Chapter 14: Pests, Fungi & Diseases

Marijuana Horticulture: The Indoor / Outdoor Medical Grower’s Bible

by Jorge Cervantes

Insects, mites, and maggots slither into grow rooms eating, reproducing, and wasting weed. Outdoors, they live everywhere they can. Indoors, they live anywhere you let them. Fungi are present in the air at all times. They may be introduced by an infected plant or from air containing fungus spores. Fungi will settle down and grow if climatic conditions are right. Pests, fungi, and diseases can be prevented, but if allowed to grow unchecked, extreme control measures are often necessary to eradicate them.


Cleanliness is the key to insect and fungus prevention. The grow room should be totally enclosed so the environment can be controlled easily. Keep the floor clean. Keep all debris off sill surface. Do not use mulch. Insects and fungi like nice hideaway homes found in dirty, dank corners, and under dead decaying leaves r rotting mulch. Growers and their tools often transport many microscopic pests, diseases, and fungi that could ultimately destroy the garden. This does not mean growers and their tools have to hospital clean every time they enter a grow room, even though that would be nice. It does mean normal and regular sanitary precautions must be taken. Growers who wear clean clothes and use clean tools reduce problems considerably. A separate set of indoor tools is easy to keep clean. Pests, diseases, and fungi habitually ride from plant to plant on dirty tools. Disinfect tools by dipping in rubbing alcohol or washing with soap and hot water after using them n each diseased plant. Another quick way to sterilize pruners is with a hand held torch. A quick heating with the torch will sterilize metal tools immediately.

Personal cleanliness is fundamental to preventing pests and diseases. Wash your hands before touching foliage and after handling diseased pants. Smart growers do not walk around buggy outdoor gardens and then visit an indoor garden. They do it vice versa. Think before entering an indoor garden and possibly contaminating it. Did you walk across a awn covered with rust fungi or pet the dog that just came in from the garden outside? Did you just fondle your spider mite infested split leaf philodendron in the living room? Avoid such problems by washing your hands, and changing shirt, pants, and shoes before entering an indoor garden.

Once a crop has been grown in potting soil or soilless mix, throw out the growing medium. Some growers brag about suing the same old potting soil over and over, unaware that these savings are repaid with diminished harvest. Used soil may harbor harmful pests and diseases that have developed immunity to sprays. Starting a new crop in new potting soil will cost more up front but will eliminate many potential problems. Used soil makes excellent outdoor garden soil.

Be careful when discarding used soil! Growers in Eugene, Oregon, tossed their outdoor soil out in the backyard for many years. The soil was about 50 percent white perlite and had a distinctive color. This oversight eventually led to the growers’ arrest.

Once potting soil is used, it loses much of the fluff in the texture, and compaction becomes a problem. Roots penetrate compacted soil slowly, and there is little room for oxygen, which restricts nutrient uptake. Used potting soil is depleted of nutrients. A plant with a slow start is a perfect target for disease, and worst of all, it will yield less!

Companion planting helps discourage insects outdoors. Pests have nowhere to go indoors, so companion planting is not viable in the grow rooms.

Plant insect and fungus resistant strains of marijuana. If buying seeds from one of the many seed companies, always check for disease resistance. In general, Cannabis Indica is the most resistant to pests, and sativa is more resistant to fungal attacks. Choose mother plants that you know are resistant to pests and diseases.

Keep plants healthy and growing fast at all times. Disease attacks sick plants first. Strong plants tend to grow faster than pests and diseases can spread.

Forced air circulation makes life miserable for pests and diseases. Pests hate wind because holding on to plants is difficult, and flight paths are haphazard. Fungal spores have little time to settle in a breeze and grow poorly on wind-dried soil, stems, and leaves.

Ventilation changes the humidity of a room quickly. In fact, a vent fan attached to a humidistat is often the most effective form of humidity control. Mold was a big problem in one of the grow rooms that I visited. The room did not have a vent fan. Upon entering the enclosed room, the humid air was overpowering. It was terrible! The environment was so humid that roots grew from the plant stems. The grower installed a vent fan to suck out moist, stale air. The humidity dropped from nearly 100 percent to around 50 percent. The mold problem disappeared, and harvest volume increased.

Indoor horticulturist who practice all the preventative measures have fewer problems with pests and diseases. It is much easier to prevent the start of a disease than it is t wipe out an infestation. If pests and diseases are left unchecked, they can devastate the garden in a few short weeks.


Sometimes, even when all preventative measures are taken, pests and diseases still slink in and setup housekeeping. First they establish a base on a weak, susceptible plant. Once setup, they launch an all out assault on the rest of the garden. They move out in all directions from the infested base, taking over more and more space, until they have conquered the entire garden. An infestation can can happen in a matter of days. Most insects lay thousands of eggs in short periods of time. These eggs hatch and grow into mature adults within a few weeks. For example, if 100 microscopic munchers each laid 1000 eggs during their two weeks of life and these eggs grew into adults, two weeks later 100,000 young adults would lay 100 eggs each. By the end of the month, there would be 100,000,000 pests attacking the infested garden. Imagine how many there would be in another two weeks!

Sprays often kill adults only. In general, sprays should be applied soon after eggs hatch s young adults are caught in their weakest stage of life. Very lightweight (low viscosity) horticultural oil spray works well alone or as an additive to hep kill larvae and eggs.

The availability of some sprays can be seasonal, especially in more rural areas. Garden sections of stores are changed for the winter, but extra stock is sometimes kept in a storage room. Look for bargains on sprays at season end sales. Today, there are many disease controls all year round.

Insect Control

Indoor gardeners have many options to control insects and fungi. Prevention and cleanliness are at the top of the control list. A logical progression to pest and disease control is outlined in the chart on this page.

Manual removal is just what the name implies – smashing all pests and their eggs in sight between the thumb and forefinger or between two sponges.

I like natural organic sprays such as pyrethrum and neem and use harsh chemicals only as a last resort. Any spray, no matter how benign, always seems to slow plant growth a little. Stomata become clogged when foliage is sprayed and covered with a filmy residue. Stomata stay plugged up until the spray wears off or is washed off. Stronger sprays are often more phytotoxic, burning foliage. Spray plants as little as possible and avoid spraying for two weeks before harvest. Read all labels thoroughly before use.

Use only contact sprays that are approved for edible plants. Avoid spraying seedlings and tender unrooted cuttings. Wait until cuttlings are rooted and seedlings are at least a month old before spraying.

Sprays and Traps

I do not recommend using chemical fungicides, fungistats, insecticides, or miticides on plants that are destined for human consumption. Most contact sprays that do not enter the plant system are approved for edible fruits and vegetables. However, there are numerous ways to control fungi, diseases, and pests without resorting to chemicals.

Spreader-Sticker fr Pesticides

Spreader-stickers improve and promote wetting and increase sticking and absorption through foliage. Spreader-sticker products increase effectiveness of fertilizers, fungicides, insecticides, etc. They are especially important to use when plants develop a waxy coating of resin. Spreader-stickers also impair insects’ respiration mechanisms and function as pesticides. One of my favorite spreader-stickers is Coco-Wet from Spray-N-Grow.


Ingredients – Abamectin derivatives include emamectin and milbemectin. Does not bioaccumulate. Used extensively on hops; abamectin is not truly systemic. It is absorbed from the exterior of foliage to other leaf parts, especially young leaves, in the process of transaminar activity.

Controls – Russet and spider mites, fire ants, leafminers, and nematodes.

Mixing – Dilute in water. Mix 0.25 teaspoon per gallon. Use a wetting agent.

Application – Spray. Works best when temperature is above 70F. Repeat applications every seven to ten days.

Persistence – One day.

Forms – Liquid.

Toxicity – Toxic to mammals, fish, and honeybees in high concentrations. Sucking insects are subject to control while beneficials are not hurt.

Safety – Wear gloves, mask, and safety glasses.

Bacillus thuringiensis (Bt) and Bacillus species

Ingredients – Bacilus thuringiensis (Bt) is the best known of several bacteria that are fatal to caterpillars, larvae, and maggots. Caterpillars, larvae, and maggots all eat Bt bacteria, which can be applied as a spray, dust, or granules. Inject liquid Bt into stalks to kill borers. Shorty after they ingest it, their appetite is ruined, and they stop eating. Within a few days they shrivel up and die; cabbage loopers, cabbage worms, corn earworms, cutworms, gypsy moth larvae, and hornworms are controlled. Commercial Bt products do not reproduce within insect bodies, so several applications may be necessary to control an infestation. Microbial Bt bacteria are nontoxic to animals (humans), beneficial insects, and plants; however, some people do develop an allergic reaction. Commercial Bt products do not contain living Bt bacteria, but the Bt toxin is extremely perishable. Keep within prescribed temperature range, and apply according to the directions. Most effective on young caterpillars, larvae, and maggots, so apply as son as they are spotted.

Get the most out of Bt applications by adding a UV inhibitor, spreader-sticker, and a feeding stimulant such as Entice, Konsume or Pheast. Bt is completely broken down by UV light in one to three days.

B. thuringiensis var. kurstaki (Btk) – introduced on the market in the early 1960s – is the most popular Bt. Toxic to many moth and caterpillar larvae including most f the species that feed on flowers and vegetables. Sold under many trade names, DiPel, BioBit, Javelin, etc, Btk is also available in a microencapsulated form, M-Trak, Mattch, etc. The encapsulation extends the effective life on foliage to more than a week.

