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Indoor Pest Problem

Posted by redthreaddiy 6 (My Page) on
Sat, Jan 1, 11 at 17:32

I brought in some plants that weren't hardy through the winter a few months ago. I brought in several pests along with them. Unfortunately, I can't correct my first mistake, so now, how do I get rid of them? They are little black bugs with wings - kinda like fruit flies. I see them crawling around in the soil and hanging out on the actual plants. They are in our Florida room, but seem to keep multiplying. gross! There are far too many plants that I don't want to lose, so how do I keep the plants but get rid of the bugs? I have been spraying malathion but it doesn't seem to do much. Thanks!


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RE: Indoor Pest Problem

  • Posted by morz8 Z8 Wa coast (My Page) on
    Sat, Jan 1, 11 at 19:30

Crawling around in the soil and black fruit fly types are surely fungus gnats. BTi (Bacillus thuringiensis subspecies Israelensis) can be safely used indoors (or anywhere safely). Use a BTi solution to water your plants on their normal schedule a few consecutive times and you will break the breeding cycle in approx 3 weeks, be rid of them.

"These persistent gnats live short, prolific lives. An adult fungus gnat lays up to 200 eggs during the one week it spends as an adult winged gnat. The adult then dies. Legless larvae hatch out in about four days. After two weeks of feeding, larvae spend about three to four days as pupae before emerging as the next generation of adults.

Most fungus gnats are merely annoying and cause relatively little damage to plants. But several species of fungus gnat larvae feed on roots, causing damage to African violets and other houseplants. Others burrow into stems and leaves. Fungus gnat-damaged plants may show signs of wilting. Gnat damage may weaken plants and make them susceptible to root rots."

None of my local nurseries carry BTi, I order online and have used both the liquid and granular forms. In a pinch, you can buy a card of mosquito dunks and float a dunk in a container of water over night, use that water to then water your plants. The dunks work, but don't give you the option of mixing stronger for heavy infestation, using less for light infestations but it's just a convenience thing.

Last time I ordered BTi, I bought Gnatrol granular (one brand name) here:

Here is a link that might be useful: Gnatrol - BTi


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RE: Indoor Pest Problem

Thanks so much - I will give your suggestions a try! I don't notice any damage to my plants and they are just very annoying. Thank you for all of your help!


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RE: Indoor Pest Problem

Fungus Gnats are common in house plants because most people are too diligent in watering and the soil the house plants are growing in is too moist for the plant but just right for these wee buggers to hatch and grow. While spending money on "stuff" can control them the simplest method is to allow the soil in the pot to dry between waterings, dry out to a depth of about 2 inches.

Here is a link that might be useful: Fungus Gnat control


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RE: Indoor Pest Problem

  • Posted by morz8 Z8 Wa coast (My Page) on
    Mon, Jan 3, 11 at 10:46

Kimser, that may work to help prevent, no so much help once you've got them established.

I've watched adult gnats fly down and crawl in and out of the drainage holes at the bottom of plant pots - they will lay eggs in any residual moisture not just pot tops.


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RE: Indoor Pest Problem

1/4 of a mosquito dunk per gallon of water should do the trick.

When growing tropical aroids (like I do) letting the soil dry this time of year is not an option unless I want them to go dormant.
When raising seedlings letting the soil dry could mean death.


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RE: Indoor Pest Problem

As the article from Colorado state says the easiest method of control is to allow the soil to dry out between waterings. About every article I have seen from about every horticulture school says the same thing, allow the soil in the pots to dry out between waterings.
The Fungus Gnat larva need a moist soil to hatch and grow in.


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RE: Indoor Pest Problem

Kimmsr, reading and following the advice of articles can be very helpful, even more so when the information in utilized in conjunction with real-life experience.

The situation with fungus gnats cannot be handled as simply as allowing the soil in the pots to dry out between waterings. One has to take into account the type of potting medium, the kind of plants, and other factors. Once established, fungus gnats seem to do quite well in potting mixes that are not overly moist, but NORMALLY moist.

Recommending Bt-I products is excellent advice. I would further suggest that the potting medium be amended in the future so that it is formulated with less with fine textured organic matter (peat moss) and a greater percentage of larger and/or inorganic particulates (perlite, granite grit, bark, etc.) I never have fungus gnats though I never allow a pot to dry out.


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RE: Indoor Pest Problem

Drying out does nothing for me. I am buying the Bt-I products and hoping for the best!


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RE: Indoor Pest Problem


The Fungus Gnat larva need a moist soil to hatch and grow in.

DOH! So do plants.


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RE: Indoor Pest Problem

It's important to know that using Bti will require 3 weeks to break the gnat's life cycle.


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RE: Indoor Pest Problem

Reading, and understanding, various articles published from reliable sources is a good way to learn. Those articles, along with real life experience that can support what is in those articles, can go a long way toward helping someone solve problems others have solved years ago. If numerous articles, from reliable sources, tell you the same thing more than likely the information is pretty good.
So if a large number of papers from respected horticulture schools say that allowing the top 2 inches of soil in a pot plagued by Fungus Gnats will break the life cycle of those pests it more then likely will. If one allows the top 2 inches of soil in a pot to dry out and finds that there are no more Fungus Gnats then that person would grasp that concept. What I have found over the years is that when this method fails it is because the person it failed on did not follow directions.


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