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Fungus Gnats AKA sciarid flies
Fungus gnats have four stages in their life cycle
Many of the controls mentioned below, will only control one or two of these life stages of the fungus gnat.
Most deal with just the larval stage, do not make the mistake of just dealing with the larvae as the adult fly will just come back and lays some more eggs!
Diatomacious Earth aka DE
Diatomacious Earth does have insect killing properties.
However only when dry!
Sprinkling it on top of you soil, isn't going to help because you need to water your plants.
Studies have shown that placing diatomaceous earth or sand on the substrate surface has little effect on fungus gnat adult emergence or inhibiting females from laying eggs because these physical barriers contain small openings that allow larvae to pupate, and adult females to lay eggs.
Cinnamon
Cinnamon is a a natural fungicicde
Some say, if you use it, to only use Ceylon Cinnamon and not Cassia.
However, I have read that some people have tried it but to little effect, whilst others say it does the job?.
I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.
If I am to advise using it, it first needs some verification, or no dice
Neem Oil
The chemicals isolated from neem can be categorized into two groups: isoprenoids and non-isoprenoids . Non-isoprenoids are amino acids, carbohydrates, flavonoids and others, while isoprenoids contain compounds such as azadirachtin. The most important compound in neem for pest control is azadirachtin, which approximates the shape and structure of hormones vital to the lives of insects. The bodies of insects absorb the neem compounds as if they were their real hormones, and this blocks their endocrine systems. The resulting deep-seated behavioral and physiological aberrations leave the insects so confused in brain and body that they cannot reproduce and their populations plummet. Additionally, their feeding cycle is interrupted. Therefore, azadirachtin acts to break the feeding and breeding cycle in many species of insects, including fungus gnats.
One quite amazing feature of neem is that it presents low toxicity to many beneficial insects which prey on plant pests. What this means is that neem can be used in conjunction with fungus gnat predators such as Steinernema feltiae[9]. In fact, studies have shown that a higher degree of control is exhibited when neem and predatory insects are applied together.
It is important to understand that neem doesn't provide the same level of control that spinosad does when used as a substrate drench for control of larvae.[10] However, when used correctly it will offer good control and reduce the Fungus Gnat population. Neem needs to be applied every 3 days as a drench. Additionally, spray the plants at the same time to target the adults, ensuring good coverage until run off. Pay particular attention to spraying the underside of leaves and spray thoroughly around the surface of the growing media where adult Fungus Gnats reside in large numbers. Always spray plants when the lights are off to avoid plant burning.
Most hydroponic stores stock neem oil under various brand names. Neem products can vary significantly in quality and purity. Speak to your hydroponic supplier and ask him/her about product options and recommended usage rates etc.
As a tip, neem can leave the final produce with a bitter taste if applied too close to harvest. For this reason, cease drenching and foliar feeding neem at least a week before harvest.
Neem Cake
Others recommend the use of neem cake amended coir substrates. However, while this can prove to be an effective method for controlling Fungus Gnats, while
the research is somewhat variable, several studies show that neem cake's active constituent azadirachtin potentially disrupts beneficial microflora (bennies) and enzyme activity in soils and substrates. Therefore, while offering effective control over Fungus Gnats, neem cake amended coir may not provide
a conducive environment for bennies such as Trichoderma spp. Other than this, the potential for azadirachtin to interrupt enzyme activity is not a good thing.
Another issue with neem cake is that it provides relatively high amounts of nutrients; i.e. neem cake contains more nitrogen (2-5%), phosphorus (0.5-1.0%), calcium (0.5 -3%), magnesium (0.3 - 1 %) and potassium (1-2 %) than farm yard manure or sewage sludge.Neem cake also provides varying levels of micronutrients. What this means is that while neem cake is a good source of fertilizer for organic growing, its use in hydroponics, where the nutrients supplied to the plants can be highly controlled through ppm of each nutrient species in solution, is less than ideal where hydroponic nutrients are used.
Coriander Oil - I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.
If I am to advise using it, it first needs some verification, or no dice
Penny Royal/Pepper Mint Oil - I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.If I am to advise using it, it first needs some verification, or no dice
There are steps to avoiding, controlling & killing fiungus Gnats
Hygene
Clean up dead leaves especially on the top of you soil in your pot, in saucers or fgravel trays etc
Places when, water will come into contact with the dead leaves, which will then start decaying and attract fungus gnats.
Pick dead leaves of the plant, they are already dead or dying and will end up falling of your plant and are a possible soure for mold & mildew, just what a gnat likes.
Overwatering
Over watering is often a cause of fungus gnats invading your grow space.
Cannabis like a wet/dry cycle and will perform it's best if grown this way!
The Dry part doesn't mean "totally dry" and the wet doesn't mean "waterloggged"!
Water your plant and get a feel how heavy the pot is, then when the pot is much lighter but still retains some moisture, water again,
A constantly moist top of your soil, will give fungus a nice place to live, which in turn gives the fungus gnats somewhere to live!
the gnats larvea will live in the top inch of your soil.
So soil management & hygene is one part of the solution.
The top of your soil can be dried out by using a fan and gently blowing air across i, this isn't really an eveysay occurance, it's more to dry the soil, once you have noticed you have gnats.
Lowering the ammount of contained water and waterlogging
Growing fabric pots, means the water in your soil goes a few ways, either out the bottom as run off, to the plant and then transpired or through evpaoration.
This mean you shouldn't have an overabundance of water in your pot.
Lightening your soil mix with perlite, will make it more airy, which is great for your plants roots but also alows your substrate to drain and regualate moisture better.
Airpots will do the same job!
Allow for a wet/dry cycle, it's the way cannabis likes it.
Mosqitio Dunks, Mosquito Bits & BT ( Bacillus thuringiensis israelensis)
Mosquito dunks
To use mosquito dunks: Fill up a gallon jug (or watering can) with clean water and toss in a mosquito dunk. ... Let the dunk soak in the water for as long as possible (at least overnight), then remove it from the water (the dunk can be reused) and use this water for fungus gnat–infested plants. Ph your water before using to warer your plant.
Mosquito Bits
To control fungus gnats, simply shake the granular Mosquito Bits onto the potting soil in houseplants and other container-grown plants. Mosquito Bits can also be mixed with potting soil prior to planting. ... After subsequent watering, the BTI (Bacillus thuringiensis israelensis) is washed below the soil surface. Fungus gnat larvae feed on the BTI ( Bacillus thuringiensis israelensis) and die.
How does Bacillus thuringiensis israelensis work?
How does Bti work? Bti spores that are eaten by mosquito larvae release toxins into the mosquito's gut, causing the larvae to stop eating and die. Bti is only effective against actively feeding larvae, and does not affect mosquito pupae or adults.
Alternatively
Yet others recommend the use of the bacterium Bacillus thuringiensis (BT). However, using BT and that of several studies sugests that, at best, BT offer only limited control and, at worst, are largely ineffective. One study that compared BT and predatory nematodes against the efficiency of pesticides concluded BT effectiveness would be reliant on the BT being applied before the Fungus Gnat populations build up and before overlapping generations develop. In another study (2011) that compared the efficiency of Steinernema feltiae, neem oil and BT to control fungus gnats the author concluded "that control with the nematode Steinernema feltiae was most successful, with an efficacy of 69-90% at 24°C air temperature. Azadirachtin (Neem-seed oil) could be an alternative under hot conditions (>28°C). Bacillus thuringiensis israelensis (BT), however, showed only a minor effect (1-51% efficacy)."