B. thuringiensis var. israelensis (Bt-i) is effective against the larvae of mosquitoes, black flies, and fungus gnats. Look for Gnatrl, Vectobac, and Bacrimos. All are lethal to larvae. Adults do not feed on plants and are not affected. Fungus gnats can cause root problems including rot. Use Bti to get rid of them as soon as they are identified.

B. thuringiensis var. morrisoni is a new strain of Bt under development for insect larvae with high pH in their guts.

B. thuringiensis var. san diego (Btsd) targets the larvae of Colorado potato beetles and elm beetle adults and other leaf beetles.

B. thuringiensis var. tenebrionis (Btt) is lethal to Colorado potato beetle larvae.

B. cereus helps control damping off and rot-knot fungus. It flourishes in water-saturated mediums and promotes beneficial fungus that attacks the diseases.

B. subtilis is a soil dwelling bacterium that curbs Fusarium, Pythium, and Rhizoctonia that cause damping off. It is commercially available under the brand names Epic, Kodiac, Rhizo-Plus, Serenade, etc. Soak seeds and apply as a soil drench.

Baking Soda

Ingredients – Sodium bicarbonate.

Controls – Powdery mildew.

Caution – Baking soda kills fungus by changing the pH of foliage surface. It functions as a fungistat, not as a fungicide, that eradicates the organisms.

Mixing – Saturate in water.

Application – Spray or dust foliage.

Persistence – One to three days.

Forms – Powder.

Toxicity – None to mammals, fish, beneficials.

Safety – Wear a mask to avoid inhaling dust.

Bleach, Laundry

Ingredients – Sodium hypochlorite.

Controls – Numerous bacteria and fungi.

Caution – Avoid skin contact and inhalation. Concentrate burns skin and stain clothes.

Mixing – Dilute 5 or 10 percent solution with water.

Application – Use as a disinfectant on containers, walls, tools, etc.

Persistence – Evaporates with little residual in a coupe of days.

Forms – Liquid.

Toxicity – Toxic to fish, beneficials, and humans if swallowed or gets in eyes.

Safety – Wear a mask and gloves when handing concentrate. Avoid skin contact and respiration.

Bordeaux Mixture

Ingredients – Water, sulfur, copper (copper sulfate) and lime (calcium hydroxide).

Controls – Most often used as a foliar fungicide. Also, controls bacteria and fends off other insects.

Caution – Phytotoxic when applied to tender seedlings or foliage in cool and humid conditions.

Mixing – Apply immediately after preparing.

Application – Agitate the mixture often while spraying so ingredients do not settle out.

Persistence – Until it is washed from foliage.

Forms – Powder and liquid.

Toxicity – Not toxic to humans and animals, but somewhat toxic to honeybees and very toxic to fish.

Safety – Wear a mask, gloves, and long sleeves.

Boric Acid

Ingredients – Available in the form of borax hand soap and dust.

Controls – Lethal as a contact or stomach poison. Kills earwigs, roaches, crickets, and ants.

Caution – Phytotoxic when applied to foliage.

Mixing – Mix borax soap in equal parts with powdered sugar to make toxic bait.

Application – Set bait out on soil near base of plants.

Persistence – Avoid getting bait wet as it disperses rapidly.

Forms – Powder.

Toxicity – Not toxic to honeybees and birds.

Safety – Avoid breathing dust.

Bug Bombs

Ingredients – often bug bombs are packed with very strong insecticides and miticides, including synthetic pyrenthrins that exterminate every pest in the room. They were developed to kill fleas, roaches, and their eggs that hide in furniture and in carpets.

Controls – According to most bug bomb labels, they kill everything in the room!

Caution – Use only as a last resort and follow the label’s instructions to the letter.

Mixing – None.

Application – Place the bug bomb in the empty room. Turn it on and then leave the room.

Persistence – Low residual. Persistence is limited to a day or two.

Forms – Aerosol.

Toxicity – Read label for details.

Safety – Wear a mask, gloves, and cover exposed skin and hair.


Ingredients – The compounds – copper sulfate, copper oxychloride, cupric hydroxide and cuprious oxide – a re common forms of fixed copper used as a fungicide and are less phytotoxic than unfixed (pure) copper.

Controls – Gray mold, foliar fungus, anthracnose, blights, mildews, and a number of bacterial diseases.

Caution – Easy to overapply and burn foliage or create a copper excess in the plant.

Mixing – Apply immediately after preparing.

Application – Agitate the mixture often while spraying, so ingredients do not settle out. Preferred temperature range for application is 65-85F.

Persistence – Last two weeks or longer indoors, if not washed off.

Forms – Powder and liquid.

Toxicity – Toxic to fish. Not toxic to birds, bees, mammals.

Safety – Wear a mask and gloves, cover exposed skin and hair.

Diatomaceous Earth (DE)

Ingredients – Naturally occurring DE includes fossilized silica shell, remains of the tiny one-celled or colonial creatures called diatoms. It also contains 14 trace minerals in a chelated (available) form.

Controls – Although not registered as a pesticide or a fungicide, DE abrades the waxy coating on pest shells and skin, including aphids and slugs, causing body fluids to leak out. Once ingested, the razor sharp particles in DE rip tiny holes in the pest’s guts, causing death.

Caution – Do not use swimming pool diatomaceous earth. Chemically treated and heated, it contains crystalline silica that is very hazardous if inhaled. The body is unable to dissolve the crystalline form of silica that causes chronic irritation.

Mixing – No mixing required when used as a dust. Mixing required when used as spray. Apply as a powder or encircle slug damaged plants and use as a barrier.

Application – Apply this spray to infestations caused by pest insects.

Persistence – Stays on foliage for a few days or until washed off.

Forms – Powder.

Toxicity – Earthworms, animals, humans, and birds can digest diatomaceus earth with no ill effects. Avoid contact with skin and eyes.

Safety – Wear a protective mask and goggles when handing this fine powder t guard against respiratory and eye irritations.

Homemade Pest and Disease Sprays

Ingredients – A strong, hot taste, smelly odor, and a desiccating powder or liquid are the main ingredients in home brewed pesticide and fungicide potions.

Controls – Homemade sprays discourage and control pests including aphids, thrips, spider mites, scale, and many others.

Caution – be careful when testing a new spray. Apply it to a single pant and wait for a few days to learn the outcome before applying to all plants.

Mixing – Make spray concentrates by mixing repellent substances with a little water in a blender. Strain the resulting slurry concentrate through a nylon stocking or a fine cheesecloth before being diluted with water for application.

Application – Spray foliage until it drips from both sides of leaves.

Persistence – A few days.

Forms – Liquid.

Toxicity – Usually not toxic to humans in dosage lethal to pests.

Safety – Wear a mask and gloves, and cover skin and hair. Avid contact with eyes, nose, lips, and ears.


Ingredients – Relatively new in the USA, neem has been used for medicine and pest control for more than four centuries in India and Southeast Asia. Extracted from the Indian neem tree, Azadirachta indica, or the chinaberry tree, Melia azedarach, neem is an antifeedant and disrupts insect life cycle. The trees are known as the village pharmacy because they supply cures for humans and animals as well as safety control countless pests and fungi. Neem powder is made from leaves. The active ingredient, azadirachtin, confuses growth hormones and pests never mature into adults to produce more young. It is most effective against young insects and is available in various concentrations. it also contains N-P-K and trace elements.

Controls – Most effective against caterpillars and other immature insects including larvae or white flies, fungus gnats, mealybugs, and leafminers.

Caution – Neem is not as effective against spider mites as neem oil.

Mixing – Often mixed with vegetable (canola) oil. Mix just before using in water with a pH below 7 and use a spreader-sticker. Agitate constantly while using to keep emulsified, throw out excess.

Application – Use as a soil drench or add to the nutrient solution. This allows neem to enter into the plant’s tissue and become systemic. Used as a spray, neem becomes a contact spray and an antifeedant when eaten by pests. Performs best in rooms with 60 percent plus humidity.

Persistence – Contact neem stays on foliage for up to a month or until it is washed off. Stays in plant system up to a month when absorbed via roots.

Forms – Emulsifiable concentrate.

Toxicity – Not toxic to honeybees, fish, and earthworms. Not toxic to beneficial insects in normal concentrations that kill target insects.

Safety – Irritates eyes; wear a mask and gloves.

Neem Oil

Ingredients – Purified extract from neem seeds. Buy only cold-pressed oil that is stronger and contains all the natural ingredients. Do not use heat processed neem oil. Cold pressed oil also contains azadirachtin, the active ingredient in neem. Brand names include Neemguard, Triact, and Einstein Oil.

Controls – Effective against spider mites, fungus gnats, and aphids. It is also a fungistat against powdery mildew and rust.

Caution – Neem oil is very effective against spider mites.

Mixing – Mix just before using in water with a pH below 7 and use a spreader-sticker. Agitate constantly while using to keep emulsified. Throw out excess.

Application – Spray on foliage, especially under leaves, where mites live. Apply every few days so hatching larvae will eat it immediately. Spray heavily so mites have little choice but to eat it. Avoid spraying the last few days before harvest. Some growers report a foul taste when applied just before harvest.

Persistence – Contact neem stays on foliage for up to a month or until it is washed off. Stays in plant system up to a month when absorbed via rots.

Forms – Emulsifiable concentrate.

Toxicity – Toxicity to beneficial insects has been reported. Not toxic to humans.

Safety – Irritates eyes, wear a mask and gloves.

