Effect of drop size, water flow, wetting agent and water temperature on hot-water weed control

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 mum) and two water flows (1.2 and 1.71 min(-1) per nozzle) were tested at two energy-dose levels (approx. 455 and 755 U 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. 100degreesC and 120degreesC). 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. (C) 2002 Elsevier Science Ltd. All rights reserved.