Evaluation of kiln-heating as a phytosanitary treatment for Ceratocystis-infested 'ohi'a (Metrosideros polymorpha) wood

Authors: HUGHES, MARC - University Of Hawaii; JUZWIK, JENNIFER - Us Forest Service (FS); CHEN, ZHANGJING - Virginia Polytechnic Institution & State University; Luiz, Blaine; Keith, Lisa

Submitted to: European Journal of Wood and Wood Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2022
Publication Date: 9/28/2022
Citation: Hughes, M.A., Juzwik, J., Chen, Z., Luiz, B.C., Keith, L.M. 2022. Evaluation of kiln-heating as a phytosanitary treatment for Ceratocystis-infested 'ohi'a (Metrosideros polymorpha) wood. European Journal of Wood and Wood Products. 72(3):207-215. https://doi.org/10.13073/FPJ-D-22-00024.
DOI: https://doi.org/10.13073/FPJ-D-22-00024

Interpretive Summary: ‘Ohi‘a (Metrosideros polymorpha) is the most widespread, highest volume, and the most ecologically and culturally valuable native hardwood tree species in Hawai'i. Unfortunately, ‘ohi‘a and the native forests that once dominated are now threatened by Rapid ‘Ohi‘a Death (ROD), a complex of two fungal diseases, caused by the fungal pathogens Ceratocystis lukuohia and C. huliohia. There is concern about the movement of the aggressive C. lukuohia through the ‘ohi‘a wood trade. There is an urgent need for an effective and practical phytosanitary treatment that can effectively treat ‘ohi‘a wood while preserving wood quality; kiln heat treatments were evaluated for this purpose.

Technical Abstract: Rapid ‘ohi‘a death (ROD) is a serious disease threatening ‘ohi‘a (Metrosideros polymorpha) in Hawaiian forests and is caused by the fungi Ceratocystis lukuohia and C. huliohia. State quarantines have restricted off-island movements of ‘ohi‘a roundwood since 2016 to prevent human-mediated spread of the pathogens. Phytosanitary treatments that eradicate viable propagules of these fungi in ‘ohi‘a poles and posts are urgently needed to expedite safe movement of these products. In this study, heat treatments of Ceratocystis-colonized poles and logs were evaluated using a dehumidification and a vacuum drying kiln on Hawai'i Island. Poles (mean 8.0 cm dia. by 2.3 m long) were placed on top of commercial loads in a kiln box of a dehumidification kiln and subjected to 60° C temperature threshold at pole core and held for at least 5 hrs. during 22 to 34-day kiln runs. In vacuum kiln trials, infected ‘ohi‘a logs (mean 22 cm dia. by 1.7 m long) were subjected to a general schedule of 56° C at 70% log radius depth and held for 30 minutes. Carrot-baiting was used to assay both heat-treated and ambient temperature control wood for presence of the pathogens before and after treatment. Neither Ceratocystis species was isolated from heat-treated wood in either kiln type; whereas, both fungal species were isolated at rates similar to pre-treatment ones for the control logs. Minimal wood degradation was observed in the heat-treated roundwood. Results of this study offer kiln heating as a phytosanitary treatment method that could allow for safe, off-island movement of ‘ohi‘a poles and posts in Hawai'i.