Not really sure if these little gnats are fungus gnats. I have dug around in the pots and see no larva (web says there are large white larva -- mine has none). But they are multiplying and needed to be gotten rid of. The Miracle Grow soil is WAY to loose - too much mulch. And it's usually very wet when purchased. I think these little gnats came into the GH from that.
Moral -- keep the fungus under control - treat before there is a problem.
1) Treat purchased soil with Physan 20 before even putting in pots. Kills fungus that fungus gnats live on. Can use if fungus starts to grow too.
2) Those little flying gnats -- if they are fungus gnats they will destroy the plant's roots - treat them early.
Things I tried:
1) Murphy's Oil soap (it's pure soap) - mix 2 TBSP with 1 cup alcohol - then add to water. I was afraid to use that much alcohol so I used 2 TBSP alcohol. Filled the squirt bottle with water. The next day I saw no difference in the # of gnats.
2) Then I tried this: Water and 3% hydrogen peroxide (4 to 1 ratio - water to peroxide). Make sure it doesn't have any other added medicinal ingredients. Let top 2" of soil dry out first then drench. This supposedly kills them on contact. I took all the plants out of the GH and treated them all. They seem to be 99% gone - tomorrow will tell.
3) Set out "traps" - either the yellow sticky -- or make your own with yellow paper with pure Vaseline jelly smeared on it.
4) Try sugar water in a yellow dish (they like yellow). Did this and tried blue and clear. There were lots of them in the yellow dishes, none in the others. Did this before I did the peroxide treatment and then realized this is a nice add on by my problem was BIG and needed immediate resolution.
You can also put a little peroxide in water periodically to help prevent fungus.
Also chamomile tea helps prevent fungus. Spray the plants every week or so.
Bottom line - keep the fungus out and you keep the fungus gnats out.
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