Nematodes
The Fungus Fly Killer nematode 50 million pack contains enough nematodes to treat an area up to 100 square metres or approximately up to 2000 2 litre pots. Ensure the compost is damp/moist before application.Mix the contents of the pack in 5 litres of water. Stir the contents. Take 0.5 litres of the concentrate and add to an 8 litre or 2-gallon watering can of clean water, and mix. Using a coarse rose, water into the compost. The concentrate can be used to fill up to 10 watering cans. A knapsack sprayer can also be used for the application.
Pathogenic nematodes (Steinernema feltiae)
Steinernema feltiae is more effective against fungus gnats than other commercially available nematode species. Mix Bti or nematodes with water, and apply as a soil drench, or spray onto media using a hand-pump spray bottle or other spray equipment, following label directions.
Formulations of nematodes may also be available in some plant centres.
These biocontrols are added to the potting compost where they will help control the eggs, larvae and pupal stages of the flies.
Do nematode soaks every 10 to 14 days until the problem is resolved.
Predatory nematodes such as S.feltiae can be used to effectively control Fungus Gnats. However, there is a caution here re hobbyist/novice indoor growers. That is, often fungus gnat populations aren't discovered by many growers until the population/infestation is very high and ordering biological controls can mean waiting several days for them to arrive, allowing the Fungus Gnat infestation to explode in the interim. This presents as a problem because the application of Steinernemo feltioe soon after Fungus Gnats are first detected, while the population is relatively low, provides the best control. However, with the application of a neem drench and foliar spray to begin attacking the Fungus Gnat population, while you wait for your Steinernemo feltiae to arrive, this presents as less of a problem. I.e. a neem drench and foliar spray will begin controlling the Fungus Gnat population and when you receive the Steinernema feltiae the population of Fungus Gnats is already under attack by neem. Because the use of neem and Steinernema feltiae are compatible you simply add the Steinernema feltiae to the substrate when you receive them.
Steinernema feltiae control the Fungus Gnat larvae by infecting, feeding, reproducing inside the fly larva and ultimately killing the larva. Nematodes such as Steinernema felitae that infect Fungus Gnats can be ordered by telephone or ordered online. Additionally, some hydroponic stores will order them for you. They arrive in a plastic container, cooled by an ice brick during transport and should be kept in the fridge (not the freezer) until use (if ordering through a hydroponic store be sure to tell the supplier to store the nematodes in a fridge until collection). Nematodes must be used within two weeks of receiving them.
It is important to note that Steinernema feltiae are most active/effective when used in air temperatures of below 28°C. For example, Koller (2011 ) found that control of Fungus Gnats with Steinernema feltiae was most successful, with an efficacy of 69-90% at 24°C. For this reason, ensure that your grow room environment is not overheated and that ambient air temperatures are conducive for Steinernema feltiae (<28°C). Additionally, what It is advised that, if dealing with a high population of Fungus Gnats is to apply the Steinernema felitae at 2-3 times the supplier recommended rate to achieve a large and stable population quickly.
Predatory Mites - predatory mites (Hypoaspis miles, Stratiolaelaps scimitus and 'Mighty Mite', Macrocheles robustus) and a predatory rove beetle (Atheta coriaria) are sometimes available by mail order from various biocontrol supply companies.
Dragonfli Hypoaspis Miles Predatory Mites - Kill Sciarid Fly/Fungus Fly Larvae & Thrip Pupae (25000).
Predatory mites feed on sciarid fly larvae, eggs and thrip pupae breaking the life cycle at the plant base. Hypoaspis can last for 4 weeks without food source allowing early introduction. Easy to apply by simply sprinkling onto the growing media at the base of plants. Available for use in temperatures above 15 degrees. Given suitable conditions Hypoaspis Miles will continue reproducing and feeding on pests until control is achieved
Hydrogenperoxide 3%
Mix with 4 parts water, pH and water in.
Contact with hydrogen peroxide will kill fungus gnat larvae on contact. After a few minutes the fizzing stops and the peroxide breaks down into harmless oxygen and water molecules. Repeat as needed.
Alternatively
Yet others state that hydrogen peroxide (H2O2) can be used for Fungus Gnat control. However, some issues present. These being H2O2 is a potent oxidising agent that attacks and breaks down all organic matter (e.g. Fungus Gnat eggs and larvae) including the roots of plants. This means that when used at too high levels it can lead to root damage/burning H2O2 is also uptaken by plants. Studies show that when H2O2 is applied to soils endogenous levels of H2O2 increase in the plant tissue. This can lead to phytotoxicity when application rates are excessive) H2O2 products can vary widely in composition, which effects the required dilution rates H2O2 reacts strongly with organic molecules rendering its oxidising potential ineffective in a short space of the time. For example, one study showed that 10 g-L-1 of peat reduced the amount of H2O2 and peroxyacetic acid from activated peroxygens by 33% and 50% respectively after 4 hours contact time. There would therefore be some concerns about whether Fungus Gnat larvae would be exposed to enough oxidising agent (ppm in solution/substrate) for enough time to ensure high mortality rates (i.e. effectiveness is reliant on time of exposure and the levels of hydrogen peroxide the Fungus Gnat larvae are exposed to whether the exposure time and the levels of H2O2 required to achieve a high mortality rate would not also prove damaging to the crop through root burning and/or phytotoxicity.
Adult fungus Gnat Flies
As I mentioned earlier Fungus Gnats are lazy sods and prefer to walk than fly.
This is where Yellow Sticky traps come in.
Sticky traps weren't invented to controll insect, they were designed for farmer and horticulturalist, in order then to identify what pests they had and then then would take the appropriate action to deal with the problem.
However sticking a stickt trap on you pot, will catch adult Fungu Gnats due to their predeliction for walking.
Remember a lot of the above information deals with the Larvae of the Fungus Gnat and doesn't deal with the adult fly.
Both Adults and Larvae need to be tackled in a two pronged approach.
Deal with only one of these and the cycle starts off again!
Topping your soil with a physical barrier.
Many people like to put a 1 inch barrier of sand on the top of their pots!
This does work by stopping the adult Fungus Gnat flies laying their eggs.
Very careful and judiscious watering is then needed to stop the sand mixing with the substrate, which will then allow access to the adult Fungus Gnats to once again lay their eggs.
Alternatively
This is another method that is commonly recommended, placing sand or diatomaceous earth on top of the media to create a barrier, which is thought to interfere with the ability of adults to lay eggs and to stop adults from emerging from the substrate. However, studies have shown that placing diatomaceous earth or sand on the substrate surface has little effect on fungus gnat adult emergence or inhibiting females from laying eggs because these physical barriers contain small openings that allow larvae to pupate, and adult females to lay eggs.
