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Appendix 2 – Plant pests and disease control

Aquaponic pest management can benefit from most of the common biological methods used in organic agriculture. However, it is important to remember that a strategy against pests should be planned according to the insects occurring in that particular area and the crop being cultivated during a specific season and a given environment.

PEST CONTROL: REPELLENTS, SOFT-CHEMICALS AND PLANT-DERIVED INSECTICIDESSoft-chemical alternatives to industrial pesticides can also be applied to deter pests. Organic mixes consisting of crushed garlic, pepper, soap and insecticidal oils can all be used to remove the threat of pests. If using soaps, make sure to use natural soaps, otherwise potentially harmful chemicals typically found in synthetic soaps can make their way into the water. Soaps can damage fish gills, so care should be used not allow too much to enter the water. Thorough coverage of the plant is necessary for effective pest control. Although observed and empirical knowledge on many of these methods suggests they work, there has not been systematic scientific research on their efficacy. Moreover, the medicinal properties of vegetables extracts used would suggest caution in their use because of toxicity risks to the fish.

Product Function/action Pest controlled Method of application

Citrus/citronella Repellent. Broad spectrum of pests.

Dissolve the product in water and spray on plants thoroughly.

Garlic oil Insecticidal properties which are enhanced if mixed with oil and soap.

Aphids, cabbage worms, leafhoppers, whiteflies, some beetles and nematodes.

Dissolve 85 g of minced garlic in 15 ml of vegetable oil and steep for 24 hrs. After, add the mix to 500 ml of water and spray on plants thoroughly.

Hot peppers, paprika (capsaicin dust)

Pest repellent. Maggot, ants. Sprinkle the dust over the plants.

Tomato leaf spray Attractant of beneficial microbes, possible toxic effect for alkaloids.

Aphids, corn earworm. Take 250 ml of fresh tomato leaves and place into 250 ml of water for 12 hrs. Strain and further dilute using another cup of water. Spray on target plants thoroughly.

Essential oils (sage, thyme)

Pest repellent. Reduces the level of feeding damage.

Broad range of pests. Mix a few drops in 250 ml of water and spray on target plants.

Alcohol extract (rosemary, hyssop, sage, thyme, etc.)

Repellent. Reduces the level of feeding damage.

Broad range of pests. Soak 250 ml of fresh leaves in 400 ml of water overnight. Strain out the leaves and use as foliar spray.

Soaps (salt of fatty acids)

Penetrates the cuticles causing dehydration and eventual death.

Soft-bodied insects: aphids, mealy bugs, whiteflies. Also mites, scales, thrips, ticks.

Use natural soaps: 1 (or more) tablespoon per 4 litres of water (adjustable depending on the plants and pests). Soaps can also be mixed with vegetable oils (see below).

Vegetable oils Suffocates pests. Aphids, mealybugs, mites, scales.

Spray on a 2 % concentration during the mornings or evenings. Commercial products should also be sold with an emulsifying agent.

Lime/ash Repellent. Broad range of pests. Finely sieve the ash and blow on wet leaves using a duster.

Starch spray (wheat flour or potato dextrin)

Trapping agent at the leaf surface.

Aphids, spiders, mites, thrips, whiteflies.

Mix 30–45 ml of potato starch in 1 litre of water along with 2–3 drops of liquid soap. Use as foliar spray.

Source: Ellis and Bradley (1996) – See Further Reading section for full reference.

Small-scale aquaponic food production – Integrated fish and plant farming184

PEST CONTROL: INSECTICIDES, PLANT-DERIVEDBiological insecticides deserve particular attention in aquaponics as not all of them are suitable for fish. Although biological insecticides are classified for organic use, most of them are toxic to fish and to beneficial insects. The table below listed a number of common insecticides and critical information for their safe use.

PEST CONTROL: BENEFICIAL INSECTSBeneficial insects can be used to control pests. This method is more applicable for large producers, as the cost can be prohibitive on a small-scale. The choice of insect must be matched to the pest insect and environmental conditions.

