2.4 Pest, Weed and Disease Control

2.4.1 Predictions

It is generally recognized that control of diseases, pests and weeds is a critical component of curbing production losses that threaten food security (Keating et al. 2014). In fact, increasing the use of antibiotics, insecticides, herbicides and fungicides to cut losses and enhance productivity has allowed dramatic increases in agricultural output in the latter half of the twentieth century. However, these practices are also linked to a host of problems: pollution from persistent organic compounds in soils and irrigation water, changes in rhizobacterial and mycorrhizal activity in soils, contamination of crops and livestock, development of resistant strains, detrimental effects on pollinators and a wide range of human health risks (Bringezu et al. 2014; Ehrlich and Harte 2015a; Esch et al. 2017; FAO 2015b). Tackling pest, weed and disease control in ways that reduce the use of these substances is mentioned in virtually every call to provide food security for a growing world population.

2.4.2 Control of Pests, Weeds and Diseases

As a closed system with biosecurity measures, aquaponic systems require far fewer chemical pesticide applications in the plant component. If seed and transplant stocks are carefully handled and monitored, weed, fungal and bacterial/algal contaminants can be controlled in hydroponic units with targeted measures rather than the widespread preventive application of herbicides and fungicides prevalent in soil-based agriculture. As technology continues to advance, developments such as positive pressure greenhouses can further reduce pest problems (Mears and Both 2001). Design features to reduce pest risks can cut costs in terms of chemicals, labour, application time and equipment, especially since the land footprint of industrial-scale aquaponics systems is small, and systems are compact and tightly contained, as compared to the equivalent open production area of vegetable and fruit crops of conventional soil-based farms.

The use of RAS in aquaponic systems also prevents disease transmissions between farmed stocks and wild populations, which is a pressing concern in flowthrough and open-net pen aquaculture (Read et al. 2001; Samuel-Fitwi et al. 2012). Routine antibiotic use is generally not required in the RAS component, since it is a closed system with few available vectors for disease introduction. Furthermore, the use of antimicrobials and antiparasitics is generally discouraged, as it can be detrimental to the microbiota that are crucial for converting organic and inorganic wastes into usable compounds for plant growth in the hydroponic unit (Junge et al. 2017). If disease does emerge, containment of both fish and plants from the surrounding environment makes decontamination and eradication more manageable. Although closed systems clearly do not completely alleviate all disease and pest problems (Goddek et al. 2015), proper biocontrol measures that are already practised in stand-alone RAS and hydroponics result in significant reductions of risk. These issues are discussed in further detail in subsequent chapters (for fish, see Chap. 6; for plants, further details in Chap. 14).