Shorthanded farmers can take advantage of automated weeders

Automated cultivators that can identify and eliminate weeds within the seed line could prove to be a life-saving technology for Central Coast vegetable growers facing employee shortages.

These modern machines developed during the last decade go one step beyond the precision cultivators that remove weeds everywhere except those that grow too close to the crop and could be damaged by the weeders.

"One key motivating factor to the use of auto weeders is the scarcity of available labor to weed fields, and in that sense, automated weeder technology has arrived at a critical time in the agricultural industry," said Richard Smith, University of California Cooperative Extension vegetable crop and weed science farm advisor based in Salinas.

Smith said he has seen improvements in automated weeders as growers have tried machines from Denmark, the Netherlands, Italy, England, France and the U.S.

"All automated weeders use cameras to detect plants, a computer to process the image and make decisions about which plants to keep and which to remove, and a kill mechanism," he said.

Kill mechanisms that operate in the seed line used by currently available machines are either a split blade that opens around keeper plants and closes between keeper plants, a spinning blade that avoids the keeper plants by placing them in a notch in the blade or a spray application of an herbicide.

Modern cultivators have already narrowed the area that must be hand weeded to a narrow band just 3 to 5 inches wide on the seed line and camera-based weeders can reduce hand labor even further.

But these machines are not cheap. Most cost well more than $100,000, and the price tag must be measured against how much the machines reduce the high cost of hand weeding.

The UC 2017 Sample Costs to Produce and Harvest Iceberg Lettuce estimated hand cultivation labor at $161 an acre and rising as the state's minimum wage goes up.

"Clearly, automated weeders are useful to growers because they remove weeds, but this technology is currently quite expensive, and growers need to make decisions on when it is economically advantageous to use them," Smith said. "Currently, automated weeders are either purchased by growers or a service company provides auto weeding for a fee."

Recent Central Coast studies provide some information on how much hand-weeding cost can be reduced by making the healthy upfront investment in an automated weeder.

Smith, California State University, Monterey Bay assistant professor Elizabeth Mosqueda and UCCE weed specialist Steve Fennimore trialed the Naio Dino from France and the FarmWise Titan from the U.S. and found they reduced hand-weeding time on average by 34%, or from 11 hours an acre to 7.3 hours.

But beyond that average number, the researchers also identified situations in which the automated weeders are more or less valuable.

"We looked at initial weed populations and the impact of auto weeding on subsequent hand-weeding time," Smith said. "This data shows that when weed populations are low, auto weeding does not speed up subsequent weeding as much as when initial weed populations are higher."

The impact weed density has on how much hand-cultivation time the machine will save can be quite substantial.

When there were just 10 weeds per square meter, for example, the study showed the auto weeders reduced hand cultivation by only around 15%.

But when pressure was much higher at 40 weeds per square meter, the machine reduced hand cultivation time by at least 40%.

Most organic farmers and some conventional growers use lettuce transplants, in part to give the crop a head start on the weeds, and auto weeders may be even more thorough in these fields.

"The machines are particularly effective for use with transplanted vegetables because recognizing the difference between the crop and the weeds is easier given the initial size difference between the transplants and germinating weeds," Smith said.

But the cost and labor-saving figures can be complex because most growers cultivate with an eye toward suppressing future weed pressure rather than just allowing the current crop enough room to grow.

"In lettuce production fields, growers try to remove as many weeds as possible from the field to reduce weed seed production and keep future weeding costs low," Smith said. "As a result, they will normally send in a crew even after using an automated weeder. Using the auto weeder will help to speed up subsequent hand-weeding operations, but the grower faces a weeding bill from both the hand weeding and auto weeding operation."

As impressive as these machines can be, however, there is a danger they will be an additional cost on top of the continued need to weed by hand.

"In cases where subsequent hand weeding or double removal is necessary, auto weeding may add an additional cost, especially in fields that have low weed populations," Smith said.

But some growers who find that auto weeders do not pencil out in hand-weeding costs saved may still be tempted to use the machines because the labor cost figures assume growers can find people to do the work, which may not always be the case.

"Even in cases with low weed populations, growers may be motivated to use auto weeders because they help manage scarce labor resources and facilitate crews to quickly and efficiently complete follow-up weeding operations," Smith said.

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)