It is estimated that 90% of grain stores harbour at least one insect species known to infest grain, underlining the critical importance of good store hygiene in the run-up to harvest.

Cleaning out grain stores is an all too familiar job for arable farmers, but it is often the simplest of jobs that can be overlooked.

Ken Black, accounts manager at environmental science firm Envu, who specialises in grain store hygiene, suggests a back-to-basics approach for protecting grain quality and avoiding costly rejections.

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“The sooner you can get stores cleaned out and start monitoring whether insect species are present, the better,” says Ken.

“Leaving stores empty for two months ahead of harvest is optimum, but with grain prices where they are, many are storing grain for longer, which makes it more challenging.”

Ken stresses that cleaning alone does not guarantee pest-free stores, nor will relying solely on pesticide treatments.

Instead, he recommends an integrated pest management strategy that encompasses thorough cleaning, regular monitoring, and targeted control measures.

Thorough clean

Removing dust, debris, and old grain residues is the first essential step.

Pests thrive in cracks, crevices, vents, and other undisturbed areas, so it’s important to clean every part of the building.

“As we know, heat rises and so too do the insects to keep warm.

“This means pests are often found at the top of grain stores on elevators or high-up ledges, so it’s important to give the entire shed a clean,” says Ken.

Even equipment stored in sheds, such as combines, can harbour pests and should be cleaned appropriately.

Monitor species

After cleaning, use monitoring traps to check for insect activity and identify whether further treatment is required.

Pheromone traps are a simple method to test whether insects are present.

Traps should be placed in corners and at wall/floor junctions at 5m intervals and checked regularly.

Insects known to infest and damage stored grain can be divided into three classes:

© Lodi UK

Primary insect pests

These insects have the ability to damage whole grains, such as the grain weevil, saw-toothed grain beetle and the rust-red grain beetle.

Primary insect pest activity increases temperature and moisture levels to create suitable conditions for secondary pests and fungi to populate.

Secondary storage insects 

These invade already damaged grain and are primarily fungus feeders.

Species include rust-red flour beetle, spider beetles and booklice.

Mites

Storage mites are significantly smaller than insect pests, measuring less than 0.5mm.

They appear as white specks or pink dust moving on the grain. There are at least 12 mite species that infect stored grain in the UK.

The most common are Acarus, Tyrophagus and Lepidoglyphus species.

Their presence typically indicates high humidity or poor drying, and often point to underlying issues such as roof leaks or improperly stored grain.

Treatment

If pest activity is detected, or if there is a history of insect infestation, a targeted insecticide spray can be treated to the fabric of the building.

“Modern pyrethroids such as deltamethrin and cypermethrin can be used.

“Although, it is worth noting these are part of the same chemical family,” says Ken.

Ensuring correct application rates and using products with a different mode of action can be beneficial for resistance management.

Visit the Insecticide Resistance Action Group on the AHDB website for more information.

“Smoke fumigants are still a key tool in the fight against insect infestations,” says Ken.

They can be used to flush pests from hard-to-reach areas such as cracks and voids, and can also improve control.

However, some insects have developed resistance to these products.

Always use appropriate personal protective equipment and safety protocols during treatment and cleaning, adds Ken.

Temperature and moisture

Closely monitoring temperature levels can prevent infestations of insects and mites from arising.

“As soon as the grain comes into store, it should be cooled, increasing its safe storage time,” he says.

According to the AHDB, grain should be cooled to below 15C within two weeks of harvest to reduce insect activity by preventing completion of insect life cycles, particularly the saw-toothed grain beetles.

Within three to four months of harvest, grain should be cooled below 12C to reduce further insect activity by preventing other insects from completing their life cycle – for example, grain weevils.

By the end of December, grain should be cooled to less than 5C to help kill adult insects and prevent mites reproducing.

Low-volume aeration (10cu m/hour/t) should be used to cool grain as soon as ducts are covered.

Grain storage temperatures

• Above 40C: Most insects die within a day
• 25-33C: Most insects breed rapidly
• 15-25C: Mycotoxin formation is most likely
• 12-15C: Most insect species stop breeding, although grain weevils may still reproduce (although slowly)
• 5C: In moist grain, mites and fungi may still increase (although slowly)
• Below 5C: Insects stop feeding and mites stop increasing

Arrival of grain

Grain temperature, grain moisture and insect activity should be monitored weekly during storage.

If pests are detected early, they can often be managed by cooling, cleaning, or drying grain.

Monitoring insect activity using pitfall traps or bait bags as grain comes into the store is beneficial.

Where grain is coming into store and long-term storage is planned, an add mix treatment can be applied directly to the grain.

However, this is costly and certain markets won’t accept grain that has been directly treated so it is important to check before use.

“Prevention is always better than cure in these scenarios, which is why grain store hygiene is so important,” says Ken.