this should help (it helped me)
This topic has been done to death. From experience I can tell you that if you have an gnat infestation you need to take multiple steps in order to eradicate them completely. Fungus gnats have a 4 week life cycle; females lay hundreds of eggs in the soil, larvae live in the soil, pupate and then emerge as adults. In order to bring control you must take measures to kill not only the adults but also the eggs and/or larvae. Easiest measures you can take are using sticky traps (of all kinds) and vacuuming daily around the pots to rid yourself of as many adults as possible... then you'll need something else to kill the larvae. For that I would recommend Bti (Bacillus thuringiensis), sold at every home improvement store as Mosquito Dunks (Mosquito Bits and other Bti products are just less available). The Bti bacteria produces a toxin or larvacide that only kills a few species of insect larvae including fungus gnat and mosquito larvae. If you get the Dunks: break it in half, crush it up good or hit it with [an old] coffee grinder (that you wont use again for grinding any coffee), soak the powdered dunk in a gallon of water for 12-24 hours and then water your plants with it. Re-apply every other week.
thanks Nullis.
the other thing i have found to help is a layer of Diatomaceous Earth on top of the soil
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[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]YARD, GARDEN, & LANDSCAPE APPLICATIONS: DEs minerals are great for the yard and gardens. [/FONT][/FONT][/FONT][/FONT]
[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]Apply DE to ant hills. Small ants, regardless of color, may require a few applications to completely eliminate them, as they burrow new hills elsewhere, after we cover their initial hill with DE, but if we keep at it, eventually they disappear. Big ants are eliminated within two applications of a reasonable amount of DE applied to their ant hill. Ants in trash cans can be controlled by either painting DE around the bottom of the trash can or sprinkling it dry around it. They'll go elsewhere, as they do not like walking over DE. Of course, you will need to find their home to completely eliminate them, but it will keep them away from areas you put DE. Sprinkled around the house foundation keeps new crawling insects from coming inside. [/FONT][/FONT][/FONT]
[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]Fire ants will need regular application of DE to eliminate them, but if you continue regular applications, it will eliminate the fire ants. [/FONT][/FONT][/FONT]
[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]We mix food grade diatomaceous earth with water to paint our fruit tree trunks with it, like a white wash. The DE keeps ants OFF our fruit trees. 1 cup applied to ½ gallon of water works well. Be sure to stir frequently as the DE settles to the bottom. Good as a white wash for wood fencing too. [/FONT][/FONT][/FONT]
[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]1 to 2 cups per gallon of water can be used to apply diatomaceous earth in a backpack or hose end sprayer for problem infestations of mites, aphids, fungus problems, etc. Food grade diatomaceous earth will turn whatever you paint or spray with it white so it may look like a white winter at your place. [/FONT][/FONT][/FONT]
[FONT=Arial,Helvetica][FONT=Arial,Helvetica][FONT=Arial,Helvetica]Food grade diatomaceous earth will not destroy earthworms, if applied to the top of the soil in worm farms and the worms are allowed to work it into the soil on their own. It is actually beneficial to the worms and compost just make sure to allow the worms to do the work and not bury them in the DE.
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more info on DE
http://wolfcreekranch1.tripod.com/defaq.html
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