Nicotine and Tobacco Sprays

Ingredients – Nicotine is a nonpersistent pesticide derived from tobacco, Nicotiana tabacum. It is a stomach poison, contact poison, and respiratory poison. This very poisonous compound affects the neuromuscular system, causing pests to go into convulsions and die. Nicotine sulfate is the most common form.

Caution – Do not swallow any if this vile poison, and avoid skin contact. Do not use around nightshade family – eggplants, tomatoes, peppers and potatoes – because they may contract Tobacco Mosaic Virus (TMV) from exposure to tobacco-based substances.

Controls – Sucking and chewing insects.

Mixing – Use a spreader-sticker.

Application – Seldom phytotoxic when used as directed. Combine with insecticidal soap to increase killing ability.

Persistence – One week to ten days.

Forms – Liquid.

Toxicity – Although naturally derived, nicotine is very toxic to most insects (including beneficials), honeybees, fish, and humans. If concentrate is ingested or built up over years, humans may develop lung cancer and other cancers.

Safety – Wear a mask and gloves; avoid skin and eye contact.

Oil, Horticultural

Ingredients – Often underrated and overlooked as an insecticide and miticide, horticultural oil is very popular in greenhouses and is regaining popularity among indoor growers. Similar to medicinal mineral oil, horticultural oils are made from animal (fish) oils, plant seed oils, and petroleum oils refined by removing most of the portion that is toxic to plants. Lighter weight oil (viscosity 60-70) is less phytotoxic. Vegetable oil is also horticultural oil.

Controls – Virtually invisible, horticultural oil kills slow moving and immobile sucking insects, spider mites and their eggs by smothering, as well as generally impairing their life cycle.

Caution – Do not use lubricating oil such as 3 in 1 or motor oil.

Mixing – Mix 3/4 teaspoon (0.75 cl) of oil spray – no more than a one percent solution – per quart (0.9 L) of water. More than a few drops could burn tender, growing shoots.

Application – Spray foliage entirely, including under the surface of the leaves. Apply oil sprays up until two weeks before harvest. Repeat application as needed. Usually three applications, one every five to ten days, will put insects and mites in check. Lightweight oil residue evaporates int the air in a short time.

Persistence – Disappears in one to three days, under normal growing conditions.

Forms – Liquid.

Toxicity – Safe, nonpoisonous, and nonpolluting insecticide. Can become phytotoxic if too heavy (viscosity)), if applied too heavily, or when temperatures are below 70F, or very humid; this slows evaporation, increasing phytotoxicity.

Safety – Wear a mask and gloves.

Oil, Vegetable

Ingredients – Fatty acids and glycerides.

Controls – Lightweight vegetable oil kills slow moving and immobile sucking insects, spider mites, and their eggs by smothering as well as generally interrupting their life cycles.

Caution – Vegetable oil does not kill as well as horticultural oil.

Mixing – Mix two drops of oil spray – no more than a one percent solution – per quart of water.

Application – Spray foliage entirely, including under surface of leaves. Stop spraying two weeks before harvest.

Persistence – Several days.

Forms – Liquid.

Toxicity – Not toxic to mammals or fish.

Safety – Wear a mask and gloves.


Ingredients – Pyrenthrum, the best known botanical pesticide, is extracted from the flowers of the pyrenthrum chrysanthemum, Chrysanth-emum coccineum and C. cinerariifoliu. Pyrenthrins – pyrenthrins, cinerins, and jamolins – are the active ingredients in natural pyrenthrun and kills insects on contact. Pyrethrum is often combined with rotenone or ryania to ensure effectiveness. Aerosol forms contain synergists.

Controls – A broad-spectrum contact pesticide, pyrenthrum kills aphids, whiteflies, spider mites, and insects including beneficials. It is very effective to control flying insects, but they must receive a killing knockdown dose, or they may revive and buzz off.

Caution – Do not mix with sulfur, lime, copper, or soaps. The high pH of these substances render it ineffective. Wash these substances off foliage with plain water (pH below 7) before applying pyrethrum.

Mixing – Mix in water with a pH below 7 and use a spreader-sticker.

Application – Spot spray infested plants. Aerosol sprays are most effective especially on spider mites. This can burn foliage – spray is ice-cold when it exits the nozzle – if applied closer than one foot. Aerosol spray contains a synergist, piperonyl butoxide (PBO) or MGK 264. Both are toxic to people. Pyrethrum dissipates within a few hours in the presence of air, HID light, and sunlight. Overcome this limitation by applying just before turning off the lights, the circulation, and vent fans for the night. One manufacturer, Whidmere, offers encapsulated pyrethrum in aerosol form called Exclude. As the spray fogs out of the nozzle, a bubble forms around each droplet of pyrethrum mist. The outside coating keeps the pyrethrum intact and extends its life for several days. When a pest prances by touching the bubble, it bursts, releasing the pyrethrum. Liquid and wettable pyrethrum applied with a pump type sprayer is difficult to apply under leaves where spider mites live.

Persistence – Effective several hours after application when the lights are on, longer when applied after light out and the fan is turned off.

Forms – Wettable powder, dust, liquid, granular bait, and aerosol.

Toxicity – Not toxic to animals and humans when eaten, but becomes toxic to people when inhaled. It is toxic to fish and beneficials.

Safety – Wear a mask and protective clothing when applying sprays or breathing in any form of pyrethrum, especially aerosols. Aerosols contain toxic PBO and MGK 464 – possible carcinogens – which are easily inhaled.

Synthetic Pyrethroids

Ingredients – Synthetic pyrethroids such as permethrin and cypermethrin act as broad-spectrum, nonselective contact insecticides and miticides. There are more than 30 synthetic pyrenthroids available in different formulations. Deltamethrin is available in different formulations. Deltamethrin is available as a sticky paint that is used as a trap when applied to stems and colored objects. Other pyrethroids include Allethrin, cyflutrin, fenprpathin, phenothrin, sumithrin, resmitherin, and telfuthrin.

Controls – Aphids, whiteflies, thrips, beetles, cockroaches, caterpillars, and spider mites. Many insects and mites are resistant to pyrethroids.

Caution – Nonselective pyrethroids kill all insects and mites including beneficials and bees.

Mixing – Follow directions on container.

Application – Follow directions on container.

Persistence – Breaks down in one to three days. Newer pyrethroids, such as Permethrin, stay active the longest.

Forms – Powder, liquid, aerosol.

Toxicity – Toxic to all insects. It is somewhat toxic to mammals.

Safety – Wear a mask and protective clothing when applying sprays or breathing in any form of pyrethrum, especially aerosols. Aerosols contain toxic PBO and MGK 4646 – possible carcinogens – which are easily inhaled.


Ingredients – Quassia is made from a subtropical South American tree, Quassia amara, and the tree-of-heaven, Ailanthus altissima.

Controls – Soft bodied insects including aphids, leafminers, and some caterpillars.

Mixing – Available in the form of bark, wood chips, and shavings. Soak 6 ounces of chips per gallon of water for 24 hours. Afterward, boil for two hours. Add a potassium based soap to increase effectiveness. Strain and col before spraying.

Application – Spray on foliage until saturated.

Persistence – Two to five days on the surface of plants.

Forms – Bark, wood chips, and shavings.

Toxicity – Safe for mammals and possibly beneficials.

Safety – Wear a mask and gloves.


Ingredients – Roteone is an extract of roots of several plants including Derris species, Lnchcarpus species, and Tephrosia species. This poison is a Nonselective contact insecticide, stomach poison, and slow acting nerve poison.

Controls – Nonselective control of beetles, caterpillars, flies, mosquitos, thrips, weevils, and beneficial insects, but death is slow. According to Hemp Diseases and Pests, target insects can consume up to 30 times their lethal dose before dying!

Caution – Kills beneficials. New evidence indicates roteone may be toxic to people and may cause Parkinson’s disease. Use only as a last resort!

Mixing – Follow directions on the package.

Application – Follow directions on the package.

Persistence – Breaks down in three to ten days.

Forms – Powder, wettable powder, liquid.

Toxicity – The effect on mammals is undetermined. Chronic exposure may cause Parkinson’s. It is toxic to birds, fish, and beneficials.

Safety – Wear a mask and gloves. Cover exposed skin and hair. Avoid skin contact.


Ingredients – This contact alkaloid stomach poison is made from stems and roots f the tropical shrub, Ryania speciosa.

Controls – Toxic to aphids, thrips, European corn borers, hemp borers, flea beetles, leaf rollers, and many caterpillars.

Caution – Somewhat toxic to beneficials and mammals!

Mixing – Follow directions on package.

Application – Follow directions on package. Apply as dust.

Persistence – Two weeks or longer.

Forms – Powder, wettable powder.

Toxicity – Toxic to mammals, birds, fish, and beneficials.

Safety – Wear a mask, gloves, and safety glasses, and cover exposed skin and hair. Avoid skin contact.


Ingredients -This alkaloid pesticide is made from the seeds of a tropical lily, Schoenocaulon officinale, native to Central and South America, and a European hellebore, Veratum album.

Controls – A contact and stomach poison, this centuries old poison controls aphids, beetles, cabbage loopers, chinch bugs, grasshoppers, and squash bugs.

Caution – Very toxic to honeybees and moderately toxic to mammals!

Mixing – Follow directions on package.

Application – Most potent when applied at 75-80F. Follow directions on package.

Persistence – Two or three days.

Forms – Powder, liquid.

Toxicity – Somewhat toxic to mammals, toxic to honeybees.

