There are a few different methods of dealing with any pests and/or diseases in your system, of course most of these require no petrochemical based sprays as these are generally very toxic to fish and also possibly the beneficial bacteria within the aquaponics system.
Caterpillars are easily controlled by applications of Bacillus thuringiensis, this is a natural soil borne bacteria which is available around the world under a number of different brand names. Often organically certified the spray is safe for aquaponic systems.
For sap sucking insects you can use chilli and garlic sprays, these are often available commercially now a days, however they should always be used in moderation, as excess and overspray is never good.
For moulds and fungus on plants you can use potassium bicarbonate sprayed onto the effected plants. Potassium bicarbonate is available under a number of different brand names around the world. It also can help a system by adding potassium, something often lacking in an aquaponics system and the bicarbonate helps to keep the pH up, as most of the time pH goes down in mature systems.
If slugs are a problem, a small saucer filled with beer will attract them and they easily drown, making disposal simple and effective. Coloured sticky traps work well for thrips, aphids and whiteflies and are a good way to monitor visitors to your aquaponic system
