To drive home the importance of farm hygiene, GRDC Grain Storage Extension national coordinator Chris Warrick retells the story of a simple test conducted by now-retired stored grain authority Phillip Burrill.
Sifting through the first 40 litres of grain from a header on its first outing after being cleaned and stored, he began looking for grain storage pests. He stopped when the headcount reached 1000 lesser grain borers.
“And this was from a harvester that was thought to be ‘clean’,” Mr Warrick says. “So it shows the potential breeding ground for insects that machinery on-farm can provide.”
Mr Warrick says this experience demonstrates that hygiene practices to prevent pests need to be applied beyond just the silos.
“Yes, we sweep up spills, we clean out the silo and, if we’re really good, we make sure our silo is designed so we can lift up the aeration ducting and clean out underneath. But we also need to think about the next steps – the things we probably don’t associate with grain storage, like our machinery in the shed or livestock feeders.”
Good hygiene across the farm is one of the most important non-chemical methods to help control pests on-farm, he says. With insect pressure and phosphine resistance growing, employing a range of chemical alternatives for prevention and control is critical.
“If we don’t take a serious look at non- chemical methods for controlling insects, the outcome is fairly well known,” he says. “We’ll end up with more resistance.”
Mr Warrick says research by the Queensland Department of Agriculture and Fisheries’ post-harvest research team shows the most effective time to undertake a whole-of-site clean-up is in the winter months, when insect breeding and migration are lowest (Figure 1).
He also recommends a structural treatment post-clean-up in silos and equipment using a product such as diatomaceous earth (DE) – a fossilised algae dust that dehydrates and kills insects without residue issues.
Figure 1: Whole farm hygiene showing how insect activity changes across the year and between silos and paddocks.
Source: QDAF
Monitor and measure
Other non-chemical prevention methods include aeration cooling systems in silos and monitoring for both temperature and insects.
“We often think about monitoring in terms of insects, but if I’ve got aeration, I’m interested in the temperature in the silo as well. This is because, if I find insects and my temperature is below 20˚C, I’m not as concerned as I would be if it was warmer,” he says.
This is due to insect breeding slowing or even stopping in cooler temperatures. Rice weevil, for example, cannot reproduce at temperatures of 15˚C or lower; lesser grain borer at temperatures less that 18˚C; and for red flour beetle the cut-off is 20˚C.
Aeration cooling is effective in managing silo temperatures to levels that insects can't reproduce or survive.
“It is also very achievable in our climate, so we should be measuring grain temperature in the silos and aiming to hit the targets for insect prevention.”
Aeration cooling provides the added bonus of helping to maintain grain quality in terms of retention of desired moisture content and prevention of mould. This can make it cost-effective if simply compared with relying on fumigation.
Using several non-chemical prevention strategies on-farm is the best defence against insects. But even the best systems are not fail-safe and having a knockdown strategy is critical should an infestation occur. Fumigation with phosphine and other gases is most common.
Whatever the treatment, Mr Warrick says sealable storage is a must. “Whether that be through newer storage, or a gas-tight option beside a shed, we need to deal with it properly,” he says.
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