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Many national and intergovernmental bodies have firmly decided that the officially endorsed paradigm for crop protection is ‘integrated pest management’ (IPM). For example, a European Union (EU) Directive (The European Parliament and the Council of Europe 2009) has obliged all professional plant growers within the Union to apply the general principles of IPM since 2014. IPM is an ecosystem-based strategy that focuses on the long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and the use of resistant varieties (Tang et al. 2005). Although aquaponics is understood to be more resilient against pathogens when compared with conventional hydroponic production (Gravel et al. 2015), it is nevertheless impossible to avoid pests and diseases. Healthy crops are first and foremost the consequence of good growth conditions and choosing an appropriate plant variety, which allow plants to achieve their high productive potential, and not the result of chemical and biological plant protection. A higher microbial diversity improves plant resistance in the rhizosphere against root diseases as well as greater nutrient uptake by the crop. Therefore, optimal plant nutrition, proper environmental conditions in the cultivation system, and intelligent cultivation techniques are essential. The management of pests and pathogens ought to minimize the application of biological and chemical products.
According to Food and Agriculture Organization (FAO), Integrated Pest Management (IPM) is defined as ‘A pest management system that in the context of the associated environment and the population dynamics of the pest species utilizes all suitable techniques and methods in as compatible a manner as possible and maintains the pest populations at levels below those causing economic injury’ (FAO 2018). Integrated crop protection and pest management (IPM) encompasses preventive measures, use of barrier-based approaches (e.g. agrotextiles), biotechnology-based methods (e.g. plant breeding), biological pest control using natural enemies, and controlled application of chemical products that are allowed in organic farming. IPM is therefore a cost-effective, environmentally sound, and socially acceptable way to manage pests and diseases.
Both in conventional hydroponics and in aquaponics, cultivation managers have to deal with different kind of biological threats. Insect pests are not only problematic because of the direct damage they cause to the plant, but also because they often act as carriers (vectors) for bacterial or viral diseases. Both insects and diseases benefit from controlled climate conditions in greenhouses: they are sheltered from rain, wind, and strong temperature fluctuations. However, these environmental conditions also allow an effective use of beneficial organisms against insects. Different management strategies should contribute to minimize pesticide use and to improve plant health. While biological pest control is part of Integrated Pest Management (IPM), there are some differences between the general concept of IPM and biological pest control (BPC) (Table 1).
Table 1: Integrated pest management (IPM) versus organic farming
Integrated pest management (IPM) Organic farming guidelines Preventive methods crop hygiene (weed removal, room disinfection etc.) physical barriers against pests (nets etc.) use of strong and resistant seedlings hygiene measures at the entrance restricting visitor numbers Use of beneficial insects against pests(Biological pest control (BPC)) Ladybird larva against aphids Fly parasitoid (Encarsia formosa) against whitefly Gall midges (Aphidoletes aphidimyza) against aphids Enthomopathogenic nematodes Enthomopathogenic bacteria and fungi Chemical control Use of synthetic pesticides not toxic to fish* could be used under controlled conditions but only as a last resort, such as Pymetrozine against aphids, whitefly Clofentezine against mites Fosetyl-aluminium against downy mildew Use of natural pesticides listed under BPC is possible too.* TER (Toxicity Exposure Ratio) = acute LC50 (mg agent/liter)/PEC (Predicted Environmental Concentration) > 100 forfish, and > 10 for aquatic invertebrates. Use of natural pesticides, such as Oils* (fennel oil against powdery mildew) Potassium bicarbonate* against powdery mildew (Oidium, Leveillula, Sphaerotheca) Sulphur* against powdery mildew (Oidium, Leveillula, Sphaerotheca) Lecithin* against powdery mildew (Erysiphe)
Check the fish safety before using any kind of phytopharmaceuticals, biological control agents or plant-based insecticides and fungicides
In contrast to conventional hydroponics, aquaponic systems are independent ecosystems with different zones (or compartments). Besides the target crops (fish and plants), the system also hosts a wide array of distinct microorganism communities (Schmautz et al. 2017), and small insects and spiders with either a beneficial, neutral or harmful effect on the crop. Aquaponic systems also usually feature a high density of fish and plants in one location, which facilitates the rapid spread of disease or pests throughout the whole system. In contrast to conventional cultivation systems, where the use of chemical pesticides is part of the daily routine, such methods are not suitable for aquaponics (Bittsánszky et al. 2015). The consequences of severe disease infection or of pest infestation are compounded, as losses or removal of either plants or fish will upset the balance between the fish, plants and water chemistry. The use of chemical products should be considered very carefully. The input of organic or inorganic chemicals could be fatal for aquatic animals as well as for the microbiological balance in the system. Therefore it is better to abstain from chemical products than to risk fatal consequences for the whole aquaculture system.
The IPM response to disease and/or pests in aquaponics is therefore constrained by: (i) the combination of fish, plants and bacteria, since fish may be sensitive to plant treatments and vice- versa, and bacteria may be sensitive to both fish and plant treatments; and (ii) the desire to maintain chemical free or organic status.
Figure 1: The five-step IPM program in aquaponics
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