Safety – Wear a mask, gloves, and safety glasses, and cover exposed skin and hair. Avoid skin, eye, ear, and nose contact. Irritates eyes and nose.


Ingredients – Numerous elements including nutrients, bacteria, and hormones.

Controls – Suspended particles in seaweed impair, and even kill, insects and spider mites by causing lesions. The particles cut and penetrate the soft bodied pest insects and mites causing their body fluids to leak out.

Mixing – Dilute as per instructions for soil application.

Application – Spray on foliage, especially under leaves where mites live.

Persistence – Up to two weeks when spreader-sticker is used.

Forms – Powder and liquid.

Toxicity – Not toxic to mammals, birds, and fish. Nonselective, kills beneficials.

Safety – Wear a mask and gloves.

Soap, Insecticidal

Ingredients – Mild contact insecticides made from fatty acids of animals and plants. A variety of soaps are available in potassium-salt based liquid concentrates. Soft soaps such as Ivory liquid dish soap, Castille soap, and Murphy’s Oil sap are biodegradable and kill insects in a similar manner to commercial insecticidal soaps, but they are not as potent or effective.

Controls- Controls soft bodied insects such as aphids and mealy bugs, spider mites, thrips, and whiteflies by penetrating and clogging body membranes.

Caution – Do not use detergent soaps because they may be caustic.

Mixing – Add a few capfuls of soap to a quart of water to make a spray. Ivory or Castille soap can also be used as a spreader-sticker to mix with other sprays. The soaps help the spray stick to the foliage better.

Application – Spray at the first appearance of insect pests. Follow directions on commercial preparations. Spray homemade mixes every four to five days.

Persistence – Soft soaps will last only for about a day before dissipating.

Forms – Liquid.

Toxicity – These saps will last only for about a day before dissipating.

Safety – Wear a mask and gloves.


Ingredients – Sulfur. Mixed with lime, sulfur is more toxic to insects but more phytotoxic to plants.

Controls – Centuries old fungicide is effective against rusts and powdery mildew.

Caution – Do not apply in temperatures above 90F and less than 50 percent humidity. It will burn foliage.

Mixing – Follow directions on package.

Application – Apply in light concentration. It is phytotoxic during hot, 90F, arid weather.

Persistence – It stays on foliage until washed off.

Forms – Powder.

Toxicity – Not toxic to honeybees, birds, and fish.

Safety – Wear a mask, gloves, and safety goggles; cover exposed skin and hair. Avoid skin, eye, ear, and nose contact. Irritates eyes, lungs, and skin.


Ingredients – Sticky traps, such as Tanglefoot resins, can be smeared on attractive yellow or red cards to simulate ripe fruit. When the pests land on the fruit, they are stuck forever!

Controls – Helps contain spider mites and non-flying insects within the bounds of the barriers. Monitors fungus gnat populations and helps control thrips. Other insects get stuck haphazardly to the sticky stuff.

Black light traps catch egg laying moths and other flying insects most of which are not plant pests. Light and fan traps attract many insects including beneficials, and their use may do more harm than god.

Sex-lure traps exude specific insect pheromones, sexual scents, of females that are ready to mate. These traps are most effective to monitor insect populations for large farms.

Mixing – Follow directions on container. Smear on desired objects.

Application – Smear Tanglefoot around the edges of pots, base of stems, and at the end of drying lines to form an impenetrable barrier-trap against mites and insects. This simple precaution helps keep mites isolated. However, resourceful spider mites can spin a web above the barrier. The marauding mites also ride the air currents created by fans from plant to plant.

Persistence – It is persistent until it is wiped off or completely fouled with insect bodies.

Forms – Sticky, thick paint.

Toxicity – Not toxic to mammals or insects. Trapped insects and mites starve to death.

Safety – Wear gloves.


Ingredients – A cold jet of water – preferably with a pH between 6 and 7 – blasts insects, spider mites, and their eggs off leaves and often kills them. Hot water vapor and steam also work as a sterilant.

Controls – A cold jet of water is an excellent first wave of attack against spider mites, aphids, and other sucking insects. Steam controls spider mites, insects, and diseases on pots, growing medium, and other grow rm surfaces.

Caution – Avoid spraying fully formed buds with water. Standing water in or on buds promotes gray mold. Do not apply hot steam to foliage.

Mixing – None.

Application – Spray the undersides with a jet of cold water to knock off sucking spider mites and aphids. Apply water as a mist or spray when predatory mites are present. The extra humid conditions impair the pest mite lifecycles and promote predatory mite health. Rent a wallpaper steamer. Get it cooking, and direct a jet of steam at all grow room cracks and surfaces.

Persistence – None.

Forms – Liquid, steam vapor.

Toxicity – Not toxic to mammals, fish, and beneficials.

Safety – Do not spray strong jet of water in eyes, up nose, or into other body orifices.

Biological Controls

Predator and parasite availability and supply have changed substantially over the last 10 years. Today, many more predators and parasites are available to home growers than ever before. Shipping, care, cost, and application of each predator or parasite is very specific and should be provided in detail by the supplier.

By definition, a predator must eat more than one victim before adulthood. Predators, such as ladybugs and praying mantises, have chewing mouth parts. Other predators, such as lacewing larvae, have piercing-sucking mouth parts. Chewing predators eat their pray whole. The piercing-sucking type, suck the fluids from their prey’s body.

Parasites consume a single individual host before adulthood. Adult parasitoids typically place a singe egg into many hosts. The egg hatches into larvae that eat the host insect from the inside out. They save the vital organs for dessert! Most often, the larvae pupate inside the host’s body and emerge as adults.

Parasites, unlike predators, hunt until the prey is almost eliminated. Predators chose to be surrounded by prey. When prey population starts to diminish a little, predators move on to find a nice, fat infestation. They never truly eradicate the pests. This is why predators work best for preventative control, but are slow to stop an infestation.

The rate at which the predators and parasites keep the infestation in check is directly proportionate to the amount of predators. The more predators and parasites, the sooner they will get infestations into check. Predators and parasites outbreed their victims, reproducing faster than pests are able to keep up with.

When predators and parasites are introduced into a garden, special precautions must be taken to ensure their well-being. Stop spraying all toxic chemicals at least two weeks before introducing the predators. Pyrethrum and insecticidal soaps can be applied up to a few days before, providing any residue is washed off with fresh water. Do not spray after releasing predators and parasites.

Predators and parasites survive best in gardens that are not sterilized between crops. Gardens with perpetual harvests are ideal for predators.

Most of the predators and parasites that do well in an indoor HID garden cannot fly. Insects that can fly often head straight for the lamp. Ladybugs are the best example. If 500 ladybugs are released n Monday, by Friday, only a few die-hards will be left. The rest will have popped off the lamp. If using flying predators or parasitoids, release when it is dark. They will live longer.

Predators are most often very small and must be introduced to each plant separately. Introducing predators to a garden and plants takes a little time and patience. Predators also have very specific climatic requirements. Pay attention to the predators’ needs and maintain them for best results.

Spider Mites

Identify – The spider mite is the most common pest found on indoor plants and causes the most problems. Spider mites have eight legs and are classified as spiders rather than insects, which have six legs. Find microscopic spider mites on leaf undersides sucking away life-giving fluids. To an untrained naked eye, they are hard to spot. Spider mites appear as tiny specks on leaf undersides; however, their telltale signs of feeding – yellowish-white spots, stippling – on the tops of leaves are easy to see. Careful inspection reveals tiny spider webs – easily seen when misted with water – on stems and under leaves as infestations progress. A magnifying glass or low-power microscope helps to identify the yellow-white, two spotted brown or red mites and their translucent eggs. Indoors, the most common is the two-spotted spider mite. After a single mating, females are fertilized for life and reproduce about 75 percent male eggs. Females lay about 100 eggs.

Damage – Mites suck life-giving sap from plants, causing overall vigor loss and stunting. Leaves are pocked with suck-hole marks and yellow from failure to produce chlorophyll. They lose partial to full function, and leaves turn yellow and drop. Once a plant is overrun with spider mites, the infestation progresses rapidly. Severe cases cause plant death.

Controls – Cleanliness! This is the most important first step to spider mite control. Keep the grow room and tools spotless and disinfected. Mother plants often have spider mites. Spray mothers regularly with miticides, including once three days before taking cuttings. Once mite infestations get out of control and miticides work poorly, the entire grow room will have to be cleaned out and disinfected with a pesticide and 5 percent bleach solution. Steam disinfection is also possible but too difficult in most situations.

Cultural and physical control – Spider mites thrive in a dry, 70-80F climate, and reproduce every five days in temperatures above 80F. Create a hostile environment by lowering the temperature to 60F and spray foliage, especially under leaves, with a jet of cold water. Spraying literally blasts them off the leaves as well as increases humidity. Their reproductive cycle will be slowed, and you will have a chance to kill them before they do much damage. Manual removal works for small populations. Smash all mites in sight between the thumb and index finger, or wash leaves individually in between two sponges. Avoid infecting other plants with contaminated hands or sponges.

Remove leaves with more than 50 percent damage and throw away, making sure insects and eggs do not reenter the garden. If mites have attacked only one or two plants, isolate the infected plants and treat them separately. Take care when removing foliage not to spread mites to other plants. Severely damaged plants should be carefully removed from the garden and destroyed.

