AusBonsai

Hi All.

I have a little problem with the Bradysia (fungus gnat) Since all this rain in Brisbane. Any tips for getting rid of this pain in the .... I've looked in the pest and disease section and done a search and couldn't find to much there either. I've also googled it but nothing really stands out that's non chemical based I'm still looking but any suggestions and experiences would be appreciated.

Cheers
Dan

Here's a pic that i found on the net to help my camera is useless taking pics that small.

G'Day Dan,

Fungus gnats or Bradysia can be a real problem, especially in wet weather. I have a long experience with them and have trialled many methods to eradicate and prevent infestations in two commercial fern nurseries in tropical Queensland. Seeing as you have already identified that you have an infestation I will start with a post on 'Eradication'. Next post is on 'Prevention'.

Fungus Gnat Control: Chemical Pesticides
The best insecticide I have come across for the control of fungus gnats is a product called Crown produced and distributed by Scotts and can be ordered through Elders, Fernland or Nuleaf. It is expensive but the dilutions go a very very long way and a small 100 mL bottle will probably last you a bonsai lifetime.

Fungus Gnat Control: Biological Control
There are two biological control organisms that predate on Bradysia larvae. Both are now available in Australia.

Hypoaspis predatory mites eat fungus gnat larvae on the surface of the growing medium and eat hatching adults. They are available from Biological Services http://www.biologicalservices.com.au/hypoaspis-m.html. Hypoaspis predatory mites work well if you have a naturally free draining coarse organic mix such as large composted pine bark nuggets. They do not survive well in saturated conditions and do not live well in inorganic growing media such as diatomite. They are released into your pots as spoon-fulls of mites living in fine organic material and vermiculite. Different release rates are used for 'control' and 'eradication'.

Steinenerma feltiae is an invertebrate gut nematode that infests and kills the larvae of fungus gnats. They are available from Ecogrow http://www.ecogrow.com.au/top10/Fungus_Gnat.html as a product called Gnatnem. Gnatnem work well if you have a more saturated growing medium and they do not survive as well in extremely coarse inogranic growing media. They are shipped as a dry poweder, rehydrated in water and applied as a spray drench. Gnatnem can 'drop' a lot of fungus gnats very quickly if applied at high rates.

best regards
Ash

Fungus Gnat prevention:

Prevention of fungus gnats without pesticides or biological control can be difficult unless you can control the amount of water present in the growing medium in a pot and the circulation of air around the pot. The following advice is based on my own trials in my greenhouses. Fungus gnat infestations were compared by counting the density of gnat adults caught on yellow sticky traps. Fungus gnats infest pots with a high organic content in the growing medium and in particular they infest pots with fine 'silty' organic material or fine and 'peaty' organic material that remains wet. In summary I recommend growers to alter their root mix to reduce the component of fine organic materials, to increase ventilation of the root zone and also to increase the circulation of air around the pots.

Fungus gnat larvae love fine organic material. I have done trials with pots of composted pine bark in a shadehouse situation. Pots of un-sieved pine bark in which the 'fines' were not removed had a higher infestation than pots in which the fines (< 2mm) were removed by sieving and washing. We used to add peat to our mix however I found that pots with peat added eventually suffered higher gnat infestations. I trialled tree-fern root fibre, coconut peat, sedge peat, moss peat, pine bark peat, Platycerium root fibre peat and even ground cork. I was searching for the 'holy-grail' gnat free peat. They were all infested by gnats. I did away with adding peat to the mix. I recommend sieving all your mix to get rid or any organic or inorganic fines. Also don't put plants in too big a pot. All that unused wet mix is great for gnats.

Fungus gnat adults are weak fliers. I have done trials with hanging plants, using low benches, high benches, wood benches, metal mesh benches, individual plinths per plant and seedling flats, growing plants with windbreaks and increasing air circulation using artificial fans. Fungus gnats have much higher infestations in propagation flats, plants on the ground and plants congested on benches. They seldom infest hanging baskets with space around and rarely infested plants on individuals plinths. The use of fans to circulate air reduced gnat infestations. I do not know if this was because the air movement prevented their spread or because the air movement dried the pots out. They infest flats and seedling beds and congested plants on benches or the ground much more readily than they do infest hanging baskets or bonsai on 'monkey poles' with space in between them. I attribute that to their poor flight. I trialled putting fans in the greenhouse to circulate air. The fungus gnat population dropped off a bit. I don't know whether this was from them being 'blown' away or because the growing medium in the pots dried out quicker when fans were used. I now use fans in prolonged wet weather in the fernhouse but do not bother with the bonsai because they are well spaced in an open airy mesh house.


regards
Ash

Thanks Ash thats a great guide. Adding a couple of bowls of vinegar has helped. I woke up this morning and checked the plants and there was only one adult flying around at the very end of my stand, furtherest away from the vinegar and many in the vinegar it self, so it seems to have worked for now. Now i just have to get rid of the hidden pain and will go on a hunt today for a pesticide. And your right they are really poor flyer's which makes me wonder how they got up here in my unit. I'm on the second floor which has a garage under the first floor so I'm up pretty high. So i think they were in my premium potting mix that i used to pot my maple in. I think I'll buy a sieve while I'm out and about for my soil so i can get the unwanted hitch hikers out of the potting mix before i create any more growing pots.

Cheers
Dan

Yes it is most likely that you got your gnats in the potting mix as larvae. Just about any bag of potting mix be it cheap or expensive can give your plants fungus gnats. Especially potting mix with wetting agents or water crystals in it that has been stored damp or mix stored in bags on the ground in a nursery. I dry all potting mixes on drying screens and sieve them prior to use. I don't store any potting mix damp or with fertilizer in it. I then wash them with a dilution of Crown and also apply Banrot granules if potting in the wet season.

So you baited the fungus gnats with Vinegar? Very interesting - that I have not tried- a good hint Dan.

best regards
Ash

Yeah I've been using potting mix with water crystals in them as well and thats a good idea about the Banrot and Crown i will have to pick some up. A few more flys have popped up since placing that vinegar but no where near as many as yesterday.

Cheers
Dan

this is a great post
thanks for all the info
Ash you have certainly done your homework
I noticed a lot of these gnats around lately and also one of my pots had lots of tiny red/brown mites,(not the bright red mites that are bad)
are they the predatory mites you mentioned ?

another question is what actual damage can the gnats or lavae do?Update ... had a look on google >the larvae feed on the roots,
they pupate into adults after 2 weeks
then the cycle starts again.

my benches are too crowded but I have no choice my whole garden is filling up

Well its nearly been a year and only every now and again I'll see a one and all I do is give the plant a bit of a spray with a 3 in 1 pest spray and there gone again. I've had mixed responses about this as I've read that they eat the roots and then I got told that they won't do anything. My maple which was the one that had the issue is still going strong and as long as the soil isn't to wet they don't come back in the mass as they had previously, which I'm pretty sure that's what caused the problem in the first place. Over watering!

just thought I'd bump this post up
with the drier weather (in brisbane ) we don't have the fungus gnats problem
however there is a tendancy to over water in the dry windy weather
and I noticed some of these gnats in a small potted macrozamia I potted
I thought it was too much water at first but after watching closely it was because I used
cymbidium orchid (pine bark chunks) on the top as a dressing
they were living in the moist bag of potting mix and had eggs all in the bark chunks

so ... just thought this might help someone, fungus gnats are a real problem
especially if they get established (during wet weather esp)
as mentioned the larvae eat the fine tips of the roots and will slow any plant right down and can kill it