Age Old Problem: Fungus Gnats

I know this has been discussed to death but I'm just hearing the same things which I've tried and haven't worked.

My newest product is Garden Alive's Knock out gnats. I've been using it for over three months now with every watering and it seemed to be working! But all of a sudden, the gnats are back with a vengence!

Any new ideas? What is a tried and proven method that works for you?

Aughhh this has been a terrible year for those pesty boogers. Let me know if you get a solution

I've had the same thing happen with the BT liquids for gnats. I almost wonder if the gnats build up a resistance to it. It's prolly more likely that as I near the bottom of my bottle... I use less & less when watering. The stuff is on the expensive side and I try to get as much mileage from a bottle as can ;o)

I'm trying beneficial nematodes this year that supposedly feast on the gnat larvae in the soil. I just applied it to my pots a couple of days ago. I am seeing a decrease in the pesky little buggers already. It's still to be seen how it works in the long run...

http://www.planetnatural.com/fungusgnat_control.html

But Knock out gnats is the beneficial nematodes... isn't it?

I read that there are two kinds, one for in soil and one for soil surface or one for gnats and one for larger insects. I don't remember which was which, maybe I should just try the cheaper one people use for lawns.

I'm also looking for Diatomaceous Earth, it's fossilized remains of animals that turned into little peices of glass. It's supossed to scratch the skin of the insects and they dry out and die. Hopefully it'll work. I'll post my results,

No... Knock Out Gnats is BT (Bacillus thuringiensis) a parasitic bacteria. There are two different strains... one that's better suited for caterpillars and worm-ish types of insects and another that's for misquito larva & fungus gnats.

The beneficial nematodes are a microscopic worm that will attack soil dwelling pests.

I use use Neem - 6 Tablespoons per gallon, sprayed on the soil once a week or so. I grow a lot of Hosta in pots and bring them into the house late winter/early spring to give them a head start and stop the winter doldrums . Fungus gnats were a real problem. Also have used chicken grit on top of the soil, and a growing mix that had no peat in it, but the Neem works better for me. Alice S.

Diatomaceous Earth does work well on fungus gnats but don't breathe the stuff (it's very fine and "poofs" out of the bag). I wear a mask for this stuff. But for me, fine horticultural sand on top of the soil and cutting back on the watering a bit does the trick quite nicely (not new but don't know what has been discused before...)

Ugh, I tried the Neem, sand and not watering as much tricks. Maybe my gnats are just extra tough?

Very tough gnats indeed!! I found the DE in a local greenhouse. Wasn't expensive. Pretty big bag for under $10.

I have also tried Diatomaceous Earth with some success. I bought a sugar shaker and put the DE in it and gently sprinkled it on the top of the soil of all my plants. (And that is very time consuming when you have over 140 plants.) I think it did help stop their reproduction. The only drawback to using the DE is that the next time I watered, it sort of washed away. So, to make sure that I stop those nasty little pests from coming back, I purchased some Dipel Dust made by Green Light. It is a powder form of the Bacillus thuringiensis. I have not had time to use it but I plan to put it on all of my plants and use it when I repot. As far as other pests, I had something eating my Bird's Nest Fern and bought Bug Stop Insect Killer, mentioned by someone else on DG. I sprayed the whole fern with it and now I have a beautiful fern that is pest free. I have not sprayed my other plants yet, but I plan to and I hope it will get rid of all the pests.

Jesse (Howdy neighbor!)...save your Dipel for leaf-eating pests (caterpillars, etc), it has no affect on the knats. You'd have better luck with a different strain of Bt called Bt israelensis. That is the one that will work on mosquito larva, black fly and knats.

The product mentioned above by poppysue is what you'd look for on the shelves (Knock Out Knats).

By the way, Congrats on saving your fern!

There is a BT israelensis type retailed under the name of Gnatrol.
The problem with BT and predatory (mites, nematodes) type of control is that they are only active for a short period of time and one gets quickly re-infected with gnats once the effect dissipated. A bag with with soil that wasn't treated or a new plant with untreated soil can cause a quick re-emerging of these critters.
Letting the soil dry out between watering works if a) your plants can take it, b) all of plants dry out at the same time :)
The only effective treatment that i found for my wet soil loving tropicals is to use a systemic soil trench.

Horseshoe, thanks for the information on the BT. I didn't know there was a difference. Since I have not yet used the Dipel, I can take it back and exchange it for the other stuff that you mentioned.

Well, the dipel is good for other things in your garden and it shouldn't go bad anytime too soon. (By the way, there is a liquid form of that type Bt by the trade name Thuricide, is you want to try a spray.)

If you decide to take it back, keep an eye out for the Knock Out Knats or the product mentioned above by PanamonCreel, Gnatrol.

Over on the Brug Forum, someone advised that a great way of controlling fungus gnats is to water your plants with water in which you've soaked a 1/4 piece of mosquito donut to one-gallon of water, soaked overnight. Several people stated that it worked very well :)

Tried it. I've heard both that people swear by it and from other that it didn't do anything. In my experience, it didn't work.