Propriatory Fungus Gnat killers
Fungus Gnat Off - Kills Larvae, not Adults - uses, natural organic plant extracts that are suspended in a naturally derived liquid.This product is suitable for use in organic cultivation.
CX Hydroponics Tanlin 20ml - Extremely concentrated – 1 ml makes 100 liters. One 20 ml bottle makes 2000 liters. Safe to use with any nutrient regiment. Will not affect beneficial microorganisms. Non-toxic and completely inert; does not interact with the plant in any way. TaNLiN, like all other CX Horticulture products, is designed specifically for consumable crops. TaNLiN is plant, pet and people safe.
Pesticide control
Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of earwigs. These pesticides have a very short persistence and so may require reapplication to keep earwig numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults.
Pest Resistance to Insecticides
It is important to note that because of the rapid reproductive rate of many pests a generation of many insects can take place in a few weeks and many generations can be produced in a single season or year. Repeated use of the same class of pesticide to control a pest can cause undesirable changes in the gene pool of a pest leading to another form of artificial selection, pesticide resistance. When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population. Through this process of selection, the population gradually develops resistance to the pesticide. The faster the development rate of the pest species, the faster the pesticide resistance occurs.
For example, resistance to two organophosphorus insecticides chlorfenvinphos and primiphos-ethyl among Fungus Gnat populations has been reported in the UK where these chemicals were commonly used. Similarly, studies have shown that some populations have become resistant to malathion and permethrin treatments due to the heavy use of malathion and permethrin which created resistance problems. Therefore, chemical drenches that are effective in one location (e.g. Australia) may not be as effective in another location (e.g. the U.S.). For this reason, three days after drenching I replace all the yellow sticky traps in the grow room with new ones and monitor these closely for the next few days to see if the treatment has been effective; i.e. spinosad will kill the larvae very quickly and adults will stop emerging from the substrate almost immediately. As a result, the number of adult flies caught on the traps should be absolutely minimal to nil several days after drenching. If reasonably high numbers, 4-5 days after treatment, are still being trapped this indicates the drench has been less effective than desirable and another type of drench should be employed. To date, I haven't found any resistance problems regarding spinosad use; however, it is something that you need to be aware of. For example, some years ago I used permethrin as a drench and found over time that the Fungus Gnat population was becoming resistant. The permethrin still worked reasonably well; however, more and more Fungus Gnats were surviving treatment. At that point I switched to another drench (spinosad) and this worked extremely well (100% control).
CO2
Fungus gnats are also attracted to excessive carbon dioxide or CO2.
Turn off CO2 tanks so you can root out the problem before your roots become the problem!
Remove Smart Organic and Exhale CO2 bags.
Turn off Charcoal burners for CO2.
Remove Yeast fermentation CO2 production.
Remove Vinegar and Baking soda CO2 production.
Landscape Fabric Pot toppers
Easy to make.
Cut a disc of landscap fabric (weed supressing fabric) slightly larger than the opening of the top of your pot.
Cut a hole in the center for the plant stem (remember the stem will get thicker as it grows, so allow for that).
Then from the center out cuy a straight line to the edge. You will now be able to put this around your stem.
then tuck the edges in!
This is a 100% deterent but 95% protection is better than no protection.
It is a good way of detering eggs being laid as there is not much real estate for the fungus Gnat to lay its eggs.
Spinosad Drench
Spinosad, produced by Dow AgroSciences, is technically an organic (considered nonsynthetic) product and certain formulations are listed for use by the Organic Materials Research Institute (OMRI) for organic use in the US and various other countries. Due to its low effective use rate, safety to the environment, safety to mammals, and safety to beneficial insects, spinosad was registered under the US EPA's reduced risk program. Spinosad was also awarded the Presidential Green Chemistry Challenge Award in 1999.
Spinosad is produced by aerobic fermentation of the actinomycète (bacteria) species Saccharopolysoro spinosa. Spinosad contains two chemicals, spinosyn A and spinosyn D. These are crystalline solids with low odor, no volatility, and with low water solubility. The half-life of these compounds on a plant leaf is about 2-16 days. Spinosad is slowly and poorly absorbed through the skin. Dermal exposures in the rat for 24 and 120 hours resulted in only 1 and 2% absorption, respectively. Spinosad, which is absorbed via the oral or dermal routes of exposure, has been found to be rapidly metabolized and eliminated from the body. For example, 95% of the spinosad residues in rats are eliminated within 24 hours (U.S. EPA). Trace residues of spinosad that may be absorbed from food or water by terrestrial and aquatic organisms have been found to be readily metabolized and excreted and, as a result, spinosad and its metabolites do not accumulate in living tissues. Spinosad elimination half-lives of around 4 days are observed in fish. Basically, spinosad has very low toxicity to non-target organisms (e.g. humans) and by agrochemical standards is the safest choice of insecticide that, arguably, can be used.
Spinosad is shown to have high efficiency when dealing with Fungus Gnat larvae. For example, one study in an insecticide non-resistant cohort showed spinosad, trichlorphon, deltamethrin, spintoram, permethrin, and malathion had the greatest effect on Fungus Gnat larvae populations respectively (i.e. spinosad provided the most effective control).Spinosad is a fast-acting material that acts on the insect primarily through ingestion, but also by direct contact. It activates the nervous system of the insect, causing loss of muscle control. Continuous activation of motor neurons causes insects to die of exhaustion within 1-2 days.
When used as a drench in low CEC substrates' such as rockwool or expanded clay, spinosad has systemic properties and is uptaken and distributed throughout the plant, offering protection against pests such as whitefly and spider mite for up to 30 days after treatment. One author concluding that "apparently, spinosad has systemic properties and quantities as low as 1 mg/plant could protect tomato plants from mite infestation "This author also concluding that the persistence (withholding period) of systemically applied spinosad to tomato was up to 45 days. However, what's interesting about this is that when spinosad is applied to substrates with varying percentage of clay and organic matter these systemic properties aren't apparent, or are greatly reduced. An immediate explanation for this is that organic matter, due to its CEC properties, binds spinosad making it unavailable for plant uptake. While more research is needed, given coir is an organic substrate and has moderately high CEC this possibly means that very little spinosad is uptaken by coir grown plants and this reduces the possibility of spinosad residues being present in the harvested product. Further, given the low levels used, low absorption rate, low toxicity and rapid metabolization by mammalian species this makes it a very efficient and safe option for killing Fungus Gnat larvae in organic substrates.
Use
There are several spinosad products/brands on the market (e.g. Conserve, Entrust, Monterey, Greenlight) with varying percentages of spinosad as the active ingredient.
For hobby growers who are producing on a small scale, the easiest way to go about things is to purchase small volumes, rather than having to store large amounts. For this reason, I typically purchase Monterey Garden Insect Spray which contains 0.5% spinosad as the active ingredient. This is used at 4 tablespoons per US gallon when applied as a media drench. This converts in metric to 15ml/L or 75ppm of spinosad in the diluted drench solution.
Depending on your locale spinosad products are available under different brand names. For example, in Australia, Yates sells Nature's Way Fruit Fly Control, Active: 0.24g/L spinosad (200ml) or Yates Success Natralyte Insect Control, Active: 1.0% spinosad (200ml). These are easily accessible options for Australian growers and would be used at 8 tablespoons per US gallon or 30ml/L (Nature's Way Fruit Fly Control) or 2 tablespoons per US gallon (7.5ml/L) with Success.
