Can hot water be used to kill Eurasian watermilfoil?

Hot water has been used as a safe and efficient strategy to control unwanted pest species in row crops and to control zebra mussel infestations of water intake and discharge pipes. The goal of this study was to determine if hot water can be used as an effective prevention strategy for killing an aquatic invasive plant species like Eurasian watermilfoil (Myriophyllum spicatum L.) attached to watercraft. In 2006, 20-cm Eurasian watermilfoil fragments with and without an apical meristem were exposed to six different water temperatures ranging from 45 to 80 C for 2-, 5-, and 10-min intervals to see if they could be killed. Fragment viability after treatment was determined in three ways: (a) the presence of living tissue at the end of a 30-day observation period; (b) change in biomass from before treatment to after treatment over the 30-day observation period; and (c) enzyme activity within fragments immediately after heat treatment. The 20-cm fragments were killed at temperatures ≤60 C. All fragments at temperatures ≤60 C lost mass, and enzyme activity was significantly reduced at temperatures ≤60 C for fragments without an apical meristem. Temperature was the most important variable causing death, and time of exposure had little effect at the tested temperatures. These results suggest that using hot water alone to kill fragments of Eurasian watermilfoil attached to watercraft may not be feasible because of the high water temperatures required. More research into additives, such as chlorine or bromine, may reveal ways to reduce the temperature of water necessary to kill plant fragments and make hot water control feasible.