Summer is that season when we keep a good eye out for pests, we even do things to prevent them because this is the perfect season for insects to breed happily. As a consequence, it is typical to let our guard down when temperatures begin to drop, thinking that we are safe, but this is a false sense of security as it is the perfect environment for the reproduction of the dreaded substrate fly.
If your plant looks droopy and is surrounded by a bunch of flying bugs, it's very possible that you're suffering from one of the most common and heavy pests: the black fly, substrate fly, or fungus fly. Don't worry, today you will learn how to identify it, know the damage it does to your plants and most importantly: how to eliminate it.
What is substrate fly?
The first time I saw one of these bugs I thought that the plant was being strangely surrounded by mosquitoes, and the sciarids (Sciridae) barely measure between 2 to 4 mm, they are dark gray or black, with very elongated legs and at first glance they look like these insects although a little smaller. When they are larvae, they measure between 4 to 5 mm and are translucent in color.
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 fly and the female fly come together, the female deposits about 200 eggs in the substrate of your plant that hatch in just 3 days. These fly larvae spend 3 weeks feeding and living inside the substrate, then turning into cocoons and reborn as winged flies; which in turn emerge into the world and remain at the bottom 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 be carriers of viruses and diseases for the plant and, as if that were not enough, they leave the plant susceptible to attack by terrible fungi such as Fusarium, Pythium or Botrytis. Having such an accelerated life cycle, it becomes very difficult to control this pest, especially if it is allowed to pass for a long time.
How to tell if your plant has substrate
flyThe first telltale sign is the small mosquitoes fluttering on the leaves, because they don't fly very well, they are lazy and they don't stray far from the plant, although they can reach nearby plants. Don't rely on the season, because while 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 take a good look at the surface. Stir the substrate a little, move the pot and see if small gnats come out. The larvae are noticeable if you look closely, because although they are transparent, you will be able to notice their movement. If you can, attach adhesive strips and check to see if they have been trapped. It doesn't matter if you have one or two, act as quickly as possible because if you are careless they will spread to all your plants and it will be a nightmare to fight them.
When the larvae do their thing and over-reproduce, the plants will look saggy, with pale leaves on which the gnats will stick. You may also notice that the plant develops fungal infections and if you delay too long, it will die because infections usually take the roots.
How to get rid of black fly
- Regulates 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 immersion watering) and check that the plant drains very well. That said, you should let the surface of the substrate dry well between waterings while fighting the black fly, as this dryness will weaken and slow down the growth cycle of the larvae.
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- Disinfect the leaves and substrate. If you have detected the pest in time, it will be quite easy to eliminate it. Try first with natural remedies: neem oil, applied to the substrate and leaves with irrigation water. Another option is to use potassium soap in the irrigation water, which would kill larvae and flies quickly.
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- Prevents and/or slows down the growth of fungi. One of the worst effects of the substrate fly is that it facilitates the growth of fungus in the root. To prevent this from happening or to stop the infection, it is advisable to apply a broad-spectrum fungicide.
- Eliminate adult flies. Flies don't hurt, but they are ugly and reproduce. You can set traps for them by 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 won't 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 eggs that hatch. It is the most questioned option, because although it is simple and economical, it does not eliminate the eggs and also kills the beneficial bacteria in the substrate.
- Natural predators. It's probably not an option for houseplants, but for uncontrolled, hard-to-control substrate fly infestations in gardens or large tracts of land, it's possible to get natural predators to kill the pest. An example is beetles called Atheta Coriaria or a worm called Steinerma Feltiae.
Prevention is the key
- Clean the substrate of your plants well. Remove dry, damaged leaves that have fallen and are rotting, as this creates the perfect environment for the larvae to feed.
- Remove weeds from the substrate. This is particularly important in outdoor plants.
- Space out your plant's waterings well. Waterlogged soil attracts flies and allows larvae to proliferate happily. Allow the first few centimetres of the substrate to dry before watering again, especially in the colder seasons.
- Sprinkle vermiculite on 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.
- You can use drafts (such as indoor fans) to scare away flies. Adults are very clumsy and don't fly very hard, so they won't be able to get close to plants.
- Indoors, it is advisable to use window screens to prevent harmful insects from entering.
- There are those who claim that planting garlic or placing cloves in the substrate scares away flies, as they hate the smell.
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