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Pest Guide – Fungus Gnats

Pest Guide: Fungus Gnats

Cannabis growers face several challenges, and fungus gnats are one of the most common and frustrating of these. These tiny black flies reproduce quickly and repeatedly, and if you don’t stop them early on they can cause a great deal of trouble. Whether you’re growing inside or outside these bugs can be a problem, but either way treating an infestation is relatively simple and cost-effective. There are plenty of commercial and DIY ways to get these bugs under control.

In this guide, we’ll explain what these bugs look like and how to identify them. We’ll also show how to get rid of them with various natural and man-made means, and we’ll tell you how to keep them out of your cannabis garden after they’ve been eliminated.

What is a Fungus Gnat?

As mentioned above, fungus gnats are small mosquito-like flies. They look much like fruit flies, but they’re easily distinguishable under a microscope. These common garden pests have a never-ending life cycle that goes like this:

  • Adults lay eggs in the soil, which hatch into larvae.
  • The larvae feed on plants’ root hairs, causing severe damage.
  • The larvae develop into maggots in a few days, cocooning themselves before hatching into adults and continuing the cycle.

To defeat fungus gnats in a cannabis garden, it’s best to catch them as early as possible. Especially after buying your own pot seeds online, you’ll want to stay ahead of the game, so you don’t waste your time having to re-germinate a whole new crop from scratch.

Detecting Fungus Gnats on Marijuana Plants

Before taking steps to manage an infestation, growers must first learn to identify the signs of a fungus gnat infestation. It’s necessary to distinguish these gnats from common fruit flies, as eradication requires two separate approaches.

  • Fungus gnats are black, gray, or dark brown.
  • Fruit flies are orange, yellow, or brown.
  • Fruit flies are bigger than gnats.

As soon as an infestation is detected, decisive action is crucial. One of the best ways to confirm the problem is with sticky cards, which are available at all garden centers. Choose yellow cards to attract more gnats. Put the cards in the soil with the plants and leave them for a few days. If there are bugs stuck to the cards after that time, there’s a problem.

Another easy way to detect an infestation is to cut a potato and stick the cut end into the soil. If the cutting is full of maggots after several hours, you likely have a fungus gnat infestation on your hands.

How Do Fungus Gnats Harm Cannabis Plants?

Although we touched on it briefly above, fungus gnats do most of their damage in and under the soil. Fungus gnat larvae feed on plant’s roots and cause irreversible damage in severe cases. The damage leads to stunted growth and yellowing of foliage due to the plant’s inability to absorb water and nutrients. As the damage gets worse, the plants may die unless corrective actions are taken. Read on to learn how these gnats end up becoming introduced into a grow room or greenhouse.

Why and How Do Fungus Gnats Get Into the Grow Room or Outdoor Garden?

There are many reasons why you may see these gnats crawling in the soil or flying around your plants. Most of these reasons come down to simple human error, but in some instances fungus gnats may be brought in by larger animals or new plants.

  • Overwatering plants: A common reason for fungus gnat infestations is that plants are given more water than necessary. Inexperienced cannabis growers often encounter such problems. Overwatering leads to waterlogging, which creates the ideal environment for a gnat infestation. Wet, warm soil is a great place for these gnats to lay eggs, and once that’s done, the trouble begins.
  • Too much CO2 in the environment: Experienced cannabis cultivators often introduce carbon dioxide into their grow rooms to accelerate plant growth. This maximizes yield and shortens harvest time while increasing the product’s potency. Despite these benefits, CO2 supplementation often has detrimental effects. High levels attract gnats, and if they’re already present, they’ll multiply even faster. If you’re fighting a fungus gnat infestation, it’s best to turn off the CO2 generator for a while.
  • The soil being used: Certain growth media are more conducive to infestation than others are. While all soils have their different benefits, they can also cause fungus gnat issues. If you’re using a soilless mix such as compost, coco, or peat, be very wary of gnat infestation, and ensure your medium is allowed to fully dry in between watering.
  • Poor ventilation: Your grow room’s ventilation system and atmosphere will prevent (or cause) pests such as fungus gnats. If the environment isn’t right, you’re more likely to have problems. Air circulation, humidity, and temperature are the most crucial considerations, and all these factors can be controlled with a proper ventilation system.

