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How To Kill Fungus Gnats With Hydrogen Peroxide

Discussion in 'Sick Plants and Problems' started by Reverend Bud, Feb 5, 2010.

  1. 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.

    by Xeger

    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.

    Attached Files:

  2. does tht seriously work?
  3. very useful information Reverend bud..thx again
  4. #4 shurbuzzd, Feb 8, 2010
    Last edited by a moderator: Feb 8, 2010
    This sound like the problem I'm having. I tried to stert some seeds in leftover potting soil and I nudged a seed to see if it was starting to sprout. It rolled over and what I thought may have been root was actully some sort of larvae. It shruk back into the soil and did the same on the seed which was cracked open.
    From now on I'll germinate in a Ziplock with rockwool cubes. And definitely use the solution to get rid of the Critters.
  5. I plan on using some Epsoma organic potting soil in the next week or two and i have noticed fungus gnats in the bag. What can I do to get rid of them before i plant my seedlings and then transplant to bigger pots? Can I zap the soil in the microwave? Or do i mix my soil with perlite, let it dry out, and then pour in hydrogenperoxide and water before planting?
  6. Hi Rev,

    Some rep may be coming your way soon!

    I just now found a 80 lb bag of sand in the garage, lugged it to my grow area and filled a 5 gallon bucket with it, in preparation for a task I have been putting off for a couple of weeks. As soon as the lights come on (in another hour), I had planned on topping all of my potted plants with a 1/2 inch or so of this sand to kill off the fungus gnat population.

    Over a month ago, I had rescued a few over-nuted plants by flushing and then giving each a quarter cup of blood meal. Apparently, that's like a dinner bell for fungus gnats!

    I've been dreading this task for a few reasons - I have 20+ pots to treat, I hate the idea of sand all over my grow area floor, and I'm concerned about adding organic nutes when I water (will the sand trap the good stuff like a filter?). Plus I think it might get ugly when I go to transplant the ones in the smaller pots into larger pots.

    So while waiting for my indoor sunrise, I found this thread. If the H2O2 will work once and for all to end this critter problem, all the down sides that come with the sand treatment go away.

    It'll probably be another week before my LED plants get as dry as you describe, so I won't know right away. So look for rep from from me in a couple of weeks! I'll update this post with the results a week after all my plants have been treated.

    Thanks in advance for your post!
  7. great tips in that post. Thanks Rev.:):smoking:
  8. Great Thread...Thanks. I would + rep you but I don't know how....:D
  9. OK, Rev. I went ahead and gave you some rep, although I'm not sure my fungus gnat problem is resolved. Probably my fault for not giving it a whole-hearted effort.

    I bought two quarts of H2O2 and put that in 2 gallons of water. I should have used 3 times that much, so I didn't really give a "normal" watering and I only hit my flowering room, since that's where the problem really is - although there are a few flying around the veg area too.

    I did this yesterday, and added water today because my HID plants were dry again. I could still see a lot of adults flying around, but also infants of all sizes crawling all over the soil.

    I'll give it a week, but I fully expect that I have not eradicated them In that case, I will go ahead with the sand treatment.

    Still, I appreciate the post.
  10. I used this eradicating formula last evening on my Gnats and will report back when I have the outcome...Thanks + Rep

    P.S. - I have tried Neem Oil and it seemed to work at first then the gnats came back in full force.

  11. Okay...after further research I have this to contribute...I found this on another web forum. Hope this helps as I feel much better about using this method last evening.

    Hydrogen Peroxide (H2O2) is a clear sharp smelling substance very similar in appearance to water (H2O). Like water it is made up of Hydrogen (H2) and Oxygen (O2), however H2O2 has an extra Oxygen atom in an unstable arrangement. It is this extra atom that gives H2O2 its useful properties. H2O2 has been used for many purposes including cleaning, bleaching, sterilizing, rocket fuel, animal feed treatment and in addition many miraculous claims about its health benefits have been made. This article isn't about any of these; instead it will concentrate on horticultural applications. H2O2 is of great use for both hydroponics and dirt/soilless gardening.

