Stored grain researchers are working to address the challenges of storing grain in the warm, humid climate north of the Tropic of Capricorn

As grain production expands across northern Australia, growers are increasingly turning to on-farm storage to maximise profits and flexibility.

However, storing grain in the warm, humid climate north of the Tropic of Capricorn presents unique challenges requiring careful management and investment in suitable infrastructure.

A three-year GRDC project on behalf of the Cooperative Research Centre for Developing Northern Australia (CRCNA) has found that the grain storage challenges faced by most growers around the country – moisture levels, pest infestations, and resistance to fumigants and contact insecticides – are considerably elevated for far north growers.

The project included a grain sampling survey, pest and resistance profiling, insect trapping, and the development of control protocol and region-specific information for the integrated management of key grain insect pests.

Researchers also conducted multiple grower interviews and industry-scale phosphine and sulfuryl fluoride fumigations

The rise of far north grain

Traditionally known for sugarcane and cattle production, northern Australia is emerging as a frontier for cotton, grain and pulse crops in a shift driven by profit potential and the benefits of crop rotation and diversification.

Queensland Department of Agriculture and Fisheries (QDAF) senior research scientist Dr Rajeswaran Jagadeesan says long-term rotational cropping of grains, such as sorghum, maize and barley, or pulses including mungbeans, chickpeas and soybeans, has increased net profits for sugarcane growers in northern Queensland by up to $2000 per hectare per year.

Similarly, growing fodder crops in the Northern Territory’s cotton country promoted crop diversity and supported the local livestock industry.

Initially, many grew grain crops on contract, trucking them to bulk handlers and traders soon after harvest. However, on-farm storage gives greater flexibility to sell the crop when prices are higher or when there is local demand, saving on freight costs.

Key findings

Dr Jagadeesan says long-term insect trapping confirmed pest pressure was high across the north, particularly in farm storages during the wet season from October to April.

“We see a similar species spectrum in other tropical countries like Indonesia, Thailand and India,” he says.

The most common pest found across all sites was red flour beetle (RFB), and the proportion of other insect pests varied between regions.

Samples from northern Queensland contained 21 per cent highly resistant species of flat grain beetle (FGB), while the NT samples were dominated by the lesser grain borer (28 per cent) and in far north WA the saw-toothed grain beetle (SGB) (23 per cent).

The three species spend most of their life cycle outside grains, compared with internal feeders such as lesser grain borer and rice weevil.

Resistance testing found a surprisingly high 40 per cent of the populations were strongly resistant to phosphine, including 91 per cent of red flour beetle (RFB) in 2022-23 and 50 per cent of FGB.

“For a region where grain storage is picking up or at its infancy, in only five to six years, I think that’s quite a high frequency of resistance,” Dr Jagadeensan says.

“This project [also] revealed the existence of RFB resistance in samples from Broome and Kununurra. I think it can be a forewarning for the whole of WA.”

Figure 1: The proportion of insect species identified in the total number of grain samples (280) collected and screened.

Source: Jagadeesan et al. (2024)

Top: Test insect cages placed at the bottom of a silo, reflecting typical field insect infestation scenarios. Bottom: Test insect cages placed at the top of the silo (close to the hopper), reflecting typical field insect infestation scenarios. Photos: courtesey Dr Rajeswaran Jagadeesan

Industry recommendations

The eight recommendations from the project are:

• structural integrity – use gas-tight sealable grain storage to Australian Standard 2628-2010 for reliable fumigation
• storage hygiene – regularly clean storage areas and dispose of waste grain, also clean all harvest and grain handling equipment
• regular monitoring – use probe traps and sieve grain samples from the hopper
• resistance testing – if resistance is suspected, send a sample of insects and infested grain to the nearest QDAF regional office for testing and recommendations for alternative treatments
• aeration – use an automated aeration system to reduce grain temperature and even out the moisture profile. This can reduce how often grain must be treated
• structural treatments – use chemicals registered for structural treatments of grain storage. Diatomaceous earth was less effective in high-humidity environments
• grain protectants – a mixture of spinosad, chlorpyriphos-methyl and s-methoprene is effective against multiple species at 35°C and 75 per cent humidity but is registered for use only in cereal grains
• fumigants – the current phosphine label rate over a seven-day exposure period was effective at 25°C and above, although strongly resistant FGB and eggs of pulse beetles (cowpea bruchids) are likely to survive the concentration achieved in farm silos. An alternative is one-third of the top rate of sulfuryl fluoride at 500g per hour per cubic metre over five days. This was effective against seven of the region’s major pest species, including phosphine-resistant populations. However, sulfuryl fluoride is not yet registered for use in pulses or oilseeds.

More information: Dr Rajeswaran Jagadeesan, raj.jagadeesan@daf.qld.gov.au