We plant lovers don’t want to witness plants being harmed by pests. The problem enters our homes, which is gross, therefore we especially don’t want to see pests in our houseplants! Fungus gnats are pesky, winged insects with little wings that resemble mosquitoes and are about the size of fruit flies. The good news is that compared to many other pests, these plant flies cause significantly less harm, and even better, they’re rather simple to get rid of.
Long legs, transparent wings, and a preference for nutrient-rich, damp soils are characteristics of fungus gnats. These little flies may be seen flying around plant containers, but unlike some more dangerous pests, you won’t observe them actually chewing on the plant’s foliage. However, you will see them in the soil, feeding on the organic matter and hairs from plant roots. Do not underestimate the damage that these bugs can still do if not addressed.
Even though adult fungus gnats only live for about a week, they can have a big impact in that short time by producing up to 300 eggs under the correct circumstances. With such a quick turnaround and a brief life cycle of about 3–4 weeks, populations can grow incredibly quickly.
It’s rather simple to tell if your plant has a fungus gnat issue. Since these plant flies can’t fly very well, they usually stay rather near to the plant. They’ll probably be moving in zigzag patterns while you watch them. It’s typical to witness all the different phases of this bug at once because they reproduce so quickly. It’s likely that some bugs still in their larval stage will be visible if you gently agitate the soil. They inhabit the earth where they eat organic debris and have translucent bodies and glossy, black heads.
Our plants are getting ready to settle in for the upcoming cold season as winter approaches here in North Dakota. Unfortunately, that signals that these pesky bug populations are about to reach their peak. During this time, dormant plants use less water, which causes their soil to stay moist for longer. Gnats thrive in moist soils because they promote root rot and fungus. Be cautious when bringing delicate plants inside to overwinter since you run the risk of inviting unwelcome pests into your house.
Your plants will start to exhibit signs of stress if ignored and neglected. Fungus gnats don’t directly harm plant leaves, but they eat the root hairs and deplete the soil of vital minerals. This may result in abrupt plant withering and yellowing of the leaves, sluggish development, and a general decline in vigor.
When tackling any pest, you should always start with natural management approaches. The least hazardous and disruptive to your plant and house are typically natural and organic remedies, while chemicals may occasionally be required as a second line of defense. Fortunately, most fungus gnat populations may be controlled and eliminated naturally provided they are discovered and dealt with in a timely manner. Remember that one plant container can hold three to four generations of bugs, so you’ll probably need to apply your favorite approach more than once. Gnats in your indoor plants can be managed in the following ways:
Do not overwater. Before watering your indoor plants, allow the top couple of inches of soil to dry up. This will not only stop fungus gnats from deciding that your plant would make the best place for them to live, but it will also interfere with their reproductive cycle and assist to reduce populations that have already moved in.
Activate sticky traps. Not just for mice, either! Sticky traps are easy fixes for many pest issues. Gnats that are moving will be caught if you place them immediately on the soil’s surface. To stop them from laying eggs, remove them from the trap, discard them, and replace it frequently (every two to three days). Particularly effective at drawing these insects, yellow traps are.
Create vinegar and cider traps.
Mix equal volumes of cider and vinegar in a shallow dish or can to act as a trap for fruit flies. Lay the trap on the soil surface inside the container or even next to the damaged plant. The concoction will attract the bugs, who will then fall into it and drown.
Bring in useful nematodes. Although it may seem counterproductive to introduce additional bugs into the equation, doing so is a simple way to reduce pest numbers. Nematodes are incredibly minute, worm-like insects that are frequently invisible to the unaided eye. In their larval stage, they attempt to infiltrate fungus gnats and other insects, releasing a bacteria that eventually consumes the pest from the inside out. When you think about it, it’s awful and disgusting, but not as disgusting as allowing gnats to devour your prized houseplants!
If all else fails, there are always insecticidal goods and sprays to keep pest numbers under control. There are many products available that either target the adult stage or the larval stage, but either is OK. You should be able to get rid of these unpleasant plant flies in a few of weeks as long as you successfully target one phase of their life cycle and reapply often.
Larvae are easily eliminated with hydrogen peroxide since it kills them immediately upon contact. Infuse your soil with a solution made of four parts water and one part hydrogen peroxide.
To destroy larvae, neem oil can also be put to the soil after being diluted with water. Neem oil can also be sprayed on surfaces to instantly kill adult flies. Last but not least, pyrethrin sprays contain extracts that are harmful to a variety of pests and can instantly kill flies and fungus gnat larvae.
Fungus gnats can affect the health of your houseplants even though they don’t transmit any diseases that are dangerous to humans. Your plants will thank you by giving off a lush, healthy appearance to enliven your home if you keep pests at away.
Why do my potting soil have tiny insects in it?
In comparison to a fungus gnat, the shore fly (right) has a more substantial body and shorter antennae (left).
Small flies called fungus gnats are pests that attack soil, potting soil, other container materials, and other sources of organic decay. Their larvae devour roots and can be a concern in greenhouses, nurseries, potted plants, and interior plantscapes. Their larvae mostly consume fungi and organic debris in soil. Indoor houseplants may produce adult fungus gnats, which can be a nuisance.
