Killing weeds with pulsed microshocks from a flat plate electrode
This is the third post with details of Dan’s research into electric weeding undertakenas part of the AgResearch lead Herbicide Resistance management project. In this work, he was looking at easy ways to apply very small electric shocks to weeds, without having to carefully place a point-electrode against the plant stem. The electric spatula describes the flat-plate electrode he came up with; it is a out the size and shape of a kitchen spatula or fish-slice and could be used as a hand-weeding unit or part of a robotic system. The research was published in the Journal of Agronomy and is published Open Access, so anyone can download the full paper for free!
One of the interesting observations is that when plants such as redroot (Amaranthus powellii) are treated with pulsed microshocks, they don’t explode as can be seen with high energy electric weeder systems. In fact, usually nothing happens at all for several days, Dan gets worried “it didn’t work”, and then the plants start to senesce or bleach, before collapsing and dying. The picture above shows healthy plants that were not treated, and other plants in various stages of collapse and death depending on the amount of energy applied.
The paper uses megajoules (MJ) as the measure of energy needed per hectare. As a guide, a litre of diesel contains about 38 MJ of energy, or alternatively, 1 MJ is the amount of energy in about 26mL of diesel.
Abstract
Seeking an easy-to-deploy, energy-efficient, non-herbicide weed control method, we tested a flat-plate electrode to apply pulsed electric microshocks (PMS) to a grass and four broadleaf weed species. The method could be deployed via a hand-held unit or as part of a fully automated system to control escape-weeds in field crops. The effectiveness of treatments and relative energy discharges applying similar electric doses to the plant leaves or to the plant when pressed to the soil by a flat-plate electrode were compared.
The method killed only half of the treated ryegrass (Lolium multiflorum “Winter Star”) plants, well below our target rate, but significantly reduced growth rates and indicated an effective treatment of
< 1.0 MJ ha-1 for treating five plants m-2 is possible.
Wireweed (Polygonum aviculare), redroot (Amaranthus powellii), prostrate amaranth (Amaranthus deflexus), and hairy nightshade (Solanum nitidibaccatum) plants were successfully controlled with the energy required to kill 100% of seedlings varying from 0.1 to 0.9 MJ ha-1, indicating that broadleaf weeds are more susceptible. This easily met our target effectiveness and efficiency goals. The discharged energy increased when the electrode pressed the plant to a dry soil surface rather than to leaves only and increased further when pressed to a wet soil surface.
