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Posted:  14 Aug 2015 20:43  
Has anyone out there had any trouble with fungus gnats in living walls?
Posted:  14 Aug 2015 22:58  
DISCLAIMER: I have never personally installed or maintained a living wall, so take this as general horticultural experience and knowledge, not first-hand actuarial advice...

Oh, baby!  Living walls could end up being the Typhoid Mary of fungus gnat problems.  Because they are packed with innumerable small plants with root systems totally dependent on the moisture they receive from frequent irrigation cycles and are a catch-all for leaf litter and other detritus, they represent a perfect breeding ground for fungus gnats.

The stand-alone "plug-and-play" walls and other types that use 3" or 4" potted plants in a matrix of space-holders are going to behave just as any other potted plant in constant contact with moisture would behave; the "hard-wired" kinds, which have plugs planted directly into their structure, will have bits of growing medium and dead roots and leaves mixing with the substrate and the irrigation water, again furnishing gnats with a desirable habitat for breeding and larval development.

So how to cope with these issues?  Well, if you're a "green" vendor, you've got a problem.  You can't very well use the layer of sand technique to form a barrier to the entry/exit of gnats in the soil, and nematodes may not be able to satisfactorily establish themselves in walls with little organic substrate, and they will be subject to wash-out by drip irrigation systems.  Wick systems would avoid that last issue, but where there is organic matter and moisture, there will be gnats.

Can they be staved off using pesticides?  Maybe, but most pesticide drenches stipulate that you not irrigate again until at least 7 to 10 days after application of the drench, to allow the chemical time to work.  Something like Marathon II might be a candidate, because it's odorless, but avoid anything with an objectionable odor, because the odor will be reactivated each time you irrigate the wall, at least for awhile.

That's all I've got, but I know we have some living wall veterans and experts lurking about, and I'm sure they'll come on with some specific advice for you.
Posted:  17 Aug 2015 17:52  
What we ran into was that the irrigation emitters were too small for the biologicals that we wanted to use.
Posted:  17 Aug 2015 18:37  
That problem could be solved by just spraying the nematodes into the growing matrix using the coarsest spray nozzle you can on a 2-gallon garden pump sprayer.  That way you can be sure to get even coverage with your suspension of nematodes and water instead of being captive to the drip patterns of the emitters.  This is purely speculation on my part, but it seems to make intuitive sense.
Posted:  17 Aug 2015 19:16  
Julie, would a wick style green wall system like SuitePlants LivePanel solve your problem with regards to the biologicals you want to use? I know replacing the system likely isn't an option, but may be worth considering for future installs.

SuitePlants LivePanel
Posted:  18 Aug 2015 14:40  
The wall is 12 ft. by 40 ft.  I can't see them replacing the system, with that kind of investment.  I did not choose it, as I am the sub-contractor.  I just am responsible for solving the problems.
Posted:  18 Aug 2015 21:50  
Back in the day, you could have hung Shell No-Pest Strips in the space and annihilated the adult gnats as well as the larvae and pupae, probably.  But nowadays, that's not a legal use of the product, and it can only be hung in unoccupied spaces like vacation cabins and garages, which would need to be ventilated after removal of the strips before they can be inhabited again after treatment.  But that stuff used to work like a charm.  Ralph Snodsmith and other radio plant gurus would suggest putting an infested houseplant into a large, clear plastic trash bag with a hunk of the strip and closing it up overnight to "fumigate" the plant.  I tried it a few times, and it did work.  Nasty stuff, though, that Vapona.

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