Fungus Gnats! - Knowledgebase Question

Watertown, Co
Question by holycrosskid
October 18, 2010
Help! I have a problem with fungus gnats in my two Meyer Lemon Trees. The plants are in my house and the flies have been bugging us all summer. Now they spread all over the tree itself, and it looks like the plant has a disease because they cover the entire plant! What should I do?!


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Answer from NGA
October 18, 2010

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Here are two strategies for controlling fungus gnats: They breed in moist potting soil, so you can break the breeding cycle by allowing the surface of the soil to dry out. If you have plants that need moist soil simply place a quick draining and fast drying layer of gravel or sand on top of the potting soil. This will act as a barrier to the soil. Or, you can drape plastic wrap over the soil (cut a slit so you can place it close to the stems of your plants, then overlap the cut ends so the pests cannot find a way to the potting soil). You have to be a little patient with this method because you have to wait through the next generation's maturation before they are gone for good. In other words, once the generation now already in the soil become adults and die off without being able to reproduce, there should be no more gnats. Since you have them hanging around the branches of your plants, why not make a couple of sticky traps to catch at least some of the adults? I just use bright yellow index cards (or spray paint plain white ones with yellow paint), smear them with petroleum jelly and use paperclips to hang them from the branches. Just un-bend half of a paperclip and it will make a handy hanger that you can adjust to fit the size of the branch. Replace the traps as they become filled with fungus gnats. Another method is to use a product called Gnatrol as a soil drench, another is to use an insecticidal soap as a soil drench. Of course, always follow the label instructions carefully. I hope this helps!

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