The motivation is straightforward. Hazelnut is a high-value perennial nut crop, with global production concentrated in Turkey and Italy and expanding in the United States and Chile. In Oregon’s Willamette Valley, hazelnut supports many growers and rural communities and supplies a key raw ingredient for confectionery products, including chocolate-based goods. But weed management in hazelnut orchards is a persistent challenge. Tree rows are permanent, mechanical access is limited because cultivation can damage the shallow root system, and weeds compete with young trees, reducing growth, productivity, and long-term orchard performance. Effective in-row weed control during the first years after planting is critical for rapid canopy development and for maintaining the clean orchard floor required for efficient nut harvest.

That challenge has traditionally been met with repeated herbicide applications in the planted row combined with flail mowing the alleyways. Continued reliance on herbicides intensifies selection pressure for resistant weed populations, and in Oregon hazelnut orchards, herbicide-resistant weeds have already been documented, including Italian ryegrass and annual bluegrass. Recent work has identified multiple herbicide-resistance cases in annual bluegrass, underscoring how vulnerable perennial orchard systems are to resistance evolution under repeated chemical applications. The search for nonchemical tools capable of diversifying weed management programs has therefore become urgent.

Electric weed control is one promising area, but most existing systems deliver energy to weed foliage. In aboveground contact systems, electrodes touch plant tissues, allowing current to pass through the weed and into the soil. Electricity flowing through the plant increases tissue temperature, disrupts cellular integrity, and can result in plant death. These systems are generally most effective on young, herbaceous, and well-hydrated weeds, but they can be bulky, energy-demanding, and nonselective, requiring careful application to avoid crop injury. PEF differs from these alternating-current systems because it delivers short, high field-strength electrical pulses rather than continuous energy. The pulses disrupt cellular membranes through electroporation, a process in which an external electric field destabilizes the lipid bilayer. When the induced membrane disruption is temporary, cells may recover; when it is severe or prolonged, electroporation becomes irreversible, leading to loss of membrane function, cellular leakage, and tissue death.

Soil-applied PEF goes one step further: instead of contacting weed foliage, electrodes are inserted into the soil or placed on opposite sides of a defined soil volume, and short electrical pulses are discharged between electrodes of opposite polarity. Current moves through conductive soil-water pathways, and biological targets are exposed when seeds, propagules, roots, or emerging seedlings intersect the effective electric field. Previous work has shown that soil-applied PEF can suppress plant-parasitic nematodes and soilborne pathogens, suggesting that a lethal electrical dose can be delivered to below-ground targets. From a biological perspective, germinating weed seeds and vegetative propagules may be particularly suitable targets because germination activates membrane systems, increases tissue hydration, and establishes conductive plant-soil pathways that facilitate current flow through living tissues. Electroporation theory predicts that metabolically active cells are more susceptible to irreversible membrane destabilization when critical transmembrane potentials are reached.

The Oregon team, led by Pamela Medeiros dos Santos, Tatiana Benedetti, and Marcelo L. Moretti, evaluated soil-applied PEF in a six-month-old experimental hazelnut orchard at the Lewis-Brown Research Farm near Corvallis, on a Malabon silty clay loam with 5 percent organic matter. Treatments included a nontreated control, a hand-weeded control, and soil-applied PEF at 1, 10, and 100 joules per cubic centimeter, applied once in July 2025 using a vertical-pin soil electrode system that generated millisecond-duration pulses at a field strength of 200 volts per millimeter. The stationary electrode frame consisted of two rows of 12 pins of positive and negative polarity, spaced 30 centimeters apart, treating a 60-centimeter swath and an estimated soil volume of approximately 0.018 cubic meters per placement. Weed control was assessed visually up to 60 days after treatment, and crop response was evaluated through visual injury ratings and physiological measurements, including leaf chlorophyll content, photosystem II quantum efficiency, and stomatal conductance.

The field results were sobering for weed control but reassuring for the trees. PEF at 1 and 10 joules per cubic centimeter produced 0 percent weed control at every assessment, indistinguishable from the nontreated control. The highest energy density, 100 joules per cubic centimeter, produced minor numerical suppression, reaching 25 percent visual weed control at 1 and 3 days after treatment, but this response was not statistically different from the nontreated control and declined to below 13 percent at 30 and 60 days. Only hand weeding controlled weeds, primarily yellow nutsedge, consistently reaching 100 percent across all evaluation dates. Crop injury, by contrast, was negligible throughout the study. Injury ratings were 0 percent for the control, hand-weeding, and the lowest PEF treatment at all evaluation dates, with only 2.5 percent injury observed later in the season for the two highest energy treatments. Physiological measurements showed no consistent treatment effects over time; chlorophyll content increased as leaves matured, photosystem II efficiency remained similar across treatments, and stomatal conductance increased quickly after treatment and then remained within a similar range among treatments through 60 days. The temporal variation was likely driven by seasonal and environmental factors rather than the electrical treatment itself.

In parallel greenhouse experiments, the researchers planted tubers of yellow nutsedge and seeds of barnyard grass and Palmer amaranth in containers and incubated them in moist soil for 0, 3, 5, or 7 days before applying PEF at 0, 25, 50, or 200 joules per cubic centimeter using a parallel-plate applicator. One aluminum electrode was placed at the bottom of the container before filling with soil, and a second was placed on the soil surface with a spring-loaded mechanism ensuring consistent contact, forcing current vertically through the entire soil column. Plants were harvested 28 days after treatment, and shoots and roots were separated, dried, and weighed. Redundancy analysis indicated that, after accounting for species effects, energy density and incubation time explained a small but significant portion of the multivariate variation in biomass, with incubation time the strongest experimental predictor, followed by energy density. Species identity accounted for the majority of total variation in biomass response.

