A direct-fired steam weeder

P>Flame weeders are a valuable weed management tool for organic growers and potentially for non-organic producers, if the number of registered herbicides continues to decrease. However, they have a number of problems including low-energy efficiency, fire risk and reduced performance in windy conditions. Steam has been shown to be a superior means of heat transfer to weeds and therefore steam weeders should outperform flame weeders. However, producing sufficient quantities of steam on tractor-mounted equipment has been problematic, because the standard designs of pressurised steam boilers are ill-suited for agricultural use. The 'direct-fired steam' weeder described here, is considered to resolve this problem, by spraying water as a fine mist directly into hot exhaust gases from a burner, causing it to evaporate quickly, thus negating the needs for a pressurised system. This design is diesel powered, but could also be run on renewable fuels such as vegetable oil, addressing concerns about the use of non-renewable 'fossil fuels' for thermal weeding. This approach is considered both effective in terms of steam generation and sufficiently practical and low enough in inherent risk for agricultural use. Production of commercial steam weeders based on this concept has commenced in New Zealand.