Aeration cooling for pest control

Stored Grain Aeration cooling

Grain aeration provides growers with a powerful tool to maintain grain quality during harvest and storage. Aeration cooling may not eliminate the need for chemical insect control, but it will dramatically slow insect development.

 Key Points

  • Grain temperatures below 20°C significantly reduce mould and insect development.
  • Reducing grain temperature with aeration cooling protects seed viability.
  • Controlling aeration cooling is a three-stage process — continual, rapid and then maintenance.
  • Stop aeration if ambient, relative humidity exceeds 85 per cent.
  • Automatic grain aeration controllers that select optimum fan run times provide the most reliable results.

Aeration cooling for pest control 1

Aeration cooling for pest control

While adult insects can still survive at low temperatures, most young storage pests stop developing at temperatures below 18–20°C (see Table 1).

At temperatures below 15°C the common rice weevil stops developing.

At low temperatures insect pest life cycles (egg, larvae, pupae and adult) are lengthened from the typical four weeks at warm temperatures (30-35°C) to 12-17 weeks at cooler temperatures (20-23°C).

Aeration cooling for pest control 2

An effective insulator

Without aeration, grain is an effective insulator and will maintain its warm harvest temperature for a long time.

Like housing insulation, grain holds many tiny pockets of air within a stack — 100 tonnes of barley requires a silo with a volume of about 130 cubic metres, 80m3 is taken up by grain and the remaining 50m3 (38 per cent) is air space around each grain.

Seed viability

Research trials reveal that wheat at 12 per cent moisture content stored for six months at 30-35°C (unaerated grain temperature) will have reduced germination percentage and seedling vigour.

Aeration cooling


Aeration cooling can be achieved with air-flow rates of 2–3 litres per second per tonne delivered from fans driven by a 0.37 kilowatt (0.5 horsepower) electric motor for silos around 100t.

Research carried out by the Department of Agriculture, Fisheries and Forestry (DAFF), Queensland shows that with the support of an aeration controller, aeration can rapidly reduce stored grain temperatures to a level that helps maintain grain quality and inhibits insect development.

During trials where grain was harvested at 30°C and 15.5 per cent moisture, grain temperatures rose to 40°C within hours of being put into storage.

An aeration controller was used to rapidly cool grain to 20°C and then hold the grain between 17–24°C during November through to March.

Before replicating similar results on farm, growers need to:

  • Know the capacity of their existing aeration system.
  • Determine whether grain requires drying before cooling can be carried out.
  • Understand the effects of relative humidity and temperature when aerating stored grain.
  • Determine the target conditions for the stored grain.

Air used for cooling grain

Varying ambient conditions affect stored grain differently depending on the combination of temperature and relative humidity outside the silo and the temperature and moisture content of the stored grain (see Table 2).

Aeration cooling for pest control 3

Grain with a higher moisture content can be cooled quickly with low-humidity air due to the evaporative cooling effect that occurs inside the storage.

The relative humidity of the ambient air affects the efficiency of grain cooling.

In an ideal world we would select air for cooling that is low in temperature and relative humidity, but these conditions rarely occur.

Air movement within the stack

Grain at the top of the stack is the hottest, as heat rises through the grain and it is exposed to the head space in the silo (see Figure 1).

As the air in the head space heats and cools each day, it creates ideal conditions for condensation to form and wet the grain on the top of the stack.

Be aware aeration drying requires specifically-designed equipment and the process is much slower than aeration cooling or hot-air drying.

The cooling process

Aeration cooling for pest control 4

Operating an aeration fan for cooling requires a planned control program, which is best done with an automatic aeration controller.

But even without an aeration controller growers need to aim for the same run time, following the same process.

Without aeration, grain typically increases in temperature immediately after it enters the storage.

The initial aim is to get maximum air-flow through the grain bulk as soon as it enters storage, to stop it from sweating and heating.

When first loading grain into storage, run the aeration fans continuously from the time the grain covers the aeration ducts for the next 1-3 days, until the cooling front reaches the top of the storage.

