Plot-scale field studies were conducted to evaluate the efficacy of steam for the control of cropland weeds in comparison with common herbicides. Weed densities, biomass, or emergence after treatment were measured. Steam (3,200 kg/ha, energy dosage equivalent to 890 kJ/m2, speed of 0.8 m/s) and glyphosate (560 g ai/ha) gave similar control (> 90%) of seedling common lambsquarters and seedling redroot pigweed. Applied at heading, steam was comparable to glyphosate in reducing green foxtail biomass at heading 2 wk after application. Steam applied at a rate of 3,200 kg/ha significantly reduced weed biomass (mixed stand, treated at seedling stage) 9 wk after application compared with the control, whereas steam applied at a rate of 1,600 kg/ha (1.6 m/s) did not. Biomass of downy brome treated with steam was reduced more at anthesis than at the seedling growth stage. Emergence of common lambsquarters, redroot pigweed, and black nightshade was not affected by steam application. Amount of steam applied, weed species, and growth stage are key factors in determining control effectiveness.
Nomenclature: Glyphosate; black nightshade, Solanum nigrum L. #3 SOLNI; downy brome, Bromus tectorum L. # BROTE; common lambsquarters, Chenopodium album L. # CHEAL; green foxtail, Setaria viridis L. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE.
Additional index words: Kochia scoparia L. Schrad., KOCSC, paraquat, pelargonic acid, SALIB, Salsola iberica Sennen & Pau.