Smear a layer f Tanglefot around the lips of containers and at the base of stems to create barriers spider mites cannot cross. This will help isolate them to specific plants. Smear a layer of Tanglefoot at each end of drying lines when hanging buds t contain spider mites. Once foliage is dead, mites try to migrate down drying lines to find live foliage with fresh, flowing sap.

Biological – Neoseiulus (Amblyseius) californicus and Mesoseiulus (phytoseiulus) longipes, are the two most common and effective predators. Phytoseiulus persimilis, Neoseiulus (Amblyseius) fallacius, Galendromus (Metaseiulus) occidentalis, and Galendromus (Typhlodromus) pyri predators are also available commercially.

When prperly applied and reared, predatry spider mites work very well. There are many things to consider when using the predators. First, predators can eat only a limited number f mites a day; the average predator can eat 20 eggs or 5 adults daily. As son as the predator’s source of food is gone, some mites die of starvation while others survive on other insects or pollen. Check with suppliers for release instructions of specific species. A general dosage of 20 predators per plant is a good place to start. Predatory mites have a difficult time traveling from plant to plant, so setting them out on each plant is necessary. Temperature and humidity must be at proper levels to give the predators the best possible chance to thrive. When spider mites have infested a garden, the predatory mites cannot eat them fast enough to solve the problem. Predatory mites work best when there are only a few spider mites. Introduce predatory mites as son as spider mites are seen on vegetative growth., and release them every month thereafter. This gives predators a chance to keep up with mites. Before releasing predators, rinse all plants thoroughly to ensure all toxic spray residues from insecticides and fungicides are gone. The fungus, Hirsutella thompsonii, trade name Mycar, kills spider mites.

Sprays – Homemade sprays often lack the strength to kill infestations but work as a deterrent by repelling mites. Popular homemade sprays include Dr. Bonner’s soap, garlic, hot pepper, citrus oil, and liquid seaweed combinations. If these sprays do not deter spider mites after four to five applications, switch to a stronger spray: neem oil, pyrethrum, horticultural oil, or nicotine sulfate, cinnamaldehyde.

Insecticidal soap does a fair job of controlling mites. Usually two or three applications at five to ten day intervals will do the trick. Horticultural oil smothers eggs and can be mixed with pyrethrum and homemade sprays to improve extermination.

heavy duty chemical miticides are available but are not recommended on plants that will be consumed by humans. If using any chemical miticide, be sure it is a contact poison and not systemic.


Identify – Aphids, also called plant lice, are about the size of a pinhead. They are easy to spot with the naked eye, but use a 10X magnifying glass for positive identification. Aphids are found in all climates. Normally grayish to black, aphids can be green to pink – in any color, aphids attack plants. Most aphids have no wings, but those that do, have wings that are about four times the size of their bodies. Aphids give birth to mainly live female larvae, without mating, and can pump out 3 to 100 hungry larvae every day. Each female reproduces between 40 and 100 offspring that start reproducing soon after birth. Aphids are most common indoors when they are plentiful outdoors. Install yellow sticky traps near base of several plants and near the tops of other plants to monitor invasions of winged aphids, often the first to enter the garden. As they feed, aphids exude sticky honeydew that attracts ants that feed on it. Ants like honeydew so much that they take aphids hostage and make them produce honeydew. Look for columns of ants marching around plants, and you will find aphids.

Damage – Aphids suck the life-giving sap from foliage causing leaves to wilt and yellow. When infestation mounts, you may notice sticky honeydew excreted by aphids. They prefer to attack weak, stressed plants. Some species prefer succulent, new growth, and other aphids like older foliage or even flower buds. Look for them under leaves, huddled around branch nodes, and growing tips. This pest transports (vectors) bacterium, fungi, and viruses. Aphids vector more viruses than any other source. Destructive sooty mold also grows on honeydew. Any aphid control must also control ants, if they are present.

Controls – Manually remove small numbers. Spot-spray small infestations, and control ants. Introduce predators if problem is persistent.

Cultural and physical control – Manual removal is easy and works well to kill them. When affixed to foliage – sucking out fluid – aphids are unable to move and easy to crush with fingers or sponges dipped in an insecticidal solution.

Biological – Lacewings, Chrysoperla species, are the most effective and available predators for aphids. Release one to 20 lacewings per plant, depending on infestation level, as soon as aphids appear. Repeat every month. Eggs take a few days to hatch into larvae that exterminate aphids. Gal-midge, Aphidoletes aphidimyz, is available under the trade name Aphidend; parasitic wasp, Aphidius matricaria, is available commercially as Aphidpar.

Ladybugs also work well to exterminate aphids. Adults are easily obtained at many retail nurseries during the summer months. The only drawback to ladybugs is their attraction to the HID lamp – release about 50 ladybugs per plant, at least half of them will fly directly into the HID, hit the hot bulb, and buzz top their death. Within one or two weeks all the ladybugs will fall victim to the lamp, requiring frequent replenishment.

Verticillium lecanii (fungus) – available under the trade name of Vertalec – is very aphid specific and effective.

Control ants by mixing borax hand soap or borax powder with powdered sugar. Ants eat the sweet mix and borax kills them. They excrete sweet borax mix in the nest where other ants eat the feces and die.

Sprays – Homemade and insecticidal soap sprays are very effective. Apply two to three times at five to ten day intervals. Pyrethrum (aerosol) applied two to three times at five to ten day intervals.

Bees and Wasps

Identify – Bees and wasps that sting are usually from a half inch to more than an inch long. Most have yellow stripes around their bodies and others have none. They are especially attracted to indoor gardens when weather cools outdoors – they move right in.

Damage – They cause no damage to plants but can become a nuisance in grow rooms and hurt like hell when they sting.

Controls – Occasionally a problem indoors, bees and wasps are most efficiently controlled with sprays.

Cultural and physical control – They enter grow rooms through vents and cracks, attracted by the growing plants, a valuable commodity in the middle of the cold winter! Screen all entrances to the room. Install more circulation fans to make flying difficult. Wasp traps, sweet flypaper, and Tanglefoot impair these pests. Bees and wasps are also attracted to the hot HID and fly into it and die.

Biological – Unnecessary.

Sprays – Pyrethrum is recommended. Stuff small nests into a wide mouthed jar – do it at night when the wasps are quiet – and place the jar in a freezer for a few hours. Use Sevin, Carbaryl, only if there is a problem with a wasp nest.

Beetle Borers

Identify – Larvae from several boring beetles tunnel or bore into stems or roots. Look for their entry hole and dead growth on either side of the entry hole along the main stem, often discolored and accompanied by sawdust. Borers are more common outdoors than indoors.

Damage – Tunnels inside the stem and roots; curtails fluid flow, and causes plant parts to wilt. If borer damages the main stem severely, fluid flow to the entire plant could stop, causing death.

Controls – Seldom a problem indoors. Borers often cause so much damage on a particular stem that it has to be removed and destroyed.

Cultural and physical control – Handpick all beetle grubs.

Biological – Several mixes of beneficial nematodes control these borers in soil.

Sprays – Bacillus popilliae is specific to beetles or rotenone individually injected into stems.

Caterpillars and Loopers

Caterpillars and loopers leave plenty of droppings on the plant. The droppings accumulate in between buds. Droppings fall out when the buds are hung to dry; inspect below the hung buds to find the poop droppings.

Identify – From half inch to four inches, caterpillars and loopers are cylindrical with feet, ften green, but can be virtually any color from white to black. Caterpillars have sets of feet the entire length of the body, while loopers have two sets f feet at either end of the body. Loopers place their front feet forward, arch their body upward in the middle, and pull their rear sets of legs forward. Some have stripes, spots, and other designs that provide camouflage. Seldom a problem indoors, caterpillars and loopers are in a life stage – between a larva and a flying moth or butterfly – and are most common when prevalent outdoors. One way to check for caterpillars and loopers is to spray one plant with pyrethrum aerosol spray and shake the plant afterward. The spray has a quick knockout effect, and most caterpillars will fall from the plant.

Damage – These munching critters chew and eat pieces of foliage and leave telltale bites in leaves. Some caterpillars will roll themselves inside leaves. An infestation of caterpillars or leafhoppers will damage foliage and slow growth, eventually defoliating, stunting, and killing a plant.

Cultural and physical control – Manually remove.

Biological – Trichogramma wasps, spined soldier bug (Podisus maculiventris Podibug).

Sprays – Homemade spray / repellent, hot pepper and garlic. Bt, pyrethrum, and rotenone.


Identify – Leafhoppers include many small, 0.125 inch long, wedge shaped insects that are usually green, white or yellow. Many species have minute stripes on wings and bodies. Their wings peak like roof rafters when not in use. Leafhoppers suck plant sap for food and exude sticky honeydew as a by-product. Spittlebug and leafhopper larvae wrap themselves in foliage, and envelop themselves in a saliva-like liquid, plant sap.

Damage – Stippling (spotting) similar to that caused by spider mites and thrips on foliage. Leaves and plant lose vigor, and in severe cases death could result.

Cultural and physical control – Cleanliness! Black light traps are attractive to potato beetles.

Biological – the fungus, Metarhizium anisopliae, is commercially available under the trade name Metaquino.

Sprays – Pyrethrum, rotenone, sabadilla.

Leaf Miner

Identify – Adult leaf miner flies lay eggs that hatch into one-eighth-inch long maggots. You seldom see the maggots before you see the leaf damage they create when they tunnel through leaf tissue. Leaf miners are more common in greenhouses and outdoors than indoors.

