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SCIARA FLY  (Sciaridae – Fungus Gnat)



 

Sciaridae and their offspring, the fungus gnat larvae, are the bane of soil/sphagnum peat and coco growers. Their presence in coir grown crops is extremely common. Because coco coir is organic it decomposes in its wet state. This causes the release of nitrates as part of the decomposition process. This nitrate release is what attracts Sciaridae adults who then lay eggs in the media which hatch into the fungus gnat. This is where the problem starts. Fungus gnats are a considerable problem when they become established. Most damage is caused to the plants by the larvae (fungus gnat) as they chew on and devour the fine root hairs of the plants.  Other than this, fungus gnats are known to be vectors for pythium and fusarium. Thus, damage can occur on two levels 1) fungus gnats damage the roots and 2) root pathogens can be introduced into the crop.

 

Life Cycle

 

Adult female fungus gnats prefer to lay eggs in growing medium that is microbially active and damp.

 

Each female will lay about 200 transparent eggs (each about one millimeter long) into moist soil or coco substrate. After about one week the larvae hatch.

 

The development time from egg to adult is around three weeks at 21°C, but faster at higher temperatures e.g. only 17 days at 25°C.

 

Additionally, it has been shown that at higher temperatures (24 °C and 28 °C) a higher degree of egg laying females is produced and that survival rates from egg to adult are higher.

 

Growrooms conditions and moist coco substrate (and soils containing sphagnum moss etc) are thus highly favourable to sciarid fly/fungus gnats.

 

The adults with do not actually do any damage to the crop (ie. they do not feed on leaf material). They only ingest liquids and live only long enough to mate and produce eggs.

 

On the other hand, the larvae (fungus gnat) wreak havoc as they devour the roots of the plants.

 

Sciarid larvae are white, elongate, legless maggots with a distinctive black shiny head. At this stage the larvae feed on developing mycelium and uncontrolled will burrow into pinheads and small buttons forming a sponge-like mass. Mature larvae may grow as much as 8.0 mm (1/4 of an inch) in length and can remove mycelial attachments at the base of the stalk and in severe infestations may enter stalks and caps. They can be found around the roots of host plants and sometimes on the surface of the media.  The green or brown gut contents of the larvae can be seen through the transparent body wall.  The pupae develop in the media, then emerge into the next generation of adults.

 

Identification and Prevention

 

Sciara fly are tiny, dark, fragile-looking insects. On close inspection the Sciara Fly (often called scarid fly) resembles a tiny (approx 1-2mm) fruit fly or mosquito. They are black and have veined wings and long antennae extruding from the head.

 

Sciara fly can be difficult to detect in their early stages (while adult numbers are low). Yellow sticky yellow traps are an invaluable tool for identifying the presence of Sciara fly in your grow room. Additionally, yellow sticky traps will catch loads of the adults, so if you have sciaridae/fungus gnat be sure to place sticky traps around the crop (vertically hang them from lights above the plant canopy) and place them on top of pots (horizontally) – Sticky cards laid horizontally near the substrate soil surface catch more sciaridae than cards hung vertically, but the combination of both works best.

 

Another effective means of detecting the presence of fungus gnat larvae is to insert 1/4 inch slices or wedges of potato into the growing medium. Larvae will migrate to the potato and start feeding within a few days. The potato slices should be turned over to look for larvae present on the underside.

 

Fungus gnats thrive in moist and humid environments. This makes wet organic substrates such as coco substrate ideal for fungus gnats. For this reason, place two inches of perlite on top of the substrate and avoid overwatering.

 

Treatment

 

Chemical (Author’s Choice 1)

 

I’m going to seemingly contradict myself somewhat again. Ie. It must be pretty obvious that I’m not a great fan of chemical pesticides for use in indoor cropping or elsewhere; however, there is a time and place where chemical pesticides can be used safely. This said…

 

To date, I have found pyrethroid-based synthetic pesticides such as permethrin, applied as a soil drench, is the most effective way of totally eradicating fungus gnats. Short-persisting contact insecticides such as those containing pyrethrins, soaps, oils, and neem, do not provide sufficient long-term control of fungus gnat and require repeat applications at short intervals (every 2-3 days) to exhibit effects.

 

About Permethrin

 

Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent.

