# Grain storage insecticide: identify the pest and treatment site first

URL: https://leafwrit.com/ie/grain-store-pest-control/
Reviewed: 2026-10-29

**Grain storage insecticide starts with the pest and the place it is used.** The common pests of stored grain are weevils, saw-toothed beetles and mites; the empty store, the grain and the fumigation each have different options.

Before you call anyone, write down three things: what the pest is (or what you suspect), where it was found (empty building, equipment or the grain itself), and what the grain is meant for (milling, malting, seed, feed sale or use on the farm). Give the same three answers to every adviser and contractor, so they quote for the same job.

## Identify the pest: grain weevil, saw-toothed beetle or mite

Grain weevils damage grain by feeding on the endosperm, while saw-toothed beetles and mites attack the germ. Grain weevils were the traditional pest of stored grain in Ireland because they bore into the grain. The saw-toothed grain beetle, a tropical species, became more dominant with the combine harvester, which damaged grain enough to allow feeding. Mites cause tainting and may carry fungal spores and bacteria such as Salmonella.

Describe what you actually see, one finding at a time: live insects, grain damage, mould, heating, smells and condensation are separate records, so do not put them all under “weevils” until the pest is confirmed. Photograph the affected place with the date and the bay or position written on the picture, and say whether the problem is in one lot or in several bays. Collect insects from the grain or from store residues following the sampling instructions of the diagnostic service, and label grain, dust and insect samples separately. A simple sketch of the bin helps: mark the grain surface, intake point, walls, ducts and unloading equipment, and put each observation on it with its approximate depth. Say whether a sample came from a probe, a conveyor discharge or the top of a heap, and ask the adviser before comparing samples taken in different ways.

## Empty store and grain bin insecticide treatment

Most empty stores contain pests which can contaminate newly stored grain, and cleaning alone will not control them. When a store is emptied, all remaining grain residues should be removed and burnt. The store is then thoroughly cleaned, vacuumed and treated with insecticide. Walls, floors, ceilings, ducts, roofing spaces, grain conveyors and their environs are all cleaned, and cracks and crevices are cleaned, disinfected and filled. Mites can be controlled by pre-harvest store disinfection.

Feed bins are inspected empty, at least annually on cattle and sheep farms and preferably twice or more a year on intensive pig and poultry units. The inspection covers leaks from damaged joints and seals, structural damage and corrosion, and caked residues on bin surfaces and in augers. Damage is repaired so the bin is damp proof, bird proof and vermin proof, and a bin is cleaned and allowed to dry fully before refilling.

Trace the route the grain takes, starting outside the building: tipping area, pit, elevator, conveyor, dryer, holding area and the final bay. Ask which parts have been emptied and which still hold residues, and note any equipment shared with another store or crop, such as mobile augers and trailers. Give the contractor the real layout, point out the places that are hard to reach, and mention earlier repairs or leaks.

When you ask a contractor for a quotation, ask which areas are included and which are left out, how the work will be checked in closed ducts and cavities you cannot see from the floor, and who clears accumulated grain, removes the waste and confirms that the equipment can go back into service. Treat a structural repair and a pest treatment as two jobs with a named person responsible for each. Write down what was really cleaned, with the date, the area and who did it; if a conveyor or a bay was left out, do not write “store prepared”.

## Grain condition, moisture and temperature

Many pests are secondary, feeding on previously damaged grain, so grain for storage should be good quality whole (unbroken) grain free of moulds. Drying to 13% moisture content or lower is important in preventing or limiting infestation. Lowering grain temperature to 15 °C or lower helps to control insect pests (below 5 °C for mites).

Biological activity of insects, mites, fungi and the grain itself doubles at every 10 °C rise in temperature. Mites tolerate temperatures and moistures so low that drying and ventilation cannot control them completely. Acid treatment controls mould growth but not insects or mites.

Tell your storage adviser how the grain is actually preserved: dried, treated another documented way, or waiting for processing. Ask for monitoring and operating instructions that fit that system, the grain species and the planned storage time. Describe how and with which instrument readings are taken, and ask how to check that the instrument and the sampling method are suitable. Keep the readings from different parts of the store separate instead of averaging them, so a bad patch stays visible, and mention recent fan operation, power cuts, blocked ducts or a change in grain depth.

If the contractor suggests moving or processing the grain, agree where it goes and how its identity is kept, and ask whether the receiving area and the trailer need to be inspected first.

