Search continues for phosphine alternatives

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It seems unlikely there will be a single solution to replace the highly effective phosphine. Rather, a suite of alternatives will be required, applied with tactical precision to extend the life of phosphine and maintain Australia’s export commitment of nil live insects in grain shipments. Nitrogen seems likely to play a major role as a phosphine alternative, with field trials at bulk storages and on-farm underway this year (see Oxygen starvation trial).

Another controlled-atmosphere strategy being investigated is the use of ozone.

Ozone approach

As with nitrogen, ozone – or O3 (as compared to oxygen gas O2) – has been recognised for decades as an effective way to kill stored-grain insects. Although Murdoch University’s Professor YongLin Ren, who leads several phosphine-alternative research projects for the Plant Biosecurity Cooperative Research Centre (CRC), says the technology is not new. Technical advances mean it could be an accessible and viable treatment.

The ozone research is being undertaken through the Plant Biosecurity CRC’s partner Kansas State University in the US.

When O3 is applied at a rate of 200 parts per million in laboratory trials, it kills all stages of strongly resistant stored-grain insects within two days.

Professor Ren says field trials using O3 as a treatment in small-scale farm storages are likely to be held within the next six months. Other trials are planned to evaluate ozone in combination with nitrogen.

Sulfuryl fluoride

GRDC-supported research through the Plant Biosecurity CRC and led by Associate Professor Paul Ebert at the University of Queensland is focusing on the synergistic or additive effects of various chemical combinations. 

Sulfuryl fluoride is an alternative that provides a resistance-breaker effect in the bulk-grain-handling system for the treatment of strongly resistant rusty grain beetles (Cryptolestes ferrugineus). However, it is more expensive than phosphine and has restrictions on its use to prevent residue issues. Professor Ebert says the combination of phosphine and sulfuryl fluoride is showing promise as a way to control insects in a suitable timeframe at reduced cost. He says 100 per cent control of all life stages of rusty grain beetle has been achieved with one-third of the concentration of phosphine combined with half the dose of sulfuryl fluoride needed when either is used alone.

A sublethal dose of the botanical pesticide dimethyl disulphide (DMDS) makes phosphine 10 times more effective against strongly resistant lesser grain borer.

Several other gases and volatile compounds that enhance the activity of phosphine in a variety of ways are also being investigated. Victorian researcher Dr Ross Mann is examining the potential of volatiles from fungi as part of the Plant Biosecurity CRC work. Endophytic fungi live symbiotically with their host plants and emit volatiles to protect the plants from insect pests. Strains of fungi have been identified that produce volatile chemicals capable of killing the lesser grain borer, red flour beetle and rusty grain beetle.

Silica potential

The Plant Biosecurity CRC is investigating silica as a contact protectant for stored-grain insect control. Several synthetic silica compounds are being assessed and initial laboratory trials have identified compounds that provide strong control against key grain pests within 10 days. Field validation is now underway, with results showing possible competitive advantages for the silica compounds in price and efficacy.

The Plant Biosecurity CRC is also working on two possible market opportunities. One is the use of silica compounds as an admixture in grain flows. The other is as a structural treatment where the silica product acts as a barrier to insect movement when applied to both external and internal surfaces of structures used for the bulk storage of grains.

More information:

Professor YongLin Ren
y.ren@murdoch.edu.au

Associate Professor Paul Ebert
p.ebert@uq.edu.au

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GRDC Project Code NPB00013, Plant Biosecurity CRC Codes 3114, 3099

Region National, North, Overseas, South