Chemicals to treat insects in stored grain

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 (ie, 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 knock-down 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. 

Notes on Table 2:

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 (500g/L) and S-methoprene (30g/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.

Notes on Table 3

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.

Notes on Table 4:

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 (500g/L) and S-methoprene (30g/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; thorougly 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 (eg., 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 35^oC and 70%RH, but take ten weeks at 22.5^oC 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 30cm of grain at the rate of 1kg/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.