South Australian grain growers rely heavily on phosphine to keep stored grain insect free.
Domestic and international markets demand high-quality grain, free of insects, and phosphine is extensively used to protect against grain storage pests.
It is a universal phytosanitary treatment of grain silos, seeds, plants, dried fruit and other products. Phosphine treatment leaves no residue and is effective in targeting grain pests at all stages of their life cycle.
It is also popular, due to its relatively low cost, easy application, ability to be used on other commodities, and having no impact on seed germination or milling quality of grain.
Due to the widespread and continued use of the treatment, producers can run the risk of pests developing resistance to phosphine. Graingrowers can take certain steps to reduce the risk of this happening.
The conditions throughout summer in SA are ideal for infestations of grain storage pests. Grain stored for an extended period of time, such as for livestock feed or seed for the next season, has an increased risk of pest infestations.
According to data from the GRDC-funded National Resistance Monitoring for Insect Pests of Stored Grain project, 94.7 per cent of insect populations tested from South Australian farms were 'weakly' resistant to phosphine.
This included pests such as lesser grain borer, flat grain beetle, rice weevil, flour beetle and saw-toothed grain beetle.
The high rates of 'weak' resistance indicates there is a much higher likelihood of resistant genes in the overall population becoming more prevalent and occurring in different combinations, to potentially result in strongly resistant populations.
These rates of resistance largely occur due to ongoing phosphine misuse by underdosing or having leaking fumigation structures and multiple fumigations on the same grain batch.
Concerningly, 2.63pc of pest populations sampled from farms in SA in 2021 showed strong resistance to phosphine. In all samples analysed, lesser grain borer (Rhyzopertha dominica), showed strong resistance.
Weak resistance can be controlled with existing phosphine label rates but it is much harder to control strong resistance.
When treating stored grain, ensure:
For further information, please refer to the GRDC's Grain Storage Fact Sheet - Grain Fumigation - A Guide.
To help growers manage their use of phosphine and confidently prevent resistance, SA grains biosecurity officer Shafiya Hussein, in collaboration with GRDC project lead Chris Warrick, will conduct a series of free workshops across the state in July.
The workshops will focus on how to pressure test grain storage structures and the recommended rates of phosphine to control and manage resistance.
Graingrowers implementing a routine monitoring system of on-farm stored grain by sieving grain monthly, can help to detect pests early and maintain effective pest resistance control and management.
The Grains Farm Biosecurity Program is an initiative to improve the management of, and preparedness for, biosecurity risks in the grains industry at the farm and industry levels.
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