Oh, I wish it were warmer so everything could just go outside!

One company say that the beneficial nematodes start working and you'll start seeing results in 24 hours. And that the product will work up to 18 months. Truth or stretching the truth?

If you would like to get rid of fungus gnats...cut back on your watering! No need for chemicals. Fungus gnats breed in wet soil. Unless your houseplants get tons and tons and tons of light (which is rare in houses, especially in the winter), or, you have them in a green-house, there isn't one that needs to be watered more than once a week! Not ferns, not spaths......ok, I give my ferns a little drink in between major waterings. Plus, you can acclimate (very gradually) your houseplants to getting less water. Group your plants together to help conserve moisture. The trick is to maintain healthy moist soils, not wet ones. Stick your index finger in the dirt....if it's dry up to almost the second knuckle...then it's time to water. Leaves drooping? Time to water! Don't let your plants sit in water for more than 3 hours. I worked for Amlings (a mid-sized nursery concern in Illinois) as an interior landscape techinician for a real long time. Another organic cure is that you can put diatomaceous earth about 1/8 inch thick on top of the soil. Slices those fungus gnat larvae right up! People in offices get VERY annoyed by fungus gnats, as they fly right at your face..they are attracted to what you exhale (CO2). People in offices in air-tight buildings also don't want pesticides! April

My plants have all gone bone dry pretty deep and I've observed gnats on and probably laying eggs on the soil. Some of my orchids cannot dry out or will die.

Will diatomaceous earth cut up the nematodes??? This is really important! Does anyone know?

Diatomaceous earth should help you out a lot. Be sure to get the "food grade" variety, if you can. If not, the regular should work just fine. April

Fungus gnats, white flies and other mini fliers can be a big problem because you have to get the timing right no matter what control you use and you need to use potting mixes that are not contaminated. I mention timing because while all stages of the insect may be present at one time, controls affect only one stage. Sprays of Isotox or BT isralensis need to be repeated every 4 to 6 days at least 3 times so it will have a chance to break the life cycle. I isolate infested plants under plastic until I am sure it worked. Sticky traps are great to indicate infestations and will collect hundreds of the flies as they emerge but they can keep a fly from ever laying eggs if the trap is placed correctly at soil level. I try to avoid most of the problem by pasturizing the soil in the microwave. 1 gallon of soil, 2 cups of water on high for 10 minutes. Let cool with the cover in place so the steam is active for a longer time. This helps avoid overwatering too because it helps the water penetrate soil particles so there is less water between particles but the water is still available inside the soil particles for the plant to use. Jessamine

I wish I could go back and cook all the soil, ANYTHING to be rid of these things! I HATE them. I think I've gotten that point accross, huh?

Anybody know if the Diatomaceous earth will harm the beneficial nematodes?

I don't think it is likely. Nemetodes are usually down in the root zone, Jessamine

Great! I'll use both! Maybe I'll finally get some closure on this little problem!

Found it - Gnat Balls

12 oz Boric Acid Powder
1 cup Flour
.25 cup Sugar
1 Minced Onion
.5 cup Shortning

As with handleing any dangerous compound plz use precautions - rubber gloves (etc)

Will it hurt the plants?

don't know - left it away from the plants by itself - the boric acid - is a "nasty substance" found the recipe on the net - take precautions when handleing any dangerous compond, chemical, etc.

The food products might lure my not too bright but extremely sweet pup. When the greenhouse is built, it sounds like something I should try.

Please use gloves when handleing chemicals of this nature.

I finally got rid of mine this last winter by adding Chicken Grit to top of soil. About 1/2 inch so it will keep the soil dry on top. Note: the Grit must be made up of oyster shells not granite.

I kill the flying ones with the cheapest spray I could find. Black Flag Flying insect killer for mosquitos, flies and Gnats at Wallmart. 2.00 or less a can.

The two products togather worked for me.

Diatomaceous earth was a mess. Try sticking your finger into one of the pots. Then it did not do the job.

I was having a problem with white flies in the greenhouse. There was a discussion somewhere about using earth worm castings and that would get rid of the white flies. I got some and put about 1 inch as a top dressing on many of the pots in my greenhouse. It did get rid of the white flies and as an added benifit, the fungus gnats are gone.

I had tried the dry sand on the surface, the theory being that they did not like the dryness. I had more than with a wet surface, definatly they loved the sand. But the earthworm castings seemed to do the trick. I was no longer trying to get rid of the fungus gnats, I was just spraying every week or so with the Black Flag flying insect killer when they got too thick. Now I don't have any....and I keep the surface fairly damp. The greenhouse this time of year is just too hot and I have to mist and water daily or the plants will die.

Anyway I got 1cu sacks at the local building supply for $10 each. I needed 2. It was a cheap fix and I didn't have to worry about bad chemicals. Hope this helps someone. Cheaper than the Knock out Gnats, that was a continual thing, very time consuming and did not help my situation.

