Possibly one of the most common insects that plant hobbyists will notice around their indoor plants, is the fungus gnat. These small, dark coloured, flying insects are attracted to humidity and moisture in the soil. Their larvae feed on rotting roots, and the fungus that grows on wet soil and plant debris; plants that have been overwatered are particularly susceptible to infestations. Although fungus gnats are not harmful to your plant – in fact, they are arguably beneficial, as they aid in the decomposition process of organic material (rotting roots) – their presence and erratic flight patterns can become a nuisance.
Avoid attracting fungus gnats: start by ensuring your plant is not being overwatered. Many plants will tolerate the first inch of topsoil drying moderately between watering; dry soil is a less hospitable environment for fungus gnats.
Aerate the soil: using an aerator or chopstick-like tool, gently poke holes and ‘fluff’ the soil every few weeks. Not only does loose soil promote a healthy root system, but aeration improves oxygen flow to the roots, aiding in the root drying process.
Apply diatomaceous earth: a mild and organic powder, a lot goes a long way. If applying topically to the soil, 1/8 teaspoon per square inch of soil should be effective. Alternatively, diatomaceous earth can be mixed with soil at a 10% dio earth : 90% soil ratio. Diatomaceous earth decimates soil-dwelling insects by causing microscopic abrasions to their bodies.
Use sticky traps: fungus gnats are attracted to the bright yellow colour of the sticky trap. However, they are poor at flying, so traps are most effective when placed close to the soil. Trapping adult flies prevents further egg laying.
With perseverance and consistent care, fungus gnats can be controlled and eradicated! When bringing new plants into your home consider a quarantine period to monitor for the presence of fungus gnats (and other insects), or implement some of these practices as prevention.