Fungus Gnats and Their “Cousins”

[Pompeii]

Fungus Gnats and Their “Cousins”

Cheryl J. Shenkle

Regardless of how much you clean, sterilize or trap, Fungus Gnats seemingly appear out of thin air specifically to eat the moist roots of any plant that they can find.  They can ride in on plants brought in for the winter, Poinsettias, Easter flowers, spring flowers and all bags of soil mix.  It’s impossible to avoid dealing with them at some time.

For those who plant spring seeds indoors, this isn’t a surprise, but it is certainly a problem that all plant growers face at one time or another.  When the seeds germinate, a Fungus Gnat will begin looking for the tender new arrival, intent on burrowing into the soil to lay eggs which will attach to the new roots and suck nutrients from them.  The plants may begin to wilt for no obvious reason, develop fungal diseases, root rot and eventually die.

Fungus Gnats live for up to three weeks and during that time they will lay up to 200 eggs in the top 2-3 inches of growing medium.  Old soil, peat, compost or leaf detritus on the soil surface are most likely to attract them as they like damp decomposing matter.

Getting rid of them is complex.  Luckily they tend to remain close to the plants they are laying eggs around.  If a pot is bumped, they will probably fly away but land close by.  You must diligently remove both the flying adults and larvae during a period of three weeks or more.

When bringing any plant into the house, gently pull the root ball from the pot onto a newspaper.  Laying it on its side, let it dry as much as possible without the plant wilting.  Check for flying insects and sprinkle the root ball sides generously with Diatomaceous Earth before replacing it in the cleaned pot.  If the plant needs repotted, now may be the best time. Top off the soil level with at least half an inch of well washed and dried sand to prevent the adults from laying eggs and to prevent the larvae climbing up out of the soil. Do not overwater or leave sources of water near the plant.  Place the plant in a location away from other plants for a couple of weeks.

There is usually no need for serious chemicals or sprays as some simple organics will do the job.  BT Dunks or Bits, “Bacillus thuringiensis, added to your watering can will treat all soil parts as you simply maintain your houseplants.  Just tuck some into a tea ball or piece of fine netting to slowly add their bacteria to the water without allowing the larger particles to clog the spout of your watering can. Since Fungus Gnats can be a year round problem, continuous treatment is a good idea.

Watch the corner of nearby windows for evidence of Fungus Gnats.  They will also breed and emerge from damp cracks around your kitchen sink or in the bathroom. Sticky yellow cards can be cut into small shapes to fit in and around plants to track and deter Fungus Gnats.

In addition to Fungus Gnats, a couple of other small pests can cause confusion because their size and color is very close.

Fruit Flies can also appear at any time of the year, particularly in the summer and fall during canning season.  Washing all fruit and veggies as they come into the house will remove eggs.  Placing a small shallow cup of vinegar or fruit juice into a Baggie and poking a few small holes will lure them to their deaths. Leave this beside a small night light when you go to bed. This past summer, I had a hoard of Fruit Flies, the likes of which was beyond belief and which lasted for months despite our best efforts.  It turned out that an electronic badminton racket not only killed zillions, but provided us with some exercise and entertainment.  The final cure was to add a long narrow attachment to the vacuum and clean up all I could several times a day.  I actually counted as I cleaned them up and my husband never failed to ask for a report of the day. We never found the actual source.  After a few weeks of using every trick we could, the days came when I was hard pressed to find any to dispatch.  It was almost disappointing!

Last but not least are Drain Flies.  They look like fruit flies with larger, more rounded wings.  You will generally find them relatively close to any drain that has accumulated the gelatinous slime that every drain boasts.  A simple cleaning with a drain cleaner works great.  Other treatments may include bleach solutions or boiling water added frequently, but all treatments could prove dangerous and need to be used with great care.

 

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Certified Master Gardeners are local volunteers trained by Penn State to answer Horticulture questions with properly researched information. For a “best practices” answer to your question, call Penn State Jefferson County Extension to leave a message at 849-7361, Ext 508, e-mail cjs5618@psu.edu, or mail your question to 186 Main Street, Suite 3, Brookville, PA 15825. 

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