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Notice of Decision To Revise a Heat Treatment Schedule for Emerald Ash Borer

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Animal and Plant Health Inspection Service, USDA.




We are advising the public of our decision to revise a heat treatment schedule for the emerald ash borer in the Plant Protection and Quarantine Treatment Manual and to retain the current treatment schedule with a different treatment number. Based on the findings of a treatment evaluation document, which we made available to the public for review and comment through a previous notice, we believe that the revised treatment schedule will be sufficient to treat emerald ash borer.


Effective Date: January 19, 2011.

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Dr. Inder P. S. Gadh, Senior Risk Manager-Treatments, Regulations, Permits, and Manuals, PPQ, APHIS, 4700 River Road Unit 133, Riverdale, MD 20737-1236; (301) 734-8758.

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The regulations in 7 CFR chapter III are intended, among other things, to prevent the introduction or dissemination of plant pests and noxious weeds into or within the United States. Under the regulations, certain plants, fruits, vegetables, and other articles must be treated before they may be moved into the United States or interstate. The phytosanitary treatments regulations contained in part 305 of 7 CFR chapter III (referred to below as the regulations) set out standards for treatments required in parts 301, 318, and 319 of 7 CFR chapter III for fruits, vegetables, and other articles.

In § 305.2, paragraph (b) states that approved treatment schedules are set out in the Plant Protection and Quarantine (PPQ) Treatment Manual.[1] Section 305.3 sets out a process for adding, revising, or removing treatment schedules in the PPQ Treatment Manual. In that section, paragraph (a) sets out the process for adding, revising, Start Printed Page 3078or removing treatment schedules when there is no immediate need to make a change. The circumstances in which an immediate need exists are described in § 305.3(b)(1).

In accordance with § 305.3(a)(1), we published a notice [2] in the Federal Register on August 25, 2010 (75 FR 52305-52306, Docket No. APHIS-2010-0059), in which we announced the availability of a treatment evaluation document (TED). The TED recommended revising treatment schedule T314-a, which provides a heat treatment schedule for ash logs, including firewood, and all hardwood firewood that are moved from emerald ash borer (EAB, Agrilus planipennis) quarantined areas. The TED also recommended retaining the current T314-a as a general treatment for various wood pests (rather than just EAB); we stated that we planned to redesignate this treatment schedule as T314-c in the Treatment Manual.

We solicited comments on the notice for 60 days ending October 25, 2010. We received four comments by that date, from State governments. The comments are discussed below.

The previous T314-a had indicated that ash logs, including firewood, and all hardwood firewood must be heat treated at 71.1 °C (160 °F) for 75 minutes in order to kill any EAB that may have infested those products. The TED concluded that this treatment could be changed to heat treatment of those products at 60 °C (140 °F) for 60 minutes. The TED cited three publications in support of this conclusion. The commenters addressed each of these publications.

Myers et al. (2009) [3] evaluated a number of possible time-and-temperature combinations for heat treatment of logs and firewood and found that a minimum heat treatment of 60 °C for 60 minutes was an effective quarantine treatment of ash firewood against EAB.

One commenter stated that the experiment in Myers et al. (2009) that most closely approximated the treatment described in the TED (i.e., 60 °C for 60 minutes) used a wet bulb depression method of heating (moist heat), which greatly increased the rate of heating. This commenter stated that, because the recommended revision to T314-a does not include the rate or method of heating, it may or may not replicate the treatments used in Myers et al. (2009). The commenter stated that given the potential differences in heating methods, it is safer to go with one of the higher temperatures evaluated in Myers et al. (2009), 65 °C for 30 minutes, which also produced no EAB emergence.

The commenter is incorrect; while other experiments in Myers et al. (2009) were evaluated with wet bulb depression, the experiment with heat treatment at 60 °C for 60 minutes was conducted in ambient humidity.

Another commenter stated that, in experiment 2 in Myers et al. (2009), because of the use of the wet bulb depression, the heating rate of the wood was 30 percent faster than in any of the other experiments.

The heating rates in all of the Myers et al. (2009) experiments are higher than what would be found in most commercial kilns, though there are some exceptions. In any case, we have not found generally that heating rates affect treatment efficacy; APHIS does not have any heat treatments that specify heating rates. Rather, the key to effective heat treatment is maintaining the treated articles at the stated minimum temperature for the stated time.

One commenter stated that the firewood used in experiment 2 was not handled in a similar fashion to that used in the other experiments. The pieces used in this experiment were cut approximately 30 days prior to testing, and stored at 4 °C. The commenter stated that the authors mention this inconsistency and state, “ * * * this would have resulted in some additional drying of the firewood before the treatment. Although the extra storage did not impact emergence from the control groups, it may have increased the insects' susceptibility to the heat treatments as the wood moisture content would have decreased over this period.”

