In response to my query I received a number of replies: they are
appended below and I hope this will help others who are having pest
problems: For fungus gnats we tried a soil drench of Trumpet 80WP-worked
great-yellow stickies are empty now.
From Gill Dean:
we are using biocontrol for our thrip problems - we use a mite which
comes in a slow release colony that you just hang on the flat. i
previously used this in durham in the uk and it was great, here it
doesnt seem to be quite so reliable - we are also having to spray with
trumpet sometimes. it seems that the mites work best as a prevention
rather than as a cure when you have a lot of thrips.... they are also
not very pesticide resistant and i think this is what we are struggling
with - i think that as we have to spray sometimes we kill off the mites
we also have an aphid problem, for which we drench with othene, a
systemic insecticide. i have seen some mention of using othene for
thrips but i don't really know if this works! if you are going to drench
the insecticide must be systemic and i know there arent many of them
around. orthene is systemic but i am not sure if it gets into all
tissues of the plants - for aphids
which feed from the phloem sap it works fine but i dont know about
thrips which just scrape at the epidermis. might be worth a try tho!!
if you want more info on the biocontrol or the orthene please let me know!
From Tamara Western:
The phytotron here at McGill uses bio control as a major part of their
pest control system (they only resort to chemicals if really necessary).
They even sent information to me when I was still at UBC last spring to
help deal with a thrip problem we had there -- it seemed quite effective
(at least up until the time I left to move here).
Here is the web site http://ww2.mcgill.ca/biology/Phytotron/phyto1en.htm
They even have a section there about pest management/bio control and
both Mark and Claire are really helpful (I believe Claire is the one you
ought to contact).
From Grant Cramer:
Try imidocloprid. Its a systemic.
From Albrecht von Arnim:
we're using a systemic pesticide called 'Admire', from Bayer i think. We
preventively wet the soil around freshly planted seedlings, and it seems
to work well. It takes a few days to take effect if you decide to
soak-treat already thrips-infested flowering plants.
From Patricia Conklin:
In response to your ? regarding fungus gnats, I know that Gardens Alive
sells a Bt soil drench that is supposedly effective. Haven't tried it as
I haven't (yet) had a problem with fungus gnats, but I would guess that
it would be compatible with indoor pesticide regulations. The link to
this product is
From Nicole Pence:
go to this site: http://www-u.life.uiuc.edu/mailman/listinfo/aergc
and subscribe to their mailing list and post the question. There have
been past discussions relating precisely to this situation in the past.
He can probably search the archives for related postings. Most of the
subscribers to this forum are greenhouse/plant growth facility people in
education and research institutions - they have a lot of practical
experience and give good advice.
From Debra Skinner:
we have had good results for fungus gnats using the soil applied Bt
solutions. you can get these from the local garden store, it is a Safer
product called caterpillar killer. I mix it 3ml/ 1 litre and soak it
into the soil by pouring a small amount into the flats and let the soil
take it up. Usually about three applications works. we also spray
household fly spray (containing d-trans allethrin) but it isn't
necessary if you keep up with the bt to kill the worm stages.
Thrips are more difficult and for this we spray with Orthene which works
very well but smells terrible. We actually take the flats out of our
small growth chambers and put them into the fume hood to spray them, so
perhaps you could do this too? It is a systemic insecticide so perhaps
it would work with soaking?? we have never tried. we dilute this 3ml
We have tried insecticidal soap for aphids but this kills arabidopsis dead!
From Jennifer Normanly:
We are in a similar situation, so I'll be curious to know what advice
you get. We had an infestation of fungus knats about a year and a half
ago and were advised to spray our Arabidopsis plants with a dilute
solution of Sevin. We counted the bugs on a weekly basis (using yellow
sticky paper traps) and observed a population burst, then they subsided.
We also have temperature control problems in that room and I suspect
that the infestation might be associated, but we haven't kept careful
enough records to know for sure.
From Allan Shapiro:
Gnatrol has worked really well for us against fungus gnats. You don't
even need to do a drench--merely water as usual with the stuff in it. I
used that extensively at Berkeley (where gross overuse and overwatering
led to major problems) and once or twice here at Delaware.
Thrips, on the other hand, are not controlled by this. We've only
sprayed with stuff you can't use. One suggestion--don't grow legumes and
Arabidopsis in the same room. The thrips build up explosively on the
legumes without causing a lot of damage and then descend on the
Arabidopsis the minute the legumes leave the room. We had an
unfortuneate experience due to the need to grow Medicago (another
researcher) and Arabidopsis (us) in the same greenhouse room. We
couldn't even do crosses with that stuff because we'd open up the
flowers and see the thrip larvae muching on the last of the pollen.
Since then, we've forced the legume people to do regular sprays on a
calendar if they have to grow in the same room with Arabidopsis.
From Jim Tokushisa:
We have been using 0.1g of 70% granular Imidacloprid (Confidor WG *70*)
per liter water. It comes from Bayer Cropscience.
From Andrew Bent:
We find that Marathon works very well. For thrips though, it is often
best to just clear out the room, clean it, and start over again. This
has been discussed previously; you might search the archives of this
newsgroup for other discussion.
From Scott Poethig:
We put nematodes in the soil before we plant--these work great for
thrips, at least for a while. You can always add more later. As for
fungus gnats, the best solution is probably to change your soil mix. We
had a big problem with Premier Pro Mix and went back to using Metro Mix
200. Metro Mix 200 is of somewhat variable quality (i.e. sometimes they
put too much wetting agent in it and it then makes plants very unhappy),
but we have never had a fungus gnat problem with it.