Aquaponic Pest Control

Life in our aquaponics system not only exists as the African catfish swimming in our tanks, and the plants growing in our flower beds, but also as the pests creeping inside our greenhouse. Pests thrive in our system as they're provided with delicious food and a warm environment. Given the presence of pests, especially their notable prevalence the last weeks, I decided to document my process of pest control in our aquaponics system. Below, I provide an indication of how I managed our pests (slugs and aphids) and my experience with them.

SLUGS

I realized there were slugs in our flower beds three ways:

1. By physically seeing them (image 1)

2. Slime on the leaves

3. Holes in leaves from where slugs had been eating

Image 1 - A slug feasting on a leaf in one of our flower beds

From my experience, slugs are the simplest pests to get rid of. That doesn't mean it's easy, but it is straightforward.

After a quick google search I found a basic effective method. I learnt that slugs are attracted to the yeast in beer. They drink the alcohol and then drown. May sound cruel, but hey - it's better then devouring your precious kale, isn't it? I decided to give it a try and build my own slug trap.

I found the perfect contraption - cut bottom halves of plastic bottles, with openings on the side for easy entry. I also used an open plastic container. I used the cheapest beer offered at our bar and filled the plastic containers up to a height of about 5cm. I placed 4-5 tubs in the beds where I knew we had slugs. Within one day of placing the beer tubs there were drowned slugs in the traps (image 2). Following, I emptied the tubs in our compost.

Image 2 - Plastic tubs with beer used as slug traps

APHIDS

Aphids are small insect pests which suck the sap from plants. I quickly detected we had an aphid problem when I saw small little insects on some plant stems and the underside of some leaves. This was particularly true for the Szechuan button. I wanted to identify what insect pest species they were. So, I grabbed some samples and placed them under the microscope (image 3). I discovered them to be aphids - a common garden pest.

Image 3 - Szechuan button flower infected by aphids. Photo taken using a microscope.

There are various methods to remove aphids, some more invasive than others. Given that aquaponics is a circular and very delicate system, and since we have live fish, there are some VERY IMPORTANT NOTES to remember to not harm the fish:

• Do NOT use oil-based pesticides
• Do NOT use soap-based remedies

If you do use oil or soap-based remedies, they must be heavily diluted and never sprayed directly into the fish tanks. The least invasive method is to spray the aphids loose with high pressured water. This is the only method I have used as far. I used the neon green jet and hose in our tool shed. If you use this method, attempt to do it on a relatively sunny day and in the morning so that the leaves can dry as fast as possible.

Using high pressured water to remove aphids was effective. However, it took me a few hours to remove as many as possible, and still it seemed impossible to remove all of them. Further, the following days I realized the plant was limp and contained many dead leaves, which is most likely the result of wetting the plant so much and due to the high water pressure. I would argue this method to be a temporary solution, and not effective for large aphid invasions. In such a situation, it may be more useful to use more invasive methods such as organic (at-home) herbicides.

The first is a do-it-yourself organic herbicide recipe, with chili, garlic, onion, and water. You can find loads of recipes online. For this method, after creating your concoction and allowing it to settle for a few days, spray the mixture onto the leaves of the plant - not on the roots nor directly into the water as this may harm the fish. The garlic is particularly toxic due to containing sulfur, and the aphids should die off and be repelled.

Aside from a DIY recipe, another option, which I am currently experimenting with, is using 'compost tea'. This leached compost liquid is made through the extraction of oils, flavonoids, minerals and vitamins from (organic) plant material. At the moment I am starting to conduct an experiment using compost juice as an organic pesticide (stay tuned for a follow-up!). I could not find much research online on it's use and effectiveness in pest control, so I thought it may be worth doing a trial test.