“Green” Ways to Control Fungus Gnats and Spider Mites [PHOTOS]

Many futurists predict that the lowly cockroach would emerge as the dominant species on Earth should humanity wipe itself out in a nuclear war. But ask any Interiorscaper, and they’d likely say fungus gnats or spider mites would reign supreme.

These two pests have become the “fly in the ointment” of many ‘scapers as they are tough to monitor and control, and often distract and annoy clients.

With so many office buildings focusing on green environments and Leadership in Energy and Environmental Design (LEED) guidelines, the somewhat effective chemical pesticides are now out of the question.  So let’s put it bluntly, is there ANY way to control these buggers without using chemical insecticides?

Yes! Over the years, Interiorscapers have shared with us some ways to take out fungus gnats and spider mites naturally, and some of the most effective methods are with other living organisms available locally or online.

“Most Interiorscapers think that one application will do the trick, but that‘s not usually the case,” said Kathy Fediw, a LEED-certified trainer and consultant for Texas-based Johnson Fediw Associates. “Repeat applications are usually necessary, so keep track of your treatments and make sure you keep them up to date until you no longer see any activity.”

 

Nematodes a “Gnatural” Enemy

Predatory Nematodes attacking a fungus Gnat Larvae Photo Credit: Ontario Ministry of Agriculture

Microscopic worms called nematodes that attack fungus gnat larvae, can be purchased online and arrive in powder packets. The solution is mixed into your watering application and within days, as the plants consume the water, the nematodes feast on gnat eggs in the soil. You can even inject the solution directly into plants or apply with spray equipment.

Commonly available nematodes that prey on the larvae, such as Steinernema feltiae, are effective many fly larvae and soil-dwelling enemies of greenhouse-grown plants. They are sold under such trade names as “BioSafe,” “BioVector,” “Scanmask,” and “Guardian.” Most parasitic nematodes packaged for sale have a shelf life of several weeks or even months if refrigerated.

 

Mighty Mites

Our heroic predatory mite (on right) stalks a two-spotted mite on a bromeliad leaf

Ironically the best way to control the most common enemies you encounter, such as the two-spotted spider mite, is by attacking them with a different mite species that do not harm plants or people. Like the nematodes, common “predatory” mites can be mail-ordered from a horticultural warehouse or purchased from any number of online gardening vendors. Here are some common species you should consider according to Purdue University Entomology Dept.:

  • Phytoseiulus persimilis – once they eat the spider mites, they eat each other (cool!)
  • Metaseiulus occidentalis – effective in temperatures that average between 44 degrees and 89 degrees Fahrenheit.
  • Phytoseiulus longpipes – the brother of  Phytoseiulus persimilis bred in Africa and can stand warmer ambient temperatures

 

Predatory mites and nematodes have been exempted from federal and state registration requirements (Vol. 47, Fed. Reg. 23928, 1982), which means they can be used legally without restriction.

Sticky Cards useful for controlling and monitoring pests
Simple yellow notecards coated with a sticky adhesive that attract and trap pests are commonly used to discover and/or monitor a pest problem.  Sticky Cards are also a visible way to let your customer know you are responding to a pest complaint or staying proactive. The cards can be cut into small pieces and laid on top of the soil surface.

 

Methods CONTROL or LIMIT but don’t ELIMINATE
I am not a bug guy, but I do work for a company that cares about the success of Interiorscapers. You should consult your local extension office before you attempt to biologically attack pests.

Even then, you should test your nematode or mite applications in a small area first. Biological control is a preventative measure, not a reactive measure, many interiorscapers who have used biological control successfully scout and record the number of fungus gnat and spider mites present before and after release of biological control agents.

For more detailed information and even more ways to control mites and gnats organically, visit Johnson Fediw’s site at www.JFAConsultingBiz.com. The Bug Factory sells many of the biological pest controls discussed above and gives detailed usage guidelines. You can find them online at www.thebugfactory.ca (Neither company is connected to NewPro, nor did they pay for this mention.)

What are some tried-and-true methods you have used to control pests naturally? Please share in the “reply” area below.
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  • This was recommended to me by Steve from Greenchat. He uses bug lights. I tried and they definitely help.
    My experience is that there is not one treatment in particular that works 100%, you have to combine several and hope for the best.
    The main problem is by the time a client calls, he usually want the gnats to be gone right away so the natural control is not always the best solution.

    • Could you elaborate on the bug lights? how do you use them and how long, assuming its not an Ancient Chinese Secret 😉

  • I have had success using a little soap in my watering can for fungus gnats larvae, I have also had success using Lysol spray on the top of the soil when adults are active.
    There are many times clients complain about the gnats and I don’t ever see them…these two methods I use anyway and the clients get satisfaction.
    Once I have gained control I do not use these products again.

    • Thanks for sharing Dale. I think I know the answer to this, but why don’t you use a particular method again? Does ti lose effectiveness in a location?

  • Melissa

    First, make sure there is no standing water under the plant. Cover the entire soil surface with DE (diamotaceous earth) Put the plant on extreme water restriction. No new flies should emerge but adult may hang around for up to 10 days. Another option is to remove the top 2″ of soil and replace with new dry soil.

    • Nancy Oden

      what if you service the account bi-monthly, have a bunch of topsiders on this account that have felt liners in the bottom and you need to leave them standing in 1/2 inch of water?

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