Efficacy of heat for weed control varies with heat source, tractor speed, weed species and size

Abstract

The efficacy of a direct-fired, tractor-mounted steam weeder was compared with that of a flame weeder. At a tractor speed of 3 km h⁻¹, steam killed 100% of 10-day-old mustard plants, sown as a surrogate weed, and flame killed 92%. Plant survival increased with increasing tractor speed, but was always lower for the steam weeder. Mean survival over all speeds was 40% for steam and 74% for flame. By contrast, for 15 agricultural weed species, at a tractor speed of 3 km h⁻¹ weed survival for both weeders was similar. At 3 km h⁻¹ both methods killed Stellaria media and Veronica agrestis at all growth stages assessed, but neither killed Lolium perenne. Plants of all the other species were killed when the treatments were applied soon after emergence (cotyledon stage), but as the plants increased in size they became more resistant to heat, either because the terminal or axillary meristems were protected by soil, or because meristems were protected by thickened stems and leaves as the plants aged.