For plant maintenance people, the worst pest problems are the ones you don’t notice until it’s too late. A fungus gnat infestation is a good example and can be very problematic. Show
Fungus gnats are common pests in the United States, found everywhere from greenhouses to interiorscapes. They’re attracted to damp places where fungi are most likely to grow. They are the most common interior landscape pest due to the fact that their numbers can rise so quickly. Because of their flying habit, most customers are not tolerant of a single one and often demand immediate eradication. This is one pest that it is a good idea to have a preventative treatment program for. Why Are Fungus Gnats So Destructive?While the adults do not feed directly on plant material, they can transmit plant pathogens as they fly. The larva live in the soil and feed on the roots of plants and organic matter. Most larger plants can handle the gnat’s larva feeding but this feeding can leave open wounds where pathogens can move in. How to Identify Fungus GnatsFungus gnat adults are small but relatively easy to identify. They have long legs and resemble tiny mosquitos in body type and size (2.5 mm). Their wings are clear with a Y-shaped pattern. Although fungus gnats fly, they tend to hop from place to place when on soil. Adults are gray or black in color, Larvae are tiny, translucent, legless maggots with distinctive shiny black heads that can grow up to 8 mm long.Do not get fungus gnats confused with shore flies, another problematic gnat. Adult shore flies are similar in size (2.5 mm) to fungus gnats, but are strong fliers that are stoutly built with short legs and antennae. Shore fly adults look like little fruit flies, having black bodies, reddish eyes, and dark wings with five distinctive light-colored spots on each wing. The spots on the wings are a key for identification and can easily be seen while the flies are at rest. They tend to thrive in moister conditions then fungus gnats, like in drains, but they can be found in plant material as well. Unlike fungus gnat larvae, shore flies do not cause direct plant damage. However, under extremely high populations, frass deposits on plant foliage can accumulate, decreasing the visual quality of the plant. The Life Cycle of a Fungus GnatThe adults live just seven to ten days, and in this time the female fungus gnats can lay up to 300 eggs. The eggs are laid in the soil where there is adequate moisture. Once they hatch, they will start to feed on plant roots and fungi near the surface of the soil. They will grow to about 8 mm long. They will then pupate and the adult gnat will emerge to take flight. The total length of their life will depend on temperature. At 80˚F they can complete their life cycle in as little as 12 days. Do You Have a Fungus Gnat Infestation?CLEAR INDICATORS:
It’s Time to Take Back Control: How to Get Rid of Fungus GnatsBecause fungus gnats are most fond of moist soil conditions, it is important not to over water plants. Try to let the top of your soil dry out between waterings. Removing the top layer of soil will not help with management. A good control option is to use beneficial nematodes. These are microscopic worms that are applied with water to the soil. Steinernema feltiae is the species of nematode that works extremely well for this pest. They target the larva stage, preventing the gnats from completing their life cycle. Once nematodes are applied, you will not see a decline in the adult population for about a week unless you are trapping for the adults. For adults, using yellow sticky cards will trap them and prevent them from laying more eggs. If you have shore flies you can use beneficial nematodes for control; however, S. feltiae is not the best nematode due to its cruising foraging strategy. Insect parasitic nematodes that use a cruising foraging strategy typically are found throughout the growing media profile and are looking for sedentary insects like fungus gnat larvae. Steinernema carpocapsae, on the other hand, uses an ambush strategy where it remains on the surface of the growing media where shore fly larvae predominantly are found. Repeat applications of beneficial nematodes may be needed to control these fly pests. If fungus gnats are a reoccurring problem, a preventative program might be needed. Preventing Fungus Gnats InfestationsThe best way to prevent this common pest is with smart watering practices and a preventative drench program of beneficial nematodes. They can stop an outbreak from ever happening. Talk to your nematode supplier about frequency of application for a preventative program. Fungus gnats can be tough to get rid of once an infestation has taken over your account, so early detection and prevention is important. By monitoring your plants and keeping a strict watering and preventative nematode application, you can keep your plants free of fungus gnats. Battling other common indoor plant pests? Check out my Professional’s Field Guide to Plant Pest Control for information on Spider Mites, Whiteflies, Thrips, Mealybugs, Aphids, and Scale insects. Fungus Gnat photo courtesy Arthur Chapman via https://www.flickr.com/photos/arthur_chapman/3450753821/
Often mistaken for mosquitoes, fungus gnats are very small and range from 3 to 4 mm in length. These insects are grey to black in colour and have slender legs and segmented antennae that are longer than their heads, which help distinguish them from the closely related shore fly. Fungus gnats are also easily identified by the Y-shaped vein in their wings. Signs of an infestationAs fungus gnats are relatively tiny, detecting an infestation may be difficult. Adult fungus gnats are attracted to light and may congregate on windows or glass doors. Since the pests remain incapable of travelling great distances, such gatherings indicate a nearby infestation. Fungus Gnats RemovalThe first step to effective control of fungus gnats is to find breeding sources and eliminate them or to modify the conditions that encourage breeding. This will naturally eliminate fungal gnat populations. If adult population is high or infestations are heavy, treating with appropriately labelled insecticidal products will remedy the infestation. Many over-the-counter soil treatments and trapping methods are available to gardeners and homeowners. However, for large and challenging infestations, contacting a pest control professional is recommended for effective treatments that will successfully eliminate infestations and help prevent future re-infestations. How to prevent Fungus Gnats from invadingThe first step to effective control of fungus gnats is to find breeding sources and eliminate them or to modify the conditions that encourage breeding. This will naturally eliminate fungal gnat populations. If adult population is high or infestations are heavy, treating with appropriately labelled insecticidal products will remedy the infestation. Many over-the-counter soil treatments and trapping methods are available to gardeners and homeowners. However, for large and challenging infestations, contacting a pest control professional is recommended for effective treatments that will successfully eliminate infestations and help prevent future re-infestations. Habitat, Diet, and Life CycleHabitatWidely distributed, fungus gnats thrive particularly well in forested areas around the world. Given their poor flying abilities, they nest close to their breeding spots. Potential sites of infestation include the wet humus-rich soils or potting mix of potted plants indoors and outdoors, swamps, decaying vegetation, greenhouses, compost piles, and other sources of decaying organic matter. DietAdult fungus gnats have a liquid diet and primarily consume water and flower nectar. During the larval stages, they feed on decaying organic matter and fungi. Life CycleAlthough adult fungus gnats only live an average of 10 days, females lay approximately 150 eggs in their lifetime. They deposit the eggs directly onto food sources like damp plant soil. Hatching within a week, fungus gnat larvae feed for up to two weeks before pupating and adults emerge approximately a week later. Fungus gnats produce several generations each year and are most active during warmer weather. Depending on the temperature, they complete their life cycle in 21 to 40 days. Commonly Asked QuestionsWhy do I have fungus gnats?Adult fungus gnats are attracted to light and may congregate on windows or glass doors. Since the pests remain incapable of travelling great distances, such gatherings indicate a nearby infestation. As fungus gnats are relatively tiny, detecting an infestation may be difficult. How worried should I be about fungus gnats?During the larval stage of the life cycle, fungus gnats feed on plant roots. In doing so, they damage the roots and stunt the growth of the plants. Additionally, adults and larvae spread plant pathogens that cause collar rot, root rot, damping off, and wire stem diseases. Otherwise, adults are not capable of biting or harming humans nor do they cause any structural damage and are therefore considered to be nuisance pests. |