Allowing rodents such as rats and mice to thrive in and around grain stores can result in serious grain losses, contamination and structural damage to buildings and stored machinery.

Each year a rat can produce about 15,000 droppings, 6 litres of urine and shed about 300,000 hairs, while its smaller cousin, the mouse, can leave about 30,000 droppings and 1 litre of urine.

For every 1kg of food eaten by a rodent, a further 3kg has been contaminated by this high output of excreta.

See also: 6 top tips for minimising compaction at harvest

Rats can also carry 45 different diseases that are potentially harmful to humans, including Weil’s disease, E coli, dysentery and enteritis.

With increasing emphasis on food quality through assurance schemes such as Red Tractor, infestations and contamination can result in grain being rejected by the end user at great cost to the grower.

Ahead of harvest, Farmers Weekly asked Michael Flatters of Fen Tiger Pest Control for his top tips on how to shore up your grain store and keep the furry fiends away from your produce.

Michael Flatters. © Tim Scrivener

Like pest control in growing crops, an integrated pest management strategy is required to control rodents around grain stores.

Before using chemical control, always exhaust options that discourage rats and mice from entering the store by reducing access points and keeping the area clean and tidy.

© Tim Scrivener

Rats tend to live outside the store and only enter to feed. They also have relatively poor vision and rely on established trails and their sense of smell to find entry points. They do not like open spaces.

With this in mind, ensuring the area surrounding the store is free from cover will discourage entry. Spray off and clear weeds and remove anything stacked against walls to take away easy access under facia panelling.

Mice live indoors all year round and it is more difficult to prevent them from moving into buildings, so control is focused inside.

© Tim Scrivener

While newer stores pose a lower risk of rodents gaining access, many grain stores on UK arable farms are older buildings, sometimes in a poor state of repair, with many points of entry.

Ventilation fan rooms are a primary entry point in old stores and many have louvre doors that give rodents easy access to the stored grain inside.

© Tim Scrivener

Old wooden doors (above left) are another easy entry point to older buildings and can be replaced by more secure roller-shutter type doors. Roller-shutter doors need to be maintained – particularly seals along the bottom (above right) where gaps can appear.

© Tim Scrivener

Reducing access points for rodents doesn’t need to be expensive – tin sheet for gaps under doors, mesh inside louvre doors and cement or expanding foam mixed with wire wool or chicken wire are useful to block holes and cavities where rats and mice can squeeze through. Rememeber, rats can pass through a hole the size of your thumb and mice can squeeze through a pencil-sized gap.

You can never completely rodent-proof an old building, but addressing all low-level entry points will help minimise pest levels.

© Tim Scrivener

Fluorescent tracers in powder or bait form create glow-in-the-dark trails or droppings to indicate activity and its location in the building. This helps to pinpoint where to target poison baits, poison foam and traps.

© Tim Scrivener

There are various bait options to control rodents around the grainstore, but one bait won’t suit every situation. The palatability to the target pest is the most important consideration.

Whole wheat bait (top left) is best used against rats when they are used to eating grain, so it matches their daily diet and doesn’t raise suspicion.

© Tim Scrivener

Extruded blocks (top right) are suited to a situation where no other food sources are available, as it is the least palatable bait. They are also best deployed against rats rather than mice and are often used in stored machinery such as combines during the winter. They must be fixed to prevent rodents carrying them away.

Soft block bait (bottom right) is the most palatable and can be used against both rats and mice. The blocks are made from food-grade ingredients, with added oils and fats, so is ideal in buildings where other food sources are available. Like extruded blocks, they must be fixed in place.

Trio (bottom left) is mouse-specific bait that appeals to the feeding habits of mice, ensuring they feed for long enough to consume a lethal dose of rodenticide. It contains sunflower seeds, maize and rolled oats.

All pictured baits contain the active ingredient difethialone and deliver enough poison to kill rats and mice in a single dose. Other actives on the market include difenacoum, bromodialone and brodifacoum, which are also suited to some situations.

© Tim Scrivener

It should be noted that in parts of the UK, rats and mice have developed resistance to difenacoum and bromadiolone.

© Tim Scrivener

When deploying grain-based baits, use bait boxes to avoid exposing the poisons to non-target animals. These should be checked regularly to ensure bait is contained and replace where required.

Baits should only be left out while pests are active and grain-based baits should be avoided in areas where grain is currently being stored to avoid cross-contamination. Always remove dead rodents and dispose of safely.

Rats and mice can now be controlled by Racumin foam, a new product from Bayer that relies on the pests picking up the active ingredient coumatetralyl on their coat as they move past and ingest it when grooming.

For indoor use only, it can be applied in areas of a building where the pests are known to pass, such as runways, tracks and access holes.

Bait boxes are ideal for foam applications (see above) when targeting mice. Mice spend 70% of their time off the ground, so place the boxes at multiple levels, including beams, ledges and in fan tunnels.

Traps (see right) are a useful part of an integrated control strategy for rats and mice. Wooden box traps are the best choice for rat control, with smaller traps suitable for mice.