eliminate the environmental conditions that encourage breeding

By Mike Turany, Plant Solutions | March 13, 20012 | topics: Fungus Gnats, Environmental Conditions

What Gnat is That?

Fungus Gnats, Fruit Flies, Shore Flies, Moth Flies, and March Flies can appear in large numbers in and around buildings. Shore Flies and March Flies will enter buildings seasonally as flying adults, but cannot reproduce in the enclosed building environment.  Fungus Gnats, Fruit Flies, and Moth Flies, however, can enter buildings and develop indoors through all life stages. Their reoccurrence will perpetuate when the indoor environment is conducive to the development of these pests.  None of these common kinds of gnats bite or sting people or animals, but they are a nuisance and do prompt complaints.

As your interior plantscape company, the type of gnat that concerns us is the Fungus Gnat, which could continue to live in your plants and be an annoyance. While no one can completely prevent gnats from entering the building, there are simple prevention and control measures that can be taken to ensure that Fungus Gnats will not reproduce in your plantscape.

Whose Gnat is That?

These small flies and gnats thrive under moist conditions, especially where there is an abundance of decaying fruit, vegetation, mulch, algae and fungi. A rainy day, an addition to the landscaping, seasonal color changes, over-seeding of rye grass, or turf re-sodding always corresponds to an abundant population of gnats within a month. Moist and decomposing grass clippings, compost, organic fertilizers, mulches and organic top-dressings like decorative bark are favorite breeding spots; not to mention plumbing or irrigation system leaks, drainage issues, free-standing water or water retention ponds which also continue to provide an advantageous habitat for gnats and far worse pest problems. Gnats may also get brought into buildings while still in their larval stage in cut flower arrangements, fresh fruit and vegetables, and in the soil of blooming houseplants, and interior foliage.

What Can We Do?

Steps can be taken outside of buildings to control areas where organic material or moisture accumulates where there is potential for gnat breeding. And indoors measures can be taken to quickly remove food waste and regularly clean water drains with gooseneck plumbing in kitchens where such debris can accumulate and provide a breeding site for these gnats, especially Moth Flies.


Eliminate the environmental conditions that encourage breeding:

  • Dispose of all food/beverage waste and containers each evening before you leave the office.
  • Once a week, run hot water and bleach down all kitchen sink drains to remove soap scum and food debris in the drains.  Doing this each Friday afternoon will prevent gnat breeding over the weekend.
  • If standing water is observed outside in the landscaped areas, notify your building/facilities maintenance team to determine and eliminate the cause (a leaky sprinkler head, for example).
  • Resist the temptation to provide your plants with an extra sip of water, ice or any other beverage, especially the sugary ones.


Once Fungus Gnats have been identified, we will:

  • Monitor and trap them with yellow sticky traps placed in on the soil of the plant.
  • Permit the soil to go dryer between our watering to eliminate their preferred breeding environment.
  • Apply Food Grade Diatomaceous Earth (DE) Powder to the surface of the soil
  • Apply Gnatrol, a biological control agent Bacillus thuringiensis subspecies israelensis (Bti) when watering, which is toxic only to gnat larvae
  • Replace the plant completely if no other measures prove effective in controlling the gnats.

Please keep in mind that there may be other plants in your, office which Plant Solutions are not contracted to care for, as these are ‘personal plants’ that have been brought in by other office staff.  Please encourage your coworkers who have such personal plants, to also take the preventive steps noted above to reduce and eliminate the opportunity for gnats to breed in their plants.