Question
Thank you so much!

P.S Someone else mentioned to me that I could water the plants once with rubbing alcohol and that this would kill the bugs without damaging the roots. What do you think about this?

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Followup To

Question -
Hi there,
My question is regarding the identification of a plant pest. I have several houseplants, many of them succulents, and have recently noticed a few of them (succulents and tropical type leafy hangers) showing signs of what I thought was too much moisture. This diagnosis made some sense at first due to my area抯 lack of sun for a few weeks (arriving just after a good watering). The recent fate of my 揗oon Cactus?also seemed to fit these lines: the 搒tem?or green base of the plant rotted from the bottom up as if eaten from the inside.  However, after noticing in other plants more of this 搑otting from the base of the plant outward,?a closer inspection detected very small, black fly-like bugs crawling around in the soil (I didn抰 see any fly).  They seemed to go reasonably deep, though I抦 not sure if they were attacking the roots directly.  Most of the plants affected share the same window (the same as the 揗oon Cactus? though not all of the plants in the same space seem to be affected. There is one African Violet in another room which is affected but it抯 neighbor (a succulent) is not. This neighbor is of the same species as one of the other unaffected plants from the first window.  In each case too much moisture seems to have at least made the plant more vulnerable. Also, it is possible that this pest was first introduced by potted herbs brought from an outdoor market. Any help that you can give me in identifying and eradicating these bugs would be greatly appreciated!  I love my plants匢抦 new to plant care, but I抳e had some of these guys for three years now and this new disease is devastating!  Thank you.

Ps. I抳e recently had a problem with fruit flies. Since the bugs seem to be in all of the dampest plants, do you think that these bugs might be young fruit flies?


Answer -
Hi Arielle,

Apparently you have an infestation of fungus gnats. The gnats themselves rarely cause damage to the plants, but the same conditions that are conducive to fungus gnats (wet soil) is also a contributor to root and stem rot. It is the wet condition of the soil not the gnats that is damaging your plants.

Adult fungus gnats fly around and are an annoyance, but they are not harmful to people. Each gnat lives for about 5 days. The trick is to get rid of the next generation ?the nearly invisible gnat larvae that live in the top layer of the soil. The larvae feed on decaying organic matter. Decaying pine bark in potting mixes and decaying plants roots feed the larvae.

Try to keep the soil as dry as possible. Remove all loose soil from the surface and put a light layer of coarse coir (coconut husk) or sand or diatomaceous earth on the soil surface. These substances have sharp edges that carve up the larvae. (Recent studies indicate that fine-textured peat moss also deters gnat larvae.)

Another safe technique is to place ?inch slices of raw potato on the surface of the soil to attract the larvae. After a day or so, discard the slices along with the larvae inside. Repeat this until there are no more larvae in the potato.

For more serious infestations try Knock-Out Gnats to treat fungus gnats available from Gardens Alive for about $20. See

http://www.gardensalive.com/item_display.asp?ProductNumber=1962.

Another bio-control method is Gnat Not, a parasite that destroys gnat larvae and other soil pests. It comes on a sponge in plastic (5 weeks shelf life) that is rinsed into water and applied to the soil. For information, go to http://www.goodbug-shop.com/gnatnot.htm

Detection trick: Add a little water to the soil and then look very closely for tiny fungus gnat larvae swimming in the water as it pools on the surface. You need good light and good eyes to see them. If you don't, then your plant is probably gnat free.

Prevention is often the best remedy. Use sterile potting mixes that are free of bark chips. The potting mix should have ample drainage material, such as perlite so that it drains well and allows the soil to dry out frequently. Fungus gnats can nearly always be traced back to overwatering and/or poor soil quality.

Please let me know if any of this is unclear or if you have any additional questions.
  
Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

Visit my web site at www.HorticulturalHelp.com

If this information has been helpful, please remember to give me a rating and nomination.  

Answer
Hi Arielle,

While it is true that the alcohol would probably not damage the roots, it is NOT true that the alcohol would effectively treat the fungus gnat larvae. The person who offered that advice is confusing the alcohol treatment for mealybugs with the treatment for fungus gnats.

Please let me know if any of this is unclear or if you have any additional questions.
   
Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

Visit my web site at www.HorticulturalHelp.com

If this information has been helpful, please remember to give me a rating and nomination.