At times, the producers of Zygocactus or Peperomia may notice the beginning of necrosis or totting of plant tissue at the soil line.


This tissue may continue to decline until the plant finally collapses to the soil surface. This problem may have been caused by fungus gnats.


The adult fungus gnat, a tiny, black fly, approximately 1/8 inch in length, is a weak flier and is most visible near or on the soil surface or under leaves. Fungus gnats can become quite abundant under the highly humid conditions of greenhouse production and it appears that excessive watering will enhance the development of injurious fungus gnat populations.



The soil inhabiting black-headed fungus gnat larva is the stage which actually feeds on plant roots, root hairs and lower stem tissues. Feeding is particularly injurious to seedlings, rooted cuttings or young plants and feeding injuries can predispose seedling plants to fungal attack.



The larvae of the fungus gnat are white and may reach 1/4 inch in length .  Sometimes the brownish pupae, as seen in these pictures, are visible on the soil surface.


A fungus gnat larva with insect-pathogenic nematodes inside (Photo courtesy of Thermo-Trilogy Corporation).



Comparison of potato plugs used to sample for larvae with a dime. Also shown is a larva feeding on a slice of carrot. These plugs or slices are placed into the soil with just the top visible.  They are removed after a few days and inspected for the presence of larvae.  This tool is used to evaluate efficacy of both chemical and biological controls. 


Fungus gnat adult as seen on a yellow sticky card.


A shore fly adult as seen on a yellow sticky card.


An adult parasitoid as seen on a yellow sticky card.  This particular wasp attacks and kills flies!


     More information on Fungus Gnats can be viewed at "Insect and Related Pests of Flowers and Foliage Plants". Click here to go there now! or Fungus Gnats


Lance S. Osborne:
Copyright 2016 [University of Florida, MREC]. All rights reserved.
Revised: Oct. 2015