I bought ScanMask and it's worked miracles. Better than anything else I've ever tried and it's very easy to apply too. Just shake some over the dirt with a spoon and irritate the soil.

I bought it from planet natural like some one suggested above w/ free shipping and handling. This was a while though. They don't have it listed on their site as far as I can tell but email them and they'll direct you to it.

This message was edited Nov 15, 2007 1:20 PM

the only place i've ever had them was on houseplants and the chicken grit got rid of them quickly. diatomaceous earth wouldn't work because it has to be dry to work and when you water a plant, you would have to re-apply. it looks like you found a good product in ScanMask.

i had that problem and someone said nine parts water one part hydrogen peroxide and water the plants with it --shoulda seen the little buggers squirmin outa the medium-gottem good=another said spray full strength on the soil but i didnt try that

I keep trying hydrogen peroxide for mold on the top of my pots and for some reason, it hasn't been doing anything. But I'll keep it in mind for gnats.

Watering w/ hydrogen peroxide once in a while is supposed to be good for the plants, isn't it?

yes, that's what i've heard. you know how some plants will only bloom after a rain (rain lily) or how a resurrection fern will only "come to life" after a rain? supposedly if you spray the plant with a mix of peroxide and water, it will be the same as a true rain.

Re: boric acid - from Wikipedia

"Boric acid is poisonous if taken internally or inhaled although it is generally not considered to be much more toxic than table salt (based on its mammal LD50 rating of 2660mg/kg body mass).[1][unreliable source?]. The Thirteenth Edition of the Merck Index indicates that the LD50 of boric acid is 5.14 g/kg for oral dosages given to rats, and that 5 to 20 g/kg has produced death in adult humans. The LD50 of sodium chloride is reported to be 3.75 g/kg in rats according to the Merk Index. According to the Dutch Health Council(1998/19) Boric Acid should be regarded as if it impairs fertility in humans(R60).

However, boric acid is toxic to unborn infants. Also, it has been associated with low birth weight, eye malformations and problems with the nervous system.[citation needed"

I use Boric acid, applied once in the spring, to a flagstone walk to keep the ants from tunneling up through cracks in the morter under the flagstones. Works very well and lasts all season. Never had the pleasure of gnats. My only house plants are amaryllis.

I use boric acid to mix in with corn flour in little cups to put in the pantry for flour beetles. I can't beat them :( My mom doesn't want to throw everything out.

I've used hydrogen peroxide for the gnats and it didn't do anything for me. They just fly over them and lay more eggs.

I purchased Scanmask again and it worked, again. I love Scanmask!

Did you purchase Scanmask again from Planet Natural? I checked their site and couldn't find it. How much does it cost?

Last year the fungus gnats wiped out most of my seedlings. I generally start in small styrephoam salad dressing containers and move up the seedlings to cell packs when they have a true leaf or so. The larvae love the tiny seedling roots. They can wipe out a whole container of seedlings before I even realize it. (I have lots and lots of seedlings -- wouldn't mind trying chicken grit, but don't know where to get that. Also may try some worm castings as I actually saw some for a reasonable price at Walmart and I'm sure the seedlings would love that.)

So as recommended on other posts, I tried Bt. combined with sticky fly traps. After 4 weeks of use I started to see a great decrease in the gnats and then for 2-3 weeks after that everything seemed real good. But then the population began to grow and they are again killing my seedlings and I haven't stopped using the stuff and even increased the strength. What, do they get immuned to the Bt. ?

Some above post mentioned Black Flag. Doesn't that harm the plants...or wouldn't it kill seedlings?

For some reason, I can't find it either so I email them when ever I need to buy it and they send a link. I think it was $20-30. I can't remember. If you have an infestation of fungus gnats in your sunroom right off the kitchen... It's worth it!

I'm not familiar with other products except for Knock Out Gnats or something like that. It's BT. and didn't make a dent at all. Scanmask is the only thing that's worked for me.

About your seedlings, are you sure that dampen off disease isn't partially responsible for killing your seedlings? Even though I sterilized everything and grew in all different kinds of containers and bags, dampen off always found my seedlings. So, again, I had to look for a product and I found the only one that ever worked for me, Hydroguard. There's a less expensive product called No Damp or something like that. I tried all the recommended things like hydrogen peroxide, cinnamon, etc. Nothing but that worked for me.

See, with all my luck, gardening is a VERY expensive hobby. Other people have it too easy!

Thanks CaptMicha. I've had damp off before as I have been growing seedlings for 8 or more years now. There's a definite difference. With damp off you can usually see a little section of constriction on the seedling stem where it just falls over and there are still roots in the mix. With fungus gnats there is not the constrictriction on the seedling stem, but all the roots are gone up to the bottom of the stem of the seedling. This is fungus gnats. I went ahead and emailed Planet Natural so hopefully I will get a response soon.

But thanks for the No Damp information should I ever have that problem again. I just adjusted temperatures, moisture level, lighter potting mix, and air circulation and I haven't had any problem with damp off. So hopefully I won't.