 

Technically, permethrin is claimed to be non systemic (or has limited systemic activity) and therefore will not be uptaken by the roots and translocated to the leaf and flowers of the plant. However, R M Garcinuño et al (2006) demonstrated that in hydroponics (water based systems) some uptake and translocation might occur with:

 

[Quote]

 

“After 16 days of growth, the plants were harvested, and their tissues were microwaved digested and analyzed by reversed-phase liquid chromatography. Although only minor quantities of each pesticide were detected in plant tissues, their amount in the roots was higher than in the stems. No accumulation was noted in the cotyledons (emerging leaf), and only 2% of linuron was detected in the leaves.” 1

 

[End Quote]

 

Contrary to these findings, in research conducted by Bélanger et al (1979) on the use of permethrin in soil it was shown that while permethrin persisted in the soil for 28 days, permethrin did not translocate into the edible parts of the vegetables but was present in the root system of onion and lettuce.2

 

These findings indicate that the use of permethrin in organic, high CEC substrates is a very safe and non-toxic way of dealing with fungus gnats. Ie. residue in the combustible end produce is highly unlikely.

 

However, it is important to note that permethrin applied via foliar, directly to leaf/or and flower is another matter. Residues will remain present for some time.


Permethrin and Beneficial Bacteria and Fungi

 

Beneficial bacteria and fungi will continue to colonize in organic substrates treated with permethrin.

 

In soil the average half-life of permethrin in aerobic soils is 39.5 days, with a range from 11.6 to 113 days. Permethrin binds tightly to soil and other organic matter (eg. coco substrate) and is broken down primarily by microorganisms.

 

The toxicity of several fungicides, insecticides and acaricides to the biological control agent Trichoderma viride has been evaluated in laboratory tests. The effects of the pesticides on the spores and mycelium of Trichoderma viride and on the antagonistic activity of this fungus to Fusarium graminearum showed that permethrin was non-toxic to both the spores and the ‘mycelium’ (vegetative part of a fungus, consisting of a mass of branching, threadlike hyphae) of Trichoderma viride. 3

 

Research by S.E. Maloney et al (1988) it was shown that permethrin was the most rapidly transformed of the pyrethroids by microbes and deltamethrin was the most persistent. Additionally, it was shown that in the case of Bacilus cereus, the half-life of permethrin was reduced from 21 days to below 5 days as a result of microbial interaction with permethrin.4

 

In yet more research Mathur, S. P et al (1980) tested permethrin in organic soil and found permethrin “suppressed the soil microbial population and biochemical activity rather consistently though not markedly.”5

 

Usage

 

Take care when using permethrin products as they are toxic (wear gloves and a mask when mixing and using and handle with care).

 

25gram sachets of Coopex WP 250g/kg (produced by Bayer) are widely available in Australia. Mix one sachet to 10ltrs of water and use as a drench. This equates to 625ppm of permethrin in the drench (Ie. 25% active = 6.25g of permethrin per 10L or 0.625g per litre. = 625ppm).

 

Thoroughly, drench the media with diluted product which has been pH adjusted to 5.8 and leave for two hours.  After this, flush with pH 5.8 adjusted water and resume your normal nutrient regime. As permethrin binds tightly to organic substrates it will remain present in the media for some time.

 

Note: If Coopex WP 250g/Kg powder isn’t available in your locale you can easily use another permethrin product at 625ppm as a drench. Speak to an agricultural supplier about product options.

 

Some trade names of permethrin products include Axe, Ambush, BW-21-Z, Cellutec, Ectiban, Eksmin, Exmin, FMC-33297, Indothrin, Kafil, Kestril, NRDC 143, Pounce, PP 557, Pramiex, Qamlin and Torpedo.

 

Warning: Permethrin is highly toxic to fish and other aquatic organisms. It is also highly toxic to cats. After you flush the medium of permethrin be sure to dispose of the runoff safely. The runoff will contain relatively low ppm of permethrin and it is advised that this should be diluted further and watered into soil (where it will bind tightly) away from rivers etc.

 

REFS

 

  1. R M Garcinuño, P Fernandez Hernando, C Camara (2006)  Removal of carbaryl, linuron, and permethrin by Lupinus angustifolius under hydroponic conditions.
  2. Bélanger& Herman A. Hamilton (1979) Determination of disulfoton and permethrin residues in an organic soil and their translocation into lettuce, onion and carrot
  3. Toxicity of some pesticides to Trichoderma viride Pers. T. Baicu (1981)
  4. S.E. Maloney, A. Maule, and A. R. Smith (1988) Microbial transformation of the pyrethroid insecticides: permethrin, deltamethrin, fastac, fenvalerate, and fluvalinate.
  5. Mathur, S. P., Belanger, A.; Hamilton, H. A.; Khan, S. U.(1980) Influence on microflora and persistence of field-applied disulfoton, permethrin and prometryne in an organic soil.

