Monday, December 17th, 2018...10:47 pm

Larvae of Fungus Gnats

TheGardenLady received the following question from Mattie:

About two weeks ago I got a Peace Lily. Everything was going great. But then the leaves started to droop. So my friend has been giving me advice. Today I was pulling the cutting the dead roots and there were milly worms (?) in it. What should I do to prevent this and help save my plant?

Since there are no photos of the “worms” you describe, TheGardenLady thinks that you may have the larvae of fungus gnats in the soil of your Peace Lily. You either brought the plant with the larvae in the soil or your other house plants may have had the fungus gnats in the soil but the infestation may not have been so bad that you many not have noticed them.  Fungal gnats can be a major problem with indoor plants and can be difficult to get rid of – but we will try.

You are doing the correct thing in getting rid of the dead or rotting parts of your plant. Since your plant has been taken out of the soil to accomplish this, get rid of the soil completely. Do not compost the soil. Throw the soil in the trash. (Had you not removed the plant from its soil, you should still discard at least the top two or three inches of the soil.) Wash the roots of the plant while it is out of the soil and repot it in sterilized potting soil. You can add some sand to the potting soil. The larvae do not like gritty soil.

You can buy and use a fungicide for fungus gnats – there are many different brands, so follow directions for their use. This Garden Lady does not like to use chemicals indoors and has heard that many of the safer fungicides really do not do a good job in getting rid of fungus gnats; but many sources still suggest using them. So you have to decide whether to go this route or not.

Whether you do use a fungicide or not, do buy or make your own yellow sticky traps and put one of the traps into the pot next to your Peace Lily plant.

You should also stick them in your other indoor plants. For some reason, fungus gnats and other insect pests of plants are attracted to the color yellow and the glue on the traps captures them. All indoor plant nurseries use them. When you check your traps, you will see if you still have the insect problem because you will find fungus gnats stuck to the traps. You can then treat your other plants if needed until, hopefully, you will have gotten rid of the insects.

When you have replanted you Peace Lily, get some small sharp stones or grit, or use diatomatceous earth to put on the top of the soil in the flower pot. The larvae do not like to crawl through rough material.

Now, water your plant, but be sure that the water does not sit in the pot. After you water your plant, allow the soil to dry out before watering it again. Never let the soil get too wet. And in the future let the soil dry out between watering. Soggy soil is a breeding ground for fungus gnat larvae and other insects.

TheGardenLady hopes you will be able to save your Peace Lily. However, if the infestation of fungus gnats is so heavy that you cannot eliminate them or if your Peace Lily is so weakened that you can not bring it back to life, TheGardenLady is sorry to tell you that you may have to discard the plant. Still check any other plants in your house to see if they, too, have any infestation. You may have to treat them, as well.

Keep checking all your plants – if you keep the yellow sticky traps in the pots, you can tell when the fungus gnats are gone. And the important thing now is to not over-water any of your indoor plants. See here

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