Heat Treatment of Firewood for Emerald Ash Borer: Case Studies

The emerald ash borer—most of us have heard of this exotic species that is killing so many of our beloved ash trees. The Forest Service and others are working hard to stop its spread and the recent article, Heat Treatment of Firewood for Emerald Ash Borer (Agrilus planipennis Fairmaire): Case Studies by Xiping Wang, Richard D. Bergman, Brian K. Brashaw, and Scott W. Myers, provides current research.

Emerald ash borer

Emerald ash borer

The movement of firewood within emerald ash borer- (EAB) infested states and into adjoining areas has been a contributor to its spread throughout the United States and Canada. In an effort to prevent further human-aided spread of EAB and to facilitate interstate commerce, the USDA Animal and Plant Health Inspection Service and cooperating states in the EAB quarantine have established a heat treatment process to be used as a mitigating treatment to allow movement of firewood from EAB quarantine areas.

Firewood producers have since been faced with challenges implementing heat treatment processes and meeting the treatment standard for firewood. This article presents four case studies, conducted at firewood heat treatment facilities, with the aim of addressing these challenges. Different heat treating strategies were used in each of these facilities to meet the particular needs of the operation. A step-by-step operating procedure was developed for heat treatment operation and temperature monitoring of both kiln and firewood samples during the heating process.


Firewood baskets are placed into the kiln. The monitoring firewood samples were placed in the three baskets of the back row in the lower level. One instrumented piece was placed into each basket.

This study, published in the Journal of Forestry, July 2014, evaluated different types of temperature sensors and probes and data loggers for their applicability in the heat treating process and constructed easy-to-install temperature monitoring systems suitable for field heat treatment operations of different scales. Through the four case studies, the study demonstrated the effectiveness of a step-by-step operating procedure for conducting heat treatment runs and monitoring the temperatures of both the kiln chamber and firewood samples during the heat treatment process.

The case studies also revealed some potential errors when the operating procedure was not carefully followed. These include the following: not selecting the largest firewood pieces for temperature monitoring; inaccurate or inappropriate temperature sensor installation; and monitoring samples not allocated at the cold spots. Each of these issues could potentially compromise the effectiveness of the heat treating process and result in an underestimation of the time required to achieve the treatment requirements. Further research is needed to examine the possibility of developing generic thermal verification guidelines that are primarily based on kiln conditions (dry-bulb and wet-bulb temperatures of the heating medium), thus eliminating the need for physically monitoring the core temperatures of the firewood samples.