Growers should not waste time in cleaning out their empty grain stores to avoid the build-up of damaging insect pests.

With the grain price slump, some may still have a proportion of last year’s crop in-store, hoping for an improved price, so time may be tight ahead of the upcoming harvest.

However, Bayer rural hygiene manager Ken Black says waiting until the last minute to clean stores will dramatically increase the risk of quality loss later on.

“You can lose a huge amount of value from your crop when insects infest a store and a thorough clean is a very easy fix.

“Residual insecticides applied in store also work best when applied early, as they can control adult insects as well as the subsequent generations, giving the best level of control,” he adds.

Mr Black explains that grain store pests can be split into two categories – primary and secondary – and the three biggest threats for UK growers can be seen below.

© Tim Scrivener

The grain weevil is the most common primary pest in grain stores. Adults and larvae have mouthparts capable of causing direct feeding damage and can completely destroy whole grains.

© Tim Scrivener

The rust-red flour beetle is a secondary pest, thriving on grain damaged by primary pests such as the grain weevil. When present in high numbers, flour beetles can significantly exacerbate primary pest damage and cause grain moulding.

© Tim Scrivener

Another secondary pest is the saw-tooth grain beetle, with larvae feeding on the germ of broken or damaged grain. Entire grains are less susceptible, so preventing damage during combining will help reduce risk.

Mr Black says cleaning all storage space, roof space, ventilation tunnels and underfloor ducts of any grain and dust will remove food sources that harbour insects until the new crop fills the store.

Once clean, use pheromone traps – which cost just £1-2 each – to monitor levels of insect pests and if they are present, treat with an insecticide.

“If you put traps in the right place and don’t find any insects, you could save some money by not needing an insecticide application to the fabric of the building at all.

“In a typical store you should use four traps in each bay and one in the fan tunnel. If insects are detected, a treatment should be used, as populations can multiply very quickly,” says Mr Black.

Various options are available for killing grain store pests, with smoke generators and fogs offering a quick knockdown of insects.

However, a liquid treatment such as K-Obiol (deltamethrin) offers two months of residual protection in the fabric of the building.

Other fabric treatments on the market are organophosphate-based, so operator and environmental safety profiles aren’t as strong and resistance to the group has been confirmed in insect populations.

“You could rotate K-Obiol with an organophosphate such as Reldan (chlorpyrifos) for resistance management, but increased reliance on store hygiene to reduce pest pressure is much more important,” says Mr Black.