Site description.

Two field studies were conducted in Oregon in 2023 and 2024 in areas with a natural high density of C. esculentus. The first study was conducted at the Lewis Brown research farm in Corvallis, OR (lat. 44.56°N, long. 123.22°W), in 2023, on a fallow field of Chehalis silty clay loam soil (0 to 20 cm: 20% sand, 49% silt, 31% clay). The studies commenced in Jun 2023 in an area where C. esculentus reached ∼20 to 25 cm in height at the Biologische Bundesanstalt, Bundessortenamt, and CHemical industry (BBCH) 19 stage. The second study was conducted on a commercial organic-certified highbush blueberry farm in Grants Pass, OR (lat. 42.23°N, long. 123.27°W), situated on Evans loam soil (0 to 20 cm: 44.3% sand, 40.7% silt, 15.0% clay). This field had a history of unsuccessful control of C. esculentus with plants measuring 15 to 20 cm in height in Jun 2024 at the BBCH 19 stage.

Treatment and equipment details.

The experiments were arranged as a randomized complete block design with four replicates. Experimental units measured 3 × 6 m at both locations. All treatments at each site received an initial application on the same date (site-specific as presented in Table 1). Treatments requiring multiple passes then received sequential applications ∼4 and 8 weeks after the initial application. The treatment structure comprised: a nontreated control (NTC); single application of mowing only; single or multiple application of EWC only, at tractor speeds of 0.5, 1, 2, or 3 km·h⁻¹ (with site-specific energy doses); EWC followed by mowing [EWC at 1 km·h⁻¹, then mowing 4 weeks after treatment (WAT)]; and mowing followed by EWC (mowing, then EWC at 1 km·h⁻¹ 4 WAT).

Table 1. Application rates, timing, and dates of electrical weed control and mowing treatments for C. esculentus studies in Corvallis, OR, USA (2023), and Grants Pass, OR, USA (2024).

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Mowing operations executed by a walk-behind rotary mower (Premier 26; DR Power Equipment, Waukesha, WI, USA). EWC was performed using either alternating current (AC) or direct current (DC) tractor-mounted commercial units. The equipment selection was based on availability and dimensions that would be compatible with the cropping system. The Corvallis study used a 30-kW unit (EH-30 Thor; Zasso™ Group, Zug, Switzerland) connected to a 77-kW tractor (5100GN; John Deere, Moline, IL, USA). The electrical weeder consisted of an oil-cooled generator producing a peak power of 30 kW of AC at 180 V and 60 Hz that is mechanically powered by the tractor engine power take-off (PTO). For energy calculation, a power factor of 0.8 was assumed based on the manufacturer’s recommendation. Electric current is transferred to a triphase transformer that can be configured to increase voltage from 3.5 to 12 kV. Cables transfer the high-voltage current to an applicator mounted on the front of the tractor. The applicator consists of metal electrodes arranged 1.2 m in width. The electrodes are the parts in contact with weed foliage and soil during operations (Fig. 1A-C).

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The Grants Pass study used a Zasso™ XPower XPS system, a DC electrical weeding unit designed specifically for perennial cropping systems such as orchards and vineyards. The system was mounted on the rear of a 60-kW narrow tractor (T4.80; New Holland, New Holland, PA USA) and powered via the tractor’s PTO, which mechanically drives the onboard generator. This generator produces DC and can deliver a peak power of 24 kW to the applicator. For energy calculation, a power factor of 0.9 was assumed based on the manufacturer’s recommendation. The rear-mounted applicator, measuring ∼30 cm in width and equipped with metallic electrodes, features a compact design that allows EWC application adjacent to the planting row (Fig. 1D-F). At Grants Pass, treatments were applied on both sides of the blueberry planting rows.

The nominal electric energy density per area applied was determined by the speed of operation using the following equation:$$E\left({\text{kJ·m}}^{\text{-2}}\right)\hspace{0.17em}=\hspace{0.17em}\text{Power}\left(\frac{\text{kJ}}{\text{s}}\right)\times \text{PF}\times \frac{\text{1}}{\text{speed(}\frac{\text{m}}{\text{s}}\text{)}}\times \frac{1}{\text{width(m})}$$ [1] where E indicates applied energy (kJ·m⁻²), power indicates the generator power (kW = kJ·s⁻¹), PF indicates power factor, speed indicates the speed of operation (m·s⁻¹), and width indicates the width of the treated area (m).