## Grain store insecticide and grain weevil insecticide options

Pest eradication and control in stored grain is best carried out by the professionals who offer this service. Where moderate infestations occur, the stored grain can be protected by admixtures of insecticides such as pirimiphos-methyl (Actellic). Synergised pyrethroids can be applied by fogging or spraying to remove pests from elevators, bins and structures.

Chemical control is becoming increasingly difficult as products that farmers could apply are withdrawn from the market, so prevention is the best means of control. Check Irish authorisation in the DAFM product database, which can be searched by Product Name, Active Substance or Function/Crop. The Actellic name in that database belongs to the Actellic Smoke Generator, and pirimiphos-methyl is on its active substance list, so when a supplier offers an Actellic or pirimiphos-methyl product for mixing into grain, look up that exact product and its use on the grain before you agree to it.

Before you accept a proposal, ask for the full marketed product name, the formulation, the current Irish authorisation reference and the method of application. Ask which target it addresses: an infestation inside the grain, or pests on the building and equipment surfaces, and what evidence was used to identify the pest. Show the adviser the surfaces that grain will touch later. For a treatment of the grain itself, give the lot size and where it is going, and settle the exact authorised use on the label before any dose is calculated. Keep the label and the written job instruction.

## Pesticide fumigation and aluminium phosphide

Fumigants used for pest control include aluminium phosphide and carbon dioxide. Carbon dioxide is considered ineffective against weevils. Fumigants eliminate an existing infestation but give no protection against re-infestation.

For a fumigation enquiry, give the specialist the whole picture: the building, the grain, who is on the premises, how the store is reached, what happens next door, the exact fumigant and who will carry out the work. Ask the provider to explain the site assessment, how the area will be closed off, how people will be told, and how the store is released. Point out adjoining livestock housing, rooms where people stay, shared ventilation and regular deliveries. Agree who controls the site and who briefs farm staff and other contractors, get the job instructions in writing, and let nobody into the treated store before the specialist clears it. Do not guess a waiting time; use the specialist's release instruction, and see the [pre-harvest interval records](/ie/pre-harvest-interval-records/) for how to record it.

Entering or cleaning a confined bin or store carries risks: substantial dust, carbon dioxide or other harmful gases that may build up, and dangerous fungal spores, for which a suitable respirator mask with an appropriate filter is worn. Nobody enters a bin alone. Check whether non-users could be exposed, for example people working nearby, visitors, and cleaning or maintenance staff.

Think through who passes the store in a normal week: drivers, livestock staff, maintenance workers and family members, and any shared passage or neighbouring work area. Make the agreed restrictions clear to each of them. Do not remove guards, enter a bin or work at height just to finish a checklist; give the contractor the equipment manual and ask the person responsible for farm safety to plan isolation and access. A vessel that looks empty is not necessarily safe to inspect.

## After treatment: keep the grain history and the buyer's view

Link the treated lot and the store reference to the specialist's report, and keep the product details, the work done, the restrictions and the real release information. Note any move to another bay or vehicle. Agree a monitoring plan, and decide in advance what result would make you call the specialist again. For the link between harvest lots and storage places, use the [field and crop records](/ie/field-crop-records/): write down the lot, the treatment, the monitoring result and the release instruction.

Tell the adviser where the grain is going and give the buyer's specification, then ask who confirms acceptance after treatment. If grain has already left, keep the retained samples, weighbridge references and loading dates, and ask how the buyer should be told. If the grain has mould or other contamination, get a separate decision on whether it is fit before it is transported. If a buyer rejects or holds a lot, keep their reason with the lot history.

## Grain storage pesticides and aluminium phosphide training

Choose grain storage pesticides by the pest and by what you treat, the empty store or the grain. The DAFM database lists aluminium phosphide on its active substance list and products sold as Phostoxin and Talunex. The label of the product you intend to buy is the legal instruction for it, so read the Irish label for who may use it before booking anything. For aluminium phosphide training courses, ask a provider on the [training guide](/ie/pesticide-training-ireland/) which of its courses covers fumigation.

## Next step

Look up the exact Irish authorised use of a product in the [pesticide register](/ie/pesticide-register-ireland/), then record the treated lot and the harvest interval with the [field and crop records](/ie/field-crop-records/) and the [pre-harvest interval records](/ie/pre-harvest-interval-records/).