 

Predatory Nematodes – Biological Control

 

Predatory nematodes such as Steinernema feltiae can be used to effectively control fungus gnats. However, there is a proviso here re hobbyist/novice indoor growers. This is, often fungus gnat populations aren’t discovered by many growers until the population/infestation is high and ordering biological controls can mean waiting several days for them to arrive – allowing the fungus gnat infestation to explode. The problem is Steinernema feltiae work most effectively when fungus gnats are detected early. Other than this, optimal control comes from several applications over the course of a crop cycle (dependent on cropping method and at which point of the crop cycle a fungus gnat infestation is identified) and the most effective predators, Steinernema feltiae, have a shelf life of two weeks (stored in the fridge).

 

This said…

 

Steinernema feltiae

 

Steinernema feltiae is extremely effective against fungus gnats in indoor growing environments. They 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 but 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 receival.

 

Application soon after fungus gnats are detected provides optimum control. Two or three applications throughout the crop cycle should keep fungus gnat populations low throughout a 10-12-week cropping period.

 

Hypoaspis miles.

 

Another biological control agent is the soil-predatory mite, Hypoaspis miles. This mite completes its life cycle (egg to adult) in 7 to 11 days. It normally inhabits the top layers of the growing medium (as does the fungus gnat), where it feeds on fungus gnat larvae.

 

Populations of Hypoaspis include both sexes, but the males are much smaller and rarely seen. Eggs hatch in about 2-3 days, and the life cycle is completed in about 11 days. These predatory mites feed on the young larvae of fungus gnats in the soil, and are most effective when applied to soil before fungus gnat populations are establised. Hypoaspis consume 1-5 larvae per day and can survive as a scavenger by feeding on algae and plant debris.

 

Hypoaspis are for preventative control only, before fungus gnat populations are high.

 

A word of caution about a few commonly recommended fungus gnat control options

 

Various fungus gnat control methods are recommended by growers on forums. However, some of these methods are shown to be largely ineffective in studies. For example, some recommend mixing diatomaceous earth (DE) into the substrate to control fungus gnat larvae. DE is composed of siliceous skeletonized diatoms, which remove the insect cuticle waxes, absorb oils and waxes on the outer cuticle, or disrupt the integrity of the insect cuticle resulting in extensive loss of water from the insect body. However, the use of DE relies on the insect to make direct contact with it, and while some larvae may come into contact with DE others may not. Further, when wet/damp, DE loses its effectiveness. Therefore, as hydroponic substrates are irrigated (wet/damp) DE is a largely ineffective control measure for fungus gnat larvae.

 

Others recommend the use of neem cake amended coir substrates. However, while this can prove to be an effective method for controlling fungus gnats, studies also show that neem cake’s active constituent azadirachtin disrupts beneficial microflora (bennies) and enzyme activity in soils and substrates.[1], [2], [3], [4] Therefore, while offering effective control over fungus gnats, neem cake amended coir will not provide a conducive environment for bennies such as Trichoderma spp.

 

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.[5] Other than this, neem cake also provides varying levels of micronutrients. What this means is that while neem cake is a good source of fertilizer for organic soil 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 standard hydroponic nutrients (formulated for inert substrates or coir) are used.

 

For what it is worth, give neem cake amended coir substrates a miss and instead deal with fungus gnats in other ways.

 

Another method that is commonly recommended is to place 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.[6]

 

Others recommend the use of the bacterium Bacillus thuringiensis (BT). However, my own experiences with using BT and that of several studies are 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.[7] In another study (2011) that compared the efficiency 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).” [8]

 

Yet others state that hydrogen peroxide can be used for fungus gnat control. However, some issues present. These being; 1) hydrogen peroxide is a potent oxidising agent that attacks and breaks down all organic matter (e.g. fungus gnat larvae) including plant roots. This means that when used at too high levels it can lead to root damage/burning and phytotoxicity; 2) hydrogen peroxide products can vary widely in composition, which effects the required dilution rates; 3) hydrogen peroxide reacts strongly with organic molecules rendering its oxidising potential ineffective in a short space of the time. There would, thus, be some concerns about whether 1) 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) and 2) whether the exposure time and the levels of hydrogen peroxide required to achieve a high mortality rate would not also prove damaging to the crop. For example, hydrogen peroxide needs to be used in relatively large amounts of 100 ppm for 5 minutes to kill condia of Fusarium oxysporum and these rates are phytotoxic to crops. Additionally, as far as I am aware there is no research that documents the use of hydrogen peroxide as a substrate drench for control of fungus gnats. There’s possibly a good reason for this! That is, theoretically/hypothetically hydrogen peroxide makes for a bad option to control fungus gnats (at least on paper).

