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Heat Treatments (Hot-water Immersion, High Temperature Forced Air, Vapor Heat) As Alternative Quarantine Control Technologies for Perishable Commodities

Hot-water immersion, high temperature forced air, and/or vapor heat are three heat treatment technologies that can be used for post-harvest insect control for perishable commodities such as fresh fruits (e.g., mangos, papaya, persimmon, citrus, bananas, carambola), fresh vegetables (e.g., peppers, eggplant, tomatoes, cucumber, and zucchini squash), bulbs, and cut flowers (Tsang et al. 1995, UNEP 1994, 1992, APHIS 1993, Hansen et al. 1992). Heat treatments for disinfestation of fruit have been used since 1929 when Baker and co-workers developed a vapor heat treatment against the Mediterranean fruit fly (Couey 1989). However, interest in heat treatments waned with the development of chemical fumigants, which could be applied cheaply and easily. Today, with the increasing cost of developing new chemicals and regulatory restrictions on existing ones, interest in heat disinfestation has been revived (Couey 1989).

Currently, methyl bromide is the most commonly used fumigant for controlling quarantine pests on perishable commodities; however, methyl bromide can only be used on certain commodities at specific temperatures and dosages because some commodities are highly sensitive to its use (e.g., certain tropical fruits imported from Hawaii) (Hara et al. 1994). The percentage of global consumption of methyl bromide used to treat perishable commodities is estimated to be 8 percent or 6,500 tonnes (UNEP 1994). Almost half of the methyl bromide used for commodity treatments are for disinfestation of exported fruits and nuts (e.g., papaya, mango, dried fruits, grapes, berries, nectarines, cherries, apples, walnuts, and pistachios). Methyl bromide fumigation is also the predominant treatment used for pests in vegetable shipments (e.g., cucumbers, squash, tomatoes) imported into many countries (UNEP 1994). Lastly, methyl bromide fumigation is widely used by many countries as a standard quarantine treatment for various arthropod-infested flowers and foliage. Across these uses, methyl bromide application rates vary depending on the temperature, exposure period, and commodity (Folwell 1996).

Heat treatment technologies are currently a relatively simple, non-chemical alternative to methyl bromide that can kill quarantine pests (insects and fungi) in perishable commodities, as well as control some postharvest diseases. Unlike methyl bromide, heat treatments do not pose significant health risks from chemical residues and, as a result, are more appealing to consumers than methyl bromide fumigation (Couey 1989). Furthermore, heat has been approved as a quarantine treatment by the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) against pests (mainly fruit flies) for several perishable commodities.

In most cases, heat treatments are performed by the country of origin before a product is exported. The temperature, duration, and application method is both cultivar and commodity specific and must be very precise to kill pests without damaging the commodity. Heat is unsuitable for highly perishable products such as asparagus, nectarines, avocados, or leafy vegetables as their shelf-life and marketability is reduced (UNEP 1994, Couey 1989). Fruit responses to heat varies depending on the condition of the fruit prior to treatment (Mitcham et al. 1994), the commodity concerned, the temperature and duration of treatment, as well as the mode of heat application (i.e., hot air vs. water). If not properly applied, heat treatments (as well as methyl bromide treatments) may result in commodity damage, which typically is manifested as browning fruit surfaces, uneven ripening, and breakdown of the fruit flesh. However, beneficial effects of heat treatment, include reduced susceptibility to chilling injury in avocados and persimmons (Lay-Yee 1994).

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Heat Treatment Methods and Research

The majority of quarantine research on heat treatment methods for perishable commodities is conducted by the USDA, Agriculture Research Service (ARS) in Florida, Texas, Washington State and Hawaii. Many studies have shown that heat treatments do not affect market quality of the commodity and can meet the mandated USDA Probit 9 security level of quarantine pest control, which allows no more than 3.2 survivors out of 100,000 larvae (99.9968 percent mortality) at the 95% confidence level (Baker 1939, McGuire 1991), when the core of the fruit reaches a sufficiently high temperature. Heat treatment methods, as well as approved quarantine heat treatments and on-going research on potential quarantine heat-treatments for perishable commodities, are discussed below.

