Phosphine – use it properly or lose it
Phosphine is still an effective fumigant, but it must be used in a sealed, gas-tight storage or silo.
That is the plain message from grain storage expert Peter Botta as growers gear-up to harvest this year’s crops.
Mr Botta emphasises the importance of phosphine and its lasting effectiveness: “It is inexpensive, easy and safe to use when done correctly, and can be accessed by growers,” he says.
“All recorded levels of resistance found on-farm can be controlled when using label rates in sealed, gas-tight storage,” he says.
“Resistance is a symptom of failed fumigation, which is typically caused when either the fumigation is done in an unsealed structure, the rate used is insufficient or the fumigation period is too short.
“Resistance management is all about using the correct structure or system.”
Mr Botta says some growers who have experienced phosphine resistance may have replaced it with another chemical, such as ProFume®, but not changed to a gas-tight storage system.
“There is the option to rotate ProFume® and use it as a break to incorporate different chemistries but the reason why phosphine is not working is because people are not using it in gas-tight silos,” he says.
“If that doesn’t change then the same thing will happen with ProFume®.”
Phosphine resistance has increased in the past 10 years because many grain silos fail to meet the gas-tight standard needed for fumigation.
Mr Botta also emphasises that there is a difference between sealed and gas-tight. A gas-tight silo is one that passes a five-minute half-life pressure test according to Australian Standard AS2628. To kill grain pests at all life cycle stages, gas concentration levels must remain at 300 parts per million for seven days or 200ppm for 10 days.
Research has found silos with just small leaks can have phosphine levels as low as 3ppm near the leak source and generally much reduced gas levels throughout the rest of the silo.
When fumigation has been completed, silos should be opened and ventilated using an aeration fan for one day. If there is no aeration fan, open the silo top and ventilate for five days. The minimum withholding period is two days after ventilation and the total fumigation time is seven to 10 days.
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