Assessment timings differed slightly by site due to logistics and alignment with operational decision windows. At Corvallis (local site), we measured control of C. esculentus at 14, 56, and 80 d after initial treatment (DAIT), adding an early 14-DAIT rating to capture short-term responses. At Grants Pass, to accommodate travel time, budget, and grower scheduling, evaluations were conducted at 28, 56, and 80 DAIT. Weed control was visually assessed on a scale from 0% (no control) to 100% (complete control). At 80 DAIT, the aboveground biomass of C. esculentus was collected at the Grants Pass site from a randomly selected 0.25-m² quadrat/plot, then dried, and weighed. Biomass data were not collected in the Corvallis study.

Tuber density and viability.

Tubers of C. esculentus were collected from experimental plots in Corvallis and Grants Pass, OR. For both locations, one soil sample per plot was collected to a depth of 20 cm. In the Corvallis study, sampling was performed by excavating an area of ∼530 cm², resulting in a total soil volume of 10.6 dm³. In the Grants Pass study, each sample consisted of 6 kg of soil and 5 dm³. Collected soil was thoroughly washed, and tubers and roots were recovered in a 2-mm sieve. Tubers were then separated from the roots and remaining soil debris by a series of washes. Following recovery and cleaning, tubers were counted and gently dried with paper towel, and the fresh weight was recorded. Average tuber weight (g/tuber) was computed as the total fresh mass of tubers divided by the number of tubers (Corvallis: 100; Grants Pass: n). Tuber density was estimated by dividing the number of tubers recovered by the volume of soil sampled.

The C. esculentus tubers were planted in flats filled with a substrate composed of sphagnum peatmoss, perlite, pumice, dolomite, limestone, and a pH-adjusted Sunshine #4 Sungro^® professional growing mix (Sun Gro Horticulture, Agawam, MA, USA). The flats were maintained in a greenhouse with daytime and nighttime temperatures of 24 and 15 °C, respectively. New shoot emergence (%) was recorded 4 weeks after planting as (number of emerged shoots ÷ number of tubers planted) × 100 for each plot flat. Emerged shoots were then clipped at the substrate surface, dried, and weighed. To standardize across sites, total fresh mass was also expressed on a per-tuber basis by dividing by the number of tubers planted for each plot.

Statistical analysis.

All statistical analyses were performed in R (version 4.3.1; R Core Team, Vienna, Austria). Treatment was included as a fixed effect, and blocks were included as random effects. Weed control ratings were analyzed using generalized linear mixed models (GLMMs) with a β distribution implemented in the glmmTMB package (Brooks et al. 2017). Weed biomass, tuber weight, and dry weight of emerged plants were analyzed using linear mixed models (LMMs) with square-root transformation in the lme4 package (Bates et al. 2015). Tuber counts and plant emergence counts were analyzed using GLMMs with a negative binomial distribution to account for overdispersion (glmmTMB package). Model assumptions were checked before inference. For GLMMs, residual diagnostics were evaluated using DHARMa plots (Hartig 2022), and for LMMs, assumptions required for analysis of variance were verified through residual inspection. When significant treatment effects were detected, mean separation was performed using Fisher’s least significant difference test at α = 0.05 with the agricolae package (Mendiburu 2023). Planned contrasts were conducted to further evaluate treatment effects on weed control at 80 DAIT and on biomass, comparing a single pass at 0.5 and 1 km·h⁻¹ with the average of two sequential applications at 2 km·h⁻¹ and three sequential applications at 3 km·h⁻¹. For weed control 80 DAIT only, contrasts were also used to test the sequence of integrated methods, comparing EWC followed by mowing with mowing followed by EWC.

Corvallis (2023, AC system).

