Mark Sheppard from Pest Education Services & Training looks at the history of fumigation and outlines the key points to consider when planning a fumigation job.
Over the past couple of decades, in the region of 95% of all fumigants used post-harvest in Australia (on structures and on commodities) have been phosphine and methyl bromide products.
Since 2005, when ‘The Montreal Protocol on Substances that Deplete the Ozone Layer’ required a phase out of methyl bromide for applications other than quarantine and pre-shipment purposes, those involved in the chemistry of fumigants have given increased focus on safety and environmental attributes, as well as performance factors.
The assessment of existing and new fumigants has had to take into account the release of greenhouse gases and damage to the ozone layer, maximum residue limits (MRLs) in food and animal feed, whether the fumigants have broad spectrum management control and resistance issues.
The research and development of new fumigation treatment options can be grouped into five general areas:
- Old fumigants being looked at again
- Different fumigants being combined together to work more effectively and in some cases more safely
- The development of new fumigants
- A focus on controlled atmospheres
- Heat and cold treatments as alternatives to fumigation What follows is a brief overview of the developments.
Old fumigants in new forms
Hydrogen cyanide (HCN) – is one of the oldest and most toxic insect fumigants. It is the fumigant of choice where a rapid treatment is required for rodents in commodities and enclosures or where germination must be preserved. HCN should not be used where there is moist conditions or the ambient / commodity temperature is lower than 26°C.
Gaseous phosphine (100%) – not necessarily new but the development of safer application equipment has improved fumigator safety.
Sulfuryl fluoride – used for many years against drywood termites in the USA under the tradename, Vikane. Now a useful management tool against phosphine-resistant pests.
Ethyl formate (C3H6O2) – occurs naturally in vegetation and a range of processed foods like vegetables, fruit, beer and milk and breaks down into formic acid and ethanol (naturally occurring compounds). Currently registered for use in disinfestations of packaged dried fruit but due to its flammability it is of more interest when used in combination products.
Vapormate – approximately 83% carbon dioxide and 16.7% ethyl formate. This combination is registered for cereal grain, nuts, oil seeds, fresh fruit, vegetables and commodities, for application by pressurised cylinders. In these proportions the product is non-flammable and the components deliver a synergistic effect. It is rapid acting, with fast
breakdown to naturally occurring compounds, providing no withholding periods and no issues with residual chemicals.
Eco2Fume – 98% carbon dioxide and 2% phosphine. The gas is premixed, eliminating spontaneous flammability, enabling the fumigator to easily vary concentration levels and exposure periods to penetrate foods and non-foods quickly, as specified on the product label. The gas yields no waste by-products and is residue free.
New fumigants, gaseous compounds
Fumigas (C2N2 ), also known as ethanedinitrile (EDN) or cyanogen – currently registered for the treatment of export logs in Australia and also being tested as a soil fumigant. The original patent for this new fumigant shows its potential as a good replacement for methyl bromide, with similar exposure times, often better penetration into commodities and no impact as an ozone or greenhouse gas.
Carbonyl sulfide waits for commercialisation. This naturally occurring compound is present in the atmosphere, in water, soil and plants and is a potential fumigation alternative to methyl bromide and phosphine in grain treatments.
Propylene oxide is in use as an ethylene oxide replacement in the USA. It looks promising for food fumigation where sterilisation, not just disinfestation is needed.
Controlled atmosphere fumigation (CAF)
This is the process of altering the proportion of atmospheric gases – oxygen, nitrogen and carbon dioxide – in a storage or fumigation enclosure to create insecticidal conditions. There are three main advantages for using CAF:
- no toxic gases used,
- it is suitable for organic producers and
- can be manufactured on site.
Good examples of CAF involve use of nitrogen generators and hermetic (low oxygen) storage to give the insecticidal atmosphere.
Heat and cold
Basically this involves the exposure of living organisms to temperatures above 55°C and below -18°C.
The exposure time depends on the temperature and the material being treated. Even at -18°C, some insects can survive for more than 24 hours. However, at temperatures above 55°C, heat treatment can be very fast. At 62°C, insects will die after less than a minute of exposure.
However, it takes time for the lethal temperatures to be achieved at the pest location. If the insect is within commodities like wood, then the exposure time needs to increase to give the heat or cold time to penetrate to, and be maintained on, the insect. In a fumigation treatment, penetration of the fumigant may be similarly slow.
Most importantly for any fumigation treatment or fumigation alternative, success is delivered with ‘CT’, monitoring, training and retraining.
‘CT’ is the combination of sufficient concentration (C) for sufficient period of time (T) to achieve a 100% kill. In delivering ‘CT’, quite simply, the fumigation enclosure must be gas tight.
As a great mentor and friend of mine, Jan van Someren Graver, always used to say, “If you are not monitoring you are not fumigating.”
What about training? With safety and stewardship integral to professional fumigation, operators need to focus on quality training and continual re-training. The risks to operators and the potential adverse affect on food / feed quality and germination means the health consequences and liability issues of a poor treatment are significant. Operators should consider the quality of the training, not simply how cheap or how quick the qualification can be obtained.
A great step forward is the focus of some fumigant manufacturers and some fumigant suppliers in providing product stewardship accreditation and reaccreditation to use their products correctly and safely.
With the many and varied, new and revived fumigant treatments, pest managers and fumigators need to keep a close watch on developments. Gone are the days where you can utilise a single fumigation treatment for all your jobs. You need a portfolio of methods available to be able to choose the best treatment for the job – trained, certified, experienced and ready to go.
Exciting times ahead!