When mixing and applying the drench be sure to adhere to any safety warnings on the product label and wear gloves and eyewear. Mix with mains water and pH adjust to 5.8 before applying the drench to the substrate. It is important that you thoroughly drench the entire surface area of the substrate evenly to ensure all larvae come in contact with the spinosad (spinosad is most effective as a contact spray/drench). Drench the media evenly and well. Apply when the lights first turn off and leave in substrate overnight before flushing with a 1 /2 strength pH adjusted nutrient solution an hour before the lights come on. Go back to your normal nutrient irrigation regime thereafter. What I also do is spray around the tops of the pots with a permethrin or deltamethrin based fly spray to kill adult Fungus Gnats that reside on the substrate surface.
The Chemical-Free Way (A scholarly Article)
Over the years, various biological controls have been developed and used by commercial growers for control of insects above the soil line. The natural enemies of insect pests are categorized as predators, parasitoids and pathogens. Predators catch and eat their prey, compared to parasitoids that lay their eggs on, in or near their host insect to later feed on them.
Pathogens are insect disease-causing organisms that infect insects causing them to become sick or interfere with their normal processes. While both chemical pesticides and biological controls can “control” insects and “suppress” insects, biologicals offer another option in the grower’s tool bag. This is of interest for growers wanting to reduce the amount of chemical pesticide applications and for growers of organic crops. However, biological control of insects below the soil line in the root zone can be a greater challenge, since there are less options available.
Insect-suppressing fungi
Some of the insect-pathogenic fungi that can be used as microbial control agents for potting soils and growing media include Beauveria, Metarhizium and Paecilomyces. All three genera are naturally occurring and found around the world. All have different species and isolates to suppress different host insects.
For example, Beauveria bassiana is a fungus that produces conidia, a non-motile spore of the fungus that penetrates the outer hard cuticle covering of the insect. The fungus develops inside the insect, killing it after a few days. Beauveria bassiana controls insects that either live in the root zone or have a stage of development in the root zone, such as thrips, root weevil and some grubs.
Like Beauveria bassiana, Metarhizium anisopliae is also a naturally occurring fungus. Once in contact with the body of an insect host, the fungus germinates and the hyphae that emerge penetrate the outer cuticle cover of the insect, developing inside the insect and killing it after a few days. Metarhizium anisopliae is a fungus used as a biological insecticide to control fungus gnats, thrips and some types of grubs.
Paecilomyces lilacinus is another fungus that’s used as a microbial nematicide to control pathogenic nematodes. It parasitizes adult nematodes and kills eggs, juveniles and adult females of plant parasitic nematodes.
These fungi are effective for control of some root zone insects, as labelled, however, they’re not available in preformulated growing media and must be applied by the grower during the crop cycle. These are live organisms and care must be taken for their handling, storage and use for effective insect control. Some must be stored at cool temperatures, and once the package is opened, must be used immediately. Keep in mind that fungi are less robust than bacteria and may have compatibility interaction with certain chemicals that could render them useless. Therefore, growers should contact the specific manufacturer or dealer for specific storage and use recommendations.
Insect-suppressing bacteria
For years, growers have used Bacillus thuringiensis (Bt) for the control of caterpillars and worms above the soil line. Bt was first discovered in the early 1900s and commercialized in the mid-1960s. The pathogenic action of this bacterium occurs after ingestion by the insect. Spores and crystalline inclusions containing insecticidal endotoxins interact in the insect midgut, causing disruption of natural cell membrane permeability. This results in gut paralysis and death of the insect within a few hours or weeks, depending on the isolate and insect type.
Early work in the 1990s suggested that maybe other types of Bacillus bacteria could suppress certain soil insects. In 2010, Kuhne Heller published the results of their findings at the International Peat Symposium called “Sciarid Fly Larvae in Growing Media—Biological Control Measures.” In their research, they evaluated the black fungus gnat (Bradysia difformis) and types of pathogenic fungi as sites for selective egg laying and larval feeding on fungal hyphae of Botrytis cinerea, Fusarium species and Phoma betae in petri dishes.
It was known that black fungus gnats are attracted to and feed on plant pathogenic fungi that cause plant disease. For comparative purposes, they also included two bacterial species, Bacillus pumilus and Pseudomonas flourescens, to evaluate insect feeding and egg laying. After four days, the pathogenic fungi were completely consumed by adult flies and fungus gnat eggs were present on the petri dish. However, no feeding activity and only a few eggs were observed on the petri dishes with the bacterial strains (Bacillus pumilus and Pseudomonas flourescens).
Interestingly, PRO-MIX BIOFUNGICIDE+MYCORRHIZAE was introduced to the market more than 10 years ago. This product contains Bacillus pumilus PTB180, a type of bacteria that’s been shown to suppress certain insects that have a stage of development in growing media. Over the years, Premier Tech Horticulture received reports from growers indicating reduction of fungus gnats and thrips in their greenhouse crops. PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE is enriched with Bacillus pumilus PTB180 bacteria that colonize developing root systems and suppress disease-causing organisms, such as Pythium, Fusarium and Rhizoctonia.
In addition, the Glomus intraradices fungi contained in PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE attach to and colonize root systems, working in symbiosis with plants. Endomycorrhizal fungi benefit the host plant by increasing acquisition of water and nutrients (especially phosphorus, copper and zinc) by forming an extensive mycorrhizal hyphal network that attaches to the plant root system. In exchange, the plant provides soluble sugars to the fungus. This symbiotic relationship between fungi and plant results in overall improved plant growth. To further explore this insect suppression observations, a research study was conducted in conjunction with Laval University.
The pioneering laboratory work from Kuhne Heller (2010) mentioned that fungus gnats don’t lay their eggs randomly on moist surfaces of growing media. They preferably laid their eggs on hyphae of certain phytopathogenic fungi (Botrytis cinerea, Fusarium species and Phoma betae) on which their larvae will feed rather than on other fungi or soil bacteria (B. pumilus). If the pathogenic fungi are reduced, then the environment is less favorable for fungus gnats, which results in reduction of egg laying and populations.
The series of research experiments conducted over several years included several short-term bedding crops and long-term ornamental crops (cyclamen, poinsettia). Research results indicated that PRO-MIX BIOFUNGICIDE+MYCORRHIZAE suppresses both insect pests, fungus gnats and thrips to an average level of 30% and 22%, respectively, during the whole crop-growing period.
We also observed that the diminution of fungus gnat infestation could reach up to 67% for a specific time during plant culture. By reducing the fungal food sources of certain root zone-dwelling insects with Bacillus pumilus (PTB180 bacteria), there’s an indirect suppressive effect on insect populations. PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE is now labelled to suppress two major pests in greenhouses: fungus gnats that attack root systems and thrips that pupate into the growing medium.
Premier Tech is currently conducting additional research tests to further investigate the potential to reduce other pests with biologicals.
Fungus gnats have four stages in their life cycle
- Eggs
- Larvae
- Pupae
- Adult fly
Many of the controls mentioned below, will only control one or two of these life stages of the fungus gnat.