IDENTIFICATION
The Orfelia and Bradysia species of fungus gnats, often known as darkwinged fungus gnats (Sciaridae), are small, delicate-looking insects that resemble mosquitoes in appearance. Fungus gnats have segmented antennae that are longer than their heads and thin legs. They can be distinguished by their lengthy antennae from shore flies with shorter, bristle-like antennae that are more hardy, also seen in greenhouses, and linked with algae and decaying organic debris. Fungus gnat adults typically measure between 116 to 18 inches in length, while some species can grow up to 12 inches in length. The common Bradysia species have Y-shaped wing veins and light gray to transparent wings.
Adult fungus gnats are drawn to light, so you may initially see them flying close to windows indoors. However, fungus gnats are rather poor flyers and typically don’t move around much indoors in contrast to more active species like the common housefly (Musca domestica). Fungus gnats frequently hang around potted plants and fly across growing medium, foliage, compost, and wet mulch piles (or rest there).
In potting soil or damp organic waste, females lay their small eggs. Larvae have an elongated, whitish-to-clear body and a shiny, black head. They consume compost, root hairs, fungi, leaf mold, grass clippings, and organic mulch. If the environment is particularly damp and there are lots of fungus gnats, larvae may produce slime trails on the surface of the medium that resemble those of little snails or slugs.
DAMAGE
Adult fungus gnats don’t bite people or harm plants; instead, their presence is primarily seen as an annoyance. However, a huge population of larvae can harm the roots of a plant and impede its growth, especially in seedlings and young plants. In interior plantscapes and with houseplants, significant root damage and even plant mortality have been noted when high populations were linked to damp, organically rich soil. Therefore, a wilting houseplant may not be a sign of a water shortage but rather root damage from fungus gnat larvae or (more frequently) from other causes of unhealthy roots. The more typical causes of wilting plants, however, include excessive or insufficient water, root decay fungus, and unfavorable soil conditions (such as inadequate drainage or waterlogging).
Greenhouses, nurseries, and sod farms are more frequently affected by severe fungus gnat damage. Although larvae also consume plant roots outside, they typically don’t cause much harm.
LIFE CYCLE
Egg, larva (with four larval stages or instars), pupa, and adult are the four phases through which fungus gnats develop. In moist organic medium, where females lay eggs and larvae feed, the small eggs and oblong pupae are found. Eggs hatch around 75oF in about 3 days, larvae take about 10 days to transform into pupae, and adults appear in about 4 days. Depending on the temperature, a generation of fungus gnats (from female to female) can be produced in around 17 days. They will grow more quickly and produce more generations per year as the temperature rises.
Each year, there are numerous overlapping generations of fungus gnats. In California’s interior, they are most prevalent outside in the winter and spring months when water is more readily available and the weather is colder. In damp coastal areas and indoors, they can occur at any time of the year.
MANAGEMENT
The majority of the fungus gnat’s life is spent as a larva and pupa in organic matter or soil, hence methods of control that concentrate on these early stages rather than the movable, transient adults are more effective. The use of physical and cultural management strategies, particularly the elimination of excessive moisture and organic waste, is essential for minimizing fungus gnat issues. This pest can be be managed by commercially available and naturally occurring biological control agents. Although insecticides are frequently discouraged for use in managing fungus gnats in and around the house, they are regarded as an important control tool in some commercial plant production.
Adults can typically tell if a problem is present just by looking at it. Adults can be seen napping on vegetation, soil, buildings, windows, or even in flight. Check plant containers for excessive moisture and organic waste, which larvae use as food, in addition to looking for adults. Using yellow sticky traps, adults can be captured. Sometimes, to check for larvae, chunks of raw potato placed in pots with the cut sides (not the peels) down.
Avoid overwatering and maintain proper drainage since fungus gnats prefer moist environments, particularly where there is an abundance of rotting vegetation and fungi. Between waterings, let the container soil’s top surface dry. Eliminate any leaks in the irrigation or plumbing system and clean up any standing water. Compost, organic fertilizers, mulches, and moist, decaying grass clippings are other popular breeding grounds. Because it will frequently be contaminated with fungus gnats, incompletely composted organic matter should not be used in potting soil without being pasteurized first. Enhance the potting mix’s drainage (e.g., increase the proportion of perlite or sand in the mix). Reduce the amount of organic waste surrounding structures and crops. Don’t use excessive amounts of manure, blood meal, or other organic fertilizers. To aid in preventing pests from entering the home, screen and caulk leaky windows and doors.
If your plants are afflicted, don’t relocate them to other locations where the flies might emerge and infest further pots. You might want to throw away highly afflicted plants in some circumstances.
Purchase only pasteurized potting or container mix, and use it. Before utilizing potting soil, commercial gardeners frequently heat or steam it to kill flies and the algae and microorganisms they feed on. Gardeners at home can solarize soil:
- dampen it.