Botanical insecticides Origin Effect on pests Conditions for use

Nicotine (aqueous extract of tobacco)

Plant Neurotoxic insecticide. Toxic to fish.

Neem (Azadirachta indica) Plant Potent antifeedant. Needs repeated treatments, every 10 days.

Toxic to fish, may be used as foliar spray away from water. Does not harm beneficial insects. Also fungicide.

Pyrethrum (Chrysanthemum cinerariaefolium)

Plant Natural neurotoxic insecticide. Broad spectrum insecticide, also kills beneficial microorganisms.

Toxic to fish, may be used as foliar away from water. Low persistence, easily destroyed with light in 1–3 days.

Rotenone (Derris elliptica, Lonchocarpus spp., Tephrosia spp.)

Plant Natural insecticide effecting a broad spectrum of pests.

Extremely toxic to fish, may be used as foliar spray away from water. Suitable for plant nurseries before transplant to aquaponic unit.

quassia (Quassia amara) Plant Causes phagodeterrence in insect larvae.

Wood extract spray. Non-toxic to fish.

Ryania (Ryania speciosa) Plant Calcium channel disruptor for cells of pests.

Use sparingly and with caution as moderately toxic to fish.

Sabadilla Plant Interferes with nerve membrane of pests.

Use with caution, toxic effects still not well known for fish.

Diatomaceous earth (DE) Inorganic Abrasive dust absorbs lipids from the waxy outer layer of insects’ skeletons (i.e. ants), causing them to dehydrate.

Wear a mask when applying to avoid dust inhalation. Non-toxic to fish.

Sulphur (powdered or lime sulphur)

Inorganic Pest repellent and effective insecticide against mites.

Can also be used as fungicide.

Copper Inorganic In the form of Bordeaux mix as an insect repellent.

Copper is also a fungicide, but avoid over-accumulation in water – toxic to crustaceans.

Source: Copping, 2004; Shour, 2000; Soil Association, 2011; IFOAM, 2012 – See Further Reading section for full reference.

Beneficial insect/organism Type Pest to control

Adalia bipunctuata Predatory beetle Aphids

Aphelinus abdominalis Parasitoid Aphids

Chrysoperla carnea Lacewings Aphids

Aphidus colemani Predatory wasp Aphids

Cryptolaemus montrouzieri Predatory beetle Mealybug

Coccidoxenoides perminutus Parasitoid wasp Mealybug

Trichogramma spp. Parasitoid Caterpillars

Heterorhabditis megidis Nematode Chafer grub larvae

Steinernema carpocapsae Nematodes Codling Moths

Cydia pomonella Granular virus Codling Moth

Anagrus atomus Parasitic wasp Leafhoppers

Dacnusa sibirica and Diglyphus Parasitoid Leaf miners

Chilocorus nigritus Predatory beetle Scale insects

Hypoaspis miles Predatory mite Sciarid fly and thrips

185Appendix 2 – Plant pests and disease control

DISEASE CONTROL: ENVIRONMENTALMany fungal diseases are dependent of temperature and humidity, and as such, controlling the environmental factors can mitigate the disease. If the environmental factors cannot be controlled, it may be better to choose resistant crops or varieties.

Disease Disease agent Plants Target Temp. (°C) Humidity

Root rot Pythium spp. Lettuce Roots 28–30 Waterlogged soil

Downy mildew Pseudoperonospera cubensis

Cucumber, zucchini, squash

Leaves 20–25 Leaf wetness for 1 hour

Powdery mildew Sphaerotheca fuliginea Cucumber, zucchini, squash

Leaves 27 –

Verticillium wilt Verticillium spp. Various Stems 21–27 Moist soil

Fusarium wilt Fusarium oxysporum Cucumber, squash zucchini

Stems 25–27 –

Early blight Alternaria solani Tomato, potato Leaves 28–30 Free moisture

DISEASE CONTROL: INORGANIC CHEMICALSome inorganic compounds can be used to treat fungal diseases, and many of these are acceptable to use in aquaponic units. The table below outlines a few of these options.

Substance Condition of use

Clays Foliar application.

