Fungus Gnats

What Are Fungus Gnats?

Fungus Gnats can become the grower’s worst nightmare. These are short-lived flying insects that lay eggs in the soil. Also known also as Sciarid flies, from the Mycetophilidae and Sciaridae families, these airborne, fast-breeding, short-lived insects resemble tiny grey-black mosquitoes. They are also easily mistakable for drain or fruit flies, measuring around 1/8th of an inch long.

When noticed buzzing around plants, their presence means trouble for any growing organism in the immediate vicinity. Adults live about a week and lay up to 300 eggs. Larvae emerge between four to six days later. Their plant feeding cycle then lasts a full two weeks before turning into pupas.

Their entire life cycle from gestation to adult is about 3-4 weeks. This also means that a single plant can be host to several generations of larvae simultaneously.

Fungus gnats are so named because of their larvae’s favorite food. The gnats lay their eggs in decaying topsoil. In turn, the larvae which emerge, which look like tiny maggots, love to feast on fungus and decaying matter around them. Wet soil is where fungus and decaying matter all come together in a unique biological soup. In addition to fungus, the root hairs and tender young roots of cannabis plants are also in danger.

A bad larvae infestation of fungus gnats could damage or even kill young cannabis plants. Larvae can also cause slowed growth. Adult fungus gnats also spread diseases like Pythium, a common source of root rot, via their feet as they land on plants.

How To Spot A Fungus Gnat Invasion

Seedlings or adult plants that are sickly or die for no easily apparent reason could be a sign of infestation. Other signs to look for include: wilted leaves, yellowing, spots, or drooping. When adult plants show these signs, there can be a significant larvae infestation that should be addressed immediately. Plants also tend to grow far more slowly or stop growing altogether when affected by Fungus Gnats, not to even mention the smaller yields.

How To Eliminate The Problem

Fungus gnats are attracted to certain environments, so the easiest way to get rid of them is to change the growth conditions that attract them. Fungus gnats need fungus, and if you don’t have any, these mobile destroyers will move elsewhere. However, that is often easier than it sounds as the fungus is often flying around as spores. These spores will remain inactive, however, until they find the right conditions to survive.

The easiest way to eliminate the issue is to stop overwatering the soil. Without wet topsoil, there is no fungus. Where there is no fungus, there can be no gnats.

How To Eliminate An Infestation Issue Quickly

Beyond over watering here are a few quick tips to quickly address the problem beyond overwatering:

  1. Install a yellow gnat catcher. Fungus gnats love the color and will fly towards it and then stick. For particularly bad infestations, put up several. That way you make inroads on the adult population.
  2. Avoid watering plants for a few days beyond reducing watering in general. As mentioned earlier: No more wet topsoil equals no more fungus, and thereby no more fungus gnats.
  3. Kill the larvae before they hatch. One of the best ways to do this is to treat the top layer of the soil with Neem Oil. The solution is available at any grow or specialist cannabis shop, including online. Neem oil generally is a great addition to the box of essential cannabis cultivation tools as it also kills many other different kinds of pests who also love cannabis (including Aphids, caterpillars, and white flies).
  4. Apply diatomaceous earth to the affected soil. This is an organic insect killer made of fossilized shells. The microscopic shards puncture the exoskeletons of insects, draining their body of fluids, but pose no damage to pets or humans (including being accidentally ingested). Use a powder duster to apply. Both supplies are easily available to purchase online.
  5. For particularly pernicious infestations, beyond mixing up the above methods, try organic pesticides. Apply every other day. Hydrogen Peroxide mixed with water can also be a way to put an immediate kibosh on the problem as you implement other options. Commercial greenhouses often use the insect growth regulator diflubenzuron, which will kill the larvae for between 1 to 2 months.

While the presence of Fungus Gnats is never good news, it can be an excellent learning point. Experienced and new growers alike can take this unfortunate situation and turn it into an opportunity to strengthen their cultivation discipline and to improve their overall cultivation environment.

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