The article comes from the August issue of Farmer 2024 magazine.
In the context of damage caused by storage pests, the first thing that comes to mind is often the grain weevil. It is not the only unwelcome guest in warehouses, although it must be admitted that in Polish conditions it poses the greatest threat. In order for grain to be stored safely until the moment of sale, constant monitoring is necessary – prevention is always better and cheaper than intervention. Sometimes, however, we will have to resort to more radical methods.
Pest threat
On a global scale, estimates indicate that grain losses amount to about 10% due to pests feeding in granaries. These are shocking figures. And it would be even worse if it weren't for the fact that we have the ability to control pests in grain that has already been stored. In Poland, the losses are smaller, but we are still talking about up to 5% of grain damaged by various types of storage pests. What's more, they are no longer even guests, but rather tenants on our farms. About 90% of farms in Poland may have such unwanted tenants (at least one species of storage pest, usually the grain weevil), which means that control and control of them becomes a priority during grain storage.
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At what temperatures do storage pests thrive?
Heat and humidity are conducive to the development of storage pests, similarly to typical field pests. For example, the optimum temperature for the grain weevil is a temperature range of 26-30°C. However, this does not mean that it will not appear at lower thermometer readings in the warehouse. It can develop at a temperature of 15°C. It is also favoured by air humidity above 50%. Grain mites, on the other hand, are able to develop at a temperature of 3°C, and they cause the greatest damage at temperatures close to the optimum for the grain weevil. Let us add here that grain mites – i.e. the flour mite, the house mite, the hairy mite (classified as mites) – do not feed on grain with a moisture content lower than 12%. That is why it is so important for the grain to be properly dried before pouring it into either a flat storage facility or a silo. It should be added, however, that the mites do not start feeding "on their own", because they attack grain previously damaged by other pests, e.g. by the weevil. On the other hand, the flour beetle, for example, develops best when the temperature exceeds 32°C and humidity 75%.
The mere presence of pests in the warehouse in its own way leads to a certain increase in the temperature of the stored goods (as well as their humidity). All pests, as living organisms, give off heat. In a situation where the humidity of the grain increases as a result of the presence of pests, we are talking about the phenomenon of dry heating. By feeding on dry raw material, they increase its humidity parameters, and indirectly in this way contribute to a significant deterioration in the quality of the grain, which is consequently infected with fungal diseases. For example, in places where the weevil feeds, the temperature of the grain is much higher – it can be increased by even 10°C.
Remember that the presence of cereal pests may completely disqualify the use of grain in the next season as seed material. Due to the appearance of pests, the grains may not be able to germinate, they are damaged already in the bud.
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How to prepare the warehouse and grain for storage?
Prevention is cheaper than intervention
Warehouses must be ventilated. This is the basis for safe grain storage. We all know perfectly well that grain is not always stored in ideally prepared places. However, if we decide to store in old buildings, in attics, etc., remember to force air flow. It is therefore worth opening all possible windows and doors – e.g. on colder or frosty, but at the same time dry days. If possible, it is worth installing nets in such places, which will be an obstacle not only for insects, but also for birds, among others.
In mid-August it is too late for full prevention, because it should really start with preparing the combine. Here, let us remember that it is the working elements of the combine that are a kind of bridge facilitating pests' access to the storage facilities where they can later develop.
At the same time, factors that limit the existence of pests – as already mentioned – are the temperature of the grain and humidity. It is best for the grain to have a moisture content of about 13-14 percent (or lower), and at the same time the temperature should be below 13°C. The lower the grain temperature and humidity, the longer we can store the grain.
What to do if pests have already appeared in the warehouse?
Generally, we do not have many options for chemical pest control in warehouses, if they do appear. Aluminum phosphide and magnesium phosphide-based products are available that act gaseously. Aluminum phosphide-based products include: APS, APS Pellets, APS Tablets, Delicia Gastoxin, Greenphos pellets, Greenphos tablets, Sobieski 56T, Quickphos tablets, Quickphos pellets, Phostoxin tablet, Matserphos tablets, Masterphos pellets.
Contact and gas-based preparations based on pirimiphos-methyl (both for spraying and fumigation) work. We have at our disposal products such as Actellic 500 EC, Rovar 500 EC, Wołek 500 EC. In turn, for fumigation, you can use, for example, Actellic 20 FU, Celtic Świeca 20 FU, Rovar 20 FU.
Substances such as deltamethrin (e.g. K-Obiol Max) or pyremethrins are also used to control storage pests.
However, if protection is performed in a warehouse where grain is already present (or rather such places are referred to in August), then even greater attention must be paid, for example, to whether a given solution can be used. For example, the label of one of the products based on pirimiphos methyl sodium states that "in the case of protection of stored malted barley, it is necessary to conduct tests to assess malting capacity".
In order to perform a disinfestation procedure, the best option is to commission this activity to a specialized company that will perform such an activity not only effectively, but above all safely. At the same time, you can count on the highest quality of the procedure due to the use of special equipment designed for disinfestation. Precision is equally important here, which is guaranteed by companies specialized in this field.
Remember that after a treatment to eliminate warehouse pests, you should always wait before re-entering the premises. Before you can safely enter the warehouse after disinfestation, the room must be thoroughly ventilated. At the same time, you should not open it too early, because the appropriate concentration of, for example, gaseous agents must be maintained in the warehouse for a specified period of time. However, for the entire treatment to be safe, the grain warehouse should be sealed beforehand – this way, the gas concentration will also be optimal for the required time. Companies are also equipped with meters that will check whether there is no gas in the room, and during the treatment, they control the amount of the substance released.
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In Mazovia, a grain warehouse with grain stored there burned down
Losses in storage are the same as in field production
In general, losses caused by storage pests can be as large as those that occur during field production due to the impact of disease-causing pathogens or the feeding of "field" pests. Therefore, monitoring of the grain storage is as important as ongoing inspection of the plantation. Intervention that is too late is always associated with certain losses, and its absence can lead to the grain being completely unsuitable for further sale or use as seed material. Therefore, ongoing control and possible intervention are a continuation of work on the quality of the material, but this time after production.