Holding firewood for 30 days prior to treatment is not unrealistic for a commercial operation. In addition, the control group used in that experiment clearly indicates the presence of viable EAB in the wood at the time of treatment. Finally, the experiment involving treating the firewood at 60 °C for 60 minutes used firewood held for fewer than 10 days.

Myers et al. (2009) states: “In experiment 3, adult emergence was observed in firewood in 45, 50, and 55 °C treatments for both 30- and 60-min time intervals, whereas no emergence occurred in any of the 60 or 65 °C treatments.” One commenter expressed concern about the analysis of the data that led to this conclusion. This commenter stated that, in the treatment that is referred to as 60 °C, that temperature was in fact the “target temperature” in the experiment (60 °C for 60 minutes). The firewood in that experiment had a mean treatment temperature of 62.2 °C±0.2 and a maximum treatment temperature of 63.8 °C±0.4. The treatment with a target temperature of 55 °C for 60 minutes actually produced a mean and maximum treatment temperature that was closer to 60.0 °C. In that experiment, the commenter noted, some EAB did survive.

The experiments in Myers et al. (2009) were conducted consistent with how APHIS heat treatment schedules are administered. APHIS heat treatment schedules do not indicate a mean temperature to be held during the treatment period; rather, they specify a minimum temperature that must be maintained throughout the treatment period. Thus, the experiment in which firewood was held at 60 °C for 60 minutes corresponds to how treatment schedule T314-a will be administered.

One commenter stated that the results of the Myers et al. (2009) experiments on EAB prepupae that were removed from logs and subjected to various time-temperature combinations should not be considered applicable to the discussion of a heat treatment standard for firewood, except to note that the treatment time and temperature were sufficient to kill EAB. Since these treatments occurred in petri dishes, the commenter stated, the raw data from this experiment cannot be compared to the raw data from the experiments that used real pieces of firewood.

We agree with this commenter. We interpreted the experiments on EAB prepupae as providing useful information corroborating the results of the other experiments in Myers et al. (2009).

The TED cited two other publications, by McCullough et al. (2007) [4] and Nzokou et al. (2008),[5] as consistent with the results of Myers et al. (2009). One commenter noted that McCullough et al. (2007) states: “No A. planipennis survived when chips were exposed to 60 °C for ≥ 2 h in either of our studies, but 50% of the prepupae did survive 1 h of exposure to 60 °C.” The commenter Start Printed Page 3079stated that this statement would not support the recommendation to change T314-a.

That specific statement in McCullough et al. (2007) appears to be in error; the rest of the publication describes experiments in which wood chips were held at 60 °C for 20 minutes and 2 hours, with no experiment involving treatment at 60 °C for 60 minutes. As noted in the TED, McCullough et al. (2007) reported that EAB prepupae were killed at 60°C for 120 minutes, but not when held at the same temperature for 20 minutes.

Another commenter noted that McCullough et al. (2007) did not test treatment at 60 °C for 60 minutes and stated that the publication thus did not provide any data to support the current 30-minute treatment recommendation for firewood.

The treatment revision recommended in the TED was for treatment at 60 °C for 60 minutes, not 30 minutes. The McCullough et al. (2007) data is thus consistent with the TED's recommendation. We also note that McCullough et al. (2007) does not evaluate the treatment schedule described in the TED; McCullough et al. (2007) used small chips, which are more prone to drying during treatment than a piece of firewood, and monitored air temperature, not wood temperature, which would be lower. The TED cited the McCullough et al. (2007) results as being consistent with the recommended revision of T314-a, not as supporting it directly.

One commenter stated that Nzokou et al. (2008) did not test logs treated at 60 °C for 60 minutes. Another commenter noted that Nzokou et al. (2008) concludes with the suggestion that “kiln heat treatment at a level of 65 °C or greater could be an effective sanitization process for EAB-infested logs and wood materials.” These commenters stated that Nzokou et al. (2008) does not support lowering the current treatment requirement to 60 °C for 60 minutes.

As with McCullough et al. (2007), the TED cited Nzokou et al. (2008) as consistent with the recommended revision to T314-a, not as supporting it. Nzokou et al. (2008) observed the emergence of emerald ash borer from logs heated to 60°C for 30 minutes, but there was no emergence at 65°C for 30 minutes.

While Nzokou et al. (2008) conclude that 65 °C is an effective treatment, the authors did not test treatment times longer than 30 minutes. For kiln heat treatments of firewood, we prefer to extend treatment times rather than increase treatment temperature. A typical firewood kiln will operate 12 to 36 hours (or longer) during a heat treatment run, so it is not difficult to extend a treatment by 30 minutes. In addition, many of the existing kilns in the United States use hot water to produce heat. That design limits the internal temperature of the kiln to approximately 70 °C and makes it difficult to produce internal wood temperatures greater than 60 °C. Thus, requiring heat treatment at 65 °C for 30 minutes treatment would be as effective as the revised T314-a but may not be as practical to administer.

