So which insect do you have?
- Fungus gnats are tiny winged black insects, one of the most common houseplant annoyance, they aren't strong flyers and hangout mostly near wet plant soil or in household drains. They are attracted to CO2, which explains why they are constantly flying up your nostril. Fungus gnats live up to 2 weeks, and can lay up to 200 eggs in moist soil, which hatch in about a week and feed off plant roots for another 2 weeks.
- Fruit flies are lighter colored and larger, they hangout mostly around exposed fruit, rotten foods, or inside leaky refrigerators. They thrive on exposed or spoiling foods, such as juices on your refrigerator seal, leftover food matter inside your dish washer, or organic matter decaying inside your garbage. Fruit flies will lay eggs just about anywhere with leftover food, in excess of over 500 eggs at a time.
To effectively remove these pests, a combination of traps and habitat control are in order.
1. Yellow Sticky Traps
Using sticky traps is much like throwing a bandaid on your problem. Although it's not a long term solution, it will immediately reduce the number of annoying pests flying around. Something about the bright color yellow attracts all types of pests, fungus gnats, fruit flies, white flies, aphids, and others, perhaps because it mimicks sunlight. Generally the brighter the yellow, the better, and once they land, they're stuck.
Sticky traps are slightly expensive for what you're getting, the cheapest we found was around $7 for some plastic stakes and strips of yellow sticky paper. Hold onto those stakes when you're done with the first batch, you can always reuse them with yellow construction paper or cardboard.
Tanglefoot is a great sticky trap coating you can reuse on the cardboard, or coat yellow and orange plastic cups to attract the insects. It's about $8 for 8 ounces, which should last you a very long time.
2. H2O2 Drench
To kill the larvae hiding in the soil, you'll need a good mixture of hydrogen peroxide (H2O2). You can get 3% H2O2 at your local supermarket, or online (case of 12 is only $20).
First, wait for the top soil of your planter to completely dry, gnat larvae cannot develop in dry soil as the drought suspends their development. Next, mix 1 part H2O2 to 4 parts water and water normally. The mixture will not harm your plants, in fact rain water carries trace amounts of H2O2, which oxygenates the soil. Fungus gnat larvae on the other hand will die on contact.
3. Neem Oil Spray
For extra measure, mix a little neem oil with water in a pressure hand sprayer and spray the top potting soil in each of your planters. In case the H2O2 missed any, the oil will linger and interfere with the remaining insects. As we mentioned before in an aphid control article, neem is an organic solution that does not kill on contact, but interferes with the insects' natural hormones so that they "forget" to eat and mate. It does leave a residue after taste on edibles, but for indoor aesthetic plants, it's a perfect solution for your insect problems.
4. Control the Habitat
Perhaps most important, you'll want to eliminate the insect's habitat that has formed inside your home. For fruit flies this means keeping a clean house, cleaning up any food matter, and securing your rubbish. For fungus gnats, this means pruning your houseplants regularly, removing dead or dying leaves that the insects feed on. Also let the soil dry thoroughly before each watering, since gnats thrive in humid conditions.
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