However, do not operate the aeration fans on continuous mode if the ambient relative humidity is higher than 85 per cent for extended periods of time as this will wet the grain.

After the aeration fans have been running continuously for 2–3 days to flush out any warm, humid air, reduce run time to 9–12 hours per day during the coolest period, for the next seven days.

The goal is to quickly reduce the grain temperature from the mid 30s°C down to the low 20s°C.

An initial reduction in grain temperature of 10°C ensures grain is less prone to damage and insect attack, while further cooling becomes a more precise task. During this final stage, automated aeration controllers generally run fans during the coolest periods of the day, averaging 100 hours per month.

Grain temperature is gradually reduced as low as possible and then maintained throughout the storage period.

The risks of getting it wrong

Running aeration fans on timers that are pre-set for the same time each day will not ensure the selection of the most appropriate air for grain quality maintenance.

The biggest risk with running aeration fans without a controller is forgetting or not being available to turn fans off if the relative humidity exceeds 85 per cent.

Operating fans for extended periods of a few hours or days in humid conditions can increase grain moisture and cause moulding.

Aeration controllers are designed to automatically select the best time to run aeration fans. Fans on these systems only run when the conditions will benefit the stored grain.

Aeration cooling for pest control 5

Cooling or drying — making a choice

Knowing whether grain needs to be dried or cooled can be confusing but there are some simple rules of thumb.

For longer-term storage grain must be lowered to the correct moisture content.

Grain that is dry enough to meet specifications for sale (12.5 per cent for wheat or 13.5 per cent for sorghum) can be cooled, without drying, to slow insect development and maintain quality.

Grain of moderate moisture (up to 15 per cent for wheat and sorghum)

can be either cooled for short periods to slow mould and insect development or, dried providing the right equipment and conditions are available.

After drying to the required moisture content, grain can be cooled to maintain quality.

High-moisture grain (for example, 16 per cent or more for wheat and sorghum) will require immediate moisture reduction before cooling for maintenance.

Installation and maintenance tips

When retrofitting an aeration system, avoid splitting air-flow from one fan to more than one storage. Each storage will provide

a different amount of back-pressure on the fan resulting in uneven air-flow and inefficient or even ineffective cooling.

If buying an aeration controller be aware that most controllers need to be installed by an electrician.

The preferred mounting location for aeration controllers is outside where the sensors can get ambient condition readings but are sheltered from the direct elements of the weather.

To avoid the chance of a dust explosion, avoid installing aeration controllers in a confined space.

Ensure your electrician installs wiring properly insulated and protected from potentially-damaging equipment, such as augers.

Monitoring a must

Aeration cooling for pest control 6

Aeration controllers reduce the amount of time operators need to physically monitor grain storages and turn fans on and off, but units and storage facilities still need to be checked regularly.

Most controllers have hour meters fitted so run times can be checked to ensure they are within range of the expected total average hours per month.

Check fans to ensure they are connected and operating correctly.

The smell of the air leaving the storage is one of the most reliable indicators if the system is working or not.

The exhausted air should change from a humid, warm smell to a fresh smell after the initial cooling front has passed through the grain.

Animals can damage power leads and automatic controller sensors and fan blades or bearings can fail, so check these components regularly.

Check for suction in and feel for air-flow out of the storage vents when the fans are running.

Keeping grain at the right moisture and temperature levels will reduce the likelihood of insect infestations, but stored grain still needs to be sampled regularly and monitored for any changes.

If possible, safely check the moisture and temperature of the grain at the bottom and top of the stack regularly.

Western Region Grain Storage Pest Control Guide

Grain Storage monitoring

The tolerance for live pests in grain sold off farm is nil. With growers increasing the amount of grain stored on farm, an integrated approach to pest control is crucial.

KEY POINTS

  • Effective grain hygiene and aeration cooling can overcome 85 per cent of pest problems.
  • When fumigation is needed it must be carried out in pressure-tested, sealed silos.
  • Monitor stored grain monthly for moisture, temperature and pests.

