A leading grain storage specialist is encouraging growers to act now to control storage pests with summer temperatures highly conducive to an increase in insect populations in on-farm silos and bunkers.

Development agronomist with the Queensland Department of Agriculture and Fisheries (DAF) Philip Burrill, who is involved with GRDC’s Grain Storage Extension Project, says warm grain temperatures help pest insects breed rapidly in on-farm storages.

“Growers need to be checking storages and organising fumigation now, as storage insects not only destroy your grain, but they can hold you back from potential grain sales,” Mr Burrill says.

GRDC understands the importance of on-farm storage to the grain growers and invests in the Grain Storage Extension Project to ensure industry has access to the latest information about storage best practice, as well as a direct hotline to industry specialists on 1800 WEEVIL.

Mr Burrill says concerning results from a field trial last season provides growers and advisers with an indication of the speed with which insect populations in on-farm storage can increase.

The trial counted storage pests in a one tonne bag of wheat in October and found lesser grain borer (Rhyzopertha dominica) numbers increased rapidly from zero to approximately 200 insects per tonne in the first four weeks of storage. By the end of January, the population had multiplied to 12,000 per tonne and by late March, there were 29,000 lesser grain borers per tonne.

“Growers need to sample and sieve grain in storage every month. I would also recommend using insect probe traps pushed into the grain surface to help find storage pests while they are still in low numbers,” Mr Burrill says.

“Using both an insect sieve and probe traps is a reliable way to detect storage pests. If growers control insects early, less damage to grain will occur and fumigation will be more effective.”

Mr Burrill says the key to successful grain fumigation was for growers to ensure they were controlling the full life cycle of storage pests.

“Remember, if you sieve out five adult beetles in a litre of grain, there could be as many as 450 pests in that grain sample. We simply do not see all the eggs, larvae and pupae stages,” he says.

Mr Burrill recommends growers consider the following steps for effective fumigation:

• A storage that is sealable and gas-tight to the Australian Standard AS2628 will hold high gas concentrations for the required time to kill all insect life-stages. Pressure test silos to identify leaks. Repair seals on hatches, patch up leaks.
• Phosphine application rates are based on the internal volume of the gas-tight, sealable silo to be fumigated. Regardless of how much grain is in the silo whether it is full or empty, the rate is the same. Check the phosphine label dose rate required for the silo volume you are fumigating. For example, a 100 tonne wheat capacity silo requires 200 phosphine tablets.
• Consider using phosphine ‘bag chains’ or ‘blankets’. They may be easier to apply and remove than tablets.
• Cool, aerated grain under 25˚C requires a longer fumigation time, usually 10 days minimum. Check the grain temperature and the phosphine label.
• For larger storages and silos (greater than 150 tonne capacity), aim to use a recirculation system during the first four to five days of fumigation to distribute gas quickly throughout the grain bulk.
• Always refer to fumigation product label directions to ensure safe and correct product use including dose rates, fumigation and ventilation times.

Table 1: GRDC grain storage specialist Philip Burrill from DAF is encouraging growers to check grain storages for insects with summer conditions ideal for a rapid increase in pest populations. Photo: GRDC

For more information, GRDC has produced the Grain Storage GrowNotes and also invests in the Stored Grain Information website. To speak with a GRDC grain storage extension specialist call 1800 WEEVIL.