An integrated approach to manage pests and resistance to phosphine in stored grain

Project Number

3036

Project Type & Status

Core-Complete

Project Leader

Researchers

Dr Jo Holloway
Phosphine resistance

Impact Delivery Themes

An integrated approach to manage pests and resistance to phosphine in stored grain

Final Report Summary

The main aim of this research project was to develop sulfuryl fluoride (SF) as a viable 'phosphine resistance breaker' to enable industry to use phosphine as the key grain disinfestant in the foreseeable future. Developing alternatives to phosphine has been an industry priority in view of the development of strong resistance in key pest species; specifically the rusty grain beetle, (Cryptolestes ferrugineus), which survives the current phosphine label rates. 

The main objective of this project was to provide a range of SF fumigation protocols to industry as an alternative to phosphine and to manage strongly phosphine resistant pests. In addition, researchers aimed to support activities and interventions that limit the incidence and spread of resistance to grain treatments and facilitate practice changes consistent with effective resistance management. The ultimate goal is to protect the stored grain from insect pests and enable industry to sustain its market access.

Recommendations

Results from recent resistance monitoring demonstrates clearly that the selection pressure on phosphine is continuing and there have been instances of strong resistance in saw toothed grain beetles, which is a new resistance for the industry. It is imperative that judicial use of alternative fumigants such as SF be adopted by industry to reduce this ongoing pressure on phosphine.

We recommend the use of SF only as a ‘break fumigant’ in storages where strongly phosphine resistant rusty grain beetles are prevalent to reduce the selection pressure on SF. We strongly recommend that farmers be discouraged from using SF unless they have a strong case of phosphine resistance, where current phosphine label rates fail to control infestations. Although resistance to SF is unknown, widespread and frequent use of SF could lead to resistance development in key pest species. This will jeopardise the long-term viability of SF as an effective phosphine resistance management tool.

Resistance monitoring protocols for SF developed in this project should be implemented in the monitoring program to enable industry for early detection of resistance in key pest species. Moreover, rotation of phosphine with SF should significantly reduce selection pressure on both fumigants

New phosphine fumigation protocols developed in the current project to manage strongly resistant rusty grain beetles should be adopted by the industry through proper registration processes and changes to current label. Several fumigation protocols established in the laboratory need field validation to gain industry confidence.

Finally, the national extension network will be used to encourage direct participation by all end-users in the implementation of the deliverables to fulfil their obligations for the ‘National Phosphine Resistance Management Strategy’.

Conclusions

  • Rusty grain beetle (Cryptolestes ferrugineus) is currently being considered as the most important pest issue for bulk handlers due to its strong level of phosphine resistance.

  • Over the last 5 years, the industry has witnessed a significant drop in incidences of strongly resistant rusty grain beetle infestation problems, mostly due to the adoption of sulfuryl fluoride (SF) as a resistance breaker.

  • For the first time, a range of practical fumigation protocols were developed for SF at two temperatures (25 and 30ºC) to mitigate the strongly phosphine resistant pests populations including the rusty grain beetles (Cryptolestes ferrugineus), rice weevils (Sitophilus oryzae), rust-red flour beetles (Tribolium castaneum) and lesser grain borers (Rhyzopertha dominica)

  • A CT product of 400 mg-h/L at 30°C over 7 days exposure period is required to achieve complete control of all four key pests.

  • Almost half the concentration of SF is required over 7 days exposure period at 30°C than that required at 25°C.

  • As temperature has significant influence on the effectiveness of SF against four key stored grain pests, we can utilise this aspect in our fumigation strategy to optimise the efficacy of SF by fumigating when grain is warm.

  • We recommend avoiding SF fumigations using shorter exposure periods (>4 days), even at the highest registered CT product of 1500 mg-h/L at 25°C, as several pest species will survive.

  • ‘Time to reinfestation’ was evaluated at two GrainCorp sites in Queensland that suggested that a successful fumigation with SF could provide at least 3 months until fumigation is required again

  • Although not included in the main objectives, the research team utilised its industry network (GrainCorp and CYTEC Australia) in a proactive way to establish new phosphine fumigation protocols to control strongly phosphine resistant rusty grain beetles (protocols established at three different temperature regimes).

  • Once validated through industry-scale field trials, these new phosphine protocols will be subjected to registration process and subsequent label changes so that industry will be able to use them legally

Based on the field trial results, researchers concluded that to achieve complete control of all five major pests, three key factors need to be aligned correctly: accurate determination of the grain temperature, a uniform distribution of fumigant within the grain mass and maintaining the target concentrations for the specified exposure period/s.

Download the full Final Report.

 

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