    What Does Hydrogen Peroxide do?
    H2O2 is an unstable molecule, when it breaks down a single oxygen atom and a molecule of water is released. This oxygen atom is extremely reactive and will attach itself to either another O- atom forming a stable Oxygen molecule or attack a nearby organic molecule. Both the stable and O- forms will increase the level of dissolved oxygen. This is the method by which H2O2 is beneficial. Pre treating the water supply with H2O2will drive out the Chlorine many cities use to sterilize it. This will also degrade any pesticides or herbicides that might be present as well as any other organic matter. Well water can be high in methane and organic sulfates, both of which H2O2 will remove. Many disease causing organisms and spores are killed by Oxygen, the free Oxygen H2O2 releases is extremely effective at this. H2O2 will help eliminate existing infections and will help prevent future ones. It is also useful for suppressing algae growth. The free Oxygen atom will destroy dead organic material (i.e, leaves roots) in the system preventing them from rotting and spreading diseases.

    Over Watering
    Roots require Oxygen to breathe and low levels are the main cause of almost all root diseases. Both soil and hydroponic plants often fall prey to the same syndrome although it is rarely recognized as what it really is. Hydroponic crops often fail due to "root rot" and soil crops succumb to "over watering." The real cause of both these problems is a shortage of Oxygen at the root zone. In a soil system the soil consists of particles, a film of water on the particles and air spaces between the particles. When too much water is put into the soil the air spaces fill with liquid. The roots will quickly use up what Oxygen is dissolved in the water, if they haven't drunk enough of the liquid to allow air back in to the soil spaces they will stop working. In this situation roots will start dying within twenty-four hours. As the roots die the plants ability to drink water and nutrients will decrease, this will cause symptoms of nutrient deficiencies (mostly pale, slow, weak growth), and strangely they will start to wilt like they don't have enough water. It is easy to make a fatal mistake at this point and add more water.

    In a Hydroponic system the cause is a more direct simple lack of oxygen in the solution; this may be from inadequate circulation and/or aeration. High reservoir temperatures also interfere with Oxygen's ability to dissolve in the water. Temperatures above 70F (20C) will eventually cause problems, 62F-65F (16C-18C) is recommended. The same symptoms will appear as with soil plants but you can also check the roots. Healthy roots should be mostly white with maybe a slight yellowish tan tinge. If they are a brownish color with dead tips or they easily pull away there is at least the beginning of a serious problem. An organic, ‘dirt like' rotting smell means there is already a very good chance it is too late. As roots die and rot they eat Oxygen out of the water, as Oxygen levels are even further depleted more roots die, a viscous circle may be well under way. Reduced Oxygen levels and high temperatures both encourage anaerobic bacteria and fungi. The plants may still be saved but you will have to work fast.

    How Hydrogen Peroxide prevents root rot/over watering.
    When plants are watered with H2O2 it will break down and release Oxygen into the area around the roots. This helps stop the Oxygen from being depleted in the water filled air spaces until air can get back into them. High Oxygen levels at the roots will encourage rapid healthy root growth. In a Hydroponic system H2O2 will disperse through out the system and raise Oxygen levels as it breaks down. Strong white healthy roots with lots of fuzzy new growth will be visible. This fuzzy growth has massive surface area allowing for rapid absorption of the huge amounts of water and nutrients needed for rapid top growth. A healthy plant starts with a healthy root system.

    How to use it.
    H2O2 comes in several different strengths 3%, 5%, 8% and 35%, also sold as food grade Hydrogen Peroxide. The most economical is 35% which we recommend be diluted to three percent before using, as at this high concentration it can cause damage to skin and clothing. When working with food grade H2O2 it is very important that you clean up any spills or splashes immediately, it will damage almost anything very quickly. This is extra important with skin and clothing. Skin will be temporarily bleached pure white if not washed cleaned. Gloves are strongly recommended when working with any strong chemical.

