Mourning flies aren’t just annoying. They are dangerous for our plants. Rather, these are their larvae, which gnaw on plant roots after hatching. If they go unnoticed long enough, the plant is beyond help. That’s why it shouldn’t get that far. There are ways and means to prevent mourning flies. And also to combat an existing infestation effectively.

Where do mourning flies come from?

Mourning flies seem to be creatures of winter. Because it is usually the cold season when they become a nuisance at home. But these insects actually live all year round. You can access your growths in the following ways:

  • when you buy the plant there are already eggs or flies in the ground
  • outdoor pots are accessible to flies
  • Flies can also fly in through windows

In summer, however, there are plenty of predators out in the open. So their number remains small and they don’t attract much attention. In winter, when many balcony plants overwinter in the house, the situation is different. While the mosquitoes and their eggs move along with the plant, the predators remain locked out. It won’t be long before the population explodes.

Note: Mourning flies are also often referred to as fungus gnats.

Favorable Factors

In order for fungus gnats to stay with a plant and multiply diligently, two other factors play their part in addition to the lack of predators. These are:

  • inferior potting soil as an optimal breeding ground
  • constantly moist soil as an ideal environment for propagation

If your plants have these two factors, an infestation with these insects is almost challenged.

detect infestation

The flies can be found in living quarters or greenhouses. On beds they are rather rare guests. If you suspect that a plant is infested with mourning flies, you can quickly gain clarity. Gently shake the pot. When the little flies are there, they will rise in their hundreds and buzz around the plant.

Tip: Put a potato wedge in the ground. If sciarid larvae are in the soil, they will soon be gnawing on it.

Fight with patience and sand

If your plant still looks vital, you can take some time to fight the flies. In return, you can use a particularly environmentally friendly method. Cover the soil in the pot with a layer of sand. Since mourning flies only lay their eggs in the ground, there will be no further laying of eggs. If you now take a four-week break from watering, no more larvae will hatch from the eggs that have already been laid if it is dry. The remaining flies will die after just a few days because they have reached their natural lifespan.

Repot the affected plant

Not every plant can be dried out for weeks to prevent the larvae from hatching. Likewise, in the event of a severe infestation, the plant should be immediately repotted in new soil.

  • Take the plant out of the pot
  • seal old soil in a plastic bag and discard
  • Rinse roots under lukewarm water
  • repot in good quality soil
  • use a new pot or clean the old pot thoroughly
  • Do not water the plant for the first few days
Tip: You can also sterilize the old soil in the microwave or oven. In high heat, the larvae are killed. The earth can then be used again.

Yellow boards as flycatchers

Mourning flies like the color yellow, as do some other flying pest species. For this reason, special yellow boards are available on the market that you can use to combat these insects effectively. The board is attached to a stick that is inserted into the potting soil. The color attracts insects. One copy after the other ends up on the yellow board. The flies can no longer take off because it is covered with an adhesive film. Depending on the severity of the infestation, you may have to replace fly-covered yellow boards with new ones several times.

Beneficial nematodes

Nematodes are a biological agent that can be used effectively to control pied fly larvae. The roundworms can be obtained over the Internet. Don’t worry, they are safe for us humans and for plants. In order for them to be able to do their work, however, ideal conditions must prevail. For example, moist soil and a soil temperature between 15 and 25 degrees Celsius. It is safest if you follow the seller’s instructions exactly. Fighting the larvae will take about 14 days.

Tip: keep the soil moist but do not water excessively. Otherwise there is a risk that you will flush the nematodes out of the soil again.

Bring predatory mites into the house

Predatory mites go on a rampage and capture fungus gnat larvae. They are satisfied and so are we plant owners. Only the larvae, they are becoming fewer and fewer. Eventually the last larva will be caught. Then the hungry predatory mites eat each other up. This is a means of combating that leaves no traces. Predatory mites can be purchased cheaply over the Internet. Unfortunately, they only hunt the larvae and leave the flies themselves unmolested. These may have to be combated in parallel with another agent.

Fight with 8 home remedies

Here are a few more remedies that were already used in grandma’s time to combat mourning flies:

  • Mix lukewarm water, oil, baking powder and salt
  • Spray all over the plant
  • stick several match heads into the ground
  • put whole garlic bulbs in the potting soil
  • or finely chop the garlic and scatter in the pot
  • Chop a few sprigs of parsley and put them on the ground
  • Sprinkle cinnamon powder on the ground
  • add lavender to the water
  • Alternatively, add some tea tree oil to the irrigation water
  • Put the pot in a stocking and tie it tight
  • Leave it like this for at least 4 weeks

The offer of the chemical industry

The chemical industry has also placed its “poisonous” agents on the shelves of garden centers to combat these pests. While they are effective in combating the black mourning flies and their larvae, they can also cause harm to people and pets. Particular caution is required when they are used indoors. Therefore, this remedy should be the last choice. Reaching for the chemical pack is not necessary anyway, because enough helpful and harmless means for people and the environment have been mentioned beforehand.

Prevent mourning flies

If an infestation is successfully combated, the next one can follow shortly. Make it difficult for flies to colonize the soil of your plants. Consequently, their voracious larvae also stay away. It is important to critically review your own watering behavior and change it if necessary. The top layer of soil should dry first before a plant is watered again. Also, avoid leaving water in the coaster. You can also prevent flies by covering the soil with sand or pebbles.

Quartz layer as a barrier

With a layer of quartz sand in combination with watering from below you can also prevent these annoying flies. To do this, part of the earth is first removed. Then a layer of quartz sand is sprinkled in the pot. Then it is covered with earth again. Quartz sand thus forms an invisible but effective barrier to the moist earth underneath.

Prevention with chives

Mourning flies don’t like the smell of chives . The tasty onion plant can be planted in a greenhouse or in a bed as a preventive measure. It drives away this fly species reliably and over a wide area.

sterilize soil

If possible, use quality soil, because this rarely contains harmful germs or pest eggs. Leave newly purchased soil for a few months before using it for your plants. During this time any existing larvae or flies die off. If time is short or space is not available for storage, you can sterilize smaller amounts of soil before use. For example, by heating the soil in the microwave for a minute.

Tip: Also avoid larger piles of leaves near your potted plants in the garden. They are favorite haunts of the black mourning fly larvae. The ‘risk of infection’ for your flowers is otherwise particularly high.

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