Prevention is better than cure

The combination of meticulous grain hygiene plus well-managed aeration cooling generally overcomes 85 per cent of storage pest problems. For grain storage, three key factors provide significant gains for both grain storage pest control and grain quality – hygiene, aeration cooling and correct fumigation.

Attack early: Managing grain storage pests starts before grain enters the storage with grain hygiene and structural treatments.

Hygiene

The first grain harvested is often at the greatest risk of early insect infestation due to contamination. One on-farm test found more than 1000 lesser grain borers in the first 40 litres of wheat passing through the harvester. Remove grain residues from empty storages and grain handling equipment, including harvesters, field bins, augers and silos to ensure an uncontaminated start for new-season grain. Clean equipment by blowing or hosing out residues and dust and then consider a structural treatment (see Table 2, page 2). Remove and discard any grain left in hoppers and bags from the grain storage site so it doesn’t provide a habitat for pests during the off season.

Aeration cooling

Freshly-harvested grain usually has a temperature around 30°C, which is an ideal breeding temperature for storage pests (see Table 1). Studies have shown that rust-red flour beetles stop breeding at 20°C, lesser grain borer at 18°C and below 15°C all storage pests stop breeding.

Aim for grain temperatures of less than 23°C during summer and less than 15°C during winter. When placing grain into storage, run aeration fans continuously for the first 2-3 days to push the first cooling front through the grain and to create uniform moisture conditions. Then run the fans during the coolest 9-12 hours per day for the next 3-5 days. This will push a second cooling front through the grain bulk.

Aeration cooling generally only requires air-fl ow rates of 2-4 litres per second per tonne. Finally the grain requires approximately 50 hours of appropriate quality air each fortnight during storage. Use an aeration controller that will perform the cooling process at the right time and continue to aerate the grain selecting the coolest air to run fans. An effective aeration controller will also ensure fans don’t operate when the relative humidity is higher than 85 per cent, which can re-wet and damage grain if operated for extended periods.

TABLE 1 THE EFFECT OF GRAIN TEMPERATURE AND MOISTURE ON STORED GRAIN INSECT AND MOULD DEVELOPMENT

Ineffective fumigation

Fumigation with phosphine is a common component of many integrated pest control strategies. Taking fumigation shortcuts may kill enough adult insects in grain so it passes delivery standards, but the repercussions of such practices are detrimental to the grains industry. Poor fumigation techniques fail to kill pests at all life cycle stages, so while some adults may die, grain will soon be reinfested again as soon as larvae and eggs develop. What’s worse, every time a poor fumigation is carried out, insects with some resistance survive, and pass the resistance gene into their progeny making control more diffi cult in the future.

Effective fumigation

Using the right type of storage is the first and most important step towards an effective fumigation. Only use fumigants, like phosphine, in a pressure-tested, sealed silo. Research shows that fumigating in a storage that is anything less than pressure sealed doesn’t achieve a high enough concentration of fumigant for a long enough period to kill pests at all life cycle stages. For effective phosphine fumigation, a minimum of 300 parts per million (ppm) gas concentration for seven days or 200ppm for 10 days is required. Fumigation trials in silos with small leaks demonstrated that phosphine levels are as low as 3ppm close to the leaks. The rest of the silo also suffers from reduced gas levels.

Achieve effective fumigation by placing the correct phosphine rates (as directed on the label) onto a tray and hanging it in the top of a pressure-tested, sealed silo or into a ground level application system if the silo is fitted with recirculation. After fumigation, ventilate grain for a minimum of one day with aeration fans running, or five days if no fans are fitted. A minimum withholding period of two days is required after ventilation before grain can be used for human consumption or stock feed. The total time needed for fumigating is 10-17 days.

As a general rule, only keep a silo sealed while carrying out the fumigation (for example, one to two weeks). If grain moisture content is low (8-12%) the silo can remain sealed after fumigating but regular monitoring is essential to check for insect infestation and moisture migration to the head space.