 

Bottom line, my advice is that better fungus gnat control options exist

 


[1] Kizilkaya, R. Samofalova, I. Mudrykh, N. Mikailsoy, F. Akca, I. Sushkova, S. and Minkina, T. (2015) Assessing the impact of azadirachtin application to soil on urease activity and its kinetic parameters.Turk J Agric For(2015) 39:c TUBİTAK doi:10.3906/tar-1406-85

[2] Gopal, M. Gupta, A. Arunachalam, V. Magu, S.P. (2007) Impact of azadirachtin, an insecticidal allelochemical from neem on soil microflora, enzyme and respiratory activities

[3] Elnasikh M. H., Osman A. G. and Sherif A. M. (2011) Impact of Neem Seed Cake on Soil Microflora and Some Soil Properties

[4] Wan, M.T., Rahe, J.E., 1998. Impact of azadirachtin on Glomus intraradices and vesicular-arbuscular mycorrhiza in root inducing

transferred DNA transformed roots of Daucus carota. Environ. Toxic. Chemistry 17, 2041–2050.

[5] Radwanksi, S. A. and Wickens, G. E. (1981). Vegetative fallows and potential value of the neem tree in the tropics. Econ. Botany. 35:398-414.

[6] Cloyd, R.A.; Dickinson, A.; Kemp, K.E. Effect of diatomaceous earth and Trichoderma harzianum T-22 (Rifai Strain KRL-AG2) on the fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae).J. Econ. Entomol. 2007, 100, 1353–1359. – see also Cloyd, R.A.; Dickinson, A. Effects of growing media containing diatomaceous earth on the fungus gnat Bradysia sp. nr. coprophila (Lintner) (Diptera: Sciaridae). HortScience 2005, 40, 1806–1809.

[7] Shamshad, A. Clift, A and Mansfield, S. (2008) Toxicity of six commercially formulated insecticides and biopesticides to third instar larvae of mushroom sciarid, Lycoriella ingenua Dufour (Diptera: Sciaridae), in New South Wales, Australia

[8] Koller, M. (2011) Comparison of Steinernema Feltiae, Bacillus thuringiensis israelensis and Azadirachtin to ControlSciaridae in Organic Potted Herbs

 

WHITEFLY

 

 

Several species of whiteflies exist. The greenhouse whitefly, Trialeurodes vaporariorum, is a major pest of many fruit, vegetable and ornamental crops, frequently being found in glasshouses; the citrus blackfly, Aleurocanthus woglumi, is a pest of citrus crops; the silverleaf whitefly, Bemisia argentifolii, is a pest of a number of agricultural and ornamental crops, and The cabbage whitefly, Aleyrodes proletella is a pest of various Brassica species.

 

One of the major problems with whitefly is that they prefer indoor environments (ie. greenhouses and growrooms) to outdoors. This makes them a common growroom pest.



Whitefly damage crops because both adult and juvenile whiteflies feed on the sap of plants, causing them to wilt, turn yellow, and grow poorly.

 

Plants can be seriously weakened by heavy infestations, as large quantities of plant sap can be removed in a short period, particularly by the developing nymphs.

 

The piercing-sucking mouthparts of whiteflies provide an excellent mode for transmitting disease-causing viruses from one plant to another. In 1997, tomato yellow leaf-curl begomovirus was discovered in Florida, USA. This is the worst viral disease transmitted by the whitefly, Bemisia argentifolii. The whitefly has also been shown to transmit almost 60 other viral plant diseases.

 

Life Cycle

 

All whiteflies have a similar lifecycle. Whiteflies develop from egg to adult in approximately one month depending upon temperature. Their life cycle progresses from the first, second, third and fourth nymphal stages to the pupal stage to adults.

 

Whitefly eggs are spindle-shaped and stand vertically on the leaf surface. For many species, eggs are white when first laid and turn dark grey or amber-brown with time. Eggs are laid on the underside of leaves, sometimes in a circle or crescent-shaped patterns. A female may lay up to 200 eggs.

 

The entire lifespan of the whitefly is relatively short.  The adult whitefly lifespan ranges from 6-55 days depending on a variety of factors including temperature, plant host, and species.

 

Identification

 

Whiteflys produce few initial symptoms. This can allow their population to grow until you encounter a severe infestation. As a result of a whitefly infestation plants lose vigour, leaves droop, turn yellow, wilt and sometimes die.