- Put it in a clear plastic bag or a black plastic bag.
- Make sure the pile is no more than 8 inches deep.
- Place the soil in bags in a sunny area on a slightly elevated surface, such a pallet, for four to six weeks.
For more information, see the Pest Note: Soil Solarization. To keep it from getting infected before use, keep pasteurized potting soil off the ground and in covered containers.
Use of sticky traps, which are sold in retail nursery and garden centers, may be able to lessen the problem in domestic settings where adult fungus gnats are an annoyance. To catch adults, cut yellow sticky traps into smaller squares, secure them to wooden skewers or poles, and place them in pots. Additionally, putting raw potato slices in the ground will draw fungus gnat larvae. These can be used to trap larvae away from plant roots in addition to checking pots for them. After a few days in a pot, take out the infected chunks, throw them away, and add new ones.
To get rid of fungus gnats in pots or container media, you can buy three biological control agents that are readily accessible on the market (Table 1). These include the biological insecticide Bacillus thuringiensis subspecies israelensis, predatory mites called Hypoaspis, and Steinernema nematodes (Bti). These Bti products may be the most practical for home gardeners to employ because they are widely accessible at retail nurseries and garden centers (Mosquito Bits, Gnatrol, etc.). Since Bti cannot reproduce or survive indoors, several applications spaced approximately five days apart may be necessary to manage infestations in potting media. Nematodes and Hypoaspis mites must be ordered by mail because they are live, perishable items that must be used right away. After multiple inoculative treatments to establish their populations, nematodes can self-reproduce and offer relatively long-term control of fungus gnat larvae. Other commercially available nematode species are less successful than Steinernema feltiae at controlling fungus gnats. Following the instructions on the label, combine Bti or nematodes with water and apply as a soil drench or spray onto medium using a hand-pump spray bottle or other spray equipment.
The predatory hunter flies, Coenosia spp., together with other natural enemies help control fungus gnat populations in outdoor systems like gardens and landscapes as well as interior ones like greenhouses and conservatories. These flies feed on fungus gnat larvae in the soil as they develop into larvae and catch and eat adult fungus gnats in midair. By refraining from using broad-spectrum insecticides, you can protect these and other natural enemies.
Table 1 lists naturally occurring enemies and commercially available biological pesticides for controlling fungus gnat larvae.
a spore-forming bacteria that occurs naturally and is commercially generated by fermentation. Only fly larvae, such as mosquitoes, black flies, and fungus gnats, are poisonous when Bti is given at the recommended rates and provides temporary control. Usually, multiple applications are required for long-term control. This Bt is a distinct subspecies from the one used to control caterpillars on foliage. Fly larvae are not effectively controlled by Bt that has a caterpillar label.
A predaceous mite with a light brown color that has evolved to eat in the topmost layers of damp soil. eats springtails, thrips pupae, fungus gnat larvae and pupae, and other small invertebrates. Commercial mites are frequently transported in shaker-style containers that are used for application. In commercial nurseries, the recommended rates range from half a dozen to several dozen mites per container or square foot of material. Apply before there are a lot of bugs. Hypoaspis is generally not a viable choice for use in households and won’t likely do well in individual houseplants.
This nematode works best in damp environments with temperatures between 60 and 90 °F. Using regular spray equipment, you can apply it to media and as a soil drench. Nematodes can provide season-long control in damp environments after multiple initial applications to establish populations because they multiply and aggressively seek their hosts.
These substances can be used in combination and are essentially nontoxic to humans. Many well-stocked nurseries and garden supply companies sell Bt. Commercial mail orders from specific suppliers are available for predatory mites, Bti, and nematodes.
Rarely is it necessary to use insecticides outside and inside of homes to control these insects. However, if you do use an insecticide to manage fungus gnats, you should think about employing Bti or Steinernema feltiae nematodes to control the larvae; for more information, see the section Biological Control.
Pyrethrins or a pyrethroid pesticide may offer temporary, fast-acting control if Bti or nematodes are not accessible and excessive populations are unbearable. Where adults generally rest, spray the potting soil and plant components’ surfaces. Do not attempt to spray adult gnats in flight or use aerial fogging inside. Make sure the product is labeled for your specific usage, such as “house plants,” and make sure you read and adhere to the product’s instructions.
The active components in the botanical pyrethrum, which is obtained from the blooms of specific chrysanthemums, are pyrethrins, which have little toxicity to humans and animals. To boost the efficiency of pyrethrum, several formulations contain piperonyl butoxide (PBO), a synergist made from petroleum. Pyrethroids, which are chemically related to pyrethrins and are produced from petroleum, include permethrin and bifenthrin. They are frequently more potent and persistent than pyrethrins but are also more poisonous to beneficial insects. If at all feasible, transport plants outside for treatment when using these chemicals on indoor plants or inside landscaping containers. After spraying the chemical, wait about a day before bringing the plants back inside.
Consult the UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries and the book Integrated Pest Management for Floriculture and Nurseries for advice on controlling fungus gnats in commercial flower, nursery, or greenhouse operations.