Fungus Gnat
An adult fungus gnat
Fungus gnat as a maggot
Prevent: Do not overwater, keep the relative humidity of your garden low, do not let the surface of your grow medium stay soggy. Cover hydroponic medium surfaces to prevent growth of green algae.
Identify: Fungus gnats attack your plant in their adult stage and larval stage. The maggot of the fungus gnat is almost invisible to the human eye with see-through bodies and a black head. These maggots infest the upper roots of your plants and can spread throughout the entire root system in hydroponic mediums. Maggots love dark, dank, moist, soaked environments. Check the medium at the base of your plant for these pests, fungus gnat larvae are notoriously happy in rockwool. These creatures infest root systems, damaging larger roots and consuming root hairs. This causes your plant to weaken, slow its growth, and fading in the foliage. These wounds to the roots make
marijuana insanely vulnerable to several types of fungus. Maggots love dying plant matter and will only infest more heavily the more damaged your plant becomes. Adult gnats are grey to black, very small and have very very long legs. Females lay eggs prolifically at the rate of 200 eggs weekly and will usually be found at the base of your plant along with maggots. Additionally, these little pests will stick to your sticky flowering green like crazy and are basically impossible to remove.
Fungus gnats have successfully damaged the root system of this plant. Note the yellowing leaves and the two plants leaning over as their root systems are beginning to rot.
Eradicate
Repression: Reducing surface moisture in your plants medium will slow fungus gnats reproductive cycle dramatically, the drier the better. Applying an anti-algae product around the bases of your plant will kill any growing green algae and reduce the food sources of growing maggots. Yellow sticky traps placed 2 inches from the base of your medium will snag a good chunk of departing adults.
Predators: Introducing a predator for the gnats themselves has proved ineffective at eliminating a population. The predatory soil mite
Hypoaspis and nematode
Steinemema feltiae will severely impact the insect population if introduced to soil grows. These creatures will not be effective countermeasures in hydroponic application.
Manual Removal: Impossible. You can swat a few but your threat is from what has already been laid underground.
Spray: Neem or insecticidal soap applied as a soil drench will kill eggs and larvae present in 1-3 applications. Any pesticide spray containing the fungal culture Bacillus thuringiensis var. israelensis (Bt-i) will successfully eradicate adult gnats. Apply soil drenches and spray simultaneously every 5-10 days.
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