It is important to monitor grain temperature and to keep stored grain cool and dry by regularly aerating it through mechanical aeration or by turning it. This section explains how monitoring and aeration work together to both prevent and control insect infestations.
Moisture and warm temperatures are the main factors that cause grain to deteriorate. They allow the growth of moulds and the development of an environment that is very suitable for insect development.
Grain is a very good insulator. When it is undisturbed, it holds temperature well. If warm grain is placed into storage and left undisturbed, convection currents may develop and cause hot spots and condensation. The greater the temperature differential (the difference between the temperature of the grain and the ambient temperature) the stronger the convection current. The stronger the convection, the greater the effect of heating and condensation on the grain. This is particularly evident when stored grain is not leveled and the pile forms a peak.
Convection currents in bin-stored grain.
This diagram shows the cycle of convection currents in bin-stored grain when ambient air outside the bin is cold and the grain is warm. In the bin,
Arrows represent the convection current.
Consider the moisture content of the grain at the time of storage. If the moisture content is 13 percent or higher and the grain remains warm for a long time, it can be damaged by fungal activity. Fungi may subsequently produce mycotoxins. However, when grain with a high moisture content is cooled to below +10°C, it can be stored for months without moulds forming and causing it to deteriorate.
Check the temperature of the bin every two weeks. Measure temperature by using temperature sensing cables that are permanently installed or by probing the grain with an electronic sensor device.
If devices for measuring temperature are not available,
Aeration systems preserve stored grain and keep it dry by reducing the temperature of grain and reducing moisture migration. Appropriate aeration can prevent convection currents and condensation from occurring.
Stored grains should be aerated as soon as possible after harvest, particularly if aeration can reduce the bulk temperature below +18°C. When the ambient temperature falls below that of the grain bulk, initially during the early evening, night, and early morning, you can use aeration to reduce the temperature of the grain.
If you aerate grain when the ambient temperature is above +20°C and the temperature of the grain is above +30°C, the odors produced will be more attractive to insect pests. Under very warm conditions, sanitation involving cleaning and treating grain is very important in preventing problems.
As well as preventing insect infestations, aeration is also very effective in controlling them. Once the grain temperature is reduced to below +18°C (which prevents insect feeding and reproduction) a further temperature reduction can be used to cause mortality. Refer to the disinfestation time periods required at low temperatures table.
If an aeration system is not available, turning grain outside the bin is an alternative to aerating it in the bin when the ambient air temperature falls below +15°C. Turn the grain every two to four weeks until the grain temperature reaches +15ºC. This procedure involves removing about one-third of the grain from the bin and putting it back in the bin.