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Description
Fungus gnats are small (1/8 to 1/10th in.) in length, sooty
gray or black, longlegged, flies. Their wings have a
distinctive Y-shaped vein at the tip and their legs and
antennae are long and delicate. The eggs are about 1/100 inch
in length and laid in clusters. The larvae or maggots are
white with black heads and are about 1/4th inch in length when
full grown.
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Figure 1. Fungus Gnat Larvae
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Life
History
Fungus gnats are generally found associated with highly organic soils
or potting media. The adult does not damage plants and normally moves
around on the surface of plants and growing medium. They are poor
fliers and generally considered a nuisance. Eggs are laid by the
female in the soil. After 4 - 6 days, the eggs hatch and small larvae
or maggots feed on small feeder roots and root hairs. They may also
tunnel into the base of cuttings and feed on roots and foliage close
to the soil. A flimsy cocoon is formed on or in soil where pupation
occurs. After 5 - 6 days, the adults emerge completing the life cycle.
Under greenhouse conditions there may be many generations per year.
Damage
Damage is caused by larvae feeding on the root hairs and fine feeder
roots of bedding plants. Other damage may include tunneling into the
base of cuttings. Plants attacked by fungus gnat larvae will lack
vigor and will have yellow leaves. Roots will have small brown scars
on the surface. Both adults and larvae have been implicated in
vectoring the spores of soil pathogens such as Botrytis, Fusarium,
Verticillium, Pythium, and Phoma.
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on image for larger version
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Figure 2. Fungus Gnat Adult
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Nonchemical
Control
Reduce the proportion of organic matter in your media,
eliminate wet areas around germination chambers and floors
under benches, reduce algal growth, practice good sanitation
and inspect incoming plant material. Monitor adults with
yellow sticky cards. Use Guardian Gnat Patrol
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| Just
to give you an idea of the size of adult Fungus Gnats. That is
a standard ink pen.
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on image for larger version |
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