Chemicals to treat insects in stored grain

  • A map of Eastern Australia where strong resistance to protectant insecticides has been identified
    Map of Eastern Australia where strong resistance to protectant insecticides has been identified

Knockdown of insects in infested stored grains

There are four major methods covered here:

  1. Knockdown with Dichlorvos alone, applied to grain at in-loading (Table 1). 
  2. Mixing dichlorvos knockdown with protectant insecticides for a single application to grain. 
  3. Fumigating with phosphine (´bombing´) of infested stored grain including safety, application methods and sealed silos.
  4. Fumigating with Vapormate® (this option requires a state-licenced operator, and special application and monitoring equipment approved by BOC Ltd).

Knockdown of live insects with grain-applied insecticides

Application of dichlorvos at the rates specified in Table 1 can be used to kill insects in grain. Allow three days for all insects to die after treatment, and observe the withholding periods (see below) before sale.

If grain is to be sold, use insecticides only if approved by your buyer or handler. Cereal grains include barley, maize, millets, oats, rice, sorghum, triticale, wheat.

Table 1. Dichlorvos application rates for knockdown of live adult insects in infested cereal grain
Insects Insecticide Dilution rate1 Application rate Cost2 Withholding period3

most species

dichlorvos

1.14 kg/L

500 g/L

5.3 mL

12 mL

Apply 1 L of diluted insecticide per tonne as grain is augured

12-15c

30-35c

7 days

7 days

lesser grain borer

dichlorvos

1.14 kg/L

10.5 mL

Apply 1 L of diluted insecticide per tonne as grain is augured

24-30c

28 days

moths only

dichlorvos

1.14 kg/L

500 g/L

4.4 mL

10 mL

Apply 1 L of diluted insecticide for every 20 m2 of grain surface area

10-15c

24-30c

7 days

7 days

Table 1 Notes:

ALWAYS CHECK LABELS

For insecticide trade names, see Table 9 in Stored grain management guide .

  1. Dilute liquid concentrates in water at the specified rate per litre, then spray 1 litre of the mixture per tonne of grain while auguring the grain or spray 1 litre per 20 square metres of grain surface to control moths.
  2. Costs (cents per tonne or cents per 20 square metres in 2006) for chemicals only are presented as an approximate guide.
  3. If grain is infested with lesser grain borers then the 10.5 ml rate of dichlorvos is recommended because of resistance in these insects. A withholding period of 28 days applies to this treatment.

Residual insecticides (protectants) for treating stored grains

There are three treatment tables here which cover the following on-farm treatment requirements:

  • Treating stored cereal grain (except malting barley) - see Table 2
  • Treating stored feed grains and/or seed  - see Table 3
  • Treating stored malting barley on-farm - see Table 4.

Important notes on protectant insecticides:

  • Protectants (insecticides sprayed directly on to grain at in-loading) will not always kill adult insects present at the time of treatment. These treatments are intended to control developing immature insect stages (i.e. larvae), rather than existing mature adult stages.
  • Methoprene and s-methoprene (IGR®) are ´insect growth regulators´ - they control only immature stages and will not kill adult insects .
  • Phosphine or dichlorvos are recommended for use as a knockdown treatment if adult insects are present.
  • If protectants are to be added to infested grain then the grain should be treated (fumigated) with phosphine before applying the protectants, or, alternatively, dichlorvos (Table 1) can be applied as a direct spray to grain at the same time as the protectants.
  • Adhere strictly to label rates so the Maximum Residue Limits (MRL´s) are not exceeded when your grain is sold to end-user.

Table 2 - Stored cereal grains

If grain is to be sold, use insecticides only if approved by your buyer. Cereal grains include barley, maize, millets, oats, rice, sorghum, triticale, wheat. 

Table 2. Stored cereal grains - insecticide application rates to protect stored cereal grain, except malting barley
Insecticide1 Storage period Withholding period (WHP)4 and restrictions on use
6 weeks - 3 months 3 months - 9 months
Rate / tonne2 Cost3 Rate / tonne2 Cost3

Apply a mixture of -

either
pirimiphos-methyl
(900g/L product)

4.5 mL

30-35c

4.5 mL

30-35c

No withholding period

or  chlorpyriphos-methyl (500 g/L product)

10 mL

75-80c

20 mL

150-160c

No withholding period, do not apply to rice or malting barley

or  fenitrothion (1000 g/L product)

6 mL

18-20c

12 mL

35-40c

Withholding period 90 days for the high rate

or  deltamethrin (e.g. 250 g/l product) + pip. butoxide

4 mL

15-20c

4 mL

15-20c

No withholding period (okay for malt barley & sorghum). May not be generally available

with either

methoprene (e.g. 200 g/L product),

or  s-methoprene (30 g/L product)

or s-methoprene  (300 g/L product)

5 mL

20 mL

2 mL

150-160c

5 mL

20 mL

2 mL

150-160c

No withholding period

No withholding period

Table 2 Notes:

For insecticide trade names, see Table 9 in Stored grain management guide .

