Module 6 Introduction

Ecology

In the previous modules, we broke down the components of the aquaponics system. Let’s bring it all back together now and look at the entire ecosystem. An important element that affects the whole system is managing for pests. In this module, you will complete readings and exercises that will allow you to describe the elements, importance, and challenges of integrated pest management (IPM) for integrated food production systems and diagnose common problems in plant nutrient deficiency and pest management. All of this is preparing you to design a functional aquaponics ecosystem. At the end of this module, you will complete a case-based assignment.

Learning Outcomes

Upon completion of this module, you should be able to

Describe how all components integrate as a whole aquaponics system
Identify the pests and symptoms of common plant pathogens
Plan for plant pests and pest monitoring
Identify how to combat common hypothetical or actual pests/diseases with appropriate measures for aquaponics

Common Pests and Diseases In Aquaponics

As is the case in any agricultural venture, the producer will face the challenge of dealing with pests in his/her system. Controlling pests is an important part of aquaponics. There are, however, fewer options than in traditional garden/greenhouse/crop growing, making it quite an obstacle at times. Why is it so challenging? Due to the presence of fish and microorganisms in the system, many traditional pest management techniques cannot be used. We will explore integrated pest management in depth in this module, but first, let’s begin with some photos of common pests and diseases: aphids, white flies, thrips, mites, leaf miners and powdery mildew.

Aphids
White Flies
Thrips
Mites
Leaf Miners
Powdery Mildew
Aphids are all generally small (1-3mm) and soft bodied, and have a pair of unique structures that resemble “tailpipes” near the end of their abdomen, called cornicles. Adults may or may not have wings. More than 20 aphid species can infest various greenhouse crops. Three of the most common are: Green peach aphid, Melon aphid and Foxglove aphid.
Damage: Aphids can infest most greenhouse crops. Their mere presence can ruin the beauty of a plant. They feed by inserting their stylet-like mouthparts through plant tissue directly into the phloem and removing plant sap. Feeding can cause stunting and plant/leaf deformities. Large infestations can reduce plant vigor. They produce a sweet, sticky secretion called “honeydew,” which leads to unsightly grey sooty mold. White cast skins that they leave behind as they molt from one stage to another are unsightly. Aphids are responsible for the transmission of about 60% of all plant viruses on agricultural crops world-wide.
Biology: (common greenhouse) Aphids reproduce parthenogenetically, i.e., all the insects present are females, and each female gives birth to more females without the need to mate. These females give birth to living nymphs rather than lay eggs. An unborn aphid already contains a complement of developing nymphs (=”paedogenesis”). Aphid nymphs are genetic clones of their mothers. Populations can increase explosively—newborns can reach adulthood and begin to reproduce in as little as 7 days. As a colony increases in age and size on individual plants, the proportion of winged forms increases. Aphids may be found feeding on buds, stems, and the lower surfaces of leaves. Some will migrate to new host plants and will actively search for soft, fresh plant tissue. As plants begin to form flower buds, a previously undetected aphid infestation can become terribly apparent as they move up the plant onto the recently developed stems, buds, and flowers. Aphids on the upper canopy will be easier to contact with sprays. Systemic insecticides will be most effective against those feeding on new growth. Aphids on older growth lower in the canopy are often most difficult to kill chemically, and may be responsible for producing new aphids that will reinfest the upper canopy. Green peach aphids are prone to develop winged forms on mums, and may be more likely to spread quickly throughout a mum crop. Melon aphids do not develop winged forms as readily and are not as likely to be detected on yellow sticky traps.
Monitoring/Control: White cast skins on leaves of a plant may indicate an aphid colony on the leaves or stems above. Ants are often attracted to the honeydew, so if you see ants on your plants, inspect them carefully for aphids. Group aphid-susceptible plants together for easier monitoring. Inspect plant material brought into your growing areas; do not purchase infested plants or cuttings. Inspect the greenhouse thoroughly for all sources of pests, before a new crop arrives. If possible, quarantine newly-arrived plants, and inspect thoroughly before moving them into production areas. The scouting procedure for each PMU is made up of three components: plant inspection, sentinel plants, and yellow sticky cards. Yellow sticky cards for winged adults, coupled with plant inspections for non-winged aphids, can give a good overall picture of the presence, size, and location of an infestation, and reveal if control strategies are working. Sentinel plants can indicate whether your chosen control measure was effective. There are multiple biocontrol agents from which to chose in controlling aphids, from predatory beetles, bugs and flies to parasitic wasps.

