The
              Report
No 78: Fumigation Techniques for Export Wildflowers


The full report
This is a summary of a full report of the same name published by RIRDC (Pub.No.00/41, DAV-149A) by Dr Peter Williams, Institute for Horticultural Development, Agriculture Victoria. Phone: 03 9210 9222; Fax: 03 9800 3521; Email: peter.williams@nre.vic.gov.au.  The report is available in hardcopy or downloadable from this site (under New Plant Products.

A commercial fumigant has been registered for postharvest treatment of Australia 's $27 million annual wildflower export crop after follow-up research which was core funded by the Rural Industries Research and Development Corporation (RIRDC).

The work widened the range of wildflowers able to be successfully fumigated and expanded the variety of insects that could be destroyed.

It followed up the first phase of the project which RIRDC also supported – seeking to identify potential alternatives to methyl bromide,the main fumigant then used for wildflower quarantine treatments.

Methyl bromide damages some flowers and has been identified as an ozone-depleting chemical.It is now being phased out for many uses in accordance with the Montreal Protocol,an international agreement to which Australia is a signatory.

ECO2 FUME ® ((previously named Phosfume ®),a cylinder gas formulation of phosphine is the fumigant now registered as a result of the research.

The project also looked at problems that occur in fumigation chambers and developed approaches to improve the suitable gas retention and dis- tribution,and temperature distribution during fumigation.

This aimed to eliminate hotspots in the fumigation chamber which cause a decline of flowers and reduce flower life.Equally important was the need to avoid cold spots which assist insects to survive.

The study

The objectives of the second-phase research were to:

• modify a new fumigation technique using phosphine to reduce treatment time to less than 16 hours;

• ensure experimental treatments (eg, phosphine and CO2 )provide effective control of insect pests without damaging flowers while enabling more rapid delivery of flowers from exporters to importers;and

• extend testing from the key pests already assessed to other insects known to be associated with cut flowers,to increase confidence in the technique.

Experiments were conducted in a 27 m 3 modified shipping container set up to allow introduction of the aerosol Pestigas ® ((0.4% pyrethrum and 2%piperonyl butoxide with carbon dioxide as a carrier gas),Phosfume ® ((2% phosphine with carbon dioxide as a carrier gas) and carbon dioxide.

Fumigation schedules tested involved combina- tions of Pestigas ® and Phosfume ® with exposure times of 13 and 15 hours and combinations of Pestigas ®,carbon dioxide and Phosfume ® with exposure times of eight and 13 hours. A wide range of cut flowers could be fumigated with any of the fumigation schedules tested without their marketability being impaired.Vase life experiments extended the range of flowers and foliage shown to be suitable for phosphine fumigation with most tests involving combi- nations of Pestigas ® and Phosfume ® with an exposure time of 15 hours.

Some insects survived treatment with Pestigas ® and Phosfume ® for 13 hours but most were killed in 15-hour exposures.

The application for registration,supported by data from both this and the previous project,was made on the basis of applying Phosfume ® alone or in combination with Pestigas ® for 15 hours at a minimum temperature of 15 °C.A change of name from Phosfume ® to ECO2 FUME ® was requested.

In experiments where additional carbon dioxide was applied with Pestigas ® and Phosfume ®, the eight-hour exposure failed to kill all target insects.However,the 13-hour treatment proved effective and could provide a basis for reducing the recommended fumigation time.

The addition of carbon dioxide appeared to be important as 13-hour fumigations without it were not as effective.

Work on refining the fumigation chambers involved developing approaches to improve the suitable gas retention and distribution,and temperature distribution,during fumigation. In a typical situation the heater is run off a thermostat sensor mounted near the walls for safety.This avoids the thermostat sensor getting knocked by movement of people and flower trolleys around the chamber.

Experimentation showed a system where the air is blown over the heater to warm it and then is blown into and through the chamber providing better results than if heaters were in the chamber, which caused undesired hot and cold spots.

Table 1.Effects of Fumigation on Cut Flowers and Foliage Treated with Pestigas ® and ECO2 FUME ® for 15 –16 Hours.

*some leaf blackening. Most of the flowers recorded in the table above were fumigated for 16 hours with 0.02gm -3 of pyrethrum,an initial concentration of 0.84gm -3 of phosphine and a final concentration of 0.56gm -3 .Acacia baileyana and A. pravissima were fumigated for 15 hours with 0.02gm -3 of pyrethrum,an initial concentration of 0.40gm -3 of phosphine and a final concentration of 0.36gm -3 .
 

Fig.2.Diagram of 27 m 3 commercial fumigation chamber used in disinfestation experiments with details of gas circulation and heating system.


 

The results

The phosphine formulation ECO2 FUME ® (formerly Phosfume ®)is now registered for fumigation of cut flowers.ECO2 FUME ® can be applied alone to give a phosphine concen- tration of 700ppm (approximately 1gm -3 )or in combination with Pestigas ® in which case the phosphine concentration can be reduced.

The exposure period is 15 hours at a minimum temperature of 15 °C.

This project has contributed to the registration of an exposure period of 15 rather than 16 hours.It has also demonstrated the potential for a further reduction to 13 hours if additional carbon dioxide is applied.

The range of insects controlled by the fumigation and the range of flowers shown to be suitable for fumigation have been extended.

Summary

This study has demonstrated the effectiveness of 15-hour fumigations with Pestigas ® and ECO2 FUME ® against an extended range of insect pests of wildflowers.The range of wildflowers tested and proved suitable for fumigating this way also has been extended.

Strategies for improving fumigant retention and distribution within a fumigation chamber have been developed.

These results have assisted BOC Gases in obtaining an extension of registration of Phosfume ® to cover fumigation of cut flowers for export,and a change of name to ECO2 FUME ®, which became effective last year.

The registered application conditions are a dosage of 700ppm phosphine (approximately 1gm -3 )for 15 hours at a minimum temperature of 15 °C.

Under these conditions there is minimal damage to flowers and foliage.In all tests arthropods were killed.The only exception was some eggs of two varieties of spotted mites,which survived in some fumigations.

As a result,the registration is for adult and larval stages,not eggs.It is noted that use in conjunction with Pestigas ® can reduce the phosphine concentration required.

This study has contributed to a small reduction of the exposure time required from 16 to 15 hours.It also has demonstrated that with the inclusion of additional carbon dioxide to give a concentration of about 9 –10 per cent,the exposure time for treatment of some pests can be reduced to 13 hours.

Other RIRDC wildflower and native plants reports: