Effectiveness and energy efficiency of pulsed electric microshocks for killing young weeds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū, New Zealand
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2024-08-30
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Alternatives to herbicides are needed due to increased occurrence of herbicide resistance, regulatory restrictions, and consumer preferences. This thesis presents results of research into ultra-low energy weeding systems using very short pulses of very high voltage direct current electricity. Proof-of-concept trials found that small Capsella bursa-pastoris weeds in a fallowed vegetable bed were killed by single 10 kV pulses of about 5 J. Grasses were harder to kill. In replicated greenhouse trials, small Chenopodium album plants collapsed, and three quarters were dead 4 weeks later. Shocks instantly impacted small Lolium multiflorum plants, but death rates were very low.
Applying multiple-pulse treatments using a probe electrode precisely placed against the stems of bagged plants showed Amaranthus powellii could be well controlled, but Solanum nigrum could generate adventitious roots and recover. While L. multiflorum treated with probe-electrodes again had a high survival rate, biomass reduced with increasing energy doses. Seeking a more practical application method, I showed that a flat plate electrode applying multiple pulses to the plants’ leaves or to the plant pressed against the soil was effective, with Polygonum aviculare, A. powellii, Amaranthus deflexus and Solanum nitidibaccatum weeds successfully controlled. While only half of L. multiflorum plants were killed, data indicated a 90% death rate would be achieved at 200 J plant⁻¹. Moving outdoors, I treated small plants in the ground using flat plate electrodes and achieved excellent control of Lepidium didymum, A. powellii and L. multiflorum.
Flat-plate electric weeding using pulsed microshocks is a novel development that gives effective control of individual or small clumps of weeds in the field. Observations of plant responses during almost 30 trials suggest the mode of action is not cell rupturing from resistive heating as usually claimed for electric weeding, but an increase in membrane permeability. My trials showed that small broadleaf weeds and grasses can be controlled at a density of 5 plants m⁻² using less than 1 MJ ha⁻¹, a fraction of the energy required by any other weeding system. Combined with automation technologies and artificial intelligence, it offers an autonomous, low-energy, non-chemical, selective weeding system for integrated management of weeds.
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electric weeding, non-chemical weed control, site-specific weed management, pulsed electric fields, pulsed microshocks, herbicide resistance management