BACKGROUND

The invention relates to the treatment of produce such as fresh and dried vegetables, flowers, ornamental crops, fruit and timber. More particularly the invention relates to a method and apparatus for fumigating pests and diseases from produce and products.

At present it is environmentally unsatisfactory to transport or ship from one area or country to another fresh produce such as fruit or vegetables contaminated by pests such as insects or grubs.

At present denser than air fumigants, such as methyl bromide, have been used to treat the produce prior to export. This necessitates the produce being sealed in an appropriate chamber and methyl bromide gas added to the top of the chamber. The heavier than air methyl bromide gas displaces air in the chamber and results in nearly all the pests being killed when all the air has been displaced from the chamber. Although such a method is satisfactory it has been found that use of the methyl bromide gas is not environmentally or product friendly.

An object of the invention is therefore to provide an environmentally friendly method of treating produce against pests such as insect or grub infestation which method overcomes disadvantages inherent in existing methods and offers a useful alternative choice.

Further objects and advantages of the invention will become apparent from the following description which is given by way of example only.

SUMMARY OF THE INVENTION

According to the invention there is provided a method for killing most pests and diseases on produce such as live, dead or inert fruit, vegetables, flowers, ornamental crops and other products or material, the method including the step of: treating the products or material in a vacuum chamber with a gas fumigant and/or an oxygen depleting gas for a period sufficient to kill the pest(s) after the vacuum chamber has been evacuated to the required level.

The vacuum level may never achieve an absolute level where water boils off the surface of a water bearing produce or material.

The poisonous gas fumigant or oxygen depleting gas is only introduced under vacuum and is only vented when the required time of lethality has elapsed. The poison gas fumigant or oxygen depleting gas can be introduced in a number of ways and in a number of forms.

When the time of lethality has elapsed any remaining gas is vented to the atmosphere, or captured and reused.

A number of further vacuum steps can be applied to the chamber and vented on the treated produce or material for the purpose of reducing chemical residues on the produce or material if required.

The reason for introducing the poison, gas fumigant or oxygen depleting agent (not methyl bromide) under vacuum is that when using a non-airdisplacing fumigant it is impossible to kill insects etc. in hard to reach areas, i.e. under tight leaves etc.

According to a second aspect of the invention there is provided an apparatus adapted to carry out the method according to the invention.

Further aspects of the invention will become apparent from the following description which is given by way of example only.

DESCRIPTION OF THE DRAWING

Figure 1 shows a diagrammatic view of an apparatus adapted for use in killing most pests and diseases on products treated herein.

DESCRIPTION OF THE PREFERRED EXAMPLES

The produce or material to be treated is placed in a vacuum chamber 1 which can be of any construction and dimension. In use after the produce or material is placed in the vacuum chamber 1 it is evacuated to the required level by vacuum pump 2 which can be connected via filter 3 to the chamber

- 4 -

1 . A gas fumigant and/or an oxygen depleting gas from source 4 is applied for a period sufficient to kill the pest(s) after the chamber has been closed/ sealed.

Preferably the vacuum level never achieves an absolute level where water boils off the surface of any water bearing material in the chamber.

The poisonous gas fumigant or oxygen depleting gas is only introduced under vacuum, and after the required treatment time is vented from the chamber 1 via vent 5. From vent 5 the gas is vented to atmosphere, or captured and reused. The poison gas fumigant or oxygen depleting gas can be introduced in a number of ways and in a number of forms.

A number of further vacuum treatment stages can be applied and vented. This ensures the treated produce has few chemical residues on its surface.

The applicants believe that without any one of the following components the system will not work completely satisfactory.

The fumigant is applied under high pressure through a nozzle which causes a physical shearing effect that leads to pesticides that are not fumigants acting as though they are fumigants. This effect is achieved most commonly by dissolving the pesticide in carbon dioxide and applying the fumigant under pressure. This technology was patented by BOC many years ago. The patent has now lapsed and Air Liquide now also uses the method. Generally most applications of this nature are insecticides. New research by

BOC Gases New Zealand, Crop & Food Research and Taranaki Nuchem have led to patented technologies for dissolving more complex molecules in carbon dioxide and this leads to the ability to apply fungicides, antibiotics and sanitizers through this type of system. These new technologies may well have benefits for this application.

Application of the fumigant into a partial vacuum greatly enhances the spread of the fumigant through the load in the fumigator chamber. The underlying physical process is well understood scientifically. In simple terms, in a partial vacuum there are fewer molecules for the fumigant and its propellant to crash into; thus the movement of the fumigant does not lose its impetus as quickly as it would at atmospheric pressure. It can probably be assumed that a combination of the partial vacuum and the pressurised application system leads to excellent dispersal of the fumigant material.

Use of vacuum at the end of the process causes a proportion of the pesticide residue to vaporise off the produce, thus reducing the residues and making it easier to meet CODEX and other guidelines for residual level.

Then applicants postilulate that there may be other configurations of parts of the process that will achieve the same result. For instance the pesticide may be able to be applied through a venturi system using carbon dioxide or another gas as the propellant.

282 PC17NZ97/00084

TRIAL RESULTS

VACUUM FUMIGATION OF ASPARAGUS

Pesticide: Dichlorvos

Formulatuion: Aerosol

Residue Profile (data - milligrams per kilogram)

TIME NO VACUUM AT END VACUUM AT END

OF TREATMENT OF TREATMENT

Immediately after

Fumigation 0.41 0.21

24 Hours after

Fumigation 2.83 0.01

This data show that the use of the vacuum at the end of the treatment significantly reduces the residue loading on the asparagus in comparison to the no vacuum treatment.

All treatments used vacuum of 600mg mercury at the start of the treatment.

INSECTICIDAL EFFICACY

Vacuum No Yes

Aphid mortality 89% 92.3%

Thrips mortality 89.5% 98.2%

COMMENTARY

This trial used a small vacuum tank in which it was difficult to apply the pesticide accurately. Despite this shortcoming the data shows that the

system used reduced residues and enhanced insect mortality, specially for thrips, which are of more importance for quarantine purposes than are aphids.

The treatment chemicals' effectiveness can be altered in many ways such as temperature, amount and strength of chemicals and introduced length of time of treatment and type of product and the way the chemical is introduced into the vacuum chamber.

This method of fumigation does not affect either the phytotoxicity of the produce or its shelf life and usually has acceptable residue levels of the fumigant agent after fumigation.

Residue levels are directly related to the types of poisonous gas used, temperature, the length and strength of treatment and the type of material being treated.

Thus by the invention there is provided a method and apparatus for fumigating pests from produce.

Particular examples of the invention have been described by way of example and it is envisaged that improvement and modifications can take place without departing from the scope of the appended claims.