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Fungus Gnat & Shore Fly Control

For your files: Fungus gnats (PDF)

IDENTIFICATION: Before using biological control, it is important to correctly identify the pests as either fungus gnats or shore flies. Adult fungus gnats have long, bead-like antennae, long legs, clear wings with a Y-shaped vein, and are poor flyers that tend to run along the soil surface when disturbed. Larvae have dark head capsules. Adult shore flies have short, bristle-like antennae, short legs, smokey gray wings with 5 clear spots, and are good fliers. Larvae do not have a dark head capsule.

FUNGUS GNAT (Bradysia spp.) larvae damage plants (particularly seedlings) by feeding on fine roots. They can also spread root rot diseases, such as Pythium, Phytophthora, and Fusarium. Their presence may be indicative of a greater problem, like over watering, rot, or fungus growing in saturated topsoil. Adult gnats are a nuisance to greenhouses workers and the public.

LIFE CYCLE: A complete fungus gnat life cycle takes about 5 weeks at 68°F (20°C). There are usually continuous overlapping generations in greenhouses. Females lay eggs near the soil surface. They lay 100-200 eggs over their lifetime. The eggs hatch in 4-6 days. Larvae feed for 2-3 weeks, mostly on decaying plant material, algae, and soil fungi as well as on fine root hairs and tender lower stems. The larvae pupate in the soil and adults emerge after 4-6 days.

CONTROL: There are several measure you can take to control fungus gnats. First, eliminate wet spots that produce algae and become breeding sites. Cover floors or treat under benches with a floor spray of hydrated lime to alkalize. Monitor with yellow sticky traps 1 foot (25 cm) above the soil or media surface or using yellow traps placed above the crop (see Lures & Traps). If needed, release Stratiolaelaps scimitus (formerly Hypoaspis miles) on seedlings and as soon as transplants are set out to establish it in the greenhouse before fungus gnats appear. Another approach is to apply insect parasitic nematodes and/or various bacterial products to reduce high fungus gnat populations (see Beneficial Nematodes). Please contact Sound Horticulture to determine which approach is suitable for your particular situation. Release rates may need to change throughout the season as pest pressures rise and fall, so continual monitoring and evaluation is key.

SHORE FLY (Scatella stagnalis), like fungus gnats, live in moist environments and feed on algae and decaying organic matter. They are not known to feed on healthy plant tissue.

LIFE CYCLE: Shore flies lay their eggs singly on the surface of algae. Larvae have eight pairs of short legs and a breathing tube with two dark colored openings called spiracles at the posterior end. Pupation occurs at the edge of the algae mats. Breeding takes place in stagnant and strongly saline water found in greenhouses as a result of excessive irrigation and soil leaching.

CONTROL: There are several measure you can take to control fungus shore flies. First, eliminate wet spots that produce algae and become breeding sites. Cover floors or treat under benches with a floor spray of hydrated lime to alkalize. Monitor with yellow sticky traps 1 foot (25 cm) above the soil or media surface or using yellow traps placed above the crop (see Lures & Traps). If needed, release Dalotia coriaria (formerly Atheta coriaria).