Question
  Hi, I have Fungas Gnats flying in my houseplants. I purchased the Garden Alive product called Knock-out Gnats. It works but they keep coming back. I water the plants once a week with the Knock- Out Gnats and spray bug spray on the plants. What can I do with the soil to kill the eggs. I know you had said to use soiless dirt on them. Can you remmend a product for me? What else can I do? They keep coming back! Thank-you, Mindy Linkevich

Answer
Hi Mindy,

The gnat larvae reside in the top inch or two of the soil. Scrape off and discard all loose soil until the uppermost roots are a bit exposed. Sprinkle a thin layer of sand or diatomaceous earth so the entire surface of the soil is covered. Allow the plants to dry out until they are at or close to the wilt point. The top of the soil dries out before the middle and bottom. So if you let the top couple of inches dry, then the larvae will also dry up and die.

After a week or so, put some raw potato slices on the surface of the soil to attract any larvae remaining in the soil. Turn over the slices and inspect them daily for signs of gnat larvae. Replace the potato slices as they dry up. When you no longer find larvae on the potatoes, then you have a cure.

Pro-Mix is a good soilless, peat-based potting mix. However, I don't recommend replacing all the existing soil because it is very traumatic to your plants.

If you want a quick solutuon and you don't mind using pesticides, Imidacloprid (sold as Merit or Marathon) is very effective when applied as a soil drench. One treatment will do the trick.

Please let me know if any of this is unclear or if you have any additional questions.

Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

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