 

Adult Whitefly are easily recognized – they are approximately 1.5mm long and resemble small white flies, with 4 proportionately large dull white wings. Whitefly also have 2 forward pointing antennae which rise from the top of the head.

 

Although all whitefly tend to look alike, there are two major types – greenhouse whitefly and silverleaf whitefly. The greenhouse whitefly has been recorded on over 250 plants while the silverleaf whitefly attacks over 500 hosts. Adult greenhouse whitefly are slightly less than 1/8 inch long. They have a white, waxy coating and hold their wings parallel to the leaf surface. Adult silverleaf whitefly are slightly smaller than the greenhouse whitefly and have a yellowish hue.

 

Whitefly are usually found on the underside of leaves. When heavily infested plants are shaken, white clouds of winged adults will fly into the air.

 

Additionally, yellow sticky traps can indicate when adults are present. For best results, hang or place the cards close to the top of the plant. Doors, vents and other openings where whiteflies can enter the growroom are other good sites to hang yellow sticky traps.

 

Treatment

 

For Med growers, sprays containing pyrethrum or neem give good control.

 

For severe infestations, alternating nicotine sprays with pyrethrum sprays is shown to kill a high percentage of whiteflys.

 

Additionally, horticultural oils (e.g., Sunspray, Stylet-Oil) are shown to be extremely effective. Applied as dilute sprays (eg. 2 percent), they smother the immature forms of whitefly and the eggs.

 

McPartland (2000) notes:

 

[Quote]

 

“Liu & Stansly (1995) compared five sprays against B. argentifolii in greenhouses: 96% of adults were killed by 2% Sunspray(R) Ultra-Fine horticultural oil, 68% were killed by bifenthrin (a pyrethroid), 26% by N. gossei sucrose ester, and 12% by M-Pede(R) insecticidal soap.” 1

 

[End Quote]

 

JMS Sylet Oil has found favour with growers due to its ability to control pests and disease. Stylet Oil is a technical grade white oil with unsulfonated residue. It’s manufacturer states:

 

[Quote]

 

“The purity (or unsulfonated residue) of the base oil used in Stylet-Oil is 99.1%; the purity of non-white horticultural oils is typically 92%. This difference in purity can have significant consequences: There is more active ingredient (ai) in white oils than in typical non-white horticultural oils.”

 

And:

 

“White oils do not contain aromatic hydrocarbons, thus, these compounds are not freely evaporating into the atmosphere from spray applications… Included in these aromatic compounds are suspected Carcinogenic compounds such as benzene, toluene and xylene.”

 

[End Quote]

 

It is important to note that all of the aforementioned products work on contact only so the key is to directly target the pest and apply to the undersides and tops of leaves at 3-5 day intervals.

 

Biological control

 

Encarsia, a tiny parasitic wasp, lays its eggs in the scales where the larvae develop and so kill the scale.The larvae hatch into adults, which find more scales to parasitise. The problem is, once it has done its job and there is no food source for the larvae the lifecycle stops. If a further outbreak occurs then you have to re-introduce the encarsia.

 

Delphastus pusillus, a small ladybird beetle, eat from 150 up to 600 Whitefly eggs a day. Both larvae and adults are active predators that can consume numerous eggs or nymphs. An adult Delphastus takes no longer than half a minute to handle a whitefly egg, and devours up to 160 eggs or 12 large nymphs daily. A larva consumes about 1000 whitefly eggs (less if it also eats whitefly nymphs) during its development.

 

Pesticides

 

Whitefly are renowned for their ability to become resistant to insecticides. Greenhouse whitefly has developed resistance to organochlorine, organophosphate, carbamate and pyrethroid insecticides (e.g. Georghiou 1981; Anis & Brennan 1982; Elhag & Horn 1983; Wardlow 1985; Hommes 1986). Resistance has also been found in newer insecticides, buprofezin and teflubenzuron (Gorman et al. 2000).

 

Whitefly have two life stages that are resistant to pesticides. For this reason a single application of pesticides is rarely very effective. The egg and puparium stages are least susceptible to pesticides, while the adults and youngest nymphs are the most susceptible to most pesticides. Three or four applications (at weekly intervals) kill whiteflies emerging from eggs that escaped initial applications.

 

Systemic insecticides, containing the neonicotinoid insecticides, thiacloprid, thiamethoxam, imidacloprid, or acetamiprid provide the best control; they also kill on contact, but are also taken inside the plant where they go on to protect against further attack for several weeks.

