Inspecting grain and treating storages

  • Photograph of grain silos
    Grain silos

Plan for insect control before storage

There are no simple short cuts for storing grain safely. If insects are detected as grain is out-loaded for sale, treatment is likely to delay the delivery by two to four weeks. Unless you plan for insect control and have the necessary equipment, you should not be storing grain.

Management plans should include:

  • good hygiene as an essential part of insect control
  • methods to try to prevent insect problems developing
  • inspection for insects and other quality problems
  • methods to control insects if they develop.

Methods that aim to prevent infestations, including those listed as best practices in Table 2, are:

  • cooling grain with aeration
  • treating grain by spraying with residual chemicals
  • treating grain by mixing amorphous silica powder.

Plan to treat any insects that are detected prior to sale by:

  • having at least one sealed silo as a hospital bin for fumigation of infested grain, or
  • having a calibrated sprayer to treat infested grain with dichlorvos as it goes up an auger.
Table 1. Suitable control methods for different grain types and markets
Treatment Cereal grains* for: Pulses* or oil-seeds* Any grain for organic markets
On-farm use Markets accepting residual treatments Markets not accepting residual treatments
Hygiene yes yes yes yes yes
Aeration yes yes yes yes yes
Drying yes yes yes yes yes
Controlled atmosphere yes yes yes yes yes
Phosphine fumigation yes yes yes yes* no
Dichlorvos yes yes nonono
Treatment of storages and equipment Amorphous silica yes yes yes yes no?
Residual chemicals yes yes nonono
Mixture with grain Amorphous silica yes nononono?
Residual chemicals yes yes nonono

Table 1 notes

Cereals include barley, maize, millets, oats, rice, sorghum, triticale, wheat. The only pulse crop for which phosphine is registered is field pea. Oilseeds include canola, linseed, safflower, sunflower, peanut.

yes = can be used
no = cannot be used
no? = some organic markets are reported to accept this treatment, others do not. Check with the potential buyer and organic certifying body.

Inspecting stored grain

Inspect grain in each storage for insects and other quality problems at least once a month and four weeks before the intended sale or delivery date. Use whatever methods are practical and safe. Ideally take samples of a few litres from all access points, using a grain spear for the top surface if it is safe to do so, and also from the bottom hatch. Sieve the grain to separate insects.

If any live insects are found you should consider treating the grain before delivery to bulk handlers or buyers. To ensure that sufficient time is available for treatment, grain should be inspected four weeks before the intended sale or delivery date.

In an aerated silo, the smell of the air blowing out of the grain is a guide to the state of the grain. With experience, you will notice that the smell becomes fresher after a few days of aeration at the start of storage. A musty smell later in storage is an indicator of insect and/or moisture problems. Do not use this test just after a storage has been fumigated.

High temperature is an indicator of insect or moisture problems. Push a rod at least 1-2 m into the grain, leaving it to equilibrate with the grain for an hour if it is metal or half a day if it is wood. Pull the rod out and feel how warm it is. If it is hot, take spear samples and check for insects and moulds. A probe fitted with a protected thermometer or thermocouple sensor can also be used to determine grain temperature.

Cleaning storages and equipment

Before harvest clean out all machinery and equipment used to handle grain, including headers, augers, field bins, truck bins, silos and other storages. Any equipment used to treat or handle pickled seed must be thoroughly cleaned to prevent contamination of new grain.

Special care should also be taken to clean out bags of seed, feed troughs, shed floors, heaps of old bags or any other places where grain and insects may be present. Grain and residues from cleaning should be fumigated with phosphine, buried, burned, or spread thinly over the ground away from buildings and storages.

Best stored-grain management practice and recommended equipment

  • Fumigation e.g. phosphine tablets of stored grain can only be successful against all insect life-cycle stages if carried out in a gas tight, sealed silo.
  • In most circumstances, silos should only be sealed during fumigation. Leaving a silo sealed over extended periods in Australia´s warm climatic conditions with no aeration may lead to conditions suitable for insect pests, moisture migration, moulds and grain quality deterioration. Grain that is very dry or cool is less at risk.
  • When purchasing a sealed silo it is worth including an aeration cooling system. Aeration fans not only achieve the benefits listed below but also assist with silo pressure testing and allow for faster gas ventilation times following a fumigation. Pressure test a sealable silo once a year and carry out maintenance to ensure it is able to hold fumigation gas concentrations for the required time.
  • Freshly harvested grain benefits from aeration designed to reduce grain temperature and creating uniform grain moisture conditions throughout the silo. These two factors combined with good hygiene will significantly reduce problems with grain quality and storage pests.
  • Following this initial post-harvest aeration cooling for a 2-3 week period, a decision to seal the silo and fumigate may be appropriate if it was the first silo filled or there are other hygiene factors that may have increased the risk of storage pest development.
  • Over the medium and long term, grain is best held under aeration cooling, aiming to achieve grain temperatures of 20°C or less. Automatic aeration controllers assist in achieving reliable results.
  • Check the silo monthly, sampling grain from the headspace and outlet for insect pests and quality. Insect traps placed in the grain surface will aid insect pest monitoring. When storage pests are detected, seal the silo and fumigate. Once fumigation is completed, release the silo sealing points and return silo to aeration cooling management.

Storages and equipment: treating for insects

Treating the surfaces of storages and equipment before they are used may kill insects walking on those surfaces. If the storage or equipment is not cleaned before treatment, the treatment will be less effective.

Treating with amorphous silica / diatomaceous earth powder

All surfaces of walls, floors, ledges, and machinery may be treated with amorphous silica yearly, or twice yearly in heavy traffic areas. It can be applied to surfaces in two ways:

  1. As a slurry - this is a very efficient method and is applied at the rate of 6 g/m2.
  2. As a dust - amorphous silica powder requires an air stream to move it into surfaces and into crevices at the rate of 2 g/m2. When applying the dust to large areas, use a power duster such as a Stihl SR400 or Blovac BV22. Operators of such equipment should wear disposable dust masks. Treating small storages can be achieved using a bellows-type dust blower (from horticultural suppliers) or a venturi-type gun. Dust treatment of headers after cleaning is recommended - follow the directions on the label.

Treating with chemicals

Residual chemicals can be sprayed onto the surfaces of storages and equipment to kill walking insects, but only if the grain to be handled and stored is destined for a market that accepts residues on the grain. Do not use these chemicals if oilseeds or pulses are to be stored, or if potential buyers will not accept treated grain (Table 2).

Apply these only if the grain is destined for a market that accepts residues on the grain. If the market does not accept grain residues, clean and leave, or clean and apply amorphous silica / diatomaceous earth powder.

Table 2. Insecticides to treat clean surfaces of storages and equipment to kill walking insects
Select one of these options: Insecticide (for trade names - see Table 9) Dilution rate
per L water
Application rate
Spray a mixture of two insecticides diluted in water* Mix either: 11 mL/L Apply 1 L of diluted mixture for every 20 m2 of surface area
pirimiphos-methyl®
or chlorpyriphos-methyl® 20 mL/L
or fenitrothion 10 mL/L
with 20 mL/L
carbaryl
Spray a single insecticide diluted in water Either 10 g/L Apply 1 L of diluted insecticide for every 20 m2 of surface area
azamethiphos® (may not be currently available)
or 10 mL/L
dichlorvos (500 g/L formulation)
or Slurry in water - as per label
amorphous silica
Apply a dust amorphous silica powder Dust application As per label

*Dilute each concentrate in a small amount of water before mixing together the insecticides in the spray vat and making up the total volume with water.

Refer to Table 9 in the Stored grain management guide.

Last updated 17 November 2010