Fungus Gnats in Dracaena Massangeana

Fungus Gnats

• Fungus gnats are small, mosquitolike insects approximately 1/8 inch in length with delicate bodies and slender, threadlike antennae. Females lay eggs in the soil of container plants, such as D. massangeana, producing larvae that feed on the soil and root tissue of infected plants. The larval stage lasts approximately one month, after which the adult fly emerges from the soil. Although fungus gnat larvae feed on damp, decaying organic matter found in potting soils, the adult flies do not feed at all and have a short lifespan. Fungus gnats are minor pests, as they do not bite humans or feed on healthy plant tissue as adults. The larvae do have the potential to damage recently germinated seedlings.

Environmental Controls

• Fungus gnats are attracted to moisture and decaying organic matter. The best control methods focus on altering these environmental conditions. Maintaining cultural conditions unfavorable for fungus gnat growth is sufficient to control most outbreaks without the need for potentially harmful insecticides. Allow the soil of Dracaena plants to dry thoroughly between waterings, avoid overwatering and ensure containers have adequate drainage. Remove any dead or dying tissue as soon as it is noted and keep container surfaces clear of plant debris. These steps make the soil less attractive to fungus gnats, as well as reducing the lifespan of any larvae present in containers.

Insecticides

• A number of chemical insecticides are available if environmental controls prove unsuccessful at managing infestations. Pyrethrins kill gnats and other flying insects and have low toxicity to humans. Insecticidal soaps are also effective, although they work best on the adult gnats rather than the larvae. A number of insect growth regulators are available as well. These products work by saturating the growing media with chemicals that inhibit larval growth, greatly reducing fungus gnat populations. Always apply chemical insecticides according the manufacturers instructions, and examine labels thoroughly before using insecticides.

Biological Controls

• Biological controls may be warranted in cases where environmental and chemical controls are ineffective. A number of natural organisms prey on fungus gnats at various points in their life cycle, and many are available for purchase at home and garden centers. A product containing the Bacillus thuringiensis var. israelensis bacterium is toxic when ingested by fungus gnat larvae. Nematodes are available as well, including Steinernema feltiae . These organisms enter the insect’s body and multiply rapidly, causing acute toxicity and death in fungus gnat larvae. Predatory mites are available, and certain wasp species are effective at reducing fungus gnat populations.