Research into fresh produce mechanization was dormant for years because of an over-abundance of workers and pressures from farmworker labor unions.In recent years, as the labor supply has tightened and competition from abroad has increased, growers have sought out machines to reduce labor costs and supplement the nation's unstable agricultural workforce. The federal government, venture capital companies and commodity boards have stepped up with funding. "We need to increase our efficiency, but nobody wants to work in the fields," said Stavros G. Vougioukas, professor of biological and agricultural engineering at the University of California, Davis. But farmworker advocates say mechanization would lead to workers losing jobs, growers using more pesticides and the food supply becoming less safe. "The fundamental question for consumers is who and, now, what do you want picking your food; a machine or a human, who with the proper training and support, can" ... take significant steps to ensure a safer, higher quality product, said Erik Nicholson, national vice president of the United Farm Workers of America. On the Salinas Valley farm, entrepreneurs with Mountain View-based startup Blue River Technology are trying to show that the Lettuce Bot can not only replace two dozen workers, but also improve production. "Using Lettuce Bot can produce more lettuce plants than doing it any other way," said Jorge Heraud, the company's co-founder and CEO. 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 â¿¿ and eventually harvesting â¿¿ using many of the same technologies.