know that this will kill any beneficial microbes in organic soil
but yes, it's an option
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Exactly why i was so hesitant in the first place to try this. I couldnt believe such extensive article on h2o2 hadnt even mentioned killing the bennies. But after the treatment i used compost tea and molasses to rejuvenate a healthy microorganism population. The pyrethrum works pretty well and the lady at the gardening shop says the larva are usually content chewing on organic material in soil and only in infestations will they go for roots. Plus im sure they love the molasses so as long as things go as they are now im content to coexist.
But the satisfaction i would have had taking the hose to those buggers would have been too much! Did you actually see larva? I'm having trouble distinguishing larva from other little guys. Anyone know if the larva jump around at all?
I've seen several references to cinnamon as a remedy (like this), and the reports on it seem to be about as positive as anything else. It's surprising how there's so little solid information on what does or doesn't work on this scourge.
I haven't found any insecticides to work in the past, except one: the Raid foggers that come in small orange cans. Those wiped out the exposed flies, but of course didn't kill the batch gestating in the dirt. I've sprayed regular Raid (don't remember which formula) directly into the dirt and it didn't even kill the adults.
I also read that the flies won't tolerate swiftly moving air, so I put all of my plants in front of a fan that was aimed down at them on high speed for about a week straight. Worthless; still had flies galore. Then again, this wasn't a conclusive study if the gestation period is up to two weeks.
i would avoid anything like raid, if it seeped into your soil in the next watering that would do much more damage to your roots than the larva. working with cabinets ive noticed that a lot look to be dying of thirst, after i water there are maybe 75 gnats in the drainage bowl drowning in the run off. i think when the adults can no longer feed on the sap from foliage (due to pyrethrum spray once a week) they dehydrate so long as water is not around and the set up is kept tidy. the sticky traps are your best friend, i have 2 in each cabinet clamped with the lights and they caught near 800 in 6 weeks. no visible damage to plants at these concentrations of gnats either. the main thing that pisses me off about them is with no fail they always find their way into my morning cup of coffee. every damn time.
Since I was freshly potting these plants I decided to do the cinnamon test. I bought two big-ass containers of cinnamon from Costco, stripped the top couple of inches of dirt out of three of the four pots (the last pot wasn't even full yet), and mixed the dirt and a significant amount of cinnamon in a bucket. I then re-applied the dirt, carefully creating an even layer that totally covers the underlying soil. In the last plant, the entire top half of the soil is cinnamon-infused, including a lot that's in direct contact with many of the roots.
I had already watered each of the plants, and didn't do so again.
I had some cinnamon dirt left over, so I applied it to the two other small plants I have in the house.
It has only been a week, and so far so good. I wasn't willing to make this truly scientific and have a control plant with no cinnamon, because I don't want to give these flies a foothold at all if I can help it.
I also found that after being reapplied, the looser cinnamon-infused dirt dried out pretty quickly. This will also deter the gnats, and further muddy the results of the experiment. I'll keep you peeps apprised as time goes on.
Edited by Stokestack, 19 July 2013 - 12:02 AM.
I have discovered a much less expensive method of trapping Fungus Gnats than those yellow sticky tapes. When my spouse buys fish from the market it comes in white styrofoam trays. Simply fill these white trays with about 1/2 inch of water, tap in a few drops of yellow food coloring, stir and place amongst the plants. When the little F#%@&#S land on the surface, not being seagulls they are unable to take off again. Works as well as sticky tapes or better (larger surface area) at virtually no cost. Then once a day I dump the water refill with fresh, a couple good drops of food coloring and your set. I replace daily to judge how well the control is working. The humidity increase ia a helpful bonus.
Edited by Langalier, 22 September 2013 - 09:20 PM.
I've put the yellow sticky cards in each pot, and they've been of little to no use. Even the most infested plant doesn't have all that many gnats on the card after two or three weeks.
The cinnamon I mixed with the dirt doesn't seem to have been effective either.
So I ordered Gnatrol. The definitive move would be to soak the dirt with the Gnatrol solution to kill larvae, then haul the plants into a bathroom and set off a fogger to kill the adults. I'll keep you posted.
So thankful for everyone's input on this problem! I am still infested though, and they are positively RELENTLESS!!! I suddenly have an influx of them, even though I've got my apple cider vinegar traps that catch MANY (besides the fact that I literally derive JOY out of killing the little F*%#ERS and do it over and over and over again)!! UGH!!!! I realize I am on a grower site (cuz you guys have the best input I've found so far on this topic), but I have ZERO plants growing in my house, NOR do I have rotten fruit, vegetables, or ANY food or dirty dishes or old garbage sitting out! We live in an apartment and have been plaqued with these bastards since we moved in~~I've never seen anything like it! Sure, they came and sprayed, but they are NOT addressing the situation, so I'm basically screwed. (I've come to believe that they come from deep within the sewer system, or some rotting place in the floor somewhere which is completely undetectable, or the vents posibly...who knows?!) I've tried incessantly to pinpoint exactly where they come from, but they are everywhere, not just one place!!! I mean, it's quite literally like Chinese torture sometimes! I've tried pouring copious amounts of boiling water down all the drains (I don't use bleach or any harsh chemicals), but to no avail. Besides, even though the sewage system is one of my theories, I never ever actually see them hanging around the drains! MAN this has been frustrating!!! Just letting you guys know in case anyone at all might have further input on these demons from hell. I guess I should just be thankful that they do not bite, but omg, I am OVER THEM!!!
