Question
Dear Will Creed,
My dumb cane dieffenbachia has a case of house gnats and i just dont know how to get rid of them without hurting him i have tried almost everything i have put lemon essential oil around the lip of the pot put a glass of viger evan washed the pot and roots with water (wich i have just done today)NOTHING SEEMS TO WORK!!!!!
Please help me he is droopy has bug babies in him and his leaves are brown one evan has yellow around the edge oh and also i am not going to water im for a few days since the babies like to be moist it might kill them if i liet him dry out (but not to much!!!)

Answer
Hi Patelyn,

The last sentence you wrote is the key to dealing with these annoying fungus gnats.

The larvae of fungus gnats feed on decaying organic matter. That can be rotting roots and/or soil that is kept too moist. The larvae mostly live in the top inch or two of the soil. When they mature into winged adults, they fly out in search of new places to lay their eggs. The winged adults only live for about a week before dying a natural death.

So the key is treating the larvae in the soil. The adults will take care of their own demise. Replacing the soil and rinsing the roots is not a good thing to do. Such activities may eliminate the gnat larvae, but they also damage the fragile root hairs that do most of the work. So you may kill the plant along with the gnats.

A better approach is to remove all of the loose soil from above the rootball. This will physically remove many of the gnat larvae and not harm the plant. Then you should allow the soil to dry as deep into the pot as you can before the plant starts to wilt. This drying out will deprive the larvae of the moisture they need to survive. It will also help stop the root rot that usually accompanies soil that is kept too moist. Sometimes adding a thin layer of coarse sand on the surface will help because the sharp sand edges carve up the larvae as they move to the surface.

If you are conscientious about keeping the soil as dry as possible you will see a noticeable decline in flying adults within a week or so and the gnats should be gone within a couple of weeks. Of course, you will have to monitor any other plants in your home where the adults may have laid some eggs. You may want to remove excess surface soil and reduce the watering of your other plants, as well, just as a precaution.

I have written an article on identifying and treating indoor plant pests that I will email for free to you (or anyone else) who sends a request to me at [email protected].

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

If this information has been helpful, please click the Rate Volunteer bar below and enter a rating and nomination for me. I am a volunteer on this site so Ratings are the only compensation I receive for answering plant questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC