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The influence of drop size, water flow, wetting agent and water temperature in hot-water weed control was studied in laboratory and field experiments on the test weed Sinapis alba L. (white mustard). In a laboratory study, three droplet sizes (approx. values 170, 320 and 490 μm) and two water flows (1.2 and 1.7 l min−1 per nozzle) were tested at two energy-dose levels (approx. 455 and 755 kJ m−2). A laboratory study was also done with or without a wetting agent in the hot water. In a field study the test weed was sprayed with hot water at two temperature levels (approx. 100°C and 120°C). At lower energy doses, there was a significant decrease in fresh weight per plant when the drop size was increased, and the weed-control effect was stronger with the higher water flow than with the lower flow. At higher energy doses there was a significant difference in weed reduction for coarse and medium droplets compared to fine droplets, but not for water flows. The wetting agent increased the effect of hot water by 27% on average. At the same energy-dose level, the reduction in fresh plant weight and plant numbers were generally higher at higher temperature. [Copyright &y& Elsevier]