Aeration cooling creates cool, uniform conditions throughout the grain to preserve grain quality, restrict or prevent mould growth and slow or stop insects breeding. Mould and insect development is slowed at temperatures below 200C and most insects stop reproducing at temperatures below 150C. Unlike aeration drying, aeration cooling can be achieved with airflow of 2-3 litres of air per second per tonne of grain and is best managed with an automatic aeration controller. For more information on how to manage fans for cooling see ‘Aeration cooling for pest control’ or ‘Aerating stored grain, cooling or drying for quality control’
Can I use aeration to dry grain in storage?
Aeration that provides more than 15 litres of air per second, per tonne of grain can be used to reduce grain moisture content by a few percent. The risk of using less air (smaller fans) is that moisture will be pushed partway up through the grain but not all the way out the top of the silo. This leaves a band of even higher moisture grain susceptible to mould and insect attack. For more information about aeration drying and how to manage fans for drying, see ‘Dealing with high-moisture grain’ or ‘Aerating stored grain, cooling or drying for quality control’
Where do insects come from and how do they travel?
Intermediate studies have shown insects can generally be found in vegetation areas, barns, sheds, spilt grain and hay stacks. Some species can fly over 5km, other means of travel include on machinery. The best time to clean-up around storages to prevent insects being attracted is during the cooler months of the year before they become mobile when the weather warms up. For more information see ‘Storage pests beat around the bush.’
How can I deal with insects in gain bags?
Grain could be transferred into a gas-tight, sealed storage for fumigation or in some cases it is possible to fumigate in the grain bag. Fumigating in a grain bag requires a precise application method in a completely sealed bag and a fan must be used to ventilate the gas following the fumigation. For more information on how to fumigate in a grain bag see the Grain bag fumigation video
What alternative fumigants are available?
ProFume® and VaporMate® are available alternatives to phosphine, however they can only be applied by a licensed fumigator. Carbon dioxide and nitrogen are ‘controlled atmosphere’ alternatives to phosphine which can be done by anyone providing they have access to the required equipment and knowledge. All of these alternatives require a gas-tight storage for successful control of insects and are currently more expensive than phosphine. For more information see the back pages of ‘Fumigating with phosphine, other fumigants and controlled atmospheres’
If phosphine is not working what do I do?
1) The first thing to check is that the silo is gas-tight, ie that it meets at least a three minute, half-life pressure test. (Check before filling and when full as the weight of the grain can open gaps around the bottom slide plate.)
2) Check the application rate is enough to treat the entire storage volume.
3) Check the exposure period is long enough according to the grain temperature.
4) Get an expert to ensure you’ve correctly identified the insect pest, particularly if you suspect it’s the flat grain beetle, cryptolestes spp.
For more information see ‘Fumigating with phosphine, other fumigants and controlled atmospheres’
What type of rubber and sealant is best for sealing silos?
Polyurethane based rubbers and sealants should be used for sealing silos. Silicon based products can potentially contaminate the grain. Look for a rubber with a strong memory, that is one that springs back to its original shape after being compressed.
What’s the difference between a thermosiphon and active recirculation?
The theory of a thermosiphon is that it uses ambient temperature differentials to slowly move air in a pipe between the head space and the bottom of the silo. Active recirculation uses a fan in a sealed system to circulate the air from the bottom to the headspace of the silo. The application chamber where phosphine is applied must be large and open to the grain so it can disperse if the recirculation systems stops, otherwise explosive gas concentrations can be reached. For more information see ‘Fumigating with phosphine, other fumigants and controlled atmospheres’
What are phosphine ground application devices?
Rather than putting phosphine in the headspace, some silos are equipped with a ground application system. Phosphine is applied into a chamber at ground level and disperses’ through the grain via an opening into the bottom of the silo and/or via a sealed recirculation system. The important thing is that the phosphine has a large space in the application chamber and/or room to disperse freely into the grain so the gas concentration doesn’t reach explosive levels in the confined space. For more on phosphine application see ‘Grain fumigation – a guide’ or ‘Fumigating with phosphine, other fumigants and controlled atmospheres’
Do I need recirculation?
In silos over 150 tonne a sealed recirculation system is ideal to disperse the gas in a shorter time frame. The key is that the silo is gas-tight – that is, meets a five minute, half-life pressure test and the recirculation system won’t compromise that seal in the future. For more information see ‘Fumigating with phosphine, other fumigants and controlled atmospheres’