Damage – The tiny maggots burrow between leaf surfaces, leaving a telltale whitish tunnel out line. The damage usually occurs on or in young supple growth. It is seldom fatal, unless left unchecked. Damage causes plant growth to slow and if left unchecked, flowering is prolonged and buds are small. In rare cases the damage is fatal. Wound damage encourages disease.

Controls – These pests cause little problem to indoor crops. The most efficient and effective control is to remove and dispose of damaged foliage, which includes the rogue maggot, or to use the cultural and physical control listed below.

Cultural and physical control – Smash the little maggot trapped within the leaf with your fingers. If the infestation is severe, smash all larvae possible and remove severely infested leaves. Compost or burn infested leaves. Instal yellow sticky traps to capture adults.

Biological – Branchid Wasp (Dacnusa sibirica), chalcid wasp (Diglyphus isaea), parasitic wasp (Opius pallipes).

Sprays – Repel with neem oil and pyrethrum sprays. Maggots are protected within tunnels, and prays are often ineffective. Hemp Disease and Pests suggests to water plants with a 0.5 percent solution of neem. This solution works fast and stays on plants for four weeks after application.

Fungus Gnat

Identify – Maggots, larvae, grow to 4-5 mm long and have translucent bodies with black heads. Winged adult gnats are gray to black, 2-4 mm long, with long legs. Look for them around the base of plants in soil and soilless gardens. They love the moist, dank environments in rockwool and the environment created in NFT-type hydroponic gardens. Adult females lay about 200 eggs every week to ten days.

Damage – Infests growing medium and roots near the surface. They eat fine root hairs and scar larger roots, causing plants to ose vigor and foliage to pale. Rot wounds invite wilt fungi like Fusarium or Pythium especially if plants are nutrient-stressed and growing in soggy conditions. Maggots prefer to consume dead or decaying, soggy plant material; they also eat green algae growing in soggy conditions. Adults and larvae can get out of control quickly, especially in hydroponic systems with very mist growing mediums. The adult gnats stick to resinous buds like flypaper! The gnats are very difficult to clean from the buds.

Controls – The easiest way to control these pests is with Vectobac, Gnatrol, and Bactimos, all contain Bacillus thuringiensis var. israelensis (BT-i). This strain of Bt controls the maggots; unfortunately, it is available only in large one-gallon containers. Difficult to find at garden centers, check hydroponic stores.

Cultural and physical control – Do not over water, and keep ambient humidity low. Do not let growing medium remain soggy. Cover growing medium so green algae won’t grow. Yellow sticky traps placed horizontally 1-2 inches over growing medium catches adults.

Biological – The aforementioned Bt-i works best. Alternatives include the predatory soil mite (Hypoapsis Geolaelapumites) and the nematode (Steinernema feltiae).

Sprays – Apply neem or insecticidal soap as a soil-drench.

Mealybugs and Scales

Identify Mealybugs – Somewhat common indoors, these 0.08-0.2 inch oblong, waxy white insects move very little, mature slowly, and live in colonies that are usually located at stem joints. Like aphids, mealybugs excrete sticky honeydew.

Identify Scales – As common indoors as mealybugs, scale looks and acts similar to mealybugs but is usually more round than oblong. Scales may be white, yellow, brown, gray, or black. Their hard protective shell is 0.08-0.15 inch across. Mealybugs rarely or never move. Check for them around stem joints where they live in colonies. Scales sometimes excrete sticky honeydew.

Damage – These pests suck sap from plants which causes growth to slow. They also exude sticky honeydew as a by-product of their diet of plant sap which encourages sooty mold and draws ants that eat the honeydew.

Controls – These pests present little problem to indoor growers. The easiest and most efficient control is listed under Cultural and physical below.

Cultural and physical control – Manual removal is somewhat tedious but very effective. Wet a Q-tip in rubbing alcohol and wash scale away. A small knife, fingernails, or tweezers may also be necessary to scrape and pluck the tightly affixed mealybugs and scales after they are Q-tipped with alcohol.

Biological – There are numerous species of mealybugs and scales. Each has natural predators including species of ladybeetles (ladybugs) and parasitic and predatory wasps. There are so many species of each that it would be exhaustive to lit them here.

Sprays – Homemade sprays that contain rubbing alcohol, nicotine, and saps all kill these pests. Insecticidal soap, pyrethrum, and neem oil are all recommended.


Identify – Of the hundreds and thousand of species of microscopic nematodes – sometimes, big ones are called eelworms – a few are destructive to plants. Most often nematodes attack roots and are found in the soil; however, a few nematodes attack stems and foliage. Root nematodes can often be seen in and around roots with the help of a 30X microscope. Often growers just diagnose the damage caused by destructive nematodes rather than actually seeing them.

Damage – Slow growth, leaf chlorosis, wilting several hours during daylight hours from lack of fluid flow – symptoms can be difficult to discern from nitrogen deficiency. Root damage is often severe by the time they are examined. Rot knot nematodes are some of the worst. They cause roots to swell with galls. Other nematodes scrape and cut roots, compounded by fungal attacks. Roots turn soft and mushy.

Cultural and physical control – Cleanliness! Use new, sterilized potting soil or soilless mix to exclude nematodes’ entrance. Nematodes rarely cause problems indoors in clean grow rooms.

Biological – French marigolds, Tagetes patula, repels soil nematodes, fungus (Myrothecium verrucaria, trade name DeTera ES).

Sprays – Neem is used as a soil-drench.

Root Maggot

Identify – Both the seed corn maggot and the cabbage maggot attack cannabis roots. The seed corn maggot is 1.5 to 2 inches long. The seed corn maggot converts into a fly and is a bit smaller than a common housefly. Cabbage maggots are 0.3 inch long, and the adult fly is bigger than a housefly. These pests winter over in the soil and live in unclean soil. In the spring, they emerge as adult flies and soon lay eggs in the soil at the base of young plants. The squirmy, whitish larvae hatch several days later with a ravenous appetite.

Damage – Root maggots chew and burrow into stems and rots. The seed corn maggot attacks seeds and seedling roots. Cabbage maggots attack roots, leaving hollowed out channels and holes in larger roots. Both maggots destroy small hairlike feeder roots. Wounds made by the root maggots also foster soft rot and fungal diseases.

Cultural and physical control – Cleanliness! Use fresh, new store-bought soil when planting in containers. Cover seedlings with Agronet to exclude flies, and plant late in the year to avoid most adult flies. Place a collar 18-inch of foam rubber around the base of the plant to exclude flies.

Biological – Control with parasitic nematodes, Steinernema feltiae or Heterorhabditis bacterophora.

Sprays – Kill root maggots with neem and horticultural oil used as a soil-drench.

Slugs and Snails

Identify – Slugs and snails are soft, slimy white, dark, or yellow, and occasionally striped. they are 0.25-3 inches long. Snails live in a circular shell, slugs do not. They hide by day and feed at night. Slugs and snails leave a slimy, silvery trail of mucus in their wake. They lay translucent eggs that hatch in about a month. They reproduce prolifically, and the young mollusks often eat relatively more than adults.

Damage – They make holes in leaves often with a weblike appearance. They will eat almost any vegetation, roots included. These creatures winter over in warm, damp locations in most climates. Slugs and snails especially like tender seedlings. They will migrate to adjacent gardens in quest of food.

Cultural and physical control – A clean, dry perimeter around the garden will make it difficult for them to pass. Spotlight and handpick at night. A thin layer of lime, diatomaceous earth, or salty beach sand two to six inches wide around individual plants, beds, or the entire garden will present and impassable barrier. The lime is not thick enough to alter the pH and will repel or dissolve pests. To trap, attach short one-inch feet on a wide board and leave it in the garden. The pests will seek refuge under the board. Pick up the board every day or two, and shake the slugs ff and step on them.

Poisonous baits usually have metaldahyde as a base. Confine the bait to a slug hotel. Cut a 1 x 2 inch slot in covered plastic container to make a slug and snail hotel. Place slug and snail bait inside the hotel. The hotel must keep the bait dry and ff the soil. In a slug hotel, none of the poison bait touches the soil, and the bait is inaccessible to children, pets, and birds. Place slug and snail hotels in out of the way places. Natural baits include a mix of jam and water and beer. If using beer, it must be deep enough to drown mollusks.

Biological – The predatory snail, Ruminia decolata – available commercially – is yet another way to combat plant eating slugs and snails.

Sprays – Young slugs and snails are not attracted to bait. Spray for young at night or early morning with a 50 percent ammonia-water solution.


Identify – More common in greenhouses than indoors. These tiny, winged, fast moving little critters are hard to see but not hard to spot. From 0.04-0.05 inch long, thrips can be different colors, including white, gray, and dark colors, often with petite stripes. Check for them under leaves by shaking parts of the plant. If there are many thrips present, they choose to jump and run rather than fly to safety. But often you will see them as a herd of specs thundering across foliage. Females make holes in soft plant tissue where they deposit eggs that are virtually invisible to the naked eye. Winged thrips easily migrate from infested plants to the entire garden.

Damage – Thrips scrape tissue from leaves and buds, afterward sucking out the plant juices for food. Stipples – whitish-yellowish specks – appear on top of leaves; chlorophyll production diminishes and leaves become brittle. You will also see black specks of thrip feces and little thrips. Many times thrips feed inside flower buds or wrap-up and distort leaves.

Cultural and physical control – Cleanliness! Blue or pink sticky traps, misting plants with water impairs travel. Manual removal works okay if only a few thrips are present, but they are hard to catch. Thrips can be very vexing t control once they get established.