One commenter stated that, in the commenter's experience with heat treatment of firewood, the current heat treatment requirements require a core temperature reading to be at least 160 °F for 75 minutes on the largest pieces of firewood being treated. In practice, of course, actual air temperatures inside the heat treatment chamber can vary greatly, along with the time required to heat the chamber and its contents to this minimum standard. Both the time and temperature can be greatly influenced by the way the chamber is heated, moisture content of the wood when it is placed into the chamber, outside air temperature, size of the largest firewood pieces, arrangement of the firewood inside the chamber, and management of the air flow inside the chamber. This variability is made up for by the current treatment, the commenter stated, but could be detrimental if a borderline or unproven schedule is implemented, such as the proposed schedule.

APHIS heat treatment schedules identify the time for which a specific minimum temperature must be achieved; they do not set that minimum temperature to take into account variability at a facility. Rather, heat treatment facilities are certified in accordance with the requirements in § 305.8 of the regulations as capable of properly administering treatments. The certification process allows us to determine if and where any cold spots may exist. In addition, each facility is required to record temperatures of the firewood during the heat treatment process and maintain records of each run. We recertify kilns annually to assure that heat treatment facilities continue to comply with the compliance agreement under which treatments are conducted. Thus, the concerns the commenter cites are addressed through the treatment facility certification process. The previous T314-a heat treatment schedule that the commenter refers to was not developed to address variability but based on the scientific evidence available to us at the time.

One commenter expressed concern that the proposed T314-a for hardwood firewood moved from EAB quarantined areas is not sufficient to address the risks presented by other quarantine pests that may be present in those areas.

We recognized the commenter's concern in the TED, which recommended retaining the current treatment schedule of treatment at 71.1 °C for 75 minutes for other quarantine pests in wood articles as described in §§ 319.40-5 and 319.40-6 of our regulations governing the importation of logs, lumber, and other unmanufactured wood articles. If other pests for which treatment at 71.1 °C for 75 minutes is required are present in an area, ash logs and hardwood firewood moved interstate from that area will be required to be treated in accordance with T314-c, which contains the schedule of heat treatment at 71.1 °C for 75 minutes.

Three commenters raised operational concerns with regard to having two treatments, T314-a and T314-c, for hardwood firewood moved interstate.

APHIS policy is to revise treatments to make them less stringent when scientific evidence supports doing so. Any operational issues that may arise from revising T314-a and adding T314-c as described in the TED are outside the scope of this action. We plan to work with State and local cooperating agencies, as well as the firewood industry and other private cooperating entities, to implement the new treatment schedules and resolve any confusion that may result.

Therefore, in accordance with the regulations in § 305.9(a)(2), we are announcing our decision to revise treatment schedule T314-a as described in the TED. We have also decided to retain the current T314-a as a general treatment for various wood pests (rather than just EAB) and to redesignate this treatment schedule as T314-c in the Treatment Manual.

The new treatments will be listed in the PPQ Treatment Manual, which is available at the Web address and mailing address in footnote 1 of this document.

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Authority: 7 U.S.C. 7701-7772 and 7781-7786; 21 U.S.C. 136 and 136a; 7 CFR 2.22, 2.80, and 371.3.

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Done in Washington, DC, this 12th day of January 2011.

Kevin Shea,

Acting Administrator, Animal and Plant Health Inspection Service.

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1.  The Treatment Manual is available on the Internet at​import_​export/​plants/​manuals/​index.shtml or by contacting the Animal and Plant Health Inspection Service, Plant Protection and Quarantine, Manuals Unit, 92 Thomas Johnson Drive, Suite 200, Frederick, MD 21702.

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2.  To view the notice, the treatment evaluation document, and the comments we received, go to​fdmspublic/​component/​main?​main=​DocketDetail&​d=​APHIS-2010-0059.

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3.  Myers, S. W., I. Fraser, and V. C. Mastro. 2009. Evaluation of heat treatment schedules for emerald ash borer (Coleoptera: Buprestidae). J. Econ. Entomol. 102: 2048-2055.

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4.  McCullough, D.G., T.M. Poland, D. Cappaert, E. L. Clark, I. Fraser, V. Mastro, S. Smith, and C. Pell. 2007. Effects of chipping, grinding and heat on survival of emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) in chips. J. Econ. Entomol. 100: 1304-1315.

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5.  Nzokou, P., S. Tourtellot, and D. P. Kamden. 2008. Kiln and microwave heat treatment of logs infested by the emerald ash borer (Agrilus planipennis (Fairmaire) C Coleoptera: Buprestidae). For. Prod J. 58: 68-72.

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[FR Doc. 2011-984 Filed 1-18-11; 8:45 am]