Cannabis Pests Molds and Mildew
How to stop insects and fungi from ruining your garden.
Marijuana growers face many challenges. Among the most persistent problems they encounter are insects, diseases, fungi, viruses and bacteria that harm plants.
This article will describe the most common of these problems, and prescribe preventive and corrective measures.
Some nasty buggers
The most common insects that plague marijuana indoors and outdoors are thrips, mites, whiteflies, fungus gnats, budworms, and caterpillars. Of these, mites are most prevalent in indoor grow rooms; outdoor growers generally find that leaf-eating insects like caterpillars and budworms are their most threatening insect pests.
White Fly ,Mites are tiny, mobile, hardy, and vicious.
They travel from grow room to grow room on infected clones and on the bodies and clothes of people who have come in contact with mites.
Mites live in nature and on dogs. Approximately 60% of BC's indoor grow rooms are infected with mites.
Mites puncture leaves and gorge themselves on plant juices.
In the early stages of infestation, they produce little evidence of their presence, although they can be detected by careful examination of leaf surfaces with a magnifying glass. Look for yellow or white spots on both sides of the leaves.
The spots radiate along leaf veins, and are evenly spaced.
In advanced stages, spider mite infestations are easily diagnosed, because the mites build white webbing which encapsulates plant sections.
Non-web leaf damage caused by mites can be mistakenly diagnosed as leaf spotting caused by thrips.
Thrips are larger than mites with a more linear body shape. They bite leaves and create white or yellowish marks on them, but the marks are more clustered and solidly discolored than those left by mites.
Thrips leave black fecal debris on leaves and in floral clusters.
Whiteflies are more easily seen than thrips or mites because they fly around plants, especially when plants are shaken by gardeners or air movement. As their name implies, whiteflies are pure white, and are about the size of the head of a pencil lead.
Whiteflies drink plant juices and leave residue on plant surfaces that provides sustenance for harmful fungi.
Fungus gnats and related species such as the crane fly infest soil and root zones.
They feed on roots, which causes a decrease in plants' ability to uptake nutrients.
Gnats are tiny, mobile, and dark. Crane flies resemble mosquitoes.
Budworms and caterpillars are problems primarily for outdoor growers.
Budworms burrow into ripe floral clusters; they also spin webs around floral clusters, although this is infrequent.
They eat floral clusters from the inside out, and their activities provide a vector for a pervasive cannabis fungal disease known as botrytis or gray mold.
Leaf infected by a mosiac virus
Leaf-eating caterpillars are less difficult to detect than budworms because they spend most of their time on leaves. They often manipulate leaves before eating them; their feeding habits include eating small sections of leaf in between leaf veins, or eating large chunks of leaf outright.
Mite No fun fungi
Although healthy root zones and leaves often contain beneficial fungi and bacteria, other forms of fungi and bacteria are damaging to cannabis plants.
The most pervasive fungal invader is botrytis, otherwise known as gray mold. This fungus is particularly dangerous because it is virtually undetectable in early stages, and because it attacks the ripest, phattest buds from the
Botrytis waits until cannabis flowers are dense and well developed, then it infests the buds near the core of the flower at stem level, and quickly produces gray garbage that destroys the bud's vigor and appearance. Gray mold and other pathogens can also affect harvested cannabis, even when harvested material is placed in a freezer.
Gray mold causes problems indoors and outdoors, particularly where humidity levels are above 50%, with poor aeration of plant tops. Downy mildew is almost as prevalent as gray mold, although it causes less damage and is harder to detect.
It originally appears as faint whitish or yellowish spots on leaf tops, with corresponding bumps on the undersides of leaves.
Leaves curl up and mutate as the mildew takes hold.
Powdery mildew is not downy mildew; it first appears as small bumps on the top of leaves; soon, the leaves look like they are covered in dusty grit. In some cases, powdery mildew can superficially resemble resin glands.
"Damping off" molds attack seeds before and after they have been planted.
The molds also attack emergent seedlings and seedlings that have attained as much as six inches in height. Damping off can keep seeds from sprouting at all.
Or, they kill sprouts by rotting their stems at the base.
Viruses and bacteria
Viruses affect plants, not just people, and some viruses can jump from people to plants and back again. Among the most prevalent cannabis viruses are "streak" and "mosaic" viruses that cause swirling white and yellow discolorations on leaves.
