Posted by Aimee | Posted in Insects | Posted on 21-03-2011
Pesky vermin that frequent indoor plants, fungus gnats as adults are harmless except for their reproductive abilities. The gnats however feed on decaying plant material, and delicate plant roots, which can stunt the growth of your indoor lovelies.
I picked up a batch of these wretched little fellows in a healthy looking spider plant and have battled them for over a year. The solution was to finally get serious about taking care of them and oodles of research.
A fungus gnat is a soft-bodied very tiny black fly and indoors their entire life cycle is about one month. Each adult female is capable of distributing two hundred eggs. Those eggs hatch into maggots that infect the top couple inches of potting soil, where they feed on decaying plant matter and plant roots. They then pupate and emerge as adults to perpetuate the cycle.
The last thing you want to do is go wild with insecticides in your home. Especially if you have kids or pets. Not to worry though, there are a plethora of cheap, organic, pet/child safe alternatives. The control methods are different for the fly and the larva. I recommend using a combination of several or even all of these options.
The key seems to be persistence, you want to continue treatment for a month after the last signs of the larva and adults have been seen to catch any stragglers. One surviving female has the potential to completely recreate the population! So stick to your guns folks.
To control the flies:
Use yellow sticky traps (if the females are stuck to the paper they cannot lay eggs in your plants.) The flies are drawn to the yellow. (You can also make these at home.)
Set out small bowls of apple cider vinegar and change regularly. The flies are drawn to the smell and then drown in the liquid.
Hand squishing, they are not fast fliers and each one you take out is one less that can be making babies.
To control larva (the root of the problem, no pun intended.):
Repot all indoor plants and cover the top couple inches with decorative sand to make their survival more difficult.
Let plants dry out between watering times.
Place a potato wedge a quarter inch into the soil and then throw away, entirely out of the house. Repeat this for several weeks, continuing even after signs of the flies are gone.
Drench houseplants in a BT solution. This is an organic pest control that is entirely harmless to people and pets, it targets all caterpillars though so do not use on plants that you want to promote butterfly larva on. This also dissipates quickly and is even safe for use on food.
Inoculate your soil with parasitic nematodes; these are little critters that will feast on the larva. Do not use this in conjunction with BT. Steinernema feltiae is one of the most effective against fungus gnats.