Ventilation systems bring in clean, fresh air and get rid of hot, stagnant air. If the system isn’t fully sealed, though, it may actually allow fungus gnats an entry point into your grow. Prevent these issues with a HEPA filter on the intake that stops bugs from entering.

Ways to Eliminate Fungus Gnats

If you’ve taken precautionary steps to keep fungus gnats out of the garden, they’re less likely to present a problem. However, even the most organized grow rooms may encounter issues with pests. Here are several ways to get rid of fungus gnats once you’ve established that they are present.

  • Sticky fly traps: This should be a grower’s first line of defense against pests. Fungus gnats seem to be especially attracted to yellow fly traps. Simply hang a few traps around your garden, and they’ll stop the infestation from spreading. Many growers opt to put fly traps in the grow room as soon as their seeds have been germinated, just as a preventive measure.
  • Insecticides. The easiest way to eradicate fungus gnats and other pests is with pesticides or insecticides. There are numerous options on the market. Neem oil is a great natural option, and it can be applied to the soil or the plants
  • Soil amendments. Because fungus gnats primarily cause damage within the soil and the root zone, it only makes sense to take corrective actions in those areas. Diatomaceous earth can be dusted on top of the soil to prevent gnats from digging in and laying eggs. This natural white rock is composed of the microscopic remains of marine plankton. It cuts and dehydrates bugs as they crawl, and it disrupts their life cycle.

Now that we’ve discussed some of the most common natural and organic gnat treatments, we’ll show you a few more DIY remedies for more serious infestations.

Fungus Gnat Home Remedies

If there’s already a problem and you don’t have any commercial pesticides, there are a few do-it-yourself remedies to consider. Here are a few treatments commonly used by experienced cannabis cultivators.

  • Hydrogen peroxide: This is the first thing to try as it’s the simplest. Drench the soil with peroxide to kill larvae and adult gnats. The peroxide will also kill beneficial microbes, but it’s better than dealing with a pest infestation. Once the problem is under control, use a compost mix to reintroduce these helpful organisms.
  • Apple cider vinegar: It’s another great at-home option because gnats seem to be attracted to its smell. Combine apple cider vinegar with three tablespoons of dish soap in shallow dishes. Place these homemade traps around your plants and the gnats will get trapped in the liquid.
  • Beneficial bacteria and bugs: It’s time to fight fire with fire. Certain bacteria and insects will attack fungus gnats and get them under control. Many cannabis growers see significant success with beneficial nematodes. These are an excellent choice for those using organic soils, as these tiny roundworms will kill hundreds of species of soil-loving insects. They eat gnat larvae and prohibit future reproduction. In hydroponic cannabis gardens, these nematodes won’t be of much help. However, even hydro growers can find DIY ways to inhibit gnats.
  • Bacillus Thuringiensis: This beneficial bacterium is commonly used by organic cannabis growers to control insects on plants meant for consumption. This organism is endorsed by the WHO to control harmful mosquitoes. Many growers have seen success with this product, as it can be crushed into a powder, mixed into water, and applied to the soil.

With these home remedies, you’ll find it easier to get fungus gnats under control and ensure the health of the crop.

Be Careful With Compost Piles

Compost piles are healthy and beneficial for plants, but gnats love them too. Carefully examine the compost before feeding plants. To prevent the pile from attracting insects, remove excess moisture. Compost shouldn’t feel excessively moist; rather, it should feel like a nearly dry sponge. If there are bugs in the pile, sprinkle it with diatomaceous earth or any of the above home treatments.

After treating the entire compost pile, add a little moisture to activate the treatment and kill larvae and gnats. Once the pile has dried again, cover it with plastic. Stir it up frequently and allow plenty of time for it to dry.

A Few Final Thoughts on Fungus Gnats in the Garden

It’s crucial to follow a regular checklist to look for signs of disease and pest infestation in the garden. When these problems are detected early on, most of them can be eliminated. With the tips and tricks in this guide, you’ll have a healthier and more bountiful cannabis crop. Buying cannabis seeds is very simple these days, but caring for them properly is what ensures you get the best possible buds to enjoy at the end of your efforts.