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Over time you'll start to notice an increasingly large amount of small 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.
Similarly to 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. Click on the link before continuing with this article if you're unsure as to which compost is right for your plant.
3. Repotting your plants all at the same time will reduce the chance of larvae hatching at different times, thus causing a resurgence of Gnats. Sprinkle a fine layer of Diatomaceous Earth (also known as D.E.) across the new soil to prevent the females from laying their eggs. This powder-like substance is made up of grounded diatomic mantels (think loosely of powdered seashells) that'll act as a sharp, abrasive texture that aggravates and weakens the pregnant females before they lay. Their bodies begin to be scratch and become punctured by the powder, causing dehydration and a slow death to halt another generation of these Gnats. Sprinkle a fine layer onto the soil of every plant and leave it on for several weeks. Remember that D.E. isn't harmful to plants, pets or humans, so there are no health risks to consider. Remove the powder once you feel the infestation has elapsed, which usually take three to four weeks.
4. Place all of the plants into the prepared room. Keep them here for at least a week or two to check if any more Gnats are present. The larvae will develop into adults within ten days, so keeping the plants under a watchful eye will eventually show up any live bugs.
5. Crush each airborne pest that crosses your path throughout the house, as well as in the quarantined room. Once the two week period is over, you can safely re-introduce them back into their original locations around the home.
6. 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. If another infestation arises, try replacing the top two inches of the soil for the second time and consider purchasing Diatomaceous Earth if you haven't already. Always remember that the Gnats are indeed harmless, so never get too worked up about your plants' overall health!
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.
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 a mature adult. We do 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!
If you need further advice with your houseplants, book an advice call with ukhouseplants' friendly and expert writer today! This can be done via a video or audio call on most apps, including Facebook, FaceTime & Skype. A ten-minute call costs £5.99 (US$7), or £15.99 for thirty minutes. You can ask multiple questions, including queries on plants, pests, terrariums, repotting advice and anything in between. Please consider supporting this service to keep ukhouseplants thriving!