 

This means there may be pesticide residues left at harvest if applications are applied in past week two of flower. However…

 

Treatment of Clones and Mother Plants With Systemic Pesticides

 

Whitefly can be introduced to the growing environment via clones that are sourced elsewhere. Therefore, dipping clones in a systemic neonicotinoid insecticide is a good preventative strategy.

 

Additionally, spray your mother plants with a neonicotinoid insecticide as a preventative measure. Be sure no spray drift is able to reach your crop. This may mean taking the mothers outdoors and away from the growing environment before spraying. In order to avoid pest resistance to sprays alternate product/pesticide type on a rotational basis. Spray the mother plants every 12 days as a preventative.

 

If you are dead against using pesticides, spray the mothers regularly with alternating horticultural oil and neem treatments.

 

Treatment After An Infestation (Between Crop Cycles)

 

If you have had a whitefly infestation dump all media and waste plant matter (trimmings etc) into airtight plastic bags, seal, and dispose of away from the environment. If possible, take the flowers elsewhere and dry. After this, spray the room (walls, floor, ceiling) and all equipment (light shades, lamps, pots etc) with pesticides before the next crop cycle.

 

As a secondary measure, use bug bombs that contain a synthetic pyrethroid (eg, Raid Concentrated Deep Reach Fogger which contains cypermethrin) two days after spraying pesticides.

 

Bug bombs, also known as total release foggers or insect foggers, use an aerosol propellant to fill an indoor space with chemical pesticides. Most bug bombs contain pyrethrin or pyrethroid-type insecticides, plus chemical propellents that make the fine mist that fills the room. Bug bombs can be a serious health and safety hazard, especially if you use too many or don’t follow directions.

 

Turn off extraction fans and activate the bug bomb. Once the fogger is activated leave the treated area. Most labels require you to be out for four hours. After that time, open doors and turn on the extraction fans to flush out the environment. Leave immediately after turning on the fans and stay out of the room for a couple more hours.

 

If you have asthma or a breathing condition, let someone else activate the fogger and air out the rooms before you return.

 

Keep in mind that synthetic pyrethroids not only kill bugs, but are dangerous to humans and animals also. Be sure to seal off the room tightly so no pesticide leakage occurs.

 

Warnings: The labels of most foggers require that you turn off pilot lights, gas fireplaces, and unplug any source of sparks while fogging an area. Flammable gases from bug bombs can ignite. Follow safety instructions carefully.

 

Unsafe storage of bug bombs can allow children to find them. There are no childproof features on fogger cans. Once a fogger is activated, the canister fogs until it is empty. Store foggers in high or locked locations to keep them out of reach of children.

 

When spraying pesticides: adhere to best practice and wear the appropriate safety gear (mask, gloves, safety glasses, long sleeved shirt, and trousers).

 

Preventative Spray Plants in The Following Crop Cycle After an Infestation

 

After a whitefly infestation, apply preventative non-systemic (natural) pestides while the plants are in vegetative and early flower stage in the following crop. Use neem and pyrethrum and alternate on each spray. Spray every 5 days.

 

Monitor the plants very closely (use a magnifying glass and look closely under leaves) and be sure to have yellow sticky traps in the environment. Spotting whitefly early makes control much easier!

 

THRIPS

 

 

Thrips are well documented as vectors of disease including many types of fungus and virus.

 

There are several species of Thrips that can be found worldwide anywhere between sea level and 2,000 metres above sea level.

 

Thrips are generally between 1mm and 3mm in length. They are typically grayish-yellowy brown in colour. Thrips’ wings are different from most other insects. They have a single longitudinal vein in which there are several hairs connected perpendicular to the vein. Because of this the wings appear as a fringe of hairs. Thrips’ larvae are cigar shaped and yellow-brown in colour.

 

The most apparent form of damage to the plants is associated with the insects’ feeding habits. Thrips pierce and rasp the leaf surface with their mouthparts to release the liquids from the plant’s cells. As the plant grows the damage is apparent as patches (silvery white patches) or streaks appear on the leaves. In extreme cases the leaves can appear severely disfigured.

 

A Thrip infestation can leave the plant unable to photosynthesise adequately for its needs. This can lead to a sick plant that becomes susceptible to disease.

 

Lifecyle of Thrips

 

The rate at which thrips move through their developmental cycle is highly dependent upon temperature with development occurring between 50 F and 90 F. At 20oC, development from egg to adult takes approximately 19 days, reducing to 13 days at 25oC. In simple terms, the warmer the environmental conditions are, the shorter the timespan between development from egg to adult. This makes indoor growrooms the perfect environment for thrip.