Hot-Water Immersion: Hot-water immersion consists of submerging the commodity in a hot-water bath at a specific temperature for a specified time based on the commodity being treated and the pests that may be present (APHIS 1993). For perishable food commodities, the mandated probit 9 level of fly control can be achieved by heating the core of the fruit to 43°–46.7° C (109.4°–116.1° F) with exposure times varying from 35 to 90 minutes (APHIS 1993, Gould 1988, Gould and Sharp 1992, Hallman 1989, Sharp 1986, 1990, Sharp and Picho-Martinez 1990, Sharp et al. 1988, 1989, 1989a, 1989b, Sharp and Spalding 1984, UNEP 1994). Variations are noted for different commodities, pest species, and life stages of insect pests. Hot-water is an effective heat transfer medium and, when properly circulated through the load of fruit, quickly establishes a uniform temperature profile (Couey 1989). Hot-water immersion also has the additional benefit of controlling postharvest microbial diseases such as anthracnose and stem end rot (Couey 1989, McGuire 1991). Immersion of non-food perishable commodities (such as cut flowers and bulbs) in hot water (43.3°–49° C (109.9°–120.2° F)) for 6 minutes to 1 hour is effective in destroying insect pests while maintaining product quality (Hara et al. 1994, UNEP 1994).

Hot-water immersion is currently used to successfully treat mangos infested with the Mediterranean fruit fly and several different Anastrepha species of fruit fly before importation into the United States from Mexico, the Caribbean, and Central and South America (APHIS 1993). Research performed by ARS on mangos, which are relatively resistant to heat damage, led to approval by USDA-APHIS of hot-water immersion quarantine treatments for mangos infested with fruit fly immatures (Sharp and Picho-Martinez 1990, Sharp and Spalding 1984, Sharp 1986, 1988, Sharp et al. 1988, 1989, 1989a, 1989b). Successful hot-water immersion quarantine treatments against fruit flies were also developed for papayas (Couey and Hayes 1986), guavas (Gould and Sharp 1992), and bananas (Armstrong 1982), however, these treatments are not currently approved by USDA-APHIS. Hot-water immersion treatment is not recommended for grapefruit, stone fruits (plums, nectarines and peaches), or carambolas (star fruit), because this treatment does not produce probit 9 security and/or produces unacceptable fruit damage in these specific commodities (Hallman 1989, 1991, Hallman and Sharp 1990a, Sharp 1985, 1990). Hot-water immersion of narcissus bulbs is also an APHIS-approved treatment for controlling the Stenearsonemus laticeps mite (UNEP 1994). A promising potential hot-water immersion treatment has also been developed for cut flowers and foliage (Hara et al. 1994).

High Temperature Forced Air: Recirculated air that has been heated and humidified can be forced over fruit surfaces to raise the temperature to a level that is lethal to target pest species. Heated air treatments of 40°–50° C (104°–122° F) (usually at four incrementally increased temperatures) for less than eight hours are becoming more common for fruit fly control in tropical commodities (Armstrong et al. 1989, Gaffney and Armstrong 1990, Mangan and Ingle 1992, UNEP 1994, Sharp 1989a, 1992, Sharp and Gould 1994, Sharp and Hallman 1992). Condensation on fruit surfaces or in the treatment chamber is prevented by keeping the dew-point temperature 2°-3° C below the dry-bulb temperature throughout the duration of the test. This precise control of temperature and relative humidity is advantageous because it prevents condensation inside the treatment area and on the fruit surface thus preventing fruit desiccation and scalding (Gaffney and Armstrong 1990, Sharp et al. 1991).

