Like many gardeners these days, you’ve probably heard about the importance of mycorrhizal fungi for growing plants. These fungi are crucial for transporting nutrients from various parts of your soil to the root zone. What you may not have heard is that with the growth of more fungi in a new soil mix, can come a really nasty pest:
The Fungus Gnat.
By itself the fungus gnat is not necessarily the end of your garden, but the destruction these pests cause to your roots can invite much worse problems that can wipe out your entire garden: Fusarium and Pythium. In this article, you’ll learn how the Fungus Gnat gets a foothold in your soil, what the effects are, and how to prevent them from destroying your crops.
Understanding Fungus Gnats
Fungus gnats earned their name because they eat and thrive off of a diet of fungal organic matter. They are typically helped along by very wet conditions in the soil. New living soil cultivators typically over-water when beginning this unfamiliar growing style, thus inadvertently contributing to the fungus gnat’s proliferation. If you are focusing on building a truly living soil where mycorrhizal fungi can thrive, then you really need to build an entire soil ecosystem. This leads to some temporary imbalances that you’ve got to be prepared to correct.
Wet soil is the perfect home for both fungus and decaying organic matter. There, the fungus gnat larvae eat the fungus or decaying matter and rely on the wet conditions to thrive. Often invisible to the naked eye, overwatered organic matter begins to decay within the topsoil. There, the fungus gnat lay their eggs.
Fungus gnat larvae thrive within the top 2 to 3 inches of the organic growing medium. They primarily feed on decaying matter, algae and fungi. However, these larvae will feed on plant roots and leaves found resting on the growing medium surface. And below the surface, the larvae are wreaking havoc on a plant's root structure. Unlike their adult parents, the baby larvae will do damage to a plant's root system, even though fungi are required for normal development. If plant tissue is the only thing available, the Fungus Gnat will go after it. Not only do these larvae cause lots of problems, but they are also fully grown within just two to three weeks.
It Gets Worse: The Snowballing Effects of Fungus Gnats
The worst part about these pests is that both adult and larval are known vectors of fungal pathogens. As a vector, they open up new wounds for these fungal pathogens to take hold. Most commonly, these include Fusarium, Verticillium, and Pythium.
Fusarium is a horrific plant pathogen that causes a serious disease known as crown rot. Crown rot is caused by a soil-borne fungus that can survive in the soil indefinitely. Next is a soil-borne pathogen that causes wilt and decay, known as Verticillium. This pathogen can live within the soil for years before finding water and then germinating. Once alive, it begins to eat at the plant's root structure. As the Verticillium starts to replicate, they infect part of the root world known as the xylem. The xylem system is responsible for transporting water throughout a plant, starting with the roots and transporting water up to the leaves. As Verticillium begins to grow rapidly, it blocks the vessels within the xylem. As reproduction continues, they begin to produce a toxin that travels up the xylem and into other areas of the plant.
How do we combat this problem from the start so that as an educated farmer, we can improve and speed up Mother Nature? The answer is a true living soil ecosystem. By learning to build our thriving ecosystem, inoculating certain soil-dwelling species into the living soil beds is beneficial not only for your plants but for the ecosystem that they thrive in. This method is known as Integrated Pest Management (IPM), and it often starts with beneficial predators.
Adults are brown or black, typically 3-4 millimetres long and are winged. One of the only downfalls of this beneficial predator is that the rove beetle is relatively expensive for larger farms or gardens to invest in. As intelligent farmers & gardeners, how do we deal with this? We learn to farm our own.
Only three ingredients are needed to begin to farm rove beetles. First, create a mixture blend of 60% Canadian sphagnum peat moss and 40% rice hulls. Next, mist the new mixture and place it into 3/4 of the container being used. Then, add 1/2 cup of oatmeal and 1/4 cup of water and place the oatmeal into the remaining 1/4 of the container. Finally, simply add 25-50 rove beetles to the newly mixed substrate. Let this substrate sit for a few weeks and shortly after, the larvae will begin to appear underneath the oatmeal. Within a month, the population will have at least doubled in size, a simple fix for gardeners both large and small. To increase the volume and speed of the rove beetle's population, the farmer needs to simply increase the number of substrates created. Then, the rove beetle works in a symbiotic relationship with the Stratiolaelaps scimitus, widely known as the "H-Miles Predatory Mite."
Both males and females inhabit only the top few centimetres of soil. Under a simple microscope, most stages of this mite appear similar. Eggs hatch in about 2-3 days, and the life cycle is complete in around eleven days. These predatory mites feed upon the young larvae of fungus gnats in the soil and are most effective when applied to the soil before the fungus gnat populations are established. H-Miles consume 1-5 prey per day and can survive as a scavenger by feeding on algae and plant debris.
When using these "living soil defenders," beneficial nematodes are of interest because of their ability to protect against fungus gnats for about 18 months. Once added to the soil the nematodes locate pests and enter through various body openings or the body wall. After they have entered the host pest, they inject bacteria into the pest's blood. This bacteria creates food and builds a friendlier environment for its reproduction needs. As food begins to run out of the host pest, the nematodes will simply move onto a new host. The nematodes will continue to do this until they have exhausted their food source.
The easiest way to ensure success as a new living soil farmer is to learn to be proactive instead of re-active. The more focus on feeding and improving the soil's overall health, the easier growing cannabis will become. Furthermore, by cultivating a truly living ecosystem in your soil, eventually all these elements will come into balance. Once you have ecosystem balance, even the presence of a fungal pathogen like Fusarium will not necessarily attack your garden, because there will be a predator to keep it in check. Focus on the health of your soil, and everything else will come together.