A steaming method for killing weed seeds produced in the current year under untilled conditions

• We could achieve 90% seed mortality using steam application on soil surface.
• Higher temperature and shorter duration than other methods enable to kill seeds.
• The suited operating speed for steam application differed across treatment seasons.
• Suitable steam conditions also differed across weed species and treatment seasons.

Steam application is an effective method for controlling weed seed infestation but is not efficient for applying to a broad area in open fields. To overcome this problem, we proposed a steam application method involving localized treatment of weed seeds on the soil surface produced during the current year under untilled conditions. We investigated the effects of high temperature and short exposure time depending on the operating speed on weed seed mortality. Further, we determined how seed mortality varied with steam conditions and treatment season in open fields. The operating speed increased with decreasing maximum temperature and duration times above 60 °C. Regardless of treatment season, saturated steam produced heat at a more stable temperature than superheated steam. Seed mortality of 90% was achieved at an operating speed of 0.3–1 km h−1 for Ipomoea lacunosa and 0.3–1.6 km h−1 for Lolium multiflorum, suggesting that the operating speed differed across treatment seasons. Suitable steam conditions also differed across weed species and treatment seasons. Thus, the steaming method modified according to weed species and treatment season might require shorter exposure times to disinfest weed seeds.