The use of pesticides in aquaponics is a very touchy subject, and we've seen both the good and bad side of pesticide use in aquaponic systems. 

There are many opinions on the subject with varying degrees of validity. Over all of these opinions rules a single fact:

Chemical pest management in aquaponic systems must be approached judiciously, thoughtfully and with caution, whether you are using a homemade remedy or a commercial product. 

Before I begin to talk about the controls, you must know that this information was hard-won over the course of many years. Let's talk about the options that you have for using pesticides in an aquaponic system.

Many aquaponic practitioners swear by garlic, chili and vermicompost based concoctions, and to be fair, these can be effective on specific pests. Having tried almost all of the home remedies over the years, these days I rely entirely upon commercial products. As a commercial producer I do not have the time or energy that homemade remedies require, nor do I have the luxury of using marginally effective controls.

This means that we use proven commercial products that have been studied and provide the information necessary to determine their effect on our aquaponic system- products that we know from experience kill and control pests.

Pests are inevitable in aquaponic systems, and dealing with them has always presented a very difficult dilemma for aquaponic producers, primarily because there are so few pesticides that are non-toxic, or of low toxicity to fish, but also because no one knew how much could be safely used. We learned about different pesticides in our aquaponic systems through a great deal of effort and research, and offer it to you now.

This writing will focus on organic pesticides, most of which are OMRI certified. This is primarily because we, like most commercial AP producers, produce “organic” produce and use pesticides permissible under USDA Organic Standards.

Before we begin to discuss individual brands and products, I would first encourage you to do some research on Integrated Pest Management, commonly referred to as IPM.

IPM is a pest control strategy that incorporates cultural, mechanical, chemical, and biological pest control into a larger context of economics, environment and human health.

For aquaponic producers IPM is important, not just because you are operating on a budget, (and IPM is the most cost-effective way to control pests) but because you have more complex environmental constraints than the average producer, and your customers are probably concerned about healthy food.

Operating without an IPM strategy in place could make pest control unnecessarily expensive, impact your fish health and the health of your system, or impact the health of your customers. So please examine this topic to determine what types of controls you use and when you apply them.

I’ve met people that use a single control for many months, if not years on end. They always say “It works great and I don’t have any problems,” and they might have good control, for a little while longer at least. But the unfortunate nature of greenhouse and garden pests is that they adapt very quickly to toxins in their environment, and rapidly become resistant to even the most toxic pesticides.

Varying your control methods and incorporating chemical, biological, mechanical and cultural controls in tandem helps prevent resistance developing.

We use a variety of products that exert chemical control over our greenhouse pests, including:

Pyrethrin based products (See Pyganic 1.4, Safer Endall Insecticidal soap, etc.)

Soaps (Safer products)

Azadirachtin based products (extracted from neem oil; see Azamax, etc.)

Neem oil and neem oil derivatives

*Note: Pyrethrins are very toxic and can only be considered for use in ZipGrow Tower based systems
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In order to do the math, one must understand a special rating called the LD50 or LC50. These represent the median lethal dose or Lethal Dose 50 or Lethal Concentration 50- the concentration at which half of the sample population will die. In regards to pesticides, they are often studied and the LD50 is determined for a certain time period (usually in hours or days).

While it takes some digging, most pesticides have have an LD50 rating, determined experimentally for a variety of marine organisms. Fortunately for many aquaponic practitioners tilapia spp. (Oreochromis spp.) are a common test subjects. 

When I look for LC50 numbers I typically go to the source material- scientific publications that detail experiments with different organisms and chemicals, or the Veterinary Substances Database, and use the lowest LC50 published.

For Instance: Pyrethrins

Pyrethrins are a family of very effective insecticides that most aquaponic practitioners cannot use in their systems because they are highly toxic to fish, and most practitioners have no idea how much is safe and how much isn’t.

To discover how much a system can handle, we must look at the LC50 for pyrethrum (type 1 pyrethrin), the active ingredient in Pyganic 1.4. When we look for this number we find that the LC50 (in 96 hours) for rainbow trout (Oncorhynchus mykiss) is 0.005 mg/L and for aquatic crustaceans is 0.0014 mg/L (96 hrs; Americamysis bahia). Since 0.0014 is the lower number, we’ll use this number.

We need to determine how much pyrethrin is required to hit the LC50 for your system.

Take the volume of your system in liters and multiply it by the LC50 (96 hr) value (we will use my system as an example):

4,300 gal./sys. * 3.79 L/gal. = 16,279 L/sys. * 0.0014 mg/L = 22.79 mg/sys.

Then we take the pyrethrin concentration and determine how much pyrethrin is being mixed and applied in the greenhouse.

The label recommends mixing 1-2 fluid ounces of Pyganic 1.4 with every gallon of water in compressed sprayers (what we use), which is between 2-4 Tbsp/gallon. In my greenhouse, the entire crop can be sprayed with 1.5 gallons of mix, which at the highest application rate is around 6 Tbsp (or 3 fluid ounces).

The label tells us that 0.05 lbs of active ingredient (pyrethrin) is the equivalent of 59 fluid ounces.

0.05 lbs pyrethrin/59 fluid ounces = 0.0008475 lbs pyrethrin/fluid ounce

0.0008475 lbs pyrethrin/fluid ounce * 453592 mg/lb = 384 mg pyrethrin/fluid ounce

3 fluid ounces/system * 384 mg pyrethrin/fluid ounce = 1152 mg pyrethrin/system

This number is much larger than the LC50 for the system. If I were using operating a raft system or a media bed system I would know that using pyrethrin in my system is not possible, unless I knew that less than half of LC50 value would enter my system, or around 1% of the total application (for crustaceans, or 3% for fish). However, with towers we’re able to use pyrethrin because such a small percentage of the spray actually ends up in the system solution.

These same calculations for Azamax yield the information:

Azadirachtin LC50: 7813.92 mg/sys

Total Azadirachtin typically applied: 1050 mg/sys

This tells us that Azadirachtin easily comes in under 1/2 of the LC50 value.

LC50 can be a bit complicated to determine, but there is still much more freedom to control pests in aquaponic systems than most people assume. Instead of dismissing a pesticide, do the calculations to determine whether it can or cannot be used, and use that to make your determination.

It is my experience that if you don’t want to do the calculations for pesticides in aquaponics, you’re generally very safe spraying Azadirachtin products like Azamax, as well as Botanigard. These are both great for killing aphids, thrips and whitefies- typical aquaponic system pests.

Before this ends, I must insist that you use protective garments, goggles, gloves, etc., and adhere strictly to the label as far as mixing and application goes. Also please do adhere to a Re-entry Interval or REI to insure that you and no one is exposed to the pesticides unwittingly.