  1. Always check dose rates and all other details on product label. The table above is a guide only. Products such as Relden pluS IGR® is a single tin formulation mixture containing both chlorphriphos-methyl (500 g/L) and S-methoprene (30 g/L).
  2. Dilute liquid concentrates in water at the specified rate per litre, then spray 1 litre of the mixture per tonne of grain while auguring the grain.
  3. Costs (cents per tonne in 2006) for chemicals only are presented as an approximate guide. Large pack sizes are cheaper per tonne treated than small packs.
  4. Insecticide residues must not exceed Maximum Residue Limits (MRL). Where application rates exceed MRL you must wait the withholding period to allow residues in the grain to decay to less than the MRL before selling the grain.

Seedlings of some sorghum varieties are susceptible to toxicity from organophosphorus insecticides such as pirimiphos-methyl, fenitrothion and chlorpyriphos-methyl.

Table 3 - Feed grains and seed

If grain is to be sold, use insecticides only if approved by your buyer or handler. Cereal grains include barley, maize, millets, oats, rice, sorghum5, triticale, wheat.

Table 3. Feed grains and seed - insecticide application rates for cereal grains for use on farm for seed or animal feed, or for sale for animal feed. Alternatives in Table 4 can also be used
Insecticide Storage period Withholding period (WHP)3 and restrictions on use
6 weeks - 3 months 3 months - 9 months
Rate/ tonne1 Cost2 Rate/ tonne1 Cost2

Apply a mixture of -

either  pirimiphos-methyl (900g/L product)

4.5 mL

30-35c

4.5 mL

30-35c

No withholding period

or  chlorpyriphos-methyl (500g/L product)

10 mL

75-80c

20 mL

150-160c

No withholding period

or  fenitrothion

6 mL

18-20c

12 mL

35-40c

Withholding period 90 days for the high rate

or  deltamethrin (250 g/L product) + pip. butoxide

4 mL

15-20c

4 mL

15-20c

No withholding period. May not be generally available

with  carbaryl

(check with grain buyer)

10 mL

12c

16 mL

19c

Withholding period 90 days for the high rate

Do not use carbaryl on malting barley, milling wheat, or grain for bulk handlers

Table 3 Notes:

Trade names of these insecticides are listed in Table 9 in Stored grain management guide .

  1. Dilute liquid concentrates in water at the specified rate per litre, then spray 1 litre of the mixture per tonne of grain while auguring the grain. Add dusts directly to the grain.
  2. Costs (cents per tonne in 2006) for chemicals only are presented as an approximate guide. Large pack sizes are cheaper per tonne treated than small packs.
  3. Insecticide residues must not exceed Maximum Residue Limits (MRL). Where application rates exceed MRL you must wait the withholding period to allow residues to decay to less than the MRL before you feed.
  4. Seedlings of some sorghum varieties are susceptible to toxicity from organophosphorus insecticides such as pirimiphos-methyl, fenitrothion and chlorpyriphos-methyl.

Table 4 - Malting barley on-farm

Use insecticides only if approved by your buyer or handler. Maltsters prefer barley without residual treatments, and some insects are resistant to all listed protectants, so consider non-chemical alternatives.

Table 4. Malting barley on-farm - insecticide application rates for protection of malting barley
Insecticide1 Storage period Withholding period4
6 weeks - 3 months 3 months - 9 months
Rate/ tonne2 Cost3 Rate/ tonne2 Cost3

Apply a mixture of

either  fenitrothion

6 mL

18-20c

12 mL

35-40c

90 days for high rate

or  deltamethrin (250g/l) + pip. butoxide

4 mL

15-20c

4 mL

15-20c

No withholding period. May not be generally available. Note - check with maltster before using

with either

methoprene (200 g/L product)

or  methoprene (50 g/L product)

or  S-methoprene (30 g/L product)

5 mL

20 mL

20 mL

150-160c

100-140c

230-240c

5 mL

20 mL

20 mL

150-160c

100-140c

230-240c

No withholding period

No withholding period

No withholding period

Table 4 Notes:

Trade names of these insecticides are listed in Table 9 in Stored grain management guide .

