The last time I grew cucumbers, they were taken over by afids and dystroyed. Now I'm growing watermelon and I'm having the same problem. I have an organic afid spray. Put it says you have to hit ALL of them, forit to do any good. That's been pretty tough, and now my plants are about shoot. Any way to prevent them or keep them away?
The best organic way is lady bugs and Pray-mantises.
Another way is garlic oil, but not sure about having oils and soap accidentally entering the water systems. You could shield the spraying area and grow beds to reduce over spray.
I have used vinegar, garlic and chile in a normal garden but not in aquaponics, You could try just vinegar to start with.
Anyone see a problem with garlic or chile in very small amounts entering the water?
Oh... if you have tomatoes the tomato leafs made into a tea and sprayed, is also very good.
A couple of options for you.
To make tomato leaf spray, simply soak one to two cups of chopped tomato leaves in two cups of water. Let it steep overnight. To make the spray, strain the leaves out of the liquid using cheesecloth or a fine strainer. Add another one to two cups of water to the liquid and add it to a spray bottle. To use the tomato leaf spray in your battle against aphids, spray the stems and foliage of the infested plant with the spray, paying special attention to the undersides of leaves, since that is where aphids most commonly congregate.
Caution: While this spray is very safe for humans, some people are allergic to members of the nightshade family. If you are one of them, use care in making and applying this spray.
I'm unsure about this going into the water as well....
Garlic Oil Spray Organic gardeners have long relied on garlic as part of their pest-fighting arsenal. Garlic contains sulfur, which, besides being toxic to pests, is also an antibacterial and antifungal agent. The dish soap in this mixture also breaks down the bodies of soft-bodied pests, such as aphids.
My vinegar one is . 1 cup vinegar, 3-4 cloves garlic chopped fine, 1 hot chile chopped fine, sit over night, strain, dilute with adding water if you want. spray those buggers.... Also you can try it without the chile as I'm not sure about how it may affect the system.
You could add a couple of drops of dish soap if you can isolate your spaying and not get it in or on the grow beds...
But I love Pray-mantises and if I find any I try and take them home to live in my garden.