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Australian Grain Farmers Encouraged to Consider Fumigation

16 February 2012

AUSTRALIA - With the winter harvest mostly put away, the Grains Research and Development Corporation (GRDC) is encouraging farmers considering fumigating grain stored on farm to do it wisely and carefully.

The GRDC says there are several key points when you are looking to fumigate stored grain, including effectiveness and safety.

Agri-Science Queensland grain storage expert Philip Burrill says phosphine is the single most relied upon fumigant to control stored grain pests, and as such it is everyone’s responsibility to use it wisely.

“Resistance is a problem for the entire community, and misuse of phosphine is resulting in poor insect control and increasing resistance in certain pest species,” Mr Burrill said.

“The most common problem is not fumigating in a gas tight, sealed silo. That means if you have just recently purchased a new sealable silo it should meet the Australian standard; a five minute half-life pressure test. For older existing sealable silos, passing a three minute half-life pressure test shows the silo can hold the correct phosphine gas concentrations for the required time,” he said.

A pressure test to determine whether or not a silo is properly sealed involves blowing air into the silo or storage using the aeration fan, an air compressor, hand held blower or vacuum cleaner until a small positive pressure is created. The air flow is then switched off and sealed, and then the time it takes for the pressure to halve recorded.

“Farmers may think a silo is sealed because it keeps out rain, or because it was originally purchased as a “sealed silo” but in reality even new sealable silos can have construction or design faults resulting in leaks.

“It is a good idea to pressure test silos when they full or part full of grain, which puts weight on the bottom outlet slide, a common gas leakage point. Unless tested regularly you have no way of guaranteeing your silo is gas tight.

“This is problematic because if you do have leaks, when you fumigate the gas levels won’t remain high enough to kill all life stages of stored grain pests. You may kill some of the adults, but most eggs and pupae will remain, meaning your problem insect will quickly reappear,” Mr Burrill said.

In order to kill grain pests at all stages of their life cycle (egg, larvae, pupa, adult), including pests with strong resistance, phosphine gas concentration levels need to reach and be maintained at no less than 300 parts per million (ppm) for seven days (when grain is above 25°C) or above 200ppm for 10 days (grain 15–25°C).

Growers are advised to check with silo manufacturers prior to purchase that any new “sealable silo” meets the Australian standard AS2628 which is based on a new silo meeting a five minute half-life pressure test once erected on your property. It allows growers to refer to an industry benchmark when buying a gas-tight, sealable silo.

If testing an older existing sealable silo, preferably full of grain, a three minute half -life pressure test is a good result that will provide for effective fumigations.

TheCropSite News Desk

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