Most deal with just the larval stage, do not make the mistake of just dealing with the larvae as the adult fly will just come back and lays some more eggs!
Diatomacious Earth aka DE
Diatomacious Earth does have insect killing properties.
However only when dry!
Sprinkling it on top of you soil, isn't going to help because you need to water your plants.
Studies have shown that placing diatomaceous earth or sand on the substrate surface has little effect on fungus gnat adult emergence or inhibiting females from laying eggs because these physical barriers contain small openings that allow larvae to pupate, and adult females to lay eggs.
Cinnamon
Cinnamon is a a natural fungicicde
Some say, if you use it, to only use Ceylon Cinnamon and not Cassia.
However, I have read that some people have tried it but to little effect, whilst others say it does the job?.
I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.
If I am to advise using it, it first needs some verification, or no dice
Neem Oil
The chemicals isolated from neem can be categorized into two groups: isoprenoids and non-isoprenoids . Non-isoprenoids are amino acids, carbohydrates, flavonoids and others, while isoprenoids contain compounds such as azadirachtin. The most important compound in neem for pest control is azadirachtin, which approximates the shape and structure of hormones vital to the lives of insects. The bodies of insects absorb the neem compounds as if they were their real hormones, and this blocks their endocrine systems. The resulting deep-seated behavioral and physiological aberrations leave the insects so confused in brain and body that they cannot reproduce and their populations plummet. Additionally, their feeding cycle is interrupted. Therefore, azadirachtin acts to break the feeding and breeding cycle in many species of insects, including fungus gnats.
One quite amazing feature of neem is that it presents low toxicity to many beneficial insects which prey on plant pests. What this means is that neem can be used in conjunction with fungus gnat predators such as Steinernema feltiae[9]. In fact, studies have shown that a higher degree of control is exhibited when neem and predatory insects are applied together.
It is important to understand that neem doesn't provide the same level of control that spinosad does when used as a substrate drench for control of larvae.[10] However, when used correctly it will offer good control and reduce the Fungus Gnat population. Neem needs to be applied every 3 days as a drench. Additionally, spray the plants at the same time to target the adults, ensuring good coverage until run off. Pay particular attention to spraying the underside of leaves and spray thoroughly around the surface of the growing media where adult Fungus Gnats reside in large numbers. Always spray plants when the lights are off to avoid plant burning.
Most hydroponic stores stock neem oil under various brand names. Neem products can vary significantly in quality and purity. Speak to your hydroponic supplier and ask him/her about product options and recommended usage rates etc.
As a tip, neem can leave the final produce with a bitter taste if applied too close to harvest. For this reason, cease drenching and foliar feeding neem at least a week before harvest.
Neem Cake
Others recommend the use of neem cake amended coir substrates. However, while this can prove to be an effective method for controlling Fungus Gnats, while
the research is somewhat variable, several studies show that neem cake's active constituent azadirachtin potentially disrupts beneficial microflora (bennies) and enzyme activity in soils and substrates. Therefore, while offering effective control over Fungus Gnats, neem cake amended coir may not provide
a conducive environment for bennies such as Trichoderma spp. Other than this, the potential for azadirachtin to interrupt enzyme activity is not a good thing.
Another issue with neem cake is that it provides relatively high amounts of nutrients; i.e. neem cake contains more nitrogen (2-5%), phosphorus (0.5-1.0%), calcium (0.5 -3%), magnesium (0.3 - 1 %) and potassium (1-2 %) than farm yard manure or sewage sludge.Neem cake also provides varying levels of micronutrients. What this means is that while neem cake is a good source of fertilizer for organic growing, its use in hydroponics, where the nutrients supplied to the plants can be highly controlled through ppm of each nutrient species in solution, is less than ideal where hydroponic nutrients are used.
Coriander Oil - I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.
If I am to advise using it, it first needs some verification, or no dice
Penny Royal/Pepper Mint Oil - I need to look deeper into this, as this sort advice falls in to the "Anecdotal" catagory.If I am to advise using it, it first needs some verification, or no dice
There are steps to avoiding, controlling & killing fiungus Gnats
Hygene
Clean up dead leaves especially on the top of you soil in your pot, in saucers or fgravel trays etc
Places when, water will come into contact with the dead leaves, which will then start decaying and attract fungus gnats.
Pick dead leaves of the plant, they are already dead or dying and will end up falling of your plant and are a possible soure for mold & mildew, just what a gnat likes.
Overwatering
Over watering is often a cause of fungus gnats invading your grow space.
Cannabis like a wet/dry cycle and will perform it's best if grown this way!
The Dry part doesn't mean "totally dry" and the wet doesn't mean "waterloggged"!
Water your plant and get a feel how heavy the pot is, then when the pot is much lighter but still retains some moisture, water again,
A constantly moist top of your soil, will give fungus a nice place to live, which in turn gives the fungus gnats somewhere to live!
the gnats larvea will live in the top inch of your soil.
So soil management & hygene is one part of the solution.
The top of your soil can be dried out by using a fan and gently blowing air across i, this isn't really an eveysay occurance, it's more to dry the soil, once you have noticed you have gnats.
Lowering the ammount of contained water and waterlogging
Growing fabric pots, means the water in your soil goes a few ways, either out the bottom as run off, to the plant and then transpired or through evpaoration.
This mean you shouldn't have an overabundance of water in your pot.
Lightening your soil mix with perlite, will make it more airy, which is great for your plants roots but also alows your substrate to drain and regualate moisture better.
Airpots will do the same job!
Allow for a wet/dry cycle, it's the way cannabis likes it.
Mosqitio Dunks, Mosquito Bits & BT ( Bacillus thuringiensis israelensis)
Mosquito dunks
To use mosquito dunks: Fill up a gallon jug (or watering can) with clean water and toss in a mosquito dunk. ... Let the dunk soak in the water for as long as possible (at least overnight), then remove it from the water (the dunk can be reused) and use this water for fungus gnat–infested plants. Ph your water before using to warer your plant.
Mosquito Bits
To control fungus gnats, simply shake the granular Mosquito Bits onto the potting soil in houseplants and other container-grown plants. Mosquito Bits can also be mixed with potting soil prior to planting. ... After subsequent watering, the BTI (Bacillus thuringiensis israelensis) is washed below the soil surface. Fungus gnat larvae feed on the BTI ( Bacillus thuringiensis israelensis) and die.
How does Bacillus thuringiensis israelensis work?
How does Bti work? Bti spores that are eaten by mosquito larvae release toxins into the mosquito's gut, causing the larvae to stop eating and die. Bti is only effective against actively feeding larvae, and does not affect mosquito pupae or adults.
Alternatively
Yet others recommend the use of the bacterium Bacillus thuringiensis (BT). However, using BT and that of several studies sugests that, at best, BT offer only limited control and, at worst, are largely ineffective. One study that compared BT and predatory nematodes against the efficiency of pesticides concluded BT effectiveness would be reliant on the BT being applied before the Fungus Gnat populations build up and before overlapping generations develop. In another study (2011) that compared the efficiency of Steinernema feltiae, neem oil and BT to control fungus gnats the author concluded "that control with the nematode Steinernema feltiae was most successful, with an efficacy of 69-90% at 24°C air temperature. Azadirachtin (Neem-seed oil) could be an alternative under hot conditions (>28°C). Bacillus thuringiensis israelensis (BT), however, showed only a minor effect (1-51% efficacy)."
