The main remedy in Australia, the fumigant methyl bromide, has been identified as an ozone depleting chemical and many of its uses are being phased out in accordance with the Montreal Protocol, an international agreement to which Australia is a signatory.

Alternative fumigant treatments need to be found. This report documents research on the development of techniques to replace methyl bromide.

Promising new technique

The benefits of Phosfume

Phosphine treatment also provides an alternative to insecticidal dips which may leave undesirable residues on flowers. Capital costs of establishing a fumigation facility are greater than for dipping, but this is compensated by reduced labour costs as dipping is more worker intensive.
 

Objectives: controlling insects without damaging flowers

• develop effective postharvest fumigation techniques as alternatives to methyl bromide for disinfesting Australian wildflowers destined for export; and

• ensure that new fumigation techniques would give rapid control of insect pests without damage to flowers.

Laboratory tests

Various forms of phosphine were trialled, with Phosfume« proving the most successful. Phosfume« is a cylinder gas phosphine formulation (2% phosphine with carbon dioxide as a carrier gas).

The fumigations were completed within a working day which mirrors the time required for methyl bromide treatments. A range of flowers also was screened with methyl bromide for comparison.

Fumigant concentrations used were based, where possible, on established quarantine dosages. They ranged from 0.1 mg Lû1 for phosphine to 32 mgLû1 for methyl bromide and exposure times ranged from half-an-hour for hydrogen cyanide to six hours for phosphine.

In some of the tests, flowers from various areas of Australia were air freighted in cartons to Canberra. On arrival, their stems were trimmed, placed in water and stored in a cool room at 4?C. Bunches of flowers were taken out of water and placed in 63.5 litre metal drums at 20?C for treatment with various fumigants.

Control bunches of flowers were placed in drums but not fumigated.

Following fumigation, the flower stems were trimmed, placed in fresh water and aired under a fume hood for one hour. They were then returned to the cool room. When all treatments had been completed, the flowers were repacked into cartons and air freighted back to the growers for assessment.  Large-scale tests followed

After these initial laboratory experiments identified phosphine as the most suitable chemical assessed, large-scale fumigations were undertaken.

These involved a 27m3 fumigation chamber (see Fig.1) fitted out for use of 'cylinder gas' aerosols: Pestigas (0.4% pyrethrum and 2% piperonyl butoxide with carbon dioxide as a carrier gas) and Insectigas (5% dichlorvos with carbon dioxide as a carrier gas), which are registered for disinfestation of cut flowers.

Phosfume was substituted for the Insectigas«. With 16 hours exposure at a temperature of 15?C or above, the 1 gmû3 concentration of phosphine controlled several problem pests.

Additionally it was found that if Pestigas« was applied to give a concentration of 0.02 gmû3 of pyrethrum, followed 10 minutes later by Phosfume« applied to give a concentration of 0.42 gmû3 of phosphine, a similar or better result for control particularly of eggs of the species tested was obtained. (See Table 1)

Table 1.
 

Temp. C	Pestigas g	Phosphfume kg	Phosphine concentration gm-3		Leaf rolling moth Strepsicrates ejectana						Twospotted mite Tetranychus urticae
			Initial	Final	Larvae			Pupae			Eggs			Larvae			Adults
					Live	S.aff	Dead	Live	S.aff	Dead	Live	S.aff	Dead	Live	S.aff	Dead	Live	S.aff	Dead
20.5 (19.6-22.8)	120	3.12	1.4	1.0		0	18		0	24	0	0	50	0	0	900	0	0	599
20.0	0	0	0	0	18	0	0	24	0	0	50	0	0	238	0	0	599	0	0
21.0 (16.3-23.1)	160	2.02	1.0	0.6	0	0	45	0	0	12	0	0	486	0	0	238	0	0	402
20.0	0	0	0	0	45	0	0	12	0	0	486	0	0	238	0	0	402	0	0
21.9 (19.5-26.7)	120	2.04	1.0	0.7	0	0	103	0	0	1	0	0	945	0	0	219	0	0	337
20.0	0	0	0	0	103	0	0	1	0	0	945	0	0	219	0	0	337	0	0
18.1 (17.5-18.9)	120	1.12	0.27	0.15	0	0	75	0	0	47	0	0	1750	0	0	719	0	0	1226
20.0	0	0	0	0	75	0	0	47	0	0	1750	0	0	719	0	0	1226	0	0
18.2 (16.1-22.2)	140	1.4	0.32	0.19	0	0	96	-	-	-	0	0	546	0	0	246	0	0	325
20.0	0	0	0	0	96	0	0	-	-	-	546	0	0	246	0	0	325	0	0
S. aff = Severely affected.