The species-specific results were striking. Yellow nutsedge tubers exhibited the greatest biomass and the strongest response to PEF: treatments substantially reduced shoot and root biomass at 3, 5, and 7 days after planting, often approaching zero regardless of energy density. Slope analysis showed strong negative relationships between incubation time and biomass at 25 and 50 joules per cubic centimeter, with shoot and root biomass declining by roughly 0.098 and 0.174 to 0.179 grams per day, respectively, indicating a pronounced increase in susceptibility with delayed exposure. At 200 joules per cubic centimeter, no clear incubation-time effect was observed, suggesting this energy density was sufficient to cause high levels of control regardless of tuber developmental stage. Palmer amaranth showed a significant negative relationship between incubation time and biomass at 50 joules per cubic centimeter for both shoots and roots, while barnyard grass biomass declined with increasing incubation time at 0 and 25 joules per cubic centimeter for shoots, though the magnitude of the response was smaller and less consistent across energy densities. Across species, increasing incubation time generally enhanced PEF efficacy, particularly at intermediate energy densities, indicating that delayed application coinciding with early seedling development increased treatment effectiveness.

The contrasting responses between field and container studies were likely driven by differences in applicator configuration, treated soil volume, and electric field distribution. The vertical-pin configuration used in the orchard treated a larger and more heterogeneous soil volume, where soil moisture, bulk density, organic matter, roots, and weed position likely altered current pathways. Because electric current follows the path of least resistance, portions of the treated soil volume may have received sublethal exposure, with localized regions of high intensity near electrodes and large portions of the treated volume receiving sublethal doses. The transient weed suppression observed at 100 joules per cubic centimeter may also reflect incidental direct contact between the applicator and weed foliage rather than an effect of electricity moving through the soil to the roots. In contrast, the parallel-plate configuration directed current vertically through a smaller, more uniform soil column, increasing electrode contact area and improving the likelihood that germinating seeds, tubers, roots, and emerging shoots intersected the effective electric field. The difference in energy range should also be considered, as the container experiment included 200 joules per cubic centimeter while the highest field energy was 100; greater field suppression might have occurred at higher energy densities, though increasing energy in field soil would also raise energy demand and may reduce field-scale practicality unless energy delivery becomes more targeted and efficient.

The timing effect has a clear physical explanation. As seeds imbibe water and tissues differentiate, dielectric constant and electrical conductivity increase, facilitating current flow through plant tissues. Previous studies have shown that conductivity in germinating seeds increases several-fold as water content and tissue connectivity increase; in seeds of Cardiospermum halicacabum, conductivity remained low during early imbibition but increased approximately 5 to 10 times between days 7 and 14 of germination, and in snap bean, increasing seed moisture content from approximately 25 to 50 percent resulted in substantial increases in conductivity and corresponding reductions in electrical resistance. In the present study, weed propagules incubated in soil for 3 to 5 days were generally the most affected, aligning with the idea that developing seedlings provide more continuous conductive pathways for the electrical current. Ungerminated propagules were less affected at lower energies, likely due to limited conductive pathways. Species-specific responses were also expected, as differences in seed size, morphology, and early growth patterns influence the formation of conductive pathways and recovery potential following injury.

Scalability remains a major limitation for soil-applied PEF in orchard systems. Energy treatments were expressed as nominal applied energy density, but real-time operational energy consumption, equipment efficiency, duty cycle, treatment speed, and field work rate were not measured, so field-scale energy requirements cannot be fully estimated from these data. Actual orchard energy demand would depend on treated band width, electrode geometry, soil moisture, soil electrical conductivity, contact efficiency, and the proportion of orchard floor treated. These limitations suggest that soil-applied PEF may be better suited for targeted applications, such as localized treatment of persistent weed patches or belowground pest targets, rather than broadcast treatment of large soil volumes. Alternatively, future development may need to explore other electricity-delivery pathways, including foliar application, where direct contact with aboveground weed tissues may improve energy-use efficiency and biological response.

Overall, the primary limitation of soil-applied PEF for weed control is not necessarily the biological sensitivity of weeds but the ability to deliver sufficient and uniform energy under field conditions. The container study demonstrates that growth suppression is achievable when exposure is uniform, whereas the orchard study shows that a single soil application with the vertical-pin configuration did not provide consistent weed control. Improving field efficacy will likely require application strategies that increase the probability of current passing through target tissues, including modified electrode designs, repeated applications to compensate for variability in contact, or integration with other nonchemical approaches. The high level of crop safety observed also supports further exploration of soil-applied PEF for belowground targets. Although soil-applied PEF was ineffective for weed control under the orchard conditions tested, it may become a viable component of integrated weed management in perennial horticultural systems if energy delivery and biological targeting are better aligned. The research was supported by the USDA National Institute of Food and Agriculture through the Crop Protection and Pest Management Program, with additional support from the Oregon Hazelnut Commission and Ferrero Hazelnut Company.

Subject of Research: Agricultural Science

Article Title: Hazelnut tolerance and weed response to soil-applied pulsed electric field

Article References: Medeiros dos Santos, P., Benedetti, T., & Moretti, M. L. (2026). Hazelnut tolerance and weed response to soil-applied pulsed electric field. Frontiers in Horticulture, 5, Article 1833896. https://doi.org/10.3389/fhort.2026.1833896

Image Credits: AI Generated

DOI: 10.3389/fhort.2026.1833896

Keywords: pulsed electric field, PEF, weed control, hazelnut, electroporation, nonchemical weed management, orchard systems, soil-applied technology, herbicide resistance, sustainable agriculture, tolerance, weed