 

Most of the thrips in a growrooms are females. Adult females may live for approximately 30 to 45 days. During their lifetime, female thrips may lay from 150 to 300 eggs that are inserted into plant tissue. Eggs may be laid on the upper surface or lower leaf surface depending upon the plant species.

 

Identification

 

The best method of detection is to gently shake the plants onto the palm of the hand, where the thrips will fall and be seen moving. In addition to this, sticky yellow traps that attract and trap the insects are an early means of detection.

 

Most adult thrips are slender, minute (less than 1/20 inch long), and have long fringes on the margins of both pairs of their long, narrow wings. Immatures (called larvae or nymphs) are similarly shaped with a long, narrow abdomen but lack wings. Most thrips range in color from translucent white or yellowish to dark brown or blackish, depending on the species and life stage.

 

Botannical Sprays

 

Neem oil is the healthy way to go for combating thrips. Spraying every 3 days is the most effective means of complete eradication.

Nicotine sprays are highly effective at controlling thrips. Additionally, rosemary and marjoram essential oil has been shown to be extremely effective in inhibiting the feeding activity of the thrips at 1% concentration (10ml of each in 1L solution + a surfactant).1

 

Insectides

 

Although thrips damage to leaves is unsightly, thrips activity does not usually warrant the use of insecticide sprays. There are far safer methods of control.

This said, products such as Confidor and Spinosad wiil completely elimininate a thrip infestation. Spinosad is principally toxic to plant-eating insects such as thrips. It is not a plant systemic, but will penetrate leaves to some extent.

 

Predators

 

Predators are available for combating Thrips, the most important of which is Amblyseius Cumumeris, a mite that eats the developing stages of Thrips.

 

REF

 

  1. Elisabeth H. Koschier and Katrin A. Sedy (2003) Effects of plant volatiles on the feeding and oviposition of Thrips tabaci

 

 

APHIDS





Aphids are among the most destructive insect pests on cultivated plants in temperate regions.The damage they do to plants has made them the bane of farmers and gardeners the world over. From a zoological standpoint they are a very successful group of organisms.Their success is in part due to the asexual reproduction capability of some species.

 

Aphids are familiar to most people, as they suck sap from many varieties of plants. Aphids are between 1mm and 3mm in length, and have soft bodies that are pear shaped. Most Aphids found in protected crops are pale green. Colours, however, can range from white to black, with many colours and shades in between. Aphids have antennae with as many as six segments.

 

Aphids feed on the phloem sap found in the leaves of plants. From this sap they remove amino acids and sugars for digestion.

 

Because of this, the first identification of aphids may be noticeable leaf curling and/or damage. Other obvious signs are skeletal-like white shed skins on the surface and/or underside of the leaves. Large infestations can reduce plant vigor. They produce a sweet, sticky secretion called “honeydew,” which leads to unsightly grey sooty mold.

 

Aphids produce many young, each of which is capable of reproduction in about a week. As a result, aphid populations can build to enormous levels in a short period of time.  As they feed, aphids often transmit plant viruses to the plants. These viruses can sometimes kill the plants. For instance, the cotton aphid is known to transmit over 50 plant viruses and the green peach aphid, over 100.

 

At least six aphid species of aphid is known to attack Cannabis. 1

 

Identification

 

Plant Inspection. Some form of foliar scouting must be used to monitor aphids, because yellow sticky traps will only reveal the activity of winged aphids, which are much less common than the unwinged forms.

 

Aphid control is much more successful when an infestation is detected and controlled early in a crop. There are fewer aphids, spray coverage is better while the crop canopy is sparse, and the risk of phytotoxicity is reduced. Among the worst times to first notice an aphid infestation is when they are crawling all over the flowers. Therefore, a regular scouting program should be implemented to detect aphids throughout the crop.

 

Treatment

 

Neem oil will reduce/eradicate Aphids. Insecticidal (fatty acid) soaps used at recommended rates will also control Aphid numbers. Additionally horticultural oils such as Stylet-Oil can be very effectly applied to suffocate aphid eggs, and to kill nymphs and adults.

 

Natural essential oils not only exhibit toxic action against aphids, but also may have a repellent activity. Rosemary essential oil has been demonstrated to be particularly active against aphids. 2

 

Insecticidal soap, neem oil, and horticultural oils provide temporary control if applied to thoroughly cover infested foliage. To get thorough coverage, spray these materials with a high volume of the treatment agent and target the underside of leaves as well as the top. Soaps, neem oil, and horticultural oils only kill aphids present on the day they are sprayed, so applications may need to be repeated at 5-day intervals.



