Chemical control of pest insects in stored-product protection in Germany – Present Situation and Challenges –^**

Chemische Pflanzenschutzmaßnahmen gegen Vorratsschädlinge in Deutschland – Situationsbeschreibung und Herausforderungen –

Introduction

The major part of the harvested plant products is used for food and feed – e.g. in Germany about 25% of the grain is provided for food and about 60% for feed (Statistisches Jahrbuch, 2014).

In the context of the European approach to food safety ‘From Farm to Fork’ this is one of the reasons why the protection of unprocessed stored plant products assigned to be food is part of the food and feed production chain and consumer protection. Food and feed safety and hygienic requirements are applied at each stage of production, processing and distribution. In this context, these standards are also related to stored products of plant origin. Specific hygiene rules for primary production should be considered where necessary. It is essential to ensure food safety throughout the food chain, starting with preventive consumer protection at primary production and stored-product protection.

The European Regulations (178/2002/EC and 852/2004/EC) and corresponding sector-specific national laws or rules (Lebensmittelhygiene-Verordnung-LMHV, 2010) aim to ensure that food is safe and harmless and shall not be placed on the market if it is injurious to health or unfit for human consumption implying also deteriorated, nauseous or unfavorable impacts and contaminated food (e.g. by foreign bodies or extraneous matter, pest animals/insects, heavy metals, mycotoxins, unacceptable taste or odour, decomposition, mould).

Furthermore, worldwide trading standards maintain the ‘zero tolerance’ for living insects. A presence of living pest organisms in stored plant products would jeopardize the stock itself and the supply chain for food and feed (COCERAL, 2010). Therefore, the absence of living insects, other extraneous matter and contaminants is an important aspect in stock-keeping, trade, and in preservation of crops. Harvested crops therefore have to be stored in a way that ensures high quality and is considering all mentioned requirements, storage standards (FAO, 2003) and the state of technology (e.g. cooling, air circulation).

According to Regulation (EC) No. 1107/2009 and natio­nal plant protection law, pests in simply processed or unprocessed plant products can be controlled by Plant Protection Products unless the main purpose is considered to be for reasons of hygiene (Fig. 1).

Fig. 1. Definitions of plant products and food.

In addition to an insect management of plant products by cleaning, ventilation/cooling and other effective and economically viable alternatives, treatments with Plant Protection Products are main methods to disinfest stored commodities providing that the use of chemical products in integrated pest management situations is necessary (EPPO, 2003), and consequently combined with a low pesticide-input management. Contact insecticides play an important role in the stored-product protection because fumigants are not applicable under all practical conditions, due to lack of gas tightness or other constraints. Nevertheless, fumigation with phosphine remains one of the key methods for the disinfestation of e.g. bulk grain and oilseeds (COCERAL, 2014). For insect control in infested empty structures, e.g. on farms, in ports and at retailers, phosphine, sulfuryl fluoride and carbon dioxide has taken the place of the phased out methyl bromide. Applications of carbon dioxide under high pressure conditions also serve the purpose in special uses and applications in valuable goods (e.g. herbs, spices).

Fig. 2. Plant Protection Pro­ducts authorized for uses in stored-product protection.

Fig. 3. Active substances in au­thorized PPP for uses in stored-product protecti­on in Germany.

In the recent years the number of active substances has been stabilized: nine insecticides, two acaricides and one rodenticide are authorized for applications in stored-product protection in 2015 (Fig. 2 and 3). Nevertheless, there have been cuts in the last ten years such as the non-inclusion of active ingredients in Europe, e.g. methyl bromide, dichlorvos, nitrogen and hydrogen cyanide used in stored-product protection.

Any further loss of active substances with an effective knockdown effect and a high efficacy will make it difficult to manage infestations especially in the context with the ‘zero tolerance’. For this reason, the risk of pest resistances against contact insecticides and other widely used compounds (e.g. phosphide degassing hydrogen phosphine) could occur even faster than before. According to the marginal options of chemical methods, pest control has to strengthen the role of prevention and monitoring methods. Pest control itself has to be efficient and combined with the Good Agricultural Practice (GAP) defined for all authorized uses and Good Hygiene Practice (GHP) for primary production (852/2004/EC; Annex).

Five of the insecticidal active substances used in the products for stored-product protection, authorized in Germany, are gases and more than half of these products work on the base of hydrogen phosphine: Fumigation with phosphine remains still one of the key methods for disinfestation of stored products (Tab. 1 and 2) like bulk grain and bagged cocoa beans.

