Gnat Problem

Phew, 

so I've finally gotten my Mealy Bug problem under control (was brutal) but now I still have a Gnat problem. 

I've been pouring Neem Oil (mixed with water) all over the plants and I've soaked their soil twice but still they thrive. I've ordered some Gnat stickies to catch the adults, hoping that will help. 

I have 4 pots with Habaneros and Cayenne. So I suppose I'll keep trying - I'm thinking of buying a huge bucket (as the pots are big) and filling it with Neem Oil mix and dropping them in up to the main stems (to submerge the soil). 

Anyone have any tips? 
 
It's really starting to bum me out, and it sucks putting the plants through this, I know that if I didn't have this Gnat problem they would be doing so much better. :*(
 

Bou

Extreme Member
I wonder if spreading a layer of diatomaceous earth on top of your dirt would do?
 

CaneDog

Extreme Member
Fungus gnats are tough to eliminate.  DE may help contain them, IDK, I've never tried it.  Neem oil won't do anything.  Neem cake is recommended and used by some, but I've never tried it either.  Judicious watering will help a lot and your sticky traps will make them less annoying.  There's threads on this if you search for "gnats," including a very recent one. Really getting on them usually means things like BTi and nematodes.
 
Good luck.  I hate them and there's plenty of 'em in the great Northwet.
 
I had the dreaded fungus gnats last year and they ruined my best 2 plants. Neem was ineffective but covering the top layer of soil with DE helped massively to reduce their numbers, along with ribbons of fly paper.
This year I've been militant since the start, DE top layer on the soil and bottom watering only. I saw few adults and squished them immediately, and after 3 weeks I haven't seen anymore, with the fly paper remaining unsullied.

So my best advice is maintain a layer of DE and bottom water only. In a couple of months I'll see exactly how successful this method has been when the plants are bigger... but so far, so good!
 
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LavaTonsil said:
I had the dreaded fungus gnats last year and they ruined my best 2 plants.
 
How so?  Fungus gnats are nothing more than an inconvenience for the grower, once the plant is past seedling stage. (we hate seeing them, having them buzzing about)
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Are you suggesting that fungus gnats did in an established plant?
 
I had inconsistent stunted growth which I attributed to them. They were around before I would say the plants were fully established but certainly beyond seedling stage.
Could be there were other unknown issues for sure though. I should say I did have a proper infestation; I was refreshing fly paper weekly which was more fly than paper each time.
 
LavaTonsil said:
I had inconsistent stunted growth which I attributed to them. They were around before I would say the plants were fully established but certainly beyond seedling stage.
Could be there were other unknown issues for sure though. I should say I did have a proper infestation; I was refreshing fly paper weekly which was more fly than paper each time.
 
It's highly unlikely that they were the culprit.  Never say never, but fungus gnats are really more of just a general nuisance; except in the seedling stage, when overly wet media, OR lack of organic matter, causes them to feed on tender young roots.  But fungus gnats are seldom, if ever, a realistic threat, in the absence of some other qualifier. 
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In general, they are found in all organic matter, but often avoid the surface, (in the "dangerous" larval stage) as they prefer moisture.  In nature, you'd find them in damp, shady places, where leaf litter or debris accumulates. 
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In the greenhouse or garden, fungus gnat larvae (as the adults do not actively feed) are most commonly a threat in shallow containers, where the moisture saturation zone, is consistently high in the container - effectively near the terminus of the main stem.  I live in an area where there are fungus gnats year round, and I plant in tall containers, to mitigate their effect/presence.  I can't get rid of them, but as long as they have plenty to eat, away from my roots in the formative stages, we're pretty much OK with one another.
 
Thanks for the detailed reply solid7!
I generally underwater chillies so these are even less likely to be the issue. I had spider mites on 2 plants but they were isolated in a different room and I didn't see any on the others. I
I will still maintain my irrational loathing for the little annoyances but with a little more knowledge on the subject
 
I've had the gnat problem this year for the first time really. As said, DE helps contain them, neem gives minimal help. The things I've found that work are hydrogen peroxide soil drenches (4 parts water to 1 part HP); kills the larvae. I also repotted them in new soil, as much of a pain in the a$$ that that was. 
 
ako1974 said:
I've had the gnat problem this year for the first time really. As said, DE helps contain them, neem gives minimal help. The things I've found that work are hydrogen peroxide soil drenches (4 parts water to 1 part HP); kills the larvae. I also repotted them in new soil, as much of a pain in the a$$ that that was. 
 
I had gnat last year. Ive ordered some hydrogen peroxide in case I'll be needing it.
Was the larvae visible? Did you see any damage on the roots? Did all the plants survive the hydrogen peroxide?
 
The plants sure did survive. It's tough to completely wipe out gnats, but the HP knocks them down. You're supposed to use it on a weekly basis while you have a problem, or every 5 to 6 days if the infestation is significant - I don't know how bad it is for the plants, but I guess if you have to do it for 3 or 4 weeks with no good results you may have larger problems.
 
I've done one drench so far and it really knocked them back - and, yes, I did see larvae. I put a slice of raw potato on the soil and left it overnight. In the morning, all these little black dots were crawling around the potato slice - the larvae. 
 
I also changed the soil in the most affected plants (directly throwing away the bagged soil in the outside garbage) and that made a big difference as well. When I popped some plants, I saw some larvae, but more adults that were getting back to business of laying eggs. 
 
The most noticeable damage I saw was to the leaves - I knew I had a gnat problem and it was getting worse, then some leaves started dying at the tips first, then to the back near the stem.
 
Good luck~!
 

CaneDog

Extreme Member
Some time ago, after reading about H2O2 as a potential treatment for FG's, I did a test by immersing fungus gnat larva in various H2O2 solution concentrations and their survival at root-in-soil safe concentrations as high as 1:4 was surprising - as in still wiggling the next day when I decided to dispatch them manually.  I don't remember the specifics as it's been a while and it wasn't any formal experiment, but I decided to pursue an alternative treatment.  Before embarking on an H2O2 program, I'd suggest testing your solution by dropping the potato piece into a container at your planned concentration and seeing how long they survive.
 
What about clay pebbles covering the top soil? I'm thinking when the larvas transform they cant get up and die. And the flies dont have anywhere to lay eggs.
 

CaneDog

Extreme Member
I don't know for sure, but my guess is they'd crawl right through the clay pebbles just like they'll access the soil through the drainage holes in the bottom of the pots.  I've heard sand works good because it's light-colored (I guess they don't recognize it as dirt?) and they can't work their way through it, but it's a big pain to water with sand on top of the soil.  I've tried BTi and was SUPER diligent with it, but it didn't seem to help all that much.  Now I simply focus on letting the surface dry between waterings, giving the plants more of the oscillating fan, and yellow stickies if they get bad.  A trick that works for me is I find they're most active right as I'm watering, so I put out the yellow stickies when I water and catch lots of them that way. 
 
I can keep the #'s down to where they don't really bother me, but I can't seem to ever completely stop them.
 
Thanks for all the information everyone! 

So I've been watering my chilli plants way less, and I have a layer of diatomaceous earth on top, which really seems to help. 

I still see them, but not many. 

I'm also using stickies constantly, which seem to keep their numbers down. 
 
I think I will add another fresh layer of diatomaceous earth sometime soon. 
 
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