Over time you'll start to notice an increasingly large amount of minute, black flies appear all over your home. They'll parade on the foliage, windows or light shades and will fly away when under threat. Although a large proportion of them are actually trying to escape, others will begin to deposit small eggs in the top layers of the soil, slowly developing into white larvae within a few days. These pesky critters are what will cause the damage to the plants - digesting the root systems, spreading diseases (like Pythium or Botrytis blight) and wreaking havoc around the home.
Although most active during the colder months, they can attack throughout the year. Fungus Gnats are in search of a dark, moist breeding ground to lay their eggs. There are three main ways for the Gnats to enter your home - most will enter the home through open windows or doors, but a few will be in the soil already. When purchasing a new plant from a store, always be sure to replace the top 3cm (2 inches) with a fresh batch of compost to eliminate introducing new critters. The final way is via a transplant when compost is used from a poorly-stored bag. When hoarding soil for later use, keep the lid tightly enclosed in a dark, dry location - a great example would be in a garage or shed.
Although the plants may be seen on the foliage, their larvae will only attack the roots and soil fungi. Although smaller infestations won't affect established plants, large numbers in one pot may cause a reduction of roots which in turn can cause yellowing leaves (rare).
Plants - Most plants will be affected, especially with those located in dark settings. A continuation of moist soil will also promote an attack, as they thrive best in dark, humid environments with poor soil aeration. They'll rarely attack plants that require dry soil, for example, cacti or succulents. In some cases, they'll also feed off the nectar of flowering plants, spreading potential diseases across your plant collection.
There are several methods of eradicating the Gnats and their larvae. The tips that ukhouseplants will provide have worked a treat over the last few years, so don't worry if there are other methods online.
As with Vine Weevils, there are two stages to eliminate Fungus Gnats. The first stage is to remove the larvae and THEN the airborne specimens. There's little point in only removing the adults, as the eggs or larvae will only pick up where the predecessors left off.
1. Prepare a room (ideally small) where there aren't any Gnats or plants present. Providing a 'neutral' zone where you can confidently say that there aren't bugs will aid pest regulation and the eradication process. Keep the doors shut and regularly check for any Gnats that may be hovering around the windows or lampshades.
2. Take all of your plants outside and replace the top 2cm (1 inch) of soil with the appropriate potting mix. Do them at the same time as this will reduce the chance of larvae hatching at different times. Removing the eggs and larvae before they mature will nip the infestation in the bud. Spray the new soil and foliage with garlic water; the herb's scent will deter females from the compost and therefore potential egg-laying.
3. If you'd like to be extra careful, place a thin layer (1cm, 1/3 inch) of grit onto the plants' soil. This will block the infestation in two ways - by averting the adults from laying eggs into the compost and trapping the larvae into the soil to prevent them from escaping.
4. Place all of the plants into the prepared room. Keep them here for at least a week to check if any more Gnats are present. The larvae will develop into adults within a week, so keeping the plants under a watchful eye will show up any live bugs.
5. Get a handheld hoover and suck each airborne pest that you crosses your path throughout the house. Keep an eye out for the next week, regally checking the hard-hit areas of windows and lampshades.
6. After the week, check the soil/grit and windows for any sign of an infestation in the planted-room. Once there are no more visible pests in the whole house, you can safely re-introduce them back into their original locations.
7. Always keep an eye out for more Gnats and kill or hoover each one that you see. This can be a long process to eradicate, so doing small hunts each day will make a big difference long term.
At the local plant shop or garden centre, regulate and inspect any plants that you wish to buy. Check around the hard-hit areas, for instance, the soil and lower stems, before considering the purchase. Most Gnats will come from already-affected plants, so always keep this in mind when increasing your plant-collection.
Keep the doors and windows shut during autumn and winter as this is the time for an infestation to strike.
Change the top layer of the soil when bringing any new plant from a shop. Replacing the top layer of the compost will remove any eggs & larvae that may have fallen in, or been deposited by another pest. ukhouseplants does this religiously, each time a new plant is purchased!
Regularly check for pests on your own plants. Although this may sound patronising, many gardeners forget to inspect their indoor specimens. As soon as you see a symptom, keep it quarantined and follow the steps above!
For any more questions or queries about Fungus Gnats, be sure to message us via this link or comment in the section below!
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