Copper salts Foliar application. Use with caution as copper can accumulate in the system. It is preferable to use at seedling stage before transplanting.

Sulphur Foliar application. Use with caution, as it may accumulate in the system (negatively affects plant growth).

Lime sulphur (calcium polysulphide)

Foliar application as a fungicide only. Use with caution, as it may accumulate in the system (negatively affects plant growth).

Potassium bicarbonate Foliar application. This can be also used to increase carbonate hardness (KH) which buffers the pH of the aquaponic water (see Chapter 3).

Sodium bicarbonate Foliar application, do not use to buffer the water pH as sodium accumulates in the system and negatively affects plant growth.

Calcium hydroxide (hydrated lime) Foliar application as a fungicide only.

Silicates/silicon Foliar application.

Source: Modified from IFOAM, 2012 – See Further Reading section for full reference.

Beneficial insect/organism Type Pest to control

Steinernema feltiae Nematode Sciarid flies and thrips

Amblyseius cucumeris Predatory mite Thrips

Phytoseiulus persimilis Predatory mite Thrips

Orius insidiosus Predatory bug Thrips

Amblyseius californicus Predatory mite Spider mites

Feltiella acarisuga Mite midge Spider mites

Encarsia formosa Parasitoid Greenhouse whitefly

Eretmocerus eremicus Parasitoid Greenhouse whitefly

Eretmocerus eremicus Parasitoid Whitefly

Heterorhabditis megidis Nematode Vine weevil

Phasmarhabditis hermaphrodita Nematode Slugs

Source: Olkowski et al., 2003; Soil Association, 2011 – See Further Reading section for full reference.

TABLE CONTINUED

Small-scale aquaponic food production – Integrated fish and plant farming186

COMPANION PLANTING CHARTCompanion planting is a small-scale intercropping method that is very common in organic and biodynamic horticulture. The justifying theory is that the association of different plants has either a mechanical, repellent or dissuasive effect against pests. In addition, some beneficial effects on the complex soil/plant agro-ecosystem can be encouraged by the release of substances or root exudates from beneficial plants. Although some degree of pest control has been scientifically verified, the degree of success depends on: the level of pest infestation, the crop density, the ratio between crops and beneficial plants, and the specific planting times. Companion planting can be used in combination with other strategies within an integrated plant and pest management to obtain healthier crops in aquaponic systems.

The table below gives a general overview of possible combinations according to biodynamic principles. Specific information can be obtained easily from the detailed literature available on organic and biodynamic agriculture.

Crop Companions Incompatible

Asparagus Tomato, parsley, basil –

Beans Most vegetables and herbs –

Beans, bush Irish potato, cucumber, corn, strawberry, celery, summer savory Onion

Beans, pole Corn, summer savoury, radish Onion, beets, kohlrabi, sunflower

Cabbage family (cauliflower, broccoli)

Aromatic herbs, celery, beets, onion family, camomile, spinach, chard

Dill, strawberries, pole beans, tomato

Carrots English pea, lettuce, rosemary, onion family, sage, tomato Dill

Celery Onion and cabbage families, tomato, bush beans, nasturtium –

Corn Irish potato, beans, English pea, pumpkin, cucumber, squash Tomato

Cucumber Beans, corn, English pea, sunflowers, radish Irish potato, aromatic herbs

Eggplant Beans, marigold – 

Lettuce Carrot, radish, strawberry, cucumber – 

Onion family Beets, carrot, lettuce, cabbage family, summer savoury Beans, English pea

Parsley Tomato, asparagus – 

Pea, English Carrots, radish, turnip, cucumber, corn, beans Onion family, potato

Radish English pea, nasturtium, lettuce, cucumber Hyssop

Spinach Strawberry, fava bean – 

Squash Nasturtium, corn, marigold Potato

Tomato Onion family, nasturtium, marigold, asparagus, carrot, parsley, cucumber, basil

Potato, fennel, cabbage family

Turnip English pea Potato

Source: http://permaculturenews.org/2011/12/02/companion-planting-information-and-chart/