What are the top mechanization needs for lettuce growers in the West? At the top of their list, a survey shows, are thinning and weeding machines to reduce labor requirements and production costs.

When specialty crop machine specialist Mark Siemens joined the University of Arizona (UA) staff at the Yuma Agricultural Center (YAC) in Yuma, Ariz., two years ago, he was charged with developing mechanization to make the specialty crop industry more economically competitive.

Siemens hit the ground running, meeting with vegetable growers and industry representatives to gather input about their mechanization needs. A follow-up survey asked them to rank their mechanization priorities.

Topping the requests were mechanized lettuce-thinning and weeding solutions for iceberg and romaine lettuces.

Growers in the Yuma area produce about 90 percent of the U.S. supply of salad vegetables during the winter months, and California/Arizona farmers grow about 99 percent of the U.S. lettuce crop — a $3 billion industry.

About 80 percent of the U.S. crop is grown in California’s Salinas Valley near the Central Coast during the spring, summer, and fall months. Vegetable companies shift production to Yuma County and neighboring Imperial County, Calif. for winter production.

A handful of commercial companies have released thinning or weeding machines. CEMCO Inc. has a lettuce thinner which also works in chile peppers and carrots. Garford Farm Machinery’s Robocrop machine uses a rotating disk to remove weeds between lettuce plants in the seed row. A vegetable thinner is under development by another company.

But Siemens, the ag engineer, has a few ideas up his own sleeve. He designed and developed a mechanized iceberg lettuce thinner prototype with the assistance of consulting engineer Ryan Herbon. They rolled out the machine in mid-March and thinned 42-inch-wide iceberg lettuce beds at the YAC.

Their invention is a machine vision-based thinning device that includes a digital video camera and computer, plus several “secret” gadgets. The entire setup is mounted on a steel frame and towed by a three-point hitch behind a tractor.

“This is an exciting time in the vegetable crop industry,” says Siemens, UA associate professor and ag mechanization specialist. “A lot of research is under way to improve the economic viability of specialty crops by reducing farm labor requirements. Mechanization can help provide an economically-viable vegetable industry in the U.S., rather than losing production to other countries.”

He earned his doctorate in agricultural and biosystems engineering at the UA in 1996, and prior to that served as an agricultural engineer at the USDA Agricultural Research Service Columbia Plateau Conservation Research Center at Pendleton, Ore., and as assistant professor and Extension engineer at the University of Georgia.

In the Yuma area, iceberg lettuce seed is sown about every two inches to insure a uniform and adequate stand establishment. Lettuce plants are typically thinned at the two- to three-leaf stage or older by crews of workers with hoes. They are thinned to one plant every 8-12 inches, depending on market needs.