The discolorations are almost artistic, but soon, the leaves wilt.
Several species of bacteria also attack cannabis.
Most of these bacteria manifest themselves as "blight" diseases that create spots on leaves, wilting, rotting, weak stems, and rapid decay of harvested material.
Plant infected with mites
The first line of defense against insects and other plant invaders is to prevent them from getting near plants.
Indoor growers can achieve this by carefully filtering air intakes and other vectors. Outdoor growers have a harder time preventing insects from alighting on plants.
All growers should examine plants daily with a magnifying glass, looking for insects and insect damage. Grow environment sanitation is also important; growers should maintain a pristine environment: remove all plant debris, use sterilized equipment, do not bring dogs into grow areas, make sure water and water reservoirs are disinfected, do not enter a grow area in the same clothes after visiting an infected grow area.
Fungus Gnat If spider mites establish themselves in a grow area, it is virtually impossible to get rid of them without removing all equipment and plants from the area and totally cleansing the space.
Beneficial predatory mites placed on plants before spider mite infestations take hold can help defeat spider mites.
Spraying mite-infested plants with organic soap-garlic-cinnamide sprays also kills mites.
The use of toxic poisons on cannabis, at any stage in its growth cycle but especially during flowering, is dangerous to the consumer and unethical.
Thrips can be controlled using predatory organisms and sprays, especially sprays containing pyrethrum, nicotinic acid, organic soap, and garlic.
Thrips often rely on grow medium for their reproduction, so be sure to treat grow mediums as well as plants.
Whiteflies like the color yellow; one control for whiteflies is a commercially available yellow strip coated with sticky material that attracts whiteflies and then traps them.
Parasitic wasps released before whitefly infestation can keep whiteflies from taking over a grow situation. Sprays containing pyrethrum and organic gardening soap kill some whiteflies, especially when they are airborne.
Whenever using sprays, be sure to spray the underside of leaves thoroughly, as this is where many pests live.
Fungus gnats thrive in overfertilized, over-watered grow mediums, especially those where organic fertilizer high in nitrogen has been used. Gnats can be killed by disturbing soil, heating soil, by predatory wasps, and by applying insecticidal soap, neem, rotenone, and garlic oil to gnat infestations.
Budworms and caterpillars can be controlled by shaking plants several times a day to dislodge the insects.
Preventive sprays containing insecticidal soaps and organic toxins can be used selectively during vegetative cycle, but extreme care must be taken during floral cycle.
It is usually best to watch for the gray mold-like symptoms of budworm and remove the bud or section of bud where the worm resides, rather than to risk spraying any kind of toxin on a dense, harvest-ready bud.
Virus, bacteria and mold control tips
High humidity (over 50%) and grow environment contamination should be eliminated. Grow mediums should be sterilized and then treated with beneficial fungi (such as Trichoderma and Gliocladium) and beneficial bacteria.
Light intensity should be adequate for penetration deep into plant canopy, both vertical and horizontal.
Plants should be directly in line of fans and other aeration. In-line charcoal filters and other traps should be in place on all air intakes.
Strict sanitation controls should be in place for anyone who enters a grow environment.
"Bourdeaux mixture" can be useful for controlling gray mold. A spray containing copper, Bourdeaux mixture, and a beneficial organism called Bacillus subtilis is effective against downy mildew. Spraying with bicarbonate of soda, organic horticultural oils, and sulfur can kill powdery mildew.
Some growers use sulfur burners to create airborne sulfur treatment against powdery mildew. Bacteria can be controlled using Bourdeaux mixture.
Plant infected from thrips Viruses are impossible to kill once they have infected a plant. A preventive measure to protect against viruses, other than the generic tactic of preventing them from entering grow environments, is to keep plants' immune systems healthy with proper watering, temperature, root zones, and nutrients.
If molds, fungi, viruses or bacteria take hold in a grow environment, it may be necessary to remove affected plants completely.
Near-harvest buds affected by most insects, pathogens and diseases can be partially salvaged by using them to make water hash.
Otherwise, all plants or plant parts affected must be immediately removed and destroyed, and any tools, clothing, or other materials that came in contact with the affected plants must be removed, sterilized or destroyed.
Please note that smoking or handling whole marijuana infected by molds, mildews, and fungi can cause serious
human health problems.