TABLE 2 RESISTANCE AND EFFICACY GUIDE FOR STORED GRAIN INSECTS 2010 – CEREAL GRAINS SEPTEMBER 2010 (WESTERN GRAIN PRODUCTION REGIONS).

Check regularly: Monitor stored grain at least monthly, including sampling from the top of the storage, if it can be done safely, or with a pitfall trap.Monitoring

When grain is put into storage it needs monitoring just like it does when it’s in the paddock – regularly.Check stored grain at least monthly, taking samples from the bottom, and if safe, the top of the storage.

Things to monitor:

  • Insect pests
  • Grain temperature
  • Grain moisture content
  • Grain quality and germination

Storage choices

When buying a new silo, buy a quality, sealable silo fi tted with aeration and check with the manufacturer that it meets the Australian Standard for sealable silos (AS2628). Experience has shown that at least two sealable, aerated silos on farm provide the option for an effective fumigation and delivery program. Many older silos are not designed to be sealed and cannot be used for fumigation, however retro-fitting aeration can reduce insect multiplication through grain cooling.

Seed held on farm (cereals — wheat, barley, oats)

Seed that is dry, cool and sound (not weather damaged) will remain viable for longer. In well-managed storage, germination percentages can be expected to reduce by only 5 per cent after six months. To achieve this, keep grain moisture content below 12%. Grain temperature also has a major impact on germination. Aim for grain temperatures of 20°C and below in seed storage by using aeration cooling (with auto control). Wheat at 12 per cent moisture content stored at 30-35°C (unaerated grain temperature) will reduce germination percentages and seedling vigour when stored over a long period. Position small seed silos in the shade or paint them reflective white to assist keeping grain cool. WA growers can treat seed with a grain protectant combined with a dyed grain fungicide in combination with aeration cooling to maximise insect control.

Pulse and oilseeds

Insect control options are limited for stored pulses and oilseeds. Aeration and phosphine fumigation are the main methods and controlled atmosphere (inert gasses such as carbon dioxide or nitrogen) may be an option. The effectiveness of phosphine fumigation on oilseeds is often reduced due to phosphine sorption during treatment.Monitoring gas concentrations with a gas monitor is essential to ensure the correct concentration is achieved for the correct length of time. Use sound grain hygiene in combination with aeration cooling to reduce insect activity. Small seed-size grains, such as canola, may need larger-capacity aeration fans to combat the greater amount of back pressure in the storage. Always store these grains at their recommended grain moisture content level.

PHOSPHINE RESISTANCE IS WIDESPREAD – PLAN, MONITOR AND CONTROL FOR CLEAN GRAIN

  • Dispose of grain residues and seed gradings. Clean empty storages and grain handling equipment, including harvesters, field bins and augers.
  • Sieve stored grain for the presence of insects at least monthly, or use pitfall traps. Also check grain temperature and moisture.
  • If grain temperature has been kept below 15°C by aeration, live insect numbers are likely to be low.
  • Sample grain three weeks before sale to allow time for any treatment.
  • For effective fumigations, pressure test sealable silos at least once a year to identify any leaks and ensure rubber seals are maintained.
  • Phosphine fumigation typically requires 7 to 10 days in a gas-tight sealed silo. When completed, open silo top with care, ventilate using aeration fan for one day; if not aerated, open silo top and ventilate for five days. The minimum withholding period is then two days after ventilation is completed. The total time needed for fumigation is therefore 10-17 days.
  • Sieve a half-litre sample onto a white tray. Hold tray in sunlight to warm for 20 to 30 seconds to encourage insect movement.
  • If live insects are found, identify them and fumigate in a gas-tight silo according to the label.
  • Take care when climbing silos to sample grain for insects and wear a safety harness. Sample from the base, and if safe, take

PHOSPHINE RESISTANCE – NATIONAL SITUATION

Northern & Southern Regions Grain Storage Pest Control Guide

Grain Storage pest attack

The tolerance for live pests in grain sold off farm is nil. With growers increasing the amount of grain stored on farm, an integrated approach to pest control is crucial.

