My house plants have been invaded with fungus gnats.!?

Other than changing the soil, as I have several plants, is there anything that will get rid of them? I've used GardenSafe Fungicide, 3 applications, 7 days apart and now their back. I don't want to toss these plants as I've worked hard to keep them healthy and they are beautiful.

My house plants have been invaded with fungus gnats.!?
I know of a couple very good solutions, each with their own benefits (and possible drawbacks).





1- mix Hydrogen Peroxide with clean water, I've used a solution of 3% H2O2 diluted 4-5ml per litre of water. This will kill them on the surface of the soil, and as it drenches the medium/soil, kills the larvae/eggs. Ensure there is some runoff from this so all the roots are treated. - note, technically this will also kill a few of the 'good' bacteria in the soil, but I've yet to notice any detriment from using H2O2, so long as its a fairly week solution. From what I've read, it will actually feed aerobic bacteria (good guys), while killing anaerobic bacteria (bad guys), and roots and plants love it as it breaks down quickly and provides extra oxygen.





2- extract of Neem oil (also found as Azadirachtin), same application and rougly same dilution ratio (often this is sold as for example "Neem Tech", if using commercial Neem prouduct, follow directions...or just dilute at about 5ml per litre of water.





Neem is systemic, meaning it will be absorbed by the plant to some extent, so anything seeking to eat the plant will ingest this. Can be used as a spray on foliage, and is totally safe and non-toxic. There is no waiting period for edibles as with other products.





Both of these things can be used as a foliar spray, but I found that you have to watch how much light hits a freshly sprayed plants, especially with neem or other oils, as the refraction of light that happens in the dense droplets can act as a magnifie and burn material,....this is usually only a concern with flowering plants, as in on delicate pistils for example. The Peroxide, as a drench or spray, will act as a growth booster as well.





What you're running into is likely a situation where you're sprays are only killing the adults. In the soil is where the real action is happening, so use the above and drench the soil, then use your normal sprays to get the surface of the soil to get adults. They will also be around the house in general, see below.





Diatomaceous earth can also be used as a sprinkly on top of the soil, but its very dusty and will change the soil/medium's water holding capacity to some extent. Its a pain in the ***, I find, actually, but people like it for the 'feel good' aspect of thnking that they're saving the earth, however both items above are as natural as anything and are non toxic in the levels used for this application.





Keep your house very clean. Fungus gnats like decaying matter, and will spread bacteria from such to the roots of plants and animals and you and any food you have sitting out. Keep sinks clean, don't have dirty dishes or exposed garbage sitting around, and even take a look outside to make sure garbage bins are clean and covered, etc. Keep under sinks dry, etc. There are a lot of info on these little bastards, so do some research as well to get some more in-depth info.





Hydroponic gardeners are especially aware of these things, as the ideal conditions that cause lush growth with those methods often create ideal conditions for pests as well, so read up on websites dealing with hydro as well as soil.
Reply:First of all fungus and gnats are two different problems. They are both caused however, by plants being too wet and not having enough air around them. You should water to drainage with a lot of plants, and then not water again until the top two inches of soil are dry. Once a week, if you can, put them outside in the sun or fresh air for an hour or two.





For those plants that prefer to be moist, only water about 1/4 of a cup at a time.





You could take the plants outside now and sink them into a bucket of water with a tablespoon of hydrogen peroxide or shampoo in the bucket. Do not get leaves or flowers wet, just the tops of the pots. This drowns the larvae and kills the gnats. Let soak for about 15 minutes. Then rinse them with clear water and let them dry out.
Reply:Put a layer of sand on top of the soil, it will keep the gnats from getting in and out of it