Sulfuryl fluoride is one of the two non-phosphine-releasing fumigants, in addition to carbon dioxide as an inert gas in stored-product protection. For insect control in food and feed factories and other infested empty structures, sulfuryl fluoride has taken the place of methyl bromide. Fumigation often is the last option after other alternatives of the pest control have failed or do not present feasible options. When using the authorized ProFume (containing sulfuryl fluoride) it has to be mentioned that most of the uses only imply the control of post-embryonic stages that are larvae and imago. In Germany, eggs are excluded of the authorized use because the total mor­tality during applications could not always be ensured under practical conditions. Especially at temperatures below 20°C re-infestation by hatching can occur (Flingelli et al., 2014). Therefore, under practical conditions and when used in accordance with the proposed label ProFume can be an effective fumigant for the control of stored product pests. Though, the results also reflect that the mortality of pests in all stages depends on the sensitivity of the organisms and development stages as well as on the conditions of the particular fumigation (e.g. structure of the facility, leaking rate, temperature) and cannot be easily extrapolated to other situations.

In Germany carbon dioxide is approved as an insecticide and acaricide, but only for uses in stored-product protection. The merchandized domestic amount of this inert gas has increased in stored-product protection over the last ten years. The actual volume of 11588 t carbon dioxide represents about 25% of all active substances in Plant Protection Products and 10% of all Plant Protection Products delivered in 2014 in Germany (BVL, 2015).

The uses of four contact insecticides remain on the German market. They contain diatomaceous earth, deltamethrin, pirimiphos methyl and pyrethrines as active substances. Beside this, this small number of represented substances and contact insecticides play an important role in stored-product protection, especially uses in empty facilities (Tab. 3), because in many practical situations fumigants are not applicable due to lack of gas tightness or other circumstances.

The European Directive 2011/31/EU restricts Plant Protection Products containing the approved active substance ‘pirimiphos-methyl’ (2007/52/EC) to applications with automated systems; hand–held application shall not be authorized. Therefore, the use is limited to the direct treatment of grain, excluding maize, on conveyors during putting into stock. At the end of 2013 further variations have excluded applications on rice, rye and buckwheat.

In 2011 two Plant Protection Products containing the active ingredient deltamethrin were approved; these authorized spray applications could partially compensate the limitations for pirimiphos-methyl containing Plant Protection Products, especially considering agricultural storages and smallholders.

In accordance with Regulation (EC) No 834/2007 only indoor applications using Plant Protection Products containing pyrethrines against beetles and moths are available for organic farming.

The approval of difenacoum (against brown rat, house mouse, house rat) has expired at the end of 2014 because only uses as a rodenticide in the form of pre-prepared baits placed in specially constructed, tamper resistant and secured bait boxes can be authorized according to Regulation (EU) No 540/2011. Besides this, it has to be noted that in some regions of Germany genetic resistance against difenacoum has already occured.

For the control of rodents in the agricultural area of plant-product protection only a single rodenticide remains on the market: zinc phosphide (against house mouse). However, this authorization of uses with zinc phosphide will end in April 2016. Without replacement or renewal, no rodenticide for applications in stored-product protection would be available to protect stored products of plant origin.

Since most of the commensal rodents are classified as vectors for pathogens, one of the main purposes of using pesticides in this field is the control of organisms that are harmful to human health. To meet these hygienic uses there is a great number of biocides on the German market that could cover the mentioned gap of Plant Protection Products if it is not intended to reduce direct damage to natural plant products.

Besides efficient prevention and monitoring methods and other non-chemical controlling methods (e.g. heat, cooling, biological antagonists), chemical compounds keep their important part within stored-product protection when the quality of already infested stored products has to be preserved or storage facilities should get disinfested before filling. In this context, Plant Protection Products are a tool in integrated pest management (IPM) to protect harvested plant products from common and quarantine/invasive pest species in global trade and for recovery of otherwise lost food/feed for feeding rather than for repurposing it for other uses (e.g. biogas) (G20, 2015). To support this intention, Plant Protetection Products are evaluated according to the state of science and have undergone a risk-based authorization process due to the precautionary principle (COM, 2000). Furthermore, regulatory science has to enhance translation of basic science into regulatory applications (e.g. guidelines, standards) to support optimized uses of Plant Protection Products according to integrated pest management, the best available technology and good agricultural practice (Fig. 3 and 4).

Fig. 4. Much more targeting use of pesticides.

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