Additionally, garlic sprays and nicotine sprays work effectively.

 

Pesticides

 

Because aphid numbers explode quickly resisatnce to pesticides can easily occur.

 

Alternating insecticides with different modes of action is a recognised anti-resistance strategy.

 

Control/eradication of aphids is achieved primarily with imidacloprid containing products such as Confidor and Merit.

 

Predators

 

Predators and parasites often become abundant only after aphids are numerous, so applying nonpersistent insecticides like soap or oil may provide more effective long-term control.

 

Natural enemies include predatory ladybirds, hoverfly larvae, parasitic wasps, aphid midge larvae, crab spiders,  lacewings, and entomopathogenic fungi like Lecanicillium lecanii and the Entomophthorales.

 

Predators (Aphidius – a parasitic midge/wasp) are best used to combat Aphids.

 

Small aphid populations can also be controlled by ladybird beetles and lacewing.

 

REFS

 

  1. J.M. McPartland, R.C. Clarke, and D.P. Watson (2000) Hemp Diseases and Pests. Management and Biological Control
  2. Hori M (1999) The effects of rosemary and ginger oils on the alighting behaviour of Myzus persicae (Sulzer) (Homoptera: Aphididae) and on the incidence of yellow spotted streak.

 

 

Scale Insects



 

Scale insects are divided into three groups: (1) armored scales, (2) soft scales, and (3) mealybugs. The armored and soft scales are one of the most destructive groups of insects that attack ornamental crops. Armored scales and soft scales are the most common groups (families).

 

Scale insects feed on plant sap. They have long, threadlike mouthparts (stylets) six to eight times longer than the insect itself.

 

Feeding by scales slowly reduces plant vigor. Heavily infested plants grow poorly. When plants are heavily infested with scales, leaves may look wilted, turn yellow, and drop prematurely. In extreme cases, a heavy infestation may lead to plant death.

 

Scale insects often thrive in warm, humid environments, so the growroom makes the perfect environment. Additionally, Scale insects often lay more eggs and survive better on plants receiving a lot of nitrogen.

 

A large Scale will often shelter smaller ones underneath it, protecting them from contact with insecticides.

 

Identification

 

Scales are unusual looking and many growers do not at first recognize them as insects until their population is high.

 

Many species excrete a sticky, sugary substance, called honeydew, on the leaves and stems on which they are feeding. This sticky material may serve as a growth medium for a sooty mold fungus. They also produce white, waxy mounds on stems and the undersides of leaves. These are the egg masses of the sap-sucking insect.

 

As scale insects feed on phloem tissue, heavy populations may result in wilting.

 

Soft scale can be identified as little brown oval wart-like insects that suck sap from the stems and leaves of plants. Many resemble miniature tortoise shells.

 

Armored scales are the smallest of the ‘scales’ group. Armored scales may be circular, oval, oblong, thread-like, or even pear-shaped. Armoured scale are so named because they secrete a protective cover over their bodies.

 

Mealybug are commonly found on houseplants. These small insects are 1-4 millimeters long. Infestations appear on plants as tiny, soft-bodied insects surrounded by a fuzzy, white mess around the stems and leaf nodes.

 

Treatment

 

White oil or similar petroleum based sprays reduce scale numbers significantly. Spray a mixture of insecticidal soap and horticultural oil to control scale insects. Spray at 3 – 5 day intervals being sure to get thorough coverage of tops and undersides of leaves.

 

Neem oil has been shown to be efficient also.

 

Alternating treatments between neem oil and horticultural oils may be the best way to go. Apply one treatment of insecticidal soap and horticultural oil followed up by a treatment of neem oil 3 days later. Remember these sprays are effective on contact action only so apply thoroughly. Spray when lights are off and turn fans off. Allow 6 hours before lights and fans are turned on again.

 

Biological Controls

 

Aphytis lingnanensis, a tiny wasp lays its eggs under the scale cover. After hatching, the developing aphytis larva feeds on the scale insect, ultimately killing it. The next generation of aphytis emerges about three weeks later to mate and continue the cycle. Adult wasps also feed on scales directly.

 

Metaphycus helvolus is another parasite (wasp). The females lay their eggs under the body of first and second stage scales. The grubs feed on scales and develop into adults within 2 weeks. Adults also provide control by feeding on non-parasitized scales.

 

(Next page covers formulas for use against pests)