Monitor for top quality

2 November 2001

Monitor for top quality

Keeping grain in tip-top

condition throughout storage

is the goal of our latest

baseline advice article.

Follow these guidelines and

store problems should be

few and far between

IF your store was prepared properly and the grain was cooled and dried to the recommended levels within the first few weeks, the risks of it losing condition in store this winter are minimal.

But regular monitoring is still required to ensure it stays in top condition, says CSL grain storage expert Ken Wildey.


Insect, mite, fungal and mycotoxin development is controlled by temperature, so grain should have been cooled to below 16C within a fortnight, Dr Wildey advises.

"Cooling should then be continued to near zero by December, with the exception of malting barley which should not be cooled below 10C," he recommends.

Most insects multiply rapidly at 25-33C, but will not breed below 16C, although grain weevils can continue to breed at 12C. At levels below 5C, they cannot feed and will die.

"Mites and fungi can continue to be a problem down to 5C, while mycotoxins are most likely to form between 15C and 25C."

Dr Wildey stresses growers should accept the lower the temperature is the better. "Monitor regularly – every few days at the beginning and then weekly – and keep permanent records."

Where grain heating does occur, aerate it to even out temperatures and reduce the risk of moulds, heating and sprouting.

"Check temperatures right across the bulk and it is a good idea to cool it intermittently anyway to prevent any hot spots developing."


Not only is grain at risk of spoilage until it is dried to 14.5% moisture, it is also unlikely to meet contract specifications at a higher level.

"Moisture content can change over time because it is linked to the relative humidity of surrounding air," says Dr Wildey. "So after drying, take samples on a weekly basis until grain temperature stabilises."

The moisture of surface grain layers fluctuates with ambient conditions and at 17% will allow mite infestations. "If it rises by 2% or more in a week, check for condensation, leaks and insects," advises Dr Wildey.


Insects are difficult to find but will die out during cool storage. Traps should be used to assist with monitoring, as they are 10 times more effective than sampling.

"Traps help to indicate population trends. Lay them in a 4-5m grid and leave in place for a week before examination."

Pitfall traps should be buried so the rim is level with the grain surface. Probe traps need burying vertically just below the surface. "Tie both of these trap types to marker canes and number them if you have a large store."

PC traps, which combine the features of a pitfall and a probe, should be used in pairs – at the surface and 5-10cm below.

"Empty pests on to white paper to make them more visible and record trap catches so you can react to increases in numbers. Pesticide use is justified if levels are rising."


Mites pose an increasing threat in the UK and can survive unfavourable conditions in stores during the resting phases of their lifecycles. Resistance to OPs is widespread, so a single control option is unlikely to work.

"Dried and cooled grain is at less risk from mites, but any that are there will be close to the surface," reveals Dr Wildey.

Sampling grain from different depths and sieving it through a 1mm mesh will reveal their presence. Parallel assessment of moisture content will help determine the likelihood of further infestation.

"Apart from cooling and drying, it can be useful to turn and clean the grain," notes Dr Wildey. "Otherwise growers can admix with an approved pesticide at intake, apply a surface treatment for some species or fumigate with phosphine. But physical control methods are preferred, because of the resistance problem."


Storage fungi grow within a narrow range of moisture and temperature and should be controlled to prevent mycotoxin production.

"Again, the drier and cooler the grain, the safer it is. But cooling alone is insufficient for damp grain; moisture content must be below 15%.

"Chemical treatment can be done if the grain is for animal feed, with the choice between caustic soda or propionic acid. But these give no long-term protection against insects or mites."

Rodents and birds

Making the environment unfriendly to rodents and denying birds access to food and shelter are the best deterrents.

"Birds will cease to be a problem if you can prevent roosting nearby and restrict their entry to the store with netting."

Rats may need a more robust strategy and control of an infestation is achievable within three to four weeks, says Dr Wildey. "Start by getting rid of food and free water sources and remove potential habitats." &#42



1Threats Insects, mites, fungi and rodents.

2Moisture Get grain below 14.5% as soon as possible and be prepared for surface fluctuations.

3Temperature The lower the better. Bring down to 16C within a fortnight and then down to near zero by December.

4Monitoring equipment Use moisture meters and temperature monitoring devices weekly and keep records. Pest traps are effective and will indicate trends.

5Equipment maintenance Calibrate or service equipment annually. Replace or recharge batteries regularly.

6Insects Cannot feed and thrive at temperatures below 5C.

7Mites Resistant to OPs, difficult to detect and reproduce rapidly. Keep grain below 5C to minimise problems.

8Fungi Keep grain at 14.5% moisture or below to prevent fungal growth and mycotoxin development.

9Rats and mice Remove food and shelter. Control infestations within three to four weeks with an integrated strategy.

10Birds Eliminate access to store and prevent roosting nearby.

Tip and forget? Grain storage needs to focus on staying cool, staying dry and staying in touch with the crop through routine monitoring, says storage expert Ken Wildey.

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