Controlling pests in aquaponics

Aphids are the most explosive pests in aquaponics. Their reproduction is lightning-fast : a single female can produce dozens of live clones… every day. In a heated greenhouse, an infestation can double every 24-48 hours.

They suck the sap, causing leaf deformities, stunted growth, sticky leaves, and sometimes the development of sooty mold (black fungus). They primarily target basil, peppers, tomatoes, and all young shoots rich in nitrogen.

In aquaponics, a poorly managed infestation can ruin an entire crop in a matter of days.

Fungus gnats do not appear dangerous at first glance, but their presence is a valuable indicator : it reveals that the surface of the growing bed remains too wet or that organic matter is beginning to accumulate.

The problem lies with the larvae. They live in the top few centimeters of the substrate, where they feed on fine roots. Affected plants exhibit slow growth, slight wilting despite adequate moisture, and sometimes premature yellowing.

The proliferation of midges accelerates when air circulation is poor, plants are too crowded, or evaporation is insufficient. Their presence is a clear signal that the climate needs adjusting.

Mites, especially spider mites, are extremely difficult to detect with the naked eye. Their presence is only visible through the damage they cause : speckled, discolored, dry leaves, sometimes covered in fine webbing. They almost always appear in areas that are too hot and too dry.

In aquaponics, paradoxically, this problem occurs mainly in poorly ventilated greenhouses : overall humidity is high, but the leaves remain dry on the surface because the air doesn't circulate. Mites also thrive on stressed plants, especially when the plant suffers from a calcium or magnesium deficiency.

A severely attacked plant experiences a disrupted metabolism. It expends its energy repairing damaged tissues instead of growing, which significantly affects the overall productivity of the system.

Slugs and caterpillars are less common in indoor aquaponics, but very frequent in outdoor systems. The constant humidity of the tanks, the shade under the structures, and the natural shelters created by the vegetation make it an ideal environment for them.

Their damage is immediate : leaves are perforated, edges are severed, and young shoots disappear overnight. In a system where each plant plays a role, the physical destruction of a crop can lead to a temporary decrease in nutrient absorption, altering the system's balance.

Slugs are attracted to the moisture in garden beds and are particularly active at night. Caterpillars, on the other hand, often hatch from eggs laid on leaves or are attracted to outdoor lighting.

The presence of mosquito larvae indicates an area of ​​the system where the water is stagnant. In a well-designed system, the water should always be in motion. Mosquitoes only lay their eggs in still or very slightly agitated water.

Even though these larvae are not dangerous to fish, they indicate a lack of oxygenation or flow, which can also harm nitrifying bacteria.

In systems with poorly inclined return lines, partially covered tanks, or excessively still barrels, this stagnation can occur. The solution is to improve circulation or cover attractive areas.

Beneficial insects are the cleanest, most sustainable, and most consistent approach with the spirit of aquaponics. In a greenhouse, a pest thrives because it has no predators.

For aphids, ladybugs and especially lacewing larvae are very effective. They quickly attack colonies and prevent regrowth. For mites, specialized predatory mites are used, which are particularly useful when the plant is already infested.

This method works particularly well if the infestation is treated early. The earlier you intervene, the faster the balance is restored and the less likely you are to have to "save" the plants.

Before even considering treatment, the quickest solutions often involve removing a large portion of the pests by hand. For aphids, a targeted rinse of the leaves (away from the pond) or a gentle wiping can immediately reduce the colony. For heavily infested leaves, the best course of action is sometimes to cut off and remove the affected part.

In the case of caterpillars, manual collection is very effective, especially if the plants are inspected in the morning or late afternoon. Outdoors, slugs can also be managed through nighttime inspection and regular removal, which reduces their impact before the population explodes.

Black soap is one of the few "treatment" tools usable in aquaponics, but it must be used with surgical precision. It acts on contact against aphids and mites by disrupting their external defenses. It is very effective, but it becomes dangerous if any droplets run into the pond.

The best method is to treat only the affected leaves, protecting the growing bed and water, and avoiding any spraying above the tanks. In an aquaponics system, the challenge is not just to eliminate the insect : it's to do so without disrupting the nitrogen cycle.

When the treatment is precise and limited, black soap is an excellent one-off solution to regain control.

Many infestations disappear simply by correcting the air and humidity. Gnats thrive when surfaces remain wet and air doesn't circulate. Dust mites proliferate when localized heat rises and the air stagnates.

Gentle but constant air circulation makes all the difference : it reduces stagnant humidity, evens out the temperature, and creates a less favorable environment for pests. It's also an indirect measure of health : a plant that breathes better is more resilient.

In many systems, a simple, well-placed fan or more regular ventilation cuts the problems in half within a few days.

Pests thrive where they can hide. In aquaponics, plants can become very dense, especially in well-nourished systems. This density creates shaded and humid areas where insects find shelter and breed.

One of the most effective levers is to aerate the plant mass. Light pruning, spacing out certain crops, removing lower leaves, and eliminating plant debris immediately reduces hiding places.

A clean growing bed, free of decaying leaves, attracts far fewer fruit flies. A well-maintained greenhouse, without unventilated damp areas, greatly reduces the risk of new colonies emerging.

If larvae appear in the water, the solution isn't a product, but a circulation diagnosis. You need to identify where the water is stagnating : tank corner, secondary tank, slow return channel, area under the lid. Once the area is identified, increasing water movement or oxygenation is usually enough to eliminate the problem.

Mosquitoes do not lay eggs in a moving pool. This means that a well-designed system, with proper circulation and a well-mixed surface area, is almost naturally protected against this type of pest.