Expanding the Adoption of Under-Trellis Cultivators in Vineyards to Reduce Herbicide Input

Objective 1. Evaluate the weed control performance of three under-vine cultivators (hoe blade, rotary tiller, and rotary brush) used alone or in combination.

Four field experiments were conducted in the Willamette Valley in commercial vineyards between 2019 and 2021 (Table 1). The vineyards were between 6 to 8 ft spacing between rows. Experiments were arranged as a randomized complete block design with four replicates. Each experimental unit consisted of an entire vineyard row ranging from 200 to 350 ft in length. The weed control treatments were placed in the 1.5 ft section under the rows. Experiments between March and May depending on weather and soil conditions.

A total of six treatments were included: brush weeder, rotary tiller, hoeing blade, in-row mower, hoeing blade with rotary tiller, and a nontreated reference. Cultivations were done once on each side of the vine row with an ID David in row weeder with a single-side hydraulic articulating arm mounted on the rear of the tractor. The weeder was attached to a narrow 20 hp tractor (Kubota BH2320) equipped with a PTO hydraulic pump in 2019. In 2021, the cultivator was attached to a 100 hp narrow tractor (JD 5100GN). Figure 1). In all sites, operations were performed at 1.25 mph.

Figure 1. Under-vine cultivator in use in 2018 (left) and 2021 (right).

Assessments included visual estimates of weed control using the scale of 0% for no control to 100% for complete weed control performed 30 days after treatment. We collected two samples of above-ground vegetation biomass per experimental unit. Soil water content was measured using a portable moisture probe (Hydrosense II, Campbell Scientific) at the beginning of the experiment, averaging ten measurements per site before cultivation.

Objective 2. Compare under-vine cultivation equipment to herbicide application and record operational information to estimate reliability, operation capacity, and scheduling of cultivation operation during the growing season. Grower-collaborators will be actively engaged in this objective, and their input will become the basis for the emphasis of outreach events and materials

The cultivator was left with collaborating growers interested in testing the units. The grower was responsible for recording the speed of operation, the number of acres covers per day, fuel consumption, and operation performance or issues observed.

Objective 3. Compile a list of cultivators available in the market with estimated costs, operational capacity, tractor requirement, applications, and limitations and develop extension materials and presentations to promote the adoption of this technology.

To address the lack of information related to under-vine cultivators, we have compiled a draft document listing all commercially available equipment and vendors located in the Western Region. Only equipment with US-based technical support will be included in the list. This list will be available online and will be disseminated during extension meetings.

Results and discussion

Weed control efficacy of implements was dependent on the research site (Table 1); observed variability may be attributed to differences in rainfall after treatment application. The lowest weed control was recorded in the Salem site ranging from 0 to 30% (Table 2). The field study was initiated in March 2019, when soil moisture was near field capacity (37% VWC). A total of 4.48 in of rain were recorded in the four weeks following treatments.  The wet soil condition and continued rainfall favored weed regrowth. Overall performance of the implement improved in other locations, reaching 85% weed control (Table 2).

The brush weeder implement resulted in 3 to 30% weed control across all tested sites. The brush weeder cut only a portion of the weeds present, allowing quick regrowth after treatment. Performance was better when dealing with small weed seedlings that were likely uprooted. Similarly, the in-row mower did not provide more than 20% control in Yamhill. The mower could not be used in the other locations because the weeds were too short. This implement might have better use later in the spring or early summer as a second treatment to reduce weed seed production.

Weed control with the hoeing blade was rated 26 to 70%, with greater weed control noted on sites near saturation at the time of treatment, 45 to 70% control. When used in wet soil, the hoeing blade sliced a top layer of soil but did not always disturb weed root to soil contact, thus weed regrowth was observed. The hoeing blade reduced weed biomass by 25 to 55% (Figure 1). Rotary tiller performance ranged from 3 to 85% control (Table 2). In 2019, the performance of the rotary tiller was partially limited by tractor power. The implement could not sustain its movement when the tractor engine was forced to go uphill, or excessive weed biomass obstructed its movement (Figure 2).

Figure 2. Weed biomass after treatment with different weed control implements under grape vine. Field studies were conducted in 2019 and 2021 in various locations in the Willamette Valley.

The hoeing blade provided the greatest level of control, ranging from 30 to 80% (table 2). Control was more consistent (70 to 80%) when performed in dryer soil. The two implements also provided weed biomass reduction ranging from 40 to 90% (Figure 1). The tiller plus hoeing blade outperformed the hoeing blade in some instances, likely because of greater disturbance of weed root-soil contact (Figure 3).

Figure 3. Example of rotary tiller working in the area with greater weed biomass. Greater biomass blocks the implement rotation.

Recording of operational capacity was limited. It was only possible to work with one grower in 2019, and because of maintenance problems, the equipment was only used by the research group after that. Supply chain disruption delayed delivery of repair parts and severely limited the opportunity to conduct additional research. Further, we found changing the attachments on the cultivator and their proper setup took multiple hours. The grower-collaborator used only the tiller plus rotary blade. A list of vendors of under-vine weed control cultivators was prepared, and it will be made available to growers online.

Figure 4. Example of soil after treatment with hoeing blade (left) and hoeing blade with rotary tiller (right). The tiller helps break up soil and reduce weed root-to-soil contact.