fungus gnats - how to control them

Joined : 16 May 2008 Posts : 128 Location : Canberra

Many people at some stage develop a fungus gnat
problem.
They can be tricky to get rid of.

Just wondering if anyone has any advice on controlling them?

Joined : 16 May 2008 Posts : 128 Location : Canberra

I used a neem spray called 'neemgold' for a while. it seemed to keep the numbers down but didn't knock them down all together.

I also tried yates 'confidor' every three days this also seemed to reduce numbers but they soon were back - I think this might work with many applications.

also keeping the potting mix dry will help - they only have a life cycle of only 8 days ( what a life!) so keeping the potting mix very dry should break the cycle... in theory.

Subject: Re: fungus gnats - how to control them Sat May 31, 2008 7:25 pm

I have a small problem to, in spring I am going to introduce a predator insect called Hypoaspis Miles that feeds on the fungus gnat larvae...

Trig mentioned a product called gnatrol, would like to hear info on that to...

http://www.biologicalservices.com.au/hypoaspis.htm

Joined : 07 May 2008 Posts : 341 Location : Melbourne

i am looking for an effective method of control as well, and am yet to find one. luckily i haven't had them that bad. i did use confidor on the adults and it kills them at least, don't know about the grubs though. yellow sticky traps are supposed to be good for the adults.

Subject: Re: fungus gnats - how to control them Sat May 31, 2008 7:29 pm

I have been told to top dress the pots and also having grit in the bottom of the pots as well. Apparenly they can't get through it to lay the eggs.............haven't tried it yet though.

Did you water with the confidor or spray with it? I water with rogor when I get an infestation and have one now as well Sad

watered last weekend and some still around so hoping they will be gone soon.

Also use an aerosol spray to kill the adults.
_________________
Betty

http://community.webshots.com/user/parrotsheaven

Joined : 07 May 2008 Posts : 341 Location : Melbourne

i sprayed with it, doesn't seem to harm the seedlings at all. in fact it's systemic so it probably kills the grubs as they feed on them. i was actually quite surprised it kills the adults instantly on contact, being a soft systemic chemical.

Subject: Re: fungus gnats - how to control them Sun Jun 01, 2008 12:18 am

From my exprience there are two ways to control fungus gnats. I personally had a bad........bad gnat problem last year and as of today have not seen one in several months so I guess I can help out here.

First lets look at the gnats themselves. Fungus Gnats are a type of Sciarid fly, from one to at the very most seven millimeters long. They have a slender, darkly colored body and dark wings. However, the females of several species are wingless. Their long legs and antennae with 8 to 16 segments are typical of many gnats.

Now to elminate them you need to understand their life cycle. Adult females lay about 200 transparent eggs (each about one millimeter long) into moist soil. After about one week the larvae head to the top of the soil or anywhere they can get out and hatch. The adults now feed and survive only long enought to reproduce.

The first way to get rid of them: The environmentally friendly and all that way. Good for moderate infestation.

1. Potting media - Gnats are attracted to PEAT so decreasing peat in the soil will make it less attractive for breeding.
2. Watering - Avoid excessive watering especially when adults area active. Don't allow puddles of water to build up. I have seen the larvae growing in droplets of water on the top of a seedling container.
3. Top dress with rock or even beter washed sand as gnats will just walk around through larger rocks.
4. Sticky traps placed near the soil level will catch the adults GREATLY reducing their numbers.
5. Hypoaspis miles - Do work but are more effective in garden beds than pots. They take about 2 weeks to build up. The only problem with Hypos is they are slower than gnats + larvae and find it difficult to completely kill them off.

The above will work but requires constant monitoring.

The second way: The 100% effective way but can require chems. Required for bad infestation or if you just cant get rid of the last few.

Follow steps 1 to 4 as above.

The problems with most commercial insecticides is they won't kill off ALL the larvae and due to the gnats highly evolved breeding cycle they will just build up again and they do it very quickly.

Obtain one of the following:

1. A Larvae killing bacteria called, Bacillus thuringiensis Var israeliensis. Must be Var Israeliensis ! is found under brand name VectoBac (this one can be hard to obtain)

2. A chemical called Triflumuron found in a few products available to Australia will kill the larvae and not effect anything else including Hypos. I have personally used this product with 100% sucess. It can be found....seek and you shal find.

Apply either of the above to the soil and the larvae will die off. Once the adults are reduced the problem is gone.

Subject: Re: fungus gnats - how to control them Sun Jun 01, 2008 12:24 am

In addition,

There is a snail and slug killer by Bayer that contains Methiocarb, a good larvae killer, I'm not sure what its called. A friend of mine swears by if for killing off the larvae. I was too scared to use it on my plants due to the other chems in it but could be worth looking into.

Subject: Re: fungus gnats - how to control them Sun Jun 01, 2008 2:49 pm

Joined : 16 May 2008 Posts : 128 Location : Canberra

I wonder if one of the chems used to kill larvae in turf could be used. they are pretty common at the hardware store... I will have a look and might give it a try. and keep an eye out for Triflumuron

Joined : 02 May 2008 Posts : 88 Location : Bendigo Victoria

I posted up a link in Propagation section which has an article mentioning how to avoid fungus gnats.