Gnats on an Amaryllis
Amaryllis (Hippeastrum) flowers are so spectacular, it's hard to believe the plant is related to the humble daffodil. Potted amaryllis is prized for its colorful, lily-like flowers during the winter holiday season. Planted outdoors, some amaryllis may bloom in late spring or summer. Either way, amaryllis produces a tall, thick flower stalk that grows and blooms so quickly you can almost see it moving. Plant amaryllis outdoors in U.S. Department of Agriculture plant hardiness zones 9 through 11. In zone 8, mulch garden-grown amaryllis in winter to protect the bulbs. The plant suffers from few pests, but it may occasionally be attacked by fungus gnats.
The tiny fungus gnat can become a big pest in the home as it sits around on the amaryllis plant, soil surface and nearby walls, windows and drapes. A mere 2 to 5 mm long, fungus gnats lay eggs in the soil or growing medium. Larvae hatch four days later and have glossy black heads and clear bodies. Adults resemble mosquitoes and have long antennae and slender legs. They spend more time resting than flying but can rise up and fly around when disturbed, which can be annoying when you have a large number of gnats.
While the adult fungus gnat is generally little more than a nuisance around amaryllis plants, the gnats and their offspring can vector plant diseases such as blight and wilt. Fungus gnat larvae feed on the amaryllis plant's roots, causing leaf drop, stunted growth and yellowing foliage. The larvae can usually be found an inch or less below the surface of the soil or growing medium.
To contain or prevent indoor infestations, make sure window and door screens are in good repair to keep fungus gnat adults from coming in the house. Remove organic debris from around indoor or outdoor amaryllis plants. Buy only pasteurized potting soil, or heat the growing medium to kill the flies and their food source. Allow the surface of the container's growing medium or the garden soil to dry out for a few days, because fungus gnat larvae thrive in moist conditions. Control moisture and algae around outdoor amaryllis growing in containers. Nematodes (Steinernema species), predatory mites (Hypoaspis) and Bacillus thuringiensis israelensis (Bti) provide biological control for fungus gnat larvae indoors or out. If the infestation is extremely heavy, apply insecticides containing pyrethrins -- a natural remedy -- or permethrins -- a synthetic one -- to kill fungus gnats quickly. Follow label directions for proper application.
Small flies such as shore, moth and March flies may be difficult to distinguish from fungus gnats on both indoor and outdoor amaryllis. Control methods are the same for all of these flies, so it doesn't matter which one is in your home or garden. If you want to be certain which type of gnat-like fly is infesting the amaryllis, however, catch one and take it to a local nursery or extension service office for identification. Some midges also resemble gnats. To check containers for larvae, cut a peeled potato into 1-inch pieces and bury them in the growing medium about 3/8 inch deep. Check the pieces weekly, along with the soil directly underneath. Repeat the process after using pesticides to be sure the numbers are dwindling.
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