Zap those pesky invaders: Technology sparks alternative to herbicides

A contraption with a long, low, green metal arm swept noisily along the edge of a row of almond trees in an experimental orchard just west of UC Davis. Little flashes of light sparked between the bottom of the arm and the green weeds below, and puffs of gray smoke wafted up from the stricken pests.

This tractor equipped with an electrical generator may offer one solution for organic farmers looking for new ways to get rid of weeds. Researchers here and at partner universities have embarked on a three-year project to compare how the machine performs compared to herbicides allowed in organic farming, and to hand-weeding, which has become prohibitively costly.

Electrical energy zooms through the plant down into the roots, and the heat damages cells. ″We start seeing injury in the weeds within 30 to 60 minutes after the treatment,″ said doctoral student Tong Zhen, of the Department of Plant Sciences. ″Most weeds will be killed in a day.″

Doctoral student Tong Zhen is studying the effectiveness and soil impacts of this electrical weed control device, made by the Brazilian company Zasso, He’s working with Brad Hanson, professor of UC Cooperative Extension, both in the UC Davis Department of Plant Sciences. (Trina Kleist/UC Davis)

Two weeks after treatment during an orchard trial in May, all of the treated hairy fleabane was dead, and 70 percent of the field bindweed was toast.

In addition to evaluating the effectiveness of this electrical weed control device, the multistate team also is evaluating its effects on crop safety and on the tiny organisms living in the soil. ″Maintaining soil health is an important goal of most organic producers,″ Zhen added.

The weed-zapper was demonstrated during the 2023 Weed Day held June 21, and it’s the focus of research by Tong, staff research associate Seth Watkins and principal investigator Brad Hanson, all in the Department of Plant Sciences. In addition to studying the zapper’s effectiveness, they are looking at soil health and crop safety after repeated uses in both almond and blueberry fields that are managed organically. Colleagues at Oregon State University are testing the device in cherry orchards, and colleagues at Cornell University are testing it in apple orchards.

Machines with vision, herbicide tests and Google Street View

More research presented during Weed Day included:

• Efficacy and crop safety of fluridone in pomegranates. Postdoctoral scholar Rohith Vulchi  and Brad Hanson, a professor of Cooperative Extension.

• Effect of endothall-treated irrigation water on almond orchards. Stephen Chang, master’s degree student, and Brad Hanson.

• Machine-vision cultivators in processing tomato. Steve Fennimore, professor of Cooperative Extension in the department, and Scott Stoddard, UCCE Farm Advisor.

• Farm machinery sanitation to reduce the spread of broomrape seed. Postdoctoral scholar Pershang Hosseini and Brad Hanson.

• Chemigation strategies to manage broomrape in processing tomatoes. Doctoral student Matt Fatino and Brad Hanson.

• Orchard crop injury from simulated rice herbicide drift.  Doctoral student Deniz Inci, Brad Hanson and Kassim Al-Khatib, the Melvin D. Androus Endowed Professor for Weed Science.

Steve Fennimore and colleagues are studying the use of automated weeders in processing tomatoes. In research trials on various other crops, including lettuce, in Salinas, Calif., they found the new generation of weeders was ″very effective at removing weeds in the plant line without damage to the crop,″ Fennimore said during the UC Davis Weed Day 2023. The weeders use artificial intelligence to "see" the difference between weeds and crop plants. Fennimore is a professor of Cooperative Extension in the UC Davis Department of Plant Sciences. (Trina Kleist/UC Davis)

More research:

• Weed control efficacy and crop safety of the PPO-inhibiting herbicide tiafenacil in orchards. Recent master’s degree graduate Guelta Laguerre and Brad Hanson.

• Using Google Street View to map weeds along road networks, making weed control more efficient. Mohsen Mesgaran, an assistant professor in the department, Tong Zhen and Kassim Al-Khatib.

• Using pendimethalin for water-seeded rice. Doctoral student Aaron Becerra-Alvarez and Kassim Al-Khatib.

• Evaluation of group 15 herbicides in tree nuts. Recent master’s degree graduate Andres Contreras and Brad Hanson.