Fruits shown to tolerate treatment with hot air are mango (Mangan and Ingle 1992, Miller et al. 1991, Sharp 1992, Sharp et al. 1991), grapefruit (McGuire 1991a, Sharp 1989a, Sharp and Gould 1994), navel orange (Sharp and McGuire 1996), carambola (Sharp and Hallman 1992), persimmon (Lay-Yee 1994), and papaya (Armstrong et al. 1989). Hot air is not recommended for avocado, lychee, and nectarine at treatment controlled temperatures needed to disinfest them of quarantine pests (Sharp 1994, Kerbel et al. 1987). USDA-APHIS has approved forced air treatments for grapefruit, papaya, and mango (APHIS 1993). Fruit flies of concern are Mexican fruit fly in grapefruit from Mexico; Mediterranean fruit fly, oriental fruit fly, and melon fruit fly in papaya from Hawaii; and Mexican fruit fly, West Indian fruit fly, and black fruit fly in mango from Mexico (APHIS 1993).

Vapor Heat: Vapor-heat quarantine treatment uses heated air saturated with water vapor to heat perishable food commodities to a specified temperature and holds that temperature for a specified period to ensure that all pests (such as tephritid fruit fly immatures) within the commodity are killed (APHIS 1993, Hallman 1990, Hallman et al. 1990). Typically, the pulp temperature of the commodity is raised by the saturated water vapor to 43.3°–44.4° C (109.9°–11.9° F) during a period of 6 or 8 hours and then held at the required temperature for another 6 or 8 hours (APHIS 1993). For several varieties of cut flowers and foliage, vapor heat treatments of 1-2 hours were greater than 99.7 percent effective in controlling pests (Hansen et al. 1992).

Vapor heat (greater than 90 percent relative humidity) is approved by USDA-APHIS for treatment of clementine, grapefruit, orange, and mangos imported from Mexican fruit fly infested areas and for bell peppers, eggplants, papayas, pineapples, tomatoes, zucchini, and squash imported from areas infested with Mediterranean, Oriental, and Melon fruit flies (APHIS 1993). Vapor heat was found to be effective as a potential quarantine treatment for carambola (Hallman 1990), grapefruit (Miller et al. 1991), codling meth in sweet cherries (Neven and Micham 1996), against the Caribbean fruit fly for tropical cut flowers as well as on foliage against aphids, soft and armored scales, mealybugs, and thrips (Hansen et al. 1992, UNEP 1994).

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Costs

Hot-water immersion, high temperature forced air, and vapor heat are effective quarantine alternatives to methyl bromide fumigation for fruits and vegetables that are not susceptible to heat damage, particularly tropical and subtropical commodities, with proven efficacy against various pests and diseases. In general, methyl bromide treatment systems can range in cost from $21,000 to as much as $291,000, depending on the commodity and quantities being treated (Folwell 1996). A hot-water immersion system, on the other hand, can be easily assembled; and is durable, mobile, and inexpensive (Sharp 1989). While hot water immersion is inherently more efficient than vapor heat as a heat transfer medium and hot water treatment systems can be assembled for less than $8,000 (Sharp 1989, Hara et al. 1994), it can damage some fruits and vegetables. Hot water immersion is the only approved quarantine treatment for mangos. More than 75 commercial hot water treatment facilities are in place in Mexico, Haiti, Puerto Rico, South America, and Florida. The cost for each facility averages about $200,000. Additional facilities are planned or being constructed. APHIS/PPQ must certify each facility and ensure that inspectors are on site.

Alternatively, vapor heat and forced hot-air treatment systems are less damaging to commodities and more versatile than other treatment systems, however they are more expensive. For example, both vapor heat and hot-air treatment systems may initially require larger capital investments ranging from $20,000 to $200,000 for large commercial facilities (Williamson 1996, Sharp 1994, Hara et al. 1994).

A comparison of the capital and operating costs of these technologies is provided in Table 1. Capital costs for both vapor/forced air heat and methyl bromide treatments were calculated by dividing the costs to setup commercial treatment systems (see above) by the tonnes of fruit treated over the 20 year lifetime of the facilities at full capacity (i.e., capacities of 45,372 tonnes/yr. and 275,862 tonnes/yr. for forced air/vapor (for apples) and methyl bromide treatment systems respectively). It was also assumed that treatment systems were operational 250 days of the year and that three forced air/vapor, and one methyl bromide treatment could be completed each day. Operating costs included labor, energy, maintenance, insurance, and chemical costs in the case of methyl bromide.

