Winter vegetable farmer Jesus Tovar embraces automation to increase efficiency plus reduce the dependence and costs of hand labor to thin his lettuce crop.

Tovar’s eyes were fixed on a University of Arizona (UA)-developed automated lettuce thinner prototype crawling at one-and-a-half miles per hour. The machine was demonstrated at a field day at the Yuma Agricultural Center (YAC) in Yuma, Ariz., in March held in conjunction with the Southwest Ag Summit.

Tovar, owner of T&P Farms, grows lettuce for Ocean Mist Farms on about 2,500 acres located from San Luis, Ariz., to Bard, Calif.   

“If we look at the future, we may not have enough people to do this (thinning) work,” Tovar said. “If a (thinning) machine like this is available, that’s where we are going to go.”

A mechanized thinner purchase would depend on costs, the speed of the machine, and other factors, Tovar noted.

Lettuce seed is sown at high rates due to poor germination rates in the field. Unneeded seedlings are thinned out two weeks after germination by farm workers armed with hoes to achieve the desired plant spacing in the final stand.

Mark Siemens, University of Arizona ag mechanization specialist, says thinning lettuce by hand cost growers $100-plus an acre, depending on the location and field conditions.

“One advantage of an automated thinner is to free up labor crews for other tasks,” Siemens said. “Another advantage is to reduce thinning costs. I estimate the tractor operating cost for an automated thinner at about $25/acre. The remaining $75/acre thinning cost reduction would be divided between the actual machine cost from a manufacturer and the savings to the grower.”

If one assumes cost savings to growers at $25/acre and a thinner device was implemented on the estimated 220,000 acres of lettuce grown in California and Arizona, Siemens projects growers could save about $5.5 million annually.

Siemens is at the helm of the UA automated thinner research. The project is funded by a three-year $115,000 specialty crop block grant from the Arizona Department of Agriculture.

The UA prototype is in its second year of development. An automated lettuce thinner must perform three necessary tasks, Siemens told a crowd during an Ag Summit advanced technology session.

“Required components include a plant sensing system to identify and locate crop plants, a control system to determine which plants to keep and eliminate, and a method for removing the unwanted plants,” Siemens said.

Siemens and ag engineer Ryan Herbon have worked closely on the sensing component. Herbon owns and operates Mule Deer Automation in Silver City, N.M. Also involved in the project is Ron Gayler, UA staff technician.

The thinner prototype is designed for traditional 40- or 42-inch wide, two-line iceberg lettuce beds and the same width three-line romaine lettuce beds. Machines could be hooked together to thin several beds at a time or larger 80- or 84-inch beds.

The mechanized thinner showcased at the field day is the second generation prototype developed by the research trio.

The original tested sensing system included photoelectric sensors to sense the lettuce plants. It performed unsatisfactorily in finding the small seedlings. The switch was made to a “machine vision” sensing system featuring a digital camera which captures images on the bed under controlled lighting.