    Food grade H2O2 can be diluted to three percent by mixing it one part to eleven parts water (preferably distilled). The storage container should be opaque to prevent light from getting in and it must be able to hold some pressure. If three-liter pop bottles are available in your area they are ideal for mixing and storing H2O2. There are twelve quarter liters (250ml) in three liters, if you put in one quarter liter H2O2 and eleven quarter liters (250ml) water in the bottle it will full of three percent H2O2 and the bottle can hold the pressure that the H2O2 will generate. Three percent Hydrogen Peroxide may be added at up to three ml's per liter (2 1\2 tsp. Per gallon), but it is recommended that you start at a lower concentration and increase to full strength over a few weeks. Use every watering even on fresh cuttings. For hydroponics use every reservoir change and replace twenty-five percent (one quarter) every day. Example: In a 100L reservoir you would add three hundred ml's (3%) H2O2when changing the nutrient. You would then add seventy-five ml's more every day.

    Where to get it.
    35% food grade: called food grade because it has no toxic impurities. Of course your local hydroponics retailer, whom you can locate over the web.(there may be shipping restrictions on high strength peroxides). The local feed supplier may have it in small towns. Prices range from fifteen dollars per quarter liter to eighty dollars a gallon. One gallon will treat up to fifty thousand liters of water.

    3%5%, 8% Can be found at most drugstores or pharmacies, prices start at a less than a dollar for a one hundred-ml bottle that will treat one hundred liters.

    What to do if you already have root rot.

    In Dirt:
    Use peroxide water with an anti-fungicide and a high Phosphate fertilizer (9-45-15, 10-52-10, 0-60-0) for root growth. Or any other product with rooting hormone dissolved in it is helpful in regrowing roots and is strongly recommended. Water heavily until liquid pours out the bottom of the pot. This sound like bad idea, but it flushes out stagnant dead water and replaces it with fresh highly oxygenated water. Don't let plants sit in trays full of water, the soil will absorb this water and stay too wet. Don't water again until the pot feels light and the top inch or two of the soil are dry.

    In Hydro:
    Change your nutrients. Add H2O2 to the system. This will add oxygen and chemically eat dead roots. If roots are badly rotted and can be pulled away by hand you should pull them off. They are already dead and will only rot, causing further problems. Add a fungicide to kill any fungus that is probably present in the rotted tissue to prevent it from spreading. Increase aeration of the water, get an air pump and air stones, or more of them, for the reservoir. An air stone under every plant is usually very effective, but will require a larger air pump. Models that will do from forty to four hundred stones are available. Decrease the reservoir temperature, oxygen dissolves better in cold water and disease causing organisms reproduce slower as well. A good temperate range is 62F to 65F; anything above 70F will eventually cause a problem. It is also a good idea to remove any wilty plants from the system and put them on a separate reservoir so they don't infect plants that are still healthy.

    The key to big productive plants is a big healthy root system and Hydrogen Peroxide is a great way to keep your roots healthy. It is a must to ensure the biggest best crops possible and to increase the chances of your plants thriving to harvest. Peroxide users will rarely lose plants or crops to root disease and will harvest larger and more consistent crops.
  12. Just applied this solution to the plants in my veg chamber. It sure seemed to piss them off judging by the large numbers that flew away.

    This is my firsst season growing organic and I was trying an organic soil mix from a local nursery and got these damn pests! I have them so bad, the trichs on my buds are catching them like fly paper. I am sacrificing all my lower buds, as they are just covered with gnats that got stuck to the buds. :mad:

    That's what's great about being human...we can learn from our mistakes. I am switching back to coir. Much more expensive, but no surprises like these bastards.