As shown in Table 1, the capital costs for heat treatments are only slightly higher than that for methyl bromide on a per tonne commodity basis. Operating costs for heat treatments, on the other hand, are eight times higher than those for methyl bromide attributable primarily to longer treatment times and high energy costs. It is likely, however, that operating costs will decrease in the future as the number of commercial heat treatment facilities increases. Although the total costs for perishable commodity treatments with heat are seven times greater than that with methyl bromide on a per tonne commodity basis, the relative proportion of this cost is small when compared to the value of the commodity. Furthermore, other related costs (i.e., harvesting, packaging, storage, processing, and transportation costs to bring the commodity to market) further reduce the percent contribution of heat treatments, making it a relatively insignificant cost overall. As a result, heat treatment can be a viable alternative to methyl bromide for commodity treatment. In fact, Hawaii and many tropical countries have been using heat treatments as an alternative to commodity fumigation for decades (Williamson 1996).

Table 1. Capital and Operating Cost Comparison ($/tonne)
Cost Factor Forced Air-Vapor Heat Methyl bromide
Capital Costs 4.41 1.33
Operating Costs 25.00 3.04
TOTAL 29.41 4.37

Sources: Folwell 1996, Williamson 1996, Sharp 1989, Hara et al. 1994, Sharp 1994.