In Corvallis, both mowing and EWC treatments provided greater control of C. esculentus compared with the nontreated control (Tables 2 and 3). At 14 DAIT, mowing and EWC at 0.5 km·h⁻¹ (144 kJ·m⁻²) achieved the highest initial control (88%), although control from mowing alone declined to 26% by 80 DAIT. In contrast, sequential EWC applications sustained greater suppression. Three passes at 3 km·h⁻¹ (24 kJ·m⁻² per pass; 72 kJ·m⁻² total) provided 75% control at 80 DAIT, while mowing followed by EWC at 1 km·h⁻¹ and EWC followed by mowing at 1 km·h⁻¹ maintained 57% and 50% control, respectively.

Table 2. Effect of electrical weed control and mowing on C. esculentus control in field studies conducted in Corvallis, OR, USA (2023), and Grants Pass, OR, USA (2024).

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Table 3. Effect of electrical weed control and mowing on C. esculentus control 80 DAIT in field studies conducted in Corvallis, OR, USA (2023), and Grants Pass, OR, USA (2024).

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Grants Pass (2024, DC system).

At Grants Pass, both mowing and EWC treatments (0.5 to 3 km·h⁻¹; 86 to 518 kJ·m⁻²) provided some control of C. esculentus at 28 DAIT (18% to 38%). Despite mowing treatments ranking highest, these levels were still insufficient (Tables 2 and 3). By 56 DAIT, control from mowing declined to 35%, while single EWC applications provided 45% weed control (the difference was not significant). At 56 DAIT, two sequential applications of EWC at 2 or 3 km·h⁻¹ provided the higher control of C. esculentus (70% to 63%, respectively). Final evaluations at 80 DAIT, three-pass EWC at 3 km·h⁻¹ (86 kJ·m⁻² per pass; 258 kJ·m⁻² total) provided the greatest control (93%; Fig. 2), followed by two-pass EWC at 2 km·h⁻¹ (70%) and mowing followed by EWC at 1 km·h⁻¹ (69%). All treatments reduced weed biomass compared with the nontreated control.

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At 80 DAIT, planned contrasts confirmed that sequential applications were more effective than a single pass in both locations (Tables 2 and 3). Single applications at 0.5 and 1 km·h⁻¹ provided significantly lower weed control than the average of two and three sequential applications, representing an improvement of 27 percentage points (P < 0.001). Contrast analysis also showed that the order of integration between methods influenced weed control outcomes. Mean control for EWC followed by mowing was 61%, which was significantly lower than mowing followed by EWC (81%), a difference of 19 percentage points (P = 0.009).Weed biomass following a single application at 0.5 and 1 km·h⁻¹ (40.2 g·m⁻²) did not differ from the average of two and three sequential applications (19.1 g·m⁻², P = 0.322).

Tuber density and viability.

In Corvallis (2023), average tuber weight did not differ significantly among treatments (128 to 167 mg/tuber; Table 4). However, greenhouse assays with tubers collected from field-treated plots revealed differences in regrowth potential. The mowing followed by EWC treatment resulted in the lowest shoot emergence (38%) and reduced shoot biomass (58 mg/shoot) to almost half of the emerged shoot weight in nontreated control. These results suggest that although tuber weight was not reduced, EWC, particularly when combined with mowing, can limit regrowth of new shoots by reducing new shoot emergence and aboveground biomass.

Table 4. Tuber emergence and dry weight of aboveground shoots of C. esculentus in greenhouse studies evaluating electrical weed control and mowing treatments conducted in Corvallis, OR, USA (2023), and Grants Pass, OR, USA (2024).ⁱ

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In Grants Pass (2024), tuber production was strongly affected by treatment (Table 4). The nontreated control averaged 69 tubers/dm³ of soil with a mean weight of 260 mg/tuber. Single-pass EWC at 0.5 and 1 km·h⁻¹ produced higher tuber counts (132 and 97 tubers/dm³) compared with the control. In contrast, sequential and combined strategies presented lowest counts, with EWC followed by mowing (30 tubers/dm³) and two-pass EWC at 2 km·h⁻¹ (33 tubers/dm³), although these mean differences were not statistically different from the nontreated control. Despite these decreases in tuber density and size, greenhouse assays did not detect significant differences in shoot emergence (4% to 13% of shoot emergence) or shoot biomass (12 to 31 mg) among treatments.