Here's how to fix your gnat problem
“Many thousand glittering motes
Crowd forward greedily together
In trembling circles.”
— Translation of Hermann Hesse’s “A Swarm of Gnats,” 1911
I recently stood in the middle of our pasture and this verse came to mind as I watched a swarm of gnats, as Hesse wrote, “extravagantly carousing away” during a brief period of late afternoon sunshine.
Poetry reflections aside, I wondered: Where did all these gnats come from? Why are they infesting the air in late winter? When will they go away? What can I do to make sure they don’t come back?
I also wondered: Why is there a “g” in gnat? Did a gnat just fly up my nose?
I snorted the wayward gnat out of my nostril, but I had to do some research to answer the other questions. Here are my findings, along with other potentially useful trivia about gnats.
First, gnat is spelled with a “g” because in the Middle Ages it was pronounced with a hard “g” sound: guh-nat. I think it would be fun to revive the Old English pronunciation. That way, we could also say “garden guh-nome” and tell our garden friends that we “guh-nashed our teeth over the guh-narly insects that guh-nawed our plants.”
In fact, “gnat” is used to describe several thousand species of tiny flying insects that have a single pair of wings and sucking or piercing mouthparts; gnats are close kin to mosquitoes and sand flies. The most familiar gnat to gardeners is the fungus gnat (Sciaridae species), so named because the guh-nawing grubs feed on fungi and decaying organic matter in moist, warm soil.
Fungus gnats are pests particularly at the larvae stage when they eat tiny root hairs of plants, causing the leaves to turn yellow and the plants to wilt. The larvae’s feeding also creates wounds that allow soil-born pathogens to enter the plant’s tissue.
Houseplant gardeners and those who grow seedlings in the warm, humid climate of a greenhouse are often plagued by fungus gnats and the damage they inflict as larvae.
After a brief pupal stage, gnats emerge from the soil about three weeks after hatching. The 1/8-inch-long adults look a lot like mosquitoes: slender body shape, long legs, a clear pair of wings, and antennae. Although adult fungus gnats don’t bite, they can transmit plant diseases. To be fair, some gnats are also pollinators.
The gnats I’ve been inhaling in my pasture are born out of the relatively warm, wet soil that was recently plowed up with the grass when a tractor passed through. They are also thriving in wet soil where we just removed a large stand of invasive shrubbery, exposing the humus-rich soil for the first time in decades.
What Hesse poetically described as “so fierce a dancing” is the frenetic mating of adult gnats; with only a week left to live, they “rave, delirious, a shrill whir/shivering with joy against death.” The female gnat then lays up to 300 eggs in the soil and they hatch in about six days, thus beginning the next generation of gnats. Their rapid lifecycle can quickly lead to infestation.
Our best strategy for getting rid of the gnats outdoors is to plant ground cover so their breeding ground will not be so accessible. Warmer weather will dry the soil and bring natural gnat enemies — birds, bats and other insects — to feed on the larvae and adult gnats.
For houseplant and greenhouse gardeners, the first defense against gnat infestation is to avoid overwatering. An effective, inexpensive way to control the gnat population in indoor plant soil is to introduce predator nematodes that will attack larvae. Release the nematodes every month for prevention or every week if a gnat problem already exists.
Gnat larvae are attracted to potatoes, so gardeners can detect the presence of larvae in the soil by slicing 1/2-inch pieces of potato, burying the pieces partially under the soil surface, and leaving them overnight to see if the larvae have congregated on or underneath the potato chunks.
Household hydrogen peroxide makes an effective soil drench that kills fungus gnat larvae on contact. Mix one part hydrogen peroxide with four parts water and thoroughly wet the soil around the plant’s root zone.
Once gnats have reached the adult stage, sticky yellow insect traps can be placed near plants. The cards will also help to detect a gnat population.
I didn’t need potato chunks or sticky yellow cards to know I’ve got a gnat problem, though. Come to find out, gnats are also attracted to the carbon dioxide humans expel, so all I had to do was breathe in deeply and a gnat found its way up my nose. What a guh-narly experience!
Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, visit her blog at http://blogs.esouthernoregon.com/theliterarygardener/.