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I hope I'm posting this in the right place. 


I am constantly loosing the battle against fungus gnats. It's not the adults that are the problem but the larva. Everytime I think I have an answer they come back and go nuts. This time they have been destroying all my Onions from the inside of the bulb out.


We have a constant flood and drain system. Basically the water is always coming in and going out. 

We've tried Nematoads, BT Thuriside, Mosquito dunks,  Alchoal spray, washing all the rock out and starting over, placing cut potatoes on the rock and even flooding the system and sweeping all of the larva out. I have sticky traps every where and still can't get them controled. 


Please any ideas or suggestions? Our system is inside our house in an extra room, so there are certain things we can't use. And we can only afford low cost solutions. I'm willing to try anything! Our plants were looking great but the Tomato leaves are starting to be affected.


Thank you so much for any info!!

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You should address the problem which is most likely the constant flow watering cycle. If I were you I would try getting a timer and setting the timer to cycle on ( water) once an hour for fifteen minutes. It would be off for forty-five minutes giving the roots time to become unsaturated. Also, you should check your watewr level and make sure it is at least an inch below the surface of the grow media. That alone should eliminate you problems substantially. To kill the larva you should try spraying the roots lightly w/hydrogen peroxide- 1 part- 3 part water.  Keep fresh sticky yellow traps available to knock down the breeding population and to help identify any other types of pests that may enter from the outside. As a last resort you should consider using a pyrethrum fogger in the room while your not home.

I'm not sure pyrethrum is safe for a fish system?  Would definitely want to look it up before using it.


Yes, I think making sure the flood level is lower will probably have the most affect.  In Hydroponics too much wet media near the surface is a common cause of fungus gnat infestation.  Have you tried a vinegar or other trap?  Take a small container and use the corner of a baggie to make a funnel down in.  Then some vinegar or a bit of wine has caught lots of gnats for me.  Use a rubber band to hold the corner of the baggie in place.  The gnats mange to fly into the container through the funnel going down into it but then they can't find their way back out and usually drown in the liquid.  Just gotta find the right liquid to attract them the most.

Pyrethrins (insecticides made from pyrethrum flowers) is definitely NOT SAFE FOR FISH!!! 

 I don't know if planting Pyrethrum flowers (in a seperate pot maybe) and keeping the petals from falling and soaking into your system would do any good (seems like it might help), but again pyrethins are toxic to fish (and most non-mammals).

Pyrethrins are less toxic to mammals.

I've planted pyrethrum flowers near my garden crops and noticed less pests (less 'good' bugs too though).

Neem oil is also not generally fish safe.

You may need to try a multi layers of control, i.e vinegar traps, sticky traps, potted pyrethrum flowers, hand removal etc...all at the same time. At any rate, I wish you luck.

Since you are likely in a sunny spot (I'm assuming lots of light because of the tomato plants), try adding some sundews around your system.  Sundews are insect eating plants (very attractive) and act much the same way as the sticky tape does, but they are self cleaning and use the nutrients from the bugs to grow.  I use to sell these for a living and they are very easy to grow - they are native to the pine barrens of not exactly exoctic :)

They will not elimate the problem, but they will help control it - possibly to the point of them not effecting your onions.  

They can not be planted IN the system, the roots wont be able to handle all the nutrients/minerals in the system and will die.  The easiest thing to do is to plant them in  some containers (no holes, these are swamp plants, LOVE water logging) and set the dishes on top of your flood and drain system.  The plants don't get that big - so a bunch of small containers spread across your system would work well.  They just need lots of light, same as your tomatoes, and are good with 55 - 85 degrees.  The gnats will be drawn to there smell/pheremones and the constant water of the dish.  You'll start to see them accumulate onthe leaves after a couple days.  These plants don't like a lot of nutrients in their substrate (they seem to thrive in anerobic systems, opposite of our lovely tanks) so you can most likely use what you use in your system to plant these guys. If you collect rainwater or have distilled water around, that's what to use for these plants, no tap water.  

Not to complicated and once set up, just keep filled to the crown with water.  Good luck

Interesting Ricky, do you still sell these plants?  Or do you know where to get them?


Are there any dangers to handling these plants?  Will they attract any other insects?

Don't sell them anymore, too busy with my personal chef business.  You can find them at really good nurseries usually, stay way from any you find as novelties in supermarkets, as these are often harvested from the wild and not bred...bad stuff.  Also, dont try venus fly traps! Harder to grow - they need a winter sleep - and won't catch anything that tiny.  Sundews and American pitcher plants are the best bet.  As for attracting other bugs, if they do, they eat them, but nothing I've seen that is a pest.   If you have them outside and are worried about our friendly bees, they tend to stay away from them, but I have seen the tall version if the pitcher plant (can't remember the real name right now) devour wasps.
I like the idea if using these instead of traps since the rest of the system is using nature to do natural processes, why not complete the circle more. Also interesting to me that they thrive in the opposite type if environment.  I use them un my room to help control my fungus gnats, and in turn my carnivorous plants do well.

TCLynx said:

Interesting Ricky, do you still sell these plants?  Or do you know where to get them?


Are there any dangers to handling these plants?  Will they attract any other insects?

Very cool,

Now our summer heat might be too much for them, especially out in full sun seeing as we spent much of August with high temperatures (in the shade) of over 100 but I definitely like the idea of something that will attract and eat gnats.

Also, ZERO dander in handling them! If you have really hot summers they might be OK as long as they get some shade. There is another variety of sundew that I THINK is from africa (dont quote me) that can go down to about 30 degrees and come back from heat/ it for more info.
Big fat NO on pyrethrums. I wiped out a FT from an organic spray that I applied on the bottom side of the leaves, figuring that it would never contact the fish water. Must have been the overspray, I guess. I love the idea of the carnivorous sticky plants. How about fungus gnat predators?  I found this link:
oh, thought of another great plant this morning, butterworts - awesome catchers and just as easy to grow - the mexican variety should do well

Thank you all for the great ideas and information! I'm definitely going to look into the bug eating plants. My system is in my house so that seems like a great idea.

I have one question regarding them: Are they safe to have with children around?


Our water level stays about an inch under the top of the gravel but the gnats can be seen crawling through the gravel. I've tried the vinager traps but only caught about 3 gnats. The sticky traps are catching them like crazy... but there are still so many larva in the water/ rock.


Some one recommended treating with Mint tea? I wasn't sure how that would affect the fish though. 


Thank you all again for your suggestions, I at least have a few more ideas to try before going nuts :)


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