Nematodes
The Fungus Fly Killer nematode 50 million pack contains enough nematodes to treat an area up to 100 square metres or approximately up to 2000 2 litre pots. Ensure the compost is damp/moist before application.Mix the contents of the pack in 5 litres of water. Stir the contents. Take 0.5 litres of the concentrate and add to an 8 litre or 2-gallon watering can of clean water, and mix. Using a coarse rose, water into the compost. The concentrate can be used to fill up to 10 watering cans. A knapsack sprayer can also be used for the application.
Pathogenic nematodes (Steinernema feltiae)
Steinernema feltiae is more effective against fungus gnats than other commercially available nematode species. Mix Bti or nematodes with water, and apply as a soil drench, or spray onto media using a hand-pump spray bottle or other spray equipment, following label directions.
Formulations of nematodes may also be available in some plant centres.
These biocontrols are added to the potting compost where they will help control the eggs, larvae and pupal stages of the flies.
Do nematode soaks every 10 to 14 days until the problem is resolved.
Predatory nematodes such as S.feltiae can be used to effectively control Fungus Gnats. However, there is a caution here re hobbyist/novice indoor growers. That is, often fungus gnat populations aren't discovered by many growers until the population/infestation is very high and ordering biological controls can mean waiting several days for them to arrive, allowing the Fungus Gnat infestation to explode in the interim. This presents as a problem because the application of Steinernemo feltioe soon after Fungus Gnats are first detected, while the population is relatively low, provides the best control. However, with the application of a neem drench and foliar spray to begin attacking the Fungus Gnat population, while you wait for your Steinernemo feltiae to arrive, this presents as less of a problem. I.e. a neem drench and foliar spray will begin controlling the Fungus Gnat population and when you receive the Steinernema feltiae the population of Fungus Gnats is already under attack by neem. Because the use of neem and Steinernema feltiae are compatible you simply add the Steinernema feltiae to the substrate when you receive them.
Steinernema feltiae control the Fungus Gnat larvae by infecting, feeding, reproducing inside the fly larva and ultimately killing the larva. Nematodes such as Steinernema felitae that infect Fungus Gnats can be ordered by telephone or ordered online. Additionally, some hydroponic stores will order them for you. They arrive in a plastic container, cooled by an ice brick during transport and should be kept in the fridge (not the freezer) until use (if ordering through a hydroponic store be sure to tell the supplier to store the nematodes in a fridge until collection). Nematodes must be used within two weeks of receiving them.
It is important to note that Steinernema feltiae are most active/effective when used in air temperatures of below 28°C. For example, Koller (2011 ) found that control of Fungus Gnats with Steinernema feltiae was most successful, with an efficacy of 69-90% at 24°C. For this reason, ensure that your grow room environment is not overheated and that ambient air temperatures are conducive for Steinernema feltiae (<28°C). Additionally, what It is advised that, if dealing with a high population of Fungus Gnats is to apply the Steinernema felitae at 2-3 times the supplier recommended rate to achieve a large and stable population quickly.
Predatory Mites - predatory mites (Hypoaspis miles, Stratiolaelaps scimitus and 'Mighty Mite', Macrocheles robustus) and a predatory rove beetle (Atheta coriaria) are sometimes available by mail order from various biocontrol supply companies.
Dragonfli Hypoaspis Miles Predatory Mites - Kill Sciarid Fly/Fungus Fly Larvae & Thrip Pupae (25000).
Predatory mites feed on sciarid fly larvae, eggs and thrip pupae breaking the life cycle at the plant base. Hypoaspis can last for 4 weeks without food source allowing early introduction. Easy to apply by simply sprinkling onto the growing media at the base of plants. Available for use in temperatures above 15 degrees. Given suitable conditions Hypoaspis Miles will continue reproducing and feeding on pests until control is achieved
Hydrogenperoxide 3%
Mix with 4 parts water, pH and water in.
Contact with hydrogen peroxide will kill fungus gnat larvae on contact. After a few minutes the fizzing stops and the peroxide breaks down into harmless oxygen and water molecules. Repeat as needed.
Alternatively
Yet others state that hydrogen peroxide (H2O2) can be used for Fungus Gnat control. However, some issues present. These being H2O2 is a potent oxidising agent that attacks and breaks down all organic matter (e.g. Fungus Gnat eggs and larvae) including the roots of plants. This means that when used at too high levels it can lead to root damage/burning H2O2 is also uptaken by plants. Studies show that when H2O2 is applied to soils endogenous levels of H2O2 increase in the plant tissue. This can lead to phytotoxicity when application rates are excessive) H2O2 products can vary widely in composition, which effects the required dilution rates H2O2 reacts strongly with organic molecules rendering its oxidising potential ineffective in a short space of the time. For example, one study showed that 10 g-L-1 of peat reduced the amount of H2O2 and peroxyacetic acid from activated peroxygens by 33% and 50% respectively after 4 hours contact time. There would therefore be some concerns about whether Fungus Gnat larvae would be exposed to enough oxidising agent (ppm in solution/substrate) for enough time to ensure high mortality rates (i.e. effectiveness is reliant on time of exposure and the levels of hydrogen peroxide the Fungus Gnat larvae are exposed to whether the exposure time and the levels of H2O2 required to achieve a high mortality rate would not also prove damaging to the crop through root burning and/or phytotoxicity.
Adult fungus Gnat Flies
As I mentioned earlier Fungus Gnats are lazy sods and prefer to walk than fly.
This is where Yellow Sticky traps come in.
Sticky traps weren't invented to controll insect, they were designed for farmer and horticulturalist, in order then to identify what pests they had and then then would take the appropriate action to deal with the problem.
However sticking a stickt trap on you pot, will catch adult Fungu Gnats due to their predeliction for walking.
Remember a lot of the above information deals with the Larvae of the Fungus Gnat and doesn't deal with the adult fly.
Both Adults and Larvae need to be tackled in a two pronged approach.
Deal with only one of these and the cycle starts off again!
Topping your soil with a physical barrier.
Many people like to put a 1 inch barrier of sand on the top of their pots!
This does work by stopping the adult Fungus Gnat flies laying their eggs.
Very careful and judiscious watering is then needed to stop the sand mixing with the substrate, which will then allow access to the adult Fungus Gnats to once again lay their eggs.
Alternatively
This is another method that is commonly recommended, placing sand or diatomaceous earth on top of the media to create a barrier, which is thought to interfere with the ability of adults to lay eggs and to stop adults from emerging from the substrate. However, studies have shown that placing diatomaceous earth or sand on the substrate surface has little effect on fungus gnat adult emergence or inhibiting females from laying eggs because these physical barriers contain small openings that allow larvae to pupate, and adult females to lay eggs.
