Fungus Gnats

Pamela Harlow
Mon, 21 Mar 2011 10:16:44 PDT
The dispute between effective control vs environmental safety is easily
solved by using the BT product.  You can have it both ways!  I use Gnatrol,
but it sounds the same as Mary Sue's product.  To clarify, BT is Bacillus
thuringiensis var. israelensis.  It is not a toxin, but a living pathogen
with a very specific target, the larvae of fungus gnats.  There may be other
insect larvae that it attacks, but I am not drenching the landscape.  I am
hand-watering pots.  

I grow on a commercial scale.  Yellow cards did nothing for me, but Gnatrol
is very effective when used diligently.  Winter wrens and song sparrows
routinely sneak into the greenhouses to forage unaffected insects, with no
ill effects to the birds.

I have another observation about fungus gnats that I have never seen
reported, perhaps because most operations use toxic chemicals.  Fungus gnats
are a pest of recently potted plants only.  That is, even an infestation in
untreated pots will gradually taper off and eventually those pots will
become immune to gnats.  I think this is because tiny predator species
gradually colonize the soil.  I think I am seeing Hypoaspis creeping around,
but it could be something else doing the job.  It's another argument against
using toxic chemicals.

One last thing: if you have fungus gnats, watch the males display for the
females.  They do a wing-flicking "dance" to impress potential mates, or at
least this is my interpretation of their behavior.  I never see the females
(larger than the males) perform the display.

Pamela Harlow

-----Original Message-----
From: []
On Behalf Of Mary Sue Ittner
Sent: Monday, March 21, 2011 7:34 AM
Subject: [pbs] Fungus Gnats

I found a product that contains BT called Knock-out Gnats and used if 
very successfully. It's a soil drench and you use it once a week for 
three weeks or until your population is under control since it kills 
the larvae, not the adults, so want to go through more than one life 
cycle. Some of us are reluctant to use heavy duty chemicals and this 
solved the problem for me and I haven't had to use it again. I don't 
know whether it is available in Hungary.

Mary Sue

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