Fungus gnats are several species that belong to the family Sciaridae.The larvae can destroy healthy plant roots and kill or stunt young plants.The larvae also cause the spread of diseases such as Pythium, Verticillium, Cylindrocladium, Scelerotinia and Theila-viopsis.
The adult fungus gnats are small and measure approximately 1/8th of an inch in length.The insects are grayish or black in color with long and slender legs and antennae.Their wings are distinctly clear with few prominent veins.The larvae have black heads and creamy white or clear bodies measuring 1/4th of an inch in length.
The fungus gnats undergo complete four-stage metamorphosis to develop into adults, i.e. egg, larva, pupa, and adult.The complete development occurs in about two weeks with the larvae feeding on fungi and decayed organic matter.They thrive in moist environments although the larval and pupal stages do not perish in drought.The fungus gnats have two large generations with the leveling off or steep decline in numbers.
The control of fungus gnats can be important in managing some plant diseases.Management of fungus gnats is best achieved with a combination of non-chemical and biological methods and used together with chemical agents.Cultural methods have to be maintained regularly during the production cycle while biological methods must be initiated early when the population is still very low.Mixing insect growth regulator products with potting media are more compatible with biological control.It is noteworthy that an insecticide control program that uses a combination of treatments for adults and larvae may be necessary if a severe problem is identified.
Non-chemical methods include avoiding excessive watering of plants to avoid fungal and larval development.On the flip side, too little watering may aggravate the larval injury to plants as the larvae may bore into the plants searching for moisture.
Remove old debris, waste and old plants from greenhouses to reduce fungus gnat infestation.