Summer is that season when we become very attentive to pests, we even do things to prevent them because this is the perfect season for insects to reproduce happily. As a consequence it is typical to let our guard down when temperatures start to drop, thinking that we are safe, but this is a false sense of security as it is the perfect environment for the dreaded substrate fly to breed.

If your plant looks droopy and is surrounded by a lot of flying bugs, it is quite possible that you are suffering from one of the most common and pesky pests: the black fly, the substrate fly or the fungus fly. Don't worry, today you will learn how to identify it, what damage it does to your plants and most importantly, how to get rid of it.

what is the fungus gnat?

The first time I saw one of these bugs I thought that the plant was being strangely surrounded by mosquitoes, because the Sciridae(Sciridae) are only 2 to 4 mm long, dark grey or black in colour, with very long legs and at first glance they look like these insects, although a little smaller. When they are larvae, they are 4 to 5 mm long and translucent in colour.

The problem with this pest is not the adult flies, which, although they are ugly and annoying, do not harm the plants, but their larvae are the ones that represent a danger to the plants. Let me explain: after the male and female flies get together, the female flies lay about 200 eggs in the substrate of your plant, which hatch in just 3 days. These fly larvae spend 3 weeks feeding and living inside the substrate, then develop into cocoons and are reborn as winged flies, which in turn emerge into the world and remain on the underside of the plant feeding and repeating the cycle.

The larvae are voracious and spend this entire stage feeding on the roots and capillaries of your poor plant. Not only this, but they can carry viruses and diseases to the plant and, as if that wasn't enough, leave the plant susceptible to attack by terrible fungi such as Fusarium, Pythium or Botrytis. With such an accelerated life cycle, it becomes very difficult to control this pest, especially if it is allowed to go on for too long.

How to tell if your plant has a potato root fly

The first tell-tale sign is the little gnats fluttering on the leaves, because they don't fly very well, they are lazy and don't stray far from the plant although they can reach nearby plants. Don't rely on the season, because although they may be more common in autumn and winter, they can appear at any time of the year.

Get close to the substrate of the plant and look closely at the surface. Stir the substrate a little, move the pot around and watch for little flies. You can see the larvae if you look closely, because although they are transparent, you can feel them moving. If you can, place sticky bug-trapping strips on the pot and check to see if they are trapped. It doesn't matter if you have one or two, act as quickly as possible because if you are careless they will move all over your plants and it will be a nightmare to fight them off.

When the larvae do their thing and reproduce excessively, the plants will look droopy, with pale leaves on which the little flies will get stuck. You may also notice that the plant develops fungal infections and if you delay too long, it will die because the infections often take over the roots.

How to get rid of blackfly

- Regulate humidity. The first step is to control excess humidity, as this is essential for the development of this pest. Avoid light and frequent watering, prefer deep watering (I love to water by immersion) and make sure that the plant drains very well. That said, you should allow the surface of the substrate to dry out well between watering while fighting the black fly, as this dryness will weaken and slow down the growth cycle of the larvae.

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- Disinfect leaves and substrate. If you have detected the pest in time, it will be fairly easy to eliminate it. Try natural remedies first: Neem oil, applied to the substrate and leaves with the irrigation water. Another option is to use potassium soap in the irrigation water, which will kill the larvae and flies quickly.

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- Prevents and/or slows fungal growth. One of the worst effects of the substrate fly is that it facilitates the growth of root fungus. A broad spectrum fungicide should be applied to prevent this from occurring or to slow down the infection.

- Get rid of adult flies. Flies do no harm, but they are ugly and breed. You can trap them using a plastic bottle with vinegar, cider and citrus peel. If you poke holes in the lid using a hot nail, the fly will get in but will not be able to get out.

- The last option, for resistant pests, is hydrogen peroxide. Water the plant with hydrogen peroxide to kill the larvae and repeat the process every couple of days to take care of the hatching eggs. This is the most questioned option, because although it is simple and economical, it does not eliminate the eggs and it also kills the beneficial bacteria in the substrate.

- Natural predators. Probably not an option for houseplants, but for uncontrolled and difficult to control substrate fly infestations in gardens or large areas of land, it is possible to get natural predators to kill the pest. One example is a coleoptera called Atheta coriaria or a small worm called Steinerma Feltiae.

Prevention is the key

- Clean the substrate of your plants thoroughly. Remove dry, damaged leaves that have fallen and rotted, as this creates the perfect environment for the larvae to feed.

- Remove weeds from the substrate. This is particularly important for outdoor plants.

- Space your plant's watering well. Waterlogged soil attracts flies and allows the larvae to proliferate happily. Allow the first few centimetres of soil to dry out before watering again, especially in colder weather.

- Sprinkle vermiculite on top of the substrate, about 3 cm will be enough to prevent this pest. You can also use pebbles or similar to protect the substrate and prevent flies from being attracted to it.

- You can use air currents (such as indoor fans) to scare the flies away. Adult flies are rather clumsy and do not fly very strongly, so they will not be able to get close to the plants.

- Indoors, it is a good idea to use window screens to keep harmful insects out.

- Some people say that planting garlic or putting cloves in the soil scares flies away, as they hate the smell.

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