KEY POINTS

  • Effective grain hygiene and aeration cooling can overcome 75 per cent of pest problems.
  • When fumigation is needed it must be carried out in pressure-tested, sealed silos.
  • Monitor stored grain monthly for moisture, temperature and pests.

Prevention is better than cure

The combination of meticulous grain hygiene plus well-managed aeration cooling generally overcomes 75 per cent of storage pest problems.

For grain storage, four key factors provide significant gains for both grain storage pest control and grain quality – hygiene, aeration cooling, correct fumigation and monthly monitoring.

Attack early: Managing grain storage pests starts before grain enters the storage with grain hygiene and structural treatments.

Hygiene

The first grain harvested is often at the greatest risk of early insect infestation due to contamination.

One on-farm test found more than 1000 lesser grain borers in the first 40 litres of wheat passing through the harvester.

Remove grain residues from empty storages and grain handling equipment, including harvesters, field bins, augers and silos to ensure an uncontaminated start for new-season grain.

Clean equipment by blowing or hosing out residues and dust and then consider a structural treatment.

Bury, use or burn any grain left in hoppers and bags from the grain storage site so it doesn’t provide a habitat for pests during the off season.

Aeration cooling

Freshly-harvested grain usually has a temperature around 30°C, which is an ideal breeding temperature for storage pests (see Table 1).

Studies have shown that rust-red flour beetles stop breeding at 20°C, lesser grain borer at 18°C and below 15°C all storage pests stop breeding.

Aim for grain temperatures of less than 23°C during summer and less than 15°C during winter.

When placing grain into storage, run aeration fans continuously for the first 3-4 days to push the first cooling front through the grain and to create uniform moisture conditions.

Then run the fans during the coolest 9-12 hours per day for the next 5-7 days. This will push a second cooling front through the grain bulk.

Aeration cooling generally only requires air-fl ow rates of 2-4 litres per second per tonne.

Finally the grain requires approximately 50 hours of appropriate quality air each fortnight during storage.

Use an aeration controller that will perform the cooling process at the right time and continue to aerate the grain selecting the coolest air to run fans.

An effective aeration controller will also ensure fans don’t operate when the relative humidity is higher than 85 per cent, which can re-wet and damage grain if operated for extended periods.

TABLE 1 THE EFFECT OF GRAIN TEMPERATURE AND MOISTURE ON STORED GRAIN INSECT AND MOULD DEVELOPMENT
Chemical control

Fumigation with phosphine is a common component of many integrated pest control strategies.

Taking fumigation shortcuts may kill enough adult insects in grain so it passes delivery standards, but the repercussions of such practices are detrimental to the grains industry.

Poor fumigation techniques fail to kill pests at all life cycle stages, so while some adults may die, grain will soon be reinfested again as soon as larvae and eggs develop.

What’s worse, every time a poor fumigation is carried out, insects with some resistance survive, making the chemical less effective in the future.

Effective fumigation

Using the right type of storage is the first and most important step towards an effective fumigation.

Only use fumigants, like phosphine, in a pressure-tested, sealed silo.

Research shows that fumigating in a storage that is anything less than pressure sealed doesn’t achieve a high enough concentration of fumigant for a long enough period to kill pests at all life cycle stages.

For effective phosphine fumigation, a minimum of 300 parts per million (ppm) gas concentration for seven days or 200ppm for 10 days is required. Fumigation trials in silos with small leaks demonstrated that phosphine levels are as low as 3ppm close to the leaks. The rest of the silo also suffers from reduced gas levels.

Achieve effective fumigation by placing the correct phosphine rates (as directed on the label) onto a tray and hanging it in the top of a pressure-tested, sealed silo or into a ground level application system if the silo is fitted with recirculation.

After fumigation, ventilate grain for a minimum of one day with aeration fans running, or five days if no fans are fitted.

A minimum withholding period of two days is required after ventilation before grain can be used for human consumption or stock feed.

The total time needed for fumigating is 10-17 days.

As a general rule, only keep a silo sealed while carrying out the fumigation (for example, one to two weeks).

