Insect and Pathogen Removal Treatments for Exported Hardwood Logs

Research Issue

[photo:] Methyl bromide fumigation of logs under tarp (left in photo) at Port of Tauranga, New Zealand. (J. Juzwik, photo credit)Invasive tree disease microorganisms may be spread locally to internationally when logs from diseased trees are moved in trade. Federal and state quarantine measures have been established to prevent this from happening. In addition, treatment of logs using heat or biocidal chemicals are used to eradicate pathogens and associated insects so movement and/or local utilization of logs can safely occur.  Northern Research Station scientists and their non-Forest Service research partners have been collaborating on evaluation of various phytosanitary treatments of hardwood logs since 1996.

Oak wilt, caused by the fungus Bretziella fagacearum, is a deadly disease of oak species that is only known to exist in the USA. Oak logs obtained from trees harvested in states with oak wilt and destined (e.g. as veneer logs) for international trade are subject to quarantine pre-shipment (QPS) treatment with the chemical fumigant methyl bromide (MB). The MB schedule is one of the highest (240 g/m3 for 72 hours) for QPS commodities due to the oak wilt pathogen. MB is also used for treatment of walnut logs, burls and slabs with bark attached for killing walnut twig beetles and the thousand cankers disease fungus (Geosmitha morbida) so these wood products can be moved from the West Coast to eastern locations in the US. Thousand cankers disease is present in nine states of the Western and five states of the Eastern US and in Italy. The treatment fumigant for both diseases is currently being phased out of use because it leads to degradation of the Earth’s stratospheric ozone.

Rapid `ōhi`a death is an emerging disease known only to exist on four islands of Hawai`i.  The disease has led to extensive mortality of the state’s keystone forest tree species, `ōhi`a (Metrosideros polymorpha) since the disease was first detected on Hawai`i Island in 2011. The current state quarantine prohibits movement of `ōhi`a material off islands known to have one or both fungi that cause the disease (Ceratocystsi lukuohia and C. huliohia) unless materials are certified free of the fungus through laboratory assay or by approved heat treatment.

Economically feasible, environmentally friendly, and treatments suitable for large scale use that kill viable pathogen propagules in hardwood logs are urgently needed. Although results of previously conducted trials with alternative fumigants (e.g. sulfuryl fluoride) and heat treatments of oak logs appear promising, none has yet been approved for USDA APHIS QPS for various reasons (e.g. insufficient data, treatment degrades log quality). Kiln heat treatments of walnut twig beetle and the thousand cankers fungus have proven effective for pest and pathogen eradication, but were only conducted on small diameter and short stem sections.  Effective, affordable and practical heat treatments for commercial size logs of oak, `ōhi`a, and walnut are of great interest due to greatly reduced impact on air and water quality compared to chemical fumigants.

Recent field experiments have documented ability of vacuum steam process to kill the pathogens responsible for oak wilt, rapid `ōhi`a death, and thousand cankers disease in trials with large logs obtained from dying oak, `ōhi`a and walnut trees.  A portable, prototype vacuum steam unit was used to treat 6 foot long and 12 to 28 inch diameter logs.  Dehumidification kiln heating of small diameter `ōhi`a poles (8 foot long by 3 to 4 inch diameter) was also demonstrated to kill the rapid `ōhi`a death pathogens and a treatment schedule has been approved for use by the Hawai`i Department of Agriculture.

[photo:] Placement of temperature probes in oak logs prior to treatment with vacuum steam in portable chamber. (J. Juzwik, photo credit)

Our Research

We conduct log treatment trials with alternative chemical fumigants or with heat (either steam applied under vacuum in sealed chambers or in dehumidification or vacuum kilns) to determine their efficacy at different tested rates for killing: 1) the oak wilt fungus in sapwood of logs from oak wilt killed trees,  2) the walnut twig beetle and the canker pathogen responsible for thousand cankers disease of walnut, and 3) the rapid ‘ohi`a death pathogens in logs from infected `ōhi`a trees.

Expected Outcomes

In collaboration with USDA APHIS PPQ, USDA ARS, and university partners, we seek to develop schedules with alternative treatments that kill the target pathogens at acceptable application rates and feasible costs while minimizing degrade to the log quality as well as harm to the environment and human health. Results of our research will support approved treatments in state quarantines to allow safe log movement and/or safe utilization of diseased logs within the United States.  In addition, our research results will be used by USDA APHIS PPQ to establish acceptable treatment standards with global trading partners for safe international shipment of hardwood logs.

Research Results

Juzwik, Jennifer; Yang, Anna; Chen, Zhangjing; White, Marshall S.; Shugrue, Sarah; Mack, Ronald. 2019. Vacuum Steam Treatment Eradicates Viable Bretziella fagacearum from Logs Cut from Wilted Quercus rubra . Plant Disease. 103(2): 276-283.

Yang, A., Seabright, K., Juzwik, J., Myers, S.W., and Taylor, A. 2019. Survival of the oak wilt fungus in logs fumigated with sulfuryl fluoride and methyl bromide. Forest Products Journal 69:87-95.

Schmidt, Elmer L.; Juzwik, Jennifer; Schneider, Brian 1997. Sulfuryl fluoride fumigation of red oak logs eradicates the oak wilt fungus. Holz als Roh- und Werkstoff 55:315-318.

Research Participants

Principal Investigators

Research Partners

  • Last modified: August 20, 2019