They still lived when I watered with a diluted h2o2 mix but I talked to my local garden store and what they said led me to believe that these are more of a nuisance than anything. I don't think they cause much damage, I had them throughout the grow last time and still enjoyed nice results, aside from all the gnats i had to pick off the buds since they get stuck to the trichs.
I found this article on the web and thought it should be posted here on the City since many people ask about these little pests.
Summary: A subtly dangerous pest that can attack your plants, causing serious, permanent damage with few external symptoms!
Scientific name: Bradysia coprophila (family Sciaridae, order Diptera)
Size: 3-4mm (1/8")
Description: Slender, grey or black body; one pair of clear, unveined wings. Long legs and a tendency to fly aimlessly around, alighting occasionally on the leaves of plants.
Like many insects, fungus gnats develop through metamorphosis. They start out as larvae in the top layers of soil, develop into pupae and thence into the winged, flying adult. Total developmental time to adulthood is 2-4 weeks. During the larval stage they feed on fungi in the soil as well as decaying organic matter and plant roots. Once they reach adulthood, fungus gnats typically last just long enough to seed a new generation of larvae.
Why should I care?
These little suckers are not your friends. If you grow houseplants or any kind of potted plant, fungus gnats can become a major problem very quickly. This is because the larvae, when they run out of fungus in the soil, will start to nibble at your plants' roots! While it would take a very large developing population of gnat larvae to completely destroy a plant in this way, the gnats' feasting can seriously stunt your plant's growth, causing discoloration in the foliage and malformed branches and limbs. The larvae may also aid in the spread of plant diseases with scary-sounding names, such as: Pythium, Verticillium, Cylindrocladium, and Scelerotinia.
Fungus gnats are particularly troublesome because the larvae prefer an organic growth medium. They can actually cause more harm to potted plants grown in sterilized potting soil than to plants grown in the ground! They also thrive in moist environments, meaning that overwatered houseplants are a prime breeding ground.
Marijuana cultivators particularly need to be on the lookout for fungus gnats, as the larvae, in addition to attacking the roots of your precious ganja plants, will leave behind casings that quickly ruin the drainage properties of your soil. Cannabis requires good drainage and a steady but small supply of water, so an overwatered marijuana plant that falls victim to a fungus gnat colony has two strikes against it. If an infestation occurs during the flowering stage of the plant's growth, it could seriously reduce yield.
How do I detect them?
Like most tiny flying critters, fungus gnats have an irrational attraction to the color yellow. Purchase some yellow sticky cards from a garden center; yellow sticky tape works equally well. Place the sticky cards near your plants for a few days and observe what gets caught on it. If you see more than a few gnats, there are most likely larvae in your soil.
Once you've spotted a likely infestation, cut a slice of potato of about one square inch, and 1/4 to 1/2 inch thick. Place it on the soil in your plant's pot and wait 4-8 hours. Fungus gnat larvae really love a good snack of potato. Remove the potato and count the number of larvae that have moved onto it; this will give you a good idea of how big an infestation you're dealing with.
How do I get rid of them?
Getting rid of the adults is a snap: simply give them a sticky yellow surface to land on, and within a few days you'll have enough dead adults to make a tasty dinner of gnat casserole (YMMV). The larvae are a bit trickier. The first step toward getting rid of them is to starve your plant of water for a few days, letting the top layers of soil dry completely. Larvae cannot develop in dry soil, though they can survive a drought by suspending their development. Don't worry about killing your plant; it takes serious dedication to kill most houseplants from underwatering, while overwatering a plant can kill it very quickly.
Once the soil is dry, mix 1 part hydrogen peroxide (H2O2) solution with 4 parts water. Use 3% solution, which you can find in any drug store or in the hygiene/medicine aisle of a chain grocery store. You can use a stronger solution if you change the water mixture appropriately, and don't be too concerned with proportions; it would take a very high concentration of H2O2 to hurt your plants. Just make sure you buy pure H2O2 with no chemical additives! Hydrogen peroxide is often sold as a topical disinfectant, and things that are good for your wounds may not be so healthy for your plants.
Water your plants as you normally would, using the hydrogen peroxide solution and taking care to get good coverage of the entire top layer of soil. Use a spray bottle if desired. The soil will fizz for a few minutes after application; this is natural. The gnat larvae die on contact with the H2O2. After a few minutes the fizzing stops and the H2O2 breaks down into oxygen molecules (which your plants don't mind) and water molecules (which your plants love).
Congratulations! You've just successfully treated your fungus gnat infestation. Monitor the gnat population for a few days with sticky cards, in order to make sure you've got them all. Make sure not to overwater, and consider sometimes adding a little hydrogen peroxide to your daily waterings--in my experience, the plants react well to this little treat. Watch your plants grow big and strong and enjoy the fruits of your labors, whether they be flowers, vegetables, literal fruits, or big sticky nugs of homegrown chronic.
"simply give them a sticky yellow surface to land on, and within a few days you'll have enough dead adults to make a tasty dinner of gnat casserole"
OK, that has not turned out to be true or useful.
And didn't someone try the hydrogen peroxide and found it to be ineffective?
The most recent thing I've tried is sand. I covered the entire surface of the dirt with a half-inch of beach sand, and so far it has been pretty effective. The challenge is watering the plant without exposing the underlying dirt; I need a gentler way to pour the water over the sand to it doesn't push the sand aside and stir up dirt.
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