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Crops and Soils Bulletin June 2023 – Grain Store Hygiene Ahead of Harvest

20 June 2023

This article is produced as a part of the FAS Crops & Soils Bulletin. Subscribe now to receive the full report in your inbox monthly.

Brushing up on grain store hygiene - Prevent pests eating your grain and into your profits

While grain prices have dropped significantly from last years highs and growers are being challenged to retain their margins though better cost control, it is important not to cut corners for the sake of it whether it be time or money. This is especially true when it comes to grain handling and storage, with good hygiene practices before and during the storage period key to preserving crop quality and values whilst also avoiding expensive deductions or rejections. 

In the run-up to harvest, most machinery will get a good look over or service and grain stores and handling equipment should be treated with the same diligence. Not only should everything be in good working order, but stores and equipment should be thoroughly cleaned. After all, grain may need to be stored right through to the following summer so using the window before harvest to clean, prepare and make any repairs to the general condition of the store is therefore crucial. 

The principles of Integrated Pest Management (IPM) are a bedrock of when it comes to crop protection, whether it is in the field or in store. The three key elements are: 

  • Prevention 

This can be achieved by thorough cleaning of the store, ensuring the fabric and structure of the store is secure and making sure grain is stored at the correct moisture and temperatures. Even a small amount of dust is enough to sustain insects.  

  • Monitoring 

Remain vigilant for infestations, moulds and other issues after cleaning and once the store is filled. Using suitable equipment and records to monitor for the presence of pests before storage and also allow fluctuations in temperatures and other changes to the bulk to be monitored.  

  • Control 

Based on the results of the monitoring process growers should look to sustainable, physical and other non-chemical solutions as opposed to using pesticides where possible. Any use of pesticides should be targeted at specific species to reduce the risk of harm to non-target species. Application rates and other treatments should be at no more than necessary levels with effectiveness of treatments monitored, particularly where resistance could be an issue. 

Clean the store and equipment thoroughly from top to bottom

Most infestations in grain stores do not come from the current crop of grain however are most likely to have originated from pockets of dust and grain carried over from the previous storage period. Good hygiene and cleaning practices are therefore key to preventing pests from having these havens to survive between crops. Some key tips to achieving a clean store include: 

  • Have the right tools of the job- a good hoover with a range of attachments to get into those hard-to-reach places can make a huge difference. Not only will it remove larger pieces of debris but a hoover will also suck away all the dust. At the same time using an airline from a compressor can blow away dust from more awkward places. These tools can also help remove any fungi present. 
  • Start cleaning from the top, working your way down and going beyond the floor and walls. This means getting up to the roof area and cleaning couples, purlins and other part of the building structure where practical. Underground ducts should also be cleaned out thoroughly where possible. 

  • Look at the whole shed. Just because part of the shed is not used for grain storage, doesn’t mean that it is free from infestation. That’s why its is important to empty the shed completely of grain and other materials or machinery before starting the cleaning process.

  • Think like a bug- look for those normally unseen areas behind pillars or fixtures and fittings with even cracks in wall and floor surfaces or gaps between panels making ideal hiding places for insects.

  • Don’t just leave dust and sweepings in the shed - dispose of them as soon as the shed is cleaned out as far as possible away from the store. Remember the cleaning equipment will also now harbour insects, and these too should be removed from the building.

  • This is also the time to check the structure of the grain store and building fabric.  Stores should be waterproof and proofed against birds and rodents. Any building repairs should be carried out to prevent ingress of water through the roof or gutters.  
  • Check over fixtures, fittings and ancillary equipment. Grain in store will respire and condensation can be a problem in the roof area so ventilation systems need to be able to cope – if this can be problem, review the current set-up to see where it can be improved. Keeping the shed cool and well-aerated can also play a big role in avoiding infestations.  Lights should have shatter-proof bulbs and covers. Underground ducting should also be checked, with any disruptions rectified to allow optimum airflow. 

Monitor for the presence of pests

Once the store is clean, its important to monitor and record any pest activity to allow any remedial action to be taken. Identification and treatment of insect pests at this point is particularly important as once an infestation starts, quality can quickly deteriorate with “hotspots” formed as the level of infestation increases. 

Insect pests can be split into two types-  

  • Primary pests infest undamaged grains and one of the best known is the Grain Weevil. These are fairly easily recognised, having large snouts relative to the bodies, being dark brown in colour and are about 4mm long. The Grain Weevil damages grain in several ways, firstly both adults and larvae feed on grain and secondly females will lay their eggs within individual grains, with their young leaving visible “shot” holes in the grain as they bore their way out. 
  • Secondary pests feed on damaged grain and dust and these include the Saw Tooth Grain Beetle, which can reproduce very quickly in the right conditions, with females capable of laying up to 400 eggs in their lifetime feeding on the embryo or germ of broken and damaged grains, including those with holes created by grain weevils emerging. Saw Tooth Grain Beetles have a distinctive saw-tooth pattern on their thorax, are dark brown/black in colour and about 3mm in length. Other secondary pests include mites. As mites reproduce very quickly, infestations can develop rapidly leading to the tainting of grain with allergens and by spreading fungal spores.   

Monitoring for insect pests can be undertaken by the use of traps. These commonly take the form of pitfall or pheromone sticky traps. Start by strategically placing the traps through the store (referring to the manufacturers guidance) and should be monitored at least once a week. Increasing the number of traps over time can allow the level of infestation to be gauged and also which parts of the store are suffering from higher levels of insects. Remember some grain pests may look dead but can actually lie in a dormant state for many months, particularly in cooler conditions – so placing samples under warm sunshine can see more movement and activity.  

Rodents are capable of causing considerable damage by eating and gnawing at grains with their urine and droppings also being significant contaminants. The use of secure bait traps can be effective in not only catching but also monitoring the extent of any problem. Working with your farm pest controller can help in finding the most effective siting of traps and type. Storekeepers should consider the potential risk of contamination to any grain stocks however, as well making sure that non-target species cannot get access to the bait.  

Having good records of pest activity and locations within the store can also be extremely useful over time. Regular problem areas of the store can be identified allowing further investigation e.g. perhaps a previously unknown or diagnosed structural issue or fault. Treatments can also be more targeted towards these regular problem areas with any additional measures undertaken as required. 

Treating the empty store

Monitoring may reveal the presence of insect pests. Growers should consider their end markets before using a pesticide with some treatments on the market unsuitable for any grain being used for human consumption. Speak to your buyer if you are in any doubt. 

The last few years has seen the loss of several products and actives although growers can still treat empty stores with pyrethroids (e.g. deltamethrin) using a knapsack sprayer. Just like the cleaning process, a thorough approach is required to ensure the whole shed is treated, and once again this means going beyond the surfaces that will have direct contact with grain such as walls and flooring. Having a good sprayer is important to get into harder to reach places and the fabric of the building. Special attention should be paid to those cracks and narrow gaps that have been difficult to clean. Contractors can also be used and by using high pressure sprays or misting techniques may offer better access depending on the store design. 

Smoke products are also available (e.g. cypermethrin or pirimiphos-methyl) however these should only be used in tandem with an insecticide spray, acting as a follow-up to improve the penetration into more inaccessible areas e.g. up in the roof space of the shed. 

Treatment should be undertaken at least 6 weeks before harvest to achieve the best results and also allow follow-up monitoring to ensure the treatment has been successful. 

Finally, cleaning and treating grain stores exposes operators to significant risks from working at height, dusts and chemicals. Storekeepers therefore should put provisions in place for safe working practices and wear appropriate PPE. Before working with pesticides, labels should be read and understood to allow safe and effective application. 

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