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Important Facts About: Fungus Gnats

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What are these small black flies in my growroom?

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Fungus Gnats – The Facts

Fungus gnats are tiny, dark-winged insects that resemble mosquitoes. They are usually found in damp areas, where there is free water but also where algae grows. You will often see the adults running around the top of pots, on the soil or close by.

1. They are usually found in the top two to three inches of the soil, depending on the level of moisture in the growing medium.

2. They develop quickly and become fully grown in the period of two to three weeks.

3. They live for only 7 to 10 days.

4. Female gnats are able to lay more than 200 eggs.

5. Ideal temperature at normal room temperatures (65 degrees Fahrenheit to 75 degrees Fahrenheit; 17˚C – 25˚C).

How to Treat

To fully understand why your growroom has a fungus gnat problem, and to learn how to get rid of these little black flies from your growroom, please read on…

1. Keeping the growing area as dry as possible.

2. Cleaning up all organic material off the floor.

The larvae, on the other hand, thrive in potting soil, cocopeat and even rockwool. They also infest NFT systems and other recirculating hydroponic systems – in fact, almost anywhere that is damp and has a food source for them. They feed on algae, fungi, and decomposing plant materials but, just as often, this food source is the root system of your plants. They are usually found in the top two to three inches of the soil, depending on the level of moisture in the growing medium. If you find them amongst your plant’s roots then they are almost certainly eating your plant’s root system. They develop quickly and become fully grown in the period of two to three weeks. They then form pupae and emerge about a week later.

Fully grown gnats are weak when it comes to flying. They typically fly in short, unpredictable patterns. They live for only 7 to 10 days, but during that period female gnats are able to lay more than 200 eggs into the crevices and cracks of the growing medium. Adult female gnats are particularly attracted to growing mediums with a high moisture content, precisely the conditions we give our indoor crops. At normal room temperatures (65°F – 75°F; 17°C – 25°C), the fungus gnats complete their life cycle in three weeks to a month. In warmer grow room conditions, it is considerably faster.

Nuisance problems caused by the adult gnats are evident all year round, in grow room conditions. In fact, it is almost a given that, if you grow in soil or coco coir, you will have fungus gnat problems. It’s not a matter of “if”, it’s a matter of “when”.

These pests operate under the soil surface, so, unless you are vigilant, you may miss the first warning signs of adults walking and flying around the surface of the medium. The main cultural practice which can help reduce the speed at which fungus gnats build up is keeping the growing area as dry as possible and cleaning up all organic material off the floor, reducing the places that fungus gnats can survive and breed.

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