After fumigation has been completed, return to aeration cooling to hold the stored grain at a suitable temperature level.

Northern & Southern Regions Grain Storage Pest Control Guide table 2

Check regularly: Monitor stored grain at least monthly, including sampling from the top of the storage, if it can be done safely, or with a pitfall trap.Monitoring

When grain is put into storage it needs monitoring just like it does when it’s in the paddock – regularly.

Check stored grain at least monthly, taking samples from the bottom, and if safe, the top of the storage.

Things to monitor and record:

  • Insect pests
  • Grain temperature
  • Grain moisture content
  • Grain quality and germination

Storage choices

When buying a new silo, buy a quality, sealable silo fi tted with aeration and check with the manufacturer that it meets the Australian Standard for sealable silos (AS2628).

Experience has shown that at least two sealable, aerated silos on farm provide the option for an effective fumigation and delivery program.

Many older silos are not designed to be sealed and cannot be used for fumigation, however retro-fitting aeration can reduce insect multiplication through grain cooling.

STORAGE AND TREATMENT NOTES

cereal grains delivered to customers

Buyers and bulk handlers are changing their acceptance of grain treated with insecticides.

Before using a grain insecticide, always check with potential buyers and bulk handlers (depot) for market acceptability.

identify storage pests before selecting a treatment. Always follow label instructions carefully.

Seed held on farm (cereals — wheat, barley, oats)

Seed that is dry, cool and sound (not weather damaged) will remain viable for longer.

In well-managed storage, germination percentages can be expected to reduce by only 5 per cent after six months.

To achieve this, keep grain moisture content below 12%.

Grain temperature also has a major impact on germination.

Aim for grain temperatures of 20°C and below in seed storage by using aeration cooling (with auto control).

Wheat at 12 per cent moisture content stored at 30-35°C (unaerated grain temperature) will reduce germination percentages and seedling vigour when stored over a long period.

Position small seed silos in the shade or paint them reflective white to assist keeping grain cool.

Treating seed with a grain protectant, in combination with aeration cooling, will maximise insect control.

Pulse and oilseeds

Insect control options are limited for stored pulses and oilseeds.

Grain protectants are not registered for use on these grains. Phosphine fumigation and controlled atmosphere (inert gasses such as carbon dioxide or nitrogen) may be an option.

The effectiveness of phosphine fumigation on oilseeds can be reduced due to phosphine sorption during treatment.

Use sound grain hygiene in combination with aeration cooling to reduce insect activity. Small-seed grains, such as canola, may need larger capacity aeration fans

on stores.

Always store these grains at their recommended grain moisture content level.

PHOSPHINE RESISTANCE IS WIDESPREAD – PLAN, MONITOR AND CONTROL FOR CLEAN GRAIN

  • Dispose of grain residues and seed gradings. Clean empty storages and grain handling equipment, including harvesters, field bins and augers.
  • Sieve stored grain for the presence of insects at least monthly, or use pitfall traps. Also check grain temperature and moisture.
  • If grain temperature has been kept below 20°C by aeration, live insect numbers are likely to be low.
  • Sample grain three weeks before sale to allow time for any treatment.
  • For effective fumigations, pressure test sealable silos at least once a year to identify any leaks and maintain rubber seals.
  • Keep monthly storage records of pests found and any fumigation or chemical  treatments.
  • Phosphine fumigation typically requires 7 to 10 days in a gas-tight sealed silo. When completed, open silo top with care, ventilate using aeration fan for one day; if not aerated, open silo top and ventilate for five days. The minimum withholding period is then two days after ventilation is completed. The total time needed for fumigation is therefore 10-17 days.
  • Sieve a half-litre sample onto a white tray. Hold tray in sunlight to warm for 10 to 15 seconds to encourage insect movement.
  • If live insects are found, identify them. Select the appropriate treatment for the grain type and insect. Check labels.
  • Take care when climbing silos to sample grain for insects and wear a safety harness. Sample from the base, and if safe, take a sample from the surface of the grain.

Northern & Southern Regions Grain Storage Pest Control Guide figur 1