David Cross, head of technical training at Rentokil Pest Control and Paul Casson, technical field manager, at Rentokil Specialist Hygiene, offer this advice for silo maintenance and protection.

"SILOS ARE an attractive environment for rodents and stored product insects (SPIs) given the abundance of flour, sugar, maize, grain and animal feed they typically hold. Rodents might even be tempted to nest and shelter in these tall structures – a worrying thought for the agricultural industry, who need to conform to stringent food health and safety requirements.

It is crucial to take the right steps to prevent pests from entering these structures in the first instance, and to ensure you can detect an infestation at the earliest stage, should one occur. Given that silos contain food products or the raw ingredients for food production, which may be for human consumption once manufactured, strict legislation is in place to ensure that workers and managers follow best-practice food safety regulations.

Silos are tall, complex structures, and it is therefore easy for food stuffs to accumulate in hard-to-reach places. A deep cleaning strategy should feature high on the radar of all silo managers; as it is a powerful weapon in preventing pest infestations, and a must immediately after any contamination issue. It also plays an important role in ensuring a silo is operational all year round.

Stopping rodents in their tracks

Rodents carry and spread infections that could put the production line at risk. Salmonella, Hantavirus and Weil’s disease are just three examples of the diseases they could bring into the silo. Rats and mice can contaminate silos with urine, faeces and hair – as well as cause substantial damage through gnawing. This can lead to an increased risk of fire to any facility if their presence is undetected as they may gnaw through or damage electrical cables.

Altering the habitat surrounding the silo to make it less attractive to rodents is a key preventative step. Even if the silo itself is well-sealed, the surrounding buildings can play their part in attracting rodents if they are not sufficiently maintained. Here are some top tips to help you implement a proactive pest control strategy in any agricultural facility:

  • Seal any gaps: Mice are capable of squeezing through gaps the size of a biro to enter premises, so seal holes in the exterior of the silo or surrounding buildings with wire wool, caulk, metal kick plates or cement. Rats are also known to enter buildings through damaged drains, so it’s important to make sure that any entry points or vents are well maintained and checked regularly. If you’re unsure how rodents could be entering a building, don’t hesitate to ask pest control experts to analyse the site and make recommendations;
  • Remove any clutter and food sources: Storage containers or clutter in structures around the silo provides rodents with a place to hide, so it’s worth moving these away from walls if possible. Make sure food and waste containers are also adequately sealed. Mice can take food from up to 70 different sources in 24 hours, so placing bait for them can prove challenging. Rentokil has developed RapidPro Riddance (containing the rodenticide alphachloralose), which kills a mouse after just one feed of the trap’s lard-based solution. This is a fast-acting rodenticide, meaning the deceased mouse will typically be found close to the bait and can be disposed of easily;
  • Quick detection: Non-toxic monitoring blocks are another way to detect rodent activity as early as possible, while ensuring toxic substances aren’t deployed unnecessarily onsite. Some of these blocks contain fluorescent materials which reflect UV light, highlighting rodents’ droppings and making it easier to identify their presence;

Stored Product Insect infestations

The most common SPIs are grain weevils (Sitophilus granaries), rice weevils (Sitophilus oryzae), saw toothed grain beetles (Oryzaephilus surinamensis), flat grain beetles (Cryptolestes Spp) and flour beetles (Tribolium Spp). All of these can be responsible for the spoilage of ingredients – especially those developing from egg to adult, which can consume large amounts of food.

Farmers and food manufacturers storing grain or grain-based products in bulk can suffer the unwelcome consequences of these infestations.

Risks from an SPI infection include

  • A major loss of revenue as a result of loss of product weight;
  • SPI-infested grain that was destined for human consumption can be downgraded due to a reduction in its nutritional value;
  • Serious blockages or damage to machinery as a result of webbing, which is produced by larvae as they feed;
  • Infected grains are liable to become warmer, accelerating insect problems and leading to problems with damp, mould and even grain germination;
  • Produce can become contaminated by insect waste;
  • Non-compliance with legislation can lead to commodities being rejected.

The key is to identify and treat an infestation at the earliest stage. Fortunately, there are some steps you can take to identify and manage SPI infestations:

  • Use cone traps, probe traps and floor traps: Place these around the building, to give a good early warning sign of any activity;
  • Look out for bore holes and dust tracks: Emerging adult weevils and grain borers will leave visible exit holes in the grains. You may be able to spot insect tracks in flour or grain dust around the silo building;
  • Phosphine gas treatment: The most effective way of controlling an infestation is to fumigate the product with phosphine gas, widely used with cereal products. This is a cost-effective treatment that will not taint the product;
  • Consult the experts: Phosphine gas is heavily regulated, so if you’re dealing with an SPI infestation, it’s important that you know who to contact. For any external contractor, part of their role is to be proficient in the latest legislation changes in their area of expertise. Pest controllers are no different; if in any doubt as to what substances you can and can’t use, or how to use them, then it’s always best to check with the experts.

Working with a specialist hygiene team

Cleaning these enormous structures is challenging and it requires specialist work, which can interrupt everyday processes. To minimise disruption, it’s recommended that they are serviced with the help of a specialist hygiene team.

The team tackling a silo clean must be fully trained in confined space entry, emergency rescue, as well as the use of the correct access and safety equipment, such as gas monitors and escape kits. Using the correct ATEX-rated equipment is of paramount importance, especially when working with dusty food stuffs such as flour, as any spark from electrical equipment has the potential to ignite dust and cause an explosion. Unfortunately, this is a very real possibility, and one that is realised every year throughout the world.

Using a specialist company is the wisest option when you consider the ramifications of not doing so. Technicians will be trained in recognising the differences of how to clean structures used by various commodities. For example, sugar can set like concrete, while flour is prone to clinging onto the side of the silo. At other times a thick layer of flour can become suspended or ‘bridged’ in mid-air, when the top layer has set, and the flour beneath is emptied out.

Final words

Silo managers and specialist cleaning teams should work closely together to implement a regular and thorough cleaning routine. Ensuring the silo is regularly cleaned will mean pest activity is minimised, and product spoilage doesn’t become an issue. A frequent and consistent approach will ensure financial and reputational costs to the business don’t become an issue, and that the silo is productive all year round.