References

APHIS. 1993. Plant Protection and Quarantine Treatment Manual. United States Department of Agriculture. Animal and Plant Health Inspection Service.
Armstrong JW. 1982. Development of a hot-water immersion quarantine treatment for Hawaiian grown 'Brazilian' bananas. J. Econ. Entomol. 75:787-790.
Armstrong JW, Hansen JD, Hu BK, and Brown SA. 1989. High-temperature, forced-air quarantine treatment for papayas infested with Tephritid fruit flies (Diptera: Tephritidae). J. Econ. Entomol. 82(6): 1667-1674.
Baker, A.C. 1939. The basis for treatment of products where fruit flies are involved as a condition for entry into the United States. USDA Circular 551.
Couey HM. 1989. Heat treatment for control of postharvest diseases and insect pests of fruits. Hort Science Vol. 24(2):198-202.
Couey HM and Hayes CF. 1986. A quarantine system for Hawaiian papaya using fruit selection and a two-stage hot-water treatment. J. Econ. Entomol. 79:1307-1314.
Folwell R. 1996 (August). Personal communication. Raymond Folwell. Department of Agricultural Economics, Washington State University. Pullman, Washington.
Gaffney JJ and Armstrong JW. 1990. High-temperature forced air research facility for heating fruits for insect quarantine treatments. J. Econ. Entomol. 83(5): 1959-1964.
Gould WP. 1988. A hot water/cold storage quarantine treatment for grapefruit infested with the Caribbean fruit fly. Proc. Fla. State Hort Soc. 101:190-192.
Gould WP and Sharp JL. 1992. Hot-water immersion quarantine treatment for guavas infested with Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 85(4):1235-1239.
Hallman GJ. 1989. Quality of Carambolas subjected to hot water immersion quarantine treatment. Proc. Fla. State Hort. Soc. 102:155-156.
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Hallman GJ. 1991. Quality of carambolas subjected to postharvest hot-water immersion and vapor heat treatments. HortScience 26(2):286-287.
Hallman GJ and Sharp JL. 1990. Mortality of Caribbean fruit fly (Diptera: Tephritidae) larvae infesting mangoes subjected to hot-water treatment, then immersion cooling. J. Econ. Entomol. 83(6): 2320-2323.
Hallman GJ and Sharp LJ. 1990a. Hot-water immersion quarantine treatment for carambolas infested with Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 83(4):1471-1474.
Hallman GJ, Gaffney JJ, and Sharp JL. 1990. Vapor heat treatment for grapefruit infested with Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 83(4):1475-1478.
Hansen JD, Hara AH, and Tenbrink VL. 1992. Vapor heat: a potential treatment to disinfest tropical cut flowers and foliage. HortScience 27(2):139-143.
Hara A, Tsang M, Hata T, et al. 1994. Postharvest treatment alternatives for flowers and foliage. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. November 13-16, 1994, pp. 74-1–74-2.
Kerbel EL, Mitchell FG, and Mayer G. 1987. Effect of postharvest heat treatments for insect control on the quality and market life of avocados. HortScience 22(1):92-94.
Lay-Yee M. 1994. Responses of fruit to high temperature disinfestation. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. November 13-16, 1994, pp. 66-1.
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McGuire RG. 1991. Concomitant decay reductions when mangoes are treated with heat to control infestations of Caribbean fruit flies. Plant Disease 75(9):946-949.
McGuire RG. 1991a. Market quality of grapefruit after heat quarantine treatment. HortScience 26(11):1393-1394.
Mitcham EJ, L Neven, and B Biasi. 1994. Can sweet cherry take the heat ? In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. November 13-16, 1994, pp. 68-1–68-2.
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Neven, L.G. and E.J. Mitcham. 1996. CATTS (controlled atmosphere/temperature treatment system): a novel tool for the development of quarantine systems. American Entomologist spring 1996:56-59.
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Sharp JL. 1986. Hot-water treatment for control of Anastrepha suspens (Diptera: Tephritidae). J. Econ. Entomol. 79:706-708.
Sharp JL. 1988. Status of hot water immersion quarantine treatment for Tephritidae immatures in mangos. Proc. Fla. Stat Hort. Soc. 101:195-197.
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Sharp JL. 1989a. Preliminary investigation using hot air to disinfest grapefruit of Caribbean fruit fly immatures. Proc. Fla. State Hort. Soc. 102:157-159.
Sharp JL. 1990. Immersion in heated water as quarantine treatment for California stone fruits infested with Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 83(4):1468-1470.
Sharp JL. 1992. Hot-air quarantine treatment for mango infested with Caribbean fruit fly (Diptera:Tephritidae). J. Econ. Entomol. 85(6):2302-2304.
Sharp JL. 1994. Hot-air--alternative quarantine treatment for methyl bromide fumigation to disinfest fruits. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. November 13-16, 1994, pp. 65-1–65-6.
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Sharp JL and R.G McGuire. 1996. Control of Caribbean fruit fly (Diptera: Tephritadae) in navel orange by forced air. J. Econ. Entomol. 89:in press.
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Sharp JL, Ouye MT, Thalman R, et al. 1988. Submersion of 'Francis' mango in hot water as a quarantine treatment for the West Indian fruit fly and the Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 81(5): 1431-1436.
Sharp JL, Ouye MT, Hart W, Ingle S, et al. 1989. Immersion of Florida mangos in hot water as a quarantine treatment for Caribbean fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 82(1):186-188.
Sharp JL., Ouye MT, Ingle SJ and Hart WG. 1989a. Hot-water immersion quarantine treatment for mangoes from Mexico infested with Mexican fruit fly and West Indian fruit fly (Diptera: Tephritidae). J. Econ. Entomol. 82(6):1657-1662.
Sharp JL, Ouye MT, Ingle SJ et al. 1989b. Hot-water quarantine treatment for mangoes from the State of Chiapas, Mexico, infested with Mediterranean fruit fly and Anastrepha serpentina (Wiedemann) (Diptera: Tephritidae). J. Econ. Entomol. 82(6):1663-1666.
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Tsang, MMC, AH Hara, TY Hata, BKS Hu, RT Kaneko, and V. Tenbrink. 1995. Hot water immersion unit for disinfection of tropical floral commodities. American Society of Agricultural Engineers. 11(3):397-402.
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Williamson, M. 1996 (August). Personal communication. Michael Williamson. University of Hawaii at Menoa. Menoa, Hawaii.

Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.

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