Biological – Predatory mites, parasitic wasps, pirate bugs, fungus, Verticillium lecani, is effective.

Sprays – Homemade sprays such as tobacco-nicotine base; commercial pyrethrum, synthetic pyrethrum, insecticidal soap. Apply two to four times at five to ten day intervals.


Identify – The easiest way to check for the little buggers is to grab a limb and shake it. If there are any whiteflies, they will fly from under leaves. Whiteflies look like a small, white moth about 0.04 inch long. Adult whiteflies have wings. They usually appear near the top of the weakest plant first. They will move downward on the plant or fly off to infest another plant. Eggs connected with a small hook.

Damage – Whiteflies, like mites, may cause white speckles, stipples, on the tops of leaves. Loss of chlorophyll production and plant vigor diminishes as infestation progresses.

Cultural and physical control – Mites are difficult to remove manually because they fly. Adults are attracted to the color yellow. To build a whitefly trap similar to flypaper, cover a bright, yellow object with a sticky substance like Tanglefoot. Place the traps n the tops f the pots among the plants. Traps work very well. When they are full of insects, toss them out.

Biological – The wasp, Encarisa formosa, is the most effective whitefly parasite. The small wasps only attack whiteflies, they do not sting people! All toxic sprays must be washed off completely before introducing parasites and predators. Since the Encarsia formosa is a parasite, about 0.125 inch long, smaller than whitefly, it takes them much longer to control or even keep the whitefly population in check. The parasitic wasps lays an egg in the whitefly larva that later hatches and eats the larva alive, from the inside out – death is slow. If you use them, set them out at the rate of two or more parasites per plant as son as the first whitefly is detected. Repeat every two t fur weeks throughout the life of the plants.

The fungus Verticillium lecanii AKA Cephalosporium lecanii, trade name Mycatal, is also very effective in whitefly control.

Sprays – Easily eradicated with natural sprays. Before spraying, remove any leaves that have been over 50 percent damaged and cure with heat or burn infested foliage. Homemade sprays applied at five to ten day intervals work well. Insecticidal soap applied at five to ten day intervals. Pyrethrum (aerosol) applied at five to ten day intervals.

Fungi and Diseases

Fungi are very primitive plants and do not produce chlorophyll, the substance that gives higher plants their green color. Fungi reproduce by spreading tiny microscopic spores rather than seeds. Countless fungal spores are present in the air at all times. When these microscopic airborne spores find the proper conditions, they will settle, take hold, and start growing. Some fungi, such as bud rotting gray mold (Botrytis) are so prolific that they can spread through an entire crop in a matter of days. In fact, one grow room was located near a swamp and Botrytis spores were omnipresent in the environment. Buds and stems contracted gray mold quickly and were often reduced to a wisp of powdery foliage in short order.The grower lost four consecutive crops. Finally, the grower moved to a greener pastures and had no trouble with mold. Unsterile, soggy soil, coupled with humid, stagnant air, provides the environment most fungi need to thrive. Although there are many different types of fungi, they are usually prevented with similar methods.

Fungi and Disease Prevention

Prevention is the first step and the true key to fungi control. Cover the carpet with white Visqueen plastic. If mold should surface on the walls, spray with fungicide. Wash walls with a five percent bleach solution or Pinesol (made from natural pine oil) and apply paint that contains a fungus-inhibiting agent. Specially designed paints for damp conditions contain a fungicide and are attracted by moisture. When applied t a damp, cracked basement wall, the paint is drawn into the moist crack. Remove all mold from the walls by washing it with fungus-resistant paint. Cleanliness and climate control are the keys t preventing fungi. Few clean, well ventilated grow rooms have problems with fungi. In contrast, every dingy, dank, ill-kept indoor garden I have seen had fungal problems and yielded a substandard harvest.

Install a vent fan large enough to remove moist air quickly and keep humidity at 50 percent or less. A vent fan is the easiest and least expensive humidity control device available. CO2 generators produce humidity increasing water vapor as a by-product. Dehumidifiers draw extra electricity, and the condensed water must be removed daily. Wood, coal, and electric heat all dry and dehumidify the air. Most air conditioners can be set to a specific humidity level. if the grow rooms have a central heating / air conditioning vent, the vent can be opened to control temperature and lower humidity.

Fungus and Disease Control

Prevent fungus by controlling all the factors contributing t its growth: remove hiding places, keep room clean, lower humidity to 50 percent, and keep the air well circulated. If prevention proves inadequate and fungi appear, advanced control measures are necessary. Carefully remove and destroy dead eaves. Wash your hands after handling diseased foliage. If the problem attacks one or a few pants, isolate and treat them separately. Remember, fungi can spread like wildfire if the conditions are right. If they get a good start even after all the preventive measures are taken, do not hesitate to take extreme control methods including spraying the entire garden with the proper fungicide.

Gray Mold (Botrytis) aka Bud Mold

Identify – Gray mold is the most common fungus that attacks indoor plants and flourishes in moist temperate climates common to many grow rooms. Botrytis damage is compounded by humid (above 50 percent) climates. It starts within the bud and is difficult to see at the onset – grayish-whitish or bluish-green in color – Botrytis appears hairlike and similar to laundry lint in moist climates. As the disease progresses, the foliage turns somewhat slimy. Damage can also appear as dark, brownish spots on buds in less humid environments. Dry to the touch, Botrytis-affected area often crumbles when rubbed. Gray mold attacks countless other crops, and airborne spores are present virtually everywhere. While most commonly found attacking dense and swelling flower buds, it also attacks stems, eaves, and seeds, causes damping off, and decomposes dry, stored bud. It is also transmitted via seeds.

Damage – Watch for single leaves that mysteriously dry out on the buds. They could be the telltale signs of a Botrytis attack inside the bud. Constant observation, especially during the last tw weeks before harvest, is necessary t keep this disease out of the garden. Flower buds are quickly reduced t slime in cool, humid conditions or unsmokable powder in warm, dry rooms. Botrytis can destroy an entire crop in seven to ten days if left unchecked. Stem damage – Botrytis starts on stems and not buds – is less common indoors. First, stems turn yellow and cankerous growths develop. The damage causes growth above the wound to wilt and can cause stems to fold over. Transported by air, contaminated hands, and tools, gray mold spreads very quickly indoors, infecting an entire grow room in less than a week when conditions are right.

Control – Minimize Botrytis attack incidence with low humidity (50 percent or less), ample air circulation, and ventilation. Grow varieties that do not produce heavy, tightly packed buds that provide a perfect place for this fungus to flourish. Col (below 70F), moist climates with humidity above 50 percent are perfect for rampant gray mold growth. Remove dead leaf stems, petioles, from stalks when removing damaged eaves t avoid Botrytis outbreaks, which is often harbored by dead, rotting foliage. Increase ventilation and keep humidity below 60 percent, and keep the grow room clean! Use fresh, sterile growing medium for each crop.

Cultural and physical control – As soon as Botrytis symptoms appear, use alcohol sterilized pruners to remove Botrytis infected buds at least one inch below the infected area. Some growers amputate two to four inches below damage to ensure removal. Do not let the bud r anything that touches it contaminate other buds and foliage. Remove from the garden and destroy. Wash you hands and tools after removing. Increase temperature to 80F and lower humidity to below 50 percent. Excessive nitrogen and phosphorus levels make foliage tender, so Botrytis can get a foothold. Make sure pH is around 6 to facilitate calcium uptake. Low light levels also encourage weak growth and gray mold attack. Avid heavy crowding of plants and keep the light levels bright. Botrytis needs UV light to complete its life cycle; without UV light it cannot live. Some varieties seldom fall victim to gray mold. Many crosses are more resistant to gray mold than pure indica varieties. harvest when resin glands are still translucent. Once glands turn amber, threat of gray mold increases substantially.

Biological – Spray plants with Gliocadium roseum and Trichderma species. Prevent damping off with a soil application of Gliocladium and Trichoderma species. Hemp Diseases and Pests suggests to experiment with the yeasts Pichia guilliermondii and Candida oleophila or the bacterium Pseudomonas syringae.

Sprays – Bordeaux mixture keeps early stages of Botrytis in check as long as it is present on the foliage. Preventive spraying is advised if in high risk area, but spraying buds near harvest time is not advised. Seeds are protected from Botrytis with a coating of Captan. Check with your local nursery for product recommendations.


Identify – This fungal condition, sometimes called Pythium wilt, is often found in soil and growing mediums. It prevents newly sprouted seeds from emerging, and attacks seedlings causing them to rot at the soil line, yellows foliage and rots older plants at the soil line. It occasionally attacks rooting cuttings at the soil line, too. It is caused by different fungal species, including Botrytis, Pythium, and Fusarium. Once initiated, damping off is fatal. At the onset of damping ff, the stem loses girth at the soil line, weakens, then grows dark, and finally fluid circulation is cut, killing the seedling or cutting.

Control – Damping-ff is caused by a combination of the following: Fungi are already present in an unsterile rooting medium; Overwatering and maintaining a soggy growing medium; Excessive humidity. The disease can be avoided by controlling soil moisture. Overwatering is the biggest cause of damping off and the key to prevention. Careful daily scrutiny of soil will ensure the proper amount of moisture is available to seeds and cuttings. Start seeds and root cuttings in a fast draining, sterile coarse sand, rockwool, Oasis, or Jiffy cubes, which are difficult to overwater. Do not place a humidity tent over sprouted seedlings – a tent can lead to excessive humidity and damping off. Cuttings are less susceptible to damping off and love a humidity tent to promote rooting. Keep germination temperatures between 70-85F. Damping off is inhibited by bright light; grow seedlings under the HID rather than fluorescent bulbs. Keep fertilization to a minimum during the first couple weeks of growth. germinate seeds between clean, fresh paper towels and move seeds to soil once sprouted. Do not plant seeds too deeply, cover with soil the depth of the seed. Use fresh, sterile growing medium and clean pots to guard against harmful fungus in the soil.

