Tag Archives: fungus gnats

The Texas Triffid Ranch Occasional Newsletter and Feedlot Clearance Sale – #23

(The Texas Triffid Ranch Occasional Newsletter and Feedlot Clearance Sale is a regular Email newsletter, with archives available on the main TTR site at least a month after first publication. To receive the latest newsletters, please subscribe.)

Installment #23: “Fungus Gnats and Dryer Sheets: A Case of News Churn”

Originally published January 22, 2021.

It hasn’t happened yet, but it will soon. Right at the moment in the North Texas area, the air is too dry inside and too cold outside for them to get going, but they’re waiting. By the end of February, they’ll flitter in your peripheral vision, and by March 15, they’ll be flying up your nose with every breath. Yes, it’s almost fungus gnat season.

That’s when the calls, the Facebook posts, and the general chat queries start. Many never use the term “fungus gnat,” instead describing them as “the little black bugs that fly like they’re drunk.” Sometimes, they note that the explosion came from a new potted plant, or a neglected one in an office that was suddenly watered along with the rest. Others only notice them when they show up close, flying in their erratic manner into eyes, nostrils, and open mouths. Still others only note how many dead bugs they find on windowsills, underneath aquarium lights, inside light fixtures, and along kitchen counters. From all of these, the flow chart paths all converge on one square: “How do I control them?”

For the most part, those encountering fungus gnats have no interest in the backstory: what most assume is one species is actually about six families of insect, all adapted to consuming fungi and occasionally algae. The flying adults are usually the only sign of an issue, but they’re nothing but packages to move genomes to new concentrations of fungus. Adults lay eggs on and in soil and substrates with a significant collection of fungus and then eventually die, and the eggs hatch into larvae that chow down on fungus filaments. (At this point, it should be noted that if you’re looking for mushrooms in a philodendron pot as a sign of fungus, you’ll generally only see those mushrooms when conditions are right for fungus to spread spores for reproduction. If conditions aren’t right to encourage mushrooms, or what are better described as “fruiting bodies,” you won’t see most fungi growth in a pot without a microscope or easy access to DNA sequencing gear.) Those larvae also feed on root tips of some plants: whether they do this deliberately or because the roots have a mycorrhizal relationship with the fungi is something for which I have yet to find an answer. Likewise, when the larvae metamorphose into adults, those adults take and transmit spores from other fungus, including the fungus responsible for “damping off” disease. Office dwellers hate them, houseplant enthusiasts hate them, greenhouse workers hate them, and you don’t even want to know what hydroponics enthusiasts think about them and the distantly related “drain gnats.”

This is the point where carnivorous plant people enter, or get dragged into, the game. Venus flytraps can’t waste their time with fungus gnats, but they’re enthusiastically consumed by all four types of pitcher plants if the gnats fly into the pitchers, they’re equally eagerly consumed by sundews and other sticky-hair trap plants, and they’re a major nitrogen source for butterworts. In fact, whether in cultivation or the wild, it’s hard to find a butterwort that isn’t covered with dead and trapped fungus gnats in varying states of digestion. The good news is that butterworts and fungus gnats go together like rum and Coke (or so I hear: I can’t drink), and butterworts have no problems with entrapping and converting those tiny chunks of protein into leaves, blooms, and seeds. But will butterworts or other carnivorous plants CONTROL them?

The reality, as anybody familiar with integrated pest management will tell you, is that while carnivores will gather up an excess of fungus gnats, setting out a sundew or butterwort next to your office Spathophyllum won’t do much to stop the problem. They’ll work so long as adults are out and flying, but they don’t do a thing about larvae living inside pots or the dirt just outside the door, and those eventually grow up and start the cycle anew. It’s not as if gardeners and houseplant growers haven’t tried, and the suggestions, ranging from spreading powdered cinnamon to spraying diluted hydrogen peroxide, can be found everywhere. The vast majority of those, though, are purely anecdotal, and usually assume effectiveness because the adults die off instead of doing anything to the larvae. The overwhelming majority of pesticide sprays have the same problem, and the user has the additional issue of those sprays killing everything from lacewings to lizards that catch the overspray. So what to do?

