Aim for an upper limit of 12 per cent moisture content for farm stored wheat, barley, oats and triticale.
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The ability of stored pests to breed in dry grain varies between species.
Even those species which can breed in dry grain will breed much faster in moist grain.
The optimum relative humidity for insect development is about 70-80 percent.
In wheat, this is equivalent to a moisture content of about 14-15 percent.
Excessive moisture will cause grain protectants to break down rapidly, encourage fungi and moulds to develop and cause grain to sprout.
It is recommended that a moisture meter always be used to determine the moisture content of grain during harvest.
Stored grain should also be kept as cool as possible.
Aim for an upper limit of about 27°C. The speed at which insect populations grow is influenced by temperature, relative humidity and moisture content.
Storage pests can breed at temperatures between 15°-40°C depending on the species. Population growth is usually highest at 25°-35°C. At low temperatures (15°-20°C) insect pests multiply slowly and grain maintains its viability. At high temperatures seed viability is reduced, insect pests are more active and pesticides on grain breakdown more quickly.
Keeping Grain Cool
Grain temperature can be minimised by putting cool grain into silos (transferring cool grain in the morning, evening or night), applying white paint to galvanised iron silos, using silos made out of zincalume or colourbond, or installing an aeration system.
Growers should aim to store grain at temperatures as low as possible, preferably less than 20ºC. Every 1ºC below 26ºC will have an effect on germination retention and insect activity.
Aeration
Aeration is the process of passing cool air through grain to reduce its temperature to a level where insect development, mould growth and moisture migration are dramatically reduced. As grain is cooled, insect development slows down and is negligible at temperatures below 15°C.
Aeration systems can be used for either drying grain, cooling grain and for maintaining grain quality when stored over a longer time frame.
The benefits of aeration are:
- early harvesting of high moisture grain;
- greater harvest flexibility;
- control over grain quality;
- ability to even out moisture levels;
- cooling capacity;
- ability to even out temperature; and
- ability to prevent moisture migration.
What should you consider next
In most cases it would be impractical to replace all storage with new sealed bins.
You should have a proportion of sealed storage in your system to fumigate grain.
Where storage is to be increased, good quality sealed storage should be purchased.
Existing unsealed storage can be fitted with aeration, grain fumigated in sealed storage can be transferred to aerated storage and confidently stored until needed.
The key to successful grain storage is planning.
Understand your market’s needs, and get good information on how to meet these.
Invest in quality storage equipment, and manage your system as well as you manage the crop in the paddock.
