadequate in selecting ripe produce. In addition to blunders in deciphering color and feel, machines have a hard time distinguishing produce from leaves and branches. And most importantly, matching the dexterity and speed of farmworkers has proved elusive.
"The hand-eye coordination workers have is really amazing, and they can pick incredibly fast. To replicate that in a machine, at the speed humans do and in an economical manner, we're still pretty far away," said Daniel L. Schmoldt at the U.S. Agriculture Department's National Institute of Food and Agriculture.
In southern California, engineers with the Spanish company Agrobot are taking on the challenge by working with local growers to test a strawberry harvester.
The machine is equipped with 24 arms whose movement is directed through an optical sensor; it allows the robot to make a choice based on fruit color, quality and size. The berries are plucked and placed on a conveyor belt, where the fruit is packed by a worker.
Still, the harvester collects only strawberries that are hanging on the sides of the bed, hence California's strawberry fields would have to be reshaped to accommodate the machine, including farming in single rows, raising the beds and even growing varieties with fewer clusters.
Experts say it will take at least 10 years for harvesters to be available commercially for most fresh-market fruit — not a moment too soon for farmers worried about the availability of workers, said Lupe Sandoval, managing director of the California Farm Labor Contractor Association.
"If you can put a man on the moon," Sandoval said, "you can figure out how to pick fruit with a machine."
Contact Gosia Wozniacka at https://twitter.com/gosiawozniacka