Eliminate gnats from your houseplants.
Gnats --- particularly, fungus gnats --- are small flies that resemble mosquitoes and are typically found on or around houseplants, according to W.S. Cranshaw and R.A. Cloyd, professors of entomology at Colorado State University Extension and Kansas State University, respectively. It's a good idea to control gnats for the health of your houseplants even though they are only considered minor pests. Does this Spark an idea?
Altering Watering Practices
Gnats are drawn to high-moisture environments as this is the optimal growing condition for gnats. Adult female gnats especially like to lay their eggs in moist soil or other moist plant-growing media.
By regulating how often you water the plant, you'll be able to control and prevent the development of gnats. Cranshaw and Cloyd suggest letting the soil dry out before you water the plant again. The lack of moisture will decrease the chances of survival of the eggs and larvae. Female adults are also less likely to lay their eggs in dried-out soil.
According to entomology and horticultural science professors at the University of Minnesota, while you should aim at drying out the soil as thoroughly as you can between each watering, be careful not to let the plant wilt in the process.
Repotting
If the soil or growing medium retains moisture even though the plant was given the opportunity to dry out, consider repotting the plant. Also, repot or remove the container if too much decaying organic material is present. Examples of decaying matter include bulbs and roots of the plant. Since decaying matter serves as a food source for the gnat larvae, you can kill off the larvae by removing the food source through repotting.
Insecticides
You may need to use insecticides to treat the gnats if other methods were ineffective. The type of insecticide treatment and approach will vary depending on whether you are targeting adult gnats or larvae.
To get rid of adult gnats, persistently apply insecticides containing these ingredients: lambdacyhalothrin, cyfluthrin, bifenthrin and permethrin.
Larvae require different types of insecticides: a microbial insecticide called Bti and insecticides containing the ingredient imidacloprid. Apply the appropriate insecticide to the soil to kill both adults and larvae.
Yellow Sticky Cards
Instead of insecticides, use yellow sticky cards to capture adult gnats. Put the yellow sticky cards under the canopy of the plant or on the edge of the containers, according to Cranshaw and Cloyd. Since gnats are attracted to the yellow color, they will be caught in the traps. This is an effective way to eliminate large populations of egg-laying female adult gnats.
Insect Parasitic Nematodes
An alternative to insecticides for treating larvae is a biological method using an insect parasitic nematode, a microscopic roundworm. The species, Steinernema feltiae, is especially effective in treating gnat larvae, as stated by Cranshaw and Cloyd.
After applying the nematodes to the growing medium, the nematodes will invade the larvae, entering them through various openings such as the mouth, breathing pores and anus. Once the nematode is inside the larvae, it will emit a bacteria that digests the insides of the larvae. The larvae should die within three to four days, according to Cranshaw and Cloyd.
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