A unique way to support weed control in hazelnut crops

A Zasso electric weeding unit mounted on a tractor demonstrates its capabilities.
Photo by Marcelo Moretti, Oregon State University

An ongoing study in hazelnut orchards offers possible electric weed control (EWC) solutions for other tree nut orchards, particularly in light of increasing herbicide resistance.

Marcelo Moretti, assistant professor at Oregon State University, conducted two studies in 2021 using EWC to manage Italian ryegrass in hazelnut orchards. One study focused on the operating speed needed to provide effective weed management. The second multi-year study focuses on crop safety when using CEE.

Because hazelnuts are harvested from the ground, they are grown conventionally with no cover crops and no tillage. Mowing removes the crowns of weedy plants but requires too many passes to be effective.

For herbicides used in hazelnuts, growers are seeing resistance to all post-emergence herbicides such as paraquat and glufosinate, Moretti says. Thus, a non-chemical weed control alternative is needed.

“The end goal is to control or eliminate seed production (of weeds) in order to get the benefits of ryegrass as a cover crop, but to be able to kill it when not needed,” says Moretti.

With today’s growing herbicide resistance, commercial developers such as Zasso, RootWave and Crop.Zone have developed EWC units focused on meeting the needs of different agricultural users.

HOW THE EWC WORKS

EWC kills weeds with thermal energy. A high-voltage electrode touches the foliage of the plant, allowing an electric current to pass through the plant; the electrical resistance of the plant converts the electrical energy into heat, killing the plant. The higher the plant’s conductivity, the less energy it takes to kill the plant.

An EWC unit is usually mounted on a tractor and the unit’s generator is connected to a PTO (Power Take Off). The generator is coupled to a transformer which increases the voltage. A module controller connects to electrodes which are contained in sets of electric fingers, which provide contact of the applicator with plants and soil. Applicators vary in shape and size, which is dictated by the size of the generator. A 30 kVA generator can handle about four feet at a time.

Along with the equipment setup, the target plant and soil conditions play a role in the effectiveness of the operation. Plant factors such as morphology, developmental stage, water content and plant density all affect the effectiveness of CEE. Young herbaceous plants with high water content and particular root systems are more sensitive to CEE applications.

Soil factors include impedance, mineral composition, texture, moisture, temperature, and porosity. EWC is more effective in soils that have less conductivity, causing the electricity to stay longer in the plants, creating more heat energy. Optimal soils with low conductivity are lighter, sandy, dry and warm.

STUDY RESULTS

Moretti’s study of the operating speed needed for EWC using a Zasso unit shows that 9,000 volts at 2 mph effectively kills Italian ryegrass. When soil conditions are wetter, the unit should be operated at 5000 volts to minimize the risk of damage to the EWC unit or tractor. Although the 5,000 volt setting (at 1 mph) is less efficient, it kills ryegrass.

Moretti’s multi-year Crop Safety Study examines variables such as plant variety, electrical rates and application – with and without suckers. The study will monitor tree growth, photosynthesis rate and yield. Based on the 2021 results, EWC did not adversely affect crop safety.

Although not part of the study, Moretti observed that yellow nutsedge, Canada thistle, field bindweed and horsetail were all susceptible to EWC.

As the study progresses, cost factors will also be assessed.

As expected, the most significant limitation of CEE is the potential to cause fires. In Oregon, the EWC isn’t ideal when it’s too dry (usually after July) or too wet.

EWC provides effective weed control at 2 mph, is initially safe on hazelnuts and is safe for humans. It is compatible with existing production systems, as it does not damage irrigation lines.

Economics to be determined, but initially found to be around $50 per acre to implement – ​​comparable to conventional herbicide application – after initial investment in equipment (Moretti purchased a Zasso unit for $50,000 in 2020 for this study). The environmental benefits are that it leaves no chemical residues and requires no tillage.



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