Storage survey shows need for new strategies

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Data collected by the Plant Biosecurity Cooperative Research Centre (CRC) shows the need for new strategies to counter a rise in strong levels of insect resistance to some grain storage treatments used.

Queensland Department of Agriculture and Fisheries principal research scientist Dr Manoj Nayak says while new protocols are being developed to continue phosphine’s usefulness into the future, combinations of grain protectants, as well as the use of the fumigant sulfuryl fluoride, may have a role to play.

“We are seeing strong levels of resistance to phosphine from the rice weevil, the rusty grain beetle, and the saw-toothed grain beetle on-farm,” Dr Nayak says.

Data from the Plant Biosecurity CRC survey shows that strongly phosphine-resistant rusty grain beetle is a problem in central storages, and lesser grain borer is the main problem in on-farm storages in the southern and northern regions.

A strong level of phosphine resistance in rusty grain beetle was first noted in 2007 and continues to be a problem in these regions.

Dr Nayak says the industry needs to move away from relying on phosphine alone and needs to explore co-fumigation strategies for both growers and bulk handlers.

These include the use of phosphine with either sulfuryl fluoride or carbon dioxide, applied independently and sequentially.

“This approach would help reduce the ongoing resistance pressure on phosphine, still considered by industry as the cheapest and the most versatile fumigant,” he says.

Dr Nayak says the frequency of strong phosphine resistance from the latest data sits at 7.6 per cent on-farm and 28.5 per cent in central storages, and is mostly seen in the rusty grain beetle.

“This shows an average of 11.5 per cent of all cases found in the survey, which is a concern.”

In 30 years’ national monitoring, this is the first time the frequency of strong levels of phosphine resistance has exceeded 10 per cent.

Table 1 Number of predominantly wheat storages sampled in 2016-17.
Northern regionSouthern regionWestern region
FarmsCentral storageFarmsCentral storagesFarmsCentral storages
Table 2 Pest profils. Numbers indicate total samples tested for resistance in 2016-17 with bracketed numbers indicating those detected with strong resistance.
Pest speciesNorthern regionSouthern regionWestern region
Lesser grain borer (R. dominica)97 (16)15 (6)179 (24)21 (6)118 (0)5 (0)
Red flour beetle (T. castaneum)95 (7)19 (0)165 (27)22 (0)248 (5)20 (1)
Rice weevil (S. oryzae)40 (0)16 (0)98 (18)13 (2)35 (1)59 (0)
Rusty grain beetle (C. ferrugineus)54 (5)45 (14)68 (8)98 (70)26 (0)1 (0)
Sawtoothed beetle (O. surinamensis)34 (5)0 (0)100 (4)6 (0)112 (0)0 (0)
Total320 (33)95 (20)610 (81)160 (78)539 (6)85 (1)

GRDC Research Code NPB00013

More information:

Dr Manoj Nayak
07 3708 8539

Grain storage information and GRDC Grain Storage GrowNotes™ are available on the GRDC Stored Grain Information Hub.