  1. Always check dose rates and all other details on product label. The table above is a guide only. Products such as Relden pluS IGR® is a single tin formulation mixture containing both  chlorphriphos-methyl (500 g/L) and S-methoprene (30 g/L)
  2. Dilute liquid concentrates in water at the specified rate per litre, then spray 1 litre of the mixture per tonne of grain while auguring the grain.
  3. Costs (cents per tonne in 2007) for chemicals only are presented as an approximate guide. Large pack sizes are cheaper per tonne treated than small packs.
  4. Insecticide residues must not exceed Maximum Residue Limits (MRL). Where application rates exceed MRL you must wait the withholding period to allow residues in the grain to decay to less than the MRL before selling the grain.

Applying protectant insecticides

Protectant chemicals will work in all types of storages with no modifications required, but they must be applied evenly to grain to be fully effective. Simple, correctly calibrated application equipment is needed.

  • Apply the correct dose - underdosing will result in reduced protection, overdosing is wasteful and may cause grain to be rejected by buyers or held for longer until residues decline to levels accepted by markets.
  • Mix concentrated insecticide in clean containers with rainwater if possible - alkaline water causes insecticides to break down very quickly. Don't mix concentrates directly, dilute first, then mix. Don't hold mixed pesticides for more than a few days - mix just enough spray and use it as soon as possible
  • Apply protectants to grain while it is being augured. Spray into the auger hopper or into the auger casing. Using a flow meter.
  • High-volume pumps allow bypass to agitate liquid spary mixtures; other pump types may be used with care; thoroughly wash equipment with water afer use.
  • Calibrate your application equipment with water before every use. The spray equipment must be calibrated to spray 1 litre of solution per tonne of grain. That is, the spray rate, measured in litres per hour, must equal the auger or elevator uptake in tonnes per hour.
  • Wear protective clothing - goggles, gloves and overalls when handling protectants; avoid breathing the fumes; don't eat, smoke or put your fingers in your mouth, wash well and change your clothes when you finish.

Mixing amorphous silica / diatomaceous earth powder with grain

Amorphous silica powder (e.g. Dryacide® or Absorba-Cide®, or Abrade®, or Permaguard D10®) can be mixed with grain as an alternative to the chemical sprays.  It can be used on feed grain or grain used on the farm, but should not be used for any other grain unless potential buyers approve of its use.

The major advantages of these inert dusts are that they leave no chemical residue, have no withholding period and minimise selection for resistance. They are accepted by some organic markets. Always check with the Organic certifying body first. 

Note: These products have some serious disadvantages for mixing with grain. They are far more expensive than any other chemical treatments. Bulk handlers and some buyers will not accept grain treated with amorphous silica / diatomaceous earth because they change the handling characteristics of grain and slow movement of grain through augers.

Unlike protectant chemical insecticides which are applied to grain as a liquid spray, amorphous silica / diatomaceous earth are applied to grain as a dust. The dust collects on insects and dries them out. A pickle applicator or a special Dryacide® applicator, available from Dryacide Australia through rural supply houses, is the best way to apply such products.

Add amorphous silica powder at the rate specified on the label. If grain is dusty or infested, increasing the application rate will increase its effectiveness. Amorphous silica is not effective on high moisture grain above 12%.


Other treatment methods

Controlled or modified atmosphere (CA) refers to the process of altering the proportion of atmospheric gases oxygen, nitrogen and carbon dioxide (CO2) to produce a gas mixture toxic to insects. The advantage of the CA technique is that it provides a disinfestation method that is chemical-free and suitable for ´organic´ grain, but it is expensive.

Controlled aeration cooling can greatly reduce insect and mould activity in stored grain, as well as preserving grain quality. Aeration cooling lowers the temperature of grain by blowing cool air through it. An automatic controller is more effective than thermostats, timers or manual switches in selecting the coldest air available.

Reducing grain temperature slows insect development. For example, flour beetles can complete their development in three weeks at 35oC and 70% RH, but take ten weeks at 22.5oC and 70% RH. Although adult grain insects live a long time at cool temperatures, their young stages stop developing at temperatures below 15 oC for weevils or 20 oC for most other species.

Aeration may need to be used in conjunction with other pest control methods. It may fail to control insects because of heating of the surface layer, particularly in summer, or because of insects flying into the surface layer. Both these problems can be overcome by mixing amorphous silica into the top 30 cm of grain at the rate of 1 kg per tonne of grain. The amorphous silica is diluted when out-loading to levels that are acceptable to buyers. Painting the roof and north-western side of the storage white can reduce the effects of surface heating.

Aeration cooling is strongly recommended for seed or malting barley to maintain germination and malting quality.

Related information

Last updated 17 November 2010