 

Observations of the effects of Pestigas« and Phosfume treatments on a range of flowers are summarised in Table 2.

Table2

Species of cut flowers/foliage	Common name	Vase life observations after
		1 day		7 days
Andresonia simplex	Spiked Andresonia	good		good
Anigozanthos pulcherrimus	Kangaroo Paw	good		good
Banksia baxteri	Bird's Nest Banksia	good		good
Banksia coccinea	Scarlet Banksia	good		good
Banksia prionotes	Acorn Banksia	good		good
Banksia speciosa	Showy Banksia	good		good
Brunia albiflora	Albiflora	good		good
Chamelaucium uninatum	Geraldton Waxflower	good		fairly good
Dryandra nobilis	Golden Dryandra	good		good
Eucalyptus (foliage)	Eucalyptus	good		good
Gerbera	Transvaal Daisy	good		good
Gloriosa rothschildiana	Gloriosa Lily	good		good
Lachnostachys verbascifolia	Lambstail	good		good
Leucadendron discolor (male and female)	Discolor	good		good
Leucadendron coniferum	Sablosum	good		good
Leucadendron floridum	Floridum	good		good
Leucadendron eucalyptifolium	Eucalyptifolium	good		good
Leptospermum rotundifolium	Round Leaf Tea Tree	good		fairly good
Leucadendron	Safari Sunset	good		fairly good
Leucadendron salignum	Salignum	good		good
Leucadendron	Silvan Red	good		fairly good
Leucospermum cordifolium	Sun Burst	good		good
Ozothamnus diosmifolium	Rice Flower	good		good
Protea cynaroides	King Protea	good		good
Protea	Pink Ice	good		fairly good
Protea repens	Honey Protea	good		good
Podocarpus drouynianus	Emu Grass	good		good
Scholtzia laxiflora	Red Scholtzia	good		fairly good
Serruria florida	Blushing Bride	good		good
Telopea speciosissima	Waratah	good		good
Thryptomene calycina	Grampians Thryptomene	good		fairly good
Verticordia nitens	Yellow Morrison	good		good
Some flowers tended to fall more readily 7days after fumigation than the untreated controls; these were waxflowers, tea tree, Scholtzia and Thryptomene. Browning of tips occurred on some Leucadendrons, particularly with young soft growth and the leaves of some Proteas turned brown more rapidly on fumigated as compared with unfumigated flowers. All control flowers were rated as good.

 
 

The Pestigas/Phosfume combination was found to be effective provided material was not closely packed such that only Phosfume could penetrate.

In field trials of the technique, it was found that fumigation chambers must meet the required standard of gas tightness when Phosfume is used.

In some fumigation situations, the trials found the Pestigas/Phosfume« combination to be more effective in controling certain insects. But because Pestigas is an aerosol, it will not penetrate plant material which is closely packed in boxes. Consequently only Phosfume« can be used effectively in such situations.
 

Successful commercial trials

The flowers were successfully exported to Japan, one of the most discerning markets for cut flowers.
Acknowledgments

This research was undertaken as an initiative of RIRDC which supplied core funding.
Additional financial support and contributions in kind were received from; Associated Flowers International, Ausflora Pacific Pty. Ltd., Austbloom Pty. Ltd., BOC Gases, the Commonwealth Environment Protection agency (now the Department of the Environment), the Flower Export Council of Australia (FECA), G.W. & L.R. Winfield Enterprises Harris Park Holdings, Longford Flowers, the Partners to the Stored Grain Research Laboratory, Tesselaar Nominees and Van Wyk and Son Flower Supply.
The work of this project was also extended by funding from the Horticultural Research and Development Corporation (HRDC), the Australian Horticultural Exporters Association (AHEA) and the Nursery Industry Association of Victoria for whom a separate report will be presented.

This was a collaborative project between Agriculture Victoria, CSIRO and the WA Department of Agriculture