Well, I have a solution, one tested by experts, that’s remarkably effective. It affects fungus gnats only, and won’t injure or kill beneficial insects. It’s remarkably cost-effective, easy to apply, and available in grocery and department stores everywhere. No vile chemical smell, no dealing with insect corpses, and it won’t accidentally kill wild or domesticated animals if they get into it. In fact, I’m willing to bet that most readers already have some of this in your houses right now

You’re going to laugh.

I mean it. You’re going to laugh.

No, really. You’re going to laugh.

Okay, the secret is standard dryer sheets. 

See? I told you that you were going to laugh.

For the last two decades, commercial greenhouse operators related how putting down dryer sheets atop pots and trays kept down fungus gnat populations, but everything was anecdotal. In 2011, though, Greenhouse Product News published the first paper testing the effectiveness of dryer sheets on fungus gnats, and found…guess what, it works. (Sadly, this paper still isn’t available online, so no links, but please feel free to contact GPN for copies.) This was followed up three years later by Michigan State University, and both discovered that dryer sheets contained a compound called linalool, which was remarkably effective at repelling adult fungus gnats. The GPN paper also noted the presence of an aromatic compound that may prevent fungus gnat larvae from completing their metamorphosis from pupa to adult. Even better, this didn’t require huge amounts of material to get the desired effect.

On a purely anecdotal level, I can say that I had exceptional success with dryer sheets in a particularly tough environment. For those that remember the old Triffid Ranch gallery at Valley View Center, that mall had an absolutely horrendous problem with fungus gnats starting at the end of February and going until the middle of June, then starting again through October to the middle of November. Most of it was due to the various potted plants throughout the mall, which were haphazardly watered and cared for and probably hadn’t been repotted since the original owners of the mall abandoned their investment in the 2000s. The current owner wasn’t interested in any significant expenditure to deal with them, so fellow gallery owners had to grin (with clenched lips to keep the little monsters out) and bear it. Getting a roll of generic dryer sheets was the easy part: the real fun was hitting every last planter in the mall, including the mostly-hidden ones in the movie theater on the upper level, with at least one dryer sheet, and then switching them out once a week. Since the life expectancy of an adult fungus gnat is only a few days (I’m not sure if this is because of a lack of energy reserves or if their wings abrade from friction against the air and wear out enough that they can’t remain airborne), I figured that we’d start seeing positive results within ten days. We started seeing a drastic decrease in fungus gnats in about three days, to the point where I stopped applying dryer sheets in two weeks. When we had outbreaks later in the year, out came the dryer sheet roll, and they also were gone within a few days.

The reason I found this particularly interesting is bifold. The dryer sheet control technique has been around for decades, with hard science to back it up for one decade, and yet nobody outside of the commercial greenhouse trade seems to know about it. At plant shows and events, everyone is surprised at such an effective method. Friends keeping reptiles and amphibians, especially chameleon and tree frog enthusiasts, are even more surprised. Obviously, this is something that needs a larger audience: as with using carnivorous plants, it won’t control every insect that comes within the vicinity (this means “don’t cover your front yard with dryer sheets to keep the bugs away,” because we lost that war about 400 million years ago), but it should definitely help take the edge off for those with especial issues with fungus gnat maintenance. Even better, if this news takes off, then it’ll keep rolling around in news feeds and chat rooms (a phenomenon known as “news churn”) and become self-perpetuating, and when someone new to the field starts asking “So what do you do?”, everyone chirps in “Well, you KNOW…”

Other News

Friends and cohorts approving of the Delenn/GIR dynamic in Caroline’s and my marriage are passing on word about the death of actress Mira Furlan, and we join in the mourning. We met her once at one of Caroline’s jewelry shows in Galveston seven years ago, and we both pass our condolences, as inadequate as they are, to her family and friends.

Shameless Plugs

The definition these days of a Sissyphean task is “producing scientifically accurate dinosaur figures,” mostly because the goalposts seem to change every few days. That said, the crew at Creative Beast manages the nearly impossible: capturing the thrill of the 1970s Prehistoric Scenes model kit line from Aurora while pushing the edges of current theory on dinosaur appearance and behavior, and at a reasonable price. For lots of personal reasons dating back 40 years, a mountain accessory pack featuring the small predator Troodon had to come home, where it will remain as accurate as current research will allow. Sadly, that might be a few weeks, but that’s palaeontology.

