Vacuum Steam Treatment of Metrosideros polymorpha Logs for Eradication of Ceratocystis huliohia and C. lukuohia

A new and devastating disease, rapid ohia death (ROD), in Hawaii led to a state quarantine that regulates interisland transport of ohia wood and plant material to prevent spread of the causal pathogens. Heat treatments of ohia logs in commercial trade were considered for phytosanitary treatment. Vacuum steam (VS) was evaluated for its ability to eradicate the pathogens, Ceratocystis lukuohia and C. huliohia, in main stem logs from ROD-affected forest trees. Replicate loads of three debarked logs (24 to 43 cm in diameter, 1.7 to 2.0 m long) were VS treated at 56 degrees C for 30 min (five loads) or 60 degrees C for 60 min (four loads) at a sapwood depth equal to 70% of log radius. Percentage isolation of Ceratocystis from VS and ambient temperature logs before treatment and summarized by source tree ranged from 12 to 66% and 6 to 31% based on carrot baiting assays of tissue taken from outer and inner sapwood, respectively. No viable Ceratocystis was detected in sapwood locations for the 60 degrees C/60 min schedule or inner locations for the 56 degrees C/30 min schedule after treatment. Only one subsample (0.48%, n = 208) of the latter schedule treatment yielded Ceratocystis. Time needed for treatment ranged from 7.4 to 15 h for the 56 degrees C/30 min schedule and from 8.6 to 19.2 h for the 60 degrees C/60 min schedule. These results demonstrate that VS is an effective and efficient method for treating large-diameter ohia logs that mill owners and regulatory plant pathologists may consider for use in Hawaii.