Propriatory Fungus Gnat killers
Fungus Gnat Off - Kills Larvae, not Adults - uses, natural organic plant extracts that are suspended in a naturally derived liquid.This product is suitable for use in organic cultivation.
CX Hydroponics Tanlin 20ml - Extremely concentrated – 1 ml makes 100 liters. One 20 ml bottle makes 2000 liters. Safe to use with any nutrient regiment. Will not affect beneficial microorganisms. Non-toxic and completely inert; does not interact with the plant in any way. TaNLiN, like all other CX Horticulture products, is designed specifically for consumable crops. TaNLiN is plant, pet and people safe.
Pesticide control
Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of earwigs. These pesticides have a very short persistence and so may require reapplication to keep earwig numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults.
Pest Resistance to Insecticides
It is important to note that because of the rapid reproductive rate of many pests a generation of many insects can take place in a few weeks and many generations can be produced in a single season or year. Repeated use of the same class of pesticide to control a pest can cause undesirable changes in the gene pool of a pest leading to another form of artificial selection, pesticide resistance. When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population. Through this process of selection, the population gradually develops resistance to the pesticide. The faster the development rate of the pest species, the faster the pesticide resistance occurs.
For example, resistance to two organophosphorus insecticides chlorfenvinphos and primiphos-ethyl among Fungus Gnat populations has been reported in the UK where these chemicals were commonly used. Similarly, studies have shown that some populations have become resistant to malathion and permethrin treatments due to the heavy use of malathion and permethrin which created resistance problems. Therefore, chemical drenches that are effective in one location (e.g. Australia) may not be as effective in another location (e.g. the U.S.). For this reason, three days after drenching I replace all the yellow sticky traps in the grow room with new ones and monitor these closely for the next few days to see if the treatment has been effective; i.e. spinosad will kill the larvae very quickly and adults will stop emerging from the substrate almost immediately. As a result, the number of adult flies caught on the traps should be absolutely minimal to nil several days after drenching. If reasonably high numbers, 4-5 days after treatment, are still being trapped this indicates the drench has been less effective than desirable and another type of drench should be employed. To date, I haven't found any resistance problems regarding spinosad use; however, it is something that you need to be aware of. For example, some years ago I used permethrin as a drench and found over time that the Fungus Gnat population was becoming resistant. The permethrin still worked reasonably well; however, more and more Fungus Gnats were surviving treatment. At that point I switched to another drench (spinosad) and this worked extremely well (100% control).
CO2
Fungus gnats are also attracted to excessive carbon dioxide or CO2.
Turn off CO2 tanks so you can root out the problem before your roots become the problem!
Remove Smart Organic and Exhale CO2 bags.
Turn off Charcoal burners for CO2.
Remove Yeast fermentation CO2 production.
Remove Vinegar and Baking soda CO2 production.
Landscape Fabric Pot toppers
Easy to make.
Cut a disc of landscap fabric (weed supressing fabric) slightly larger than the opening of the top of your pot.
Cut a hole in the center for the plant stem (remember the stem will get thicker as it grows, so allow for that).
Then from the center out cuy a straight line to the edge. You will now be able to put this around your stem.
then tuck the edges in!
This is a 100% deterent but 95% protection is better than no protection.
It is a good way of detering eggs being laid as there is not much real estate for the fungus Gnat to lay its eggs.
Spinosad Drench
Spinosad, produced by Dow AgroSciences, is technically an organic (considered nonsynthetic) product and certain formulations are listed for use by the Organic Materials Research Institute (OMRI) for organic use in the US and various other countries. Due to its low effective use rate, safety to the environment, safety to mammals, and safety to beneficial insects, spinosad was registered under the US EPA's reduced risk program. Spinosad was also awarded the Presidential Green Chemistry Challenge Award in 1999.
Spinosad is produced by aerobic fermentation of the actinomycète (bacteria) species Saccharopolysoro spinosa. Spinosad contains two chemicals, spinosyn A and spinosyn D. These are crystalline solids with low odor, no volatility, and with low water solubility. The half-life of these compounds on a plant leaf is about 2-16 days. Spinosad is slowly and poorly absorbed through the skin. Dermal exposures in the rat for 24 and 120 hours resulted in only 1 and 2% absorption, respectively. Spinosad, which is absorbed via the oral or dermal routes of exposure, has been found to be rapidly metabolized and eliminated from the body. For example, 95% of the spinosad residues in rats are eliminated within 24 hours (U.S. EPA). Trace residues of spinosad that may be absorbed from food or water by terrestrial and aquatic organisms have been found to be readily metabolized and excreted and, as a result, spinosad and its metabolites do not accumulate in living tissues. Spinosad elimination half-lives of around 4 days are observed in fish. Basically, spinosad has very low toxicity to non-target organisms (e.g. humans) and by agrochemical standards is the safest choice of insecticide that, arguably, can be used.
Spinosad is shown to have high efficiency when dealing with Fungus Gnat larvae. For example, one study in an insecticide non-resistant cohort showed spinosad, trichlorphon, deltamethrin, spintoram, permethrin, and malathion had the greatest effect on Fungus Gnat larvae populations respectively (i.e. spinosad provided the most effective control).Spinosad is a fast-acting material that acts on the insect primarily through ingestion, but also by direct contact. It activates the nervous system of the insect, causing loss of muscle control. Continuous activation of motor neurons causes insects to die of exhaustion within 1-2 days.
When used as a drench in low CEC substrates' such as rockwool or expanded clay, spinosad has systemic properties and is uptaken and distributed throughout the plant, offering protection against pests such as whitefly and spider mite for up to 30 days after treatment. One author concluding that "apparently, spinosad has systemic properties and quantities as low as 1 mg/plant could protect tomato plants from mite infestation "This author also concluding that the persistence (withholding period) of systemically applied spinosad to tomato was up to 45 days. However, what's interesting about this is that when spinosad is applied to substrates with varying percentage of clay and organic matter these systemic properties aren't apparent, or are greatly reduced. An immediate explanation for this is that organic matter, due to its CEC properties, binds spinosad making it unavailable for plant uptake. While more research is needed, given coir is an organic substrate and has moderately high CEC this possibly means that very little spinosad is uptaken by coir grown plants and this reduces the possibility of spinosad residues being present in the harvested product. Further, given the low levels used, low absorption rate, low toxicity and rapid metabolization by mammalian species this makes it a very efficient and safe option for killing Fungus Gnat larvae in organic substrates.
Use
There are several spinosad products/brands on the market (e.g. Conserve, Entrust, Monterey, Greenlight) with varying percentages of spinosad as the active ingredient.
For hobby growers who are producing on a small scale, the easiest way to go about things is to purchase small volumes, rather than having to store large amounts. For this reason, I typically purchase Monterey Garden Insect Spray which contains 0.5% spinosad as the active ingredient. This is used at 4 tablespoons per US gallon when applied as a media drench. This converts in metric to 15ml/L or 75ppm of spinosad in the diluted drench solution.
Depending on your locale spinosad products are available under different brand names. For example, in Australia, Yates sells Nature's Way Fruit Fly Control, Active: 0.24g/L spinosad (200ml) or Yates Success Natralyte Insect Control, Active: 1.0% spinosad (200ml). These are easily accessible options for Australian growers and would be used at 8 tablespoons per US gallon or 30ml/L (Nature's Way Fruit Fly Control) or 2 tablespoons per US gallon (7.5ml/L) with Success.
