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Fungus Gnats

August 11, 1999

This article is a continuation of last week’s article on fungus gnats. In this issue, I will discuss chemical and biological management strategies for controlling fungus gnats in greenhouses.

Even if proper cultural management practices have been implemented (see issue No. 15 of this newsletter), fungus gnats may still be a problem. However, a number of insecticides can be used to supplement cultural management strategies. These materials are listed in Table 1. Insecticides listed in the table are categorized based on chemical class. In addition, the table notes the fungus gnat life stage (that is, adult or larva) that each insecticide works on and the restricted entry interval (REI). Be sure to read the label before using any of these materials.

Table 1. Insecticides used to manage fungus gnats in greenhouses.

InsecticidesSusceptible life stageREI (hours)*
Acephate (Orthene/PT 1300)Adult24
Chlorpyrifos (Duraguard)Larvae12
Diazinon (Knox Out)Larvae12
Bifenthrin (Talstar/Attain)Adult12
Cyfluthrin (Decathlon)Adult
Permethrin (Astro)Adult12
Insect growth regulators:
Azadirachtin (Azatin)Larvae4
Cyromazine (Citation)Larvae12
Diflubenzuron (Adept)Larvae12
Fenoxycarb (Precision/Preclude)Larvae12
Kinoprene (Enstar II)Larvae12
Pyriproxyfen (Distance/Pyrigro)Larvae12
Bacillus thuringiensis israelensis (Gnatrol)Larvae4
Potassium salts of fatty acids (insecticidal soap/M-Pede)Adult12
Horticultural oil (SunSpray Ultra-Fine)Adult4
* REI = restricted entry interval

Biological control is another option greenhouse managers have to manage fungus gnats. Biological control agents that have been shown to be effective with fungus gnats are the beneficial nematodes, Steinernema feltiae and Steinernema carpocapsae, and the soil predatory mite, Hypoaspis miles. All biological control agents are applied to the growing medium and attack fungus gnat larvae. They should be applied early before the fungus gnat population’s buildup. For more information, contact a biological control supplier.

Scouting for fungus gnats can provide greenhouse managers with important information on the effectiveness of each management strategy. Scouting involves the use of yellow sticky cards for winged adults and potato wedges or sticks for the soil-inhabiting larvae. Monitor fungus gnat populations within the crop and underneath benches or floors.

Management of fungus gnats entails a combination of pest management strategies. However, it is important for greenhouse managers to understand the conditions that lead to fungus gnat problems. This will improve the effectiveness of cultural, chemical, and biological management strategies.

Author: Raymond A. Cloyd


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