    Thanks for the help Rev. I'll post back in a couple of weeks and let you know how it's going. I'll be doing my budding plants tomorrow.
  13. Hey Doh,

    I tried the peroxide treatment and it only seemed to slow them down for a few days. Even the next day, I still saw itsy bitsy tiny baby ones crawling around in the soil.

    I continued to live with them for a few more weeks. Then I finally tried the sand treatment - covered the soil in every pot with about 1/2 inch of sand (maybe a little less than that). This really worked! Some gnats manage to hang around, but very few. It doesn't seem to be a problem with subseuqent feedings except that the water drains down a bit slower (I was worried about that). Transplants aren't a problem either because you can just dump the sand out first. It may only be a 95% fix, but I'm happy with the results and very glad I did it.
  14. Great info ! I'm loaded with gnats ! Washed the floor and pots with neem oil.
    Sprayed the lower stalks and dirt with neem oil.
    Tomorrow we do the sand and peroxide. What's the mix 5 to one ?
    This is our first grow. So being newbes didn't really notice and thought we had a nute problem. I will keep apprised on progress.
  15. Hi O.

    I suggest trying just the sand. It doesn't get rid of the gnats though. They will seem gone as long as all of your pots have a layer of sand covering the soil, but as soon as you add a pot without the sand, you'll start seeing them again.

    I find the sand is effective with even just a thin layer as long as it covers all of the soil. More sand is fine as well and stands up better to waterings. The effect of the sand is instant. Once there, the bugs can't get to the soil to lay larvae and the hatched larvae can get up through it to get out. By the next day, you'll think they're all gone.

    I haven't tried this yet, but diatomaceous earth (for aquarium use is better than the pool filter stuff) is recommended by The Rev of Skunk magazine. He says just sprinkle a little on the soil and water it in. It will actually schred the larvae!

    I'm not good about keeping sand on all of my pots all of the time. The gnats are still present, but at a level that is definitely not an issue anymore. My next soil batch will include nematodes that will eat the larvae and feed their decomposing carcasses to the roots. I'm actually hoping to still have a decent level of them to feed the nematodes!

    Good luck, bro!
  16. stretch panty hose accross the top of the pots....
    this traps them, they cant fly away and therefore wont mature and lay more eggs...
    strectch it tight...

    another great addition to any garden is a hot shot pest strip...

    these two together will rid ur garden of those fookers
  17. Stretching Panty hose is the same concept as laying sand on top of your medium, i currently am having a problem with fungus gnat larvae and i took Freakbro's advice by putting 1/4-1/2 inch of CLEAN sand on top. This will also not allow the adults to get to the soil to lay their eggs, aswell as the larvae being able to come up through the sand. Also, I'm depriving my baby of water for a couple days to let the medium dry out somewhat, this is also suppose to help rid the population. I've also replace the top 2 inches of my soil. Do NOT use diatomaceous earth this is for COLONY INSECTS and you need to use a respirator while using it! diatomaceous earth kills the larvae physically not chemically, don't use it. Sharp-grained PEAT MOSS can be dry and you can throw it on top of your soil to also shred the fuckers up. the larvae are the problem, the adults are easy to get rid of, just use a yellow pest strip and you'll have enough gnats to make a damn sandwhich with em'. It takes about 2 weeks for the larvae to develop into pupae, then 1 week from pupae to the winged flying adult Fungas Gnat! Hope this information helped.
  18. Excellent info, Father...

    Not only will it kill the bastards, but it will also ensure plants stay Root-Rot free !!!
    + rep to you for the research, dude.

  19. Thats a hella kick-ass sig dude. I love it !!!
    True wordz of wizdom...

  20. I bought some NilNat..i have a shit load of those flies in an aeroponic system feasting at my roots..i wiped down my system of any dirtiness and the next day had like 2000 of them dead on the system.

    i hope its working and its not just some huge infestation..

    Nil Nat

    it wasn't 75 bucks..but this is an online add for it.

    and here is my system.

    My Aero System

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