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Though they may be tiny in size, fungus gnats can create huge problems for growers. These small, flying insects are a common issue in indoor and greenhouse environments, especially where damp, organic-rich soil provides the perfect breeding (and feeding) ground. In adult form, the gnats are more of a nuisance than a pest, but it is their larvae that create issues beneath the surface of the soil.
In this article, we’ll take a closer look at what fungus gnats are, why they’re considered pests, and how you can prevent and control them effectively. We’ll also explore the pros and cons of using insecticidal soap, and explain why Integrated Pest Management (IPM) offers the most sustainable and plant-friendly approach to keeping fungus gnats—and other pests—in check
What is a Fungus Gnat?
Source: Vandermeer Nursery
Fungus gnats, also known as sciarid flies, are associated with damp composts, especially in house plants and seed trays. They thrive in moist, nutrient-rich environments like damp compost or overwatered potting soil. Adult females will lay their tiny, oval-shaped eggs in desirable environments like moist soil. The entire life cycle, from egg to adult, occurs over 3-4 weeks.
Why Are Fungus Gnats Considered A Pest?
Fungus gnats are considered a pest primarily due to the potential damage their larvae can cause to plants. While adult gnats are generally harmless (aside from the irritating buzzing and their attraction to human body heat and moisture), their larvae can damage roots and stunt plant growth. This occurs when the larvae feed on decaying organic matter in the soil, depriving seedlings and young plants of essential nutrients. This damage can lead to wilting, yellowing, and stunted growth in affected plants.
How To Prevent Fungus Gnats
Maintaining healthy soil is key to preventing fungus gnats. Below, we’ve listed the methods you can use to ensure your soil is efficiently maintained:
- Proper watering is key. Don’t overwater, and sticking to watering from the bottom or using the finger test will ensure that the top layer doesn’t look too inviting to the gnats.
- Choosing the right mix will also ensure that you don’t accidentally introduce the gnats to your environment. Opting for a well-draining mix that is low on organic matter (which is what the larvae love to feed on) will also act as a good preventative step.
- Consider using natural repellents and predators to keep things under control. Cinnamon bark and other essential oils are supposedly a good deterrent, while beneficial nematodes like roundworms are known to prey on fungus gnat larvae.
- Keep your growing space free from debris and organic matter, which is known to be a breeding ground for fungus gnats.
What Is Insecticidal Soap?
Insecticidal soap is a pest control solution made from potassium salts of fatty acids. It’s effective on fungus gnats, as well as other soft-bodied insects like aphids and spider mites, by breaking down their outer layer on contact. Growers apply insecticidal soap by spraying it directly onto the pests, ensuring full coverage of the insects’ bodies for it to be effective.
What Are The Downsides of Insecticidal Soap?
There are a few downsides to using insecticidal soap, which include:
It doesn’t reach the larvae in the soil
Insecticidal soap will only kill off live fungus gnats; however, it cannot penetrate deep enough into the soil to kill off any live larvae, meaning the pest infestation will not be fully treated.
Sensitive plants can be harmed
Some ingredients in insecticidal soap can be phytotoxic, causing stress to your plants. Certain plant cultivars – including leafy greens, fruit varieties and ornamental plants – are especially sensitive. It is not recommended to spray your plants with insecticidal soap on a hot, sunny day, as it can lead to leaf burn, and any oil-based solutions could create issues with residue and stomata blockages.
Does Insecticidal Soap Kill Fungus Gnat Eggs?
No. Since fungus gnat eggs and larvae are beneath the soil, insecticidal soap is ineffective against them, since it is not designed to be used as a soil drench. Those who do try to use insecticidal soap as a soil drench will find that it is diluted and broken down by organic matter in the soil, rendering it ineffective.
Protection Plus: A Better Alternative for Killing Fungus Gnats
Protection Plus™ is a FIFRA 25(b) exempt eco-friendly, oil-free insecticide and miticide that targets pests on the first application, without damaging plants.. With the highest first kill rate on first application in the industry, Protection Plus has been independently lab tested and cleared of over 490 toxic chemicals.
It is a better alternative to insecticidal soap for the following reasons:
- It can be used beneath the growing medium as a drench. Fungus gnat larvae tend to live in the top 5cm of soil. When you use Protection Plus™, you can target them and put a stop to the damage.
- Protection Plus™ is oil-free. This means that it won’t leave an oily residue on the leaves of your crops and plants, which can lead to issues with photosynthesis and stomata blockages.
- Protection Plus™ is non-systemic. This essentially means that it takes a targeted approach to killing pests and is not ingested by the pest, which can often lead to insect resistance.
- Protection Plus™ is an eco-friendly alternative to potentially harmful insecticidal soaps. It has been extensively tested to determine the absence of over 490 toxic chemicals, and is safe for use on cannabis, trees, shrubs, ornamentals, food crops and turf.
Ultimately, having an integrated pest management (IPM) plan that includes a routine weekly application of Protection Plus will ensure that your plants remain healthy and productive. As part of your IPM, we recommend regular monitoring, the safe introduction of natural predators, physical barriers like nets or covers, and thorough record keeping.