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House Plants/Plant gnats on diffenbachia


I am having a problem with gnats on my diffenbachia.  I have tried retail insect spray and have let my plants dry to the point of yellowing and wilting.  Must water but still have gnats!  I have seriously let these plants dry several inches down in the dirt and nothing seems to work.  Any suggestions?

Thanks for your help.

Hi Deborah,

Fungus gnats are almost always preceded by repotting into a larger pot and the gnat larvae are introduced by the new soil added. In addition, most folks mistakenly add soil on top of the original rootball when they repot. I realize that you have not indicated that this is what you did, but my experience tells me you probably did.

If so, remove and discard all of the loose soil you added on top of the original rootball. It is in this extra soil on top that most of the larvae reside so that will eliminate much of the problem. Then, allow the top of the remaining rootball to dry at least one-quarter of the way deep into the pot. Dieffenbachias can withstand drought quite well - better than gnat larvae.

The leaf yellowing may actually be because of root rot that usually occurs after unnecessary repotting.

If my assumptions about your Dieffenbachia are not accurate, please post or email a photo to me at my address below so I can properly assess the problem. The photo should include the entire plant, including its pot.

I have written articles on indoor plant pests, repotting and on Dieffenbachia care that I will email for free to you (or anyone else) who emails a request to me at I have also written an indoor plant care book in a PDF format that I can sell you if you contact me at my email address.

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

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Will Creed


I am the only expert in this category with professional hands-on experience and knowledge of all indoor plants. I can answer questions regarding light, water, fertilizer, repotting, pruning and humidity and temperature requirements. I can identify plant pests and provide information on safe, effective treatments. My answers are based on 35 years of professional experience and scientific research and are clear and easy to understand. I do NOT use search engines to find answers to your questions. If you read my previous posts here, you will get a good idea as to how thorough and professional my answers are.


I have over 35 years of professional indoor landscaping experience caring for plants in homes, offices, building lobbies, stores, restaurants, and other adverse environments. I have written extensively on the care of indoor plants, including a 260 page book. My specialties include Ficus trees, low light plants, repotting, pest control, and re-blooming holiday plants. Be sure to check my ratings and nominations to learn why I am the top-rated indoor plant expert. I am the only House Plant expert consistently ranked in the AllExperts Top 20.

BA, Amherst College

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