When mixing and applying the drench be sure to adhere to any safety warnings on the product label and wear gloves and eyewear. Mix with mains water and pH adjust to 5.8 before applying the drench to the substrate. It is important that you thoroughly drench the entire surface area of the substrate evenly to ensure all larvae come in contact with the spinosad (spinosad is most effective as a contact spray/drench). Drench the media evenly and well. Apply when the lights first turn off and leave in substrate overnight before flushing with a 1 /2 strength pH adjusted nutrient solution an hour before the lights come on. Go back to your normal nutrient irrigation regime thereafter. What I also do is spray around the tops of the pots with a permethrin or deltamethrin based fly spray to kill adult Fungus Gnats that reside on the substrate surface.
The Chemical-Free Way (A scholarly Article)
Over the years, various biological controls have been developed and used by commercial growers for control of insects above the soil line. The natural enemies of insect pests are categorized as predators, parasitoids and pathogens. Predators catch and eat their prey, compared to parasitoids that lay their eggs on, in or near their host insect to later feed on them.
Pathogens are insect disease-causing organisms that infect insects causing them to become sick or interfere with their normal processes. While both chemical pesticides and biological controls can “control” insects and “suppress” insects, biologicals offer another option in the grower’s tool bag. This is of interest for growers wanting to reduce the amount of chemical pesticide applications and for growers of organic crops. However, biological control of insects below the soil line in the root zone can be a greater challenge, since there are less options available.
Insect-suppressing fungi
Some of the insect-pathogenic fungi that can be used as microbial control agents for potting soils and growing media include Beauveria, Metarhizium and Paecilomyces. All three genera are naturally occurring and found around the world. All have different species and isolates to suppress different host insects.
For example, Beauveria bassiana is a fungus that produces conidia, a non-motile spore of the fungus that penetrates the outer hard cuticle covering of the insect. The fungus develops inside the insect, killing it after a few days. Beauveria bassiana controls insects that either live in the root zone or have a stage of development in the root zone, such as thrips, root weevil and some grubs.
Like Beauveria bassiana, Metarhizium anisopliae is also a naturally occurring fungus. Once in contact with the body of an insect host, the fungus germinates and the hyphae that emerge penetrate the outer cuticle cover of the insect, developing inside the insect and killing it after a few days. Metarhizium anisopliae is a fungus used as a biological insecticide to control fungus gnats, thrips and some types of grubs.
These fungi are effective for control of some root zone insects, as labelled, however, they’re not available in preformulated growing media and must be applied by the grower during the crop cycle. These are live organisms and care must be taken for their handling, storage and use for effective insect control. Some must be stored at cool temperatures, and once the package is opened, must be used immediately. Keep in mind that fungi are less robust than bacteria and may have compatibility interaction with certain chemicals that could render them useless. Therefore, growers should contact the specific manufacturer or dealer for specific storage and use recommendations.
Insect-suppressing bacteria
For years, growers have used Bacillus thuringiensis (Bt) for the control of caterpillars and worms above the soil line. Bt was first discovered in the early 1900s and commercialized in the mid-1960s. The pathogenic action of this bacterium occurs after ingestion by the insect. Spores and crystalline inclusions containing insecticidal endotoxins interact in the insect midgut, causing disruption of natural cell membrane permeability. This results in gut paralysis and death of the insect within a few hours or weeks, depending on the isolate and insect type.
Early work in the 1990s suggested that maybe other types of Bacillus bacteria could suppress certain soil insects. In 2010, Kuhne Heller published the results of their findings at the International Peat Symposium called “Sciarid Fly Larvae in Growing Media—Biological Control Measures.” In their research, they evaluated the black fungus gnat (Bradysia difformis) and types of pathogenic fungi as sites for selective egg laying and larval feeding on fungal hyphae of Botrytis cinerea, Fusarium species and Phoma betae in petri dishes.
It was known that black fungus gnats are attracted to and feed on plant pathogenic fungi that cause plant disease. For comparative purposes, they also included two bacterial species, Bacillus pumilus and Pseudomonas flourescens, to evaluate insect feeding and egg laying. After four days, the pathogenic fungi were completely consumed by adult flies and fungus gnat eggs were present on the petri dish. However, no feeding activity and only a few eggs were observed on the petri dishes with the bacterial strains (Bacillus pumilus and Pseudomonas flourescens).
Interestingly, PRO-MIX BIOFUNGICIDE+MYCORRHIZAE was introduced to the market more than 10 years ago. This product contains Bacillus pumilus PTB180, a type of bacteria that’s been shown to suppress certain insects that have a stage of development in growing media. Over the years, Premier Tech Horticulture received reports from growers indicating reduction of fungus gnats and thrips in their greenhouse crops. PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE is enriched with Bacillus pumilus PTB180 bacteria that colonize developing root systems and suppress disease-causing organisms, such as Pythium, Fusarium and Rhizoctonia.
In addition, the Glomus intraradices fungi contained in PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE attach to and colonize root systems, working in symbiosis with plants. Endomycorrhizal fungi benefit the host plant by increasing acquisition of water and nutrients (especially phosphorus, copper and zinc) by forming an extensive mycorrhizal hyphal network that attaches to the plant root system. In exchange, the plant provides soluble sugars to the fungus. This symbiotic relationship between fungi and plant results in overall improved plant growth. To further explore this insect suppression observations, a research study was conducted in conjunction with Laval University.
The pioneering laboratory work from Kuhne Heller (2010) mentioned that fungus gnats don’t lay their eggs randomly on moist surfaces of growing media. They preferably laid their eggs on hyphae of certain phytopathogenic fungi (Botrytis cinerea, Fusarium species and Phoma betae) on which their larvae will feed rather than on other fungi or soil bacteria (B. pumilus). If the pathogenic fungi are reduced, then the environment is less favorable for fungus gnats, which results in reduction of egg laying and populations.
The series of research experiments conducted over several years included several short-term bedding crops and long-term ornamental crops (cyclamen, poinsettia). Research results indicated that PRO-MIX BIOFUNGICIDE+MYCORRHIZAE suppresses both insect pests, fungus gnats and thrips to an average level of 30% and 22%, respectively, during the whole crop-growing period.
We also observed that the diminution of fungus gnat infestation could reach up to 67% for a specific time during plant culture. By reducing the fungal food sources of certain root zone-dwelling insects with Bacillus pumilus (PTB180 bacteria), there’s an indirect suppressive effect on insect populations. PRO-MIX BIOFUNGICIDE+ MYCORRHIZAE is now labelled to suppress two major pests in greenhouses: fungus gnats that attack root systems and thrips that pupate into the growing medium.
Premier Tech is currently conducting additional research tests to further investigate the potential to reduce other pests with biologicals.
excellent info article Arty, as always! We know the song, prevention is 1000% easier than cure is, but this gospel needs be sung so others may dodge this PITA affliction- 
... I like the 1-2 punch approach, nemo's and Bti, if it's a notorious problem in the growers situation.
