Rapid `ōhi`a death (ROD) is an emerging disease that threatens the health and survival of `ōhi`a (Metrosideros polymorpha), a keystone forest tree species in the Hawaiian archipelago. The disease has also limited the species’ availability for use in building construction and flooring. Scientists recently discovered that vacuum steam heat treatment kills the two fungal pathogens responsible for ROD in logs and renders them safe for off-island export and within island use.

`Ōhi`a is a keystone species and a critical component of landscape watersheds in native forests of Hawai`i. Rapid `ōhi`a death (ROD) has caused extensive mortality of `ōhi`a on Hawai`i Island since 2011, leading State officials to establish a quarantine to regulate movement of `ōhi`a off the island. Since the quarantine began, shipment of `ōhi`a logs was allowed only if DNA assays failed to detect the causal fungi. This restriction has negatively affected the `ōhi`a forest industry in the State. The need for effective, affordable, and practical methods for treating `ōhi`a logs led a Northern Research Station scientist, working in collaboration with colleagues from University of Hawai`i, Virginia Tech, and the USDA Pacific Basin Agricultural Research Center, to evaluate a vacuum steam treatment of `ōhi`a logs in a portable, prototype unit. Before treatment, the ROD fungi were consistently isolated from an average of 16 and 9 percent of ōhi`a wood samples taken at outer and inner depths, respectively. Treatment involved raising the temperature of the wood at 3.5 to 5.5 inch depths (depending on log diameter) to 133 or 140 degrees Fahrenheit for 30 or 60 minutes, respectively. Using this protocol, the fungi were eradicated from greater than 99.99 percent of the sampled locations based on after-treatment evaluation. Operational testing will be conducted next in cooperative trials with a local mill.