Biological – Apply Polygangrn (Pythium aligandrum) granules to soil and seed. Bak Pak or Intercept are applied to the soil and Deny or Dagger – forms of the bacterium Burkholderia cepacia – are put on the seeds. Epic, Kodiac, Quantum 4000, Rhizo-Plus, System 3, and Seranade also suppress many causes of damping off.

Chemical – Dust the seeds with Captan. Avoid benomyl fungicide soil drench because it kills beneficial organisms.

Downy Mildew

Identify – Sometimes called false mildew, downey mildew affects vegetative and flowering plants. Young, succulent foliage is a favorite starting place. Powdery mildew develops in temperatures below 76F.

It appears as whitish-yellow spots on top of leaves creating pale patches. Grayish mycelium spawn is on leaf undersides, opposite the pale patches. Downey mildew can spread very quickly, causing a lack of vigor and slow growth; leaves yellow, die back, and drop. The disease is in the plant system and grows outward. It is often fatal, spreads quickly, and can wipe out a crop. Avoid promoting this disease by not crowding plants. Keep temperatures above 76F and the humidity below 50 percent.

Control – Cleanliness! Use sterile growing medium. Remove and destroy affected plants, not just foliage.

Biological – Apply Serenade (Bacillus subtilis). Bordeaux mixture is also somewhat effective.


Identify – Blight is a general term that describes many plant diseases which are caused by fungus, most often a few weeks before harvest. Signs of bight include dark, blotchy spots on foliage, slow growth, sudden yellowing, wilting, and plant death. Most blights spread quickly through large areas of plants.

Control – Cleanliness! Use fresh, sterile growing medium. Avoid excess nitrogen fertilization. Avoid blights by keeping plants healthy with the proper nutrient balance and good drainage t prevent nutrient buildup.

Biological – use Serenade (Bacillus subtilis) against Brown Bloght. Use Binab, Bio-Fungus, RootShield, Supresivit, Trichpel, or SoilGuard. Use a Bordeaux mixture to stop fungal blights. Stopping blights in advanced stages is difficult; the best solution is to remove diseased plants and destroy them.

Foliar Spots and Fungi

Identify – Leaf and stem fungi, including leaf spot, attack foliage. Brown, gray, black, or yellow to white spots or blotches develop on leaves and stems. Leaves and stems discolor and develop spots that impair plant fluid flow and other life processes. Spots expand over leaves causing them t yellow and drop. Growth is slowed, harvest prolonged, and in severe cases, death results. Leaf spot is the symptomatic name given to many diseases. These diseases may be caused by bacteria, fungus, and nematodes. Spots or lesions caused by fungi often develop different colors as fruiting bodies grow. Leaf spots are often caused by cold water that was sprayed on plants under a hot HID. Temperature stress causes the spots that often develop into a disease.

Control – Cleanliness! use fresh, sterile growing medium with each crop. Move HIDs away from the garden canopy about 30 minutes before spraying so plants won’t be too hot. Do not spray within four hours of turning the lights off as excess moisture sits on the foliage and fosters fungal growth. Do not wet foliage when watering, avoid overwatering, and lower grow room humidity to 50 percent or less. Check the humidity both day and night. Employ dry heat to raise the nighttime temperature to 5-10F below the daytime levels, and keep humidity more constant. Allow adequate spacing between plants to provide air circulation. Remove damaged foliage. Avid excessive nitrogen application.

Biological – Bordeaux mixture may help keep leaf spots in check, but it is often phytotoxic when applied regularly indoors.

Sprays – Bordeaux mixture.

Fusarium Wilt

identify – Fusarium wilt is most common in warm grow rooms and greenhouses. Recirculating nutrient solutions above 75F creates perfect conditions for Fusarium. The water and nutrient solution carries this disease with it when contaminated. Fusarium starts as small spots on older, lower leaves. Interveinal leaf chlorosis appears swiftly. Leaf tips may curl before wilting and suddenly drying to a crisp. Portions of the plant or the entire plant will wilt. The entire process happens so fast that yellow, dead leaves dangle from branches. This disease starts in the plant’s xylem, the base of the fluid transport system. Plants wilt when fungi plug the fluid flow in plant tissue. Cut one of the main stems in two, and look for the telltale reddish-brown color.

Control – Use fresh, clean growing medium. Avoid nitrogen overfertilization. Preventive action is necessary. Keep nutrient solution below 75F. Hydrogen peroxide infusions will also arrest Fusarium. Always remove infested plants and destroy.

Biological – Mycostop, or Deny, or Dagger and Trichoderma.

Sprays – Treat seeds with chemical fungicides to eradicate the seed-borne infection. Chemical fungicides are not effective on foiage.

Green Algae

Identify – Slimy green algae need nutrients, light, and a mist surface on which to grow. These algae are found growing on moist rockwool and other growing mediums exposed to light. They cause little damage but attract fungus gnats and other critters that damage rots. Once rots have lesions and abrasions, diseases enter easily.

Control – Cover the moist rockwool and growing mediums to exclude light. Run an algaecide in the nutrient solution or water with an algaecide.

Powdery Mildew

Identify – First indication f infection is small spots on the tops of leaves. At this point the disease has been inside the plant a week or more. Spots progress to a fine, pale, gray-white powdery coating n growing shoots, leaves, and stems. Powdery mildew is not away limited to the upper surface of foliage. Growth slows, leaves yellow, and plants die as the disease advances. Occasionally fatal indoors, this disease is at its worst when roots dry out and foliage is moist. Plants are infected for weeks before they show the first symptoms.

Control – Prevent this mildew by avoiding cool, damp, humid, dim grow room conditions, as well as fluctuating temperatures and humidity. Low light levels and stale air affect this disease. Increase air circulation and ventilation, and make sure light intensity is high. Space containers far enough apart so air freely flows between plants. Allow foliage t dry before turning ff the lights. Remove and destroy foliage more than 50 percent infected. Avid excess nitrogen. Copper and sulfur-lime sprays are a god prophylactic.

Biological Control – Apply Serenade or spray with a saturation mix of baking soda and water.

Sprays – Bordeaux mixture may keep this mold in check. A saturation of baking soda spray dries to a fine powder on the leaf; the baking soda changes the surface pH of the leaf to 7, and powdery mildew cannot grow.

Root Rot

Identify – Root rot fungi cause roots to turn from a healthy white to a light brown. As the rot progresses, roots turn darker and darker brown. Leaf chlorosis is followed by wilting of the older leaves on the entire plant, and its growth slows. When severe, rot progresses up to the base of the plant stock, turning it dark. Root rot is most common when roots are deprived of oxygen and stand in un-aerated water. Soil pests that cut, suck, and chew roots create openings fr rotting diseases t enter. Inspect roots with a 10X magnifying glass fr signs of pest damage.

Control – use fresh, sterile growing medium. Make sure calcium levels are adequate, and do not overfertilize with nitrogen. Keep pH above 6.5 in soil and about 6.0 in hydroponic mediums to lower disease occurrence. Control any insects, fungi, bacteria, etc, that eat roots.

Sprays – Sprays are not effective.

Sooty Mold

Identify – Black sooty mold is a surface fungus that grows on sticky honeydew excreted by aphids, mealybugs, scale, whiteflies, etc. Sooty mold is only a problem on indoor plants when honeydew is present. Sooty mold restricts plant development, slows growth, and diminishes harvest.

Control – Remove insects that excrete honeydew. Once honeydew is controlled, mold dies. Wash away honeydew and mold with a biodegradable soapy solution. Rinse away soapy water a few hours after applying.

Verticillium Wilt

Lower leaves develop chlorotic yellowing on margins and between veins before turning dingy brown. Plants wilt during the day and recoup when the light goes off. Wilt soon overcomes parts of the plant or the entire plant. Cut the stem in two and look for the telltale brownish xylem tissue. The fungus blocks the flow of plant fluids, causing wilting.

Control – Use fresh, sterile soil. God drainage. Use amonical nitrogen as a source of nitrogen. Do not overfertilize.

Biological – Bio-Fungus, Rhizo-Plus.

Sprays – No chemical spray is effective.


Identify – Viruses are still a mystery. They act like living organisms in some instances and nonliving chemicals on other cases. They must enter plants via wounds. Once a virus takes over plant cells, it is able to multiply. Viruses are spread by insects, mites, plants, animals, and human vectors. Aphids and whiteflies are the worst. Infected tools also transport viruses from one plant to another. Typical symptoms of viral infection are: sickly growth, leaf and stem spots, yellowing, and low yields. Viral diseases move into the plant’s fluid distribution system and destroy it, which often causes leaf spots and mottling. A virus can completely take over a plant in a few days. Once a plant gets a virus, there’s little you can do.

Control – Always use fresh, sterile growing medium. Disinfect tools before cutting foliage and different plants. Destroy all plants infected with virus.

Biological – None.

Sprays – No chemical sprays are effective against viruses.

Marijuana Horticulture

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