Exports of horticultural produce to countries such as Japan presently depend on the use of methyl bromide as a postharvest method for insect control. Methyl bromide has recently been identified as an ozone depleting agent (Anonymous, 1993), and alternative and preferably non-chemical disinfestation methods are required to guarantee continued access to markets with quarantine restrictions. Such treatments need to control the pests without damaging the fruit. HortResearch has been investigating a range of alternatives including controlled atmospheres (Waddell et al., 1990; Whiting et al., 1992), modified atmosphere packaging (Dentener et al., 1992), coolstorage (Batchelor et al., 1985) and heat (Birtles et al., 1991, 1992; Waddell and Birtles, 1992; Lay-Yee and Rose, 1994).

Fig 1: The HAFCAT fruit treatment facility showing the research drawer unit with fruit, and computer control area

Scientific research is frequently carried out on a small scale in equipment that bears little resemblance to any of the scaled-up equipment needed to implement any of these methods under commercial conditions. To overcome this limitation, a High Air Flow Controlled Atmosphere and Temperature (HAFCAT) fruit treatment facility was designed and built in 1992 by the HortResearch Engineering Development Group.

The HAFCAT, located at the Mt Albert Research Centre in Auckland, is designed for precise, programmed control of treatment conditions, in order to define accurate kill times for pests, and tolerance limits for fruit. The HAFCAT is about the size of a shipping container and has a 1.5m³ treatment chamber which can accommodate either a 16-drawer unit for research purposes or two orchard bins of fruit (800 kg in total) for large-scale trials. Each drawer has rubber seals on the top of each side, allowing fruit and insects to be sampled during treatment with minimal disruption to the treatment conditions.

Fig 2: Drawer with insects caged on fruit, and probes measuring fruit flesh temperature

The internal atmosphere is circulated rapidly through the fruit using a centrifugal fan, giving air temperature control to within 0.1°C in the range of -5°C to 70°C and maintaining even temperature throughout the fruit. The HAFCAT is designed for air velocities up to 3m/sec through a 1.4m² cross section. Atmosphere and temperature homogeneity in the fruit is further improved by reversing the direction of the gas flow periodically using automatic switching gates in the air ducts. Maximum heating and cooling rates are about 20°C per hour. There are 48 precision temperature probes to measure fruit temperature.

Humidity is controlled with a proportional steam generator and a small finned dehumidifier coil with ice water circulation. The humidity can be controlled using a sensor in the air duct system, or by using fruit surface temperatures in the chamber. The latter avoids the build up of condensation on the fruit.

Fig 3: Computer monitor showing control of temperature, air speed, relative humidity and gas concentration

The HAFCAT provides computer control of temperature, humidity, gas velocity, and gas composition and was extensively tested before it was used for postharvest research. It has performed extremely well and has been used by entomologists to determine the temperature and time combinations that will kill insects such as leafroller, mites and mealy bug on crops such as apple, nectarine and persimmon. Similarly, plant physiologists have tested the effect of treatments that kill insects, on storage and shelf life of crops such as avocado, strawberry, tomato, apple, persimmon and summerfruit.

A controlled atmosphere capability has recently been added to the HAFCAT by the acquisition of a nitrogen producing plant and oxygen and carbon dioxide monitoring equipment. The combination of heat and controlled atmosphere has the potential to reduce disinfestation treatment times, relative to either of the treatments alone, and therefore reduce chances of damage to fruit.

With this facility HortResearch is one of the world leaders in the research and implementation of non-chemical methods for insect control, thereby assisting the New Zealand fruit growing industry in maintaining and gaining access to markets which have quarantine barriers in place for our fresh exports.

References:

Anonymous, 1993. United States Code Title 42, Sections 6501-7900

Batchelor, T.A., O’Donnell, R.L. and Roby, J.J. 1985. The efficacy of controlled atmosphere coolstorage in controlling leafroller species. Proc. 38th N.Z. Weed and Pest Control Conf.: 53-55.

Birtles, D.B., Waddell, B.C. and Maindonald, J.H., 1991. High temperature disinfestation of nectarines: lightbrown apple moth larvae. Proc. 44th N.Z. Weed and Pest Control Conf.: 61-65.

Birtles, D.B., Waddell, B.C. and Maindonald, J.H., 1992. Mortality responses of Nysius huttoni to a dry-heat disinfestation treatment for apples. Proc. 45th N.Z. Plant Protection Conf.: 269-273

Dentener, P.R., Peetz, S.M. and Birtles, D.B., 1992. Modified atmospheres for the postharvest disinfestation of New Zealand persimmons. N.Z. J. Crop Hort. Sci. 20: 203-208.

Lay-Yee, M. and Rose, K.J., 1994. Quality of 'Fantasia' nectarines following forced-air heat treatments for insect disinfestation. HortScienc 29(6): 663-666.

Waddell, B.C. and Birtles, B.D., 1992. Disinfestation of nectarines of two-spotted mites (Acari: Tetranychidae). N.Z. J. Crop Hort. Sci., 20: 229-234.

Waddell, B.C., Dentener, P.R. and Batchelor, T.A., 1990. Time-mortality response of leafrollers exposed to commercial controlled atmosphere coolstorage. Proc. 43rd N.Z. Weed and Pest Control Conf.: 328-333.

Whiting, D.C., Foster, S.P., van den Heuvel, J. and Maindonald, J.H., 1992. Comparative mortality responses of four tortricid (Lepidoptera) species to a low oxygen-controlled atmosphere. J. Econ. Entomol., 86(6): 2305-2309.