Recommended Reading

A couple of chapters into The Art of the Con: The Most Notorious Fakes, Frauds, and Forgeries in the Art World by Anthony M. Amore, and it’s easy to understand why Salvador Dali famously flooded the art market with autographed reproductions of his paintings to give palpitations to the art collector community. It also explains why so many people tell artists “Oh, your work is so INEXPENSIVE! You should charge a lot more!”, before wandering off without buying anything. And so it goes.

Music

Growing up a ridiculous distance from civilization meant missing out on a lot of music, and thankfully streaming services offer the same chance to catch up on bands that couldn’t afford radio station payola to get airplay the way cable allowed movie enthusiasts to catch up on films that you’d never have seen at the local two-screen. This causes deep dives down rabbit holes for acts that somehow never turned up over the years, and this month’s deep dive is the Dead Milkmen. A few months of their work in regular rotation, and jumpin’ Jesus on a pogo stick, you’ll never look at a burrow owl in the same way again.

“And now on Handyman’s Corner, we’re gonna reverse the polarity of the neutron flow.”

There’s absolutely no reason to believe that anybody reading this reads Greenhouse Product News magazine, unless you’re running your own commercial nursery. For those who do, GPN is a free trade publication that offers US and international subscriptions, covering new developments in propagation and distribution for greenhouse operators. And for everybody else, it’s one of the magazines I read cover-to-cover when I get each issue.

Okay, so you’re figuring “Yeah, but you’ll read anything.” That’s all too true: when left without sufficient reading material, I’ve been known to memorize guides for wallpaper application and removal. (The summer of 1976 is one I don’t want to repeat, EVER.) However, you won’t believe some of the interesting stuff you’ll come across in an issue. Case in point, I just received the July 2011 issue Saturday, and immediately glommed onto the subhead cover story “Can Dryer Sheets Repel Fungus Gnats?” Sadly, the article isn’t online yet, so let me give a synopsis for the fungus-gnat-impaired.

Every spring, I get calls from friends, cohorts, and co-workers at the Day Job, getting frantic about little black bugs that fly errratically around flowerpots and other soil-bearing containers. I explain, over and over, that these are fungus gnats. The most common genus in my vicinity, Bradysia, is completely harmless to humans, even if they are annoying. The grubs are pests when they eat the roots of potted plants, but the whole life cycle is so rapid that they’re rarely a pest for more than two or three weeks. In my case, I don’t complain, because the fungus gnats start up in my greenhouse right about the time all of my temperate sundews and butterworts come out of dormancy. Set out a few Pinguicula primulflora, which attract fungus gnats like a “FREE BEER” sign attracts fratboys, and the butterworts feed exceedingly well.

What’s a minor annoyance in a small greenhouse, though, can be a major disaster in a commercial operation, especially when the little vermin feed on particularly delicate roots of plants that can’t handle the attention. Commercial operations have many different ways to control fungus gnat onslaughts, and one of the more intriguing involved using fabric softener dryer sheets to repel them.

Want to know why I love GPN? It’s because the article starts “In fact, Bounce original brand fabric softener dryer sheets have been promoted to repel mosquitoes and ‘gnats’ in some magazines; however, there is no quantitative data to substantiate such claims.” The four authors (Raymond A. Cloyd, Karen A. Marley, Richard A. Larson, and Bari Arieli) then supply the quantitative data. Contrary to a lot of claims about homespun garden cures (*coughSuperThrivecough*), this apparently really works in laboratory experiments.

According to the paper, one of the major volatile constituents in the dryer sheets is a monoterpene alcohol called linalool, which is also used in cosmetics, apparently is the active ingredient in the fungus gnat repellent. Interestingly, the citrosa plant Pelagornium citrosum, commonly hyped as a mosquito repellent with only a small amount of data to back up those claims, is loaded with linalool.

Now, this leads to all sorts of interesting possibilities. The first is that enterprising young horticulture students should consider further research into linalool as a fungus gnat repellent, and possibly develop an improved delivery system over fabric softener sheets. The second is possibly a further evaluation of linalool as a mosquito repellent. The best one, though, is that when co-workers start nuhdzing about fungus gnats every spring, I’m going to their pots with a teddy bear and scream “The fungus gnats will die before my eyes, and they’ll know – THEY’LL KNOW – that it is I, Baron Snuggles, who encompasses their doom!” That should take care of the problem once and for all. (Hey, it worked when they were bugging me about dog’s vomit slime mold in their flowerbeds.)