Two years ago, I shared my first blog about the Zasso electrical weed control (EWC) unit—a tractor-mounted device powered by the tractor's PTO. (My first blog about the basic of EWC and unit specifications

In spring 2023, we established two organic blocks, one with almonds and one with blueberries, to further evaluate the weed control efficacy and crop safety of the Zasso unit in newly established tree and berry systems. In these trials, we tested different combinations of speed and power to control the total current/energy flowing into the ground. This approach is similar to herbicide trials where we often test at different rates to evaluate crop injury (e.g., 2X, 4X rates). Both experiments included comparisons with standard organic weed control practices such as organic herbicide (Suppress EC), mowing, and hand weeding.

In the blueberry experiment, we also applied two mulching types (sawdust and plastic), and each plot with different mulching types was treated with all the EWC treatments to evaluate the interactions between these two practices. Since blueberries are planted on berms, we only treated the berm shoulders with EWC (Figure 2).

Figure 1. Organic blueberry field with three different mulching types as treatments

Figure 2. EWC treating the shoulder of the sawdust mulching blueberry plot

Figure 3. EWC in organic almond block

2023 Findings

During the 2023 growing season, all EWC treatments showed promising weed control results. In the almond block, the highest-energy EWC treatment kept the floor weed-free for 35-40 days. In the blueberry block, where we used one drip line (versus two in the almond block), the shoulders stayed dry for most of the summer. After our first EWC application in late May (almond) and early June (blueberry), weed pressure in all EWC-treated blueberry plots remained low throughout the season, with some plots staying weed-free even longer than the same treatment in the almond block. We measured tree height, trunk diameter, and blueberry plant canopy volume, finding no significant differences in plant growth across treatments for either crop.

Figure 4. EWC untreated (top) and treated (bottom) almond plots in April 2024

2024 Focus

In 2024, we continued measuring growth data and collected soil samples for soil health analysis in both blocks. One of my research goals is to address a key grower concern about this technique by assessing the impact of EWC on soil microbes. While soil physical properties should remain unchanged (due to no soil disturbance), soil microbes—which play a crucial role in nutrient cycling—could be sensitive to electric shocks and surface temperature spikes. Then, we will look at how two years of more than 10 EWC applications will impact weed species distribution.

2025 Plans

Coming into 2025, we plan to continue the blueberry and almond work on campus and also conduct additional research in growers' fields and test it out in additional tree crops. We will continue to collect weed control efficacy data on an array of common orchard weeds in California. Lastly, we plan to start an experiment to examine how soil moisture at the time of EWC treatment affects the weed control efficacy and whether there are any effects from different irrigation regimes.

Frequently Asked Questions about EWC Technology

Q: Are there any safety concerns with EWC?

A: Yes, since this is a high-voltage application targeting above-ground vegetation, the circuit can create arcing and potentially cause fires. The manufacturer requires scouting behind the tractor during applications. Multiple EWC applications and mowing operations over a season leave dead vegetation on the ground, which can easily ignite, especially at higher power settings. We have noticed a seasonal pattern, with more fires occurring in fall than summer, and we are still investigating the causes.

Figure 5. Arcing from the applicator

Q: How does soil moisture affect EWC operation?

A: Soil moisture is an important factor. Soil that is too wet can cause generator overload by drawing too much energy. In contrast, overly dry soil has high electrical resistance, reducing current flow through plants. Our unit includes a setting to adjust power based on soil moisture, so selecting the right setting is essential for effective application. This is an area of ongoing research in California and with our collaborators in Oregon and New York.

Q: How do different weed species respond to EWC?

A: The weed growth stage matters more than species. EWC is effective on most weeds at the seedling stage but start losing efficacy with mature or flowering weeds that are woody or have less tissue moisture because electrical conductance is lower. Grasses can be challenging if they are matured and developed multiple tillers, as central tillers may avoid direct contact with the EWC applicator electrodes.

Q: How effective is EWC on perennial weeds?

A: EWC can manage bindweed and yellow nutsedge with multiple applications throughout the season. Regrowth and reemergence can occur if the vegetation does not directly contact with the electrode due to obstacles like soil clumps or overlapping plants. We are running an experiment to quantify perennial weed regrowth and reemergence.

Q: Is this unit available on the market?

A: Zasso has partnered with New Holland to bring this technology to the US. Please check out their website https://yellowblueandyou.newholland.com/en-gb/pf-global-2024/xpower-xps to look at the unit for the vineyard (XPower XPS). We will have a vineyard trial in 2025 in partnership with the farm operation and equipment distributor to evaluate the cost-efficiency of EWC in a large scale site.

Since I have been working and studying this unit for two years, I truly believe it is a valuable option for organic berry and tree fruit and nut production. It can also become an alternative to some of the post-emergent herbicides used in integrated pest management (IPM) programs in sustainable agriculture.

Our EWC project is funded by USDA NIFA Organic Research and Education Initiative. Please check out our website: https://eorganic.info/node/35946 for interviews and research updates from our collaborators: Moretti Lab at Oregon State University and Sosnoskie Lab at Cornell University. We are testing the same unit but on different crops. We also want to thank New Holland for the tractor support.

Figure 6. Equipment testing in non crop area before EWC treatment in organic almond and blueberry at UC Davis.