Weed control by water steam using a self-propelled machine equipped with a condensation chamber

In the last years public concern about environmental pollution due to pesticides has been growing and, among other consequences, this situation boosted research on physical weed control methods as an alternative to herbicides. Recent researches have been carried out about the feasibility of the use of water steam as a replacement of chemical weeding in particular conditions where no chemical residues are allowed, e.g. in organic farming. Tests carried out with a steam jet directed on the weeds confirmed its effectiveness in killing weeds, but also showed high energy requirements and very low working speed despite the high thermal contents of steam. To improve weed control efficiency, a chamber where the steam can condense on the surfaces of the plants was developed in order to exploit the high efficiency of latent heat transfer of condensing water steam, as suggested by a theoretical analysis. Preliminary lab test confirmed the validity of this approach, showing higher energy efficiency in respect to the direct application. Following these encouraging results a self-propelled machine was equipped with a condensation chamber specifically designed to perform field tests on 5 species (two dicots and three grasses), to be treated at two different growth stages. The dose-response curves obtained after treating the plots with 5 to 6 different travel velocities showed good effectiveness. The dicots were effectively controlled with doses lower than 500 kJ m-2 (corresponding to 2 km/h travel speed), while maize was able to regrow after the treatment, requiring about twice the dose.