An Introduction to Integrated Pest Management

Aquaponics happens in a controlled environment. A producer may have semi-closed or closed production areas. He/she may grow a single crop (monoculture) or have multiple plant varieties (polyculture).

Integrated pest management (IPM) is an effective and environmentally friendly approach to pest management in a greenhouse environment. It relies heavily on a combination of practices. The producer uses comprehensive information on the life cycle of pests and their interaction with their environment to inform his/her management techniques. A primary goal of IPM is to develop a system of preventive measures and manage pest damage by the most economical means possible. It is important to realize the difference in IPM approach in aquaponics and hydroponics. While chemical control is a major tool in hydroponics, it has a limited use in aquaponics due to presence of fish and beneficial microorganisms, which can be negatively affected by the pesticides. Any contact of chemicals with aquaponics water has to be avoided and no systemic pesticides should be used. Instead, IPM in aquaponics heavily relies on prevention of pests and on biological control, which has significantly advanced over the past decade.

The inability to use pesticides certainly makes crop production in aquaponics more difficult but it does ensure the plants and fish are raised in an environmentally friendly, chemical-free manner. Conditions are easier to control in a greenhouse setting than in outside aquaponics systems. There are significant benefits of growing aquaponically:

A major advantage of aquaponic systems is that crops are less susceptible to attack from soilborne diseases. Plants grown in aquaponic systems may be more resistant to diseases that affect plants grown in standard hydroponics. This resistance may be due to the presence of some organic matter in the culture water that creates a stable growing environment with a wide diversity of microorganisms, some of which may be antagonistic to plant root pathogens” (Rakocy, et al., 2006, p. 12).

Excess moisture on the surface of rafts or growing medium should be avoided to prevent algae growth, which can provide food for some opportunistic insects, such as fungus gnats. Fungus gnats can become vectors of plant diseases.

There are seven key elements in IPM: prevention, identification, monitor, control, action threshold, record keeping, and evaluation. We will look at six of these elements now, saving “control” for a little bit later in this module.

	Key Elements in IPM
	Prevention	The best offense is a good defense Growing plants in a properly balanced system is key Monitoring plants for any nutrient deficiency Environmental control (e.g., fungal gnats – moisture)
	Identification & Monitoring	Surveying the growing area on a regular basis Survey tools (methods) vary depending on the scale of the growing operation Options: (1) Hand (visual) inspection (2) Yellow (or blue) sticky traps
	Action Thresholds	The number of insects observed indicates what action needs to be taken Number might vary between (1) growing environment (2) season
	Record Keeping	Very important As time passes the records will become incredibly valuable (1) idea about patterns (2) preventive measure to implement
	Evaluating	Successful crop Cost (materials, labour, health risks, environmental damage) Multiple tactics? Ease of operation What would you do differently next season?
	Recommended Reading Somerville, C., Cohen, M., Pantanella, E., Stankus, A., & Lovatelli, A. (2014). Small-scale aquaponics food production: Integrated fish and plant farming. Rome: Food and Agriculture Organization of the United Nations. You read “Chapter 6: Plants in Aquaponics” in Module 5. Return to it now and re-read the section titled “6.5 Plant health, pest and disease control.”

Controlling Pests with Integrated Pest Management

There are various types of integrated pest management (IPM) tactics that can be used for controlling your pests. The below diagram shows the types of integrated pest management in increasing levels of intervention and toxicity. You can see that much of the work of pest management can and should be done at the lower levels (prevention) over intervention, owing to the need to maintain fish, microbiological elements, water and plants at workable, non-toxic levels. Biological pest control is therefore usually the more effective and less invasive way of pest control for aquaponics.

Adapted from PennState Extension. (n.d.). Pennsylvania Integrated Pest Management. Retrieved from
http://extension.psu.edu/pests/ipm/schools-childcare/schools/educators/resources/ipm-pyramid-of-tactics (Links to an external site.)

