Labor, Efficiency, and the Future of Weed Control

This photo highlights finger weeder cultivation of a seedline. Note significant disruption of the soil, which can upend small weed seedlings. Photo credit: Richard Smith

California vegetable growers have two new challenges. This year, two bills were signed into law that will increase the cost of labor. The minimum wage law will result in an increase from $10 per hour to $15 per hour. The pay hike will be phased in by $1 increases each year and take full effect in 2022.

The second bill removes the overtime exemption for agricultural employers resulting in employees being paid overtime after working eight hours a day or 40 hours a week (also phased in by 2022). Given that agriculture is a seasonal activity in which 10-hour days and 60-hour weeks are the norm during the growing season, growers are struggling to adapt to these changes.

Many to Be Impacted
Workers that harvest crops, irrigators, and those who are weeding and performing other cultural practices will be affected. One of the concerns is that these laws have the potential to put California growers at a disadvantage by increasing the costs of production here, thereby making production in other areas more advantageous. Growers producing crops that are more labor intensive such as leafy vegetables or smaller and organic growers, whose operations may be more labor intensive, are particularly concerned about how to adjust to these new labor costs.

In recent cost studies on Romaine hearts and organic spinach (, average hand weeding costs were $143 and $440 per acre, respectively. These
costs can vary substantially, depending on the weed pressure in particular fields. Growers have expressed the need for technologies to make hand weeding more efficient to achieve acceptable weed control in production fields. Improvements in cultural and chemical control of weeds and the introduction of new technologies are beginning to play a role in this regard.

Herbicide Reduction
In the early 2000s, the release of newly developed herbicides for all crops declined dramatically and nearly came to a standstill in vegetables. The cost for developing a new herbicide has increased to as much as $250 million to $300 million. As a result, growers are making due with older chemistries that do a good job, but that may have weaknesses controlling specific weeds. In addition, increased regulatory pressure can affect the registration status of older herbicides, which can put them at risk for being removed from the market.

As a result, many of our research efforts with herbicides have been to examine new uses of older materials to solve specific problems. Herbicides can be particularly effective in reducing the need for hand labor in vegetable crop production.

In particular, crops grown on high density 80-inch wide beds that cannot be cultivated can be exceedingly expensive to weed. For instance, we recently measured hand-weeding costs in cilantro of 238 hours per acre with no herbicide and 6.5 to 8.8 hours per acre with the use of prometryn and linuron. These materials are examples of older chemistries that were recently registered for use on this crop.

The Latest Technology
New technologies such as finger and torsion weeders, as well as automated weeders, are now gaining acceptance in California. Until recently, these technologies were primarily used in Europe where high labor costs are nothing new. Much of the development of this technology has come from that part of the world and there are now companies importing it into the U.S. market.

Finger weeders were originally developed in Michigan by the Buddingh Weeder Co. The concept was adapted and changed by Kress and Steketee companies in Germany and the Netherlands, respectively. Fingers run in the seedline and uproot small weed seedlings.

Studies on these implements showed that they reduced hand weeding in crops such as lettuce, celery, broccoli, and leeks by as much as 45% over standard cultivation, which does not remove weeds from the seedline. Given increased costs of hand weeding, U.S. growers are now showing interest in the use of finger weeders technology and U.S. distributors are seeing increased sales. Finger weeders are not a total replacement for hand weeding but make subsequent hand-weeding operations much more efficient and economical.

The Robovator and Steketee IC are automated weeders that use machine vision, computer processing of images, and a split knife to remove weeds. They have been commercially available in the Salinas Valley for the last two years.

In 2015, we evaluated their efficiency at removing weeds in lettuce following thinning. On average, in four trials, they reduced subsequent hand weeding by 37%. These studies were mostly conducted on direct-seeded lettuce, however these machines were designed for use on transplanted crops, and they may provide better weed control with that planting scheme.

Increases in labor costs will affect the costs of production of vegetable crops in California. Growers will have to adapt to these new conditions in order to stay competitive with producers in other areas. Taking advantage of production practices that help reduce weed pressure will be an important avenue for reducing costs.

In addition, continuing to find new uses of older herbicides will be necessary to extract the maximum benefit from them. New technologies are becoming more cost effective and growers will increasingly turn to mechanization as a viable strategy to effectively reduce weed pressure and stay economically competitive.