Help with gnats / larvae in my plant!

labeano2002January 8, 2009

I recently repotted my wandering jew a few months ago with some new soil. when i opened the bag of soil i noted one fruit fly escape from the bag - no big deal i thought - recently i've been seeing more and more of these flies. i kill at least five everyday but i can't seem to kill all of them. i tried making a bowl trap with banana peel and fruit juice - i caught two or three but that was it. this morning i was checking the leaves and killing the flies that were on my plant when i looked at the soil - i noticed that there are very small larvae in my soil. i don't know how to effective get rid of all of these pests. i'm only assuming these are fruit flies because that's what they look like - i've never had a problem like this with any of my other plants. please help!

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frazzledgessie(5)

I had something very similar happen to me last year. I had bought a bag of miracle grow house plant soil and there were these little "eggs" for lack of a better understanding. I had a pretty bad problem with fungus gnats. I used the yellow sticky cards and watered less and that helped, but they were still all over the place. I have since repotted everything using different soil that I mix and have not had any problems with gnats. Is that the same brand of soil that you are using?

    Bookmark   January 8, 2009 at 9:54AM
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jefe12234(4a MN)

The larvae feed on decaying organic material in the soil. Most potting soils consist primarily of peat which holds a lot of moisture and decomposes relatively quickly. This waterlogged organic soil gives the larvae everything they need to multiply. Using a largely inorganic soil with lots of coarse drainage material will reduce both the food and moisture needed by the larvae. It's also much healthier for the root system, but will require more frequent watering. When I switched my plants over to a mixture of pine bark and various gritty inorganic materials, the fungus gnats virtually disappeared. I see an occasional one every so often, but no more swarms of them.

    Bookmark   January 8, 2009 at 1:07PM
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meyermike_1micha(5)

I DITTO that jefe12234!

    Bookmark   January 8, 2009 at 6:49PM
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labeano2002

yes - i used miracle grow. i've never mixed my own soil before - i think i will repot and try that

    Bookmark   January 9, 2009 at 8:38AM
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nicole__(z5Colorado)

I put a layer of chemical garden bug killer on top of the soil, mix it in a little and within 2 weeks .....ZAP....no more flies, or knats!!!! Try to get one without diazon so it doesn't have an odor and keep away from pets.

    Bookmark   January 9, 2009 at 9:37AM
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meyermike_1micha(5)

Chemicals indoors...That is a no no....:-)

    Bookmark   January 9, 2009 at 1:26PM
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jeannie7

All this blame for what is a common problem....and one that -- when you stop and think about it....cannot be solved easily.....so why try.

The gnats come from out of doors...then come indoors---why...because that's where the food is.

Blaming a potting soil....even blaming a specific brand named potting soil is not going to solve your problem.
If your gnats disappeared when you did something, its because the gnats were disappearing on their own.

You can lay traps, you can suck them up, you can deny them food, you can water less.......and you'll still have gnats...just not in numbers....that is, until a new cycle of them arrives from the eggs and larvae that is in the soil.

Unless the infestation is driving you out of house, I suggest you take normal steps to reduce their numbers and not lose sleep over them.

    Bookmark   January 10, 2009 at 8:04PM
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birdsnblooms

Lab, what brand of soil did you buy? House plant soil is 'supposed' to be sterilized. Let's hope it is. I use a mixture of soil (different brands)/and soil-less mediums, so far, over 20 yrs, the only insects found in these soils were milipedes.
Was your soil ever outside during warm weather? It doesn't matter if the bag was sealed...more often than not, bags have teeny-tiny holes. All it takes is one pregnant insect and voila, a home and family! Or a weed seed to sprout. Especially if it was exposed to water/rain, hosing, etc.

A friend bought a bag of Hyponex..the soil was so heavy she had to hammer to break it up..She contacted Hyponex company..they sent her coupons, including a couple free bags..lol..Toni

I used to bake soil..250 for 45 mins..But I must warn you, the soil stinks while baking..lol.But by baking, weed seed and insect/eggs die. Weed seeds will not germinate..

    Bookmark   January 10, 2009 at 8:51PM
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jefe12234(4a MN)

"All this blame for what is a common problem....and one that -- when you stop and think about it....cannot be solved easily.....so why try."

This problem has been solved by myself and many others. The difference is quite obvious to anyone who has tried both peat based soils and the gritty soil mentioned above. If you don't want to change your practices, then don't. But don't dissuade someone from a proven solution, especially when you haven't tried it yourself.

    Bookmark   January 10, 2009 at 9:37PM
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tapla (mid-MI z5b-6a)

Labeano - the initial advice that Jefe gave is good advice. His comment immediately above is also spot on. If you use a soil that is well aerated and primarily composed of ingredients that don't break down quickly (pine bark, Turface, crushed granite, perlite, pumice ....., it will be very difficult to over-water, a primary reason for gnat infestations. In addition, the slow decomposition of the organic component (pine bark) is unlikely to support much in the way of gnat numbers unless you work very hard at over-watering. A high % of fine organic components in the soil, especially those that decompose quickly, and organic fertilizers like fish/seaweed emulsion can also cause an explosion in soil borne pest populations (promotes algae growth, too).

Mike also makes a good point. I would consider very carefully whether it is wise to use a "chemical garden bug killer on top of the soil", as was intimated upthread. It's probably best to accurately identify the actual pest, and then use the least offensive remedy that includes your pest in its net of effectiveness to bring the numbers of pests back to an acceptable level, or eliminate them. There are MANY chemicals that are used in outdoor applications that are wholly unsuited to, and too dangerous for, indoor use.

Al

    Bookmark   January 10, 2009 at 11:23PM
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