Biological pest control is a fascinating and effective means of controlling pests when you are in a well-constructed, controlled environment. Biological control is the beneficial action of parasites, pathogens, and predators in managing pests and their damage. Biocontrol provided by these living organisms, collectively called “natural enemies”, is especially important for reducing the number of pest insects and mites. For example, using preventative measures, such as introducing ladybugs every two weeks, helps to keep pest populations low.

Seasonal factors can contribute to disease and pest problems. Temperature and day length variations, in particular, can disrupt a system and lead to problems. You need to be aware of environmental factors that promote certain diseases and pest populations. For example, you need to keep TSS levels low in your water so plant roots don’t accumulate this organic matter which promotes fungal pathogens, or keep moisture off exposed surfaces so algae growth isn’t encouraged. With this awareness, you can act proactively, monitoring and controlling environmental conditions when possible.

It is important to remember that any disease or pest measures you implement for the plants will affect the entire aquaponics system. Your environment must be managed as organically a possible so that you do not harm the fish or the bacteria living throughout the system. When you suspect a disease or pest problem exists and you can not identify the culprit, there are labs you can send samples to for testing.

Pesticides pose a threat to fish in the aquaponics system and should therefore, not be used to control plant pests. Similarly, therapeutants (e.g., chemicals, medicines, supplements) that are often the go to to treat fish parasites and diseases also can’t be used as they harm the microbiology and plants in the aquaponics system. For example, even something like salt, which is often used to treat some fish parasites or mitigate fish handling stress, would be hugely damaging to the plants in the system. As a result, aquaponics systems require non-chemical methods of integrated pest management.

Example of non-chemical integrated pest management include:

Resistant cultivars (disease resistant plants)
Predators (e.g., parasitic wasps and ladybugs may be introduced to control white flies and aphids)
Pathogens (e.g., control caterpillars by spraying the plants with bacillus thuringiensis, a bacterial pathogen)
Antagonistic organisms
Physical barriers
Traps
Manipulation of the physical environment

The Ecosystem Approach

Aquaponics as Integrated Agro-ecosystem

A common stereotype about aquaponics is that aquaponics is just a kind of hydroponics where the fish serve as a source of nutrients replacing synthetic fertilizers. Whereas in fact, aquaponics is a different concept of food production, based on mimicking the same relationships and interactions which govern natural ecosystems. In other words, it is an example of an agro-ecosystem, which is a fundamental departure from monoculture practice adopted in agriculture in the 20th century. Monoculture is the cultivation of a single crop in a given area (monoculture, n.d.). Agro-ecosystems are superior to these conventional agricultural practices based on monoculture as they recycle nutrients, use resources like water more efficiently and greatly reduce any harmful environmental impact. They are examples of truly sustainable food production systems.

Below is a table describing the differences between hydroponics and aquaponics:

Production system:	Hydroponics	Aquaponics
Principals	Conventional	Biological
Recirculation	Possible	Closed loop
Source of nutrients	Synthetic fertilizers	Fish waste, nutrients released due to biological activity
Beneficial microorganisms	Practically excluded	Essential part of the system
Building multitrophic relationships in the system	In some extent	Yes
Balance	One-component system	Balanced
Self-regulation	No	Yes
Creating an ecosystem	No	Yes
Stability of a mature system	Not stable	Very stable
Knowledge base	Plant physiology	Ecology Plants, fish, microorganisms

Every start-up aquaponics facility, given there is no interference by chemicals, antibiotics or antiseptic equipment, will invariably become populated by numerous microorganism communities. This microbial colonization process can last from a few months to years and eventually yields an established “mature aquaponics.” It is at this endpoint that aquaponics becomes, in fact, a self-regulating artificial ecosystem. As a result, stable trophic interactions are created that serve to link all living system components. A mature aquaponics ecosystem is characterized by stabilized water parameters and increased productivity (see the diagram below).

Stability of Water Parameters in Mature Aquaponics (measuring levels of pH, temperature and EC in an aquaponics system)

Integrated food production is considered as a viable alternative to monoculture. There are many advantages to producing food in integrated systems: nutrient recycling, higher water use efficiency, and lower environmental impacts are among them. However, a robust engineering design, to ensure flawless operation of such systems remains a challenge.