Do you have little black flies buzzing around your houseplants? Most likely they are Fungus Gnats. The probable cause…soil is too moist and has not dried out between watering. Effect….Fungus Gnats love moist, organic rich soils. It’s a perfect environment for them to lay eggs. The eggs hatch, the larvae are little white wormy things that feed on roots and the organic components of the soil. The larvae finally turn into adults, the little black flies that flutter around the soil surface.
It’s a pretty common problem at this time of year. We have not really worried about watering our plants all summer. You almost cannot over water plants during the summer. Our minds tell us that when the soil starts to dry we need to pull out the watering can and give our plants a shower. But, as we enter into October the light intensity decreases, the day length decreases, and it gets cooler. That’s hard for our minds to recognize, as we are creatures of habit. And once we do, it’s too late. And it’s not the watering that’s at issue but how long the soil stays moist. This is when we see those pesky little fungus gnats that end up floating in our cup of coffee.
Solution….Well the first thing you have to do is water less frequently. This is the single most important thing you can do for your plants. Our plants are not really growing that vigorously so they do not need to be kept well watered and fed. Be sure to allow at least the top inch to dry out thoroughly between watering. That is where the fungus gnat larvae live and they do not like dry soils.
Secondly, you can develop a insecticidal spray program. This stops the adults from reproducing. If you spritz the soil surface with an insecticidal soap every 3 to 4 days it will kill off any adults that emerge. Fungus Gnats have a pretty fast life cycle. Their goal as adults is to reproduce, that’s it! But this method is more peace of mind for us and can limit the nuisance a little.
Thirdly, Attack the larval stage, organically! I like this option a lot! Get some Mosquito Bits® and sprinkle them onto the soil. They are granules that have a beneficial bacteria (Bacillus thuringensis) cultured on their surface. When you water them in, the bacteria is released, and enters the soil. The Fungus Gnat larvae come in contact with them, ingest them, and “BOOM”, controlled from within. Good bugs fighting bad bugs!
Another great tool is Diatomaceous Earth, an additional organic option. These are the exoskeletons of one celled aquatic plants. Composed mainly of silica dioxide, these exoskeletons have a lot of texture to their surface, which scratches the outer shells of insects and destroys the population. Look up Diatoms in your search function, pretty cool stuff!